Force recovery evaluation of thermo-induced shape-memory polymer stent: material, process and thermo-viscoelastic characterization

Due to their functional and biological benefits, shape memory polymer (SMP) stents have attracted the attention of researchers in the biomedical science area. The highlights of this article are the evaluation of stent performance including radial force recovery and recovery start temperature (RST) in a constrained state. The effects of polyurethane (PU) mechanical properties and fabrication method are investigated on thermo-viscoelastic properties, sample defect and shape recovery of PU and polycaprolactone (PCL) blend. Thereafter, three tubular stents fabricated with the different diameter to thickness (d/t) ratio and their mechanical behavior are examined in loading, relaxation, and unloading. Finally, the radial force recovery of the stents is measured after stimulation in temperatures up to 45 °C. Emerging more peaks in the delta tangent graph implies that samples fabricated with solution-mixing has a better viscoelastic behavior and shows fewer defects compared to the melt-mixing ones. The fabrication method was much more effective on enhancement of the storage and loss modulus compared to double increasing of Young's modulus of applied PU from 4.3 to 9 MPa. Moreover, an increase in the stent's d/t from 15 to 10 causes not only an increase in the radial stiffness and force recovery but also leads to the reduction of irreversible deformation and RST. The results of this research reveals the importance of the dimensional and geometric design of SMP stents in controlling the force recovery and RST. (paper)