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

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 (T-prog) was varied, followed by recovery under stress-free condition, enabling the determination of the switching temperature (T-sw). An almost complete recovery with shape recovery rate (R-r) values ranging from 88% to 98% was realized within a small temperature interval of Delta T-rec approximate to 30 degrees C for all composites, while T-sw was found to be close to the applied T-prog. 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 T-prog. We found that the kinetics of the shape change obtained under physiological conditions could be adjusted by variation of T-prog 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. Copyright (C) 2010 John Wiley & Sons, Ltd.