Compressive Mechanical Behavior of Partially Oxidized Polyvinyl Alcohol Hydrogels for Cartilage Tissue Repair.

Polyvinyl alcohol (PVA) hydrogels are extensively used as scaffolds for tissue engineering, although their biodegradation properties have not been optimized yet. To overcome this limitation, partially oxidized PVA has been developed by means of different oxidizing agents, obtaining scaffolds with improved biodegradability. The oxidation reaction also allows tuning the mechanical properties, which are essential for effective use in vivo. In this work, the compressive mechanical behavior of native and partially oxidized PVA hydrogels is investigated, to evaluate the effect of different oxidizing agents, i.e., potassium permanganate, bromine, and iodine. For this purpose, PVA hydrogels are tested by means of indentation tests, also considering the time-dependent mechanical response. Indentation results show that the oxidation reduces the compressive stiffness from about 2.3 N/mm for native PVA to 1.1 ÷ 1.4 N/mm for oxidized PVA. During the consolidation, PVA hydrogels exhibit a force reduction of about 40% and this behavior is unaffected by the oxidizing treatment. A poroviscoelastic constitutive model is developed to describe the time-dependent mechanical response, accounting for the viscoelastic polymer matrix properties and the flow of water molecules within the matrix during long-term compression. This model allows to estimate the long-term Young's modulus of PVA hydrogels in drained conditions (66 kPa for native PVA and 34-42 kPa for oxidized PVA) and can be exploited to evaluate their performances under compressive stress in vivo, as in the case of cartilage tissue engineering.

Porcine Decellularized Diaphragm Hydrogel: A New Option for Skeletal Muscle Malformations.

Hydrogels are biomaterials that, thanks to their unique hydrophilic and biomimetic characteristics, are used to support cell growth and attachment and promote tissue regeneration. The use of decellularized extracellular matrix (dECM) from different tissues or organs significantly demonstrated to be far superior to other types of hydrogel since it recapitulates the native tissue's ECM composition and bioactivity. Different muscle injuries and malformations require the application of patches or fillers to replenish the defect and boost tissue regeneration. Herein, we develop, produce, and characterize a porcine diaphragmatic dECM-derived hydrogel for diaphragmatic applications. We obtain a tissue-specific biomaterial able to mimic the complex structure of skeletal muscle ECM; we characterize hydrogel properties in terms of biomechanical properties, biocompatibility, and adaptability for in vivo applications. Lastly, we demonstrate that dECM-derived hydrogel obtained from porcine diaphragms can represent a useful biological product for diaphragmatic muscle defect repair when used as relevant acellular stand-alone patch.

Biomechanics of stomach tissues and structure in patients with obesity.

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.

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.

Investigation of the biomechanical behaviour of articular cartilage in hindfoot joints.

Numerical models represent a powerful tool for investigating the biomechanical behavior of articular cartilages, in particular in the case of complex conformation of anatomical site. In the literature, there are complex non-linear-multiphase models for investigating the mechanical response of articular cartilages, but seldom implemented for the analysis of high organized structure such as the foot. In the present work, the biomechanical behavior of foot cartilage is investigated by means of a fiber-reinforced hyperelastic constitutive model. The constitutive parameters are obtained through the comparison between in vitro experimental indentation tests on cartilage and numerical analysis data interpreting the specific experimental conditions. A finite element model of the hindfoot region is developed. Particular attention is paid to model cartilage in order to respect its morphometric configuration, including also the synovial capsule. The reliability of the procedure adopted is evaluated by comparing the numerical response of tibio-talar joint model with in vivo experimental tests mimicking the foot response in stance configuration.