Bifunctional polymer brush-grafted coronary stent for anticoagulation and endothelialization

At present, cardiovascular stent intervention faces clinical complications such as delayed endothelialization, late thrombosis and restenosis after implantation. In this work, a kind of bifunctional polymer brush-grafted coronary stent with anticoagulant and endothelial functions was developed. First, a block copolymer brush with zwitterionic structure consisting of sulfoethyl methacrylate (SBMA) and glycidyl methacrylate (GMA) was surface-induced grafted onto the surface of bare metal coronary stent by atom transfer radical polymerization. The diethylenetriamine NONOate (DETA NONOate), acted as nitric oxide (NO) donor to promote endothelialization, was then attached to polyglycidyl methacrylate (PGMA) brush by a reactive epoxy group to produce NO. The process of chemical modification and the release behavior of NO were characterized in detail. Moreover, the results of anticoagulant test, cytotoxicity test, endothelial cells (ECs) proliferation test and animal experiment of this bifunctional polymer brush-grafted coronary stent we proposed indicate that the zwitterion modified and NO supplied bifunctional coatings has good anticoagulant property, no cytotoxicity and significant endothelialization effect. This work opens the door to combine biological activity of NO and anticoagulant effect of zwitterions, which has great potential to address post-operative side effects associated with restenosis and late stent thrombosis.

Poly(2-aminoethyl methacrylate)-based polyampholyte brush surface with carboxylic groups to improve blood compatibility

Zwitterionic material-based polymer brush significantly prevents protein adsorption and cell adhesion, which leads to the blood compatibility. However, zwitterionic polymer itself is difficult to be modified further, for the blood compatibility since the charged balance is impaired after the modification. In this research, chemically modifiable mixed charge polymer brush is designed, without impairing its characteristics. Condensed mixed charge polymer brush will work like zwitterionic material because neighbouring opposite charge is reported to be important in the zwitterionic material. Cationic polymer brush with primary amine group, which is based on 2-aminoethyl methacrylate (AEMA), was prepared and modified by succinic anhydride to obtain carboxylic group induced poly(AEMA). The ratio of primary amine group and carboxylic group was optimized to obtain the polyampholyte brush. The blood compatibility was evaluated by measuring coagulation/complement activation, protein adsorption and cell adhesion induced by the polymer. Our designed cationic-based polyampholyte brush prevented coagulation/complement activation comparable to poly(2-methacryloyloxyethyl phosphorylcholine) brush, based on intra-monomer interaction, because condensed mix charge works like zwitterion.

Preparation of Vascular Endothelial Cadherin Loaded-Amphoteric Copolymer Decorated Coronary Stents for Anticoagulation and Endothelialization

A new strategy for preparation of blood-contact materials, with their short-term anticoagulation depending on zwitterionic structure and long-term hemocompatibility based on endothelialization, was proposed, performed, and proved. The copolymer made of sulfonamide zwitterionic and acrylic acid was designed and synthesized, and grafted to the surface of the bare metal coronary stent. Then, the vascular endothelial cadherin (VE-Cad), one of the specific antibodies of endothelial progenitor cells (EPCs), was fixed onto the copolymer chain. Finally, it is proved by in vitro blood tests that the coronary stent decorated with VE-Cad loaded-amphoteric copolymer displayed good platelet anti-adhesion characteristic. This anti-adhesion characteristic was attributed to the zwitterionic structure and the biofunctionality of specifically capturing EPCs confirmed by the results that the antibody-decorated coronary stent was trapped with EPCs. Finally, the in vivo implantation experiments of the antibody-decorated coronary stent in rabbit for 4 weeks were carried out. Results indicated that the endothelium and smooth surface of the antibody-loaded stent was found to be due to the covered effect of EPCs, without obvious intimal hyperplasia. The strategy we proposed has great potential in the design and preparation of blood-contact biomedical materials and devices.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Effect of a Novel Stent on Re-Endothelialization, Platelet Adhesion, and Neointimal Formation

AIM

Vascular endothelial-cadherin (VE-cadherin) is specifically expressed by outgrowth endothelial cells (OECs). Zwitterionic stent showed high antifouling and excellent blood compatibility. Therefore, we hypothesized that anti-VE-cadherin antibody-coated zwitterionic stents (VE-cad-Z stents) would promote re-endothelialization, reduce neointimal formation, and resist thrombus.

METHODS

VE-cad-Z stents were examined using platelet adhesion test, platelet activation, and OEC capture ability in vitro. In vivo effect of VE-cad-Z stents on re-endothelialization, thrombus-resistance, and neointima hyperplasia was investigated in left common carotid arteries of rabbits (n=15).

RESULTS

In vitro, VE-cad-Z stents showed better platelet-resistance and OEC-capture ability (DNA concentration: 297.23±22.71 versus 67.49±15.26 ng/µL, P＜0.01). In vivo, VE-cad-Z stents exhibited better patency rate than bare metal stents (BMS) (15/15 versus 12/15), and it significantly reduced platelet adhesion and neointima formation (neointima area: 1.13±0.05 versus 1.00±0.05mm(2), P＜0.01 and 3.04±0.11versus 1.05±0.06mm(2), P＜0.01, at 3 and 30 days, respectively; % stenosis: 20.99±0.98 versus 18.72±0.97, P＜0.01 and 56.46±2.20 versus 19.45±1.24, P＜0.01, at 3 and 30 days, respectively).

CONCLUSION

These data suggested that VE-cad-Z stents could specifically capture OECs, consequently promote endothelial healing, and also reduce platelet adhesion and neointima formation.