| Hydrogels are a desired material for biomedical and pharmaceutical applications due to their unique swelling properties and highly hydrated structure. To better control the synthesized hydrogels for various applications, it is necessary to have a thorough understanding of hydrogel structure and reaction mechanism. In this study, pH-sensitive hydrogel networks consisting of methacrylic acid (MAA) crosslinked with tri(ethylene glycol) dimethacrylate (TEGDMA) were synthesized by free-radical photopolymerization in the water/ethanol mixture with different ratios under various light intensity. Reaction rate was measured using Photo-Differential Scanning Calorimetry (PhotoDSC) with a modified sample pan designed for handling volatile reagents. A photo-rheometer and a dynamic light scattering (DLS) goniometer were used to follow the changes in viscosity and molecule size of the resin system during photopolymerization. It was found that the rate of polymerization increased and more compact and less swelling gels would form with a higher water fraction in 50wt% solvent/reactant mixture. This is because the weaker interaction between MAA and solvent gives a higher opportunity for propagation and a higher reaction rate. The hydrophobic TEGDMA and initiator tend to form aggregates in the solution with a higher water content, contributing to the inhomogeneous microgel formation. It was also noted that the rate of polymerization and the MAA conversion were enhanced as the light intensity increased. However, at too high a light intensity, an adverse effect was observed and the final conversion of MAA decreased to 43% at 24 mw/cm2. The optimal light intensity was about 2.0 mw/cm2 to get the PMAA gels with low residue monomers. The use of the high light intensity significantly shortened the reaction time to reach the macro-gelation and increased the swelling ratio of formed hydrogels, which can be explained by the mechanism of intra- and intermolecular reaction.; By using the desired functional hydrogels, several drug delivery systems were developed based on the selected integration of a number of micro-manufacturing modules such as soft-lithography, micro-imprinting, and polymer self-folding, to achieve multi-functionalities such as drug protection, self-regulated oscillatory release, enhanced mucoadhesion, and targeted unidirectional release. To evaluate the device performance, adhesion measurement, dynamic flow testing, and targeted unidirectional release were conducted for trans-luminal delivery of two model drugs, acid orange 8 and bovine serum albumin. The self-folding device first attached to the mucosal surface and then curled into the mucus, leading to enhanced mucoadhesion in the mode of "grabbing". Furthermore, the folded layer served as a diffusion barrier, minimizing the drug leakage in the small intestine. The resulting unidirectional release provides improved drug transport through the mucosal epithelium due to localized high drug concentration. The functionalities of the devices have been successfully demonstrated in vitro using a porcine small intestine.; The novel delivery devices will be of great benefit to the advancement of oral administration of proteins and DNAs. Since the mucus layer covers many tissues at other specific sites, the devices may be applied for ocular, buccal, vaginal and rectal administrations. The polymer self-folding at the microscale can also be applied as probe arrays for bio/chemical sensing, carriers in cell-based bioreactors, and tissue clamping. |
