Relaxation based modeling of tunable shape recovery kinetics observed under isothermal conditions for amorphous shape-memory polymers

Polymers, which allow the adjustment of shape-memory properties by variation of physical parameters during programming, are advantageous to their counterparts requiring synthesis of a new material. Here we explored the stress relaxation behaviour of polyurethane (PEU) based shape-memory polymers at temperatures from 0 degrees C to 80 degrees C and different strain values from 100% to 250%. The obtained relaxation curves could be well described by a modified Maxwell-Weichert model of two Maxwell units and a spring. The stress relaxation results in a combination of a slow and a fast decaying process. For modeling the isothermal recovery of recently introduced PEU composite scaffolds at 37 degrees C the fast relaxation could be neglected resulting in a model of a standard linear solid, which was in good agreement with the experimental data. The presented modeling approach might be helpful to define design criteria for self sufficiently moving scaffolds within a knowledge-based development process. (C) 2010 Elsevier Ltd. All rights reserved.