The Manufacture Of Biodegradable Stent And Its Effect On Matrix Metalloproteinase In Rabbits

PTCA has been established as an alternative to coronary artery bypass grafting(CABG) to treat selected patients with coronary artery disease. However, thesuccess of PTCA is limited by acute vessel occlusion and late restenosis. Stentswere developed to overcome these issues, and the first clinical application with ametallic stent was conducted in 1986 by Sigwart et al. During the last 20 years,technological advances have led to the development of new stents. Althoughintravascular stents offer the promise of addressing both the problems of acuteocclusion and late restenosis, many concerns must be addressed for long-termsafety. Because all currently available stents are metallic, they induce a varyingdegree of thrombogenesis and significant intimal hyperplasia. Late thrombosis,especially after stent implantation followed by brachytherapy, may be anotherpotential risk. The long-term development of stent malposition in cases of plaqueshrinkage/positive vessel remodeling can also occur. Moreover, the long-term (10years) effects of metallic stents in human coronary arteries are still unknown.Finally, any metallic stents remaining in place may be obstacles to additionaltreatments (eg, repeat PTCA and CABG). Drug eluting stent (DES), however, havecreated substantial increases in costs, not only for the patients but also for the entirehealthcare delivery system. This financial limitation has resulted in a DESutilisation rate of about 12% of all coronary stent devices in Europe.Intimal dissections that are tacked back in place are likely to heal rapidly.Restenosis commonly occurs within 3 to 6 months after coronary intervention, andit rarely occurs thereafter.5–7 Therefore, the clinical need for stent scaffolding islimited after this period. Considering the short-term need and the potential forlong-term complications with metallic stents, stents made of biodegradablematerials may be an ideal alternative. A biodegradable stent can also be useful forthe local administration of pharmacological agents directly to the site of PTCA toprevent late restenosis.Poly(ethylene glycol) (PEG) is biocompatible, nontoxic and hydrophilic.Although it is resistant to degradation in vivo, PEG of low molecular weights(<5000) are easily removed from the body through the kidneys. In recent years, awide variety of bioerodible copolymers containing PEG segments have beenreported .Polylactide (PLA) has been increasingly used in biomedical applications, suchas drug delivery and surgical repair because of its biodegradability, goodbiocompatibility, high mechanical strength, and excellent shaping and moldingproperties. However, PLA is hydrophobic,which can limit its applications.Moreover, as there are no functional or reactive pendant groups in its molecularchain, direct chemical modification of PLA is difficult. Therefore, much attentionhas been paid to introducing hydrophilic segments or reactive groups into PLA toimprove its hydrophilicity and biocompatibility, to conjugate drugs or to control itsbiodegradation rate.In brief, into a three-necked round-bottom flask containing LA were chargedGA and PEG. By using stannous octoate (Sn(Oct)2) as a catalyst,the mixture wasstirred at 180℃ over the oil bath for 8 hours. The reaction flask was removed fromthe oil bath and stirred at room temperature for 2 h. The solid precipitate wasfiltered out . The filtrate was concentrated in vacuum to obtain the polymers. Thecrude product was crystallized from to get the crystals. Nuclear magnetic resonance(NMR) spectra were recorded on a Bruker AV300M. Gel permeationchromatography (GPC) measurements were conducted with a Waters 410 GPCinstrument equipped with a Waters Styragel HT6E column and a differentialrefractometer detector. Fourier transform infrared (FT-IR) spectra were recorded ona Bio-Rad Win-IR instrument. The data suggested PLGA-PEG was synthesizedsuccessfully. After synthesis, the polymers were crashed into tubular stents.For synthetic polymers to be used as stents, their biocompatibility must beensured. Previous reports have suggested that tissue incompatibility may be amajor obstacle in the development of polymeric materials for intracoronary stents.In the study, rabbit vascular smooth muscle cell (VSMC) were cultured invitro and identified with immune histologic assessment. The morphologicalcharacters were observed with phase contrast microscope. Compared withcontrol ,VSMC were cultured with PLGA and PLGA-PEG, then the morphologicalcharacters were observed with phase contrast microscope. The total number of thecell were taken account everyday, and the morphological characters wererepresented on a graph. VSMC were culture on 96-well board at a dose of1.0*105/L,cell viability were detected with MTT assay on 1st ,3rd ,5th and 7th day.VSMC were culture on 6-hole board at a dose of 3.0*105/L,and cell cycle weredetected with flow cytometer (FCM) seven days later. VSMC grew well withPLGA and PLGA-PEG. Cell proliferation of PLGA group and PLGA-PEG groupwas good as control one. Flow cytometer show that the content of DNA and thedistributing of cell cycle were similar .In third part, the effects of PLGA-PEG stent on matrix metalloproteinase(MMPs) and CRP were investigated in rabbits.30 adult healthy rabbits weredivided randomly into two groups,control group(n=15)and PLGA-PEGgroup(n=15). Right iliac arteries of rabbits of PLGA-PEG group were injured byballoon denuded endothelization. PLGA-PEG stents were implanted in rabbits ofPLGA-PEG group. MMP-2,9 and pro MMP-2,9 levels of PLGA-PEG group weredetermined before implantation ,after 7 days and 30 days by SDS-PAGEZymography. It was the same with CRP.MMP-2,9 and pro MMP-2,9 levels weredetermined in control groups. The concentrations of MMP-2,9 and pro MMP-2 inPLGA-PEG group were much higher than those in control group( 11568±2219INT.mm2,10364±1429 INT.mm2,13649±1894 INT.mm2 VS 6128±1562INT.mm2,8519±2167 INT.mm2,8413±2156 INT.mm2,P<0.05). There were nosignificant differences of pro MMP-2,9 between two groups(P>0.05). InPLGA-PEG group, the levels of MMP-2,9 and pro MMP-2,9 didn't elevatedsignificantly 7 days later(P>0.05). However the MMP-2 and pro MMP-2concentrations were still higher 30 days after implantation(13935±2167INT.mm2,15628±1739 INT.mm2 VS 11568±2219 INT.mm2,13649±1894 INT.mm2,P<0.01). CRP level elevation after PLGA-PEG stent implantation highlightedpossible restenosis. A number of stent-related properties, including stentconfiguration, strut thickness and stent coating had to be modified to reducerestenosis.