Development of "heparin-like" polymers using swift heavy ion and gamma radiation. I. Preparation and characterization of the materials

Direct surface modification of poly(VDF-co-TrFE) films by surface-initiated ATRP without pretreatment

A NMR study revealed that the surface-initiated ATRP of tBA occurred due to fluorine abstraction from the TrFE units of poly(VDF-co-TrFE).

Modification of Track Etchedfluorinatea Films by Radiation Induced Graft Copolymerization

With the aim of improving the basic characteristics of Track Etched Membranes (TEMs), functionalization by graft copolymerization has been attempted in the present work. Thin films (25 μm) of poly(vinyl fluoride) (PVF) (Tedlar) were irradiated by swift heavy ions (110 MeV Si 8+ ). The irradiated films were chemically etched to form latent tracks. Atomic Force Microscopy (AFM) was used to ascertain the formation of latent tracks. Irradiation effects were studied using UV-visible spectroscopic techniques. The tracks were functionalized by gamma radiation induced grafting with 4-vinyl pyridine (4-VP). In order to anticipate the best grafting conditions, percentage of grafting was studied as a function of various reaction conditions such as (i) total dose, (ii) monomer concentration and (iii) amount of water. Maximum percentage of grafting (13.66 %) was obtained at a total dose of 57.024 kGy using 2 ml of 4-VP in 10 ml of water. The grafted films were characterized by FTIR technique

Nanoscale growth factor patterns by immobilization on a heparin-mimicking polymer

In this study, electrostatic interactions between sulfonate groups of an immobilized polymer and the heparin binding domains of growth factors important in cell signaling were exploited to nanopattern the proteins. Poly(sodium 4-styrenesulfonate-co-poly(ethylene glycol) methacrylate) (pSS-co-pPEGMA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using ethyl S-thiobenzoyl-2-thiopropionate as a chain transfer agent and 2,2'-azoisobutyronitrile (AIBN) as the initiator. The resulting polymer (1) was characterized by 1H NMR, GPC, FT-IR, and UV-vis and had a number average molecular weight (Mn) of 24,000 and a polydispersity index (PDI) of 1.17. The dithioester end group of 1 was reduced to the thiol, and the polymer was subsequently immobilized on a gold substrate. Binding of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) to the polymer via the heparin binding domains was then confirmed by surface plasmon resonance (SPR). The interactions were stable at physiological salt concentrations. Polymer 1 was cross-linked onto silicon wafers using an electron beam writer forming micro- and nanopatterns. Resolutions of 100 nm and arbitrary nanoscale features such as concentric circles and contiguous squares and triangles were achieved. Fluorescence microscopy confirmed that bFGF and VEGF were subsequently immobilized to the polymer micro- and nanopatterns.

Covalently grafted phospholipid monolayer on silicone catheter surface for reduction in platelet adhesion

We report a novel method of surface grafting a polymeric phospholipid system containing an acryloyl end group (1stearoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine) onto medical grade silicone catheters. The surface of silicone catheters was functionalized in a sequence of steps: plasma polymerization of allyl alcohol on the catheter surface, grafting acryloyl moieties and in situ polymerization of the pre-assembled acryloyl terminated phospholipids on the acryloyl functionalized catheter surface. The surface morphological changes analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), a sharp decrease in water contact angle, and appearance of N1s peak in XPS analysis indicated a successful monolayer grafting of the phospholipid. In platelet adhesion tests performed using platelets isolated from rabbit plasma, the phospholipid grafted surface showed fewer adhered platelets, without emerging pseudopodes or aggregation. However, ungrafted catheter surface showed large number of platelets in extensively spread and aggregated states. Thus, this modified phospholipid system and its simple grafting technique was very effective with regard to suppressing in vitro platelet adhesion on the silicon catheter surface.

Sulfonation of polyvinylidene difluoride resin and its application in extraction of restriction enzymes from DNA digestion solutions

Sulfonation of polyvinylidene difluoride (PVDF) resin was achieved by incubation of the resin with sulfuric acid at a moderately high temperature. The sulfonated PVDF (SPVDF) resin was studied for its ability to extract restriction enzymes from DNA digestion solutions. The SPVDF resin was effective in adsorbing restriction enzymes such as EcoRI and BamHI and the extraction procedure was easy and simple to perform. The adsorption depended upon the amount of the resin added. We found that 1 mg of the SPVDF resin could completely remove all restriction enzyme activity routinely used in DNA digestion within 2 min after its addition. Treatment of a digestion solution with the SPVDF resin did not change the reaction solution and the same digestion buffer could be used for another digestion of the same DNA with other enzymes. We also found that, in comparison with normal PVDF, the SPVDF resin adsorbed less DNA, resulting in less loss of DNA in the extraction step. The potential application of the SPVDF resin in other procedures of molecular cloning and enzyme purification is discussed.

Blood compatibility of titanium oxides with various crystal structure and element doping

BACKGROUND

Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade.

METHODS

Titanium oxide films were produced by metal plasma deposition and implantation in the form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the Fermi level of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples.

RESULTS

The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces.

CONCLUSION

Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

Use of Fluorinated Organic Compounds in Living Radical Polymerizations

Controlled/living radical polymerization (LRP) is a field of special interest because it allows tailoring well-defined macromolecular architectures such as telechelic, block, graft or star copolymers. Since the eighties, several techniques have been reported [such as the iniferter method, nitroxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), iodine transfer polymerization (ITP), and reversible addition-fragmentation chain transfer (RAFT)] giving rise to a huge number of publications and patents. This review aims at illustrating the contribution of fluorinated organic compounds in this area of research through the use of fluorinated initiators (dithiocarbamates, xanthates, tetraphenylethanes, alkoxyamines, fluorinated alkyl halides, and dithioesters) or other fluorinated molecules (ligands, solvents). Another point depicts the LRP of various fluorinated monomers (methacrylates, acrylates, styrenics, and alkenes). Finally, fluorinated block and graft copolymers prepared by LRP have been reported. A review with 165 references.