Effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule

The effects of chain flexibility of chitosan molecules on the preparation, physical, and release characteristics of the prepared capsule were studied. The chain flexibility of chitosan molecules in solution was manipulated by using chitosans with different degrees of deacetylation (DD) (67.9%, 81.3%, 90.5%, 92.2%), different pHs (2.0, 3.0, 4.0), and NaCl concentrations (0, 0.3%). The solutions were then used to encapsulate hemoglobin or dextran by the orifice method to make the capsules. Axial ratios and break strengths were used to characterize the appearance and mechanical properties of the prepared capsules. D. S. C. was employed to measure enthalpies and maximum melting temperatures to be used as a quantitative index of hydrogen bond formation in the walls of the capsules. Release rate was used as a pore size indicator. The results show axial ratios of the capsules increased with a decrease in molecular weight and also with an increase in DD of chitosan used. Axial ratios also increased when 0.3% NaCl was added to the solutions used. The effects of solution pH show that capsules prepared from pH 3.0 solutions were smaller than those from pH 2.0 and/or pH 4.0 solutions. Capsules of lower break strengths had higher axial ratios. The enthalpies of the chitosan capsules increased with increasing DD of chitosans used, and also with increasing NaCl concentration in the solutions used. However the maximum melting temperatures showed no linear relationship with the DDs of chitosan used. Maximum melting point temperatures of capsules also increased with an increase in NaCl concentrations in solutions used. The hemoglobin and dextran release percentages from the capsule at 25 degrees C for 24 h increased with an increase of DD of chitosan used. The release rate also increased with the addition of NaCl in the chitosan solution used. The release percentages of capsules prepared from pH 4.0 solutions were higher than those from pH 2.0 and/or pH 3.0 solutions. Release percentages of dextran of different molecular weights from capsules of 81.3% DD chitosan and pH 3 solutions were 52.7% for 19600 Da dextran, 26.3% for 87000 Da dextran and 12.4% for 162000 Da dextran. Copyright (C) 1996 Elsevier Science Ltd.