Vasotech, Inc.

SHREWSBURY,, MA, United States

Vasotech, Inc.

SHREWSBURY,, MA, United States
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Xiao J.,Jinan University | Feng G.,Renmin University of China | Kang G.,Jinan University | Kang G.,Shantou University | And 14 more authors.
Journal of Biomedical Nanotechnology | Year: 2015

Rationale: We reported previously, in porcine coronary arteries, that the novel biodegradable PowerStent®Absorb paclitaxel-eluting stent had improved and sustained structural strength and functional performance at one month post-implantation. Objective: To report the stent performance at 6-month follow-up. Methods and Results: Six PowerStent®Absorb and six TAXUS® stents were randomly implanted in the left anterior descending and right coronary arteries of six Tibet miniature pigs. Quantitative coronary angiography (QCA) and intravascular ultrasound (IVUS) images were obtained at the time of implantation (T0) and at 6 months (T6). Two animals were sacrificed at T6 for histopathological evaluation. At T6, QCA showed that the mean luminal vascular diameter (mLD) between the PowerStent® and the TAXUS® stents were similar (2.36±0.38 vs. 2.61±0.31, respectively). Based on the IVUS analysis, the mLD and the mean lumen cross-sectional area (mCSA) in the PowerStent-treated arteries were similar between T0 and T6 (mLD: 2.74±0.13 vs. 2.70±0.20 and mCSA: 6.81±0.62 mm2 vs. 6.68±0.94 mm2). Histopathology showed that the PowerStent®stents were well apposed to the vessel wall with no recoil, strut fracture and thrombus formation. The stents were fully covered with a layer of endothelial cells. Conclusions: At six-month post-implantation, the PowerStent®Absorb stents maintained their structural strength and functional performance. The development of restenosis was controlled, no stent thrombosis was observed and the stents were fully re-endothelialized. These results suggest the PowerStent®Absorb stent is safe and effective for up to 6 months when implanted in porcine coronary arteries. © 2015 American Scientific Publishers All rights reserved.


Ma X.,University of Massachusetts Lowell | Ma X.,Vasotech, Inc. | Oyamada S.,Brown Medical School | Gao F.,University of Massachusetts Lowell | And 11 more authors.
Journal of Pharmaceutical and Biomedical Analysis | Year: 2011

Paclitaxel and sirolimus are the two major drugs for the treatment of coronary arterial disease in current drug-eluting stents. The two drugs can effectively inhibit the in-stent restenosis through their independent pathways and show synergistic effect in preventing tumor tissue growth. We hypothesize that the combination of the two drugs in a drug-eluting stent (DES) can also effectively suppress the neointima growth in the stented artery. The present work was focused on the investigation of paclitaxel/sirolimus combination release profiles from a novel biodegradable polymer (poly (d, l-lactide-co-glycolide)/amorphous calcium phosphate, PLGA/ACP) coated stent both in vitro and in vivo. For the in vitro, the drug releasing profiles were characterized by measuring the drug concentration in a drug release medium (Dulbecco's phosphate buffered saline, DPBS, pH 7.4) at predetermined time points. For the in vivo, a rat aorta stenting model was employed. The results showed that both paclitaxel and sirolimus had a two-phase release profile both in vitro and in vivo, which is similar to the drug release profile of their individual coated DESs, and there is no evident of interference between two drugs. The data suggest that paclitaxel and sirolimus can be combined pharmacokinetically in a DES for the treatment of coronary arterial diseases. © 2010 Elsevier B.V.


Zheng X.,Wuhan University | Wang Y.,Southern Medical University | Lan Z.,University of Massachusetts Lowell | Lan Z.,Vasotech, Inc. | And 13 more authors.
Journal of Biomedical Nanotechnology | Year: 2014

Biodegradable polymers used as vascular stent coatings and stent platforms encounter a major challenge: biocompatibility in vivo, which plays an important role in in-stent restenosis (ISR). Co-formulating amorphous calcium phosphate (ACP) into poly(lactic-co-glycolic acid) (PLGA) or poly-L-lactic acid (PLLA) was investigated to address the issue. For stent coating applications, metal stents were coated with polyethylene-co-vinyl acetate/poly-n-butyl methacrylate (PEVA/PBMA), PLGA or PLGA/ACP composites, and implanted into rat aortas for one and three months. Comparing with both PEVA/PBMA and PLGA groups after one month, the results showed that stents coated with PLGA/ACP had significantly reduced restenosis (PLGA/ACP vs. PEVA/PBMA vs. PLGA: 21.24 ±2.59% vs. 27.54 ±1.19% vs. 32.12±3.93%, P < 0.05), reduced inflammation (1.25 ±0.35 vs. 1.77±0.38 vs. 2.30±0.21, P < 0.05) and increased speed of re-endothelialization (1.78±0.46 vs. 1.17±0.18 vs. 1.20±0.18, P < 0.05). After three months, the PLGA/ACP group still displayed lower inflammation score (1.33±0.33 vs. 2.27±0.55, P < 0.05) and higher endothelial scores (2.33±0.33 vs. 1.20±0.18, P < 0.05) as compared with the PEVA/PBMA group. Moreover, for stent platform applications, PLLA/ACP stent tube significantly reduced the inflammatory cells infiltration in the vessel walls of rabbit iliac arteries relative to their PLLA cohort (NF-κB-positive cells: 23.31±2.33/mm2 vs. 9.34±1.35/mm2, P < 0.05). No systemic biochemical or pathological evidence of toxicity was found in either PLGA/ACP or PLLA/ACP. The co-formulation of ACP into PLGA and PLLA resulted in improved biocompatibility without systemic toxicity. Copyright © 2014 American Scientific Publishers All rights reserved.


Oyamada S.,Brown Medical School | Ma X.,University of Massachusetts Lowell | Ma X.,Vasotech, Inc. | Wu T.,University of Massachusetts Lowell | And 9 more authors.
Journal of Surgical Research | Year: 2011

Background: Currently, preclinical stent development requires elaborate large animal models, which are time consuming and expensive. We herein report a high throughput rat aorta stenting model which could provide a rapid and low-cost platform for preclinical stent development. Methods: A total of 86 metal stents (316L stainless steel 13 mm, VasoTech, Inc.) coated with poly (D, L-lactide-co-glycolide)/amorphous calcium phosphate (PLGA/ACP) copolymer were pre-mounted on 1.5 mm × 15 mm balloon catheters and were implanted into aspirin treated Sprague-Dawley rats (500-700 g) initially using either direct placement in the abdominal aorta (group A, n = 7) or a trans-iliac approach (cut-down, group B, n = 79). The surviving rats were sacrificed at 1, 2, 4, and 12 wk post-implantation and the stented arteries were analyzed histopathologically. Results: Four rats died in group A and nine rats died in group B within 48 h post-stent implantation (mortality: 57% versus 11%, P < 0.05). All animals that died had stent thrombosis/paralysis with visible thrombus on necropsy. Histologically, neointimal growth peaked at approximately 4 wk post-implantation. Conclusion: This result suggests that human-sized stents can be successfully implanted into the rat aorta via iliac artery insertion with a significantly higher survival rate than trans-aorta implantation. The model system allows rapid (4-12 wk) assessment of stent biocompatibility with mortality/paralysis used as an indicator of stent thrombosis. © 2011 Published by Elsevier Inc. All rights reserved.


Ma X.,University of Massachusetts Lowell | Ma X.,Vasotech, Inc. | Wu T.,University of Massachusetts Lowell | Wu T.,Vasotech, Inc. | And 5 more authors.
International Journal of Clinical and Experimental Medicine | Year: 2010

Coronary artery disease (CAD) is currently a leading cause of death worldwide. Drug-eluting stents (DESs) have been dominant for the treatment of CAD in the interventional cardiology world owing to their efficacy in significantly reducing restenosis. However, late stage stent thrombosis has become a major concern. Stent platform, drug delivery vehicle and type of drug are three parts of DES and each part affects the performance of the DES. Aiming to provide a clue for the design of future DES, this review focuses on the development of the three major components of DES and their roles in restenosis and thrombosis.


Ma X.,University of Massachusetts Lowell | Ma X.,Vasotech, Inc. | Oyamada S.,Brown University | Wu T.,University of Massachusetts Lowell | And 9 more authors.
Journal of Biomedical Materials Research - Part A | Year: 2011

The purpose of this study was to optimize a novel biodegradable polymer for drug eluting stent (DES) applications. Degradation profiles of different poly(D, L-lactide -co-glycolide)/amorphous calcium phosphate (PLGA/ACP) composites coated on stents were studied both in vitro and in vivo for three months. For the in vitro study, stents were immersed into the phosphate buffered saline (37°C, pH 7.4) with constant shaking. The polymer weight loss was measured weekly and morphological changes were analyzed. The results demonstrated that approximately 60% of polymer was degraded within the three-month period and there was no significant difference between the different PLGA/ACP composites. However, the composite of 50% PLGA (65/35) with 50% ACP showed a slightly faster degradation rate than other composites. Morphologically, all stent surfaces changed from a micro-porous before degradation to a corrugated solid micro-net-like structure at two months post degradation. Based on in vitro results, 65% PLGA (65/35) with 35% ACP) coated stents were selected and implanted into rat aortas (n = 12) for the in vivo study. Microscopic observation showed that no composite was found on any of the implanted stents at 12 weeks post implantation, which indicated the selected PLGA/ACP composite is desired for DES applications. © 2011 Wiley Periodicals, Inc.


Feng G.,Wuhan University | Xiao J.,Jinan University | Bi Y.,University of Massachusetts Lowell | Bi Y.,Vasotech, Inc. | And 16 more authors.
Journal of Biomedical Nanotechnology | Year: 2016

Our previous studies have confirmed the superior biocompatibility of the poly-L-lactic acid/amorphous calcium phosphate (PLLA/ACP) scaffolds (PowerScaffold®) compared to PLLA scaffolds and their similar 6-month radial strength compared with TAXUS® stents. In order to conduct further dynamic observations on the performance of the PowerScaffold® after 12-month implantation compared with the TAXUS® stents. Twenty PowerScaffold® and 20 TAXUS® were implanted in porcine coronary arteries. At 12-month follow-up, Quantitative Coronary Angiography showed that the stent reference vessel diameter (3.19±0.25 mm vs. 2.75±0.22 mm, p < 0.05), the mean lumen diameter (3.07±0.22 mm vs. 2.70±0.17 mm, p < 0.05) and the late lumen gain (0.45±0.07 mm vs. 0.06±0.06 mm, p < 0.01) were all significantly greater with the PowerScaffold® than the TAXUS®. As well, Intravascular Ultrasound showed the stent reference vessel area (7.74±0.48 mm2 vs. 6.96±0.51 mm2, p <0.05), the mean stent area (7.49±0.46 mm2 vs. 6.53±0.47 mm2, p < 0.05) and the mean lumen area (7.22±0.50 mm2 vs. 6.00±0.48 mm2, p < 0.01) were all significantly greater with the PowerScaffold® than the TAXUS®. The luminal patency rate of the PowerScaffold® significantly increased from 72.45±6.84% at 1 month to 93.54±8.15% at 12 months (p<0.01) while the TAXUS® stents were associated with a nonsignificant decreasing trend (89.44±8.44% vs. 86.53±8.22%). Pathology indicated the average thickness of the struts degraded by 14.25±3.04 μm at 1 month, 23.39±2.45 μm at 6 months and 35.54±2.20 μm at 12 months. Immunohistochemical examination showed that the expression of inflammatory factors NF-κB gradually decreased from 1-month to 12-month (36.79±4.78 vs. 5.79±2.85, p <0.01). As the late lumen gain of arteries implanted with the PowerScaffold® increases over time with the growth of vessels, it effectively reverse the late vascular negative remodeling observed with the TAXUS® stents, providing a better option for lumen restoration treatment in clinical practice. © 2016 American Scientific Publishers All rights reserved.


Lan Z.,University of Massachusetts Lowell | Lan Z.,Vasotech, Inc. | Lyu Y.,Wuhan University | Xiao J.,Taiping Renmin Hospital | And 12 more authors.
Journal of Biomedical Nanotechnology | Year: 2014

Bioabsorbable drug-eluting stents (BDES) offer multiple advantages over a permanent bare metal stent (BMS) for coronary artery disease (CAD). However, current BDES remains two major issues: inferior radial strength and biocompatibility. PowerStent® Absorb BDES, fabricated by co-formulating amorphous calcium phosphate (ACP) nanoparticles with poly-L-lactic acid (PLLA/ACP, 98/2, w/w) and 2% Paclitaxel (PAX, w/w) was designed to address these issues. Two cohorts of 6 miniature pigs were each implanted with PLLA/PAX (control, 2% PAX, w/w) or PowerStent® Absorb BDES. After 1 month in-vivo study, histological analyses showed significantly reduced restenosis in the PowerStent® Absorb BDES cohort relative to the control cohort (44.49 ± 10.49% vs. 64.47 ± 16.2%, p < 0.05). Stent recoil (21.57 ± 5.36% vs. 33.81 ± 11.49, P < 0.05) and inflammation (3.01 ± 0.62 vs. 4.07 ± 0.86, P < 0.01) were also obviously decreased. From in-vitro studies, PLLA/ACP/PAX stent tube maintained significantly greater radial strength than control group during 6 months in-vitro degradation (PLLA/ACP/PAX vs. PLLA/PAX: before hydrolysis: 82.4 ± 1.9 N vs.74.8 ± 3.8 N; 6 weeks: 73.9 ± 1.8 N vs. 68.0 ± 5.3 N; 3 months: 73.5 ± 3.4 N vs.67.2 ± 3.8 N; 6 months: 56.3 ± 8.1 N vs. 57.5 ± 4.9 N). Moreover, ACP facilitated the hydrolytic degradation of PLLA compared with control one (62.6% vs. 49.8%), meanwhile, it also increased the crystallinity of PLLA (58.4% vs. 50.7%) at 6 months. From SEM observations, ACP created nanometer pores that enlarge gradually to a micrometer scale as degradation proceeds. The changes of the porosity may result in greatly promoting re-endothelialization. Copyright © 2014 American Scientific Publishers All rights reserved.


Ma X.,University of Massachusetts Lowell | Wu T.,Vasotech, Inc. | Robich M.P.,Beth Israel Deaconess Medical Center
Interventional Cardiology | Year: 2012

Over the past decade, drug-eluting stents (DES) have greatly transformed the field of interventional cardiology. Generally, three components are included in a DES system: a metal stent platform, a drug carrier or so called 'stent coating' and a drug. As such, stent coating plays an important role in the performance of DES. This article will review the evolution of stent coatings and their role in the development of restenosis and thrombosis. © 2012 Future Medicine Ltd.

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