The Design And Preparation Of Novel Polysaccharide-based Hydrogels For Biomedical Applications

Salecan is a novel linear (1â†'3)-β-D-glucan comprising β-1-3-linked glucopyranosyls with a small number of a-1-3-linked which was reported by our laboratory in 2010. It is consisted of the following repeating unit: â†'3)-β-D-Glcp-(1â†'3)-[β-D-Glcp-(1â†'3)-β-D-Glcp-(1â†'3)]3-a-D-Glcp-(1â†'3)-a-D-Glcp-(1â†'(Fig.1.1). As a microbial P-glucan, Salecan has excellent rheological properties, biological activities including antioxidation and non-toxicity (edible safety), it could be utilized in the food industry as a new source of thickening agent and in the medical industry for preventing and treating constipation. In addition, Salecan also has unique physicochemical properties, it affords a high density of hydroxyl groups, which can be modified to provide greater flexibility in the chemical reaserch. Based on the outstanding properties described above, in this paper, a series of novel Salecan-based hydrogel has been synthesized and their physicochemical properties such as structure, thermal stability, interior morphology, swelling behavior, mechanical properties were investigated, biocompatibility including degradation and cytocompatibility were also assessed. Finaly, cell adhesion properties and drug release behavior of some of these hydrogels were studied to evaluate their potential biomedical applications. The main contents and results are as follow:(1) Design and synthesis of a novel Salecan/poly(N,N-dimethylacrylamide-co-2-hydroxyethylmethacrylate) [poly(DMAA-co-HEMA)] semi-IPN hydrogelThe fracture strain and swelling ratio of pure poly(DMAA-co-HEMA) (PDH) hydrogel was too low, its pore structure was very dense, which was bad for the application in tissue engineering. To solve this problem, a series of novel semi-interpenetrating polymer network (semi-IPN) hydrogels containing Salecan and PDH were designed and synthesized by radical polymerization and semi-IPN technology. The concept of high strain was added to Salecan-based hydrogel system. The SEM investigations showed that the addition of Salecan into the PDH hydrogel achieved substantial changes in the final morphology. All semi-IPNs had a well-interconnected porous structure with tunable pore size ranging from 6 to 41 μm. Compression tests revealed that these semi-IPNs were robust materials with compressive modulus between 13.3 and 90.5 kPa. However, pure PDH broke at less than 50% of strain, while all the semi-IPN hydrogels did not break up to 70% of strain, the addition of high-viscous Salecan contributed to dissipate the deformation energy more efficiently and increased the fracture strain from 71.1% to 88.8%. The obvious weight loss of the semi-IPN hydrogels in PBS solution might be due to the diffusion of Salecan out of its semi-interpenetrating network with PDH. The results also indicated that the content of Salecan played an important role in the degradation process. Cytotoxicity tests demonstrated that semi-IPNs were non-toxic to COS-7 cell and had excellent potential for biomedical application.(2) Synthesis and characterization of a novel hydrogel:Salecan/polyacrylamide (PAAm) semi-IPN hydrogel with a desirable pore structure for cell adhesionPure PAAm hydrogel had a continuous morphology and a smooth texture without any apparent microporosity, and its swelling ratio was low, which was bad for the cell adhesion and tissue engineering. A novel semi-IPN hydrogels based on Salecan and PAAm were synthesized by radical polymerization/cryopolymerization and semi-IPN techniques. The mechanism of controllable pore size was successfully incorporated into Salecan-based hydrogel system. The semi-IPNs exhibited a homogeneous porous architecture with a tunable pore size in a very broad range of 5～150 μm, which exceeded that of the reported polysaccharide semi-IPN hydrogel, which can be tailored by the preparation temperature and the volume ratio of Salecan to PAAm. Mechanical measurements showed that all semi-IPNs possessed good mechanical properties, the addition of Salecan increased the fracture strain. In contrast, all cryogels can be compressed up to about 100% strain without any crack development. Cytotoxicity results suggested that semi-IPN hydrogels were non-toxic to COS-7 cells. A cell culture experiment performed using COS-7 cells revealed their appropriateness for cell adhesion due to the interconnected porous structure and the favorable swelling ratio. Together, these results make salecan/PAAm semi-IPNs promising materials for tissue engineering applications.(3) Preparation and characterization of a novel pH sensitive Salecan-g-poly(acrylic acid) (PAA) hydrogel for controlled release of doxorubicinAlthough the pure PAA hydrogel had pH-sensitive property, the release amount of the loaded drug was too low to meet the demand of a drug carrier. A new class of hydrogels was prepared in aqueous solution by the graft copolymerization of Salecan and acrylic acid (AA) for controlled drug delivery. The pH-sensitive property was successfully incorporated into the Salecan-based drug carrier. The formation of Salecan-g-PAA hydrogel can solve this problem very well. The swelling behavior of the hydrogels was shown to be highly dependent on the environmental pH, salt type and concentration, as well as the contents of Salecan and BAAm. They are almost unswellable at pH 1.2 and swollen extensively at pH 6.86. Especially, doxorubicin (DOX) as a model anti-cancer drug was very efficiently loaded into the negatively charged hydrogels (up to 69.4%) through electrostatic interactions. More importantly, the release of DOX from this intelligent system exhibited pH-responsive behavior and a sustained release pattern. For SPA2, the cumulative release profile showed a low level of drug release (about 12.3% in 24 h) at pH 7.4, and was significantly accelerated at pH 4.0 (over 40% in 6 h). Increasing the Salecan content could effectively enhance the cumulative release rate and the highest release quantity can even reach 68.1% for SPA3. Cytotoxicity experiments confirmed that all blank hydrogels were non-toxic to A549 cells, while DOX released from the drug-loaded hydrogels remained biologically active and had the capability to kill cancer cells. The results clearly suggested that the Salecan-g-PAA hydrogels may be promising carriers for controlled drug delivery.(4) Redox/pH dual stimuli-responsive degradable Salecan-g-SS-poly(IA-co-HEMA) (PIH) hydrogel for release of doxorubicinThe reducibly degradable disulfide bond crosslinker N,N’-bis(acryloyl)-cystamine (BAC) was added to the system of Salecan, itaconic acid (IA) and 2-hydroxyethylmethacrylate (HEMA) for the design of a novel Salecan-g-SS-PIH hydrogel as a drug carrier for controlled drug delivery. In comparison with the BAAm-based graft hydrogel, the addition of BAC into the system met the demand of a drug carrier. These negatively charged hydrogels had excellent colloidal stability and could effectively entrap positively charged DOX through electrostatic interactions, the loading efficiency of DOX could approach 76.9%. In vitro release studies from DOX-loaded hydrogels showed that a sustained and controlled long-term drug release has been achieved. Importantly, the hydrogel presented an obviously pH-dependent drugrelease behavior. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 3.2, only 17.7 and 13.5% and of DOX was liberated from SPIH2 even after 48 h at pH 7.4 and 6.8, while 64.7% release of DOX was attained within the same time frame at pH 3.2. Increasing the Salecan content contributed to the expansion of the hydrogel network and SPIH3 displayed a maximum swelling ratio of 30.2 g/g and the largest pore size 82.6 μm, which could effectively enhance the cumulative release rate and the highest release quantity can even reach 71.2% for SPIH3. All blank hydrogels were non-toxic to A549 cells. Whereas DOX-loaded SPIH2 exhibited comparable cytotoxicity with respect to free DOX at the same concentration, it can kill about 70%of A549 cells at a concentration of 10 μg/mL. Degradation test revealed that the hydrogel can totally degrade in 40 mM DTT/PBS solution due to the incorporation of BAC in the hydrogels, the time was 8 day, which was longer than the release time. Based on these results, it can be seen that incorporating the reducibly degradable disulfide bond into Salecan-based hydrogel system is a good way for designing safe and effective drug carrier.(5) Synthesis and characterization of a pH sensitive superabsorbent polymer:Salecan/ poly(2-acrylamido-2-methylpropanesulfonic acid-co-N-hydroxymethyl acrylamide) [poly (AMPS-co-HMAA)] superabsorbent hydrogelPoly(AMPS-co-HMAA) (PAH) hydrogel was non-degradable, which was unfavourable for the application in environment field. To address this drawback, hydrogel based on Salecan as entrapped polymer and PAH as a matrix have been prepared. "superabsorbent" concept fitted in Salecan-based hydrogel system. The swelling capacity was decreased considerably in the order of monovalent KCl> divalent CaCl2> trivalent AICl3. It was found that the semi-IPN superabsorbent hydrogel have good swelling degree with the addition of Salecan, which exceeded that of other polysaccharide semi-IPN hydrogel. The one with a higher Salecan content contributed to the expansion of the hydrogel network, SPAH3 displayed a maximum swelling ratio of 82.7 g/g, while SPAH6 had the best water retention capacity. Degradation test revealed that Salecan/PAH semi-IPN superabsorbent hydrogel can degrade due to the incorporation of Salecan in the hydrogels, which greatly increases the degradation rate. For SPAH3, the weight remaining ratio was only 1.8% after 69 day. These hydrogels had a great potential for environmental application.