Polymers Capable of Autonomous Repair
We developed novel polymeric-based adhesives that achieve intrinsic network reinforcement in both neutral and acidic conditions. The alkoxysilane-containing adhesives capitalize on free-radical polymerization and sol-gel reactions to provide self-strengthening in the aqueous environment of the mouth.
The evolution of the network structure in self-strengthening and control methacrylate-based formulations was studied using stress relaxation and dynamic mechanical analyses. With stress relaxation, a constant strain is applied and the resulting stress which corresponds to the material’s resistance to deformation is measured over time. Each test represents 8-h of loading under 0.2% strain (25°C) followed by 40 h of recovery in water (pH 7.4, 37°C). This stress relaxation and recovery procedure was repeated up to five times unless the sample exhibited permanent deformation. The polymethacrylate-based matrix, shown as C1/E1-A in the Figure, realizes both covalent and hydrogen bonding (OH•••OH). In the control formulation (C1), MES lacks hydrogen bond donor/acceptor functionality and the formation of hydrogen bonds is attributed primarily to the hydroxyl groups in the side chains (polyHEMA). For the experimental formulation (E1), in aqueous solution, the methoxysilane group in MPS are readily hydrolyzed and the formed silanol groups (Si—OH) interact with hydroxyl groups in the side chains. As a result, mobility of the backbone chain will be suppressed by the hydrogen bonds among the Si—OH•••OH and Si—OH•••HO—Si (E1-A/B in Figure). Meanwhile, covalent bonds could be gradually formed through the condensation reactions between silanol groups and/or silanol-hydroxyl groups.
In summary, the autonomous-strengthening reaction persists in the aqueous environment leading to a network with enhanced deformation resistance. The results of this work (Sarikaya et al. 2020; Sarikaya et al. 2021A; Sarikaya et al. 2021; Song et al. 2016a; Song et al. 2016b; Song et al. 2018; Song et al. 2019) illustrate a rational approach for tuning the viscoelasticity of durable adhesives for the repair and reconstruction of tissues in the oral cavity.
Song, L., Q. Ye, X. Ge, A. Misra, and P. Spencer. “Mimicking Nature: Self-strengthening Properties in a Dental Adhesive.” Acta Biomaterialia, 35:138-152, 2016.
Song L, Ye Q, Ge X, Misra A, Tamerler C and Spencer P. Fabrication of Hybrid Crosslinked Network with Buffering Capabilities and Autonomous Strengthening Characteristics for Dental Adhesive. Acta Biomaterialia 67:111-121, 2018.
Sarikaya R, Song L, Ye Q, Misra A, Tamerler C, Spencer P. Evolution of Network Structure and Mechanical Properties in Autonomous-Strengthening Dental Adhesive. Polymers 12, 2076, 2020
Sarikaya R, Song L, Yuca E, Xie SX, Boone K, Misra A, Spencer P, Tamerler C. Bio-inspired Multifunctional Adhesive System for Next Generation Bio-addivitely Designed Dental Restorations. J Mechanical Behavior of Biomedical Materials 113:104135, 2021.