One-step photochemical crosslinking of native proteins is feasible in tyrosine-rich bovine serum albumin
(1) Asia American International School, New Taipei City, Taiwan, (2) Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
Hydrogels made by crosslinking biomolecules have wide-ranging applications, including pharmaceuticals and tissue engineering. Some research groups have demonstrated crosslinking polycarbonates or oligopeptides by first attaching a tyrosine crosslinker to the backbones and then initiating crosslinking among linkers. Herein, we explored an alternative approach to make hydrogels from native proteins without pre-modification. We hypothesized that it is feasible to photochemically crosslink unmodified proteins provided that the protein is naturally abundant in tyrosine groups. We chose bovine serum albumin (BSA, a protein containing 18 tyrosine residues) as the native protein and methylene blue (MB) as the photosensitizer. To test our hypothesis, we photo-illuminated a solution of BSA and MB and observed whether a hydrogel formed. After illumination, the solution became a gel-like film whereas the solution not subject to illumination remained fluidic, indicating that photochemically crosslinking unmodified proteins is feasible. Using a microscope objective lens to focus the laser beam and a stage to move the sample, we further demonstrated photo-printing finely structured hydrogels. To illustrate a potential application of the hydrogels, we showed that the structured hydrogels can incorporate a model drug (fluorescein), and can be transferred and adhered to a model skin (pig skin), acting like a liquid bandage. In conclusion, we verified the feasibility of making hydrogels from a native protein naturally rich in tyrosine without the extra step of introducing crosslinkers to the protein backbone and demonstrated photo-printing fine structures of protein hydrogels. More work will be necessary to explore novel applications of protein hydrogels.
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