Shape memory properties of electrospun non-woven mat prepared from sol-gel crosslinked poly(e-caprolactone)

摘要

Shape Memory Polymers are a class of materials able to change their shape in a predefined way, from a temporary shape to a permanent one when exposed to an external stimulus, such as a temperature change. The development of shape memory electrospun mats may lead to the realization of smart devices, miniaturized, structured on a microanoscale, of great interest in the biomedical field. Poly(ε-caprolactone)-based non-woven fibrous mats with shape memory properties were obtained, starting from a previously synthesized triethoxysilane poly(ε-caprolactone), by combining electrospinning process and sol-gel reaction. The adoption of a crosslinking approach based on the sol-gel chemistry allows overcoming the problems of free radical approaches, where the permanence of initiators in the fibers could be deleterious for biomedical applications. In order to obtain a non-woven electrospun mat an increase of the molecular weight of the starting material was necessary previous to the electrospinning process. This was achieved through a partial crosslink reaction via sol-gel exploiting the triethoxysilane reactive terminals. After the attainment of the electrospun mat an optimized post-treatment was performed in in the presence of acid environment in order to obtain materials with different crosslinking degrees from 33% to 88%. The crosslinking degree of PCL governed the mechanical properties (storage modulus and tensile modulus) in the rubbery plateau region and, together with the micro-fibrous structure of the mat, it was correlated to the shape memory properties of the material by applying an 'ad-hoc' thermomechanical cycle. The results showed that the obtained post-crosslinked electrospun mats had excellent one-way shape memory capabilities, being able to both fix the temporary deformations and to recover the permanent shape up to 100% when heated slightly above the melting temperature. Interestingly, it was demonstrated (by means of scanning electron microscopy) that mats fibrous morphology was maintained after the application of the thermomechanical cycles.