Self-healing pHEMA hydrogel materials based on dynamic covalent bonds

다국어 초록 (Multilingual Abstract)

In this study, we conducted an in-depth investigation of a self-healing poly (2- hydroxyethyl methacrylate) (pHEMA) hydrogel based on dynamic covalent bonds. The SH-Hydrogel was synthesized via thermal polymerization using a thiol-Michael adduct crosslinker and HEMA monomer. The adduct formed by the thiol-Michael reaction exhibits reversible properties at high temperatures (90°C) due to its dynamic covalent bond, enabling dynamic equilibrium. Compared to a control hydrogel made with ethylene glycol dimethacrylate (EGDMA), an ethylene glycol-based crosslinker, the self-healing hydrogel using the Thiol-Michael based crosslinker (SH-Crosslinker) exhibited the ability to recover nearly 90% of its original tensile strength after cutting. The hydrogel solution mixture used in SH-hydrogel manufacturing was also utilized in contact lens production, and the suitability was determined by evaluating the physical properties of the resulting lenses. The fabricated contact lenses exhibited a high visible light transmittance of 97.3% and a water content of 40.4%. This is comparable to that of disposable contact lenses. Consequently, the successful synthesis of a self-healing hydrogel utilizing a dynamic crosslinker was achieved. However, due to its hydrophilic three-dimensional network structure, the hydrogel inherently contains water. For the previously mentioned SH-Hydrogel, recovery occurs at high temperatures of 90°C, which could be a critical disadvantage for a hydrogel containing water. The evaporation of water can result in reduced flexibility and compromise the structural stability of the hydrogel. To overcome this limitation, a disulfide based crosslinker (DS-crosslinker) was incorporated into pHEMA, resulting in a disulfide hydrogel (DS-Hydrogel) capable of self-healing via UV irradiation at room temperature. Disulfide bonds can achieve dynamic equilibrium not only at high temperatures but also through radical-mediated exchange reactions under weak UV irradiation. DS-Hydrogel demonstrated approximately 90% recovery under both conditions, with UV-induced recovery occurring faster than thermal treatment. Similarly, contact lenses fabricated from the DS-Hydrogel demonstrated high visible light transmittance and suitable water content, consistent with standards for commercial lenses. Furthermore, utilizing the thiyl radical generated by UV irradiation, the zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) was graft polymerized onto the surface. The covalently bonded pMPC layer enhances surface hydrophilicity and forms a stable hydration layer, conferring excellent anti-scratch and anti-fouling properties. Consequently, The engineered DS-Hydrogel was successfully integrated into pHEMA-based soft contact lenses, demonstrating multiple functionalities: robust self- healing capability, durable antifouling performance, and improved scratch resistance under physiologically relevant conditions.

목차 (Table of Contents)

• Part 1. Preparation of self-healing pHEMA hydrogels using dynamic covalent crosslinkers 2
• Ⅰ. Introduction 2
• Ⅱ. Methods 5
• 2.1 Materials 5
• 2.2 General methods 5
• 2.3 Synthesis 6
• 2.3.1 Thiol-Michael addition reaction 6
• 2.3.2 Synthesis of a self-healing crosslinker (SH-Crosslinker) 7
• 2.3.3 Preparation of pHEMA self-healing hydrogel (SH-Hydrogel) and control hydrogel sample (Control-Hydrogel) 8
• 2.3.4 Manufacture of self-healing contact lens (SH-Lens) 8
• Ⅲ. Result 9
• 3.1 Synthesis and Structural Characterization 9
• 3.2 Thermal self-healing properties 13
• 3.3 Contact lens suitablility 16
• Ⅳ. Discussion 20
• Part 2. Room-Temperature UV-Induced Self-Healing Hydrogels with Antifouling and Anti-Scratch Surfaces for Soft Contact Lenses 22
• Ⅰ. Introduction 22
• Ⅱ. Methods 26
• 2.1 Materials 26
• 2.2 General methods 26
• 2.3 Synthesis of disulfide crosslinker (DS-Crosslinker) 28
• 2.4 Preparation of self-healing and control hydrogels (DS-Hydrogel and Control- Hydrogel) 29
• 2.5 Surface functionalization of the pMPC Layer 30
• 2.6 Fabrication of contact lenses (DS-Lens) 31
• 2.7 Protein adsorption test 31
• 2.8 Surface scratch test 32
• Ⅲ. Result 33
• 3.1 Preparation of self-healing hydrogels using a disulfide crosslinker 33
• 3.2 Self-healing tests using thermal and UV-irradiation methods 35
• 3.3 UV-induced pMPC grafting onto DS-Hydrogel at Room temperature 42
• 3.4 Fabrication of pMPC-coated self-healing hydrogel contact lenses 45
• 3.5 Evaluation of protein adsorption and scratch resistance in pMPC-coated self- healing hydrogel contact lenses 47
• Ⅳ. Discussion 50
• Ⅴ. Reference 51
• Korean abstract 62