title: Hydrogels Formed by Oxo-ester Mediated Native Chemical Ligation.
abstract: Oxo-ester mediated native chemical ligation (OMNCL) is a variation of the more general native chemical ligation (NCL) reaction that is widely employed for chemoselective ligation of peptide fragments. While OMNCL has been used for a variety of peptide ligations and for biomolecular modification of surfaces, it is typically practiced under harsh conditions that are unsuitable for use in a biological context. In this report we describe the use of OMNCL for polymer hydrogel formation, in-vitro cell encapsulation, and in-vivo implantation. Multivalent polymer precursors containingN-hydroxysuccinimide (NHS) activated oxo-esters andN-cysteine (N-Cys) endgroups were chemically synthesized from branched poly(ethylene glycol) (PEG). Hydrogels formed rapidly at physiologic pH upon mixing of aqueous solutions of NHS andN-Cys functionalized PEGs. Quantitative 1H NMR experiments showed that the reaction proceeds through an OMNCL pathway involving thiol capture to form a thioester intermediate, followed by an S-to-N acyl rearrangement to yield an amide cross-link. pH and temperature were found to influence gelation rate, allowing tailoring of gelation times from a few seconds to a few minutes. OMNCL hydrogels initially swelled before contracting to reach an equilibrium increase in relative wet weight of 0%. This unique behavior impacted the gel stiffness and was attributed to latent formation of disulfide cross-links between network-bound Cys residues. OMNCL hydrogels were adhesive to hydrated tissue, generating a lap shear adhesion strength of 46 kPa. Cells encapsulated in OMNCL hydrogels maintained high viability, and in-situ formation of OMNCL hydrogel by subcutaneous injection in mice generated a minimal acute inflammatory response. OMNCL represents a promising strategy for chemical cross-linking of hydrogels in a biological context and is an attractive candidate for in-vivo applications such as wound healing, tissue repair, drug delivery, and tissue engineering.
authors.affiliation: Northwestern University, Evanston, IL 60208, Biomedical Engineering Department, Materials Science and Engineering Department, Chemical and Biological Engineering Department, Chemistry of Life Processes Institute, Institute for Bionanotechnology in Medicine, Robert H. Lurie Comprehensive Cancer Center.
authors.forename: Iossif
authors.initials: I
authors.lastname: Strehin
authors.forename: Dmitri
authors.initials: D
authors.lastname: Gourevitch
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ellen
authors.initials: E
authors.lastname: Heber-Katz
authors.forename: Phillip B
authors.initials: PB
authors.lastname: Messersmith
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