Liquid Crystal Elastomers for Small-Scale Biomedical Devices and Electronics

Abstract

Liquid crystal elastomers are a class of soft, mechanically active materials, capable of large, reversible, and non-linear deformations in response to environmental triggers that induce reversible changes in order. As such, LCEs have demonstrated great utility as soft actuators and robots, dynamic medical devices, and artificial muscles. While the large, programmable shape-changing behavior of LCEs is extensively reported, there are some critical limitations that currently impede the use of these “smart materials” for the development of micro-scale and implantable biomedical devices. 1) The chemical stability of these mechanically active materials in the context of surgical implantation has not been well studied, 2) Even though heat, light, and solvents have been studied extensively as actuation triggers, these stimuli are often not biocompatible severely limiting the biomedical applications of LCEs. 3) Because of the highly-responsive nature of LCEs, mechanical properties such as toughness, force output, and strength are often compromised, limiting these materials in their engineering applications. Here, we study previously reported LCEs as well as engineer novel LCEs for biomedical devices that overcome some of the aforementioned limitations. In the first chapter, we evaluate the chemical stability of previously reported LCE networks in a simulated physiological environment and determine their viability as substrates for 3D-responsive bioelectronics. Next, oxidation-sensitive LCE structures are developed that are able to respond to an endogenously produced signal, swell anisotropically, and eventually degrade. This programmable shape-change and degradation of the LCE stimulus can be used for the development of transient biomedical devices. Improving the mechanical properties of LCEs is of interest as it can enable the miniaturization of LCE-based biomedical devices. We engineer a semicrystalline LCE where the incorporation of semicrystallinity in a lightly cross-linked liquid crystalline network yields tough and highly responsive materials. In Chapter 5, we explore how we can employ LCEs exhibiting time-dependent deployment for the fabrication and miniaturization of small-scale deployable biomedical devices. Lastly, we show some preliminary data on how the time-dependent deployment of the photoresponsive LCEs can be further leveraged for the fabrication of deployable ultramicroelectrode arrays where probes of subcellular dimensions can controllably deploy in brain tissue.