Preparation And Preliminary Evalutaion Of Biodegradable Stents

Stents are playing an increasingly important role in the treatment ofocclusion or stenosis of physiological tubular orifices, such as bloodvessel, esophagus, bile duct, and urethral duct, because of their desirableability in providing support to expand the lumen. Stents for clinical useare often made of plastics or metal. Metallic stents have the advantages ofmechanical strength, long-term patency which made them applied tovarious types of obstructive lesions including malignant obstruction.However, they also have the disadvantages, such as obstruction due toepithelial hyperplasia, which would cause difficulty in removing the stents,thus not suitable for treating benign obstruction. In recent years,biodegradable stents have been attracting much attention as they arereported to be less likely to cause epithelial proliferation and formbio-films and most importantly, not require removal. Therefore,biodegradable stents have many features that are superior to metallic stent as an ideal stent for temporary support. In our study, biodegradable stentswere made by hand knitting or laser cutting. For braided stents, apreliminary in vivo study was conducted under dorsal subcutis of male SDrats, for laser cut stents, an in vitro study was conducted in pH7.4and6.5PBS solution respectivly.Poly (glicolide-co-lactide)(PGLA) stents were braided by a singlestrand of PGLA (glycolic acids/lactic acids (mole/mole)=90/10) filamentwith a draw ratio of3,4or5, and in vivo evaluated preliminarily in maleSD rats. The PGLA stent was implanted together with an inner plastictube to serve as a brace and outer Ni-Ti alloy stent for protection, whilethe PGLA stent was placed in between them. The stents were retrieved atdifferent time and evaluated in terms of the morphology, weight loss,water uptake, and chemical composition, together with the mechanicaland thermal properties after implanttion under dorsal subcutis of male SDrats for20days. Only the stents with a filament draw ratio of5could beseparated and removed from the inner plastic tube and outer Ni-Ti alloystent after10days of implantation. Results demonstrated that the stentswith highest draw ratio (5) had slowest changes of stent weight loss, wateruptake, crystallinity, chemical composition and radial compression strength after implantation. Moreover, the crystallinity of stent increasedwith implantation time during the investigated period and the glycolicacids (GA) segments of PGLA molecules hydrolyzed faster than the lacticacids (LA) ones. The results indicated that the filament draw ration wouldcertainly affect the degradation and mechanical properties, which wouldattribute to development of braided biodegradable stents and suggestedthat this new hand-made braided stent has great potential for supportingbenign obstruction.Five kinds of biodegradable stents, ie PLA-1, PLA-2, PLA-3,PCL-1,PCL-2, were prepared by laser cutting, and in vitro studied in pH7.4and6.5PBS solution, respectively. These stents were different from eachother by material made of, pore size on the wall of the stent and wallthickness of the stent. The stents were retrieved at different time andevaluated in terms of the morphology, weight loss, water uptake, andchemical composition, together with the mechanical properties. Resultsdemonstrated that PLA and PCL stents showed low weight loss after22days of degradation time, and pH of PBS solution had no significant effecton the degradation behavior, but number-average molecular achievedfrom GPC were decreased. Small pores could be saw on the surface of the stents. Structure parameters on the mechanical performance were explored.It was demonstrated that mechanical properties of the stent itself had arelationship with the wall thickness of the stents and pore size on the wallof the stents, and the wall thickness of the stent was a positive correlationwhile pore size on the wall of the stent was a negative relationship.Therefore, by changing the structure parameters of the stent, can make themechanical properties of the stent in line with the application.