Investigation of insulin loaded self-assembled microtubules for drug release

Self-assembled microtubules were used to entrap insulin for the preparation of new drug delivery devices. The interactions of insulin with the microtubules were probed by circular dichroism, zeta potential analysis, as well as FTIR spectroscopy. The morphologies of the insulin-loaded tubules were examined by AFM and TEM. We found that insulin loading was both pH- as well as concentration-dependent. The circular dichroism analysis indicated that, at pH range 6-7, the conformation change in the presence of the microtubules was minimal and hence would be the most appropriate conditions for insulin loading. The entrapment efficiency and release of insulin was found to be pH-dependent. Further, the controlled drug release studies indicated that, under acidic conditions, insulin release was extremely slow, and it is likely that the insulin is protected inside the microtubules. Thus, the microtubules may potentially protect the insulin from aggregation and release at lower pH (gastric pH) in ViVo. However, at pH 6.5 (closer to intestinal pH) a sustained release was observed. Such new materials may inhibit the aggregation of peptides under suitable conditions and potentially be used for drug delivery, in particular, for other peptide-based drugs.