Abstract: Additive manufacturing (AM) of load-bearing metal implants allows sustainable production of personalized implants with complex shapes and inner architectures. Implants must meet strict requirements to not harm patients, and production technique must certify their performance. Available materials, many production parameters and implant personalization on patient's needs represent limits of AM. Layer-by-layer material deposition and repeated thermal cycles typical of AM may also cause discontinuities between layers affecting implant mechanical features, and its match to the host body. In this paper the mechanical challenges that AM must overcome to replace traditional manufacturing techniques are discussed, in order to better understand whether AM has to be limited to implant personalization for exceptional cases.

Keywords: Additive manufacturing | Conventional manufacturing | Geometric accuracy | Implants | Mechanical properties

Abstract: Additive manufacturing (AM) permits sustainable production of personalized load-bearing metal implants with complex structures. Regulations prescribe that implants have to meet strict requirements to not harm patients, and production technique should allow the certification of their performance. Process, materials, operating parameters, and customization to patient's needs could limit AM. Layer-by-layer material deposition and repeated thermal cycles may make outer surface of AM implants chemically and physically uneven and rough, eliciting biological response of host tissue and hindering therapeutic success. In this paper, we discuss the clinical challenges that AM must overcome to replace traditional techniques in implant and prostheses design.

Keywords: Additive manufacturing | Clinical performance | Conventional manufacturing | Implants | Surface properties

Abstract: Polyether-ether-2-ketone (PEKK) is a high-performance thermoplastic polymer used in various fields, from aerospace to medical applications, due to its exceptional mechanical and thermal properties. Nonetheless, the mechanical behavior of 3D-printed PEKK still deserves to be more thoroughly investigated, especially in view of its production by 3D printing, where mechanical properties measured at different scales are likely to be correlated to one another and to all play a major role in determining biomechanical properties, which include mechanical strength on one side and osteointegration ability on the other side. This work explores the mechanical behavior of 3D-printed PEKK through a multiscale approach, having performed both nanoindentation tests and standard tensile and compression tests, where a detailed view of strain distribution was achieved through Digital Image Correlation (DIC) techniques. Furthermore, for specimens tested up to failure, their fractured surfaces were analyzed through Scanning Electron Microscopy (SEM) to clearly outline fracture modes. Additionally, the internal structure of 3D-printed PEKK was explored through Computed Tomography (CT) imaging, providing a three-dimensional view of the internal structure and the presence of voids and other imperfections. Finally, surface morphology was analyzed through confocal microscopy. The multiscale approach adopted in the present work offers information about the global and local behavior of the PEKK, also assessing its material properties down to the nanoscale. Due to its novelty as a polymeric material, no previous studies have approached a multiscale analysis of 3D-printed PEKK. The findings of this study contribute to a comprehensive understanding of 3D-printed PEKK along with criteria for process optimization in order to customize its properties to meet specific application requirements. This research not only advances the knowledge of PEKK as a 3D-printing material but also provides insights into the multifaceted nature of multiscale material characterization.

Keywords: anisotropy | digital image correlation | lattice structure | mechanical properties | micromechanical characterization | multiscale mechanics | nanoindentation | PEKK | viscous behavior

Abstract: Objectives: Nowadays, a wide variety of software for 3D reconstruction from CT scans is available; they differ for costs, capabilities, a priori knowledge, and, it is not trivial to identify the most suitable one for specific purposes. The article is aimed to provide some more information, having set up various metrics for the evaluation of different software's performance. Methods: Metrics include software usability, segmentation quality, geometric accuracy, mesh properties and Dice Similarity Coefficient (DSC). Five different software have been considered (Mimics, D2P, Blue Sky Plan, Relu, and 3D Slicer) and tested on four cases; the mandibular bone was used as a benchmark. Results: Relu software, being based on AI, was able to solve some very intricate geometry and proved to have a very good usability. On the other side, the time required for segmentation was significantly higher than other software (reaching over twice the time required by Mimics). Geometric distances between nodes position calculated by different software usually kept below 2.5 mm, reaching 3.1 mm in some very critical area; 75th percentile q75 is generally less than 0.5 mm, with a maximum of 1.11 mm. Dealing with consistency among software, the maximum DSC value was observed between Mimics and Slicer, D2P and Mimics, and D2P and Slicer, reaching 0.96. Significance: This work has demonstrated how mandible segmentation performance among software was generally very good. Nonetheless, differences in geometric accuracy, usability, costs and times required can be significant so that information here provided can be useful to perform an informed choice.

Keywords: 3D reconstruction | CT scans | DSC | Geometric accuracy | Mandible | Segmentation | Usability

Abstract: We investigate the two-dimensional flows of a viscoplastic fluid in symmetric channels with impermeable walls under no-slip boundary conditions. To characterise the mechanical response of the viscoplastic fluid we consider both the celebrated Bingham model and a very general class of its regularisations. In order to make the problem amenable to analysis, we assume that the aspect ratio of the channel is small so that the lubrication approximation can be used. This allows us to obtain analytical solutions, perform an asymptotic analysis of the regularised solutions and compare the results predicted by the Bingham model and its regularisations. We find that in the limit as the regularisation parameter tends to zero, the regularised flow tends to those predicted by the Bingham model only in plane channels. In channels with curved walls, the results are instead markedly different.

Keywords: Bingham model | Lubrication approximation | Regularised models

Abstract: Introduction: Flatfoot is a condition commonly seen in children; however, there is general disagreement over its incidence, characterization and correction. Painful flatfoot accompanied with musculoskeletal and soft tissue problems requires surgery to avoid arthritis in adulthood, the most common surgical approach being two osteotomies to the calcaneus and medial cuneiform bones of the foot. Objectives: This study focuses on the parametrization of these two bones to understand their bone morphology differences in a population sample among 23 normal subjects. Population differences could help in understanding whether bone shape may be an important factor in aiding surgical planning and outcomes. Methods: A total of 45 sets of CT scans of these subjects were used to generate surface meshes of the two bones and converted to be iso-topological meshes, simplifying the application of Generalized Procrustes Analysis and Principal Component Analysis, allowing the main sources of variation between the subjects to be quantified. Results: For the calcaneus, 16 Principal Components (PCs) and, for the medial cuneiform, 12 PCs were sufficient to describe 90% of the dataset variability. The quantitative and qualitative analyses confirm that for the calcaneus PC1 describes the Achilles attachment location and PC2 largely describes the anterior part of the bone. For the medial cuneiform, PC1 describes the medial part of the bone, while PC2 mainly describes the superior part. Conclusion: Most importantly, the PCs did not seem to describe the osteotomy sites for both bones, suggesting low population variability at the bone cutting points. Further studies are needed to evaluate how shape variability impacts surgical outcomes. Future implications could include better surgical planning and may pave the way for complex robotic surgeries to become a reality.

Keywords: calcaneus | flatfoot | medial cuneiform | parametrization | pes planus | principal component analysis

Abstract: This work is aimed to set-up a methodology for foot shape prediction at different flexion angles, overcoming limitations encountered when different poses are required but a limited set of acquisitions can be performed. The basic idea was to identify a fitting law able to interpolate positions of foot anatomical landmarks, and then use this information to guide the deformation of an average foot shape. First of all, mesh correspondence between foot geometries was accomplished by an established procedure based on mesh morphing. Then Procrustes analysis was applied to the dataset to remove rigid motions and estimate the average shape. Two interpolation laws (linear and quadratic) were investigated and the best one in terms of prediction of 3D landmarks’ coordinates was identified. Finally, shape geometries at any flexion angle were predicted performing a second mesh morphing guided by interpolated landmarks’ displacements from the average shape. These analyses proved that a limited number of interpolation angles provides a prediction accuracy comparable to that obtained using all the angles available in the dataset. Moreover, predicted shapes have been compared to the actual scans in terms of root mean square error between corresponding nodes, obtaining a mean value of 4.03 ± 1.39 mm, in accordance with data reported in literature.

Keywords: Accurate geometric reconstruction | Foot model | Real-time acquisition | Statistical deformation model | Statistical shape model

Abstract: Anomaly detection is the identification of any event that falls outside what is considered ‘acceptable behaviour’. This work investigates anomaly detection for automated visual inspection in the context of industry automation (‘Industry 4.0’). For this task we propose a machine vision procedure based on visual feature extraction and one-class k nearest neighbours classification. The method requires only samples of normal (non-defective) instances for the training step. We benchmarked our approach using seven traditional (‘hand-designed’) colour texture descriptors and five pre-trained convolutional neural networks (CNN) ‘off-the-shelf’. Experimenting on nine image datasets from seven classes of materials (carpet, concrete, fabric, layered fused filament, leather, paper and wood), each containing normal and abnormal samples, we found overall accuracy in the range 82.0%–90.2%. Convolutional networks off-the-shelf performed generally better than the traditional methods, although – interestingly – this was not true for all the datasets considered. No visual descriptor clearly emerged as the all-purpose best option.

Keywords: Anomaly detection | Colour | Convolutional neural networks | Texture | Visual descriptors

Abstract: Snap-fit joints represent a simple, economical and straightforward way of joining two different components. The design of the snap-fit joint is usually performed evaluating peak stresses that must be tolerated by the material without incurring into failure or plastic deformations; in addition, the force needed to join and disassemble parts is estimated in relation to ergonomic issues. Finally, the retention force, that is the force required to start disjoining parts, needs to be estimated. The evaluation of peak stresses or insertion/retention/removal forces is commonly performed through finite element method, having identified the respective deformed configuration. A different approach has been here followed considering that it is not trivial to identify the most critical condition in a full joining/disjoining cycle, when complex geometries are being considered. In detail, the snap joint has been modelled as a multibody model including a flexible body, which replicates the part that undergoes major deflections during the process. The model has been validated against experimental force – time curves, recorded for an existing joint, and it has been used to optimize a parametrised snap-fit design. As a result, the joining force has been reduced up to −84%; the disassembly force has been reduced up to −86% and the retention force has been incremented up to +7%. On the whole, a numerical framework to study these joints has been established, keeping the computational time reasonably low (about 40 min for the entire insertion and removal simulation).

Keywords: Geometrical modelling | Multibody model | Plastic components design | Snap-fit joint | Tolerance analysis

Abstract: In vitro ovarian cortical tissue culture, followed by culture of isolated secondary follicles, is a promising future option for production of mature oocytes. Although efforts have been made to improve the culture outcome by changing the medium composition, so far, most studies used static culture systems. Here we describe the outcome of 7 days cultures of bovine and human ovarian cortical tissue in a dynamic system using a novel perifusion bioreactor in comparison to static culture in conventional and/or gas permeable dishes. Findings show that dynamic culture significantly improves follicle quality and viability, percentage and health of secondary follicles, overall tissue health, and steroid secretion in both species. Model predictions suggest that such amelioration can be mediated by an enhanced oxygen availability and/or by fluid-mechanical shear stresses and solid compressive strains exerted on the tissue.

Abstract: Human computer models represent a useful tool for investigating the human body response to external static/dynamic loads or for human-centred design. Articulated Total Body (ATB) models are the simplest human multibody models, where body segments are represented by ellipsoids joined at skeletal articulations. Over the years, regression models on both living subjects’ and cadavers’ data have been developed to predict body segments properties. These models are affected by two main limitations: the only inputs are the subject’s weight and height, not considering that for the same combination different morphologies can exist; secondly, regression analyses were performed over a specific population not including peculiar morphologies (under-weight or obese). A novel methodology for developing anthropomorphic ATB models is here presented: a statistical shape model able to predict the external geometry of the human body from a limited set of anthropometric measurements was implemented and body segments were obtained by segmentation; the respective inertial properties were computed from volumes, assuming a constant density value. The properties of this new anthropomorphic ATB model were compared to those calculated by GEBOD (Generator of Body Data), a well-known programme for ATB data calculation. A virtual population of twenty subjects was analysed: with reference to the inertial properties the most relevant differences occurred at the abdomen and the thighs segments (60% relative error), while the trunk, the shoulder and the calves represent the most critical areas for the geometry reconstruction (50 mm average error). The significance of these outcomes was investigated performing multibody simulations with various scenarios.

Keywords: Accident | Articulated total body model | CAESAR database | Forensic biomechanics | Multibody modelling | Principal component analysis

Abstract: Objective: To validate the use of a polyblend tape suture in equine laryngoplasty (PL). Study design: Experimental study. Animals: Thirty-two cadaveric larynges. Methods: Each larynx was randomly assigned to 1 of 4 groups: PL with polyblend tape suture (TigerTape), without (TT) or with a cannula (TTC) in the muscular process of the arytenoid cartilage, and PL with polyester suture (Ethibond), without (EB) or with a cannula (EBC). Construct stiffness, total migration, creep, and drift values were measured after 3000 cycles. The specimens were then loaded to failure to assess their residual properties: load at failure, total energy, displacement, and 2 stiffness coefficients. Results: After cyclic testing, the total migration and creep were lower in TTC (6.36 ± 1.20 mm; 1.35 ± 0.38 mm/s) than in EB (11.12 ± 4.20 mm; 3.39 ± 2.68 mm/s) and in the TT constructs (11.26 ± 1.49 mm; 3.20 ± 0.54 mm/s); however, no difference was found with EBC (9.19 ± 3.18 mm; 2.14 ± 0.99). A correlation was found between total migration and creep (R =.85). The TTC constructs failed at higher loads (129.51 ± 33.84 N) than EB (93.16 ± 18.21 N) and EBC (81.72 ± 13.26 N) whereas the EB and EBC constructs were less stiff than TT and TTC (P <.001). Conclusion: Biomechanical properties were generally superior for the TTC constructs tested under cyclical loading. The TT and TTC constructs failed at a higher load than EB and EBC constructs. The cannula in TTC and EBC reduced the failure at the muscular process. Clinical significance: These results provide evidence to support the in vivo evaluation of the polyblend tape suture with or without a cannula in the muscular process for laryngoplasty in horses.

Abstract: A catastrophic fracture of the radial carpal bone experienced by a racehorse during a Palio race was analyzed. Computational modelling of the carpal joint at the point of failure informed by live data was generated using a multibody code for dynamics simulation. The circuit design in a turn, the speed of the animal and the surface characteristics were considered in the model. A macroscopic examination of the cartilage, micro-CT and histology were performed on the radio-carpal joint of the limb that sustained the fracture. The model predicted the points of contact forces generated at the level of the radio-carpal joint where the fracture occurred. Articular surfaces of the distal radius, together with the proximal articular surface of small carpal bones, exhibited diffuse wear lines, erosions of the articular cartilage and subchondral bone exposure. Even though the data in this study originated from a single fracture and further work will be required to validate this approach, this study highlights the potential correlation between elevated impact forces generated at the level of contact surfaces of the carpal joint during a turn and cartilage breakdown in the absence of pre-existing pathology. Computer modelling resulted in a useful tool to inversely calculate internal forces generated during specific conditions that cannot be reproduced in-vivo because of ethical concerns.

Keywords: Catastrophic carpal fracture | Computed modelling | Horse | In silico modelling | Inverse dynamic analysis | Kinematics | Micro-computed tomography | Multibody dynamic simulation | Palios | Racehorse welfare

Abstract: In this work the performances of three different techniques for 3D scanning have been investigated. In particular two commercial tools (smartphone camera and iPad Pro LiDAR) and a structured light scanner (Go!SCAN 50) have been used for the analysis. First, two different subjects have been scanned with the three different techniques and the obtained 3D model were analysed in order to evaluate the respective reconstruction accuracy. A case study involving a child was then considered, with the main aim of providing useful information on performances of scanning techniques for clinical applications, where boundary conditions are often challenging (i.e., non-collaborative patient). Finally, a full procedure for the 3D reconstruction of a human shape is proposed, in order to setup a helpful workflow for clinical applications.

Keywords: 3D printing | 3D scanning techniques | customised orthopaedic brace | low-cost technology | multimodal approach | non-collaborative patient | non-contact measurement

Abstract: In this work a new approach for the creation of Articulated Total Body (ATB) models for person-specific multi-body simulations is presented, with the main aim of overcoming limitations related to classical multi-ellipsoids ATB models, based on regression equations having only the weight and the height of the subject as input. The new methodology is based on a Statistical Shape Model (SSM), morphable according to up to 24 input parameters: the SSM was obtained from Principal Component Analysis (PCA), applied on a wide database of 3D human scans (CAESAR). The so obtained geometry can be segmented automatically to generate body segments with the respective inertial properties (mass, principal moments of inertia, and centres of mass location). The routine has been tested on a random set of 20 male subjects and the classical multi-ellipsoids models were compared to these in terms of inertial properties and 3D external geometry: the highest differences were registered at the abdomen and the thighs for what concerns the mass (60%), principal moments (75%) and centres of mass (50 mm) properties; the trunk, the shoulder and the calves are the most critical areas for the external geometry (average distance between the anthropomorphic and ellipsoids models equal to 50 mm). A contribution has been made to build person-specific multibody models. This is a valuable method since approximations made by multi-ellipsoidal models have resulted to be relevant at specific body areas, and personalised models can be a support to design and to forensic analyses.

Keywords: 3D parametric human model | Articulated total body | Forensic biomechanics | Multibody analysis | Principal component analysis (PCA)

Abstract: Benign and malignant lesions in tissues or organs can be detected by elastographic investigations in which pathological regions are spotted from local alterations of the stiffness. As is known, the shear modulus provides a measure of the stiffness of an elastic material. Based on the classical theory of linear elasticity, an elastogram yields estimations of the linear shear modulus from measurements of the speed of small-amplitude transverse waves propagating in the medium tested. In this paper, we show that the estimation of the shear modulus can be improved significantly by employing the fourth-order weakly nonlinear theory of elasticity (FOE), and indicate how the stiffness can be assessed more precisely with the use of FOE. We discuss also why FOE provides more reliable results than the fully nonlinear theory of elasticity. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.

Keywords: elastography | nonlinear elasticity | shear modulus | strain-energy density functions | weakly nonlinear theory

Abstract: Additive Manufacturing technologies have opened new perspectives for the realization of tissue and organs substitutes. The main advantages come from the possibility of using the same technology to produce artificial or biological substitutes in a wide range of outer shapes and inner reticular architectures, which may pave the way to their use to produce personalized substitutes. Additive manufacturing technologies are based on layer-by-layer material fusion and deposition. As such, they have intrinsic limitations which may hinder the possibility to produce substitutes that meet the requirements for safe clinical use. As an example, discontinuities between layers may make the outer surface of a substitute significantly uneven, rough, and may even weaken the substitute mechanical properties in such an aggressive environment as the human body. Moreover, repeated thermal cycles (fusion and solidification) drastically limit the choice of materials which can be used. Finally, the outcome of the production technology is affected by many variables that it is not trivial to control to deliver the necessary quality and repeatability of the production process for medical applications. Indeed, the surface roughness of an implantable prosthesis or organ substitute is key to modulate cell adhesion and the susceptibility to chemical attack by body fluids. Structural strength is a mandatory requirement for load-bearing prostheses (e.g., orthopedic and dental prostheses). Materials for biomedical applications must not only be 3D printable, but also biocompatible and/or possibly have to promote cells growth and to prevent inflammatory reactions. The performance of artificial, bio artificial and tissue-engineered organs needs also to be certified and guaranteed, a rather difficult task to define for devices which may be unique, being tailored on the specific needs of the patient. In this paper, it will be discussed whether this technology is sufficiently mature to replace more traditional techniques or, alternatively, whether it should be limited to a restricted range of emergency applications until the existing relevant technological gaps are filled.

Keywords: 3D printing | additive manufaturing | artificial organs | clinical | corrosion | fatigue | prostheses | strength | surface | surgical guides | wear

Abstract: The study of the spine range of motion under given external load has been the object of many studies in literature, finalised to a better understanding of the spine biomechanics, its physiology, eventual pathologic conditions and possible rehabilitation strategies. However, the huge amount of experimental work performed so far cannot be straightforwardly analysed due to significant differences among loading set-ups. This work performs a meta-analysis of various boundary conditions in literature, focusing on the flexion/extension behaviour of the lumbar spine. The comparison among range of motions is performed virtually through a validated multibody model. Results clearly illustrated the effect of various boundary conditions which can be met in literature, so justifying differences of biomechanical behaviours reported by authors implementing different set-up: for example, a higher value of the follower load can indeed result in a stiffer behaviour; the application of force producing spurious moments results in an apparently more deformable behaviour, however the respective effects change at various segments along the spine due to its natural curvature. These outcomes are reported not only in qualitative, but also in quantitative terms. The numerical approach here followed to perform the meta-analysis is original and it proved to be effective thanks to the bypass of the natural variability among specimens which might completely or partially hinder the effect of some boundary conditions. In addition, it can provide very complete information since the behaviour of each functional spinal unit can be recorded. On the whole, the work provided an extensive review of lumbar spine loading in flexion/extension.

Keywords: Biomechanics | Follower load | Lumbar spine | Mechanical tests | Multibody | ROM

Abstract: Liver cells cultured in 3D bioreactors is an interesting option for temporary extracorporeal liver support in the treatment of acute liver failure and for animal models for preclinical drug screening. Bioreactor capacity to eliminate drugs is generally used for assessing cell metabolic competence in different bioreactors or to scale-up bioreactor design and performance for clinical or preclinical applications. However, drug adsorption and physical transport often disguise the intrinsic drug biotransformation kinetics and cell metabolic state. In this study, we characterized the intrinsic kinetics of lidocaine elimination and adsorption by porcine liver cells cultured in 3D four-compartment hollow fiber membrane network perfusion bioreactors. Models of lidocaine transport and biotransformation were used to extract intrinsic kinetic information from response to lidocaine bolus of bioreactor versus adhesion cultures. Different from 2D adhesion cultures, cells in the bioreactors are organized in liver-like aggregates. Adsorption on bioreactor constituents significantly affected lidocaine elimination and was effectively accounted for in kinetic analysis. Lidocaine elimination and cellular monoethylglicinexylidide biotransformation featured first-order kinetics with near-to-in vivo cell-specific capacity that was retained for times suitable for clinical assist and drug screening. Different from 2D cultures, cells in the 3D bioreactors challenged with lidocaine were exposed to close-to-physiological lidocaine and monoethylglicinexylidide concentration profiles. Kinetic analysis suggests bioreactor technology feasibility for preclinical drug screening and patient assist and that drug adsorption should be accounted for to assess cell state in different cultures and when laboratory bioreactor design and performance is scaled-up to clinical use or toxicological drug screening.

Keywords: Adsorption | Bioreactor | Elimination | Kinetics | Lidocaine | Liver cells | Tissue engineering

Abstract: Principal components analysis is a powerful technique which can be used to reduce data dimensionality. With reference to three-dimensional bone shape models, it can be used to generate an unlimited number of models, defined by thousands of nodes, from a limited (less than twenty) number of scalars. The full procedure has been here described in detail and tested. Two databases were used as input data: the first database comprised 40 mandibles, while the second one comprised 98 proximal femurs. The “average shape” and principal components that were required to cover at least 90% of the whole variance were identified for both bones, as well as the statistical distributions of the respective principal components weights. Fifteen principal components sufficed to describe the mandibular shape, while nine components sufficed to describe the proximal femur morphology. A routine has been set up to generate any number of mandible or proximal femur geometries, according to the actual statistical shape distributions. The set-up procedure can be generalized to any bone shape given a sufficiently large database of the respective 3D shapes.

Keywords: 3D model generator | Comparative anatomy | Mandible anatomy | Mesh morphing | PCA | Proximal femur anatomy | Stochastic bone models

Abstract: Laryngoscopes are used as diagnostic devices for throat inspection or as an aid to intubation. Their blade must be geometrically compatible with patients’ anatomy to provide a good view to doctors with minimal discomfort to patients. For this reason, this paper was aimed to investigate the feasibility of producing customized blades. The customizable blade model was developed following a feature-based approach with eight morphological parameters. The thickness of such a blade was determined through numerical simulations of ISO certification tests, where the finite element mesh was obtained by morphing a ‘standard’ mesh. The following procedure was applied: the model was built from the selected parameters; the blade was tested in silico; finally, the blade was produced by additive manufacturing with an innovative biodegradable material (Hemp Bio-Plastic® -HBP-) claimed to feature superior mechanical properties. The procedure evidenced that the mechanical properties of current biodegradable materials are unsuitable for the application unless the certification norm is revised, as it is expected.

Keywords: Additive manufacturing | Biodegradable materials | Feature-based modeling | Laryngoscope blades | Mesh-morphing | Parametric drawing | Patient-specific design

Abstract: The present work illustrates the dynamization of an orthopaedic plate for internal fracture fixation which is thought to shorten healing times and enhance the quality of the new formed bone. The dynamization is performed wirelessly thanks to a magnetic coupling. The paper shows the peculiarities of the design and manufacturing of this system: it involves two components, sliding with respect to each other with an uncertain coefficient of friction, and with a specific compounded geometry; there are stringent limits on component size, and on the required activation energy. Finally, the device belongs to medical devices and, as such, it must comply with the respective regulation (EU 2017/745, ASTM F382). The design of the dynamizable fracture fixation plate has required verifying the dynamic of the unlocking mechanism through the development of a parametric multibody model which has allowed us to fix the main design variables. As a second step, the fatigue strength of the device and the static strength of the whole bone-plate system was evaluated by finite element analysis. Both analyses have contributed to defining the final optimized geometry and the constitutive materials of the plate; finally, the respective working process was set up and its performance was tested experimentally on a reference fractured femur. As a result of these tests, the flexural stiffness of the bone-plate system resulted equal to 370 N/mm, while a maximum bending moment equal to 75.3 kNmm can be withstood without plate failure. On the whole, the performance of this dynamic plate was proved to be equal or superior to those measured for static plates already on the market, with excellent clinical results. At the same time, pre-clinical tests will be an interesting step of the future research, for which more prototypes are now being produced.

Keywords: Dynamizable plate | Fracture synthesis | Internal fixation | Mechanical tests | Medical device manufacturing | Stress analysis

Abstract: The ovary is a dynamic mechanoresponsive organ. In vitro, tissue biomechanics was reported to affect follicle activation mainly through the Hippo pathway. Only recently, ovary responsiveness to mechanical signals was exploited for reproductive purposes. Unfortunately, poor characterization of ovarian cortex biomechanics and of the mechanical challenge hampers reproducible and effective treatments, and prevention of tissue damages. In this study the biomechanical response of ovarian cortical tissue from abattoir bovines was characterized for the first time. Ovarian cortical tissue fragments were subjected to uniaxial dynamic testing at frequencies up to 30 Hz, and at increasing average stresses. Tissue structure prior to and after testing was characterized by histology, with established fixation and staining protocols, to assess follicle quality and stage. Tissue properties largely varied with the donor. Bovine ovarian cortical tissue consistently exhibited a nonlinear viscoelastic behavior, with dominant elastic characteristics, in the low range of other reproductive tissues, and significant creep. Strain rate was independent of the applied stress. Histological analysis prior to and after mechanical tests showed that the short-term dynamic mechanical test used for the study did not cause significant tissue tear, nor follicle expulsion or cell damage.

Keywords: Biomechanics | Creep | Elastic modulus | Ovarian tissue | Tensile test | Viscous behavior

Abstract: A number of surgical practices are aimed to compensate for tissue relaxation or weakened/atrophied muscles by means of suture prostheses/thread lifts. The success rate of these procedures is often very good in the short term, while it is quite variable among subjects and techniques in the middle-long term. Middle-long term failures are mostly related to suture distraction, loosening or wear, coming from repeated loading cycles. In this work, an experimental device to perform ex vivo tests on prosthetic sutures has been set up. An equine laryngoplasty has been used as a benchmark, being representative of sutures aimed to compensate for atrophied muscles. The peculiarity of this experimental set up is that the suture is on-site and it has been tightened with known, repeated loads, which do not depend on thread deformation at different load levels. Preliminary tests have been performed applying over 3000 load cycles and finally a tensile test up to rupture. Force/displacement curves obtained with this experimental set up have been reported and parameters useful to classify the biomechanical performance of sutures versus time (mainly its creep behaviour), have been outlined. Results have outlined that the organ-suture system undergoes significant creep over 3000 cycles, and this should be taken into account in order to foresee its long-term behaviour; in addition, the suture anchorage to cartilage should be improved. The experimental set up can be used to perform on-site testing of sutures, taking into account the compliance and creep response at both suture anchorage ends, in order to compare different surgeries and different kinds of thread.

Keywords: Creep | Distraction | Failure | Neuropathy | Suture testing | Tissue relaxation

Abstract: In the original article, there was an error. A Conflict of Interest Statement was missed. A correction has been made to the Conflict of Interest section reporting the following detailed information.

Keywords: CBLO | ligaments | multibody | simulation | TPLO

Abstract: Intramedullary nails constitute a viable alternative to extramedullary fixation devices; their use is growing in recent years, especially with reference to self-locking nails. Different designs are available, and it is not trivial to foresee the respective in vivo performances and to provide clinical indications in relation to the type of bone and fracture. In this work a numerical methodology was set up and validated in order to compare the mechanical behavior of two new nailing device concepts with one already used in clinic. In detail, three different nails were studied: (1) the Marchetti-Vicenzi's nail (MV1), (2) a revised concept of this device (MV2), and (3) a new Terzini-Putame's nail (TP) concept. Firstly, the mechanical behavior of the MV1 device was assessed through experimental loading tests employing a 3D-printed component aimed at reproducing the bone geometry inside which the device is implanted. In the next step, the respective numerical model was created, based on a multibody approach including flexible parts, and this model was validated against the previously obtained experimental results. Finally, numerical models of the MV2 and TP concepts were implemented and compared with the MV1 nail, focusing the attention on the response of all devices to compression, tension, bending, and torsion. A stability index (SI) was defined to quantify the mechanical stability provided to the nail-bone assembly by the elastic self-locking mechanism for the various loading conditions. In addition, results in terms of nail-bone assembly stiffness, computed from force/moment vs. displacement/rotation curves, were presented and discussed. Findings revealed that numerical models were able to provide good estimates of load vs. displacement curves. The TP nail concept proved to be able to generate a significantly higher SI (27 N for MV1 vs. 380 N for TP) and a greater stiffening action (up to a stiffness difference for bending load that ranges from 370 Nmm/° for MV1 to 1,532 Nmm/° for TP) than the other two devices which showed similar performances. On the whole, a demonstration was given of information which can be obtained from numerical simulations of expandable fixation devices.

Keywords: biomechanical stability | experimental tests | flexible bodies | intramedullary nails | Marchetti-Vicenzi nail | multibody analysis | stiffness

Abstract: Implant fixed dental prostheses are widely used for the treatment of edentulism, often preferred over the screw-retained ones. However, one of the main features of an implant-supported prosthesis is retrievability, which could be necessary in the case of implant complications. In this study, the retrievability of implant-fixed dental prostheses was investigated considering two of the main factors dental practitioners have to deal with: the abutments geometry and the luting agent. Impulsive forces were applied to dental bridge models to simulate crowns’ retrievability in clinical conditions. The number of impulses and the impulsive force delivered during each test were recorded and used as retrievability indexes. One-hundred-and-five tests were conducted on 21 combinations of bridges and luting agents, and a Kruskal-Wallis test was performed on the results. The abutment geometry significantly influenced the number of impulses needed for retrieval (p < 0.05), and a cement-dependent trend was observed as well. On the other hand, the forces measured during tests showed no clear correlation with bridge retrievability. The best retrievability was obtained with long, slightly tapered abutments and a temporary luting agent.

Keywords: Abutments geometry | Coronaflex | Dental bridge | Luting agents | Retrieval

Abstract: A number of applications in the surgical practice are based on tensile sutures aimed to keep soft tissues in place and compensate the exit of neuropathies, prolapses or general tissue relaxation. Long-term behaviour of these constructs need to be carefully examined in order to define tensile forces to be applied and to compare different suture anchors. Data here reported refer to equine laryngoplasties, where a suitable loading system has been designed in order to be able to test sutures in-sito, applying known forces (“On-site testing of sutured organs: an experimental set up to cyclically tighten sutures” (Pascoletti et al., 2020 [1])). The loading protocol was made of two steps: in the first step, 3000 loading cycles have been performed; in the following step, a tensile test up to rupture was performed. Cyclic load/displacement curves allow evaluating suture distraction, as a consequence of suture migration and/or soft tissues creep. Tensile curves allow evaluating the residual thread strength and its ultimate displacement. These data can provide a detailed insight of long-term suture behaviour and can be a reference to compare different threads and/or suture anchors.

Keywords: Creep | Distraction | Failure | Neuropathy | Suture testing | Tissue relaxation

Abstract: The design of loading systems to test biologic samples is often challenging, due to shape variability and non-conventional loading set-ups. In addition to this, large economic investments would not be justified since the loading set up is usually designed for one single or for a limited range of applications. The object of this work is the development of a loading set-up finalised to on-site testing of sutures whose main function is applying a localised tensile load. The main challenges of this design process can be so summarized: • Applying cyclic tensile loads on the suture wire, mimicking the physiologic condition where both suture anchorage points have a certain compliance; • Designing a loading system as versatile as possible, in order to be able to accommodate organs with different geometries and sizes; • Keeping low both the complexity and costs of realization.All these considerations and the design calculi are here reported in detail, discussing the novelty of the system, and its main advantages.

Keywords: Anchorage points migration | Cyclic loads | On-site testing of prosthetic sutures | Suture distraction | Suture test

Abstract: Cement-retained implant-supported prosthetics are gaining popularity compared to the alternative screw-retained type, a rise that serves to highlight the importance of retrievability. The aim of the present investigation is to determine the influence of luting agent, abutment height and taper angle on the retrievability of abutment-coping cementations. Abutments with different heights and tapers were screwed onto an implant and their cobalt-chrome copings were cemented on the abutments using three different luting agents. The removals were performed by means of Coronaflex®. The number of impulses and the forces were recorded and analyzed with a Kruskal-Wallis test. Harvard cement needed the highest number of impulses for retrieval, followed by Telio CS and Temp Bond. However, abutment height and taper showed a greater influence on the cap's retrievability (p < 0.05). Long and tapered abutments provided the highest percentage of good retrievability. The influence of the luting agent and the abutment geometry on the cap's retrieval performed by Coronaflex® reflects data from literature about the influence of the same factor on the maximum force reached during uniaxial tensile tests. The impulse force was slightly affected by the same factors.

Keywords: Abutments geometry | Coronaflex | Dental cements | Dental implants | Retrievability

Abstract: The aim of this research is to develop patient-specific 3D mandible models, based on a limited number of measurements taken on the patient. Twenty Computed Tomography scans were used to build the respective 3D cad models of the mandible. Fifteen of these models were given as an input to a Principal Component Analysis software, and eight ‘principal’ mandible morphologies were produced. The following step was to identify the most efficient landmarks to ‘weight’ these morphologies when building a patient-specific model. Two further mandible computed tomography scans (a ‘normal’ mandible and a ‘severely resorbed’ one) were used to test the full procedure and to assess its accuracy. The accuracy of the 3D morphed surface resulted to range between 0.025 and 3.235 mm for the ‘normal’ mandible and between 0.012 and 1.149 mm for the ‘severely resorbed’ one having used eight landmarks to morph a ‘standard’ mandible. This work demonstrates how patient-specific models can be obtained registering the position of a limited number of points (on panoramic x-ray or on the physical model), reaching a good accuracy. This allows performing patient-specific planning and numerical simulations even for those cases where a computed tomography scan would not be available. In fact, this procedure can be interfaced with mesh morphing algorithms to automatically build finite element models. The accuracy of the procedure can be further improved, widening the mandibles computed tomography scans database and optimizing landmarks position.

Keywords: Morphing | Patient-specific models | Principal Component Analysis

Abstract: The final subject position is often the only evidence in the case of the fall of a human being from a given height. Foreseeing the body trajectory and the respective driving force may not be trivial due to the possibility of rotations and to an unknown initial position and momentum of the subject. This article illustrates how multibody models can be used for this aim, with specific reference to an actual case, where a worker fell into a stair well, prior to stair mounting, and he was found in an unexpected posture. The aim of the analysis was establishing if this worker was dead in that same place, if he had been pushed, and which was his initial position. A multibody model of the subject has been built (“numerical android”), given his stature and his known mass. Multiple simulations have been performed, following a design of experiments where various initial positions and velocity as well as pushing forces have been considered, while the objective function to be minimized was the deviation of the numerical android position from the actual worker position. At the end of the analysis, it was possible to point how a very limited set of conditions, all including the application of an external pushing force (or initial speed), could produce the given final posture with an error on the distance function equal to 0.39 m. The full analysis gives a demonstration of the potentiality of multibody models as a tool for the analysis of falls in forensic inquiries.

Keywords: accident | android | biomechanics | crime | doe | fall | forensic | multibody

Abstract: This work is focused on the analysis of the fall of a human being from a given height. With reference to forensic disputes, the final subject position is often the only evidence and foreseeing the body trajectory and the respective driving force may not be trivial. This article illustrates how multibody models can be used for this aim. A multibody model of a human subject has been built, given his stature and his known mass. This model was made of 15 segments, whose inertial properties, joint centres and volumes were deduced from anthropometric databases. This model was validated against experimental tests performed on a Hybrid III dummy: it was able to reproduce the peak impact head force with an error lower than about 10%. Some examples are produced to illustrate the usefulness of this validated model as a tool for the analysis of falls, and how it can be easily parametrized to make multiple simulations with different initial conditions/environment configurations. As such it is a valuable tool for forensic analyses.

Keywords: Anthropometric data | Fall from height | Forensic biomechancis | Multibody model

Abstract: Anterior cruciate ligament (ACL) deficiency can result in serious degenerative stifle injuries. Although tibial plateau leveling osteotomy (TPLO) is a common method for the surgical treatment of ACL deficiency, alternative osteotomies, such as a leveling osteotomy based on the center of rotation of angulation (CBLO) are described in the literature. However, whether a CBLO could represent a viable alternative to a TPLO remains to be established. The aim of this study is to compare TPLO and CBLO effectiveness in treating ACL rupture. First, a computational multibody model of a physiological stifle was created using three-dimensional surfaces of a medium-sized canine femur, tibia, fibula and patella. Articular contacts were modeled by means of a formulation describing the contact force as function of the interpenetration between surfaces. Moreover, ligaments were represented by vector forces connecting origin and insertion points. The lengths of the ligaments at rest were optimized simulating the drawer test. The ACL-deficient model was obtained by deactivating the ACL related forces in the optimized physiological one. Then, TPLO and CBLO treatments were virtually performed on the pathological stifle. Finally, the drawer test and a weight-bearing squat movement were performed to compare the treatments effectiveness in terms of tibial anteroposterior translation, patellar ligament force, intra-articular compressive force and quadriceps force. Results from drawer test simulations showed that ACL-deficiency causes an increase of the anterior tibial translation by up to 5.2 mm, while no remarkable differences between CBLO and TPLO were recorded. Overall, squat simulations have demonstrated that both treatments lead to an increase of all considered forces compared to the physiological model. Specifically, CBLO and TPLO produce an increase in compressive forces of 54% and 37%, respectively, at 90◦ flexion. However, TPLO produces higher compressive forces (up to 16%) with respect to CBLO for wider flexion angles ranging from 135◦ to 117◦ . Conversely, TPLO generates lower forces in patellar ligament and quadriceps muscle, compared to CBLO. In light of the higher intra-articular compressive force over the physiological walking range of flexion, which was observed to result from TPLO in the current study, the use of this technique should be carefully considered.

Keywords: CBLO | Ligaments | Multibody | Simulation | TPLO

Abstract: Artificial turf pitches are even more used than natural ones for their pragmatic advantages. Artificial turf does not need much maintenance and can be used in every climate conditions. On the other hands, the synthetic grass alters the players’ feeling during a match. This altered perception is mostly due to the traction forces exchanged between the player’s feet and the underlying surface in the authors’ opinion. The purpose of the study is to evaluate the frictional properties of the artificial pitches through a multi-scale approach. The phenomena at the macro-scale were investigated setting-up a test bench able to replicate a situation as near as possible to actual conditions and to evaluate the forces exchanged between surfaces. Concurrently, nano-scale tests to assess the friction properties of the grass fibers have been undertaken. Friction properties at the different scales length resulted to be different in magnitude as it could be expected, however similar trends have been observed, and differences between the analyzed samples were confirmed at both scales.

Keywords: Friction | Nano-Scratch | Synthetic Grass | Turf Pitches

Abstract: Finite element models in conjunction with adequate constitutive relations are pivotal in several physiological and medical applications related to both native and engineered tissues, allowing to predict the tissue response under various loading states. In order to get reliable results, however, the validation of the constitutive models is crucial. Therefore, the main purpose of this work is to provide an experimental-computational approach to the biomechanical investigation of soft tissues such as the dermis. This is accomplished by implementing and validating three widely adopted hyperelastic constitutive models (the Ogden, the Holzapfel, and the Gasser-Ogden-Holzapfel laws) supposed to be adequate to reproduce human reticular dermis mechanical behavior. Biaxial experimental data have represented the basis for the determination of the respective material parameters identified thanks to the definition of a cost function accounting for the discrepancy between experimental and predicted data. Afterwards, the experimental tests have been reproduced through finite element simulations. Hence, the constitutive laws have been validated comparing experimental and numerical outcomes in terms of displacements of four reference points and stress-strain relations. Hence, an experimental-numerical framework is proposed for the investigation of collagenous tissues, which could become more accurate with larger and independent experimental datasets. [Figure not available: see fulltext.].

Keywords: Anisotropy | Biaxial test | Finite element | Human dermis | Hyperelastic models

Abstract: Objective: To investigate the influence of implant design on the change in the natural frequency of bone-implant system during osseointegration by means of a modal 3D finite element analysis. Methods: Six implants were considered. Solid models were obtained by means of reverse engineering techniques. The mandibular bone geometry was built-up from a CT scan dataset through image segmentation. Each implant was virtually implanted in the mandibular bone. Two different models have been considered, differing in the free length of the mandibular branch (‘long branch’ and ‘short branch’) in order to simulate the variability of boundary conditions when performing vibrometric analyses. Modal analyses were carried out for each model, and the first three resonance frequencies were assessed with the respective vibration modes. Results: With reference to the ‘long branch’ model, the first three modes of vibration are whole bone vibration with minimum displacement of the implant relative to bone, with the exception of the initial condition (1% bone maturation) where the implant is not osseointegrated. By contrast, implant displacements become relevant in the ‘short branch’ model, unless osseointegration level is beyond 20%. The difference between resonance frequency at whole bone maturation and resonance frequency at 1% bone maturation remained lower than 6.5% for all modes, with the exception of the third mode of vibration in the ‘D’ implant where this difference reached 9.7%. With reference to the ‘short branch’ considering the first mode of vibration, 61–68% of the frequency increase was achieved at 10% osseointegration; 72–79% was achieved at 20%; 89–93% was achieved at 50% osseointegration. The pattern of the natural frequency versus the osseointegration level is similar among different modes of vibration. Significance: Resonance frequencies and their trends towards osseointegration level may differ between implant designs, and in different boundary conditions that are related to implant position inside the mandible; tapered implants are the most sensitive to bone maturation levels, small implants have very little sensitivity. Resonance frequencies are less sensitive to bone maturation level beyond 50%.

Keywords: Bone properties | CAD | Dental materials | Endosteal implants | Finite element analysis | Implant stability | Material properties | Osseointegration | Reverse engineering

Abstract: The optimization of loading protocols following dental implant insertion requires setting up patient-specific protocols, customized according to the actual implant osseointegration, measured through quantitative, objective methods. Various devices for the assessment of implant stability as an indirect measure of implant osseointegration have been developed. They are analyzed here, introducing the respective physical models, outlining major advantages and critical aspects, and reporting their clinical performance. A careful discussion of underlying hypotheses is finally reported, as is a suggestion for further development of instrumentation and signal analysis.

Keywords: Damping | Early loading | Functional loading | Implant stability | Modal analysis | Osseointegration | Resonance frequency | Reverse torque | Ultrasound

Abstract: Reliability, Learnability and Efficiency of Two Tools for Cement Crowns Retrieval in Dentistry The Open Biomedical Engineering Journal, 2018, 12: 27-35 The correct spelling of word Department in second affiliation is mentioned below: Department of Engineering, University of Perugia, Perugia, Italy The original spelling of word Department provided was: Departiment of Engineering, University of Perugia, Perugia, Italy.

Abstract: The surgical treatment of pelvic fractures has been proved to be technically challenging; 3D imaging and navigation can give a substantial benefit; a further step is here introduced with robotized fracture reduction. A specific device to be interfaced with existing surgical tables has been designed; its main specifications are allowing 3D fluoroscopy of wide areas, and housing a hexapod robot for fracture reduction. This robot can be remotely controlled by a joystick; therefore it can accurately reproduce reduction trajectories established in the pre-operative planning and it can maintain the reduced position while synthesis devices are applied. A prototype has been built and tested in order to assess its range of movement, its accuracy, and its learnability. Further efforts will address the implementation of navigated surgery and to the development of a haptic interface in order to let the surgeon sense soft tissue resistance.

Keywords: 3D imaging | Computer assisted surgery | Hexapod | Medical robotics | Pelvic fractures | Surgical Table

Abstract: Objective: To assess the influence of implant thread shape and inclination on the mechanical behaviour of bone-implant systems. The study assesses which factors influence the initial and full osseointegration stages. Methods: Point clouds of the original implant were created using a non-contact reverse engineering technique. A 3D tessellated surface was created using Geomagic Studio® software. From cross-section curves, generated by intersecting the tessellated model and cutting-planes, a 3D parametric CAD model was created using SolidWorks® 2017. By the permutation of three thread shapes (rectangular, 30° trapezoidal, 45° trapezoidal) and three thread inclinations (0°, 3° or 6°), nine geometric configurations were obtained. Two different osseointegration stages were analysed: the initial osseointegration and a full osseointegration. In total, 18 different FE models were analysed and two load conditions were applied to each model. The mechanical behaviour of the models was analysed by Finite Element (FE) Analysis using ANSYS® v. 17.0. Static linear analyses were also carried out. Results: ANOVA was used to assess the influence of each factor. Models with a rectangular thread and 6° inclination provided the best results and reduced displacement in the initial osseointegration stages up to 4.58%. This configuration also reduced equivalent VM stress peaks up to 54%. The same effect was confirmed for the full osseointegration stage, where 6° inclination reduced stress peaks by up to 62%. Significance: The FE analysis confirmed the beneficial effect of thread inclination, reducing the displacement in immediate post-operative conditions and equivalent VM stress peaks. Thread shape does not significantly influence the mechanical behaviour of bone-implant systems but contributes to reducing stress peaks in the trabecular bone in both the initial and full osseointegration stages.

Keywords: Bone properties | CAD | Dental materials | Endosteal implants | Finite element analysis | Material properties | Osseointegration | Plateau implants

Abstract: The Marchetti-Vicenzi's nail is an intramedullary device where six curved nails are kept straight by a closing ring in order to allow their insertion into the medullary canal of a long bone; in a following step, these nails stabilize the fracture due to the ring withdrawal and to the consequent elastic expansion of the nails. Pre-clinical testing of this sort of device is strongly advocated in order to be able to foresee their stability inside the medullary canal and to quantify their stiffening action on a broken bone. In this numerical work, an MB (Multi Body) model of the device has been developed, with the dual purpose of evaluating forces between the bone and the systemcomponents during its progressive opening and verifying the behavior of the stabilized bone when it undergoes external loading. Different solutions, for flexible body modeling (discretization with lumped parameters, "flexible body," "FE Part"), have been analyzed and compared in terms of accuracy of results and required computational resources. Contact parameters have been identified and criteria to simplify geometries and therefore to reduce simulation times have been given. Results have allowed to demonstrate how amoderate lateral force is able to dislocate the fracture and how the final position of the retention nut can be optimized. On the whole, a tool for the pre-clinical testing of elastic intramedullary nails has been given.

Keywords: FE analysis | Flexible bodies | Intramedullary nails | Marchetti-Vicenzi's nail | Multibody analysis | Sliding contacts

Abstract: The elbow ligamentous and bony structures play essential roles in the joint stability. Nevertheless, the contribution of different structures to joint stability is not yet clear and a comprehensive experimental investigation into the ligament and osseous constraints changes in relation to joint motions would be uphill and somehow unattainable, due to the impossibility of obtaining all the possible configurations on the same specimen. Therefore, a predictive tool of the joint behavior after the loss of retentive structures would be helpful in designing reconstructive surgeries and in pre-operative planning. In this work, a multibody model consisting of bones and non-linear ligamentous structures is presented and validated through comparison with experimental data. An accurate geometrical model was equipped with non-linear ligaments bundles between optimized origin and insertion points. The joint function was simulated according to maneuvers accomplished in published experimental studies which explored the posteromedial rotatory instability (PMRI) in coronoid and posterior medial collateral ligament (PB) deficient elbows. Moreover, a complete design of experiments (DOE) was explored, investigating the influence of the elbow flexion degree, of the coronoid process and of the medial collateral ligaments (MCL) structures (anterior and posterior bundles) in the elbow joint opening. The implemented computational model accurately predicted the joint behavior with intact and deficient stabilizing structures at each flexion degree, and highlighted the statistically significant influence of the MCL structures (P<0.05) on the elbow stability. The predictive ability of this multibody elbow joint model let foresee that future investigations under different loading scenarios and injured or surgically reconstructed states could be effectively simulated, helping the ligaments reconstruction optimization in terms of bone tunnel localizations and grafts pre-loading. Level of evidence: V.

Keywords: Coronoid process | Elbow stability | Medial collateral ligaments | Multibody model

Abstract: This work is focused on racing cars driver's training. Nine different tracks are considered and six drivers. Each driver drives on every track and performs consecutive trial sessions on each track; each session is made of various laps, and lap times are fitted using an exponential model, yielding an estimate of the initial performance, the learning constant, and the asymptotic performance. According to results, the learning curve varies significantly among pilots and among tracks; all pilots reach their session asymptotic performance in less than nine laps. The asymptotic performance in consecutive trial sessions improves significantly, and it is strongly correlated to the initial session performance (r2>0.99). As a conclusion, it is more profitable to perform separated sessions made of few laps (less than 10) rather than performing a smaller number of longer sessions. Whenever the initial lap time stops decreasing systematically, trial sessions should end because the asymptotic performance is not likely to improve further.

Keywords: Motor racing | Performance analysis | Racing car drivers | Sport analytics

Abstract: Finite element models, in conjunction with adequate constitutive relations of the materials involved, have proved to be crucial in many medical applications, such as in surgical planning. Nevertheless, a thorough numerical analysis of dermis’ mechanical response is a challenging research area because of dermis’ highly anisotropic and nonlinear behaviour. The aim of this work has been to assess the performance of two orthotropic and one isotropic hyper-elastic constitutive laws, providing an experimental-computational framework for the definition of reliable constitutive models of dermis tissue. Experimental, equi-biaxial stress-strain data obtained on human reticular dermis specimens have been exploited in order to extract, through a stochastic optimization procedure, constitutive parameters of three widely used constitutive laws: the Ogden, Holzapfel and Gasser-Ogden-Holzapfel (GOH) models. A set of specimen specific parameters and a set of best matching parameters, determined by simultaneously fitting all experimental stress-strain curves, have been obtained. The goodness of the selected laws has been assessed by means of FEM simulations performed in Abaqus (Simulia, Dessault Systèmes Inc.) which reproduce the actual specimen boundary conditions and geometry, rebuilt through an image segmentation process implemented in MATLAB (The MathWorks, Inc.). Models have been validated comparing experimental and numerical outcomes related to reference points on the specimen surface. In the preliminary fitting phase, Normalized Root Mean Square Error values were above 0.9 for the specimen-specific and above 0.54 for the best matching models. The comparison between numerical and experimental outcomes has highlighted the inadequacy of the isotropic constitutive law in reproducing the dermis behaviour, particularly at higher stretch levels. Errors obtained in the horizontal loading direction are lower than 40% for Holzapfel and GOH models, while the Ogden model reaches the 80%. Lower and more uniform errors occur in the orthogonal direction, which settles below 30% for the orthotropic laws, while it increases up to 40% in the isotropic case.

Keywords: Anisotropy | Biaxial data | Constitutive model validation | FE analysis | Human dermis

Abstract: Human Acellular Dermal Matrices (HADMs) have recently been employed in reconstructive surgeries which involve high mechanical resistance prerequisites (e.g. rotator cuff tears repair, Achilles tendon augmentation, breast reconstruction procedure, hernia repair), having proved its non-immunogenic response and promising mechanical properties. Nevertheless, a thorough mechanical characterization is needed in order to test HADMs response when subjected to stress levels comparable to those experienced in vivo, to confirm its applicability to the above mentioned surgical fields and to provide precise indications to surgeons. HADMs specimens have undergone biaxial tests through a custom made biaxial fixture interfaced with a uniaxial universal testing machine. Stress-strain curves were evaluated from biaxial loads measured by two load cells, and the optical measure of the displacement of four markers located in central area of specimens. Comparisons among the native human reticular dermis and HADMs demonstrated the loss of mechanical strength caused by the decellularization process. Moreover, the specimens resulted, on average, less extensible in the medio-lateral direction (namely, along the Langer lines) than in the cranio-caudal direction, confirming the correlation of dermis mechanical response with collagen fibers orientation.

Keywords: Biaxial characterization | Biaxial fixture | HADM | Human dermis | Soft tissues material model identification

Abstract: Background Additive manufacturing technologies are being enthusiastically adopted by the orthopaedic community since they are providing new perspectives and new possibilities. First applications were finalised for educational purposes, pre-operative planning, and design of surgical guides; recent applications also encompass the production of implantable devices where 3D printing can bring substantial benefits such as customization, optimization, and manufacturing of very complex geometries. The conceptual smoothness of the whole process may lead to the idea that any medical practitioner can use a 3D printer and her/his imagination to design and produce novel products for personal or commercial use. Aims Outlining how the whole process presents more than one critical aspects, still demanding further research in order to allow a safe application of this technology for fully-custom design, in particular confining attention to orthopaedic/orthodontic prostheses defined as components responding mainly to a structural function. Methods Current knowledge of mechanical properties of additively manufactured components has been examined along with reasons why the behaviour of these components might differ from traditionally manufactured components. The structural information still missing for mechanical design is outlined. Results Mechanical properties of additively manufactured components are not completely known, and especially fatigue limit needs to be examined further. Conclusion At the present stage, with reference to load-bearing implants subjected to many loading cycles, the indication of custom-made additively manufactured medical devices should be restricted to the cases with no viable alternative.

Keywords: Additive manufacturing | Fast prototyping | Fatigue resistance | Orthodontic implants | Orthopaedic implants | Prostheses

Abstract: Background: Double pelvic osteotomy (DPO) planning is usually performed by hip palpation, and on radiographic images which give a poor representation of the complex three-dimensional manoeuvre required during surgery. Furthermore, bone strains which play a crucial role cannot be foreseen. Objective: To support surgeons and designers with biomechanical guidelines through a virtual model that would provide bone stress and strain, required moments, and three-dimensional measurements. Methods: A multibody numerical model for kinematic analyses has been coupled to a finite element model for stress/strain analysis on deformable bodies. The model was parametrized by the fixation plate angle, the iliac osteotomy angle, and the plate offset in ventro-dorsal direction. Model outputs were: acetabular ventro-version (VV) and lateralization (L), Norberg (NA) and dorsal acetabular rim (DAR) angles, the percentage of acetabular coverage (PC), the peak bone stress, and moments required to deform the pelvis. Results: Over 150 combinations of cited parameters and their respective outcome were analysed. Curves reporting NA and PC versus VV were traced for the given patient. The optimal VV range in relation to NA and PC limits was established. The 25° DPO plate results were the most similar to 20° TPO. The output L grew for positive iliac osteotomy inclinations. The 15° DPO plate was critical in relation to DAR, while very large VV could lead to bone failure. Clinical significance: Structural models can be a support to the study and optimization of DPO as they allow for foreseeing geometrical and structural outcomes of surgical choices.

Keywords: Finite elements | Hip dysplasia | Multibody analysis | Pelvic osteotomies | Preoperative planning

Abstract: Human acellular dermal matrices (HADMs) are used in reconstructive surgery as scaffolds promoting autologous tissue regeneration. Critical to the HADM ability to remodel and integrate into the host tissue is the removal of cells while maintaining an intact extracellular architecture. The objective of this work is to develop a methodology to analyse the mechanical properties of HADMs after decellularization to identify its ideal form of treatment and its duration. Two different decellularization techniques were used as a benchmark: the first is a well-established technique (incubation in NaOH for 1–7 weeks), and the second is an innovative technique developed by this research group (incubation in DMEM (Dulbecco's modified Eagle medium) for 1–7 weeks). After decellularization, the specimens underwent uniaxial tensile tests, and experimental data were represented with stress strain curves, calculating both engineering and true values. Mechanical tests have led to the identification of the optimal method (NaOH or DMEM) and duration for the decellularization treatment; differences between engineering and true values can reach 84%, but the engineering values remain useful to make comparisons, providing reliable indications with a simpler experimental set up and data processing.

Keywords: Decellularization treatment | Human dermis | Static mechanical tests | Ultimate strain | Ultimate stress | Young's modulus

Abstract: Background: The dermis is a commonly used source tissue for biologic scaffolds; all cellular and nuclear materials need to be removed to limit the inflammatory immune response by the host organism. The decellularization is critical because it must preserve the structural integrity of the extracellular matrix. This work has analyzed a decellularization procedure commonly followed for the dermal tissue that is a chemical treatment with sodium hydroxide. The goal of this work is to identify the optimal treatment length on the basis of structural properties. Methods: Tensile tests have been performed on the native tissue and on tissues decellularized for 1-7 weeks in sodium hydroxide. The collected data have been analyzed through Tukey-Kramer test to assess if the mechanical properties (ultimate tensile stress and elastic modulus) of decellularized tissues were significantly different from the properties of the native tissue. These tests have been performed on specimens cut along two orthogonal directions (parallel and perpendicular to Langer’s lines). Results: The decellularization treatment performed with sodium hydroxide in general weakens the tissue: both the ultimate stress and the elastic modulus get lower. The structural properties along Langer lines orientation are more strongly impacted, while the structural properties orthogonal to Langer lines can be preserved with an optimal duration of the decellularization treatment that is 5-6 weeks. Conclusion: The duration of the decellularization treatment is critical not only to reach a complete decellularization, but also to preserve the mechanical properties of the tissue; 5-6 week treatment performed with sodium hydroxide allows preserving the mechanical properties of the native tissue perpendicularly to Langer lines orientation, and minimizing the impact of the decellularization process on the mechanical properties along the Langer lines orientation.

Keywords: Acellularized dermis | Allografts | Decellularization treatment | Elastic modulus | Extracellular matrix | Human dermis | Tensile tests | Ultimate stress

Abstract: Objectives: The purpose of this study was to describe the force generated by two different removal devices used to retrieve cemented crowns on implant abutments. The influence of six different operators was evaluated. Material and methods: Three replicated Coronaflex® (Kaltenbach & Voigt GmbH, KaVo Dental GmbH) and reverse hammer setups were tested. The experimental setup has employed a screw bearing a diametral hole through which a loop holder passed. The screw was attached to a force transducer (Brüel & Kjær, type 8201), and the loop holder arm was kept perpendicular to the transducer axis. The results were statistically evaluated with ANOVA. Results: The operator has resulted to play significant influence with reference to reverse hammer (coefficient of variation 43.3%) rather than with Coronaflex® (9.8%). Evaluating every single operator, more variation can still be found by considering each reverse hammer (37.5%) rather than each Coronaflex® (8.8%). Conclusion: Coronaflex® device was found to systematically reach a more repeatable and higher peak amplitude of forces compared with reverse hammer, both by experienced and inexperienced operators.

Keywords: Coronaflex® | FDP | Force transducer | Implant prosthesis | Reverse hammer

Abstract: A procedure for the constitutive analysis of bladder tissues mechanical behavior is provided, by using a coupled experimental and computational approach. The first step pertains to the design and development of mechanical tests on specimens from porcine bladders. The bladders have been harvested, and the specimens have been subjected to uniaxial cyclic tests at different strain rates along preferential directions, considering the distribution of tissue fibrous components. Experimental results showed the anisotropic, non-linear and time-dependent stress-strain behavior, due to tissue conformation with fibers distributed along preferential directions and their interaction phenomena with ground substance. In detail, experimental data showed a greater tissue stiffness along transversal direction. Viscous behavior was assessed by strain rate dependence of stress-strain curves and hysteretic phenomena. The second step pertains the development of a specific fiber-reinforced visco-hyperelastic constitutive model, in the light of bladder tissues structural conformation and experimental results. Constitutive parameters have been identified by minimizing the discrepancy between model and experimental data. The agreement between experimental and model results represent a term for evaluating the reliability of the constitutive models by means of the proposed operational procedure.

Keywords: Bladder | Computational approach | Experimental test | Non-linear mechanics | Soft tissue mechanics

Abstract: In this paper, a theoretical framework is presented for the design of hollow fiber membrane bioreactors (HFMBs) operated in closed-shell mode in the presence of high recirculation flows in the cell compartment. Navier-Stokes and Brinkman equations were used to describe fluid transport, and the convection-diffusion-reaction equations to describe transport of dissolved oxygen and glucose to cells. Numerical solutions were sought with the finite element method for the high permeability typical of new medical membranes, and operating conditions typical of therapeutic applications. Generalized charts intended to help the bioreactor designer were obtained giving the non-hypoxic (or well-nourished) fractional shell volume as a function of the main dimensionless groups influencing the magnitude of the recirculation flow. Results indicate that designs and operations promoting moderate-to-high recirculation flows in the bioreactor shell markedly enhance solute transport and permit much better cell oxygenation and nourishment, and control of the pericellular environment, than diffusion-limited bioreactors. With these charts, bioreactor design may be optimized for a given therapeutic treatment, or operation adjusted to the properties of the cell aggregate as tissue forms in tissue engineering applications, so as to provide cells with a physiological supply of oxygen and nutrients and a physiological pericellular environment.

Keywords: Bioreactor | Convection-enhanced | Hollow fiber membrane | Model | Transport

Abstract: Objective: To set up a prescreening tool for vehicle front-end design, allowing numerically forecasting of the results of EC directive tests, with reference to pedestrian lower leg impact. Methods: A numerical legform model has been developed and certified according to EC directive. The frontal end of the vehicle has been simulated through a lumped-parameters model, having considered the predesign stage when the target overall behavior is being established. The stiffness behaviors of the bumper and of the spoiler have been estimated by means of more detailed numerical models. A parametric analysis has been performed to outline the effects of bumper and spoiler stiffness, bumper vertical height, and the longitudinal distance between the spoiler and the bumper. An analytical model has been introduced to predict tibial acceleration, knee shear displacement, and knee lateral bending, given the bumper and spoiler characteristics as input. Results:The parametric analysis has demonstrated that bumper stiffness, bumper profile height, and spoiler stiffness do have an impact on knee lateral bending, knee shear displacement, and peak tibial acceleration. Increasing bumper stiffness can result in higher knee bending, knee shear displacement, and peak tibial acceleration. Increasing bumper profile height produces lower knee bending and shear displacement. Increasing spoiler stiffness can determine higher knee shear displacement and peak tibial acceleration but lower knee bending. Spoiler stiffness and position have a strong correlation: higher bumper stiffness needs to be coupled to a moved forward spoiler position. The mechanical responses of the spoiler and of the bumper can be assumed to be linear: the softening behavior of the expanded polypropylene foam balances the hardening behavior of the fascia (due to contact area increase). The predictive model is well correlated to experimental findings (R2 > 0.74) Conclusions: This simplified computer model can be used as a prescreening design tool to demonstrate general vehicle front-end design trade-offs and provide approximate results without physical testing. © 2014 Copyright Taylor and Francis Group, LLC.

Keywords: bumper | lower leg | pedestrian | spoiler | vehicle front end

Abstract: The object of this paper is testing the performance of a new device for 3D oral scanning: a two channel PTOF (pulsed time-of-flight) laser scanner, designed for dental and industrial applications in the measurement range of zero to a few centimetres. The application on short distances (0-10 cm) has entailed the improvement of performance parameters such as single shot precision, average precision and walk error up to mm-level and to μm-level respectively. The single-shot precision (σ-value) has resulted to range from 43 to 63 ps (9-10 mm), having considered the measurement range (6.5-10 mm) corresponding to 1-2 V signal; this result agrees well with estimates made from simulations. The average precision has resulted to be dependent on the number of measurements and can reach a value equal to ±25 μm, whenever the measurements frequency is sufficiently high. For example, if the required scanning speed is 1000 points/s and the required average precision is ±25 μm, then a pulses frequency of 30-50 MHz is needed, considering signal amplitude varying between 1-2 V. On the whole, the performance of this new device, based on PTOF has proven to be adequate to its employment in the field of restorative dentistry. © 2013 Elsevier Ltd.

Keywords: CAD/CAM | Intraoral scanner | Laser range-finding techniques | Pulsed time of flight | Restorative dentistry

Abstract: Intra-oral scanning technology is a very fast-growing field in dentistry since it responds to the need of an accurate three-dimensional mapping of the mouth, as required in a large number of procedures such as restorative dentistry and orthodontics. Nowadays, more than 10 intra-oral scanning devices for restorative dentistry have been developed all over the world even if only some of those devices are currently available on the market. All the existing intraoral scanners try to face with problems and disadvantages of traditional impression fabrication process and are based on different non-contact optical technologies and principles. The aim of this publication is to provide an extensive review of existing intraoral scanners for restorative dentistry evaluating their working principles, features and performances. © 2013 Elsevier Ltd.

Keywords: Confocal microscopy | Digital dental impressions | Intraoral scanner | Optical coherence tomography | Triangulation

Abstract: This work analyses blunt abdominal trauma produced by driver-handlebar collision, in low speed two-wheel accidents. A simplified dynamic model is introduced, whose parameters have been estimated on the basis of cadaver tests. This model allows calculating the peak impact force and the abdominal penetration depth; therefore the likelihood of occurrence of serious injuries can be estimated for different masses of contacting bodies and different speeds. Results have been checked against literature data and true-accident reports. Numerical simulations demonstrate that serious injuries (AIS>3) can occur even at low speeds (<20. km/h), therefore the design of protective clothing is recommendable. The model can allow both the analysis of true accident data and the virtual testing of protective equipment in the conceptual design phase. © 2013 Elsevier Ltd.

Keywords: Abdominal injury | Handlebar impact model | Road accidents | Two-wheel riders

Abstract: Under hoist transmission jacks are indispensable tools for vehicle service and maintenance. They are critical due to their high height/base width ratio, large carried weights and size, poor visibility.This work moves from the analysis of an actual accident where a trans-jack overturned; this event is one of manual handling injuries, usually classified as being struck by an object and or equipment in statistical reports. Requirements to achieve a good stability are here studied and defined; more in detail, the dynamic stability of a traveling transmission jack changing its speed has been studied as well as the stability of a transmission jack suddenly stopped due to wheel impingement since, up to now, there is not specific directive addressing these conditions.Results have demonstrated that the instability while translating is not likely to take place for usual geometries; it could become more critical for higher center of mass positions, lower points of application of the force (for example when using feet instead of hands), and for lower carried weights. On the contrary, the instability due to a sudden stop represents a real possibility; it becomes more critical for higher center of mass heights, higher pushing forces, or higher points of application of the force.The introduction of a translation speed limit is therefore strongly recommended. Other operative advice are that higher points of application of the pushing/pulling force are convenient when changing the traveling speed of a transmission jack, while lower handles position should be used while moving at constant speed. © 2014.

Keywords: Dynamic instability | Handle position | Overturning | Transmission jack | Vehicle maintenance

Abstract: The correct estimation of stem boundary conditions in hip arthroplasty cannot be performed simply by subtracting the prosthesis volume from the bone volume: the stem implant path needs to be taken into account. Digital mock-up is a technique commonly applied in the automotive field which can be used for this aim. Given a certain femur, a stem, and an implantation path, the volume of the removed bone stock can be evaluated, as well as the final contact area between the bone and the stem, and, section by section, the residual cortical bone thickness. The technique proved to be useful: if the stem implant path is not considered, the removed bone stock volume can be underestimated up to 6%, while the contact area extension can be overestimated up to 28%. On the whole, a new methodology has been set up and tested, which can be usefully employed to accurately establish stem boundary conditions in the pre-operative planning stage, and in order to perform a reliable structural stress analysis. The methodology implemented here by experienced researchers can be made available to surgeons, setting up an apposite software suite.

Keywords: Bone-implant interface | Finite element method | Hip stem | Primary stability

Abstract: The mechanical behaviour of skin is very important as regards dermatology, surgery and impact trauma. Engineered skin substitutes can bring significant medical benefit, in particular to patients with extensive burn wounds, even if current skin substitutes do not restore normal skin anatomy and its natural mechanical properties. This work considers the mechanical characterization of a particular layer of skin: dermis. Dermis can be used as a filling material and as support in different areas of reconstructive plastic surgery such as post mastectomy reconstructive surgery and abdominal surgery. The aim was to verify the influence of the decellularization treatment on its properties. The specimens were subjected to uniaxial static tests performed with Bose Electroforce® 3200 and experimental data were represented with engineering and real time stress-strain curves. To begin, descriptive parameters were identified for stress vs. strain curves, such as ultimate tensile strength and maximum Young's modulus, and they were subsequently compared through multivariate analysis of variance to determine the influence of specimen cut orientation and decellularization treatment duration. Dermis, that had been decellularized over 5 or 6 weeks, exhibited mechanical properties comparable with natural ones and ultimate tensile strength and maximum Young's modulus were shown to be considerably higher in real time curves than in engineering ones. © 2013 WIT Press.

Keywords: Decellularization treatment | Human dermis | Static characterization

Abstract: Artificial turf is being used more and more often. It is more available than natural turf for use, requires much less maintenance and new products are able to comply with sport performance and athletes' safety. The purpose of this paper is to compare the mechanical and biomechanical responses of two different artificial turf infills (styrene butadiene rubber, from granulated vehicle tires, and thermoplastic rubber granules) and to compare them to the performance of natural fields where amateurs play (beaten earth, substantially).Three mechanical parameters have been calculated from laboratory tests: energy storage, energy losses and surface traction coefficient; results have been correlated with peak accelerations recorded on an instrumented athlete, on the field.The natural ground proved to be stiffer (-15% penetration depth for a given load), and to have a lower dynamic traction coefficient (-48%); the different kinds of infill showed significantly different stiffnesses (varying by more than 23%) and damping behaviour (varying by more than 31%). In running, peak vertical accelerations were lowest in the artificial ground with thermoplastic rubber granules, while, in slalom, both artificial grounds produced higher horizontal peak accelerations compared to the natural ground.Results are discussed in terms of their implications for athletic performance and injury risk. © 2013 Copyright Taylor and Francis Group, LLC.

Keywords: damping | friction | hardness | injury | traction

Abstract: This work is aimed at designing and constructing a loading rig for the synthetic hemi-pelvis; this system has been conceived with the goal of applying differently oriented articular forces in order to experimentally test the stress distribution and the stability of surgical reconstructions like, for example, hip arthroplasty or pelvic fixation. This device can be interfaced with a usual loading machine; it preserves the anatomy of the hemi-pelvis; it is simply constrained and it allows the simulation of all physiologic activities. Moreover, the visual accessibility of the peri-acetabular area has been guaranteed and this is imperative in order to be able to perform full-field analyses like a thermoelastic or photoelastic stress analysis. First experimental trials have shown a good repeatability of loading-unloading cycles (<1.2%), a low hysteresis (<2.4%) and a good dynamic behaviour (up to 10 Hz loading frequencies).

Keywords: Dynamical loading | Hip arthroplasty | Mechanical test | Pelvic fractures | Pelvis | Thermoelastic stress analysis

Abstract: The fundamental passive mechanical properties of the bladder need to be known in order to design the most appropriate long-term surgical repair procedures and develop materials for bladder reconstruction. This study has focused on the bladder tissue viscoelastic behavior, providing a comprehensive analysis of the effects of fibers orientation, strain rate and loading history. Whole bladders harvested from one year old fat pigs (160 kg approximate weight) were dissected along the apex-to-base direction and samples were isolated from the lateral region of the wall, as well as along apex-to-base and transverse directions. Uniaxial monotonic (stress relaxation) and cyclic tests at different frequencies have been performed with the Bose Electroforce ® 3200. Normalized stress relaxation functions have been interpolated using a second-order exponential series and loading and unloading stress-strain curves have been interpolated with a non-linear elastic model. The passive mechanical behavior of bladder tissue was shown to be heavily influenced by frequency and loading history, both in monotonic and cyclic tests. The anisotropy of the tissue was evident in monotonic and in cyclic tests as well, especially in tests performed on an exercised tissue and at high frequencies. In contrast, transverse and apex-to-base samples demonstrated an analogous relaxation behavior. © 2012 - IOS Press and the authors. All rights reserved.

Keywords: cycle number | damping | Dynamic | relaxation | stiffness | viscoelastic

Abstract: A hip prosthesis implant produces a significant deviation in the stress pattern compared with the physiologic condition. In this work, the stress patterns are evaluated experimentally on synthetic femora, by means of thermoelastic stress analysis. Two factors have been considered: stem implantation and head offset. Stress maps were obtained using differential thermography and correlated to these factors. Thermoelastic stress maps have demonstrated to be sensitive to the implant and the head offset. In detail, the standard deviation of stresses can reduce from 5% to 50% (with reference to the physiologic one), depending on stem design; peak stresses change their position or disappear for different implant position or press-fitting, the sensitivity of average stresses to the offset is at least equal to 0.07 MPa/mm. On the whole, a methodology was developed, allowing the experimental evaluation and comparison of the stress distributions produced by different implants. © 2010 World Scientific Publishing Company.

Keywords: hip implant | synthetic femora | Thermoelastic stress analysis

Abstract: This chapter deals with the structural analysis of bone elements, performed both numerically and experimentally. Among numerical techniques, the finite element method is discussed at length, focusing on its applications to bone biomechanics. The main steps involved in the method are analyzed from the practical perspective, and guidelines about dealing with commonly recurring problems are provided. As for experimental methods, considerable space is devoted to full-field techniques, with special attention to the lesser-known method of thermoelastic stress analysis. The main aim of this chapter is to illustrate how numerical and experimental methodologies can complement each other, explaining why it is beneficial to pursue both approaches.

Abstract: The purpose of this study was to establish whether players' perceptions in football competitions played on artificial turf can be influenced by the pitch under examination, the kind of infill material used, the weather conditions and by player's role in the team. A multifactorial statistical analysis was made of the results obtained from over 1600 U.E.F.A. questionnaires completed by amateur footballers. Pitch and weather factors were demonstrated to be relevant to the aspects investigated. Conversely, the players' role and the infill material were significant for only a few aspects; for each variable, the analysis indicated the most favourable conditions. Overall, the analysis provided insight into amateur players' favourable feelings about artificial turf, compared with its natural alternative (actually made of earth, without grass in the case of amateur players). © 2008 Elsevier Ltd. All rights reserved.

Keywords: Amateur football players | Artificial turf | Ergonomics | Survey

Abstract: A review of recent literature revealed a very high success rate of implants used to support a mandibular overdenture as an alternative to the conventional removable dentistry. Today there are already several prosthetic solutions for the same clinical situations: in particular, the implant support can be different depending on the type of implants used and their layout. It is well known that the success or the failure of implants interfaced with bone depends, taking into account a favourable biological reaction, on the structural condition of the biomechanical system constituted by the bone structure and the implant. Knowledge of the strain/stress pattern can allow one to establish if bone maintenance, resorption or addition is more likely to take place. In this work two different kinds of implant supports for overdenture retention were compared by means of FEM: they differed in the number of implants, their dimension, their location inside the mandible and, finally, in the presence/absence of a beam connecting all implants and making them all linked. Clinical follow-up was assessed by means of technetium 99m-MDP scintigraphy. The obtained results agree with the clinical experience.

Keywords: Biomechanics | Bone remodelling | Bone scintigraphy | Dental implants | FEM | Nuclear medicine

Abstract: A thermoelastic stress analysis was done for the evaluation of an thermoelastic effect by using differential thermocameras equipped with array detectors that defies certain limitations of other thermocameras. In addition, the measurement of very small temperature changes does no longer require the use of highly sensitive infrared detectors and a lock-in amplifier. This method is based on a Fourier analysis. An error analysis showed that both absolute and percentage errors are acceptable for most applications. Overall, this method is found to be reliable.

Abstract: Many applications in orthopaedic surgery require the creation of personalised design models that can serve as the basis for navigation in computer aided surgery systems or be used to create a personalised model to perform structural analysis during pre-operative planning or post-operative follow-up. The paper introduces a method for developing a three-dimensional (3D) patient-specific model of a femur bone from an antero-posterior radiograph. A generic femur was employed and was altered on the basis of bone boundaries visible on radiographs. Morphological errors were evaluated against 3D models obtained from computed tomography (CT) scans. When only the antero-posterior radiograph was used, the average radius estimation error was 4.8 mm, the average percentage area estimation error was 14%, and the average percentage estimation error for inertial moments was 15%. If both the medial-lateral and the anterior-posterior radiographs were used, these errors were 2.0 mm, 5% and 7%, respectively. The procedure described can be profitably employed whenever CT scans are not available, such as during a retrospective analysis, or when CT scans cannot be justified because of X-ray exposure and cost considerations. © IFMBE: 2005.

Keywords: 3D model | CT | Femur morphing | Radiographs

Abstract: Thermography was applied in a frequency range that was seldom analyzed. The high excitation frequencies and the uniform specimen loading allowed the assessment of the thermoelastic effect, even using an ordinary thermocamera, which was commonly assumed to be inadequate to evaluate thermoelasticity. The thermoelastic effect was assessed by means of a procedure based on Fourier analysis, so it was possible to filter the signal noise. The methodology allows the evaluation of both loading frequency and stress amplitude.

Keywords: Infrared thermocamera | Spectral analysis | Stress analysis | Thermoelasticity

Abstract: The object of this paper is an investigation of the relationship existing between two experimental techniques, both aimed at the assessment of micro-plastic phenomena and micro-friction inside a material: thermographic analysis and specific damping measurement. A model has been developed here considering the main thermal effects during fatigue tests, and a theoretical relationship between temperature increment and specific damping has been proposed. Successively, an extensive experimentation has been carried on groups of specimens made of two different metals, stressed by means of an Amsler vibrophore. Different stress amplitudes (80-270 MPa) and frequencies (80-160 Hz) have been employed. The analysis of experimental results has allowed the validation of the suggested model, leading, on one side, to the development of a further experimental technique for the evaluation of specific damping, and, on the other side, to the employment of specific damping measurement for the assessment of fatigue in metals. © 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Elastoplastic behaviour | Fatigue | Hysteresis strain energy | Internal damping | Thermal | Thermographic analysis

Abstract: When a metallic material is highly stressed, its internal specific damping capacity increases showing a nonlinear behavior. In spite of this, the most part of experimental methods employ nonhomogeneous stress fields measuring only a volumetric average, often called structural damping. To overcome this problem the procedure herein presented extends the applicability of the plain traction or compression methods to higher frequency range (up to 300 Hz). The introduced methodology corrects for elastic energy and dissipated energy relative to the test machine and to the fixtures. The experimental procedure is based on the acquisition of a decay signal when the test machine excitation force has been removed. Two different methods to extract the pattern of internal damping versus material strain have been compared: one is based on least square exponential fitting while the other employs an autoregressive model. Best results have been obtained combining the two techniques taking into account also the variation of Young’s modulus with strain. The resulting curves of the loss factor as a function of strain amplitude for three steels and two cast irons are presented. © 1998 ASME.

Abstract: The analysis of bone-remodelling processes by means of the relative radiographic follow-up has been proven to be a useful clinical diagnostic tool. A previous study has introduced a computerized, automatic, video-densitometric analysis. The main point of this procedure is that it potentially allows an objective, quantitative analysis of bone remodelling processes. This assertion is addressed by the present study. In particular, this study attempts to assess the repeatability of this procedure and to identify the main sources of noise.

Keywords: Bone-remodelling | Design of experiments | Diagnostics | Digital radiography | Factorial plane | Hip prosthesis | Image processing | Robustness | Video-densitometric analysis

Abstract: When a patient undergoes an arthroprosthesis implant, the stresses acting on the bone are redistributed, and correspondingly, the bone density adjacent to the entire prosthesis changes its pattern. In order to study these phenomena an automatic methodology has been developed: this methodology is based on the bone density measured on X-ray. The method is compared to other bone densitometry methods and to more recent bone remodeling pattern recognition methods; it turns out to be cost-effective and it has the advantage of allowing back-dated investigation exploiting the numerous existing radiograph records relative to arthroplastic follow-up. The results of the set-up videodensitometric analysis show the method not only has diagnostic capability, but also can effectively support prostheses designers; moreover, the results obtained offer a capable support to real-time observation of remodeling processes and to the biomechanical assessment of the behavior of bone implant systems. For the clinical practice a risk index has been set up in order to systematize the numerous data collected from the measuring mesh grids and to monitor dangerous situations, which can end in implant failure. © 1997 Academic Press Limited.

Abstract: Video-densitometric analysis has proved useful in the study of bone remodelling, however, for more efficient results, an investigation procedure that enables the comparison of X-rays is needed. In the present research an automated method has been developed which considerably speeds up the entire procedure through the implementation of specially designed C++ software. At present, a sequence of six X-rays can be analysed in about 1 h irrespective of the number of areas to be investigated, which can be arbitrarily increased (200 or more). Analysis is fast as well as more reliable and accurate. In clinical practice, the results offer an effective support to observations on the biomechanical behaviour of bone implant systems.

Keywords: arthroprosthesis implants | Bone remodelling | follow-up assessment | video-densitometric analysis | X-ray analysis