Development and characterization of a polymer based on the biomimicry of the intervertebral disc

Abstract

The development and characterization of a functional graded composite material based on the biomimicry of the human intervertebral disc is reported in this research. The material consists of concentric radial polyurethane layers, synthesized using a condensation polymerization chemical reaction, found on methylene diphenyl diisocyanate, glycerol and castor oil as reagents. The proportions in the components of the polyol, glycerol and castor oil, were modified to generate a change in the degrees of cross-linking in the chains of the material, resulting in slightly rigid layers, as in the structure of the intervertebral disc. Two radial gradations were made through a rotating assembly and the complex modulus of the constituent polyurethane layers was used as the gradation criteria since the complex modulus provides a general description of the mechanical behaviour. After the gradation process, the graded material was characterized by means of a dynamic mechanical analysis that determines its viscoelastic properties, like storage modulus, loss modulus, complex modulus and tan δ. Moreover, with its behavioural pattern to compression and flexion, we performed a comparative analysis of the improvement of the mechanical properties of its constituent materials. The development of this study under biomechanical and chemical guidelines came together with two proposals of graded materials with high versatility and functionality in terms of frugality and stability for temperatures changes, as well as absorption and dissipation of mechanical energy. Furthermore, it serves as a tool for the elaboration of machines elements under combined load of compression and flexion at a low cost.