A VISCOELASTOPLASTIC MODEL TO INTERPRET DENTAL CEMENTS RESPONSE TO A NANOINDENTATION TEST

Nowadays employment of dental resins of different types has become a standard procedure. Providing a complete characterization of their mechanical behaviour is mandatory to improve their characteristics, design, and usage. In this study, we applied the nanoindentation technique to obtain experimental data to be fitted. Then, a genetic algorithm combined with a gradient algorithm were applied to find the best set of the mechanical parameters that characterize the Burger model in series with a frictional element, able to predict the nanoindentation process. Furthermore, with this approach one type of test permits to obtain mechanical parameters useful to characterize the viscoelastoplastic response of these materials

Parametric Analysis of Orthopedic Screws in Relation to Bone Density

A global study of geometry and material properties of orthopedic screws was performed, considering not only the effect of each single factor (screw pitch, number of threads, fillet angle, etc.) but also their interactions with respect to bone density

Minimum performance level definition for bone plate testing according to standard: A preliminary study

In silico modeling of osteosynthesis medical devices allows the reduction of the time required for experimental tests and the introduction of “simulation-driven design”. Using a wise combination of these techniques and analytical calculations, it is possible to relate the experimental results, which are mandatory for regulatory purposes, to the plate physiological application and prevent the occurrence of complications in the early stages after the orthopedic device implantation on humans and animals

Versatile electrical stimulator for cardiac tissue engineering—Investigation of charge-balanced monophasic and biphasic electrical stimulations

The application of biomimetic physical stimuli replicating the in vivo dynamic microenvironment is crucial for the in vitro development of functional cardiac tissues. In particular, pulsed electrical stimulation (ES) has been shown to improve the functional properties of in vitro cultured cardiomyocytes. However, commercially available electrical stimulators are expensive and cumbersome devices while customized solutions often allow limited parameter tunability, constraining the investigation of different ES protocols. The goal of this study was to develop a versatile compact electrical stimulator (ELETTRA) for biomimetic cardiac tissue engineering approaches, designed for delivering controlled parallelizable ES at a competitive cost. ELETTRA is based on an open-source micro-controller running custom software and is combinable with different cell/tissue culture set-ups, allowing simultaneously testing different ES patterns on multiple samples. In particular, customized culture chambers were appositely designed and manufactured for investigating the influence of monophasic and biphasic pulsed ES on cardiac cell monolayers. Finite element analysis was performed for characterizing the spatial distributions of the electrical field and the current density within the culture chamber. Performance tests confirmed the accuracy, compliance, and reliability of the ES parameters delivered by ELETTRA. Biological tests were performed on neonatal rat cardiac cells, electrically stimulated for 4 days, by comparing, for the first time, the monophasic waveform (electric field = 5 V/cm) to biphasic waveforms by matching either the absolute value of the electric field variation (biphasic ES at ±2.5 V/cm) or the total delivered charge (biphasic ES at ±5 V/cm). Findings suggested that monophasic ES at 5 V/cm and, particularly, charge-balanced biphasic ES at ±5 V/cm were effective in enhancing electrical functionality of stimulated cardiac cells and in promoting synchronous contraction

A METHODOLOGICAL APPROACH TO INTERPRET AND COMPARE THE VISCOELASTIC BEHAVIOR OF BIOLOGICAL TISSUES AND HYDROGELS

Cell behavior is strongly influenced by the physical properties of the microenvironment and complex mechanotransduction mechanisms are involved in cell and tissue development, homeostasis and even pathologies. Thus, when developing materials mimicking the extracellular matrix of healthy or pathological tissues their mechanical features should be closely considered. In this context, nanoindentation is a powerful technique for mechanically characterizing biomaterials and hydrogels at the cell-length scale, however, standardized experimental protocols and data analysis techniques are lacking. Here, we propose a methodological approach for quantitatively analyzing and comparing the time-dependent mechanical responses of different samples. As an explanatory study, stress-relaxation nanoindentation tests were performed on human and pig lung samples and on hydrogels in order to quantify and compare their viscoelastic properties

Native human dermis versus human acellular dermal matrix: A comparison of biaxial mechanical properties

BackgroundHuman Acellular Dermal Matrices (HADMs), thanks to its mechanical resistance and it’s not immunogenic response, is used in reconstructive surgery such as breast reconstruction procedures and hernia repairs. There is the need to investigate the mechanical response of HADMs when subjected to in vivo-like stresses. AimsIn order to supply additional guidance to surgeons, in this work equi-biaxial experimental curves of native and decellularized human dermis are presented because it is essential to investigate the engineered tissue response when subjected to stresses comparable to those that occur in vivo. Methods HADMs specimens were biaxially characterized exploiting a customized biaxial conversion device entirely realized through rapid prototyping methods, and the HADM response to mechanical stimuli comparable to the in vivo deformation state was explored. From the derived data, stress-strain curves were evaluated, and the elastic moduli were extracted from the curve toe-region. As an indication of the fibre rearrangement rate, the slope of the stress-strain curve at higher strains was evaluated in a semi-log plane. Results The mean elastic modulus at low strains for the medio-lateral direction (along Langer lines) resulted from 35 per cent to 87 per cent higher than the cranio-caudal one. Furthermore, medio-lateral specimens show lower rearrangement velocities at higher strains. Considering both directions, the decellularization process leads to a deterioration of the mechanical properties of the matrix.ConclusionThe tested HADMs maintained the typical anisotropic dermis behaviour, dependent on the collagen network predominantly oriented along the Langer lines. Moreover, comparisons among HADMs and the native human reticular dermis demonstrated the mechanical strength loss at lower strains caused by the decellularization process