Studies On Synthesis And Application Of Biodegradable Injectable Hydrogels

Hydrogels, which possess three-dimensional network structure and full of water, have been the hotspot in biomedical field. Because their liquidity, size, elasticity and stiffness properties are readily regulated and designed, they could extremely mimic the extracellular matrix and living tissue. Compared to traditional preformed hydrogel, injectable hydrogel is a kind of novel material which could avoid large surgical incisions and much more adaptable to match the complicated situation and shape in vivo. Furthermore, we eager to prepare biodegradable and bioresorbable biomaterials which avoid the second operation after their support or repair mission is over. In this thesis a serial of biodegradable injectable hydrogels was designed and preliminary studied their applications.Firstly, a brief view of the development and application of injectable hydrogels was described, mainly from the aspects such as choice of materials, cross linking strategies, biomedical applications and non-invasive in vivo long-term monitoring.Temperature-sensitive tri-block copolymer PEO-PPO-PEO hydrogels, which physically crosslinked based on hydrophobic interaction, has been studied as drug carriers and tissue repair scaffold. But it could not be biodegraded and its 3D morphology in vivo is hard to maintain. Later, the researchers used biodegradable polyester, such as PLA, PCL, PLGA, etc. instead of PPO segment and developed a lot of ABA or BAB (A represents hydrophilic segment and B as hydrophobic one) triblock polymer hydrogels. Wherein the synthesis process of BAB-type copolymer is more convenient which directly obtained by ring-opening polymerization using PEG initiate the cyclic lactone. Unlike ABA copolymer showed a thick paste, the BAB type product always powder solid that easier to save, transport and more popular. In order to obtain the biodegradable BAB type hydrogel, PCLA-PEG-PCLA triblock copolymer was synthesized by one-step ring-opening polymerization. The influence of molecular weight, hydrophilic/hydrophobic ratio and CL/LA ratio to the phase transformation temperature were investigated. The sol-gel-precipitation phase diagram is depicted and the probable mechanism of gelation should be micro phase separation changed the system crystal orientation. In vitro drug delivery experiment results that the materials have good sustained micro molecular drug & protein release effect. Human oral mucous fibroblasts (OMFs) and skeletal muscle cells (SMCs) were used to evaluate the cytocompatibility of hydrogel with the respects of morphology, proliferation, viability in vitro. In vivo experiments demonstrate that it could effectively and rapidly form a gel in the subcutaneous tissue of rats, and the gel can be biodegraded within a few months. Further histological analysis showed that a slight acute inflammatory response caused by the hydrogel in the first two months after injection and there is no severe tissue lesions. After three months the inflammation subside on their own. All results suggest the PCLA-PEG-PCLA hydrogel have the application potential for maxillofacial soft tissue engineering.In order to obtain an injectable hydrogel of which gelation time is controllable and with higher intensity, chemical cross linkage was designed. Natural polysaccharides dextran (Dex) was modified as Dex-GMA to give their side chains with ?, ?-unsaturated carbonyl groups. HS-PEG-SH is thiol group end-caped PEG and its -SH group could react with the ?, ?-unsaturated carbonyl groups of Dex-GMA by thiol-Michael addition making the original polymer solution cross-linked. The gel time, swelling ratio and gel modulus could be adjusted by changing factors such as PEG molecular weight, Dex-GMA grafting yield and polymer concentration. In vitro drug release experiment using BSA as the model of protein drugs proved that this material released drug slowly. In vitro cytotoxicity of hydrogel was evaluated using COS-7 cell by MTT method and it was found that there was non-toxic when the gel concentration is less than 48 g/L.In clinical application, there is a greater demand of the functional biodegradable injectable hydrogels, such as hydrogel with functions of tracer or visualization used for embolization or organization filling. It is of great interest to monitor the implants real-timely using non-invasive detecting techniques. Thus we prepared MRI-visible hydrogels which based on chitosan and PEG. The macromolecular chelator of Gd(?), Ch-DTPA was synthesized by functionalization of chitosan with diethylene triamine pentacetic acid (DTPA). The PEG end-capped with aryl aldehyde, PEG-DA, was prepared as cross linker. Based on Schiff's base reaction, the hydrogels can be obtained in just 1 min by mixing the aqueous solutions of Ch-DTPA and PEG-DA at ambient temperature. The gelating procedure is pH sensitive, the hydrogels exhibit self-healing in an environment with pH value of 4.5 to 5.3. The morphology of the lyophilized gel was observed on SEM. In vitro release behavior of the hydrogel was tested also using rhodamine B as model drug. The MRI contrast enhancement effect of Gd(?)-binding hydrogels were investigated both in vitro and in vivo on rats. The results revealed that the hydrogels showed strong signals on T1 weighted MR images, and the hydrogels could always be detected before complete biodegradation. By analyzing the transvers MRI signals, the degradation type of the gel also could be evaluated. The histology result shows inflammation caused by the material which probably because gel pH value is lower than the physical environment. The future work should focus on pH adjustment in order to reduce or eliminate inflammations.Based on the in vivo degradation properties of the polycarbonate, we also explored the method to introduced polycarbonate segment into the hydrophilic drug carrier (micelle, water gel, etc.) and prepared polycarbonate which could be functionalized conveniently by "click reaction". Firstly, cyclic carbonate monomer with terminal alkyne pendant groups was synthesized. Then mPEG-PPC was obtained by ring-opening polymerization using mPEG as macro initiator to initiate the monomer. This copolymer could form micelle in solution. In order to increase its stability and decrease the critical micelle concentration (CMC), more hydrophobic PCL segment was introduce to the copolymer to form ABC type tri-block copolymer mPEG-PPC-PCL. Next fluorescent tracer Rhodamine B with azide group was grafted onto the tri-block copolymer by click reaction and obtained mPEG-PPC-g-Rh-PCL. 1H-NMR, FT-IR and GPC were performed to characterize the copolymer, and CMC, particle size and distribution of the polymer micelle solution is also determined. Results proved that mPEG-PPC-g-Rh-PCL solution possess stable particle size and lower CMC, and it may be a good potential fluorescent tracer and drug carrier. At the same time, the copolymer mPEG-PPC-PCL also has the potential as a drug carrier, which could be further targeted to the group and other functional modification.