Study Of In-vitro Degradation Behaviors Of Poly (Lactide-co-glycolide) Films And Coatings

In order to avoid the restenosis after percutaneous transluminal coronary angioplasty (PTCA), the drug-loaded polymer coating is prepared on the surface of stents to prevent proliferation of smooth muscle cell, thus, drug-eluting stent (DES) become the most effective therapeutic method in percutaneous coronary intervention (PCI).In this work, we employed biodegradable aliphatic polyesters poly(lactide-co-glycolide) (PLGA), which has drawn outstanding attention for its good biocompatibility and biodegradability, as the drug-loaded coating on stents. The PLGA films and coatings on 316L stainless steel tube and stents, which are prepared by dipping or spraying methods, were placed into Hank's simulation body's liquid in pH7.4 at 37°C to investigate their in-vitro degradation behaviors. The changes of molecular weight, molecular weight distribution (polydispersity), weight loss, composition and thermal properties of the polymer samples were characterized by SEM, GPC, ~1H-NMR and DSC techniques.In this paper, we examined the effects of the composition of copolymers and configuration of monomer on the degradation behaviors of the PLGA films. Results indicate that the degradation rate of PLGA could be adjusted by changing the compositions of the copolymer and enhanced with the glycolide content increasing. It is suggested that the copolymers PLGA 70/30 and PLGA 80/20 are potential materials as coatings on coronary stents. The degradation rate of the crystalline poly(L-lactide-co-glycolide) films is slower than that of the amorphous poly(DL-lactide-co-glycolide) films.In addition, we investigated the influences of films and coatings preparing process and methods on the surface morphology and the degradation behaviors of the PLGA films. The initial surface appearances of films and coatings prepared by dipping and spraying are different, and the degradation rates of the sprayed films and coatings are degraded faster than that of the dipped films and coatings. The test results of PLGA films with or without porous prepared by solvent-casting method show that the degradation rate of the PLGA non-porous films is faster than that of porous films before their weight lossing quickly and their structure collapse, however, it is reverse at later degradation, further, the PLGA porous films collapses before the non-porous films. The appearances of the coatings on stents prepared with either dipping or spraying after brushing 30 days remaine unbroken and satisfy the requirement for PTCA implantation.The degradation environment factors, such as liquid flowing effect and frequency of changing degradation liquid, which affect the degradation behaviors of the PLGA films and coatings, are also surveyed. The results show that in flowing solution, the changes of morphology, weight and molecular weight are more slowly compared with static degradation. That attributes to the micro-circumstance on polymer surface. The higher the frequency of changing degradation liquid, the slower the degradation rate of films. It is similar to the liquid flowing effect.