title: Alkylation of human hair keratin for tunable hydrogel erosion and drug delivery in tissue engineering applications.
abstract: Polymeric biomaterials that provide a matrix for cell attachment and proliferation while achieving delivery of therapeutic agents are an important component of tissue engineering and regenerative medicine strategies. Keratins are a class of proteins that have received attention for numerous tissue engineering applications because, like other natural polymers, they promote favorable cell interactions and have non-toxic degradation products. Keratins can be extracted from various sources including human hair, and they are characterized by a high percentage of cysteine residues. Thiol groups on reductively extracted keratin (kerateine) form disulfide bonds, providing a more stable cross-linked hydrogel network than oxidatively extracted keratin (keratose) that cannot form disulfide crosslinks. We hypothesized that an iodoacetamide alkylation (or "capping") of cysteine thiol groups on the kerateine form of keratin could be used as a simple method to modulate the levels of disulfide crosslinking in keratin hydrogels, providing tunable rates of gel erosion and therapeutic agent release. After alkylation, the alkylated kerateines still formed hydrogels and the alkylation led to changes in the mechanical and visco-elastic properties of the materials consistent with loss of disulfide crosslinking. The alkylated kerateines did not lead to toxicity in MC3T3-E1 pre-osteoblasts. These cells adhered to keratin at levels comparable to fibronectin and greater than collagen. Alkylated kerateine gels eroded more rapidly than non-alkylated kerateine and this control over erosion led to tunable rates of delivery of rhBMP-2, rhIGF-1, and ciprofloxacin. These results demonstrate that alkylation of kerateine cysteine residues provides a cell-compatible approach to tune rates of hydrogel erosion and therapeutic agent release within the context of a naturally-derived polymeric system.
authors.affiliation: Department of Chemical, Paper and Biomedical Engineering, Miami University, 650 E. High Street, Oxford, OH 45056, USA.
authors.forename: Sangheon
authors.initials: S
authors.lastname: Han
authors.affiliation: Department of Chemical, Paper and Biomedical Engineering, Miami University, 650 E. High Street, Oxford, OH 45056, USA; Department of Biomedical Engineering, University of Akron, Auburn Science and Engineering Center 275, West Tower, Akron, OH 44325, USA.
authors.forename: Trevor R
authors.initials: TR
authors.lastname: Ham
authors.affiliation: Department of Chemical, Paper and Biomedical Engineering, Miami University, 650 E. High Street, Oxford, OH 45056, USA.
authors.forename: Salma
authors.initials: S
authors.lastname: Haque
authors.affiliation: Department of Chemical, Paper and Biomedical Engineering, Miami University, 650 E. High Street, Oxford, OH 45056, USA.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Sparks
authors.affiliation: Department of Chemical, Paper and Biomedical Engineering, Miami University, 650 E. High Street, Oxford, OH 45056, USA. Electronic address: sauljm@MiamiOH.edu.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Saul
mesh_terms: D016475:3T3 Cells; D000478:Alkylation; D000818:Animals; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D002448:Cell Adhesion / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003692:Delayed-Action Preparations / Q000138:chemical synthesis*; D006801:Humans; D020100:Hydrogels / Q000737:chemistry*; D053564:Keratins, Hair-Specific / Q000737:chemistry* / Q000494:pharmacology*; D051379:Mice; D023822:Tissue Engineering / Q000379:methods*
chemical_list: D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D020100:Hydrogels; D053564:Keratins, Hair-Specific
keywords: Antibiotic; Ciprofloxacin; Recombinant human BMP-2; Recombinant human IGF-1; Regenerative medicine