Preparation And Characterization Of Multi-functional Bacterial Cellulose Materials

Bacterial cellulose(BC), also named as microbial nanocellulose, is a kind of cellulosic material with a three dimensional structure, which is produced by microorganisms through fermentation. It owns lots of extraordinary advantages such as high water holding capacity, high degree of polymerization and high crystallinity, relatively high wet tensile strength, excellent biocompatibility and so on. It has great potential in the broad medical applications including wound dressings, artificial blood vessels, and tissue engineering. However, pristine BC does not possess antibacterial ability, has poor mechanical properties when in a highly swollen state, and has no capability in controlled drug release. Additionally, the nanofibril network structure of pristine BC is so dense that it makes animal cells do not have enough space to grow and differentiate. These drawbacks make pristine BC hydrogel cannot be extensivel y used in the fields of wound dressing and tissue engineering, which has significantly limited the development of BC in the medical area.In order to overcome the disadvantages and insufficiencies of BC materials and to have a better use in the field of wound dressing and tissue engineering, two functional BC materials were prepared in this study. The first one is an ionic crosslinking bacterial cellulose-chitosan(BC-Ch) hydrogel composite. By immersing pristine BC into chitosan solution followed by crosslinking with addition of sodium citrate, BC-Ch composite hydrogels were produced. The physicochemical properties of BC-Ch composite hydrogels were evaluated through transmittance analysis, infrared spectroscopy, SEM, thermogravimetric analysis, water content analysis, tensile test, antimicrobial activity test, and the investigation on release behavior of model drugs Naproxen and bovine serum albumin(BSA). Results showed that BC-Ch composite hydrogels possessed a denser fibril network with smaller pores compared to pristine BC hydrogels. The transmittance of BC-Ch hydrogels increased gradually because of the dissolution of chitosan when the p H value of the hydrogel environment decreased to 2.2. BC-Ch hydrogels are stable except the p H value of the hydrogel environment was lower than 2.2. Due to the addition of chitosan, the thermal stability of the BC-Ch underwent a stepwise decomposition, which is different from pristine BC. In the antibacterial test, the BC-Ch hydrogel showed high growth inhibition with an antibacterial rate of 99.9% against Escherichia coli and Staphylococcus aureus. The average tensile strength and elongation at break of BC-Ch composite hydrogels showed significantly higher than those of pristine BC. The Young’s modulus of BC-Ch was 4 times higher than pristine BC. When Naproxen was used as the model drug, almost no effect on drug release behavior was observed with the pristine BC and BC-Ch hydrogel materials. But when the p H value of the environment changed to 2.2, the release efficiency of naproxen in the both materials significantly slowed. When BSA was used as the model drug, BC-Ch composite showed a suitable drug delivery capacity when the p H value was 6.4 and 8.0. These results showed that the BC-Ch composite is a potential candidate for wound dressing materials.The second one is a microporous BC hydrogel. By Immersing BC into hydrogen peroxide followed by addition of sodium chlorite to violently react with hydrogen peroxide to produce a large number of bubbles, which generate micropores with diameters ranging from 50 to 800 μm in BC hydrogel. The physicochemical properties of the microporous BC were evaluated through infrared spectroscopy, water content analysis, optical microscopy, SEM, tensile test, and MTT test. Results showed that no cellulose was oxidized. Water content of microporous BC achieved 99%, indicating no difference compared to pristine BC. The size of pores in the microporous BC could be regulated by changing the mass volume ratio of sodium chlorite to hydrogen peroxide. The shape of internal pores of microporous BC was irregular. The results in tensile test showed that the average tensile strength and elongation at break of microporous BC were lower than those of pristine BC hydrogel. MTT test on microporous BC displayed a higher viability as compared to that growing on the surface of pristine BC. There are several advantages to produce microporous BC by using the current technology. The method is not only simple, which means it is easy to be performed, but also a ― green ‖ route without pollution. The obtained microporous BC could be a promising scaffold biomaterial for applications in bone tissue engineering.