An asymmetrical dual coating on the stent prepared by ultrasonic atomization

Solid implantable devices for sustained drug delivery

Implantable drug delivery systems (IDDS) are an attractive alternative to conventional drug administration routes. Oral and injectable drug administration are the most common routes for drug delivery providing peaks of drug concentrations in blood after administration followed by concentration decay after a few hours. Therefore, constant drug administration is required to keep drug levels within the therapeutic window of the drug. Moreover, oral drug delivery presents alternative challenges due to drug degradation within the gastrointestinal tract or first pass metabolism. IDDS can be used to provide sustained drug delivery for prolonged periods of time. The use of this type of systems is especially interesting for the treatment of chronic conditions where patient adherence to conventional treatments can be challenging. These systems are normally used for systemic drug delivery. However, IDDS can be used for localised administration to maximise the amount of drug delivered within the active site while reducing systemic exposure. This review will cover current applications of IDDS focusing on the materials used to prepare this type of systems and the main therapeutic areas of application.

Multimodal effects of asymmetric coating of coronary stents by electrospinning and electrophoretic deposition

Drug-eluting stents (DESs) are drug-coated vascular implants that inhibit smooth muscle cell proliferation and limit in-stent re-stenosis. However, traditional DESs release a single drug into the blood and cannot cope with complex mechanisms in atherosclerosis and body responses. The present study aimed to develop a novel multimodal stent by fabricating asymmetric coating with electrophoretic deposition and electrospinning. Herein, we use heparin-loaded alginate (Hep/Alg) and atorvastatin calcium-loaded polyurethane (AtvCa/PU) coatings on the stent luminal and abluminal surfaces, respectively. Scanning electron microscopy (SEM) micrographs showed that the alginate coatings had uniformity and thin thickness. Meanwhile, the PU fibers were formed without beads, with an acceptable diameter and suitable mechanical properties. PU nanofiber revealed minimal degradation in a 1-month study. The release of AtvCa and Hep continued for 8 days without a significant initial burst release. None of the stent coatings were cytotoxic or hemolytic, and PU nanofibers supported the survival of human umbilical endothelial cells (HUVEC) with high adhesion and flattened morphologies. The results indicate that electrophoretic deposition and electrospinning have significant potential for achieving asymmetric coating on stents and a promising approach for dual drug release for multimodal effects in vascular stent applications.

A zwitterionic hydrogel coated titanium surface with high-efficiency endothelial cell selectivity for rapid re-endothelialization

Coronary stent implantation is an effective procedure for percutaneous coronary intervention treatment. However, its long-term safety and efficacy are still hindered by the in-stent restenosis and late thrombus formation. Herein, an anti-biofouling and endothelial cell selective zwitterionic hydrogel coating was developed to simultaneously enhance the nonspecific resistance and rapid re-endothelialization of the titanium surface. An endothelial cell selective peptide, REDV, could be simply conjugated on the zwitterionic carboxybetaine (CB) hydrogel to prepare the REDV/CB coating. It was found that the REDV/CB hydrogel layer maintained antifouling properties, which could inhibit the protein adsorption, bacterial adhesion, platelet activation and aggregation, and smooth muscle cell proliferation. More importantly, the co-culture study confirmed that the conjugated REVD peptide could specifically capture endothelial cells and promote their migration and proliferation, and simultaneously decrease the adhesion and proliferation of smooth muscle cells. Therefore, the antifouling and endothelial cell selective coating proposed in this work provides a promising strategy to develop an intravascular stent for promoted re-endothelialization and inhibited neointimal hyperplasia in clinical applications.

Inhibition of in-stent restenosis after graphene oxide double-layer drug coating with good biocompatibility

In this study, we designed a double layer-coated vascular stent of 316L stainless steel using an ultrasonic spray system to achieve both antiproliferation and antithrombosis. The coating included an inner layer of graphene oxide (GO) loaded with docetaxel (DTX) and an outer layer of carboxymethyl chitosan (CMC) loaded with heparin (Hep). The coated surface was uniform without aggregation and shedding phenomena before and after stent expanded. The coating treatment was able to inhibit the adhesion and activation of platelets and the proliferation and migration of smooth muscle cells, indicating the excellent biocompatibility and antiproliferation ability. The toxicity tests showed that the GO/DTX and CMC/Hep coating did not cause deformity and organ abnormalities in zebrafish under stereomicroscope. The stents with GO double-layer coating were safe and could effectively prevent thrombosis and in-stent restenosis after the implantation into rabbit carotid arteries for 4–12 weeks.

Evaluation of the suitability of a fluidized bed process for the coating of drug-eluting stents

Drug-eluting stents are often coated using single-stent coating techniques. In pharmaceutical industry, single-tablet coating is unthinkable. Instead large batches of tablets are coated in fluidized bed apparatuses or pan coaters. Therefore, it was the aim of this work to evaluate whether stents can be coated using a fluidized bed process. For this purpose stents were coated with the model fluorescent drug triamterene embedded in ammonium methacrylate copolymer. Different stent lengths as well as different coating yields were assessed and also a drug-free topcoat was evaluated. The coated stents were analysed regarded coating layer mass, drug content, surface structure, coating thickness and drug release. Furthermore, coating yield and stent defect rate were examined. Except for one stent configuration good results were obtained without optimization of process parameters which indicates the suitability of the method to coat large amounts of stents simultaneously in principle. Drug release was tuneable over a wide range of time spans and a wide range of drug loadings was produced. Further work will be necessary to transform the results of this study from a model stent to a clinically relevant product.