| dc.description.abstract | Cross-linked polymer materials, especially hydrogels and elastomers, have been increasing in usage for many applications, not only in daily life but also in industry and the biomedical field. Therefore, materials with biodegradable, self-healable, or recyclable abilities are essential for future development. The role of the cross-linking agents in the polymer material was undervalued in terms of biocompatibility, mechanical properties, degradability, recovery, and reusability. In this thesis, we developed a series of cross-linker to provide different functions for the covalently cross-linked polymer materials.
In chapter two, an innovative zwitterionic dimethacrylate 2-[2-{2-(Methacryloyloxy)ethyldimethylammonium}ethyl-phosphate]ethyl disulfide (MPCSS) for the development of biodegradable and biocompatible hydrogels with entirely bio-inspired phosphocholine (PC) structure was reported. The MPCSS cross-linker includes the zwitterionic group providing nonfouling properties and a disulfide bond that can be degraded by reducing agents and enzymes. Moreover, MPCSS has an opposite arrangement of charged groups to that in the 2-methacryloyloxyethyl phosphorylcholine (MPC) monomer. The hydrogels developed from MPCSS and MPC allow stronger mechanical properties upon electrostatic interaction between the oppositely charged groups and the higher water content than the MPC gels with the conventional cross-linker. The biocompatibility and fouling characteristics of MPC/MPCSS hydrogels were systematically investigated. Moreover, the degradation of MPCSS cross-linked hydrogels was evaluated through their weight loss and rheological data. Ultimately, MPC/MPCSS hydrogel was demonstrated in situ to encapsulate NIH-3T3 fibroblasts and provide an excellent 3D environment, facilitating cell remodeling and growth as a tissue scaffold.
In chapter three, three aromatic disulfide cross-linkers, named SS1, SS2, and SS3, were synthesized to create self-healable and recyclable elastomers. The disulfide bond is a reversible covalent bond with lower bonding energy than the carbon bond. So that the SS bond can be cleft by mechanical forces before the carbon bond is broken. The reversibility helps the disulfide bond reform, providing the self-healing ability to the elastomer, even in room conditions without any extra external stimuli. Moreover, combining the hydrogen bond into the structure of the disulfide cross-linker, in the case of SS2 and SS3, can enhance the self-healing efficiency of the elastomer at room temperature. The self-healing rate can reach 100% after 12h under 10 MPa pressure. The elastomer can be remolded after being cut into small pieces without reducing mechanical properties. The SS1, SS2, and SS3 cross-linkers can be used with many monomers, including TRIS, HEMA, HEA, and BMA, to prepare the elastomers with self-healing ability.
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