| The feasibility of using iontophoresis to facilitate the transdermal delivery of insulin has been explored for replacing the daily multiple subcutaneous injections. The tendency of insulin to form a reversible or irreversible aggregate in the reservoir is of great concern since it has been observed to decrease the efficiency of iontophoretic delivery. Since the iontophoresis-facilitated transdermal delivery involves the application of an electrical potential across the insulin reservoir, the electrochemical field could be responsible for the observed aggregations and also conformational changes of insulin molecules.; This dissertation research focused its the investigation on the kinetics of insulin aggregation induced by the application of electrochemical field. For this investigation, an experimental setup was developed for continuous monitoring of insulin aggregation in an electrochemical field. Effects of physicochemical and electrical parameters on the rate of insulin aggregation were evaluated. The rate was observed to increase, as increasing the concentration and pH of buffered insulin reservoir, as well as the intensity and duration of current application. Several stabilizers of different types were found effective in reducing the rate of insulin aggregation, particularly those, which could minimize the electrostatic interactions between insulin molecules. It is believed that a partial unfolding of insulin molecules, and the exposure of hydrophobic amino acid residues, induced by an electric current application, could be the major cause of insulin aggregation.; Changes in the fourth derivative spectra of insulin indicated the occurrence of conformational changes in insulin molecules in the electrochemical field. The microenvironment of tyrosine, a hydrophobic aromatic residue was noted to change upon the application of electrochemical field. Tyrosine was observed to be more buried as the duration of current application prolonged. The conformational changes in insulin molecules was further confirmed by the circular dichroism studies which also revealed that alpha-helix of insulin molecules was transformed into beta-strand in the electrochemical field. The conformational changes were found to depend on the physicochemical of insulin reservoir and the electrical parameters of the electrochemical field applied, and noted to be reversible. By using stabilizers, such as salts and amino acids, it was possible to reduce these electrochemical field-induced conformational changes in insulin molecules. |
