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Hyperbranched polymers increase the stimuli-responsiveness of hydrogels

Chimala, Prathyusha
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1659535558381657

Abstract Details

2022, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
Stimuli-responsive hydrogels that undergo a change in properties including stiffness and swelling in response to external stimuli are becoming important in many fields such as sensors, soft robots, and mimicking extracellular matrix (ECM) matrix for biomedical applications. However, it has been suggested that in order to observe meaningful changes differences in hydrogel stiffness of several kPa are required and are limited. To address this issue, we have tuned the polymer architecture and synthesized hydrogels using hyperbranched polymer and compared its properties with the conventional linear polymer. Hyperbranched polymer poly(2-hydroxypropyl methacrylate-stat-pyridyl disulfide ethyl methacrylate) (hb-poly(HPMA-stat-PDSEMA)) was synthesized using 2-((2-(((dodecylthio)carbonothioyl)thio)-2- methylpropanoyl)oxy)ethyl acrylate (ACDT) as a chain transfer monomer via reversible addition-fragmentation chain transfer polymerization (RAFT) technique. Thiol containing reduced hyperbranched polymer was crosslinked with poly(ethylene glycol)-dinorbornene (PEG-diNB) to prepare hydrogels. Hydrogels synthesized were softened using mercaptoethanol via thiol-disulfide exchange reactions and compared the results with the hydrogels prepared using linear polymer. Softening experiments with these gels resulted in stiffness changes of around 8.5 kPa after a thiol-disulfide exchange reaction using a small-molecule thiol, compared to only 4.5 kPa for similar gels prepared using linear polymers. Hydrogels with repair damage or healing ability are important in areas such as biomedical applications. Healing ability is restricted in the covalently crosslinked hydrogels due to permanent crosslinks and for these dynamic covalent linkages are required. In order to meet this challenge, we used our disulfide-containing dynamic hydrogels and introduced hydrogen peroxide (H2O2) as a healing agent, and fast healing was observed for around fifteen minutes. Healed hydrogels with higher values of storage moduli could be obtained by using hyperbranched polymer. Hyperbranched polymer gels were more stimuli responsive than the linear polymer gels. In my thesis, polymer architecture was also explored to prepare shape-changing bending hydrogels. Here, I aimed to build artificial muscle-like hydrogel actuators by synthesizing stimuli-responsive shape-changing bending hydrogels. Bilayered hydrogels were synthesized using linear and hyperbranched polymer gels and the layers were glued with PEG-diacrylate solution. Hydrogels exhibited bending response and the bending angle was controlled by tuning thiol to ene ratios of the hydrogel mixture. Hydrogels were flattened when exposed to the small-molecule thiol such as mercaptoethanol due to a decrease in the crosslinking density by thiol-disulfide exchange reactions. In order to achieve the reversible bending of the hydrogels which are an important essence of artificial muscle materials, we also tried to bring the hydrogels back to bending shape using H2O2. But we were unable to bring the hydrogels back to bending shape due to possible polymer diffusion between the hydrogel layers. These bending hydrogels have potential applications in the field of soft robotics and micromanipulators.
Neil Ayres, Ph.D. (Committee Member)
David Smithrud, Ph.D. (Committee Member)
Hairong Guan, Ph.D. (Committee Member)
99 p.
Polymers
Hyperbranched polymer; Hydrogel; Bending hydrogel; Linear polymer

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Citations

  • Chimala, P. (2022). Hyperbranched polymers increase the stimuli-responsiveness of hydrogels [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1659535558381657

    APA Style (7th edition)

  • Chimala, Prathyusha. Hyperbranched polymers increase the stimuli-responsiveness of hydrogels. 2022. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1659535558381657.

    MLA Style (8th edition)

  • Chimala, Prathyusha. "Hyperbranched polymers increase the stimuli-responsiveness of hydrogels." Doctoral dissertation, University of Cincinnati, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1659535558381657

    Chicago Manual of Style (17th edition)

ucin1659535558381657
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This open access ETD is published by University of Cincinnati and OhioLINK.