Visible Light-Induced Graft Polymerization And Its Bioapplication Reserach

The graft polymerization technique can be used for surface or bulk modification of common polymer materials, thus the surface or bulk properties can be improved. Graft polymerization has been utilized in many fields, such as packaging, food and biomedicine. Ultraviolet irradiation is a general method for graft polymerization. However, due to its high energy, ultraviolet deactivates the bioactive compounds such as DNA or protein.For the special requirements of biomedical fields, it is necessary to develop the visible light-induced graft polymerization owing to its low energy and mild circumstance.This dissertation was designed to study visible light-induced surface graft polymerization and hemicellulose-graft-acrylic acid hydrogels with commercial isopropyl thioxanthone (ITX) and camphorquinone (CQ) as the initiators, respectively. And the bio-merits of the visible light-induced graft polymerization for enzyme immobilization and drug release were also investigated. The main results and significance are summarized as follows:1. The supporting matrix polypropylene nonwoven fabrics (PPNWF) with dormant groups were prepared through the abstracting hydrogen-coupling reation under UV irradiation. Then visible light-induced graft crosslinking polymerization was performed to initiate polymerization of bifunctional monomer poly(ethylene glycol) diacrylate (PEGDA), resulting in the formation of a highly crosslinked, nonswelling and flat "molecular net-cloth".The xylanase was in situ entrapped simultaneously with the formation of PEGDA network for hydrolysis of corncob hemicelluloses. The immobilization yield and immobilization density can be tuned by some polymerization factors. This method can effectively maintain the activity of immobilized xylanase, that is, the immobilized xylanase can be reused for batch-wise hydrolysis. It retained 80% of its original activity after 25 cycles and 60% after 50 cycles. When compared with UV-formed PEGDA net-cloth with the same amount of xylanase, the visible light-induced product showed impressive advantages, whereas, the decrease in xylanase activity aggravated with the increase of UV irradiation time.Moreover, for hydrolysis of corncob hemicelluloses by free and immobilized xylanases at the same dosage, the reaction rate of free xylanase was quicker than that of immobilized enzyme, but the extent of hydrolysis was roughly the same.2. The hemicellulose-graft-acrylic acid hydrogels (HC-g-PAA)were formulated through visible light-induced polymerization using camphorquinone (CQ) as photoinitiator and N,N-methylenediacrylamide as crosslinking agent to initiate the graft polymerization of acrylic acid onhemicellulose backbone. Effect of acrylic acid/hemicelluloses, amount of CQ and amount of crosslinking agent on the equilibriumswelling ratios of the hydrogels were determined, and the results showed that the hydrogels were pH-responsive. The swelling behavior of thehydrogels at various pH values was divided into three parts:the fast increasing area (pH 2-6), the slow increasing area (pH 6-9), and the slowingdown area (pH 9-11).The network expanded in basic buffers, while shrunk when subjected to acidic condition. Furthermore, BSA, employed as the model protein drug, was in situ photoencapsulated in the hydrogel through the visible light-induced polymerization. The in vitro release of BSA indicated the pH-sensitive release performance. For simulation of gastrointestinal tract conditions, almost all BSA remained in the hydrogel in the simulated gastric buffer (pH 2.0) and started to release in the simulated intestinal buffer (pH 7.4), indicating the hemicelluloses-based hydrogel exhibited a desired protective effect for oral administration of BSA.The synthesized hemicellulose-graft-acrylic acid hydrogels with pH-sensitivity can be prepared by a visible light-induced photopolymerization and are suitable for in situ encapsulation of proteins, offering promise for application in biomedical fields, especially for controlled drug release.3. Isopropyl thioxanthone semi-pinacol (ITXSP) radical was formed by UV-induced abstracting hydrogen process from the surface of polycaprolactone (PCL) film, and then coupling with the corresponding surface radical. Then visible light-induced graft cross-linking polymerization was performed to initiate polymerization of poly(ethylene glycol) diacrylate (PEGDA) and acrylic acid, resulting in formation of the nano-scaled hydrogel layer. The graft yield and thickness of hydrogel layer can be controlled by varying the exposure time and monomer composition.The swelling ratio of surface-attached hydrogel thin film was much lesser than the bulk hydrogels with a same crosslinking density. And the swell occurred in the normal direction due to the constraint of the supporting substrate. When BSA was used as the model protein drug, the in vitro release test showed a more cumulative release in acidic solution than that in neutral buffer, owing to a squeezing mechanism for nano-scale hydrogels.