Bioinspired Monomers With Enhanced Hydrogen Bonding to Improve Adhesive Performance

Objectives: The adhesive layer is prone to challenges when considering the overall performance of a restoration system and is typically the site of recurrent failure. In this work, we investigate how bio-inspired monomers with enhanced hydrogen bonding may reinforce the adhesive network and and promote bonding with other species present in the oral environment (e.g., collagen).
Methods: Two novel monomers with pendant hydrogen bonding groups were developed. A methacrylamide containing 2-ureido-4[1H]-pyrimidinone (UPy) and a methacrylate containing trehalose, forming UPy-MMA and TMA, respectively. Experimental resins consisting of common adhesive monomers (e.g., hydroxy ethyl methacrylate – HEMA, urethane dimethacrylate – UDMA) were formulated. To explore the impact of the pendant hydrogen-bonding moieties, UPy-MMA or TMA were incorporated into adhesive resins as a partial replacement to HEMA. Fourier-transform infrared spectroscopy (FT-IR), Dynamic mechanical analysis (DMA), water swelling, and bonding strength analyses were used to characterize the different formulations.
Results: While the novel monomers developed here copolymerize with common adhesive monomers (HEMA, UDMA, etc.) there are notable variations to the in situ adhesive polymerization. For example, UPy-MMA modified resins have an enhanced degree of conversion (DC) and observed increase in polymerization rate (R_p). This is attributed to increases in viscosity of the adhesive resin as HEMA is replaced with UPy-MMA, which favors autoacceleration behavior. Furthermore, thermally modulated FTIR confirms that additional hydrogen-bonding is observed in the modified adhesive resins. However, the stability of these non-covalent interactions is sensitive to water uptake (e.g., storage time), which is the topic of ongoing studies.
Conclusions: Increased hydrogen bonding can improve the mechanical integrity of adhesive materials due to non-covalent interactions within the polymer network as well as with the surrounding environment/substrate. Our work reveals that model adhesive formulations containing UPy-MMA or TMA monomers facilitates these types of interactions.