Hydrophobic chitosan sponges modified by aluminum monostearate and dehydrothermal treatment as sustained drug delivery system

• We aim to develop simple method to prepare hydrophobic chitosan sponge.
• It was orderly performed by simple mixing, freeze dry & dehydrothermal treatment.
• Dehydrothermal treatment converted ionic bond into amide bond (stable in water).
• Aluminum monostearate (Alst) enhanced hydrophobicity of the prepared sponge.
• Alst reduced swelling of the sponge thus facilitated sustained asiaticoside release.

The aim of this study is to develop hydrophobic chitosan sponges by using novel simple preparation technique in which hydrophobicity of chitosan was modified by aluminum monostearate (Alst) and dehydrothermal treatment (DHT). Alst was able to dissociate and to cleave stearate ion in 2% w/v lactic acid. Composite dispersion of chitosan and Alst (CLA) could be easily prepared by simple mixing at room temperature. The pH value of the CLA dispersions and particle size of the chitosan–Alst complex in the system comprising low chitosan concentration significantly increased by mixing time. The dispersions were further fabricated into sponges by using lyophilization technique and DHT. FT-IR spectra analysis indicated amidation between amino group of chitosan and carboxyl group of stearate side chain after DHT. Contact angle measurement was applied to evaluate hydrophilic/hydrophobic properties of the prepared sponges. Swelling behavior of the sponges was investigated in three different medium namely acetate buffer (pH 4.0), phosphate buffer (pH 7.4) and carbonate buffer (pH 10.0). Drug release study was conducted in phosphate buffer pH 7.4 at 37 °C by using asiaticoside as a model drug. Contact angle measurement revealed that addition of Alst and DHT enhanced the hydrophobicity of the materials. Swelling of the sponges decreased as Alst amount increased. Swelling behavior of the sponges was coincident with the release of asiaticoside in which the sponge containing higher Alst amount apparently exhibited the sustained release character. Release of asiaticoside from CLA sponges fitted well with first-order kinetic and the exponent value (n) in power law model indicated that the main release mechanism was Fickian diffusion. From this study, we found the potential of the prepared hydrophobic chitosan sponges for further application as drug-sustained-release, porous wound dressing.

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