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theses

Ideal properties of biomaterials for tissue engineering applications include biocompatibility, tissue mimicry, the ability to support cell attachment and growth, biodegradability, and control of biochemical and mechanical properties. Type-I collagen, a protein found throughout many tissues throughout the body, can be extracted from animal tissue and used to make fibrillar hydrogels or scaffolds for tissue engineering. While these collagen scaffolds have many of the optimal design parameters for biomaterials, the lack of control of scaffold properties is highly disadvantageous for its use in new tissue engineering paradigms. Previous studies have focused on developing a photoreactive collagen that could be biochemically and mechanically tuned via the application of light by functionalizing collagen with methacrylic acid to create collagen methacrylamide (CMA). This dissertation focuses on the characterization, continued development, and applications of CMA as a collagen-based biomaterial for tissue engineering. We demonstrated that fibrillogenesis of CMA, in contrast to type-I collagen, is thermoreversible. CMA can reversibly cycle between two states: it ii forms fibrillar hydrogels at 37 °C, and disassembles into a liquid suspension at temperatures less than 10 °C. The CMA synthesis procedure was revisited to better understand how methacrylation caused thermoreversibility. Of two methods used for conjugation, one results in a thermoreversible collagen. Thermoreversibility was not specific to the methacrylic acid - other compounds were conjugated and found to make collagen thermoreversible. In using circular dichroism spectroscopy to characterize the temperature-dependent protein structure of collagen, we found that collagen fibrils were displayed a unique signal; the fibril spectrum was seen as a negative peak at ~204 nm in contrast to the triple-helix signal in collagen's monomeric form that is characterized by a positive peak at ~222 nm. This signal was exclusive to the collagen fibril, and was used it as a tool to monitor collagen fibrillogenesis among other changes in collagen higher order structure Finally, we developed a method of free-form fabrication of CMA, where hydrogels are constructed through self-assembly, photocrosslinking of specific geometries, and cold-melted to remove regions that were not exposed to light. Customized hydrogels can be fabricated with or without cells, or further processed into sponges. Hydrogels were also shown to be biocompatible in a subcutaneous implant model. In comparison to many 3D printing strategies, CMA free-form fabrication is very simple to implement and is inexpensive, prompting continued development of CMA in tissue engineering and regenerative medicine.

ETD_7570

Ph.D.

Includes bibliographical references

by Kathryn Emily Drzewiecki

doi:10.7282/T3W0988G

ETD doctoral

The author owns the copyright to this work.