Development of hydrogel patch for controlled release of alpha-hydroxy acid contained in tamarind fruit pulp extract

The aim of this study was to develop hydrogel patch using crosslinked chitosan-starch as polymeric matrix for controlling the release of the natural alpha-hydroxy acid (AHA) contained in the extract of tamarind's fruit pulp. The chitosan (MW 100 000) was blended with corn, tapioca or rice starch in various ratios and then crosslinked with glutaraldehyde. The physical characteristics, mechanical resistance, bio-adhesion property and surface morphology of the prepared hydrogel patches with and without the extract were investigated. The release patterns of the hydrogel patches containing the extract were investigated by measuring the amount of tartaric acid, a major AHA present in the tamarind's fruit pulp extract, accumulated in the receptor medium of the vertical diffusion cell at various time intervals over a period of 6 h. The results indicated that the formulations of chitosan: corn starch 4.5:0.5 with glutaraldehyde 0.02% w/w (C_4.5T_0.5G_0.02) or 0.04% w/w (C_4.5C_0.5G_0.04), chitosan: tapioca starch 4.5:0.5 with glutaraldehyde 0.04% w/w (C_4.5T _0.05G_0.04) or 0.05% w/w (C_4.5T _0.5G_0.05), and chitosan: rice starch 4.5:0.5 with glutaraldehyde 0.04% w/w (C_4.5R_0.5G_0.04) and chitosan: rice starch 4.0:1.0 with glutaraldehyde 0.03% w/w (C _4.0R_1.0G_0.03) provided the flexible and elastic patches with good bio-adhesive property. The tensile strength values ranged from 5 to 15 N mm^-2 and the elasticity ranged from 30 to 60%. The addition of the extract in these formulations significantly increased the tensile strength values of the obtained patches. The patch of C _4.0R_1.0G_0.03 formulation containing the extract showed relatively highest porosity, corresponding to its highest amount (12.02 ± 0.33 mg) and rate (0.452 ± 0.012 mg mm^-2 min ^-1/2) of tartaric acid released. The amounts of tartaric acid released from the developed hydrogel patches were proportional to a square root of time (Higuchi's model), particularly the release from C_4.0R _1.0G_0.03 (R², 0.9978 ± 0.0020) and C_4.5R_0.5G_0.04 (R², 0.9961 ± 0.0024) patches.