Effect of Hydration on Tensile Response of a Dual Cross-linked PVA Hydrogel
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BRIEF TECHNICAL NOTE
Effect of Hydration on Tensile Response of a Dual Cross-linked PVA Hydrogel R. Meacham1 · M. Liu2 · J. Guo2 · A.T. Zehnder2
· C.-Y. Hui2
Received: 22 October 2019 / Accepted: 27 April 2020 © Society for Experimental Mechanics 2020
Abstract Background Little is known about the effect of water content on the mechanical properties of dual cross-linked hydrogels. Objective To quantify the changes in the mechanical response and equilibrium modulus in a PVA hydrogel as a function of the hydration level. Methods A dual cross-linked hydrogel was tested in tension to a stretch of 1.3 at two stretch rates and in a stress relaxation test. The equilibrium modulus was calculated using the final relaxation stress value. Results The stiffness of the hydrogel increases significantly as the gel dries. Conclusions The equilibrium modulus is found to be linear with the hydration level and approximately 2× stiffer at 60% hydration relative to 90%. Keywords Viscoelastic · Tension test · Finite deformation · Large strain · Drying · Stress relaxation Hydrogels are polymer networks that are able to absorb water. Typically, synthetic hydrogels are brittle and have low mechanical strength when swollen. To overcome this, more complex polymer networks have been introduced to create hydrogels with better mechanical properties [1]. One example is double network gels that contain two intertwined polymer networks [2]. The high mechanical toughness of double network gels comes from selecting the two polymer networks such that one network will break when a high stress is applied. This dissipates energy in the gel and allows the second network to continue to be loaded. A limitation of such gels is the irreversible damage caused by the failure of the first network. One alternative to double network gels is dual crosslinked gels [3, 4]. Instead of having two polymer networks as in a double network gel, dual cross-linked gels have one polymer network that is cross-linked both chemically and physically. The chemical bonds act as a permanent network.
A.T. Zehnder
[email protected] 1
Clarkson University, Potsdam, NY 13699, USA
2
Cornell University, Ithaca, NY 14853, USA
The physical cross-links act as the breakable network to dissipate energy. Once the physical bonds are broken and the energy is dissipated, new physical bonds can be formed to heal the material. Previously, the mechanical properties of dual crosslinked poly(vinyl alcohol) (PVA) hydrogels have been studied over a range of temperatures and loading rates, but always when the gel was fully saturated [5–9]. In applications the gel may be subject to drying, thus the goal here is to quantify the effect of drying on stiffness. Water absorbed into polymers is known to act as a plasticizer, reducing the glass transition temperature, stiffness and strength [10]. However relatively little research has been published on the effects of hydration on the mechanical response of hydrogels. Truong et al. [11] studied the effect of hydration on resilin-mimetic protein-based hydr
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