Study On Bacterial Cellulose Degradation By Cellulase In A Simulated Body Fluid

Bacterial cellulose, which exhibits many desirable properties, including excellent mechanicalproperties, high moisture permeability and good biocompatibility, has become a promisingmaterial for wound care, artificial blood vessels and tissue engineering applications in thebio-medical fields. Bacterial cellulose can be degraded into glucose monomers by cellulases innature. However, it cannot achieve biodegradation in the human body because there is nochemical or enzymatic process that can cleave the β-1,4-glycosidic linkage and convert thecrystalline cellulose fibrils into glucose. If bacterial cellulose can’t degrade in the body, it wouldincrease the possibility of the crystal adhesion, infection of stone formation, foreign bodies, evenrestrict the growth of the surrounding normal tissues along the stent surface. Accordingly, therealization of in-body degradation of cellulose can hardly be achieved unless through the use ofcellulases, as shown previously.The degradation of BC by different kinds of cellulases was studied. Furthermore, thefreeze-dried method and adsorption method were adopted to fix cellulases on the surface of BC.The degradation process and the degradation behavior of cellulase/BC composite membranes werestudied in a simulated human body environment. The works are introduced as follows in detail:(1)The degradation of BC by different kinds of cellulases was studied. The change ofcellulase activity in a simulated human body environment and the influence on the degradation ofBC by the ratio of β-glucoside enzyme were discussed. The results revealed that the neutralcellulase has the highest degradation activity under the condition of simulated human bodyenvironment. Cellulase activity reduced along with time in a simulated body fluid but there was nodeactivation. BC could be degraded by cellulases in the long term. At the same time, theβ-glucoside enzyme played a great role in promoting BC degradation. When the ratio came to60%, the rate of BC degradation was the highest. (2) The freeze-dried method was used to fix cellulases on the surface of BC. The degradationprocess and behavior of cellulase/BC composite membranes in a simulated human bodyenvironment were studied. The experimental results showed that the freeze-dried method could fixcellulase on the surface of BC effectively. The release rate of cellulase fixed on the BC reached9.0%to12%. The mechanical properties of cellulase/BC composite membranes prepared viafreeze-dried method declined a lot compared to the original bacterial cellulose membrane. Thematerials could keep mechanical properties within a week basiclly. At the same time, cellulase/BCcomposite membranes prepared via freeze-dried method could realize stable degradation in asimulated body fluid. When the quality of cellulases fixed was10to30mg, materials could bedegraded within2w. When the quality of cellulase fixed was1to5mg, materials could bedegraded within24w. When the quality of cellulases fixed was0.5mg, materials could’t bedegraded fully within24w due to the low quality of cellulase and slow degradation rate.Cellulase/BC composite membranes prepared via freeze-dried method had good biocompatibilityin vitro and in vivo. Cells can grow and proliferate well along the surface of cellulase/BCcomposite membranes. The inflammatory response of materials was also very weak.(3) The adsorption method was used to fix cellulases. The cellulases maintained the activityand had the uniform distribution. The experiment realized regulated degradation of BC throughcontrolling adsorption condition and the amounts of cellulases fixed. At the same time, theadsorption method was compared to freeze-dried method on the degradation of BC. Thedegradation process and properties were also analyzed. The results showed that the cellulasesfixed by adsorption method distributed more even and secure than the freeze-dried method. Therelease rate of cellulase fixed by adsorption method on the BC reached5.0%to8.0%in asimulated body fluid.The cellulase/BC composite membranes prepared via adsorption method hadhigher mechanical strength during the degradation when cellulases fixed had the similar quality.The materials could keep mechanical properties for24d. The cellulase/BC composite membranesprepared via adsorption method could be degraded stable and slow. When the quatity of cellulasesfixed was from0.72mg to3.67mg, materials could be degraded completely within24w indifferent degree. When the quatity of cellulases fixed was less than0.72mg, materials did notachieve full degradation within24w. Cellulase/BC composite membranes prepared via adsorptionmethod also had good biocompatibility in vitro and in vivo.