Mireya Matos

Numerical model of vertebral unit for the nucleus pulposus prosthesis analysis

This paper presents a physiological model of a L4-L5 Functional Vertebral Unit (FVU) based on dimensions extracted from the literature, which is used as a platform for simulation of Nucleus pulposus prostheses prototypes. CAD computational tools and finite element simulations were used for stress analysis considering the anisotropy of the outer annulus fibrosus, and the incompressibility of the inner nucleus pulposus. The mechanical behavior of the FVU is compared to a similar model without nucleus under compressive loads. Numerical results show higher displacements and stress values in the annulus fibrosus that show the importance of the nucleus. The model was modified in order to include tentative design of prosthetic prototypes of the Nucleus pulposus using three different shapes: circular, oval and adjusted to the outer annulus fibrosus geometry, all based on the concept of a Silicone gel-filled prostheses. Finally, the results show that the adjusted design has a better performance at restraining deflections.

Desarrollo de prótesis de núcleo pulposo — Modelo de elementos finitos de una unidad funcional de la columna vertebral y caracterización de materiales

The development of a prosthetic device for the replacement of the nucleus pulposus of the intervertebral disc is being widely studied in the recent years, with a great variety of designs and materials used. In this work is shown an approach to the elaboration of prosthesis for the nucleus pulposus, following the principal requirements about biomechanics and biocompatibility. For this, a 3-D model of a functional spinal unit (FSU) of the lumbar spine was made, with the aim of study de biomechanics of the intervertebral disc. A 3-D reconstruction of the L4–L5 segment was built using Axial Computarized Tomographies. Stress analyses of the model was perform using the Finite Element Method. The selection of the material to use in the prosthesis elaboration is of great importance for the biocompatibility of the device. Therefore, a research about chitosan hidrogels crosslinked whit genipin is being started. Both of these materials are proved to be biocompatible, giving a hint about their possible use. Mechanical testing in compression shown the fragility of the chitosan hidrogels, but their morphology could make them able for other biomedical applications. The reaction kinetics between chitosan and genipin was studied with dinamic rheometry, showing the change of the hidrogels from a liquid solution to a viscoelastic solid.