Star-PCL shape memory polymer (SMP) scaffolds with tunable transition temperatures for enhanced utility

Abstract

Thermoresponsive shape memory polymers (SMPs) prepared from UV-curable poly(ε-caprolactone) (PCL) macromers have the potential to create self-fitting bone scaffolds, self-expanding vaginal stents, and other shape-shifting devices. To ensure tissue safety during deployment, the shape actuation temperature (i.e., the melt transition temperature or T_m of PCL) must be reduced from ∼55 °C that is observed for scaffolds prepared from linear-PCL-DA (M_n ∼ 10 kg mol⁻¹). Moreover, increasing the rate of biodegradation would be advantageous, facilitating bone tissue healing and potentially eliminating the need for stent retrieval. Herein, a series of six UV-curable PCL macromers were prepared with linear or 4-arm star architectures and with M_ns of 10, 7.5, and 5 kg mol⁻¹, and subsequently fabricated into six porous scaffold compositions (10k, 7.5k, 5k, 10k★, 7.5k★, and 5k★) via solvent casting particulate leaching (SCPL). Scaffolds produced from star-PCL-tetraacrylate (star-PCL-TA) macromers produced pronounced reductions in T_m with decreased M_nversus those formed with the corresponding linear-PCL-diacrylate (linear-PCL-DA) macromers. Scaffolds were produced with the desired reduced T_m profiles: 37 °C < T_m < 55 °C (self-fitting bone scaffold), and T_m ≤ 37 °C (self-expanding stent). As macromer M_n decreased, crosslink density increased while % crystallinity decreased, particularly for scaffolds prepared from star-PCL-TA macromers. While shape memory behavior was retained and radial expansion pressure increased, this imparted a reduction in modulus but with an increase in the rate of degradation.