Investigating the Hydrolytic Degradation of Liquid Crystalline Elastomers towards their use in Biomedical Applications

Liquid crystalline elastomers (LCEs) have many interesting properties for use as biomaterials (e.g., molecular anisotropy to guide cell behavior, dynamic actuation); however, many important properties (e.g., degradation) are underexplored. Here, we compare the hydrolytic degradability of 3D printable thermotropic LCE chemistries and find that networks formed through a two-step, base-catalyzed thiol-Michael addition oligomerization followed by thiol-ene photocrosslinking degrade most readily. Integrating more hydrophilic chain extenders (e.g. poly(ethylene glycol)) accelerates degradation, but compromises LCE performance due to a reduction in liquid crystal content. The influence of hydrolytic degradation on thermal and mechanical properties of representative LCEs is then monitored over time. As materials slowly undergo heterogenous surface erosion, nematic-to-isotropic transition temperatures increase, while properties such as actuation potential, alignment, and mechanical anisotropy remain stable until mechanical integrity is ultimately lost. NMR, X-ray scattering, and DSC studies, reveal that thermal changes stem from retained degraded fragments enriched in mesogens, which increase liquid crystal interactions per unit volume and demand more thermal energy to disrupt the nematic state. We are now investigating the incorporation of light-responsive nanoparticles into degradable LCE scaffolds for light-mediated dynamic actuation towards biomedical applications.