Nonvolatile and Shape-Memorized Bacterial Cellulose Gels Swollen by Poly(ethylene glycol)

Abstract

Bacterial cellulose (BC) provides a unique kind biopolymer gel, containing over 99wt.-%water, produced by bacteria of genus Acetobacter. The BC gels have various useful properties such as softness, translucence, biocompatibility, and water retention ability. This is why the BC gels receive much attention as potential soft materials for medicine, cosmetic, food, and etc. However, a large amount of water in the BC gels is quite easily squeezed out under small pressure and also easily dried in atmosphere. Thus, it is difficult to use the BC gels as engineering materials in practical applications. In order to overcome these limitations, many attempts were made to improve the mechanical strength of the BC gels. Recently, a breakthrough had come in gel science; synthetic tough hydrogels with anomalously high mechanical strength were developed by a double-network (DN) structure. Based on this technique, the BC gels with DN structure resulted higher mechanical strength than usual BC gels. However, another problem is still unsettled about easy drying of BC gels in atmosphere; desiccation-tolerant, nonvolatile BC gels have been keenly sought. Here, we have developed novel nonvolatile and thermo-responsive BC gels by introducing poly(ethylene glycol) (PEG) as nonvolatile solvents in BC gels instead of water solvent. It is known that PEG has good biocompatibility, nonvolatile, and water solubility, and shows various physical properties, depending on its molecular weight. Therefore, we tried to prepare different nonvolatile BC gels with different physical properties by changing the molecular weightMw of PEG; the BC gels were swollen in three kinds of PEG melts, which are of Mw 200 (named ‘BC/PEG 200 gel’), 1000 (named ‘BC/PEG 1000 gel’), and a mixture of 200 and 1000 (named ‘BC/PEG 200–1000 gel’), where PEGs of Mw 200 and 1000 are in liquid and solid states at room temperature, respectively. Also, we found the BC/PEG 200–1000 showed shape-memory property. In the present paper, we report these interesting and useful properties of the BC/PEG gels.