Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels with Bio-Friendly Toughening Agents

Inspired by the avoidance of toxic chemical crosslinkers and harsh reaction conditions, this work describes a poly(vinyl alcohol)-based (PVA) double-network (DN) hydrogel aimed at maintaining biocompatibility through the combined use of bio-friendly additives and freezing-thawing cyclic processing for the application of synthetic soft-polymer implants. This DN hydrogel is studied using techniques that characterize both its chemical and mechanical behavior. A variety of bio-friendly additives are screened for their effectiveness at improving the toughness of the PVA hydrogel system in monotonic tension. Starch is selected as the best additive for further tensile testing as it brings about a near 30% increase in ultimate tensile strength and maintains ease of processing. This PVA-starch DN sample is then studied for its tensile fatigue properties through cyclic, strain-controlled testing to develop a fatigue life curve. Though an increase in monotonic tensile strength is observed, the PVA-starch DN hydrogel does not bring about an improvement in the fatigue behavior as compared to the control. Although synthetic hydrogel reinforcement is widely researched, this work presents the first fatigue analysis of its kind and it is intended to serve as a guide for future fatigue studies of reinforced hydrogels.