Controlling the Switching Temperature of Biodegradable, Amorphous, Shape-Memory Poly(rac-lactide)urethane Networks by Incorporation of Different Comonomers

Biodegradable shape-memory polymers have attracted tremendous interest as potential implant materials for minimally invasive surgery. Here, the precise control of the material's functions, for example, the switching temperature T(sw), is a particular challenge. T(sw) should be either between room and body temperature for automatically inducing the shape change upon implantation or slightly above body temperature for on demand activation. We explored whether T(sw) of amorphous polymer networks from star-shaped rac-dilactide-based macrotetrols and a diisocyanate can be controlled systematically by incorporation of p-dioxanone, diglycolide, or epsilon-caprolactone as comonomer. Thermomechanical experiments resulted that T(sw) could be adjusted between 14 and 56 degrees C by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks. Furthermore, the hydrolytic degradation rate could be varied in a wide range by the content of easily hydrolyzable ester bonds, the material's hydrophilicity, and its molecular mobility.