There is a need to develop other protein-based hydrogels that resemble the natural extracellular matrix with more predictable composition and greater control over degradation.The objective of this work was to synthesize an injectable and photo-polymerizable hydrogel based on keratin extracted from poultry feather for encapsulation and delivery of stem cells in tissue regeneration. Since feather keratin is rich in cysteine residue, allylation of sulfhydryl groups was used for functionalization of keratin. Keratin was extracted from feather barbs by reducing the disulfide bonds in cysteine residues to sulfhydryl groups (-SH). Next, the free thiol groups were converted to dehydroalanine (Dha) by oxidative elimination using O-(2,4,6-Trimethylbenzenesulfonyl) hydroxylamine. Then, the Dha moieties were converted to s-allyl cysteine by reaction with allyl mercaptan to produce keratin allyl thioether (KeratATE) biopolymer. Human mesenchymal stem cell (hMSCs) were suspended in the aqueous solution of KeratATE, injected into a mold, and photo-polymerized to generate a KeratATE hydrogel encapsulating hMSCs. KeratATE hydrogels had <5% mass loss in collagenase solution after 21 days of incubation whereas the mass loss was 15% in trypsin solution. Degradation of KeratATE hydrogel was strongly dependent on trypsin concentration but independent of collagenase. KeratATE hydrogel supported differentiation of the encapsulated hMSCs to the osteogenic and chondrogenic lineages to the same extent as those hMSCs encapsulated in gelatin methacryloyl hydrogel. The results suggest that keratin allyl thioether hydrogel with controllable degradation is a viable matrix for encapsulation and delivery of stem cells in tissue regeneration.
Danial Barati, Safaa Kader, Seyed Ramin Pajoum Shariati, Seyedsina Moeinzadeh, Roger H. Sawyer, Esmaiel Jabbari, Synthesis and characterization of photocrosslinkable keratin hydrogels for stem cell encapsulation, Biomacromolecules, 18(2): 398-412 (2017).