Preclinical Study Of Novel Fully Bioresorbable Scaffolds In A Porcine Coronary Artery Model

Part ?The Feasibility,Safety and Biocompatibility Evaluation of Poly-L-Lactic Acid/Amorphous Calcium Phosphate Scaffolds in Porcine Coronary ArteriesBackground:Currently,poly-L-lactic acid(PLLA)as the representative material of the fully bioresorbable scaffolds(FBS)had been demonstrated good prospects of clinical application.However,PLLA as the single material used in coronary scaffolds still have many insufficiencies such as the inflammatory reactions induced by acidic metabolites which may lead to scaffold deformation,scaffold embrittlement,delayed endothelial repair and proliferation of vascular smooth muscle cells,and eventually result in the risks of scaffold restenosis and in-stent thrombosis.Our previous vitro studies demonstrated amorphous calcium phosphate(ACP)can improve the biocompatibility of PLLA material.Objective:To assess the feasibility of a novel bioresorbable PLLA/ACP scaffolds delivery system for coronary applications in porcine model.After scaffolds implantation,we assess the safety and biocompatibility of PLLA/ACP scaffolds by comparison with PLLA scaffolds.Methods:A total of 12 scaffolds(6 PLLA/ACP,6 PLLA)were randomly implanted into the coronary arteries of 12 pigs.The clinical symptoms,blood cell count,liver and kidney function,myocardial enzyme levels were compared between the two groups at the time of before and 1-day,3-day,7-day,14-day,28-day after stent implantation.NO(pmol/L),CRP(ng/ml),VEGF(pg/ml),ANG ?(pg/ml)in the serum of coronary arterial blood were detected before and 28-day after stent implantation.Quantitative coronary angiography(QCA)was used to measure and calculate the reference vessel diameter(RVD),mean lumen diameter(MLD)and percentage of diameter stenosis(DS%).Hematoxylin-eosin staining and elastic tissue staining were used to calculate the neointimal area,injury scores,inflammation scores,fibrin scores and endothelial scores.Immunohistochemical staining method was used to examine the expression levels of NF-?B,eNOS,PECAM-1 and a-SM-actin in the vessels of stented segment.Results:The QCA analysis showed that all 12 scaffolds were successfully deployed at the predetermined diameter,and the stented vessels and the distal branches were open without any sign of peripheral embolization or thrombosis.At 28 days follow-up,the MLD and percent diameter stenosis were not significantly different between the two groups.The blood cell count,liver and kidney function,myocardial enzyme levels were also not significantly different between the two groups.The level of VEGF and NO in PLLA/ACP group were higher than that of PLLA group respectively(309.86 ±49.37 pg/ml vs.222.04 ± 55.16 pg/ml,P<0.05);(129.96± 9.52 ?mol/L vs.79.55 ±16.55?mol/L,P<0.05).Histological analysis indicated that inflammation scores and fibrin scores of PLLA/ACP group were less than that of PLLA group(1.19±0.32 vs.l.78±0.46,P<0.05),(0.89±0.36 vs.1.44±0.40,P<0.05),while endothelialization scores was greater(0.39±0.47 vs.2.36±0.64,P<0.05).Neointimal area in PLLA/ACP group were less than that of PLLA group(1.70±0.25mm2 vs.2.17±0.33mm2,P<0.05).Immunohistochemistry showed that the expression of eNOS and PECAM-1 in PLLA/ACP group were greater than that in PLLA group respectively 38.53±4.25 vs.27.53±3.55,P<0.01),(29.40±3.84 vs.19.78±3.50,P<0.05),while NF-?B protein expression was less(22.07 ± 3.18 vs.28.59 ± 3.54,P<0.05).Conclusion:ACP alleviates the inflammatory response following the implantation of a PLLA scaffold,promotes the growth of endothelial cells,accelerates re-endothelialization and restores endothelial cell structure and function.The addition of ACP to PLLA appears to have a promising future in FBS.PLLA/ACP scaffolds are much better than PLLA scaffolds for coronary applications.Part ? Coronary Angiography and Intravascular Ultrasound Evaluation at 1-Month and 6-Month After Implantation of Novel Fully Bioresorbable Poly-L-Lactic Acid/Amorphous Calcium Phosphate Scaffolds in Porcine Coronary ArteriesBackground:Poly-L-lactic acid(PLLA)as the single material used in coronary scaffolds still have many insufficiencies in physical properties,such as the insufficient radial strength and strut fracture,which can result in the risks of in-stent restenosis and thrombosis.To improve the mechanical properties of PLLA,we add nanoscale amorphous calcium phosphate(ACP)(biological ceramic material)into PLLA(polymer material)to create the PLLA/ACP composite material scaffold.Our previous vitro studies demonstrated amorphous calcium phosphate(ACP)can improve the radial strength of PLLA material.Objective:To assess the PLLA/ACP scaffold performance at 1-month and 6-month follow-up by using coronary angiography and intravascular ultrasound methods.Methods:Six PLLA/ACP scaffolds and 6 PLLA scaffolds were implanted to the coronary arteries of 12 miniature pigs.Quantitative coronary angiography(QCA)was used to measure the reference vessel diameter(RVD),mean lumen diameter(MLD)and late lumen gain(LLG).According to IVUS we calculate the strut malapposition rate(SMR)at post implantation,strut overlap rate(SOR)at 1-month and 6-month.QIVUS was applied for measurements of reference vessel area(RVA),mean stent area(MSA),mean lumen area(MLA)and luminal patency rate(LPR)at 1-month and 6-month.Results:QCA results indicated that MLD of PLLA/ACP scaffolds at both 1-month and 6-month were greater than those of PLLA scaffolds(2.29±0.16mm vs.1.96±0.21 mm,P<0.05)(2.47±0.22mm vs.2.08±0.25mm,P<0.05).LLL of PLLA/ACP scaffolds at both 1-month and 6-month were less than those of PLLA scaffolds(0.6±0.19mm vs.0.97±0.15mm,P<0.05)(0.42±0.20mm vs.0.75±0.22mm,P<0.05).IVUS indicated that the post MSR,1-month MOR and 6-month MOR were all significantly less with the PLLA/ACP scaffolds than the PLLA scaffolds(5.84%±3.56%vs.17.72%±4.86%,P<0.05)(4.85%±3.58%vs.12.85%±4.77%,P<0.05)(6.17%±4.63%vs.17.65%±4.29%,P<0.05).QIVUS indicated that at 1-month,MSA,MLA and LPR of the NFBS were all greater than those of DES(6.23±0.33 mm2 vs.5.54±0.38 mm2,P<0.05)(4.31±0.46 mm2 vs.3.41±0.58 mm2,P<0.05)(72.07%±6.84%vs.56.27%±6.44%,P<0.05);at 6-month,MSA,MLA and LPR of the NFBS were all also greater than those of DES(6.35±0.45 mm2 vs.5.35±0.51 mm2,P<0.05)(4.76±0.46 mm2 vs.3.77±0.46 mm2,P<0.05)(78.01%±12.29%vs.61.69%±9.76%,P<0.05).Conclusions:The PLLA/ACP scaffolds had less stent recoil,better lumen patency rate than PLLA scaffolds.PLLA/ACP scaffolds can maintain the structural strength and functional performance for 6 months.The results suggest the PLLA/ACP scaffolds is safe and effective for up to 6 months when implanted in porcine coronary arteries.Part ? Twenty-Four-Month Long Term Comparison between Novel Fully Bioresorbable Scaffolds and Drug-Eluting Stents in Porcine Coronary ArteriesBackground:Although metallic drug-eluting stents(DES)have dramatically improved the outcome of patients with cardiovascular disease,the nondegradable stent left forever can actually prove harmful by sustaining inflammation,increasing the incidence of ISR and ST,and promoting negative remodeling.In this context,stents made of biodegradable PLLA/ACP can be completely replaced by healed tissue and allow positive remodeling.Our previous studies had confirmed the superior biocompatibility of poly-L-lactic acid/amorphous calcium phosphate(PLLA/ACP)scaffolds(NFBS)over PLLA scaffolds within 1 month,and the equivalently adequate radial strength of PLLA/ACP scaffolds at 6-month in porcine coronary arteries.Purpose:The purpose of this study is to conduct further dynamic observations on the performance of NFBS after being implanted to the porcine coronary artery model for 24 months through comparison with that of DES.Methods:Twenty-five NFBS and 25 DES were implanted to the coronary arteries of 25 miniature pigs.The scaffold performance was observed continuously through coronary angiography,intravascular ultrasound(IVUS)and histological analysis for 24 months.Quantitative coronary angiography(QCA)was used to measure and calculate the reference vessel diameter(RVD),mean lumen diameter(MLD)and late lumen gain(LLG).QIVUS was applied for measurements of reference vessel area(RVA),mean stent area(MSA),mean lumen area(MLA)and luminal patency rate(LPR).Hematoxylin-eosin(HE)staining to measure and calculate the mean strut thickness(MST)of scaffolds strut and inflammation scores.NF-?B immunohistochemical staining to examine the expression of NF-?B in the vessels of stented segment.Scanning electron microscope(SEM)was used to observe the degree of re-endothelization and the structure of the scaffold.Stereoscopic was used to observe the degradation shape and outline of the scaffold strut.Results:QCA results indicated that at 24-month,both the RVD,MLD and LLG of the NFBS were greater than those of DES(3.63±0.21mm vs.3.21±0.25mm,P<0.05),(3.39±0.27mm vs.2.78±0.33mm,P<0.05),(0.47±0.13mm vs.0.06±0.26mm,P<0.05).IVUS indicated that at 24-month,RVA,MSA and ML A of the NFBS were all greater than those of DES(9.31±0.54mm2 vs.8.18±0.56 mm2,P<0.05),(8.99±0.62 mm2 vs.6.59±0.62 mm2,P<0.05),(8.59±0.81 mm2 vs.5.95±0.77 mm2,P<0.01);the LPR at 24-month was significantly increased from that of 1 month in NFBS(92.10±4.59 vs.74.31±6.23,P<0.01)while in DES presented a tendency of decrease(72.85±9.80 vs.86.81±5.92,P>0.05).SEM indicate the surface of NFBS developed a tight arrangement of endothelial cells with complete coverage at 6 month.Stereoscopic observations revealed the stent struts had retained a clear shape at 1 month,and reduced uneven thickness with indistinct edges and progressed corrosion-like changes at 12 months.Pathology indicated the MST of the struts decreased from 153.94±6.97?m at 1-month to 133.73±5.05?m at 12-month.Immunohistochemical examination showed that the expression of inflammatory factors NF-?B reduced gradually from 1-month to 24-month(36.79±4.78 vs.4.53±2.55,P<0.01).Conclusions:The lumen of PLLA/ACP scaffolds increased with the growth of reference vessels in 24 months.It achieves LLG and solves the defect of late vascular negative remodeling in Drug-eluting stents effectively,which has provided a better option for lumen restoration treatment in clinical practices.