The aim of the present work is to propose an approach to the biomechanical analysis of oesophagus by defining an appropriate constitutive model and the associated constitutive parameters. The configuration of the different tissues and layers that compose the oesophagus shows very complicated internal anatomy, geometry and mechanical properties. The coupling of these tissues adds to the complexity. The constitutive models must be capable of interpreting the highly non-linear mechanical response. This is done adopting a specific hyperelastic anisotropic formulation. Experimental data are essential for the investigation of the tissues' biomechanical behaviour and also represent the basis for the definition of constitutive parameters to be adopted within the constitutive formulation developed. This action is provided by using a specific stochastic optimization procedure, addressed to the minimization of a cost function that interprets the discrepancy between experimental data and results from the analytical models developed. Unfortunately, experimental data at disposal do not satisfy all requested information and a particular solution must be provided with regard to definition of the lateral contraction of soft tissues. The anisotropic properties of the tissues are investigated considering the configuration of embedded fibres, according to their mechanical characteristics, quantity and distribution. Collagen and muscular fibres must be considered. The formulation provided on the basis of axiomatic theory of constitutive relationships and the procedure for constitutive parameters identification are described. The evaluation of constitutive parameters requires the analysis of data from experimental tests, that are extracted from the literature. Result validation is performed by comparing the experimental data and model results. In this way a valid basis is provided for the investigation of biomechanical behaviour of oesophagus, looking at deeper information from the experimental point of view that should offer data to be implemented in the procedure for a more detailed and accurate problem definition.

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 aim of this work is to investigate the instantaneous mechanical response of tendons by the use of an anisotropic elasto-damage constitutive model. This study addresses the analysis of the mechanical behaviour of healthy tendons during physiological loading and to degeneration phenomena. These are correlated with aging or traumatic events such as chronic or acute overloading during sporting activities. Histo-morphometric considerations suggest the adoption of a transversally isotropic constitutive model that describes the anisotropy of the material. The non-linearity of its overall mechanical response is taken into account by using a hyperelastic approach and also evaluates softening behaviour related to damage phenomena. The values of the parameters adopted within the analytical model are estimated both for human tendons previously subjected to cyclical loading and for specimens not subjected to cyclical loading. The results obtained by adopting this analytical model are compared with the experimental data in order to evaluate the capability of the model to describe the mechanical response of the tissue.

A viscoelastic constitutive model for the periodontal ligament (PDL) capable of accounting for large strains, anisotropy, and inelastic time-dependent effects was developed. Anisotropy characteristics are determined by the composite nature of the tissue and, in particular, by the distribution of collagen fibres. Time-dependent viscous phenomena are due to microstructural modifications during loading, such as fluid fluxes moving through the solid matrix and the internal rearrangement of fibers and constitutive adaptation. The viscoelastic model presented here was implemented in a general purpose finite element code. In vitro experimental tests were carried out on the PDL specimens of adult pigs to obtain stress-relaxation and cyclic stress-strain curves. The comparison of experimental and numerical results revealed good correspondence and confirmed the capability of the formulation assumed to properly interpret the viscoelastic behavior of the PDL.

Articular cartilage is a complex connective tissue with the fundamental functions of load bearing, shock absorption and lubrication in joints. However, traumatic events, aging and degenerative pathologies may affect its structural integrity and function, causing pain and long-term disability. Osteoarthritis represents a health issue, which concerns an increasing number of people worldwide. Moreover, it has been observed that this pathology also affects the mechanical behavior of the articular cartilage. To better understand this correlation, the here proposed review analyzes the physiological aspects that influence cartilage microstructure and biomechanics, with a special focus on the pathological changes caused by osteoarthritis. Particularly, the experimental data on human articular cartilage are presented with reference to different techniques adopted for mechanical testing and the related theoretical mechanical models usually applied to articular cartilage are briefly discussed.