Aldo Garcia-Sandoval

Neural implantable devices serve as electronic interfaces facilitating communication between the body and external electronic systems. These bioelectronic systems ideally possess stable electrical conductivity, flexibility, and stretchability to accommodate dynamic movements within the body. However, achieving both high electrical conductivity and mechanical compatibility remains a challenge. Effective electrical conductors tend to be rigid and stiff, leading to a substantial mechanical mismatch with bodily tissues. On the other hand, highly stretchable polymers, while mechanically compatible, often suffer from limited compatibility with lithography techniques and reduced electrical stability. Therefore, there exists a pressing need to develop electromechanically stable neural interfaces that enable precise communication with biological tissues. In this study, a polymer that is softening, flexible, conformal, and compatible with lithography to microfabricate perforated thin‐film architectures is utilized. These architectures offer stretchability and improved mechanical compatibility. Three distinct geometries are evaluated both mechanically and electrically under in vitro conditions that simulate physiological environments. Notably, the Peano structure demonstrates minimal changes in resistance, varying less than 1.5× even when subjected to ≈150% strain. Furthermore, devices exhibit a maximum mechanical elongation before fracture, reaching 220%. Finally, the application of multi‐electrode spinal cord leads employing titanium nitride for neural stimulation in rat models is demonstrated.

A recent development in bioelectronic devices involves the utilization of multifunctional polymers as substrate material. Dynamically softening, thin-film polymers reduce the mechanical mismatch between device and tissue after implantation and therefore improves the device–tissue interaction. However, when implementing a new material into the fabrication of fully functional and chronically viable devices, there are specific challenges that need to be addressed. The key for all multimaterial devices is to ensure a good adhesion and connectivity between the different layers. That is especially true if one of the materials is sensitive to stimuli such as temperature and moisture. This review will give an overview on the development of a variety of neural interfaces for recording and stimulation with softening shape memory polymers (SMPs) as substrate material. This review discusses specific requirements for device fabrication, testing, and durability.