Photo-Cross-Linked Hydrogel Replication of Small Objects: A Multistep Final Project for Undergraduate Polymer Laboratories

We developed a multipart laboratory experiment on the synthesis of free-standing hydrogels for junior to senior undergraduate students. In this experiment series that runs over the course of multiple 3-h lab periods, small everyday objects belonging to the students are reproduced as hydrogels by first creating negative templates in thermally cured poly(dimethylsiloxane) molds (PDMS), followed by simultaneous photopolymerization and cross-linking using N-vinylpyrrolidone and poly(ethylene glycol) diacrylate in the molds. After being cured at room temperature, the molds are bisected and the objects are recovered. Second, the students optimize the synthesis of poly(N-vinylpyrrolidone)/poly(ethylene glycol) diacrylate (PVPON/PEGDA) hydrogels via UV-induced polymerization in test-batch scale quartered Petri dishes. Next, using the optimized hydrogel synthesis and the molds from part one, PVPON/PEGDA replicas of their objects are obtained by simultaneous photopolymerization and cross-linking in a UV cross-linking device. Finally, students present their results, methodology, and proposals for industrial scaleup to the class. The students are encouraged by steady progress toward their goal of making a freestanding hydrogel replica of their object and applying their knowledge toward developing a reproduceable protocol. They learn to control synthetic parameters including mixing ratios, polymerization time, and UV intensity as well as readjusting their synthesis procedure based on their understanding of structure-property concepts. This experience provides students with an introduction to polymer synthesis and methodologies familiar to both academic research and industry, which builds confidence in their ability to conduct independent research and development.