The Study Of Adaptive Fracture Fixation Device Based On Shape Memory Polymers

As a type of intelligent polymers, shape memory polymer and their composites can percept external stimuli, and react to the corresponding stimulation. Compared with conventional materials, shape memory polymers can serve as sensors, controllers and drives, and can initiate to deformation, which endows them great potentials in aerospace and medical applications.In this paper, shape memory polymer fracture fixators are based on the feature of active deformation. The primary tests for application of the device are verified in both experimental and theoretical aspects. First, the mechanical properties and parameters were characterized and obtained from experiments.Secondly, the thermal viscoelastic constitutive equation was established to stimulate the shape memory behavior of shape memory polymers. Through the comparison of experimental and theoretical results, the validity of theoretical model was verified, and deformation mechanism was explained. This study provides the theoretical and experimental support for the application of shape memory polymer in fracture fixation.This research contains following aspects:(1) dynamic mechanical analysis(DMA) experiments and isothermal uniaxial tensile, thermal stress relaxation and creep experiment tests were carried out to character the dynamic mechanical properties and static mechanical properties. The time-temperature equivalence equation was employed to determine the basic thermal viscoelastic material parameters. The changes of mechanical properties under cyclic loading were tested upon during load cycling experiments; the shape memory behavior of fracture fixations was studied through the experiments of shape memory cycle testing;(2) Correction the shape memory polymer viscoelastic constitutive equation was made. Recursive algorithm was used to compile Prony series constitutive equation into the UMAT subroutine, later based on that the ABAQUS software model was built to simulate the shape memory behavior;(3) The adaptive fracture fixation device based on the shape memory polymer was designed. Through uniaxial tensile test and the three-point bending test analysis, the tensile modulus, flexural modulus of the scale model structure, and tensile resilience, flexural restoring force were obtained, which provides data support for fracture fixation devices. By in vitro functional assays, the effect of fixing, and fixed demolition, adaptive feature and the feasibility of a shape memory polymer fracture fixation device, were verified.