Preparation And Characterization Of Thermoresponsive BC/PNIPAM Composite Hydrogel

Bacterial cellulose(BC)has an extensive application prospect in the biomedical field due to its unique nanometer fiber network structure,good biocompatibility,high water content and good mechanical toughness.With the progress of composite material technology,BC materials with special performance have been developed,which further broadens the application field of BC.Poly-(N-isopropyl acrylamide)(PNIPAM)is a kind of temperature-responsive materials with the low critical solution temperature(LCST)of 32°C,and is widely used for the preparation of temperature responsive intelligent composite materials.In order to obtain BC composites with temperature responsiveness and to explore the potential applications of BC materials,BC/PNIPAM temperature-responsive hydrogel materials was successfully prepared in the study,through using the BC as a matrix material.Radical polymerization was initiated after NIPAM monomer penetrated in the BC fiber network.At a temperature near the LCST of BC/PNIPAM hydrogel,a great change of the hydrogel membrane in light transmittance was found.Firstly,uniform transparent BC hydrogel membrane was obtained via static fermentation with the screened Gluconacetobacter xylinus strain(ATCC 23770)in laboratory.Three different BC/PNIPAM hydrogel composite materials with different content of PNIPAM were obtained eventually,by making NIPAM monomer seeped into the BC internal fiber network under the condition of 80°C and a radical polymerization reaction was initiated.As at temperature below the LCST,the transparency of the material has the same as the BC,while at temperature above the LCST,the transparency of the composite material decreased significantly.The composite appeared almost an opaque state when the temperature reached 60°C.Then PNIPAM content in three different BC/PNIPAM composite hydrogels was determined with element analysis.By using infrared,thermo gravimetric and differential scanning calorimetry methods the BC/PNIPAM composite hydrogel was studied through a series of characterization.In order to further verify the influence of temperature-responsive properties of the composite on its transmission of light,this study used ultraviolet-visible-near infrared spectrophotometer to detect the changes in hydrogel light transmittance under the conditions of different temperature.The results showed that the light transmittance of BC/PNIPAM hydrogel had obvious changes when temperatures changed from high to low.In addition both wavelength range and content of PNIPAM in the composite membrane affected the absorbance of composite materials.The composite material has a good application prospect in the field of temperature control of light path.In order to explore microscale mechanism in light transmittance differences of the BC/PNIPAM composite hydrogel under different temperatures,the study used field emission scanning electron microscopy(FE-SEM)to observe internal structure of the rapidly frozen and freeze-dried BC/PNIPAM hydrogel composite materials under the condition of different temperatures,and to count the fiber diameters.Images confirmed that the microstructure of composite hydrogel had larger difference under different temperatures.At low temperature,the hydrogel absorbed water and swelled,so that PNIPAM filled in BC fiber network,contributing to more thicker fiber diameters.While at high temperature PNIPAM hydrogel would lose water and turned contraction,and PNIPAM aggregated together into multiple gel particles to occupy the BC network space,so that the fiber diameter did not change very much as compared with the pure BC.Due to swelling and deswelling of the PNIPAM,the internal clearance of the BC/PNIPAM composites changed under conditions of different temperature,therefore the material may be used as the temperature control switch in the study of drugs permeation.This work used sodium benzoate as a model drug to study drug penetration in different BC/PNIPAM composite hydrogel with different PNIPAM content under different temperatures.Experimental results showed that accumulated penetration volume of sodium benzoate in 32 h under the temperature of 37°C was significantly higher than that under the temperature of 20°C,which proves that the composite has a good application prospect in the field of controlled drugs penetration.Finally,the biocompatibility of the composites was evaluated.Through comparison of two kinds of cytotoxicity test kit(MTT and CCK 8),experiments showed that the CCK-8 was more suitable for the toxicity assessment of BC hydrogel materials.Meanwhile both the growth ratio of cells and fluorescence staining results showed that the cells grew well on native BC and three different PNIPAM-contained BC/PNIPAM composite membranes and no difference was found in cell proliferation.The results of confocal microscope showed that cells performed spindle type and showed good growth morphology on both BC/PNIPAM and BC material surface.Overall,the newly synthesized BC/PNIPAM composite hydrogel materials in this work can be expected to be used as an intelligent window as a light control switch,as well as to be used in the temperature controlling drug penetration.What is more,the material with no obvious cytotoxicity suggests that the composites have great potential in the biomedical field.