The success of drug eluting stents (DESs) has been challenged by the manifestation of late stent thrombosis after DES implantation. The incomplete regeneration of the endothelial layer poststenting triggers adverse signaling processes precipitating in thrombosis. Various approaches have been attempted to prevent thrombosis, including the delivery of biological agents, such as estradiol, that promote endothelialization, and the use of natural polymers as coating materials. The underlying challenge has been the inability to release the biological agent in synchronization with the temporal sequence of vascular wound healing in vivo. The natural healing process of the endothelium after an injury starts after a week and may take up to a month in humans. This article presents a novel DES formulation using a hemocompatible polyurethane (PU) matrix to sustain the release of probucol (PB), an endothelial agonist, by exploiting the greater difference in the solubility parameters of PB and PU. This results in the formation of crystalline PB aggregates retarding drug release from PU. The physicochemical properties of PB in PU were confirmed using differential scanning calorimetry and X-ray diffraction. Drug-polymer compatibility was examined using infrared spectral analysis. Also, in vitro studies using primary human aortic endothelial cells resulted in the selection of 5% w/w PB as the optimal dose, to be further tested in vitro and in vivo. This work develops and tests a promising new DES formulation to enable faster endothelial cell proliferation poststenting, potentially minimizing the incidence and severity of thrombotic events after DES implantation.

The hydrogel template method was used to fabricate homogeneous drug–PLGA microparticles. Four drugs (felodipine, risperidone, progesterone, and paclitaxel) were loaded into the PLGA particles with the homogeneous size of 10 µm, 20 µm, and 50 µm. The drug loading into the PLGA microparticles was 50% and higher. The felodipine–PLGA microstructures of four different sizes showed that the drug release kinetics is dependent on the total surface area available for drug release. The smaller the particle size, the release rate was faster. Two types of microparticles (10 µm diameter and 10 µm height, and 50 µm diameter and 5 µm height) showed zero-order release and complete release was observed within 2 weeks. The release rate, however, was not exactly proportional to the surface area. Different drugs which were loaded into the same PLGA formulation showed different release profiles. The main difference was on the initial burst release. The overall release profile seems to be similar for different drugs, if the release profile is adjusted to eliminate the burst release. The initial burst release appears to be inversely related to the water-solubility of a drug, i.e., the lower the water-solubility of a drug, the higher the burst release. The hydrogel template method allowed preparation of homogeneous particles with predefined sizes with high drug loading. It allowed study on the effect of size and shape on the drug release kinetics. With the microparticles of homogeneous size and shape, the drug release kinetics can be projected based on the size of microparticles and water-solubility of a drug. The ability of making homogeneous particles is expected to provide better prediction and reproducibility of the drug release property of a given formulation.

1,3-Dipropyl-8-cyclopentyl xanthine (DPCPX) is a highly selective antagonist of the adenosine A(1) receptor (A(1)R). The A(1)R mediates mitogenic effects of adenosine in coronary artery smooth muscle cells (CASMC). DPCPX plays a role as an antimitogen and reduces CASMC proliferation by the blockage of A(1)R. A drug-eluting stent (DES) loaded with DPCPX was prepared. The water solubility of DPCPX is 1.6 microg/mL at pH 3-9, and 38.1 +/- 2.3 microg/mL at pH 11. A series of DPCPX-eluting stents were formulated in polyurethane (PU) films with different dose densities and film thicknesses. The release of DPCPX from the PU-coated stents was nearly linear. The release rate and duration were effectively controlled by adjusting the film thickness with the same drug concentration. The eluted DPCPX from the PU films was effective in preventing CASMC proliferation, regardless of stimulation by 2-chloro-N-6-cyclopentyladenosine (CCPA), a highly selective A(1)R agonist. A(1)R specific antagonist DPCPX was effective in preventing CASMC proliferation and holds great promise for intracoronary delivery from DESs to test the role of the A(1)R signaling pathway for prevention of in-stent restenosis.