Liquid crystal elastomers (LCEs) combine the elasticity of polymer networks with the fluidity and responsiveness of liquid crystals. LCEs can respond to a variety of external stimuli – heat, light, electric and magnetic fields – with large and reversible shape-changes. However, the response is typically slow and requires large external fields. Here, we present our recent work with LCE bilayers and LCE composite materials that respond quickly, reversibly, and with 3-D shape changes to various externa stimuli, including heat, light, and electric fields. We also demonstrate the use of LCE composites as responsive substrates for dynamic cell culture. While conventional nematic LCEs are relatively unresponsive to electric fields, conductive LCE composites reversibly contract and expand in response to a 40 V electric field. The response time ( 0.1 – 10 Hz) and amplitude of shape change (1 – 20 %) can be tuned through variation of the external field and carbon black content. Neonatal rat ventricular myocytes remain viable on LCE-carbon black bilayer substrates, and aligned myocyte cell sheets were successfully grown on LCE-composite bilayers by stimulating the LCE substrate continuously during cell culture. 5% reversible extensional strains were applied during cell culture through stimulation with an electric field or through direct local heating. The resulting cells showed improved alignment when grown on responsive LCE substrates.<br/><br/>Next, we prepared LCEs with a reversible network crosslinking. LCEs synthesized through transesterification reaction can be re-aligned and re-shaped by heating above the reversible crosslink temperature. Reversible LCEs are typically stiffer than polysiloxane-based LCEs, but through tailoring of the network composition and crosslink density, reversible LCEs with a glass-transition below room temperature are achieved. Reversible LCEs simplify the processing and preparation and exhibit larger reversible strains compared with traditional polysiloxane LCEs. This work demonstrates fast and reversible shape changes in LCE nanocomposites and the potential of this class of materials for mechanical assist devices, dynamic substrates, or tissue scaffolds.

Liquid crystal elastomers with a reversible and multistimulus response

249th National Meeting (2015)

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