“Design and Development of a Novel Auxetic Bone Plate for Long Bone Fractures”

Abstract

Injuries cover about 11% of World’s Disease Burden depicting fractures to be the leading cause of trauma. Fracture occurs due to force impact or osteoporosis. Fracture healing is nothing but a complicated process. Fracture fixation techniques focus on imparting reduction to fractured fragments and bring about healing. Internal fixation of long bone fractures using metallic plates has been going on since centuries and recently advancements have been in synthesizing biodegradable plates as well. The purpose of this research is to create an Auxetic Polymer Bone Plate as internal fixator for long bone fractures that renders micro-movement due to its counter intuitive behavior and reduces the effect of stress shielding and will allow for the same range of motion as the natural bone does. Micro-movement induces callus formation which tends to be a crucial step for fracture healing. The plate tends to provide negative Poisson’s ratio due to its geometry (rotating squares), that had formerly been scrutinized theoretically by Grima and Evans (J Mater Sci Lett 19(17):1563–1565, 2000) and practically investigated by Ali et al., (J Mater Sci: Mater Med 25: 527–553, 2014) for the development of Oesophageal stents. The device was manufactured by using additive manufacturing technique with the described geometry. Polyurethane was carefully chosen as a material for the fabrication of Auxetic device because of its biocompatibility and non-toxic effects. The plate was then tested for mechanical properties such as Tensile and Compression testing to determine the strength of the plate and the geometry enforced i.e. the strength of the hinges to endure the applied load. Tensile and compressive test also helps determine whether the plate will exhibit the Auxetic effect by measuring both longitudinal and transverse extensions which will confirm its negative Poisson’s ratio. The tensile testing of the Auxetic polyurethane specimens showed that the mean of the Poisson’s ratio of the samples stretched between -0.68 and -0.87 at different uniaxial tensile load values. The Auxetic structure of our device allows for efficient fixation because its negative Poisson’s ratio offers micro-movement, thereby causing fixation with relative stability rather than absolute stability. The Auxetic bone plate can be superior to contemporary plate fixation systems such that it has a modulus of elasticity closer to that of the bone, it demands meaningfully small contact points, and stress shielding does not ensue. Its Auxetic nature helps align and sustain the bone fragments with small fracture gaps in order to impart appropriate assembly to accomplish bone healing.