Novel polymeric coatings with the potential to control in-stent restenosis--an in vitro study

Effect of Poly(Oxanorbonene)- and Poly(Methacrylate)-Based Polyzwitterionic Surface Coatings on Cell Adhesion and Gene Expression of Human Keratinocytes

Polyzwitterions are generally known for their anti-adhesive properties, including resistance to protein and cell adhesion, and overall high bio-inertness. Yet there are a few polyzwitterions to which mammalian cells do adhere. To understand the structural features of this behavior, a panel of polyzwitterions with different functional groups and overall degrees of hydrophobicity is analyzed here, and their physical and biological properties are correlated to these structural differences. Cell adhesion is focused on, which is the basic requirement for cell viability, proliferation, and growth. With the here presented polyzwitterion panel, three different types of cell-surface interactions are observed: adhesion, slight attachment, and cell repellency. Using immunofluorescence methods, it is found that human keratinocytes (HaCaT) form focal adhesions on the cell-adhesive polyzwitterions, but not on the sample that has only slight cell attachment. Gene expression analysis indicates that HaCaT cells cultivated in the presence of a non-adhesive polyzwitterion have up-regulated inflammatory and apoptosis-related cell signaling pathways, while the gene expression of HaCaT cells grown on a cell-adhesive polyzwitterion does not differ from the gene expression of the growth control, and thus can be defined as fully cell-compatible.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

Development of a Bioactive Polymeric Drug Eluting Coronary Stent Coating Using Electrospraying

Drug-eluting stents are now routinely used in the treatment of acute coronary syndromes caused by coronary artery disease. Whilst the sustained release of anti-proliferative drugs from these devices has greatly reduced the need for repeat revascularisation procedures, this approach is not suitable for all patients and appears to delay regrowth of the endothelium, necessitating the use of prolonged dual anti-platelet therapy. Although the development of more advanced stent platforms and drug coatings has produced modest improvements in performance, these devices have not fully addressed the limitations experienced with their first-generation counterparts. In the present study, we developed a novel stent coating that provides controlled sirolimus release from a bioactive polymer (accelerate™ AT) that has previously been shown to support endothelial cell growth in vitro. A bespoke electrospray deposition process provided control over the coating thickness, surface roughness, drug load, and release kinetics. The resultant optimised coating combines rapid release of an anti-proliferative agent from a bioactive polymer coating that promotes re-endothelialisation, thereby offering potential protection against in-stent restenosis and thrombosis. This novel, dual-action coating therefore has significant therapeutic potential, with the enhanced control of drug load and release kinetics offered by electrospray deposition also opening up opportunities for more personalised treatment approaches. Further development and evaluation of these technologies in vitro and in vivo is therefore warranted.

Clinical outcomes of chronic kidney disease patients treated with everolimus-eluting stents (EES) and paclitaxel-eluting stents (PES)

BACKGROUND

The target lesion revascularization of paclitaxel-eluting stents (PES) has been reported to be lower than that of sirolimus-eluting stents in patients on hemodialysis (HD). However, the comparison of PES and second generation drug-eluting stents in CKD patients has not been fully investigated. We compared clinical outcomes of everolimus-eluting stents (EES) and PES in CKD patients.

METHODS

Hundred and forty seven CKD patients (eGFR<60mLmin(-1)1.73m(-2)) treated with PES (n=74, from May 2007 to December 2009) and EES (n=73, from January 2010 to January 2013) were enrolled in the study. Major adverse cardiac events (MACEs) were defined as death, non-fatal myocardial infarction, and ischemia driven target lesion revascularization.

RESULTS

The incidence of 36-month MACE was significantly lower in EES, non-HD group compared to PES, non HD group (0% in EES group and 13.5% in PES group, respectively, P<0.01). There was no significant difference in MACE between EES and PES in HD patients (5.4% in PES group and 5.5% in EES group, P=0.98). In multivariate analysis, PES group and PES ISR were independent factors for worse incidence of MACE.

CONCLUSIONS

In CKD patients, PES was associated with worse clinical outcomes in non-HD patients as compared with EES.

Fabrication of nonbiofouling metal stent and in vitro studies on its hemocompatibility

In recent years, there has been increasing interest for the surface modification of biomaterials in order to improve their surface properties. The bare metal stents surface based on 3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate polymers has shown an excellent antifouling and blood compatibility by using surface-initiated atom transfer radical polymerization. Surface structure, morphology, wettability, and element content were characterized by scanning electronic microscope, static water contact angles measurement, X-ray photoelectron spectroscopy measurement, respectively. The results showed zwitterionic brushes were successfully fabricated on bare metal stents. The blood compatibility of bare metal stents before and after modification was evaluated by platelet adhesion tests, hemolysis assay, morphological changes of red blood cells, coagulation time tests, plasma recalcification time assay, complement activation, and platelet activation at molecular level. Moreover, the cytotoxicity was also to be characterized. All assays showed after the modification with zwitterionic brush the metal stents displayed a property of excellent blood compatibility and low cytotoxicity.

Induction of mesenchymal stem cell chondrogenesis by polyacrylate substrates

Mesenchymal stem cells (MSCs) can generate chondrocytes in vitro, but typically need to be cultured as aggregates in the presence of transforming growth factor beta (TGF-β), which makes scale-up difficult. Here we investigated if polyacrylate substrates modelled on the functional group composition and distribution of the Arg-Gly-Asp (RGD) integrin-binding site could induce MSCs to undergo chondrogenesis in the absence of exogenous TGF-β. Within a few days of culture on the biomimetic polyacrylates, both mouse and human MSCs, and a mesenchymal-like mouse-kidney-derived stem cell line, began to form multi-layered aggregates and started to express the chondrocyte-specific markers, Sox9, collagen II and aggrecan. Moreover, collagen II tended to be expressed in the centre of the aggregates, similarly to developing limb buds in vivo. Surface analysis of the substrates indicated that those with the highest surface amine content were most effective at promoting MSC chondrogenesis. These results highlight the importance of surface group functionality and the distribution of those groups in the design of substrates to induce MSC chondrogenesis.

Surface modification of biomaterials: a quest for blood compatibility

Cardiovascular implants must resist thrombosis and intimal hyperplasia to maintain patency. These implants when in contact with blood face a challenge to oppose the natural coagulation process that becomes activated. Surface protein adsorption and their relevant 3D confirmation greatly determine the degree of blood compatibility. A great deal of research efforts are attributed towards realising such a surface, which comprise of a range of methods on surface modification. Surface modification methods can be broadly categorized as physicochemical modifications and biological modifications. These modifications aim to modulate platelet responses directly through modulation of thrombogenic proteins or by inducing antithrombogenic biomolecules that can be biofunctionalised onto surfaces or through inducing an active endothelium. Nanotechnology is recognising a great role in such surface modification of cardiovascular implants through biofunctionalisation of polymers and peptides in nanocomposites and through nanofabrication of polymers which will pave the way for finding a closer blood match through haemostasis when developing cardiovascular implants with a greater degree of patency.

Effects of some anti-diabetic and cardioprotective agents on proliferation and apoptosis of human coronary artery endothelial cells

BACKGROUND

The leading cause of death for patients suffering from diabetes is macrovascular disease. Endothelial dysfunction is often observed in type 2 diabetic patients and it is considered to be an important early event in the pathogenesis of atherogenesis and cardiovascular disease. Many drugs are clinically applied to treat diabetic patients. However, little is known whether these agents directly interfere with endothelial cell proliferation and apoptosis. This study therefore aimed to investigate how anti-diabetic and cardioprotective agents affect human coronary artery endothelial cells (HCAECs).

METHODS

The effect of anti-diabetic and cardioprotective agents on HCAEC viability, proliferation and apoptosis was studied. Viability was assessed using Trypan blue exclusion; proliferation in 5 mM and 11 mM of glucose was analyzed using [3H]thymidine incorporation. Lipoapoptosis of the cells was investigated by determining caspase-3 activity and the subsequent DNA fragmentation after incubation with the free fatty acid palmitate, mimicking diabetic lipotoxicity.

RESULTS

Our data show that insulin, metformin, BLX-1002, and rosuvastatin improved HCAEC viability and they could also significantly increase cell proliferation in low glucose. The proliferative effect of insulin and BLX-1002 was also evident at 11 mM of glucose. In addition, insulin, metformin, BLX-1002, pioglitazone, and candesartan significantly decreased the caspase-3 activity and the subsequent DNA fragmentation evoked by palmitate, suggesting a protective effect of the drugs against lipoapoptosis.

CONCLUSION

Our results suggest that the anti-diabetic and cardioprotective agents mentioned above have direct and beneficial effects on endothelial cell viability, regeneration and apoptosis. This may add yet another valuable property to their therapeutic effect, increasing their clinical utility in type 2 diabetic patients in whom endothelial dysfunction is a prominent feature that adversely affect their survival.

2-year follow-up of a randomized controlled trial of everolimus- and paclitaxel-eluting stents for coronary revascularization in daily practice. COMPARE (Comparison of the everolimus eluting XIENCE-V stent with the paclitaxel eluting TAXUS LIBERTÉ stent in all-comers: a randomized open label trial)

OBJECTIVES

The purpose of this study was to compare the safety and efficacy of the Xience V (Abbott Vascular, Santa Clara, California) everolimus-eluting stent (EES) with the Taxus Liberté (Boston Scientific, Natick, Massachusetts) paclitaxel-eluting stent (PES) at 2-year follow-up.

BACKGROUND

COMPARE (Comparison of the everolimus eluting XIENCE-V stent with the paclitaxel eluting TAXUS LIBERTÉ stent in all-comers: a randomized open label trial) demonstrated a superior clinical outcome of EES over PES at 1 year in all comers. Whether this superiority is maintained after discontinuation, at 12 months, of dual antiplatelet therapy is unclear.

METHODS

Patients undergoing percutaneous coronary intervention with limited exclusion criteria were randomly allocated to EES or PES. The 2-year pre-specified endpoints are composites of safety and efficacy and stent thrombosis.

RESULTS

Follow-up was completed in 1,795 of 1,800 patients (99.7%). The groups had similar baseline characteristics. At 2 years, significantly fewer EES patients took dual antiplatelet therapy (11.4% vs. 15.4%, p = 0.02). The primary composite of all death, nonfatal myocardial infarction, and target vessel revascularization occurred in 9.0% of EES patients and 13.7% of PES patients (relative risk [RR]: 0.66; 95% confidence interval [CI]: 0.50 to 0.86) driven by a lower rate of myocardial infarction (3.9% vs. 7.5%; RR: 0.52; 95% CI: 0.35 to 0.77) and target vessel revascularization (3.2% vs. 8.0%; RR: 0.41; 95% CI: 0.27 to 0.62), in parallel with a lower rate of definite or probable stent thrombosis (0.9% vs. 3.9%; RR: 0.23; 95% CI: 0.11 to 0.49). Differences significantly increased between 1- and 2-year follow-up for the primary composite endpoint (p = 0.04), target vessel revascularization (p = 0.02), and definite or probable stent thrombosis (p = 0.02).

CONCLUSIONS

The substantial clinical benefit of the EES over the PES with regard to measures of both safety and efficacy is maintained at 2 years in real-life practice with an increasing benefit in terms of safety and efficacy between 1 year and 2 years.

Properties and transport behavior of perfluorotripentylamine (FC-70)-doped amorphous teflon AF 2400 films

Teflon AF 2400 films are known to imbibe solvents, making films in the presence of solvents less fluorous than they might otherwise be. Herein, we demonstrate that doping films with perfluorotripentylamine (Fluorinert FC-70) maintains the fluorous nature of Teflon AF 2400 and improves transport selectivity for fluorine-containing organic compounds. Density measurements on the FC-70-doped films reveal that free volume decreases dramatically as the dopant concentration increases (0-12 wt %) and then increases to approach that of pure FC-70. Remarkably, films from 0 to 12 wt % FC-70 have the same w/v concentration of Teflon AF 2400, indicating that FC-70 fills the free volume of Teflon AF 2400. This is consistent with the observed increased storage modulus and significant decrease (compared to undoped films) of solute diffusion coefficients in the same range of FC-70 concentrations. In contrast, FC-70 at concentrations greater than 12 wt % dilutes Teflon AF 2400, leading to a decrease of storage modulus and dramatic increase in solute diffusion coefficients. Sorption of chloroform decreases from 11.8 g of chloroform/100 g of film (pure Teflon film) to 3.8 g of chloroform/100 g of film (27 wt % FC-70-doped Teflon film), less than the solubility of chloroform in pure FC-70 (4.06 g of chloroform/100 g of FC-70). Solute partition coefficients from chloroform to FC-70-doped films generally decrease with increased dopant concentration. However, within a series of toluenes and nitrobenzenes, selectivity for F-containing solutes over analogous H-containing solutes increases as dopant concentration increases if the substitution is on the aromatic ring but not if it is on the methyl group (toluene). Transport (partitioning × diffusion) rates, as they involve both thermodynamic and kinetic factors, are not simply related to composition.