Shape Morphable Hydrogel/Elastomer Bilayer for Implanted Retinal Electronics

Abstract

Direct fabrication of a three-dimensional (3D) structure using soft materials has been challenging. The hybrid bilayer is a promising approach to address this challenge because of its programable shape-transformation ability when responding to various stimuli. The goals of this study are to experimentally and theoretically establish a rational design principle of a hydrogel/elastomer bilayer system and further optimize the programed 3D structures that can serve as substrates for multi-electrode arrays. The hydrogel/elastomer bilayer consists of a hygroscopic polyacrylamide (PAAm) layer cofacially laminated with a water-insensitive polydimethylsiloxane (PDMS) layer. The asymmetric volume change in the PAAm hydrogel can bend the bilayer into a curvature. We manipulate the initial monomer concentrations of the pre-gel solutions of PAAm to experimentally and theoretically investigate the effect of intrinsic mechanical properties of the hydrogel on the resulting curvature. By using the obtained results as a design guideline, we demonstrated stimuli-responsive transformation of a PAAm/PDMS flower-shaped bilayer from a flat bilayer film to a curved 3D structure that can serve as a substrate for a wide-field retinal electrode array.

Integration of hydrogels in microfabrication processes for bioelectronic medicine: Progress and outlook

“…Bioelectronic devices that use hydrogels as substrate and/or encapsulation can be fabricated using drop casting and spincoating methods to deposit the gel on a flat surface such as a glass or silicon carrier (Macron et al, 2019;Zhou et al, 2020), or dip coating of arbitrarily-shaped surfaces (Yin et al, 2018). An alternative technique to coat hydrogels on organic or inorganic surfaces is initiated chemical vapor deposition (iCVD), where monomer, initiator and crosslinker are introduced in vapour phase in a vacuum chamber.…”

Full-field, conformal epiretinal electrode array using hydrogel and polymer hybrid technology

“…Shape morphable materials, including shape memory polymers 18 and hydrogels 19 , can not only provide shape reconfiguration responding to various stimuli but also may be packaged into a compact, folded state for implantation. Among those materials, hydrogels can be designed to respond to different stimuli, including temperature 20 and moisture 21 , which are two stimuli that can indicate implantation within the body. Hydrogels can be fixed at an arbitrary shape by dehydration and recover to their hydrated shape after swelling.…”

A Novel PDMS-Based Microfeature-Size Fabrication Method for Biocompatible and Flexible Devices

“…Flexible, elastic, and durable soft materials lead the path for future electronics applications in diagnostics and personal healthcare [1]. As a biocompatible, flexible, simple processing, optically transparent, and cost-effective polymer, PDMS (polydimethylsiloxane) is one of the most frequently applied substrate layers [2,3] in various applications including wearable sensors [4,5], epiretinal prosthetics [6][7][8], electronic textiles [9,10], stretchable conductors [11,12], etc. PDMS can be made in different shapes to fit biological tissues.…”