Applicability of electrospun polypropylene carbonate polymers as a drug carrier for sirolimus.

Polypropylene carbonate (PPC), a biodegradable aliphatic polyester, exhibits one particular advantage over other polyesters, which is that following degradation in vivo, it primarily produces H2O and CO2, causing minimal side effects. Although PPC exhibits limited mechanical strength, and is therefore not able to serve as a scaffold to support tissue regeneration, it may be suitable for drug delivery; however, this requires further investigation. In the present study, electrospinning was applied to generate PPC polymers containing sirolimus, a cell growth-inhibiting drug which is used to treat restenosis. The properties of PPC-sirolimus polymers were examined using scanning electron microscopy, differential scanning calorimetry and in vitro degradation assays. Drug loading and entrapment efficiency were determined, and in vitro sirolimus-release from the polymer was assessed. Furthermore, the effect of PPC-sirolimus polymers on cell growth was measured using an MTT assay in vitro. The results of the present study demonstrated that electrospun PPC polymers formed a uniform three-dimensional, grid-intertwined, net-like structure; the surface of the polymers was smooth and the diameter was similar to 3 mu m. Differential scanning calorimetry analysis demonstrated that sirolimus existed in an amorphous state in the polymer. Following soaking in PBS for 4 weeks, the polymer swelled and the net-like structure broke down and fragmented. Sirolimus loading and entrapment efficiency were 10.3 +/- 3.2 and 95.1 +/- 10.6%, respectively. Sirolimus-release from PPC-sirolimus polymers continued for 28 days in PBS. PPC-sirolimus markedly inhibited the growth of rat aortic adventitial fibroblast cells, an effect which was not observed with PPC alone. The results of the present study suggest that PPC polymers are a promising alternative drug carrier for sirolimus.