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

Bladder tissue passive response to monotonic and cyclic loading

The fundamental passive mechanical properties of the bladder need to be known in order to design the most appropriate long-term surgical repair procedures and develop materials for bladder reconstruction. This study has focused on the bladder tissue viscoelastic behavior, providing a comprehensive analysis of the effects of fibers orientation, strain rate and loading history. Whole bladders harvested from one year old fat pigs (160 kg approximate weight) were dissected along the apex-to-base direction and samples were isolated from the lateral region of the wall, as well as along apex-to-base and transverse directions. Uniaxial monotonic (stress relaxation) and cyclic tests at different frequencies have been performed with the Bose Electroforce® 3200. Normalized stress relaxation functions have been interpolated using a second-order exponential series and loading and unloading stress-strain curves have been interpolated with a non-linear elastic model. The passive mechanical behavior of bladder tissue was shown to be heavily influenced by frequency and loading history, both in monotonic and cyclic tests. The anisotropy of the tissue was evident in monotonic and in cyclic tests as well, especially in tests performed on an exercised tissue and at high frequencies. In contrast, transverse and apex-to-base samples demonstrated an analogous relaxation behavior

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

In silico biomechanical design of the metal frame of transcatheter aortic valves: multi-objective shape and cross-sectional size optimization

Transcatheter aortic valve (TAV) implantation has become an established alternative to open-hearth surgical valve replacement. Current research aims to improve the treatment safety and extend the range of eligible patients. In this regard, computational modeling is a valuable tool to address these challenges, supporting the design phase by evaluating and optimizing the mechanical performance of the implanted device. In this study, a computational framework is presented for the shape and cross-sectional size optimization of TAV frames. Finite element analyses of TAV implantation were performed in idealized aortic root models with and without calcifications, implementing a mesh-morphing procedure to parametrize the TAV frame. The pullout force magnitude, peak maximum principal stress within the aortic wall, and contact pressure in the left ventricular outflow tract were defined as objectives of the optimization problem to evaluate the device mechanical performance. Design of experiment coupled with surrogate modeling was used to define an approximate relationship between the objectives and the TAV frame parameters. Surrogate models were interrogated within a fixed design space and multi-objective design optimization was conducted. The investigation of the parameter combinations within the design space allowed the successful identification of optimized TAV frame geometries, suited to either a single or groups of aortic root anatomies. The optimization framework was efficient, resulting in TAV frame designs with improvedmechanical performance, ultimately leading to enhanced procedural outcomes and reduced costs associated with the device iterative development cycle

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

A multibody model for the optimization of hip arthroplasty in relation to range of movement

Abstract Background The dislocation of the prosthesized hip is a relevant postoperative complication; this adverse outcome is dependent on the specific patient anatomy and on the artificial joint design. The geometry of the reconstructed hip is one of the key factors and it is usually designed at the time of the pre-operative planning when the stem model and size, the head diameter and its offset, and the acetabular cup orientation are selected. Aims In this work, the authors have developed a numerical model to support the pre-operative planning, allowing assessing the hip range of motion, once the geometry of the implant has been defined. Methods A multi-body model of a prosthesized hip has been developed, and a dislocating movement has been applied; the software is able to assess the entity of displacements and of applied forces which can produce hip dislocation. Results As a proof of concept, multiple combinations of geometric factors have been examined that are the head diameter, the acetabular cup anteversion and its inclination, reaching a total number of 675 configurations. This software is able to analyse and compare all configurations in few minutes. Conclusion The developed numerical model can be a support to quickly compare a great number of solutions from the point of view of hip stability, reaching a comprehensive view of all possibilities, and giving a contribute to the final aim that is surgery optimization, in relation to each specific patient