(573g) Surface Functionalization of Silk Protein Films to Control Bioadhesion

This work focuses on the design, synthesis, and characterization of silk fibroin materials as biomaterial substrates with tailored surface chemistries designed to promote or abrogate interactions with cells and other proteins. Due to its biocompatibility and versatility, silk fibroin finds utility in a wide variety of applications such as drug delivery, wound dressings, and tissue engineering. Though this protein is frequently chemically modified, the low degrees of functionalization remain a challenge for many applications. To address this issue, surface-initiated controlled radical polymerizations were used to modify the hydrophilicity and charge of silk surfaces. Polymer chains were grafted using a two-step method, where the first reaction enriched reactive sites for the initiator (controls graft density), and the second reaction grew polymer chains from the surface of the protein (controls graft length). Monomer composition was used to tailor the chemical properties of the grafted chains, where three types of monomers were investigated: ionic, zwitterionic, and hydrophilic monomers lacking charge. Control of polymer graft density and spatial location of the grafted chains was assessed by AFM and achieved by tailoring where the initiator attachment sites on the film were located. ATR-FTIR spectra was used to characterize the films before and after grafting, and the formation of new peaks characteristic of the polymer confirmed successful reaction. Water contact angle measurements and protein attachment studies, including attachment of albumin and fibrinogen, show a reduction in both contact angle and protein attachment after polymerization. Protein deposition and cell attachment were both reduced on more hydrophilic films, however the charge of a surface appears to play a more significant role compared to its hydrophilicity. Specific focus to modify the silk with grafted polymer chains that are designed to interact with the intestinal microenvironment is ongoing work. In summary, silk fibroin films with spatial control of grafted polymers were synthesized using atom transfer radical polymerization and varying composition was found to permit tailoring of surface hydrophilicity and protein and cell attachment. Ultimately, this new approach to modify silk fibroin is anticipated to enable the tailoring of silk-protein interactions to enhance compatibility and/or fouling of implanted biomaterials.