Dissertation
Durable photografted zwitterionic hydrogel coatings to decrease biofouling and increase lubricity for biomaterials
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007232
Abstract
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.
Details
- Title: Subtitle
- Durable photografted zwitterionic hydrogel coatings to decrease biofouling and increase lubricity for biomaterials
- Creators
- Adreann Peel
- Contributors
- C Allan Guymon (Advisor)Marlan R Hansen (Committee Member)Kristan S Worthington (Committee Member)Beth A Rundlett (Committee Member)Eric E Nuxoll (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemical and Biochemical Engineering
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007232
- Number of pages
- xx, 219 pages
- Copyright
- Copyright 2023 Adreann Peel
- Language
- English
- Date submitted
- 04/20/2023
- Date approved
- 04/30/2023
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Biomaterials and implants have developed immensely in recent years, improving longevity and quality of life. For example, cochlear implants restore hearing to patients who suffer from profound hearing loss. However, the body responds to foreign objects by attaching proteins and cells, which can lead to tissue buildup around the implant. The function of these implants is negatively affected by such tissue, such as weakening of signal and loss of tonal resolution for cochlear implants. This work uses a zwitterionic hydrogel to mitigate this deleterious response to biomaterials within the body. Zwitterions have positive and negative charges in their chemical structure, which bind high amounts of water and repel proteins and cells from adhering. While zwitterionic hydrogels do prevent biological elements from adhering, hydrogels are inherently weak and do not adhere well to many biomaterials. This research examined the material properties and what compositional and processing alterations could enhance them. The process of attaching the hydrogel, photografting through light-induced polymerization, was altered with changes in polymerizing conditions and then measuring the strength of adhesion. The balance between the desired properties of the zwitterions and the molecules that provide network structure was examined to achieve a mechanically stable layer which repels proteins and cells. The durability of the coatings to physical challenges such as drying and forces, including friction and bending, were determined. Finally, two interpenetrating networks composed of zwitterions were investigated for increased toughness. Results indicate that stable and durable photografted zwitterionic hydrogel coatings are feasible, enabling reduced adhesion biological moieties and improvements for a wide variety of biomaterials.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9984425391802771
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