How does atmospheric pressure cold helium plasma affect the biomechanical behaviour on alkali-lesioned corneas?

BACKGROUND: Melting corneal ulcers are a serious condition that affects a great number of animals and people around the world and it is characterised by a progressive weakening of the tissue leading to possible severe ophthalmic complications, such as visual impairment or blindness. This disease is routinely treated with medical therapy and keratoplasty, and recently also with alternative regenerative therapies, such as cross-linking, amniotic membrane transplant, and laser. Plasma medicine is another recent example of regenerative treatment that showed promising results in reducing the microbial load of corneal tissue together with maintaining its cellular vitality. Since the effect of helium plasma application on corneal mechanical viscoelasticity has not yet been investigated, the aim of this study is first to evaluate it on ex vivo porcine corneas for different exposition times and then to compare the results with previous data on cross-linking treatment. RESULTS: 94 ex vivo porcine corneas divided into 16 populations (healthy or injured, fresh or cultured and treated or not with plasma or cross-linking) were analysed. For each population, a biomechanical analysis was performed by uniaxial stress-relaxation tests, and a statistical analysis was carried out considering the characteristic mechanical parameters. In terms of equilibrium normalised stress, no statistically significant difference resulted when the healthy corneas were compared with lesioned plasma-treated ones, independently of treatment time, contrary to what was obtained about the cross-linking treated corneas which exhibited more intense relaxation phenomena. CONCLUSIONS: In this study, the influence of the Helium plasma treatment was observed on the viscoelasticity of porcine corneas ex vivo, by restoring in lesioned tissue a degree of relaxation similar to the one of the native tissue, even after only 2 min of application. Therefore, the obtained results suggest that plasma treatment is a promising new regenerative ophthalmic therapy for melting corneal ulcers, laying the groundwork for further studies to correlate the mechanical findings with corneal histology and ultrastructural anatomy after plasma treatment.

In silico assessment of the reliability and performance of artificial sphincter for urinary incontinence.

BACKGROUND: The standard artificial urinary sphincter (AUS) is an implantable device for the treatment of urinary incontinence by applying a pressure loading around the urethra through an inflatable cuff, often inducing no-physiological stimulation up to tissue degenerative phenomena. A novel in silico approach is proposed to fill the gap of the traditional procedures by providing tools to quantitatively assess AUS reliability and performance based on AUS-urethra interaction. METHODS: The approach requires the development of 3D numerical models of AUS and urethra, and experimental investigations to define their mechanical behaviors. Computational analyses are performed to simulate the urethral lumen occlusion by AUS inflation under different pressures, and the lumen opening by applying an intraluminal pressure progressively increased under the AUS action (Abaqus Explicit solver). The AUS reliability is evaluated in terms of tissue stimulation by the mechanical fields potentially responsible for vasoconstriction and tissue damage, while the performance by the intraluminal pressure that causes the lumen opening for a specific occlusive pressure, showing the maximum urethral pressure for which continence is guaranteed. RESULTS: The present study implemented the procedure considering the gold standard AMS 800 and a novel patented AUS. Results provided the comparison between two sphincteric devices and the evaluation of the influence of different building materials and geometrical features on the AUS functionality. CONCLUSIONS: The approach was developed for the AUS, but it could be adapted also to artificial sphincters for the treatment of other anatomical dysfunctions, widening the analyzable device configurations and reducing experimental and ethical efforts.

Artificial sphincters: An overview from existing devices to novel technologies.

Artificial sphincters (ASs) are used to replace the function of the biological sphincters in case of severe urinary and fecal incontinence (UI and FI), and gastroesophageal reflux disease (GERD). The design of ASs is established on different mechanisms, e.g., magnetic forces or hydraulic pressure, with the final goal to achieve a implantable and durable AS. In clinical practice, the implantation of in-commerce AS is considered a reasonable solution, despite the sub-optimal clinical outcomes. The failure of these surgeries is due to the malfunction of the devices (between 46 and 51%) or the side effects on the biological tissues (more than 38%), such as infection and atrophy. Concentrating on this latter characteristic, particular attention has been given to the interaction between the biological tissues and AS, pointing out the closing mechanism around the duct and the effect on the tissues. To analyze this aspect, an overview of existing commercial/ready-on-market ASs for GERD, UI, and FI, together with the clinical outcomes available from the in-commerce AS, is given. Moreover, this invited review discusses ongoing developments and future research pathways for creating novel ASs. The application of engineering principles and design concepts to medicine enhances the quality of healthcare and improves patient outcomes. In this context, computational methods represent an innovative solution in the design of ASs, proving data on the occlusive force and pressure necessary to guarantee occlusion and avoid tissue damage, considering the coupling between different device sizes and individual variability.

Patient-specific stomach biomechanics before and after laparoscopic sleeve gastrectomy.

BACKGROUND: Obesity has become a global epidemic. Bariatric surgery is considered the most effective therapeutic weapon in terms of weight loss and improvement of quality of life and comorbidities. Laparoscopic sleeve gastrectomy (LSG) is one of the most performed procedures worldwide, although patients carry a nonnegligible risk of developing post-operative GERD and BE. OBJECTIVES: The aim of this work is the development of computational patient-specific models to analyze the changes induced by bariatric surgery, i.e., the volumetric gastric reduction, the mechanical response of the stomach during an inflation process, and the related elongation strain (ES) distribution at different intragastric pressures. METHODS: Patient-specific pre- and post-surgical models were extracted from Magnetic Resonance Imaging (MRI) scans of patients with morbid obesity submitted to LSG. Twenty-three patients were analyzed, resulting in forty-six 3D-geometries and related computational analyses. RESULTS: A significant difference between the mechanical behavior of pre- and post-surgical stomach subjected to the same internal gastric pressure was observed, that can be correlated to a change in the global stomach stiffness and a minor gastric wall tension, resulting in unusual activations of mechanoreceptors following food intake and satiety variation after LSG. CONCLUSIONS: Computational patient-specific models may contribute to improve the current knowledge about anatomical and physiological changes induced by LSG, aiming at reducing post-operative complications and improving quality of life in the long run.

Porcine Small Intestinal Submucosa (SIS) as a Suitable Scaffold for the Creation of a Tissue-Engineered Urinary Conduit: Decellularization, Biomechanical and Biocompatibility Characterization Using New Approaches.

Bladder cancer (BC) is among the most common malignancies in the world and a relevant cause of cancer mortality. BC is one of the most frequent causes for bladder removal through radical cystectomy, the gold-standard treatment for localized muscle-invasive and some cases of high-risk, non-muscle-invasive bladder cancer. In order to restore urinary functionality, an autologous intestinal segment has to be used to create a urinary diversion. However, several complications are associated with bowel-tract removal, affecting patients' quality of life. The present study project aims to develop a bio-engineered material to simplify this surgical procedure, avoiding related surgical complications and improving patients' quality of life. The main novelty of such a therapeutic approach is the decellularization of a porcine small intestinal submucosa (SIS) conduit to replace the autologous intestinal segment currently used as urinary diversion after radical cystectomy, while avoiding an immune rejection. Here, we performed a preliminary evaluation of this acellular product by developing a novel decellularization process based on an environmentally friendly, mild detergent, i.e., Tergitol, to replace the recently declared toxic Triton X-100. Treatment efficacy was evaluated through histology, DNA, hydroxyproline and elastin quantification, mechanical and insufflation tests, two-photon microscopy, FTIR analysis, and cytocompatibility tests. The optimized decellularization protocol is effective in removing cells, including DNA content, from the porcine SIS, while preserving the integrity of the extracellular matrix despite an increase in stiffness. An effective sterilization protocol was found, and cytocompatibility of treated SIS was demonstrated from day 1 to day 7, during which human fibroblasts were able to increase in number and strongly organize along tissue fibres. Taken together, this in vitro study suggests that SIS is a suitable candidate for use in urinary diversions in place of autologous intestinal segments, considering the optimal results of decellularization and cell proliferation. Further efforts should be undertaken in order to improve SIS conduit patency and impermeability to realize a future viable substitute.

Mechanical behaviour of healthy versus alkali-lesioned corneas by a porcine organ culture model.

BACKGROUND: Cornea is a composite tissue exhibiting nonlinear and time-dependent mechanical properties. Corneal ulcers are one of the main pathologies that affect this tissue, disrupting its structural integrity and leading to impaired functions. In this study, uniaxial tensile and stress-relaxation tests are developed to evaluate stress-strain and time-dependent mechanical behaviour of porcine corneas. RESULTS: The samples are split in two groups: some corneas are analysed in an unaltered state (healthy samples), while others are injured with alkaline solution to create an experimental ulcer (lesioned samples). Furthermore, within each group, corneas are examined in two conditions: few hours after the enucleation (fresh samples) or after 7 days in a specific culture medium for the tissue (cultured samples). Finally, another condition is added: corneas from all the groups undergo or not a cross-linking treatment. In both stress-strain and stress-relaxation tests, a weakening of the tissue is observed due to the imposed conditions (lesion, culture and treatment), represented by a lower stiffness and increased stress-relaxation. CONCLUSIONS: Alkali-induced corneal stromal melting determines changes in the mechanical response that can be related to a damage at microstructural level. The results of the present study represent the basis for the investigation of traditional and innovative corneal therapies.

Infrapatellar Fat Pad Gene Expression and Protein Production in Patients with and without Osteoarthritis.

Osteoarthritis (OA) is one of the most common joint disorders. Evidence suggests that the infrapatellar fat pad (IFP) is directly involved in OA pathology. However, a comparison between OA versus non-OA IFP is still missing. Thus, the aim of this study was to compare IFP molecular, adipocytes and extracellular matrix characteristics of patients affected by OA, and patients undergoing anterior cruciate ligament (ACL) reconstruction. We hypothesized that not only inflammation but also changes in adipocytes and extracellular matrix (ECM) composition might be involved in OA pathogenesis. Fifty-three patients were enrolled. IFP biopsies were obtained, evaluating: (a) lymphocytic infiltration and vascularization; (b) adipocytes area and number; (c) adipo-cytokines and extracellular matrix gene expression levels; (d) IL-6 and VEGF protein production; (e) collagen fibers distribution. OA IFP was more inflamed and vascularized compared to ACL IFP. OA IFP adipocytes were larger and numerically lower (1.3-fold) than ACL IFP adipocytes. An increase of gene expression of typical white adipose tissue genes was observed in OA compared to ACL IFP. Collagen-types distribution was different in the OA IFP group compared to controls, possibly explaining the change of the biomechanical characteristics found in OA IFP. Statistical linear models revealed that the adipocyte area correlated with BMI in the OA group. In conclusion, inflammation and fibrotic changes of OA IFP could represent novel therapeutic targets to counteract OA.

Interaction phenomena between a cuff of an artificial urinary sphincter and a urethral phantom.

Male urinary incontinence is highly prevalent, leading to a miserable quality of life. The artificial urinary sphincter (AUS) is the device that closely simulates the function of the biological urinary sphincter. The precise evaluation of occlusion mechanisms and of interaction phenomena occurring between AUS cuff and urethral duct is fundamental for more reliable design. The action induced in the interaction with urethral duct under a specific pressure depends on its constitutive material and structural characteristics. The methods of experimental and computational bioengineering are exploited to investigate mechanical functionality of the coupled system, as AUS and urethral duct. Experimental tests are developed to investigate the response when the AUS is inflated around a urethral phantom. Numerical model of the cuff is developed mimicking the experimental tests for the validation. Subsequently, numerical models are exploited to interpret the interaction of the cuff with urethral phantoms considering the influence of urethral size and of tissues mechanical behavior, mimicking healthy and degraded configurations. The investigation provides useful information on the behavior of AUS cuff with urethral duct evaluating the action induced and represents a support for planning an extension of experimental tests on animal and human urethral samples.

Experimental investigation of the biomechanics of urethral tissues and structures.

NEW FINDINGS: What is the central question of this study? Prostheses for treatment of urinary incontinence elicit complications associated with an inadequate mechanical action. This investigation aimed to define a procedure addressed to urethral mechanical characterization. Experimental tests are the basis for constitutive formulation, with a view to numerical modelling for investigation of the interaction between the tissues and a prosthesis. What is the main finding and its importance? Horse urethra, selected for its histomorphometric similarity to human urethra, was characterized by integrated histological analysis and mechanical tests on the biological tissue and structure, leading to constitutive formulation. A non-linear, anisotropic and time-dependent response was found, representing a valid basis for development of a numerical model to interpret the functional behaviour of the urethra. Urinary dysfunction can lead to incontinence, with an impact on the quality of life. Severe dysfunction can be overcome surgically by the use of an artificial urinary sphincter. Nonetheless, several complications may result from inappropriate functioning of the prosthesis, in many instances resulting from an unsuitable mechanical action of the device on the urethral tissues. Computational models allow investigation of the mechanical interaction between biological tissues and biomedical devices, representing a potential support for surgical practice and prosthesis design. The development of such computational tools requires experimental data on the mechanics of biological tissues and structures, which are rarely reported in the literature. The aim of this study was to provide a procedure for the mechanical characterization of urethral tissues and structures. The experimental protocol included the morphometric and histological analysis of urethral tissues, the mechanical characterization of the response of tissues to tensile and stress-relaxation tests and evaluation of the behaviour of urethral structures by inflation tests. Results from the preliminary experiments were processed, adopting specific model formulations, and also providing the definition of parameters that characterize the elastic and viscous behaviour of the tissues. Different experimental protocols, leading to a comprehensive set of experimental data, allow for a reciprocal assessment of reliability of the investigation approach.

A review of the effects of some endocrinological factors on respiratory mechanics.

CONTEXT: Endocrinological factors have been recently described to affect respiratory mechanics. OBJECTIVE: To review recent literature data, most of all obtained by the end-inflation occlusion method, describing the effects of molecules of endocrinological interest such as endothelin, erythropoietin and renin-angiotensin, on respiratory mechanics parameters. METHODS: The papers considered in this review were found by inserting in Pubmed/Medline the following indexing terms: hormones, endothelin, erythropoietin, angiotensin and respiratory mechanics. RESULTS: It was found that the above cited molecules, beside their well known physiological main effects, exhibit influences on respiratory mechanics, most of all on the airflow resistance, which was described to be increased by endothelin and angiotensin, and decreased by erythropoietin. CONCLUSIONS: A number of molecules of biological interest exhibit unexpected influences on respiratory mechanics. The clinical effects depend on the consequences of modified inspiratory pressure values the respiratory muscles have to perform for a given breathing pattern.

The volume dependence of stress relaxation in the rat respiratory system.

AIM: To investigate the volume dependence of respiratory system stress relaxation in anesthetized, positive-pressure ventilated rats. MATERIALS AND METHODS: The effects on respiratory system stress relaxation of changing the end inflation volume while keeping tidal volume constant, and of changing the tidal volume while maintaining constant end inflation volume, were separately studied by the end-inflation occlusion method. These changes were obtained by inflating the respiratory system starting from different volumes above functional residual capacity. RESULTS: We found that: (1) a simple exponential equation well describe the visco-elastic pressure drop for different inflation modalities; (2) the stress relaxation-linked, visco-elastic pressure drop, increases with increasing the tidal volume and keeping the end-inflation volume constant, but is independent from the end-inflation lung volume at constant tidal volumes; (3) time constant values show a significant increment with end-inflation volume at constant tidal volume but result independent from tidal volume variation at constant end-inflation volume. CONCLUSIONS: Stress relaxation-linked pressure dissipation increases with increasing tidal volume independently from end-inspiratory volume.

A review of recent findings about stress-relaxation in the respiratory system tissues.

This article reviews the state of the art about an unclear physiological phenomenon interesting respiratory system tissues, i.e., stress-relaxation. Due to their visco-elastic properties, the tissues do not maintain constant stress under constant deformation. Rather, the stress slowly relaxes and falls to a lower value. The exact molecular basis of this complex visco-elastic behavior is not well defined, but it has been suggested that it may be generated because of the anisotropic mechanical properties of elastin and collagen fibers in the alveolar septa and their interaction phenomena, such as reciprocal sliding, also in relation to interstitial liquid movements. The effects on stress-relaxation of various biochemical and physical factors are reviewed, including the consequences of body temperature variations, respiratory system inflammations and hyperbaric oxygen exposure, endocrinal factors, circulating blood volume variations, changes in inflation volume and/or flow, changes in intra-abdominal pressure because of pneumoperitoneum or Trendelenburg position. The effects of these factors on stress-relaxation have practical consequences because, depending on visco-elastic pressure amount which is requested to inflate the respiratory system in different conditions, respiratory muscles have to produce different values of inspiratory pressure during spontaneous breathing. High inspiratory pressure values might increase the risk of respiratory failure development on mechanical basis.

How does sutures pattern influence stomach motility after endoscopic sleeve gastroplasty? A computational study.

The relatively recent adoption of Endoscopic Sleeve Gastroplasty (ESG) amongst obese patients has gained approval within the surgical community due to its notable benefits, including significant weight loss, safety, feasibility, repeatability, and potential reversibility. However, despite its promising clinical outcomes and reduced invasiveness, there is still a lack of standardised procedures for performing ESG. Multiple suture patterns and stitching methods have been proposed over time, yet rational tools to quantify and compare their effects on gastric tissues are absent. To address this gap, this study proposed a computational approach. The research involved a case study analyzing three distinct suture patterns (C-shaped, U-shaped and Z-shaped) using a patient-specific computational stomach model generated from magnetic resonance imaging. Simulations mimicked food intake by placing wire features in the intragastric cavity to replicate sutures, followed by applying a linearly increasing internal pressure up to 15 mmHg. The outcomes facilitated comparisons between suture configurations based on pressure-volume behaviours and the distribution of maximum stress on biological tissues, revealing the U-shaped as the more effective in terms of volume reduction, even if with reduced elongation strains and increased tissues stresses, whereas the Z-shaped is responsible of the greatest stomach shortness after ESG. In summary, computational biomechanics methods serve as potent tools in clinical and surgical settings, offering insights into aspects that are challenging to explore in vivo, such as tissue elongation and stress. These methods allow for mechanical comparisons between different configurations, although they might not encompass crucial clinical outcomes.

Ex vivo, in vivo and in silico studies of corneal biomechanics: a systematic review.

Healthy cornea guarantees the refractive power of the eye and the protection of the inner components, but injury, trauma or pathology may impair the tissue shape and/or structural organization and therefore its material properties, compromising its functionality in the ocular visual process. It turns out that biomechanical research assumes an essential role in analysing the morphology and biomechanical response of the cornea, preventing pathology occurrence, and improving/optimising treatments. In this review, ex vivo, in vivo and in silico methods for the corneal mechanical characterization are reported. Experimental techniques are distinct in testing mode (e.g., tensile, inflation tests), samples' species (human or animal), shape and condition (e.g., healthy, treated), preservation methods, setup and test protocol (e.g., preconditioning, strain rate). The meaningful results reported in the pertinent literature are discussed, analysing differences, key features and weaknesses of the methodologies adopted. In addition, numerical techniques based on the finite element method are reported, incorporating the essential steps for the development of corneal models, such as geometry, material characterization and boundary conditions, and their application in the research field to extend the experimental results by including further relevant aspects and in the clinical field for diagnostic procedure, treatment and planning surgery. This review aims to analyse the state-of-art of the bioengineering techniques developed over the years to study the corneal biomechanics, highlighting their potentiality to improve diagnosis, treatment and healing process of the corneal tissue, and, at the same, pointing out the current limits in the experimental equipment and numerical tools that are not able to fully characterize in vivo corneal tissues non-invasively and discourage the use of finite element models in daily clinical practice for surgical planning.

Mechanical characterization of porcine ureter for the evaluation of tissue-engineering applications.

Introduction: Clinics increasingly require readily deployable tubular substitutes to restore the functionality of structures like ureters and blood vessels. Despite extensive exploration of various materials, both synthetic and biological, the optimal solution remains elusive. Drawing on abundant literature experiences, there is a pressing demand for a substitute that not only emulates native tissue by providing requisite signals and growth factors but also exhibits appropriate mechanical resilience and behaviour. Methods: This study aims to assess the potential of porcine ureters by characterizing their biomechanical properties in their native configuration through ring and membrane flexion tests. In order to assess the tissue morphology before and after mechanical tests and the eventual alteration of tissue microstructure that would be inserted in material constitutive description, histological staining was performed on samples. Corresponding computational analyses were performed to mimic the experimental campaign to identify the constitutive material parameters. Results: The absence of any damages to muscle and collagen fibres, which only compacted after mechanical tests, was demonstrated. The experimental tests (ring and membrane flexion tests) showed non-linearity for material and geometry and the viscoelastic behaviour of the native porcine ureter. Computational models were descriptive of the mechanical behaviour ureteral tissue, and the material model feasible. Discussion: This analysis will be useful for future comparison with decellularized tissue for the evaluation of the aggression of cell removal and its effect on microstructure. The computational model could lay the basis for a reliable tool for the prediction of solicitation in the case of tubular substitutions in subsequent simulations.

Biomechanics of Hollow Organs: Experimental Testing and Computational Modeling.

Hollow organs are visceral organs that are hollow tubes or pouches (such as the intestine or the stomach, respectively) or that include a cavity (such as the heart) and which subserve a vital function [...].

Unveiling the effects of key factors in enhancing gastroesophageal reflux: A fluid-structure analysis before and after laparoscopic sleeve gastrectomy.

BACKGROUND AND OBJECTIVES: Gastro-oesophageal reflux disease (GERD) consists in the passage of gastric acid content from the stomach to the oesophagus, causing burns and deteriorating the quality of life. Laparoscopic Sleeve Gastrectomy (LSG) could induce de novo GERD and worsen pre-existing GERD because of the higher gastric pressurisation, reduction of stomach volume and a wider His-angle. In the proposed work, various computational gastric 2D models were developed to understand the effects of variables such as the His-angle, the antral dimension, and the bolus viscosity on the reflux increase. METHODS: Fluid-Structure Interaction (FSI) computational models which couple the solid mechanics of the gastric wall, and the fluid domain of the bolus, have been developed to shed light on biomechanical aspects of GERD after LSG. A closure was imposed to the lower oesophageal sphincter (LES) mimicking what happens physiologically after food intake. RESULTS: Results showed that the configuration prone to higher reflux flow was the post-surgical 65° model with a staple line starting directly from the pylorus without antral preservation, for all considered viscosities. Increasing viscosity, reflux flow decreased. Post-surgical refluxes were higher than pre-ones and decreased with increasing antrum preservation. CONCLUSIONS: These results could be a starting point for analysis of anatomical features, bariatric surgery and GERD occurrence. Further studies based on 3D geometries need to be performed.

Influence of transurethral catheters on urine pressure-flow relationships in males: A computational fluid-dynamics study.

BACKGROUND AND OBJECTIVE: In the field of urology, the pressure-flow study (PFS) is an essential urodynamics practise which requires the patient's transurethral catheterization during the voiding phase of micturition to evaluate the functionality of the lower urinary tract (LUT) and reveal the pathophysiology of its dysfunctionality. However, the literature evidences confusion regarding the interference of the catheterization on the urethral pressure-flow behaviour. METHODS: The present research study represents the first Computational Fluid-Dynamics (CFD) approach to this urodynamics issue, analysing the influence of a catheter in the male LUT through case studies which included the inter-individual and intra-individual dependence. A set of four three dimensional (3D) models of the male LUT, different in urethral diameters, and a set of three 3D models of the transurethral catheter, diverse in calibre, were developed leading to 16 CFD non-catheterized either catheterized configurations, to describe the typical micturition scenario considering both urethra and catheter characteristics. RESULTS: The developed CFD simulations showed that the urine flow field during micturition was influenced by the urethral cross-sectional area and each catheter determined a specific decrease in flow rate if compared to the relative free uroflow. CONCLUSIONS: In-silico methods allow to analyse relevant urodynamics aspects, which could not be investigated in vivo, and may support the clinical PFS to reduce uncertainty on urodynamic diagnosis.

Mechanical Characterization of Human Fascia Lata: Uniaxial Tensile Tests from Fresh-Frozen Cadaver Samples and Constitutive Modelling.

Human Fascia Lata (FL) is a connective tissue with a multilayered organization also known as aponeurotic fascia. FL biomechanics is influenced by its composite structure formed by fibrous layers (usually two) separated by loose connective tissue. In each layer, most of the collagen fibers run parallel in a distinct direction (with an interlayer angle that usually ranges from 75-80°), mirroring the fascia's ability to adapt and withstand specific tensile loads. Although FL is a key structure in several musculoskeletal dysfunctions and in tissue engineering, literature still lacks the evidence that proves tissue anisotropy according to predominant collagen fiber directions. For this purpose, this work aims to analyze the biomechanical properties of ex-vivo FL (collected from fresh-frozen human donors) by performing uniaxial tensile tests in order to highlight any differences with respect to loading directions. The experimental outcomes showed a strong anisotropic behavior in accordance with principal collagen fibers directions, which characterize the composite structure. These findings have been implemented to propose a first constitutive model able to mimic the intra- and interlayer interactions. Both approaches could potentially support surgeons in daily practices (such as graft preparation and placement), engineers during in silico simulation, and physiotherapists during musculoskeletal rehabilitation, to customize a medical intervention based on each specific patient and clinical condition.

Mechanical Behaviour of Plantar Adipose Tissue: From Experimental Tests to Constitutive Analysis.

Plantar adipose tissue is a connective tissue whose structural configuration changes according to the foot region (rare or forefoot) and is related to its mechanical role, providing a damping system able to adsorb foot impact and bear the body weight. Considering this, the present work aims at fully describing the plantar adipose tissue's behaviour and developing a proper constitutive formulation. Unconfined compression tests and indentation tests have been performed on samples harvested from human donors and cadavers. Experimental results provided the initial/final elastic modulus for each specimen and assessed the non-linear and time-dependent behaviour of the tissue. The different foot regions were investigated, and the main differences were observed when comparing the elastic moduli, especially the final elastic ones. It resulted in a higher level for the medial region (89 ± 77 MPa) compared to the others (from 51 ± 29 MPa for the heel pad to 11 ± 7 for the metatarsal). Finally, results have been used to define a visco-hyperelastic constitutive model, whose hyperelastic component, which describes tissue non-linear behaviour, was described using an Ogden formulation. The identified and validated tissue constitutive parameters could serve, in the early future, for the computational model of the healthy foot.