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Abstract
Bioelectronics are bio-interfacing devices that can be used for interrogating fundamental biological mechanisms and performing electronic diagnosis and therapy. A variety of conventional bioelectronics (to name a few, pacemakers, neurostimulators, cochlear implants, insulin pumps) have been developed to impact and heal millions of people each year. Compared to inorganic metals or silicon, conjugated polymers, which offer broad optoelectronic (light absorption/emission, conducting, semiconducting, etc) properties, have shown tremendous advantages, due to low mechanical modulus, solution processability, and chemical versatility. As a result, conjugated polymers have shown the promise for developing new generations of soft bioelectronics, allowing direct interfacing with biological tissues. To further enable biocompatible bioelectronic-tissue interfaces, the developments of implantable bioelectronics need to encompass a variety of functional properties, intimate contact with dynamic tissues, and suppressed foreign-body response. However, these properties pose significant challenges and remain largely missing for conjugated polymers for bioelectronics.For my Ph.D. dissertation, I focused on designing functional semiconducting polymers which can greatly expand their chemical and physical properties towards improving the biocompatibility of semiconducting polymer-tissue interface. Based on these designs, I fabricated active transistor devices with biocompatible characteristics for interfacing with biological tissues.
First, to resolve the limitation of conventional methods for functionalizing high-performance semiconducting polymers, I developed the “click-to-polymer” (CLIP) approach as a universal platform to facilely perform both bulk and surface functionalization on the side chain of conjugated polymers. A variety of functional units can be incorporated from this approach with little sacrifice to the electrical performance. Moreover, functional applications including photopatterning and biochemical sensing were demonstrated.
Second, to achieve intimate and robust interfacing with wet biological tissues, I developed bioadhesive polymer semiconductors by creating an interpenetrated double network between newly designed bioadhesive polymers and a redox-active semiconducting polymer. The bioadhesive polymer semiconductor showed significantly improved adhesion on bio-tissues while maintaining a comparable electrical performance to the neat semiconducting polymer. Furthermore, the bioadhesive polymer semiconductor exhibited abrasion resistance, high stretchability, and good biocompatibility, which are highly desirable for stable biointerfaces. I further developed a bioadhesive and stretchable electrochemical transistor for stably capturing electrophysiological signals with adhesive attachment on tissues.
Third, to improve the immune compatibility of semiconducting polymers, I designed new polymer structures with both backbone and side chain engineering. The selenophene incorporation in the backbone suppressed the foreign-body response as evidenced by a decrease of collagen density and immune cell populations, and a downregulation of the pro-inflammatory cytokines. The side chain grafting of immunomodulatory groups via the in-film functionalization approach showed a further suppression of the foreign-body response. Meanwhile, the immune-compatible semiconducting polymers only exhibited a minor decrease in the transistor performance relative to the neat one.
Future perspectives on designing polymer semiconductors for bioelectronic-tissue interfaces are given at last.