Bioinspired Wet Pressure-sensitive-adhesives and Shape Memory Polymers for Biomedical Applications

Neural interfaces-integrated devices provide a promising technology enabling the diagnosis and treatment of neurological diseases and disorders by detecting and stimulating nervous action using bioelectronics. Nerve cuff electrodes are a class of neural integrated devices that consist of a flexible polymeric substrate that wraps a target nerve in cuff-shaped and single- or multi-channel electrodes that detect and/or stimulate nerves via excitation or inhibition of the target nervous action for neuromodulation. In this study, a new cuff-closing method is described, which uses shape memory polymer (SMP) cuffs and wet pressure-sensitive-adhesives (PSAs), for less invasive implantation. SMP cuffs wrap around a target nerve through shape recovery induced by exposure to physiological conditions, then fixed by wet PSA instead of suturing, to facilitate snugly fitting and easier and quicker setup for implantation. To demonstrate the feasibility of the proposed cuff devices, research was performed on three key scientific/technological issues, namely: 1) bioinspired wet PSA suitable for physiological conditions, 2) SMPs with enhanced softening and shape recovery properties, and 3) underwater adhesion of the designed SMPs and wet PSAs. First, the relationship between cohesion and adhesion of bioinspired catecholic PSAs, containing various amines, was studied to develop wet PSAs. The cation- interaction between catechol and amine groups contributed to the high cohesion of the PSAs and their high cohesion significantly increased adhesion under physiological conditions. Second, new thiol-ene/acrylamide SMPs were designed to improve shape recovery properties for facile implantation, using dopamine acrylamide (DAc) as a hydrophilic monomer. Finally, adhesion tests, for the designed wet PSAs to SMPs, demonstrated that the adhesion of PSAs to DAc-modified SMPs increased with an increase in the DAc molar ratio of SMPs to reach a sufficiently high ratio for permanent joints to be formed under physiological conditions. The closure method using wet PSA and SMP substrates, discussed in this study, is proposed as an advantageous method for designing minimally invasive nerve cuffs.