Factors That Influence Successful Base Catalyzed Thiol-ene Hydrogel Synthesis
Nolan Morrison ’22
Brandon Vogel, Chemical Engineering
James L. D. and Rebecca Roser Research Fund
Ethoxylated trimethylolpropane tri-3-mercaptopropionate (ETTMP) and poly(ethylene glycol) diacrylate (PEGDA)-based hydrogels are a promising candidate for injectable, localized drug delivery due to the potential for non-swelling behavior and controllable drug release properties. However, we find that existing literature synthesis methods suffer from slow gelation times or a lack of reproducible procedures. In this work, we present a repeatable synthesis procedure, along with a sensitivity analysis of the major variables that impact successful synthesis. Our methods allow the hydrogels to be reliably synthesized in a polymer concentration range of 15 to 90 wt.%, resulting in gelation times between 2 min and 1 h with equilibrium moduli between 3.5 and 190 kPa. Furthermore, base-catalyzed conjugate Michael curing led to 16.35 min and 1.67 min gelation times for buffer pH values of 6.5 and 8, respectively. Additionally, we show that ETTMP purification directly controls the concentration of mercaptopropionic acid (MPA) necessary to inhibit the Michael addition. Lastly, we find that a stoichiometric mixture of ETTMP and PEGDA has a freezing point range of -17.9 ºC to -27.2 ºC and can be stored at -20 ºC for 2 months without crosslinking, as opposed to 2 days at room temperature, making storage and shipment of mixtures possible.