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The main purpose of tissue engineering is to fabricate and exploit engineered constructs suitable for the effective replacement of damaged tissues and organs, and able to perfectly integrate with the host’s organism without eliciting any adverse reaction. Ideally, autologous materials represent the best option, but they are often limited due to the low availability of compatible healthy tissues. So far, one therapeutic approach relies on the exploitation of synthetic materials: they exhibit good features in terms of impermeability, deformability and flexibility, but present chronic risks of infections and inflammations. Alternatively, biological materials, including naturally derived ones and acellular tissue matrices of human or animal origin, can be used to induce cells growth and differentiation, which are needed for tissue regeneration: however, this kind of materials lacks satisfactory mechanical resistance and reproducibility, affecting their clinical application. In order to overcome the above-mentioned limitations, hybrid materials, which can be obtained by coupling synthetic polymers and biological materials, have been investigated with the aim to improve biological compatibility and mechanical features. Currently, the interest in these mate-rials is growing, but the ideal ones have not been found yet. The present review aims at exploring some applications of hybrid materials, with particular mention to urological and cardiovascular fields: in the first case, the efforts to find a construct that can guarantee impermeability, mechanical resistance and patency will be herein illustrated; in the second case, the search for impermeability, hemocompatibility and adequate compliance will be been disclosed.

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 [...]

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.

The infrapatellar fat pad is an adipose tissue in the knee that facilitates the distribution of synovial fluid and absorbs impulsive actions generated through the joint. The correlation between morphological configuration and mechanical properties is analyzed by a computational approach. The microscopic anatomy of the infrapatellar fat pad is studied aiming to measure the dimension of adipose lobules and the thickness of connective septa. Results from histomorphometric investigations show that the infrapatellar fat pad is an inhomogeneous tissue, constituted by large lobules in the superficial part and smaller lobules in the deepest one. Finite element models of the infrapatellar fat pad are developed. The first model considers the inhomogeneous conformation of the infrapatellar fat pad, composed of micro- and macro-chambers, while the second model considers a homogeneous distribution of adipose lobules with similar dimensions. Computational analyses are performed considering the static standing configuration and the passive flexion–extension movement. The computational results allow us to identify the different stress and strain fields within the tissue and to appreciate the variation of the mechanical performance of the overall system considering the distribution of adipose lobules. Results show that the distribution of adipose lobules in macro- and micro-chambers allows major deformation of the infrapatellar fat pad, decreasing the stress inside the tissues.

The mechanical characterization of adipose tissues is important for various medical purposes, including plastic surgery and biomechanical applications, such as computational human body models for the simulation of surgical procedures or injury prediction, for example, in the evaluation of vehicle crashworthiness. In this context, the measurement of human subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) mechanical properties in relation to subject characteristics may be really relevant. The aim of this work was to properly characterize the mechanical response of adipose tissues in patients with obesity. Then, the data were exploited to develop a reliable finite element model of the adipose tissues characterized by a constitutive material model that accounted for nonlinear elasticity and time dependence. Mechanical tests have been performed on both SAT and VAT specimens, which have been harvested from patients with severe obesity during standard laparoscopic sleeve gastrectomy intervention. The experimental campaign included indentation tests, which permitted us to obtain the initial/final indentation stiffnesses for each specimen. Statistical results revealed a higher statistical stiffness in SAT than in VAT, with an initial/final indentation stiffness of 1.65 (SD ± 0.29) N/30.30 (SD ± 20) N compared to 1.29 (SD ± 0.30) N/21.00 (SD ± 16) N. Moreover, the results showed that gender, BMI, and age did not significantly affect the stiffness. The experimental results were used in the identification of the constitutive parameters to be inserted in the constitutive material model. Such constitutive characterization of VAT and SAT mechanics can be the starting point for the future development of more accurate computational models of the human adipose tissue and, in general, of the human body for the optimization of numerous medical and biomechanical procedures and applications.

Ski boots are known to cause vasoconstriction in the wearer’s lower limbs and, thus, cause a “cold leg” phenomenon. To address this problem, this work provides a computational framework for analysing interactions between the ski boot and the lower limb. The geometry of the lower limb was derived from magnetic resonance imaging and computed tomography techniques and anthropometric data. The geometry of the ski boot shell was obtained by means of three-dimensional computer aided design models from a manufacturer. Concerning the ski boot liner, laser scanning techniques were implemented to capture the geometry of each layer. The mechanical models of the ski boot and the lower limb were identified and validated by means of coupled experimental investigations and computational analyses. The computational models were exploited to simulate the buckling process and to investigate interaction phenomena between the boot and the lower limb. Similarly, experimental activities were performed to further analyse the buckling phenomena. The obtained computational and experimental results were compared regarding both interaction pressure and displacements between the buckle and the corresponding buckle hooks. These comparisons provided reasonable agreement (mean value of discrepancy between the model and mean experimental results in the tibial region: 20%), underlining the model’s capability to correctly interpret results from experimental measurements. Results identified the critical areas of the leg, such as the tibial region, the calcaneal region of the foot and the anterior sole, which may suffer the most due to the hydrostatic pressure and compressive strain exerted on them. The results highlight that computational methods allow investigation of the interaction phenomena between the lower leg and ski boot, potentially providing an effective framework for a more comfortable and ergonomic design of ski boots.

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.

LSG is one of the most performed bariatric procedures worldwide. It is a safe and effective operation with a low complication rate. Unsatisfactory weight loss/regain may occur, suggesting that the operation design could be improved. A bioengineering approach might significantly help in avoiding the most common complications. Computational models of the sleeved stomach after LSG were developed according to bougie size (range 27–54 Fr). The endoluminal pressure and the basal volume were computed at different intragastric pressures. At an inner pressure of 22.5 mmHg, the basal volume of the 54 Fr configuration was approximately 6 times greater than that of the 27 Fr configuration (57.92 ml vs 9.70 ml). Moreover, the elongation distribution of the gastric wall was assessed to quantify the effect on mechanoreceptors impacting satiety by differencing regions and layers. An increasing trend in elongation strain with increasing bougie size was observed in all cases. The most stressed region and layer were the antrum (approximately 25% higher stress than that in the corpus at 37.5 mmHg) and mucosa layer (approximately 7% higher stress than that in the muscularis layer at 22.5 mmHg), respectively. In addition, the pressure–volume behaviors were reported. Computational models and bioengineering methods can help to quantitatively identify some critical aspects of the “design” of bariatric operations to plan interventions, and predict and increase the success rate. Moreover, computational tools can support the development of innovative bariatric procedures, potentially skipping invasive approaches.

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.

The surgical treatment of urinary incontinence is often performed by adopting an Artificial Urinary Sphincter (AUS). AUS cuff represents a fundamental component of the device, providing the mechanical action addressed to urethral occlusion, which can be investigated by computational approach. In this work, AUS cuff is studied with reference to both materials and structure, to develop a finite element model. Materials behavior is investigated using physicochemical and mechanical characterization, leading to the formulation of a constitutive model. Materials analysis shows that AUS cuff is composed by a silicone blister joined with a PET fiber-reinforced layer. A nonlinear mechanical behavior is found, with a higher stiffness in the outer layer due to fiber-reinforcement. The cuff conformation is acquired by Computer Tomography (CT) both in deflated and inflated conditions, for an accurate definition of the geometrical characteristics. Based on these data, the numerical model of AUS cuff is defined. CT images of the inflated cuff are compared with results of numerical analysis of the inflation process, for model validation. A relative error below 2.5% was found. This study is the first step for the comprehension of AUS mechanical behavior and allows the development of computational tools for the analysis of lumen occlusion process. The proposed approach could be adapted to further fluid-filled cuffs of artificial sphincters.

Male urinary incontinence is a widespread healthcare problem, leading to a miserable quality of life. Artificial urinary sphincter (AUS) is a device inserted mostly around the urethra in adult males, which mimics the urinary sphincter by providing a closure during urinary storage and a subsequent open to permit voiding. The interaction phenomena occurring between AUS cuff and urethral duct represent a fundamental problem in the investigation of AUS reliability and durability. In this work, computational methods are exploited to deeply investigate the mechanics of interaction phenomena occurring between urethral duct and AUS device. Experimental studies are performed on urethral tissues, and structural tests are carried out on the overall urethral duct to obtain a large set of information required for mechanical properties definition. The mechanical behavior of AUS cuff is investigated using mechanical and physicochemical procedures. The cuff conformation is acquired by computed tomography techniques for the definition of the numerical model. Numerical analyses are developed to evaluate the mechanical response of urethral duct in interaction with AUS cuff, considering the lumen occlusion process for maintaining urinary continence. Finally, the investigation of the compressive stress and strain fields within urethral tissues allows the identification of device performance and reliability in correlation with surgical practice.

Gastric diseases are one of the most relevant healthcare problems worldwide. Interventions and therapies definition/design mainly derive from biomedical and clinical expertise. Computational biomechanics, with particular regard to the finite element method, provides hard-to-measure quantities during in-vivo tests, such as strain and stress distribution, leading to a more comprehensive and promising approach to improve the effectiveness of many different clinical activities. However, reliable finite element models of biological organs require appropriate constitutive formulations of building tissues, whose parameters identification needs an experimental campaign consisting in different tests on human tissues and organs. The aim of the reported here research activities was the identification of mechanical properties of human gastric tissues. Human gastric specimens were tested at tissue, sub-structural and structural levels, by tensile, membrane indentation and inflation tests, respectively. On the other hand, animal experimentations on tissue layers from literature pointed out the mechanical response at sub-tissue level during tensile loading conditions. In detail, the analysis of experimental results at sub-tissue and tissue levels led to a fibre-reinforced visco-hyperelastic constitutive formulation and to the identification of gastric layers mechanical behaviour. Results from experimentations on human samples were coupled with data derived from animal models. Data from sub-structural and structural experimentations were exploited to upgrade and validate the constitutive formulations and parameters. The developed investigations led to a reliable constitutive framework of human gastric tissues that both describe stomach mechanical functionality and allow computational investigations. Indeed, the comparisons among average computational data and experimental medians provided the following RMSEs (Root Mean Square Errors): 0.89 N, 0.15 N for corpus and fundus during membrane indentation test, respectively, and 0.44 kPa during inflation test. Accounting for the magnitude of experimental and computational data, the RMSEs can be considered low and acceptable because they concerned biological samples. In fact, biological tissues and structures are affected by a high inherent inter-samples' variability, which is detectable in both the geometrical configuration and the mechanical behaviour. The specific values of the here reported RMSEs ensured the reliability of the achieved parameters and the quality of the overall developed procedure. Reliable computational models of the gastric district could become efficient clinical tools to find out the main crucial aspects of bariatric procedures, such as the mechanical stimulation of gastric mechano-receptors. Moreover, the methods of computational biomechanics will permit to run the preliminary tests of new and innovative bariatric procedures, on one hand, predicting the successful rate and the effectiveness, and, on other hand, reducing the use of animal testing.

Lower urinary tract dysfunction pertains to symptoms related to the lower urinary tract (LUT), with consequent incontinence. Artificial urinary sphincters (AUS) are adopted to obtain continence conditions, mainly in male subjects, via urethral occlusion by applying pressure load, mostly operating on the basis of an empirical approach. Considering the frequent access of elderly patients to this surgical practice, tissue degradation related to aging phenomena must be investigated. Computational models of the LUT structures and the AUS systems have been designed to evaluate tissues mechanical stimulation and degenerative phenomena for reciprocal interaction. Virtual solid models of the LUT have been developed starting from biomedical images, as histological/morphometrical data. Segmentation procedures have been exploited to provide the three-dimensional reconstruction, and subsequent discretization techniques led to the finite element model. Contemporarily, a finite element model of a typical AUS device was developed. Numerical analyses have been performed to analyze interaction phenomena between AUS and LUT. Different conditions were investigated, modifying both loading conditions, as intraluminal pressure and AUS action, and urethral tissues properties. Particular attention was devoted to tissues parameters, aiming to evaluate the influence of tissues degeneration because of aging and/or pathologies.

Objective: Degenerative phenomena may affect esophageal motility as a relevant social-health problem. The diagnosis of such disorders is usually performed by the analysis of data from high-resolution manometry (HRM). Inter- and intraobserver variability frequently affects the diagnosis, with potential interpretative and thus therapeutic errors, with unnecessary or worse treatments. This may be avoided with automatic procedures that minimize human intervention in data processing. Methods: In order to support the traditional diagnostic process, an automatic procedure was defined considering a specific physiomechanical model that is able to objectively interpret data from HRM. A training set ( N = 226) of healthy volunteers and pathological subjects was collected in order to define the model parameters distributions of the different groups of subjects, providing a preliminary database. A statistical algorithm was defined for an objective identification of the patient's healthy or pathological condition by comparing patient parameters with the database. Results: A collection of HRMs including subjects of the training set has been built. Statistical relationships between parameters and pathologies have been established leading to a preliminary database. An automatic diagnosis procedure has been developed to compare model parameters of a specific patient with the database. The procedure was able to match the correct diagnosis up to 86% of the analyzed subjects. Conclusion: The success rate of the automatic procedure addresses the suitability of the developed algorithms to provide a valid support to the clinicians for the diagnostic activity. Significance: The objectivity of developed tools increases the reliability of data interpretation and, consequently, patient acceptance.

Bariatric surgery includes a variety of procedures that are performed on obese people and aim at decreasing the intake of food and calories. This goal is usually pursued by reducing stomach capacity and/or absorbing capability. Adjustable gastric banding is the most common and successful operation. In general, bariatric surgical procedures are effective, but are often associated with major complications. Surgical procedure and post-surgical conformation of the stomach are usually defined on clinical and surgical basis only. Instead, the optimal configuration should be identified by analyzing the mechanical functionality of the stomach and the surrounding structures, and the relationship between food intake, nutrient adsorption, mechanical stimulation of stomach wall and feeling of satiety. A novel approach to bariatric surgery is required, integrating competences in the areas of biomechanics, physiology and surgery, based on a strong interaction between engineers and clinicians. Preliminary results from coupled experimental and computational investigations are here reported. The analyses aim to develop computational tools for the investigation of stomach mechanical functionality in pre- and post-surgical conformations.

The infrapatellar adipose body (Hoffa's fat pad, IFP) is situated between the patellar tendon, the femoral condyle and the tibial plateau. The IFP consists of lobules of white adipose tissue delimited by thin connective septa. The actual structural functionality of the IFP is debated and should pertain to a cushioning role in the knee joint, providing to distribute and to damp mechanical stresses during articular activity. The present study is aimed to analyze the correlation between histological configuration and mechanical properties of the IFP, compared to other adipose tissues, partially differentiated by composition and conformation. Histological and ultrastructural methods were exploited to analyze the microscopic anatomies of IFP, knee (KSF) and abdominal (ASF) subcutaneous fat tissues. Numerical micro-models of the different tissues were developed by using histo-morphometric data, as the size of adipose lobules, the thickness of the septa and their composition. Numerical analyses made it possible to evaluate the mechanical functionality of the different fat tissues considering the characteristic loading conditions, as compressive and shear actions. The results pointed out the actual mechanical relevance of IFP and KSF, while ASF exhibited different mechanical properties. Furthermore, the contribution of connective septa and adipose lobules to compressive and shear mechanical behavior was elucidated. This preliminary investigation represents the basis for biomechanical interpretation and the definition of more refined model to be developed on the acquisition of additional histological and morphometric data.

Bariatric surgery is performed on obese people aiming at reducing the capacity of the stomach and/or the absorbing capability of the gastrointestinal tract. A more reliable and effective approach to bariatric surgery may integrate different expertise, in the areas of surgery, physiology and biomechanics, availing of a strong cooperation between clinicians and engineers. This work aimed at developing a computational model of the stomach, as a computational tool for the physio-mechanical investigation of stomach functionality and the planning of bariatric procedures. In this sense, coupled experimental and numerical activities were developed. Experimental investigations on pig and piglet stomachs aimed at providing information about stomach geometrical configuration and structural behavior. The computational model was defined starting from the analysis of data from histo-morphometric investigations and mechanical tests. A fiber-reinforced visco-hyperelastic constitutive model was developed to interpret the mechanical response of stomach tissues; constitutive parameters were identified considering mechanical tests at both tissue and structure levels. Computational analyses were performed to investigate the pressure-volume behavior of the stomach. The developed model satisfactorily interpreted results from experimental activities, suggesting its reliability. Furthermore, the model was exploited to investigate stress and strain fields within gastric tissues, as the stimuli for mechanoreceptors that interact with the central nervous system leading to the feeling of satiety. In this respect, the developed computational model may be employed to evaluate the influence of bariatric intervention on the stimulation of mechanoreceptors, and the following meal induced satiety.

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.

The infrapatellar fat pad (IFP) is an intracapsular but extrasynovial structure, located between the patellar tendon, the femoral condyles and the tibial plateau. It consists of white adipose tissue, organised in lobules defined by thin connective septa. The aim of this study is the morphometric and ultrasonographic analysis of IFP in subjects without knee pathology during flexion‐extension movements. The morphometric study was conducted on 20 cadavers (15M, 5F, mean age 80.2 years). Ultrasound was performed on 24 volunteers with no history of knee diseases (5M, 19F, mean age: 45 years). The characteristics of the adipose lobules near the patellar tendon and in the deep portion of the IFP were evaluated. Numerical models were provided, according to the size of the lobules. At histological examination, the adipose lobules located near the patellar tendon were larger (mean area 12.2 mm(2) ± 5.3) than those at a deeper level (mean area 1.34 mm(2) ± 0.7, P 0.05). In the sagittal plane, the reduction of thickness of the superficial layer (with large adipose lobules) during flexion was 20.6%, whereas that of the deep layer (with small adipose lobules) was 1.3%. Numerical simulation of vertical loads, corresponding to flexion of the knee, showed that stress mainly developed within the interlobular septa and opposed bulging of the lobules. The characteristics of the lobular arrangement of the IFP (large lobules with superficial septa in the superficial part and small lobules with thick septa in the deep one), significant changes in the areas and perimeters of the superficial lobules, and the reduced thickness of the superficial layer during flexion all indicate the dynamic role played by the IFP in knee kinematics.

The present work aims to assess, via numerical modeling, the global passive mechanical behavior of the healthy abdominal wall under the action of pressures that characterize different daily tasks and physiological functions. The evaluation of a normal range of intra-abdominal pressure (IAP) during activities of daily living is fundamental because pressure alterations can cause several adverse effects. At this purpose, a finite element model is developed from literature histomorphometric data and from diagnostic images of Computed Tomography (CT), detailing the different anatomical regions. Numerical simulations cover an IAP up to the physiological limit of 171 (0.0223MPa) mmHg reached while jumping. Numerical results are in agreement with evidences on physiological abdomens when evaluating the local deformations along the craniocaudal direction, the transversal load forces in different regions and the increase of the abdominal area at a IAP of 12mmHg. The developed model can be upgraded for the investigation of the abdominal hernia repair and the assessment of prostheses mechanical compatibility, correlating stiffness and tensile strength of the abdominal tissues with those of surgical meshes.

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.

The infrapatellar fat pad (IFP) can be regarded as a peculiar form of fibro-adipose tissue localized close to the synovial membrane and articular cartilage. The aims of the present study were to analyze the microscopic anatomy of the IFP through histological and ultrastructural methods, comparing it with that of the subcutaneous tissue of the abdomen and of the knee. Ten specimens of IFP were sampled from bodies of the Donation Program of the University of Padua without a history of osteoarthritis. The IFP consisted of white adipose tissue, of lobular type, with lobules delimited by thin connective septa. The IFP lobule areas were smaller (p < 0.05) and the interlobular septa were thicker (p > 0.05) than those of subcutaneous tissues of the abdomen, whereas the IFP lobule areas were larger (p < 0.05) and the interlobular septa were thinner than those of the subcutaneous tissue of the knee (p < 0.05). The IFP adipocytes present a mean area of 3,708 ± 976 µm2 with a large intercellular space, whereas the mean area of the abdominal tissues was greater (6,082 ± 628 µm2; p < 0.05). At scanning electron microscopy the IFP adipocytes were covered by thick fibrillary sheaths, creating a basket around the adipocytes. The structural characteristics of the IFP (lobular aspect of the adipose tissue, thickness of the septa with scarce elastic fibers) could act as a plastic portion aimed at the absorption of pressure variation during knee articular activity. The extensive distribution of nerves suggests a possible role of the IFP as a mechanoreceptor, corresponding to a tridimensional connective mesh working in the proprioceptive regulation of the activity of the knee joint.

Even though bariatric surgery is one of the most effective treatment option of obesity, post-surgical weight loss is not always ensured, especially in the long term, when many patients experience weight regain. Bariatric procedures are largely based on surgeon's expertise and intra-operative decisions, while an integrated in-silico approach could support surgical activity. The effects of bariatric surgery on gastric distension, which activates the neural circuitry promoting satiety, can be considered one of the main factors in the operation success. This aspect can be investigated trough computational modelling based on the mechanical properties of stomach tissues and structure. Mechanical tests on gastric tissues and structure from people with obesity are carried out, as basis for the development of a computational model. The samples are obtained from stomach residuals explanted during laparoscopic sleeve gastrectomy interventions. Uniaxial tensile and stress relaxation tests are performed in different directions and inflation tests are carried out on the entire stomach residual. Experimental results show anisotropic, non-linear elastic and time-dependent behavior. In addition, the mechanical properties demonstrate to be dependent on the sample location within the stomach. Inflation tests confirm the characteristics of time-dependence and non-linear elasticity of the stomach wall. Experimental activities developed provide a unique set of data about the mechanical behavior of the stomach of patients with obesity, considering both tissues and structure. This data set can be adopted for the development of computational models of the stomach, as support to the rational investigation of biomechanical aspects of bariatric surgery.

Nowadays, the investigation of aortic wall biomechanics is a fundamental tool in clinical research and vascular prosthesis design. This study aims at analyzing the biomechanical behavior of aortic tissues using a coupled experimental and computational approach. Considering the typical fiber-reinforced configuration of aortic tissues, uni-axial tensile tests along six different loading directions were performed on specimens from pig aorta. Starting from the obtained experimental data, a suitable constitutive framework was defined and a methodology for the identification of the constitutive parameters was developed using the inverse analysis of mechanical tests. Transversal stretch versus loading stretch and nominal stress versus loading stretch curves were evaluated, showing the anisotropic and nonlinear mechanical behavior determined by tissue conformation with fibers distributed along preferential directions. In detail, experimental data showed different mechanical responses between longitudinal and circumferential directions, with a greater tissue stiffness along the longitudinal one. The reliability of the developed constitutive framework was evaluated by the comparison between experimental data and model results. The mentioned analysis can be considered as a useful tool for the development of reliable computational models, which allow a better understanding of the pathophysiology of cardiovascular diseases and can be applied for a proper planning of surgical procedures.

The aim of this study was to analyze the magnetic resonance imaging (MRI) volumetric and morphometric characteristics of the infrapatellar fat pad (IFP) and the suprapatellar fat pad (SFP) in normal controls, moderate and end-stage osteoarthritis (OA) patients. Forty-four MRI images of the three groups were collected: a) 17 patients undergoing meniscectomy with Outerbridge score 0 (control group); b) 15 patients undergoing meniscectomy with Outerbridge score 3/4 (moderate OA group); and c) 12 patients undergoing total knee replacement (end-stage OA group). Volume, depth, femoral and tibial arch lengths of IFP were quantified. The hypointense IFP signals were also scored. The SFP volume, oblique, antero-posterior and cranio-caudal lengths were determined. IFP and SFP characteristics were compared between groups. A decrease of IFP volume, depth, femoral, and tibial arch lengths in moderate and end-stage OA compared to controls were observed. A difference in IFP hypointense signal was found between groups. No differences were found in SFP characteristics between the groups. In controls and moderate OA patients, correlations were found among the different MRI characteristics of both IFP and SFP, while in the end-stage OA group correlations were found only in SFP. We evidenced differences of the IFP MRI morphometric characteristics between the groups analyzed, supporting an important role of IFP in OA pathology and progression. On the contrary, no differences were highlighted in SFP analysis suggesting that this fat pad is not clearly involved in OA, probably due to its peculiar localization and different function.

Introduction This work reports a set of results on the mechanical response of foot plantar tissues in healthy and degenerative conditions during the gait cycle, by means of a computational approach. Methods A three dimensional finite element model of the foot was developed starting from the analysis of biomedical images. Different constitutive models were defined to interpret the mechanical response of the biological tissues. In particular, a specific visco-hyperelastic constitutive formulation was provided for foot plantar soft tissue considering the general features of tissue mechanics. Degenerative phenomena induce histomorphological alterations and modification of the mechanical properties, as stiffening and lower damping capabilities. Different constitutive parameters for healthy and degenerative conditions were identified by the inverse analysis of experimental data from mechanical tests. Results The three dimensional numerical model interprets the capability of the plantar soft tissue to act under mechanical actions in different conditions during the phases of the gait cycle. Conclusion Numerical results highlight aspects of the different stress and strain distributions at the heel strike and the midstance of the healthy and degenerative conditions. Level of evidence V.

The Infrapatellar Fat Pad (IFP) lies between patella, femur, meniscus and tibia and properly fills the space between these structures. This fatty structure facilitates distribution of synovial fluid and may act to absorb impulsive actions generated through the joint. In case of Osteoarthritis (OA), IFP is found to be affected by inflammation, hypertrophy and fibrosis. The aim of the present study is to analyze the correlation between microscopic characteristics and mechanical properties of the IFP in healthy and OA conditions. The microscopic anatomy of the IFP was analyzed through histological methods, whose results showed that the IFP affected by OA maintains similar lobules configuration but thicker interlobular septa. Geometrical data together with the morphological analysis of lobules and septa represented the basic data to provide numerical micro-models of the IFP. Numerical analyses were developed to evaluate the mechanical behavior considering the characteristic loading conditions as compressive, torsion and shear actions. The results were applied to identify the parameters of a homogenized hyperelastic constitutive formulation that interprets the IFP mechanics. The constitutive formulation was implemented within a finite element model of the knee, which was applied to evaluate the overall mechanical functionality of the knee structures. The results pointed out the actual mechanical relevance of IFP and the loss of proper stress-strain behavior of the OA IFP under mechanical loads.