Mechanically active scaffolds from radio-opaque shape-memory polymer-based composites

Abstract

The formation of functional tissue is strongly dependent on biochemical as well as physical signals. A common approach in tissue engineering is the application of passive scaffold systems with fixed morphology and stiffness. In this paper, we explored whether mechanically active scaffolds, exhibiting self-sufficient shape changes under physiological conditions, can be prepared from radio-opaque shape-memory polymer composites (SMPCs). The influence of different thermomechanical treatments on the kinetics of the shape change was studied. Radio-opaque SMPCs were obtained by incorporation of barium sulfate (BaSO4) microparticles (up to 40 wt%) into an amorphous polyether urethane (PEU) via co-extrusion technique. The shape-memory properties of the composites were investigated by cyclic, thermomechanical tensile tests consisting of a specific shape-memory creation procedure (SMCP), in which the programming temperature (Tprog) was varied, followed by recovery under stress-free condition, enabling the determination of the switching temperature (Tsw). An almost complete recovery with shape recovery rate (Rr) values ranging from 88% to 98% was realized within a small temperature interval of DTrec30-C for all composites, while Tsw was found to be close to the applied Tprog. The feasibility of actively moving scaffolds was demonstrated using model scaffolds, where originally square-shaped pores were temporarily fixed in an expanded circular shape at different Tprog. We found that the kinetics of the shape change obtained under physiological conditions could be adjusted by variation of Tprog between 1 and 6 hr. Such radio-opaque scaffolds could serve as model scaffolds for investigating the active mechanical stimulation of cells in vitro or in vivo.