Considerations for hydrogel applications to neural bioelectronics

Hydrogels have been applied across a wide range of biomedical applications due to their versatility, but more recently have garnered interest as materials in bioelectronics due to the capacity to tailor their mechanical and biological properties. Hydrogel coatings in particular have been used to impart softness at the bionic device interface, deliver therapeutics and control cell interactions through presentation of peptides and growth factors. Additionally, the use of dynamic hydrogel properties has been harnessed as shuttles for the implantation of flexible electrode arrays. In all of these applications, the hydrogel must be designed not only to provide the desired performance, but also have no unexpected impacts on the surrounding tissues, such as extensive swelling that can compress the cells at the interface. Appropriate selection and design of hydrogel systems for bioelectronics requires an understanding of the physical, chemical and biological properties of hydrogels as well as their structure-property relationships. This review covers the design rationale for application of hydrogels systems for use in bioelectronic devices with a focus on in vivo applications.