Utilizing a degradation prediction pathway system to understand how a novel methacrylate derivative polymer with flipped external ester groups retains physico-mechanical properties following esterase exposure

Objective: The region of failure for current methacrylates (i.e. derivatives of acrylates) are ester bond linkages that hydrolyze in the presence of salivary and bacterial esterases that break the polymer network backbone. This effect decreases the mechanical properties of methacrylate-based materials. Methods: The ethylene glycol dimethacrylate (EGDMA) or novel ethylene glycol ethyl methacrylate (EGEMA) discs were prepared using 40 mu L of the curing mixture containing photo/co-initiators for 40 s in a PTFE mold at 1000 mW/cm(2). The degree of conversion was used as a quality control measure for the prepared discs, followed by physical, mechanical, and chemical characterization of discs properties before and after cholesterol esterase treatment. Results: After 9 weeks of standardized cholesterol esterase (CEase) exposure, EGDMA discs showed exponential loss of material (p = 0.0296), strength (p = 0.0014) and increased water sorption (p = 0.0002) compared to EGEMA discs. We integrated a degradation prediction pathway system to LC/MS and GC/MS analyses to elucidate the degradation by-products of both EGEMA and EGDMA polymers. GC/MS analysis demonstrated that the esterase catalysis was directed to central polymer backbone breakage, producing ethylene glycol, for EGDMA, and to side chain breakage, producing ethanol, for EGEMA. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to esterase biodegradation and changes in mechanical and physical properties than EGDMA. Significance: EGEMA is a potential substitute for common macromer diluents, such as EGDMA, based on its resistance to biodegradation effects. This work inspires the flipped external group design to be applied to analogs of current larger, hydrophobic strength bearing macromers used in future dental material formulations. (C) 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.