Biomedical subjects

Jim Silver

Publications and source records attributed to Jim Silver.

3 recordsLinked to original sources

PubMed2005

Biodegradable membrane-covered stent from chitosan-based polymers.

Membrane-covered devices could help treat disease of the vasculature such as aneurysm, rupture, and fistulas. They are also investigated to reduce embolic complication associated with revascularization of saphenous vein graft. The aim of this study is to design a clinically applicable biodegradable membrane-covered stent based on the natural polysaccharide chitosan, which has been developed. The mechanical properties of the membrane is optimized through blending with polyethylene oxide (70:30% Wt CH:PEO). The membrane was able to sustain the mechanical deformation of the supporting self-expandable metallic stents during its deployment. The membrane was demonstrated to resist physiological transmural pressure (burst pressure resistance >500 mm Hg) and presented a high-water permeation resistance (1 mL/cm(2) min(-1) at 120 mmHg). The CH-PEO membrane showed a good hemocompatibility in an ex vivo assay. Heparin and hyaluronan surface complexation with the membrane further reduced platelet adhesion by 50.1 and 63% (p = 0.05). The ability of the membrane-covered devices to be used as a drug reservoir was investigated using the nitric oxide donor sodium nitroprusside (SNP). SNP-loaded membranes displayed significantly reduced platelet adhesion.

Biodegradation, Environmental↗

PubMed2004

Radionuclides-hyaluronan-conjugate thromboresistant coatings to prevent in-stent restenosis.

Catheter-based brachytherapy is one of the most effective modalities to inhibit hyperplasia following revascularization procedures. Radioactive stents have failed, however, to prevent clinical hyperplasia due to excessive late lumen loss on the edge of the devices. Numerous strategies have been proposed to circumvent the drawbacks of irradiation therapies, such as the use of more appropriate radionuclides or the "hot-end" stents approach. This paper describes versatile radioactive devices obtained by coating plasma functionalized surfaces-stents or catheters-with a hyaluronan (HA)-diethylenetriamine pentaacetic acid (DTPA) conjugate (HA-DTPA) complexed with a gamma or beta radionuclide. Yttrium and indium were used as radionuclide models, due to their suitability for endovascular radiotherapy. X-ray photoelectron microscopy and time-of-flight secondary ions mass spectrometry analyses confirmed the successful immobilization of the HA-DTPA conjugate on both the metallic (NiTi) and polymeric (Teflon) plasma functionalized surfaces. HA-DTPA-coated surfaces were significantly more hydrophilic than bare surfaces (39.5 degrees vs. 67 degrees on NiTi substrate and 29 degrees vs. 128 degrees on Teflon substrate). Therapeutic doses of yttrium and indium were easily loaded onto the surfaces and remained stable over 2 weeks with a radionuclide loss of about 6%. The HA-DTPA-coated Teflon surfaces presented significantly less fibrinogen adsorption than uncoated materials in an in vitro flow model. This approach, which combines the hemocompatibility of HA-coated surfaces and the anti-proliferative effects of an appropriate radiotherapy, constitutes a promising methodology to alleviate the restenosis induced by existing devices.

Adsorption↗

PubMedDate not supplied

Bioactive coatings of endovascular stents based on polyelectrolyte multilayers.

Layer-by-layer self-assembly of two polysaccharides, hyaluronan (HA) and chitosan (CH), was employed to engineer bioactive coatings for endovascular stents. A polyethyleneimine (PEI) primer layer was adsorbed on the metallic surface to initiate the sequential adsorption of the weak polyelectrolytes. The multilayer growth was monitored using a radiolabeled HA and shown to be linear as a function of the number of layers. The chemical structure, interfacial properties, and morphology of the self-assembled multilayer were investigated by time-of-flight secondary ions mass spectrometry (ToF-SIMS), contact angle measurements, and atomic force microscopy (AFM), respectively. Multilayer-coated NiTi disks presented enhanced antifouling properties, compared to unmodified NiTi disks, as demonstrated by a decrease of platelet adhesion in an in vitro assay (38% reduction; p = 0.036). An ex vivo assay on a porcine model indicated that the coating did not prevent fouling by neutrophils. To assess whether the multilayers may be exploited as in situ drug delivery systems, the nitric-oxide-donor sodium nitroprusside (SNP) was incorporated within the multilayer. SNP-doped multilayers were shown to further reduce platelet adhesion, compared to standard multilayers (40% reduction). When NiTi wires coated with a multilayer containing a fluorescently labeled HA were placed in intimate contact with the vascular wall, the polysaccharide translocated on the porcine aortic samples, as shown by confocal microscopy observation of a treated artery. The enhanced thromboresistance of the self-assembled multilayer together with the antiinflammatory and wound healing properties of hyaluronan and chitosan are expected to reduce the neointimal hyperplasia associated with stent implantation.

Animals↗