Chitosan–alginate–CaCl2 system for membrane coat application

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Abstract

Water‐based formulations are preferred for membrane coat application because they do not require the use of noxious solvents. A novel aqueous chitosan–alginate–CaCl2 system was evaluated as a potential formulation to produce water‐insoluble membranes of biodegradable polymers. Chitosan–alginate coacervates were prepared by controlled reaction of chitosan (0.25% w/v) and sodium alginate (0.25% w/v) solutions. Coherent membranes were obtained by casting and drying the coacervates suspended in aqueous CaCl2 solutions (0.05–0.07% w/v). Increasing the calcium content did not modify membrane thickness (25–26 μm), but reduced the water vapor transmission rate from 658 to 566 g/m2/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 calcium to attain maximum mechanical strength. They also had higher water vapor transmission rates than corresponding films prepared from fresh coacervates. On the basis of the properties of the cast film and its storage stability, the chitosan–alginate–CaCl2 system can be considered for potential membrane coat application. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1134–1142, 2001

Section snippets

INTRODUCTION

Chitosan is a deacetylated derivative of chitin that has generated much research activity because of its favorable properties. It is a biodegradable and biocompatible polymer of low toxicity and good medical functionality, and has been developed into antithrombogenic materials,1 wound dressings,2 and controlled‐release drug delivery systems.3,4 Chitosan is also a potential carrier for gene therapy5 and the immobilization of cells6 and enzymes.7

Sodium alginate is a natural linear polysaccharide

Materials

Chitosan (Aldrich Chemical Company) was deacetylated by established methods13 to obtain samples with 95% degree of deacetylation. The degree of deacetylation was determined by a first‐derivative ultraviolet (UV) spectrophotometric method.17 Sodium alginate (Laminaria hyperborea, BDH Laboratory Supplies, UK) was used as received. The molecular weights of the chitosan and sodium alginate samples, determined by solution viscosity methods,13 were 1.48(±0.06)× 105(n = 3) and 1.40(±0.07) × 105(n

Membranes Obtained from the Chitosan–Alginate–CaCl2 System

Mixing the chitosan and sodium alginate solutions under the prescribed conditions gave rise to a suspension of fine fibrous chitosan–alginate coacervates, together with unreacted chitosan and alginate molecules. When cast and dried, the reaction mixture produced flexible, coherent membranes.13 On the other hand, isolation of the coacervates, by centrifugation of the reaction mix, followed by resuspension in distilled water and casting, yielded brittle membranes that tear easily. The coherence

DISCUSSION

Coacervation between chitosan and alginate occurred by electrostatic attraction between the two oppositely charged polymers. The reaction mixture that resulted from the addition of the chitosan solution to the alginate solution comprised of chitosan–alginate coacervates dispersed in a sodium alginate solution. On casting and drying, the sodium alginate molecules provided a supporting matrix for the water‐insoluble coacervates to give a coherent and flexible membrane. Separation of the

CONCLUSION

Chitosan–alginate coacervates suspended in distilled water can be cast into coherent membranes of 26 μm on the addition of 0.05% w/v CaCl2 into the suspension just prior to casting. The membranes had a tensile strength of 9.33 MPa and 1.72% strain at break. Increasing the CaCl2 concentration to 0.07% improved the respective mechanical properties to 17.13 MPa and 2.66%, and reduced the water vapor transmission rate of the membrane to 566 g/m2/day. The suspension of coacervates in the absence of

Acknowledgements

This study was supported by a National University of Singapore grant (R‐148‐000‐019‐112). Ms. Lishan Wang is a recipient of the National University of Singapore graduate scholarship.

REFERENCES (23)

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    Production, properties and uses of alginates

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