Low temperature shape memory recovery of 3D printed poly(D,L-lactide) networks : investigating the potential for long time scale applications

Abstract

Shape memory polymers (SMPs) are materials able to retain a macroscopic deformed state until an external stimulus triggers recovery to the original geometry. Recent research on SMPs has shown how the recovery can be modelled a priori, so that an adequate thermal and mechanical conditioning can be imparted to obtain the desired behaviour. Whereas most applications of SMPs require the recovery process to be fast (seconds), it can be speculated that the right conditioning and the right chemistry of the material can promote a slow recovery behaviour (weeks). Such slow recovering SMPs could be exploited for tissue engineering applications. This field is constantly researching new in vitro strategies and processes that better mimic human tissues native environment and development, particularly by the use of polymeric scaffolds for three-dimensional cell culturing. Following the rationale of mimicking natural tissue development, it has been envisioned that a slowly expanding artificial microenvironment might promote the formation of an organised tissue. This strategy could be enabled by fabricating shape memory scaffolds and instructing the construct to slowly recover from a compressed state to the expanded one, with kinetic similar to the natural tissue growth. Furthermore, scaffold fabrication and shape memory properties, synergistically combine with the use of stereolithography 3D printing (STL). This additive manufacturing technology enables the production of 3D parts with complex geometries and microscale detail, making it the perfect candidate for the fabrication of microporous constructs. Additionally, STL printing results in highly crosslinked networks with innate shape memory properties. Given the above considerations, it is the scope of this work to provide evidence of prolonged recovery kinetics – i.e. one week – of polymeric biomaterials suitable for the STL fabrication of porous scaffolds. This contributes the first investigation of its kind, independently from the field of application. The objective of this work is also to model the shape memory behaviour of the material through existing linear viscoelasticity approaches and predict experimentally observed behaviour during the prolonged recovery. The work will report the synthesis of the biomaterials and their formulation into photo-curable resins for STL printing, as well as the printing testing on a desktop and a professional apparatus.