An elastoplastic constitutive model to simulate the non-linear behaviour of chitosan material for nerve regeneration guide tubes applications

Neurotmesis is the most severe injury a peripheral nerve can endure. One of the strategies to treat this type of nerve injury is the tubulization technique, consisting of bridging the two nerve tips enclosed by a tube made of a compatible biomaterial. Chitosan scaffolds is one of the most popular (and successful) solutions used for the tubulization technique. After implanting the chitosan tube, it will experience mechanical stimuli due to natural movements, inducing strain-stress states in the biomaterial. It is relevant to characterize the mechanical behaviour of chitosan scaffolds in order to improve the structural design of chitosan tubes. 
First, in this work, it is proposed an elastoplastic constitutive model to predict the nonlinear behaviour  of chitosan scaffolds in both compression and tensile conditions. Then, using the data available from experimental tests documented in the literature, the most relevant mechanical properties for the proposed elastoplastic constitutive model were retrieved, allowing the construction of phenomenological laws for each required mechanical property. The proposed phenomenological law is capable to provide the Young's modulus, the tangent modulus and the yield stress (in both compression and tensile states) as a function of the degree of deacetylation.