Tough Hybrid Hydrogels Adapted to the Undergraduate Laboratory

Polymer materials are indispensable in our daily lives. This makes polymer technology of critical importance in higher education. In particular, hands-on experiment-based practicals/laboratories with a focus on polymer science are of tremendous value in the undergraduate curriculum. Along these lines, hydrogels are highly cross-linked polymer networks which show some unique properties such as water absorbance and large extensibility, making them particularly well-suited in various biomedical applications. The properties of hydrogels can be systematically varied via changes in composition. In this practical laboratory, we use hybrid hydrogel formulations containing alginate and polyacrylamide to explore the consequences of compositional changes on mechanical behavior. Mechanical properties are determined using a simplified tensile test that is amenable to large groups of students using standard laboratory equipment. We used marbles to induce an extensional force and a ruler to measure the elongation of the gel as a function of the attached weight. Hereby, stress-strain curves can be obtained, and students are able to compare the difference between single and double network hydrogels as well as quantify the influence of network composition. This practical combines the use of chemical synthesis (i.e., reactant calculations) with practical skills which makes it interesting to use in a third year chemical/biomedical course. Furthermore, students can learn how to deal with chemicals and gain insight in polymer chemistry and its wide applicability, making it particularly well-suited for students coming from outside the traditional chemical science background.