(395g) Biodegradable Linker Incorporation into Main-Chain Liquid Crystalline Polymer Networks for Inducible Changes to Biomaterial Scaffolds

Liquid crystals are rigid molecules that form ordered phases, and the reaction of liquid crystals into a polymer network directly connects molecular ordering and rubber elasticity. Switching between an ordered liquid crystalline phase and the isotropic phase results in changes in polymer chain conformation on the molecular scale, translating into changes observable on the macroscale. Because of their anisotropic properties and ability to display shape-morphing behavior, liquid crystalline networks have attracted interest as well-controlled substrates for biological applications. However, most liquid crystalline substrates lack the ability to degrade nor permit remodeling in vitro or in vivo. This work generates main-chain liquid crystalline polymer networks that include a disulfide spacer that is susceptible to reducing stimuli using alkyne-azide click chemistry. Stable, non-degradable networks were synthesized by reacting dialkyne functionalized liquid crystalline monomer (5yH) with diazide terminated polyethylene glycol oligomers (PEG600) and a tetrafunctional azide polyethylene glycol crosslinker (4arm-PEG2k). The networks display sub-ambient glass transitions, tunable stiffness, and shape-morphing properties, including the ability to actuate, which is a reversible extension and contraction of the material. The networks also support the attachment and growth of human mesenchymal stem cells. To increase relevance for biomaterial applications, networks that degrade in response to biological environments were generated using a diazide spacer that contains an internal disulfide bond (PEGSS). The disulfide linkage can be reduced by L-glutathione (GSH), an antioxidant tripeptide sequence naturally produced by cells. The inclusion of PEGSS in the reaction generates materials with similar thermomechanical properties and liquid crystalline phase behavior as non-degradable networks but substituting varying amounts of non-degradable polyethylene glycol oligomer (PEG600) with the disulfide-containing monomer (PEGSS) permits tuning of the extent of degradation. Ongoing work is quantifying the impact of degradation on thermomechanical properties, network order, and shape morphing. This research seeks to deliver anisotropic, biodegradable cell culture scaffolds that we envision will offer the unique ability to alter cell and protein ordering within scaffolds, as well as the opportunity to provide inducible changes in network organization.