The short-term effects on restenosis and thrombosis of echinomycin-eluting stents topcoated with a hydrophobic heparin-containing polymer.

Although drug-eluting stents (DESs) have become the most effective means of treating coronary artery disease, safety concerns regarding their thrombogenicities remain to be surmounted. Here, we report on a novel type of DES capable of preventing restenosis and thrombosis. The DES was prepared by coating a bare metal stent with echinomycin (an anti-proliferative drug) in polyurethane by a spray drying method. Hydrophobic heparinized polymer was then topcoated onto stent over echinomycin/PU layer by dipping to improve hemocompatibility. The two-layered stent was characterized regarding surface and cross-sectional morphology, drug release pattern, platelet adhesion in vitro, and restenosis in vivo. It was found that the heparin topcoat acts as a diffusion barrier that allows the controlled release of drug in a sustained manner. Also, the heparin coated layer effectively reduced platelet adhesion, indicating excellent hemocompatibility. From the animal test using pigs, it was evident that the developed DESs can minimize neointimal proliferation and thrombus formation. The devised hydrophobic heparinized polymer-coated DES effectively reduced both restenosis and thrombosis, suggesting that they have potential as tools for the treatment of coronary artery diseases.

Self-assembled nanoparticles based on glycol chitosan bearing hydrophobic moieties as carriers for doxorubicin: in vivo biodistribution and anti-tumor activity.

Self-assembled nanoparticles, formed by polymeric amphiphiles, have been demonstrated to accumulate in solid tumors by the enhanced permeability and retention effect, following intravenous administration. In this study, hydrophobically modified glycol chitosans capable of forming nano-sized self-aggregates were prepared by chemical conjugation of fluorescein isothiocyanate or doxorubicin to the backbone of glycol chitosan. Biodistribution of self-aggregates (300 nm in diameter) was evaluated using tissues obtained from tumor-bearing mice, to which self-aggregates were systemically administered via the tail vein. Irrespective of the dose, a negligible quantity of self-aggregates was found in heart and lung, whereas a small amount (3.6-3.8% of dose) was detected in liver for 3 days after intravenous injection of self-aggregates. The distributed amount of self-aggregates gradually increased in tumor as blood circulation time increased. The concentration of self-aggregates in blood was as high as 14% of dose at 1 day after intravenous injection and was still higher than 8% even at 3 days. When self-aggregates loaded with doxorubicin were administered into the tumor-bearing mice via the tail vein, they exhibited lower toxicity than but comparable anti-tumor activity to free doxorubicin. These results revealed the promising potential of self-aggregates on the basis of glycol chitosan as a carrier for hydrophobic anti-tumor agents.

Inhomogeneity of the ultrafast insulator-to-metal transition dynamics of VO2.

The insulator-metal transition (IMT) of vanadium dioxide (VO2) has remained a long-standing challenge in correlated electron physics since its discovery five decades ago. Most interpretations of experimental observations have implicitly assumed a homogeneous material response. Here we reveal inhomogeneous behaviour of even individual VO2 microcrystals using pump-probe microscopy and nanoimaging. The timescales of the ultrafast IMT vary from 40±8 fs, that is, shorter than a suggested phonon bottleneck, to 200±20 fs, uncorrelated with crystal size, transition temperature and initial insulating structural phase, with average value similar to results from polycrystalline thin-film studies. In combination with the observed sensitive variations in the thermal nanodomain IMT behaviour, this suggests that the IMT is highly susceptible to local changes in, for example, doping, defects and strain. Our results suggest an electronic mechanism dominating the photoinduced IMT, but also highlight the difficulty to deduce microscopic mechanisms when the true intrinsic material response is yet unclear.

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane). III. In vivo biocompatibility and biostability.

To investigate the effects of polymer chemistry and topology (linear or graft copolymer) on in vivo biocompatibility and biostability based on cage implant system, various hydrogels, composed of short hydrophilic [polyethylene oxide (PEO)] and hydrophobic block, were prepared by polycondensation reaction. Poly(tetramethylene oxide) (PTMO) or poly(dimethyl siloxane) (PDMS) was chosen as a hydrophobic block because of their wide utilization as a biomaterial. By using the specimens retrieved from rats killed after 1, 2, 3, 5, and 7 weeks' implantation, cellular and material responses were assessed. Most hydrogels showed a comparable value of macrophage density to Pellethane(R), control polymer, whereas they did significantly lower foreign body giant cell (FBGC) density and coverage because of the presence of PEO. However, PEO block length and polymer topology did not affect macrophage adhesion and FBGC formation in our polymer composition. The hydrogel based on PDMS alone showed significantly lower macrophage density and FBGC density than Pellethane(R), indicating that PDMS plays a role in inhibiting cellular adhesion. The results obtained from gel permeation chromatography curve and Fourier transform infrared spectra exhibited that all the polymers were susceptible to oxidative degradation in vivo. Although Pellethane(R) revealed surface degradation by 5 weeks in vivo, hydrogels showed rapid degradation in the bulk within 2 weeks because of the penetration of oxidative chemicals released from phagocytic cells into PEO domain of phase-separated hydrogels. The more significant degradation was observed in the hydrogels with longer PEO block and PTMO as a hydrophobic block instead of PDMS. It was evident that the minor degradation could be achieved by grafting PEO and adopting PDMS as a hydrophobic block in the hydrogel.