Durable photografted zwitterionic hydrogel coatings to decrease biofouling and increase lubricity for biomaterials
Creators: name: Peel, Adreann
Publisher: name: University of Iowa
Year: 2023
Subjects: antifouling
durability
lubricity
photografted coating
zwitterion
public abstract
Cochlear Implants
Materials Science

description: Biomaterials have advanced significantly in recent years, enabling better patient care, increasing quality of life, and providing more healthcare options. For example, cochlear implants (CI), one of the most successful neural prostheses, restore hearing to those who have profound sensorineural hearing loss. However, biomaterials and implants are still plagued by challenges, one of the biggest being the foreign body response. Any material or object that is placed in vivo triggers a response, beginning with protein and cell adhesion and resulting in degradation or encapsulation of the material. For implants that are meant to interface biologically, tissue buildup often proves deleterious. In the case of CIs, capsule formation attenuates the electrical stimuli limiting the efficacy and tonal resolution for the signal sent to the auditory nerves and can lead to loss of any residual hearing. Zwitterionic hydrogel coatings have shown promise in inhibiting the foreign body response and scarring surrounding medical implants, due to the high-water binding capabilities of the positive and negative charges in the polymer backbone. By employing simultaneous photografting and photopolymerization, a durable crosslinked coating can be achieved which is covalently attached to the desired surface. This work investigates the balance between the two photoinitiators that induce photografting and bulk polymerization, to ensure the hydrogel is well photografted to the substrate surface without compromising the bulk hydrogel properties. The ability to alter the adhesive properties and failure mode by altering polymerization conditions including photoinitiator concentration and light intensity, duration, and wavelength ranges is demonstrated. The ratio between crosslinker and zwitterionic monomer also allows for a compromise between mechanical stability from the crosslinker and antifouling capabilities from zwitterions. With a lower (5-30%) amount of crosslinker, films are sufficiently stable and show excellent reduction in fouling leading to a 90% decrease in cell and protein attachment. The crosslinker ratio also allows tuning of the hydrogel properties, including compressive modulus and equilibrium swelling. Additionally, zwitterionic coatings impart lubricity which can lead to a reduction of up to 95% in friction relative to uncoated polydimethylsiloxane which leads to a substantial reduction in required insertion force for CI. With incorporation of adequate amounts of crosslinker, zwitterionic monomer, and photoinitiator, the hydrated coating remains attached and viable under significant normal forces and bending. Failure due to bending or normal force only begins to occur after drying in ambient conditions for 60 minutes, demonstrating excellent durability under those conditions. Further advancements in coating durability have been realized when combining zwitterionic monomers in dual network systems wherein two distinct, interpenetrating domains, one comprised of each zwitterion, are formed into one coating. Dual networks lead to lower swelling and higher compressive and tensile moduli, demonstrating improved mechanical stability, while combining antifouling properties from both zwitterions. Successful engineering of photografted zwitterionic hydrogel coatings shows great promise for improving CIs and could dramatically reduce complications for other implants and biomaterials due to biofouling or trauma during implantation.