Preparation, Performance And In Vitro Behavior Of Eva Based Stent Films

Stents have been widely used in treating the occlusion or stenosis of physiological tubular structures, such as esophagus, bile duct, prostate, urethral duct and blood vessel. Because they could provide support orNexpanding the lumen and don't need open lumen with surgery, the patient's quality of life has been greatly improved. However, restenosis occurs frequently when stents are applied, the drug-eluting stent (DES) was introduced to reduce incidences such as in-stent restenosis and complications.Generally, the coating materials of DES are mainly no degradable or biodegradable polymers. However, few studies have reported the application of various polymeric blends as the coating material. EVA copolymer is a safety and biocompatibility material, its permeability of drug related with many factors and the permeability may be changed with plasticizer or many polymer blending.In this study, we employed the PLA/EVA blend and PEG/EVA blend as coating materials to prepare two kinds of coating films: a single layer drug-free coating film and a bi-layer drug-loaded coating film. The prepared stent coatings were investigated by X-ray diffraction analysis (XRD), scanning electronic microscopy (SEM) and mechanical tests. In general, the surfaces of the films were smooth and flat and the paclitaxel content of drug-loaded films is homogeneous. The mechanical tests showed that the increase of drug content, PLA or PEG of the coatings significantly led to the decrease of the maximum elongation and maximum tensible strength, and the increase of the modulus of elasticity.Then the swelling performance and quality loss variations of drug-free coatings have been studied. The existing state and molecular weight change of components in the coatings before and after the experiment also is characterized by XRD and GPC test. The results showed that the adding PEG can improve the swelling of EVA film properties, and the degradation of the PLA components caused quality loss of the coatings.And we designed a stent coating film which consisted of a drug-loaded layer and a drug-free EVA-alone backing layer. The amount of paclitaxel permeated through the backing layer was far lower than that of paclitaxel released from the drug-loaded layer, indicating that the coating releases drug molecules in a unidirectional fashion. The release profile can be divided into two stages: the early faster release rate stage (1–14 days) and followed by a decrease in release rate stage (14–63 days). The release profiles of coatings incorporated PTX could be affected by drug loading and the contents of the PLA or PEG. The higher of drug content in the coatings means higher drug release quantity. PLA can promote the drug release while that of PEG slow down the drug release. Therefore, the blending other polymer with EVA can change permeability of EVA, and then adjust drug release behavior. The polymeric blends could be useful drug carrier materials for drug-loaded stent coating capable of releasing drug in a highly tunable manner.