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: 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: Computational image aesthetics aims at determining what makes an image look pleasing. Assessing image aesthetics usually relies on the extraction of suitable image features related, for instance, to image composition (e.g. rule of third, depth of field), texture, shape and colour. It is widely accepted that colour, in particular, plays a major role in this context. The objective of this study was to investigate potential relationships between the most significant colours in an image (the colour theme, or palette) and the aesthetic rating. To this end we defined a procedure for colour palette extraction and its characterisation by a set of 21 hand-crafted features. Rank-based correlations between the features and manually-assigned aesthetic ratings were assessed by Spearman’s correlation coefficient. Experimenting on a total of 4,647 images from the public dataset EVA we found that 12 features were significantly associated with image aesthetics, although the overall correlation strength was at best weak. In particular, perceived aesthetic rating correlated positively with saturation (indicating a slight preference for colourfulness) and negatively with colour temperature (suggesting a slight preference for warm colours). A significant positive correlation (but again weak) also emerged between perceived aesthetic and harmonic colour schemes

Keywords: Aesthetic rating | Colour | Image aesthetics | Visual perception

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: 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: Indeterminate lung nodules detected on CT scans are common findings in clinical practice. Their correct assessment is critical, as early diagnosis of malignancy is crucial to maximise the treatment outcome. In this work, we evaluated the role of form factors as imaging biomarkers to differentiate benign vs. malignant lung lesions on CT scans. We tested a total of three conventional imaging features, six form factors, and two shape features for significant differences between benign and malignant lung lesions on CT scans. The study population consisted of 192 lung nodules from two independent datasets, containing 109 (38 benign, 71 malignant) and 83 (42 benign, 41 malignant) lung lesions, respectively. The standard of reference was either histological evaluation or stability on radiological followup. The statistical significance was determined via the Mann–Whitney U nonparametric test, and the ability of the form factors to discriminate a benign vs. a malignant lesion was assessed through multivariate prediction models based on Support Vector Machines. The univariate analysis returned four form factors (Angelidakis compactness and flatness, Kong flatness, and maximum projection sphericity) that were significantly different between the benign and malignant group in both datasets. In particular, we found that the benign lesions were on average flatter than the malignant ones; conversely, the malignant ones were on average more compact (isotropic) than the benign ones. The multivariate prediction models showed that adding form factors to conventional imaging features improved the prediction accuracy by up to 14.5 pp. We conclude that form factors evaluated on lung nodules on CT scans can improve the differential diagnosis between benign and malignant lesions.

Keywords: computed tomography | form factors | lung cancer | radiomics

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: 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: One of the main limitations in subject-centred design approach is represented by getting 3D models of the region of interest. Indeed, 3D reconstruction from imaging data (i.e., computed tomography scans) is expensive and exposes the subject to high radiation doses. Statistical Shape Models (SSMs) are mathematical models able to describe the variability associated to a population and allow predicting new shapes tuning model parameters. These parameters almost never have a physical meaning and so they cannot be directly related to morphometric features. In this study a gender-combined SSM model of the human mandible was setup, using Generalised Procrustes Analysis and Principal Component Analysis on a dataset of fifty mandibles. Twelve morphometric features, able to characterise the mandibular bone and readily collectable during external examinations, were recorded and correlated to SSM parameters by a multiple linear regression approach. Then a cross-validation procedure was performed on a control set to determine the combination of features able to minimise the average deviation between real and predicted shapes. Compactness of the SSM and main modes of deformations have been investigated and results consistent with previous works involving a higher number of shapes were found. A combination of five features was proved to characterise predicted shapes minimising the average error. As completion of the work, a male SSM was developed and performances compared with those of the combined SSM. The features-based model here proposed could represent a useful and easy-to-use tool for the generation of 3D customised models within a virtual interactive design environment.

Keywords: Features selection | Mandible | Morphometric measurements | PCA | Predicted shapes | Statistical shape model | Subject-specific model

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: 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: Radiological examination of pulmonary nodules on CT involves the assessment of the nodules’ size and morphology, a procedure usually performed manually. In recent years computer-assisted analysis of indeterminate lung nodules has been receiving increasing research attention as a potential means to improve the diagnosis, treatment and follow-up of patients with lung cancer. Computerised analysis relies on the extraction of objective, reproducible and standardised imaging features. In this context the aim of this work was to evaluate the correlation between nine IBSI-compliant morphological features and three manually-assigned radiological attributes – lobulation, sphericity and spiculation. Experimenting on 300 lung nodules from the open-access LIDC-IDRI dataset we found that the correlation between the computer-calculated features and the manually-assigned visual scores was at best moderate (Pearson’s r between -0.61 and 0.59; Spearman’s ρ between -0.59 and 0.56). We conclude that the morphological features investigated here have moderate ability to match/explain manually-annotated lobulation, sphericity and spiculation.

Keywords: Lung cancer | Morphological features | Pulmonary nodules | Radiomics

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: Colour and texture are two perceptual stimuli that determine, to a great extent, the appearance of objects, materials and scenes. The ability to process texture and colour is a fundamental skill in humans as well as in animals; therefore, reproducing such capacity in artificial (‘intelligent’) systems has attracted considerable research attention since the early 70s. Whereas the main approach to the problem was essentially theory-driven (‘hand-crafted’) up to not long ago, in recent years the focus has moved towards data-driven solutions (deep learning). In this overview we retrace the key ideas and methods that have accompanied the evolution of colour and texture analysis over the last five decades, from the ‘early years’ to convolutional networks. Specifically, we review geometric, differential, statistical and rank-based approaches. Advantages and disadvantages of traditional methods vs. deep learning are also critically discussed, including a perspective on which traditional methods have already been subsumed by deep learning or would be feasible to integrate in a data-driven approach.

Keywords: Colour | Deep learning | Texture | Visual recognition

Abstract: Computer-assisted analysis of three-dimensional imaging data (radiomics) has received a lot of research attention as a possible means to improve the management of patients with lung cancer. Building robust predictive models for clinical decision making requires the imaging features to be stable enough to changes in the acquisition and extraction settings. Experimenting on 517 lung lesions from a cohort of 207 patients, we assessed the stability of 88 texture features from the following classes: first-order (13 features), Grey-level Co-Occurrence Matrix (24), Grey-level Difference Matrix (14), Grey-level Run-length Matrix (16), Grey-level Size Zone Matrix (16) and Neighbouring Grey-tone Difference Matrix (five). The analysis was based on a public dataset of lung nodules and open-access routines for feature extraction, which makes the study fully reproducible. Our results identified 30 features that had good or excellent stability relative to lesion delineation, 28 to intensity quantisation and 18 to both. We conclude that selecting the right set of imaging features is critical for building clinical predictive models, particularly when changes in lesion delineation and/or intensity quantisation are involved.

Keywords: Computed tomography | Intensity quantisation | Lesion delineation | Lung nodules | Radiomics | Stability | Texture features

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 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: The most recent developments of Fused Deposition Modelling (FDM) techniques are moving the application of Additive Manufacturing (AM) technologies toward new areas of investigation such as the biomedical, aerospace, and marine engineering in addition to the more consolidated industrial and civil fields. Some specific characteristics are required for the components designed for peculiar applications, such as complex geometries, lightweight, and high strength as well as breathability and aesthetic appearance specifically in the biomedical field. All these design specifications could be potentially satisfied by manufacturing with 3D printing techniques. Moreover, the development of purpose-dedicated filaments can be considered a key factor to successfully meet all the requirements. In this paper, fabrication and applications of five new thermoplastic materials with fillers are described and analyzed. They are organic bio-plastic compounds made of polylactic acid (PLA) and organic by-products. The growing interest in these new composite materials reinforced with organic by-products is due to the reduction of production management costs and their low environmental impact. In this study, the production workflow has been set up and described in detail. The main properties of these new thermoplastic materials have been analyzed with a major emphasis on strength, lightweight, and surface finish. The analysis showed that these materials can be particularly suitable for biomedical applications. Therefore, two different biomedical devices were selected and relative prototypes were manufactured with one of the analyzed thermoplastic materials. The feasibility, benefits, and performance of the thermoplastic material considered for these applications were successfully assessed.

Keywords: Additive manufacturing capability | Biomedical applications | Design | Mechanical properties | Organic bio-composite filament | Roughness

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: 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: 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: Current Fused Deposition Modelling (FDM) techniques have promoted the extension of 3D printing technologies to new applications ranging from the biomedical, aerospace, and submarine fields, to some specific applications in manufacturing and civil fields. The expansion of the fields of application, generally, entails considering peculiar characteristics, such as complex geometries or requirements as low density. Furthermore, the breathability, the pleasantness to the touch, aesthetic appearance and a strong visual identity, that can be achieved by means of 3D printing, are especially requested for some applications such as biomedical. For the improvement of the manufacturing of these parts, the design of a dedicated filament is a relevant issue to be taken into account. polylactic acid (PLA) and organic by-products from agricultural waste. The study includes a preliminary illustration of the main properties of these materials and a biomedical application of such bio-plastic compounds through experimental testing in order to assess the suitability to FDM printing. In particular, the performance in terms of lightweight, strength and roughness have been evaluated. The interesting final properties make these materials suitable for biomedical applications as it is shown in this study for the neck collar prototype reported. In addition, such innovative bio-composite materials allow reducing the cost of environmental impact as well as the production management costs.

Keywords: Additive manufacturing capability | Bio-plastic compounds | Biomedical applications | Mechanical properties | Organic bio-composite filament | Roughness

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: 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: The pre-operative planning of a hip arthroplasty entails the choice of the prosthetic hip model and of the position of both joint components with reference to bone. Assessing the impact of geometrical factors on the final hip range of motion (ROM) is not trivial, since it requires performing 3D evaluations. Nonetheless, it deserves to be studied since hip impingement and dislocation are still relevant complications in hip arthroplasty.This work pertains a numerical model for the assessment of the hip ROM in relation to cotyle position. External/internal rotation is considered as a benchmark, and multiple combinations of acetabular anteversion/inclination are considered.According to results, over two hundred different geometric configurations can be examined in few minutes, and the cotyle position can be so optimized with relevant benefits in term of hip ROM.

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: PLA is an organic polymer that lends itself to multiple applications. It is commonly used in fused deposition modeling technology (FDM), which operates by depositing successive layers of material. The material extrusion, in the form of a wire, follows an imposed pattern, which influences the static and dynamic behavior of the final component. In the literature there are many works concerning the mechanical characterization of the PLA but, due to the natural orthotropy of the FDM process and, above all, to the ascertained influence of the particular technical system with which the operations are performed, it is necessary to characterize the extruded material through different metrological techniques. In order to allow the use of this technology for structural elements production, in the present work, quasi-static tests have been carried out to characterize the material and the process considering the three spatial growth directions (x, y and z). In particular, uniaxial tensile tests were performed for the determination of mechanical strength, modulus of elasticity and percentage elongation.

Keywords: 3D Printing | Acrylonitrile | Butadiene styrenepolylactic acid | FDM | Rapid prototyping | Tensile strength

Abstract: When a new material for the realization of an implantable device in the bone is being studied, in addition to its chemical-physical-mechanical characterization, tests regarding osteointegration are performed. Usually, researchers evaluate the ability of biomaterials to bind to the bone under load-bearing conditions, through animal experiments in the phase of a preclinical study, provided the respective authorization by the ethics committee. In more detail, plugs made of the material under investigation are prepared and implanted into a weight-bearing portion of the skeleton of animals (typically into the knee joint of goats, pigs, rabbits or dogs); after a pre-set time, the animal is sacrificed, the bone element is extracted, it is tested mechanically – generally by means of a pull-out test – and finally it is examined histologically. Mechanical tests often require demanding specimen preparation, which could bias results. In the scope of a research regarding the interface behaviour of a ceramic plug (two different ceramic plugs) compared to a titanium one, the authors have suggested a novel testing technique which allows to perform ‘push-in’ tests, instead of the more common pull-out tests. This methodology has been followed here to compare titanium versus ceramic plugs at different times from implant (0, 3 months, 1 year) into goat knees. As a result, the study reports the shear resistance of bone–plug interfaces. The statistical analysis of the data allowed us to establish that titanium plugs systematically exhibit a higher resistance (p&lt;0.10); this resistance undergoes a significant increment as time passes (p&lt;0.07) due to progressive osteointegration.

Keywords: Biomaterial interface | Bone | Mechanical test | Osteointegration

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: 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