Chitosan-alginate-CaCl2 system for membrane coat application

Water-based formulations are preferred for membrane coat application becaus e they do not require the use of noxious solvents. A novel aqueous chitosan alginate-CaCl2 system was evaluated as a potential formulation to produce w ater-insoluble membranes of biodegradable polymers. Chitosan-alginate coace rvates were prepared by controlled reaction of chitosan (0.25% w/v) and sod ium alginate (0.25% w/v) solutions. Coherent membranes were obtained by cas ting and drying the coacervates suspended in aqueous CaCl2 solutions (0.05- 0.07% w/v). Increasing the calcium content did not modify membrane thicknes s (25-26 mum), but reduced the water vapor transmission rate from 658 to 56 6 g/m(2)/day, and improved the tensile strength of the membranes from 9.33 to 17.13 MPa. Differential scanning calorimetry, Fourier transform infrared spectroscopy, and elemental analyses of the chitosan-alginate coacervates indicated they were stable for up to 4 weeks of storage in distilled water at ambient temperature. Membranes of the stored coacervates required less c alcium to attain maximum mechanical strength. They also had higher water va por transmission rates than corresponding films prepared from fresh coacerv ates. On the basis of the properties of the cast film and its storage stabi lity, the chitosan-alginate-CaCl2 system can be considered for potential me mbrane coat application. (C) 2001 Wiley-Liss, Inc. and the American Pharmac eutical Association.