title: Tailoring the dependency between rigidity and water uptake of a microfabricated hydrogel with the conformational rigidity of a polymer cross-linker.
abstract: Many diverse applications utilize hydrogels as carriers, sensors, and actuators, and these applications rely on the refined control of physical properties of the hydrogel, such as elastic modulus and degree of swelling. Often, hydrogel properties are interdependent; for example, when elastic modulus is increased, degree of swelling is decreased. Controlling these inverse dependencies remains a major barrier for broader hydrogel applications. We hypothesized that polymer cross-linkers with varied chain flexibility would allow us to tune the inverse dependency between the elastic modulus and the degree of swelling of the hydrogels. We examined this hypothesis by using alginate and poly(acrylic acid) (PAA) modified with a controlled number of methacrylic groups as model inflexible and flexible cross-linkers, respectively. Interestingly, the polyacrylamide hydrogel cross-linked by the inflexible alginate methacrylates exhibited less dependency between the degree of swelling and the elastic modulus than the hydrogel cross-linked by flexible PAA methacrylates. This critical role of the cross-linker's inflexibility was related to the difference of the degree of hydrophobic association between polymer cross-linkers, as confirmed with pyrene probes added in pregel solutions. Furthermore, hydrogels cross-linked with alginate methacrylates could tune the projection area of adhered cells by solely altering elastic moduli. In contrast, gels cross-linked with PAA methacrylates failed to modulate the cellular adhesion morphology due to a lower, and smaller, elastic modulus range to be controlled. Overall, the results of this study will significantly advance the controllability of hydrogel properties and greatly enhance the performance of hydrogels in various biological applications.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: John J
authors.initials: JJ
authors.lastname: Schmidt
authors.forename: Jae Hyun
authors.initials: JH
authors.lastname: Jeong
authors.forename: Vincent
authors.initials: V
authors.lastname: Chan
authors.forename: Chaenyung
authors.initials: C
authors.lastname: Cha
authors.forename: Kwanghyun
authors.initials: K
authors.lastname: Baek
authors.forename: Mei-Hsiu
authors.initials: MH
authors.lastname: Lai
authors.forename: Rashid
authors.initials: R
authors.lastname: Bashir
authors.forename: Hyunjoon
authors.initials: H
authors.lastname: Kong
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000464:Alginates / Q000737:chemistry*; D000818:Animals; D001672:Biocompatible Materials / Q000138:chemical synthesis* / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000737:chemistry*; D055119:Elastic Modulus; D005456:Fluorescent Dyes; D020100:Hydrogels / Q000138:chemical synthesis* / Q000494:pharmacology; D057927:Hydrophobic and Hydrophilic Interactions; D008689:Methacrylates / Q000737:chemistry*; D051379:Mice; D055616:Microtechnology; D041681:NIH 3T3 Cells; D011721:Pyrenes; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D000464:Alginates; D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D005456:Fluorescent Dyes; D020100:Hydrogels; D008689:Methacrylates; D011721:Pyrenes; D014867:Water; C006903:carbopol 940; C030984:pyrene