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Dynamic Soft Materials with Controllable Mechanical Properties

Perera, M. Mario
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897

Abstract Details

2020, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
Stiffening and softening of cellular environments governs many aspects of biological processes. Commonly these processes are investigated in vitro using soft materials of varying stiffnesses. Recently, soft materials that undergo stiffness changes over time have gained increasing attention as synthetic extra cellular environments for studies in regenerative medicine, in vitro cell culture, and biomimetic soft materials. However, most currently available dynamic soft materials suffer from a lack of control over their dynamic mechanical properties, or the do not possess sufficient biocompatibility. To address this issue, we have prepared new dynamic soft materials with controllable matrix softening and stiffening in this thesis that recapitulate the stiffness changes in biological systems. The main goal of this thesis was to exploit the chemistries to impart controllable and on-demand temporal stiffness changes into different soft materials. Gelatin-based dynamic hydrogels containing both alkyl sulfide and disulfide crosslinks have been successfully prepared by crosslinking thiolated polymers prepared using reversible addition-fragmentation chain-transfer (RAFT) polymerization and a norbornene-modified gelatin using a thiol-ene click reaction. The swelling ratio and storage moduli (G') were controlled by varying the thiol to ene molar ratio in the initial reaction mixture. The dynamic behavior of disul?des was used to soften the hydrogel through thiol exchange reactions with a mono thiol. Conversely, hydrogel sti?ening was achieved through a secondary thiol–norbornene cross-linking between PEG-diNB and free thiols in the hydrogel. structure of the thiol-containing RAFT polymers (i.e. co-monomer type, and comonomer ratio) were easily tuned to obtain hydrogels with the desired mechanical and physical properties. These dynamic hydrogels demonstrated controllable sti?ness changes over a physiologically relevant stiffness range. The cytocompatibility of dynamic hydrogels towards fibroblast cell culture and the role of dynamic matrix softening on fibroblast cell behavior were also investigated. The hydrogels and the softening strategy were cytocompatible, and cultured fibroblasts cell area reduced upon softening the initially sti?est gels. Thermoresponsive gels containing N-isopropylacrylamide were prepared at physiological temperature, demonstrating the potential of these dynamic gels to be used in future in vivo applications. Strategies to impart reversible stiffness changes into gels have also been investigated. Wavelength controlled disulfide-diselinide exchange chemistry was used to impart reversible stiffness changes in disulfide-containing organogels. The gels demonstrated matrix softening and stiffening for multiple cycles with more than 85% recovery of moduli between consecutive stiffness changes. Finally, this thesis reports our attempt to prepare poly(propylene fumarate) (PPF) composites with enhanced hydrophilicity and superior mechanical properties that could be used for orthopedic tissue engineering. A thiol-ene click reaction between PPF and thiol-containing hydrophilic RAFT polymers was attempted, and the observations of the reaction were explained with appropriate control thiol-ene reactions. Collectively, this work illustrates how controlling the structure and chemistry of synthetic polymers can be used to impart controllable bulk material properties to polymer networks, and how they can be applied to study cellular behavior with matrix dynamics. Challenges and future directions for dynamic gels are also be discussed.
Neil Ayres, Ph.D. (Committee Chair)
James Mack, Ph.D. (Committee Member)
Peng Zhang, Ph.D. (Committee Member)
132 p.
Polymers
Hydrogels; Dynamic; Gelatin; Organogels; softening; Stiffening

Recommended Citations

Citations

  • Perera, M. M. (2020). Dynamic Soft Materials with Controllable Mechanical Properties [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897

    APA Style (7th edition)

  • Perera, M. Mario. Dynamic Soft Materials with Controllable Mechanical Properties. 2020. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897.

    MLA Style (8th edition)

  • Perera, M. Mario. "Dynamic Soft Materials with Controllable Mechanical Properties." Doctoral dissertation, University of Cincinnati, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595847753887897

    Chicago Manual of Style (17th edition)

ucin1595847753887897
301
© 2020, some rights reserved.Creative Commons License Dynamic Soft Materials with Controllable Mechanical Properties by M. Mario Perera is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.