Effect of stents coated with a combination of sirolimus and alpha-lipoic acid in a porcine coronary restenosis model

The aim of this study was to evaluate antiproliferative sirolimus- and antioxidative alpha-lipoic acid (ALA)-eluting stents using biodegradable polymer [poly-l-lactic acid (PLA)] in a porcine coronary overstretch restenosis model. Forty coronary arteries of 20 pigs were randomized into four groups in which the coronary arteries had a bare metal stent (BMS, n = 10), ALA-eluting stent with PLA (AES, n = 10), sirolimus-eluting stent with PLA (SES, n = 10), or sirolimus- and ALA-eluting stent with PLA (SAS, n = 10). A histopathological analysis was performed 28 days after the stenting. The ALA and sirolimus released slowly over 30 days. There were no significant differences between groups in the injury or inflammation score; however, there were significant differences in the percent area of stenosis (56.2 ± 11.78 % in BMS vs. 51.5 ± 12.20 % in AES vs. 34.7 ± 7.23 % in SES vs. 28.7 ± 7.30 % in SAS, P < 0.0001) and fibrin score [1.0 (range 1.0–1.0) in BMS vs. 1.0 (range 1.0–1.0) in AES vs. 2.0 (range 2.0–2.0) in SES vs. 2.0 (range 2.0–2.0) in SAS, P < 0.0001] between the four groups. The percent area of stenosis based on micro-computed tomography corresponded with the restenosis rates based on histopathological stenosis in different proportions in the four groups (54.8 ± 7.88 % in BMS vs. 50.4 ± 14.87 % in AES vs. 34.5 ± 7.22 % in SES vs. 28.9 ± 7.22 % in SAS, P < 0.05). SAS showed a better neointimal inhibitory effect than BMS, AES, and SES at 1 month after stenting in a porcine coronary restenosis model. Therefore, SAS with PLA can be a useful drug combination for coronary stent coating to suppress neointimal hyperplasia.     

Mechanical properties and in vivo performance of a novel sliding-lock bioabsorbable poly-<Emphasis Type="Italic">p</Emphasis>-dioxanone stent

A bioabsorbable poly-p-dioxanone (PPDO) stent with a novel sliding-lock structure was fabricated to treat stenotic peripheral vessels. The sliding-lock PPDO stents have greater radial strength (107 kPa) than PPDO stents with conventional net-tube structure (32 kPa). The sliding-lock PPDO stents were implanted into the iliac arteries of pigs, and implantation success rate was 90% indicating the feasibility of this design. Additionally, we found that sliding-lock PPDO stents kept vessels patent, although by 3 and 6 months post implantation, luminal diameter decreased slightly due to intimal hyperplasia. At 1 month post implantation, the stents were sparsely covered with endothelial cells, and by 6 months, the stents were mostly absorbed and inflammatory reaction gradually decreased as the stents were absorbed. This study shows favorable mechanical strength, degradability and efficacy for the sliding-lock PPDO stents, and supports further research and development of this unique design of polymer stents for applications in vascular devices.     

Computational investigation of GanAl (n = 1–15) clusters by the density-functional theory

Low-lying equilibrium geometric structures of aluminum-doped gallium cluster Ga_nAl (n = 1–15) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied with the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated for the ground-state structures within the same method. The growth pattern for Ga_nAl (n = 1–15) clusters is Al-substituted Ga_n + 1 clusters and it keeps the similar frameworks of the most stable Ga_n + 1 clusters except for Ga₈Al and Ga₁₃ Al clusters. The Al atom substituted the surface atom of the Ga_n + 1 clusters for n < 12. Starting from n = 12, the Al atom completely falls into the center of the Ga-frame. The Al atom substituted the center atom of the Ga_n + 1 clusters to form the Al-encapsulated Ga_n geometries for n > 12. The odd−even oscillations from Ga_nAl (n = 5) in the dissociation energy, the second-order energy differences, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced. The stability analysis based on the energies clearly shows the clusters from n = 5 with an even number of valence electrons are more stable than clusters with odd number of valence electrons.     

Biocompatibility of Coronary Stent Materials: Effect of Electrochemical Polishing

Percutaneous Transluminal Coronary Revascularization (PTCR) is now a widely accepted treatment modality for atherosclerotic coronary artery disease. Current multicenter randomized trials comparing PTCR with the more invasive Coronary Artery Bypass Grafting could not show long‐term significant survival differences. During the last two decades progress has been made to further optimize PTCR. The most logic approach to treat atherosclerotic coronary narrowings is to remove the atherosclerotic material using especially developed devices. Several trials, however, could not show a significant beneficial outcome after use of these devices compared to plain old balloon angioplasty. Another approach was to implant a coronary prothesis (stent), scaffolding the diseased coronary artery after PTCA. This approach resulted in a decreased restenosis rate at follow‐up. The beneficial effects of stenting, however, was not found to be related to the inhibition of the neointimal cellular proliferation after vascular injury, but simply to be the mechanical result of overstretching of the treated vessel segment. The most important remaining clinical problem after stenting remains the neointimal hyperplasia within the stent, resulting in a significant stent narrowing in 13 to 30 % of patients. Further efforts to improve the clinical results of coronary stenting should focus on the reduction of this neointimal hyperplasia. Neointimal hyperplasia after stent implantation results from (1) a healing response to the injury caused by the stent implantation and (2) a foreign body response to the stent itself. Factors that seem to influence the neointimal hyperplastic response are genetic, local disease related, stent delivery related and stent related factors. Biocompatibilisation of coronary stents by looking for more biocompatible metal alloys, optimized surface characteristics and optimized stent designs should result in a better late patency. Furthermore drug eluting and radioactive stents are under development in order to decrease the neointimal hyperplastic response.     

Evaluation of fluorinated polymers as coronary stent coating

In this report, some fluorinated polyphosphazenes and polymethacrylates were selected for evaluation as coronary stent coating. After applying the polymer film by dipcoating, the stents were implanted in porcine coronary arteries. No acute thrombotic occlusions were observed. The neointimal proliferation was studied by a 6 week follow-up of the minimal lumen stented diameter, using quantitative coronary analysis. All polymers demonstrated a slight hyperplasia, resulting in a 10–20% lumen narrowing at follow-up. Only for one fluorinated polymethacrylate, PFM-P75, a minimal neointimal response (3% lumen narrowing) was found. ©2000 Kluwer Academic Publishers     

Retardation of grain growth in electrodeposited Cu by an electric field

The application of an external dc electric field E = 5 kV/cm during the annealing of electrodeposited Cu foil at 150–195 °C retarded grain growth. The time dependence of the grain size both with and without the field was

Nitinol Carbofilm coated stents for peripheral applications: Study in the porcine model

Purpose: Testing the safety and foreign body reaction (FBR) of a nitinol self-expandable carbon-coated stent system in the porcine animal model at different follow-up (FU) periods. Methods: Fifteen minipigs received 30 carbon-coated self-expandable nitinol stents in iliac arteries. Explants were carried out at 7 (3 animals), 30 (4 animals), 90 (4 animals) and 180 (4 animals) day FU, for evaluation of acute, sub-acute and chronic biological response to the implanted devices. Histological, immunohistochemical, histomorphometric and scanning electron microscopy (SEM) analyses were performed to assess inflammatory reaction, endothelialization process, neointimal growth and cellular composition. Results: Thirty stents were successfully implanted. No mural thrombi were observed at gross examination or by angiography. Histologically no significant inflammatory reaction was detected: the stents appeared covered by a thin monolayer of endothelial cells even at 7 day FU. The neointima presented homogeneous growth and moderate thickness after 30, 90 and 180 days explants (0.38± 0.36 mm, 0.33± 0.30 mm, 0.27± 0.25 mm respectively). Internal and external elastic laminae were intact in 95% of stented arteries. Histological data validations of vessel endothelialization was obtained with SEM for the seven day follow-up group. Conclusions: This study showed good remarkable technical performances, minimal FBR and biocompatibility comparable with other available pre-clinical experimentations.     

Polysaccharide-based nanoparticles formation by polyeletrolyte complexation of carboxymethylated cashew gum and chitosan

Polyelectrolyte complex nanoparticles of chitosan and carboxymethyl cashew gum (CMCG) were prepared with CMCG with two different degrees of substitution (DS = 0.16 and 0.36). The effects of polymer concentration, molar mixing ratio (n ⁺/n ⁻) and mixing order of reactants on particle size distribution and zeta potential were investigated. Nanoparticle structure was elucidated by Fourier transform spectroscopy. Particle size of CH/CMCG DS = 0.16 dispersions was smaller than with DS 0.36 for all n ⁺/n ⁻ ratio investigated. Particle size smaller than 200 nm was obtained when CMCG with DS = 0.16 was used for particle formation. The polydispersity index values were small when CMCG DS 0.36 was used. Increasing the concentration of CMCG led to larger particle size. Zeta potential values for almost all molar mixing ratios were found to be positive (10–32 mV).     

Synthesis and characterization of multi-lamellar mesostructured hydroxyapatites using a series of fatty acids

A family of lamellar mesostructured hydroxyapatites are synthesized using five terminal linear aliphatic carboxylic acids (capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid with the general formula of C _n−1H_2n−1CO₂H, n = 10, 12, 14, 16, 18). The study of X-ray diffraction shows that the hydroxyapatite samples exhibit similar multi-lamellar mesostructure and their interlamellar spacing is proportional to the carbon numbers of carboxylic acids. The transmission electron microscopic images on the products prove the parallel aligned configuration. Fourier transform infrared spectra displays the characteristic components of hydroxyapatite in as-prepared samples. Thermogravimetric analysis, elemental analysis (C, H), and inductively coupled plasma analysis were further used to confirm the organic and inorganic composition of the products.     

Photoluminescence and thermal stability of yellow-emitting Sr-α-SiAlON:Eu<Superscript>2+</Superscript> phosphor

Novel α-SiAlON:Eu²⁺-based yellow oxynitride phosphors with the formula Sr_0.375−x Eu _x ²⁺Si_12−m−n Al _m+n O _n N_16−n (m = 0.75, n = x = 0.004–0.04) have been prepared by firing the powder mixture of SrSi₂, α-Si₃N₄, AlN, and Eu₂O₃ at 2,000 °C for 2 h under 1 MPa nitrogen atmosphere. The luminescence properties, the dependence of the activator concentration of Eu²⁺ and the thermal stability of Sr-α-SiAlON:Eu²⁺ phosphor have been investigated in comparison with Ca-α-SiAlON:Eu²⁺ phosphor. Similar to Ca-α-SiAlON:Eu²⁺ phosphor, Sr-α-SiAlON:Eu²⁺ phosphor has the excitation wavelength ranging from the ultraviolet region to 500 nm, and exhibit intense yellow light. The strongest luminescence was achieved at about x = 0.02 with the emission peak at 578 nm, slightly shorter than that of Ca-α-SiAlON:Eu²⁺ phosphor at 581 nm. Temperature-dependent emission intensity of Sr-α-SiAlON:Eu²⁺ phosphor is comparable to that of Ca-α-SiAlON:Eu²⁺ phosphor. The results suggest that the different position of the emission peak for Sr- and Ca-α-SiAlON:Eu²⁺ depends on the composition and the Stokes shift, and the thermal stability is nearly independent of Sr and Ca or fixed by the network of (Si, Al)–(O, N) in α-SiAlON at the same Eu²⁺ concentration.     

Coronary artery bypass grafting versus percutaneous coronary intervention in end-stage kidney disease: A systematic review and meta-analysis of clinical studies

The most significant complication of end-stage kidney disease (ESKD) is cardiovascular disease, mainly coronary artery disease (CAD). Although the effective treatment of CAD is an important prognostic factor, whether percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) is better for treating CAD in this group of patients is still controversial. We searched Pubmed/Medline, Web of Science, Embase, the Cochrane Central Register of Controlled Trials articles that compared the outcomes of CABG versus PCI in patients with ESKD requiring dialysis. A total of 10 observational studies with 39,666 patients were included. Our analysis showed that when compared to PCI, CABG had lower risk of need for repeat revascularization (relative risk [RR] = 2.25, 95% confidence interval [CI] 2.1–2.42, p < 0.00001) and cardiovascular death (RR = 1.19, 95% CI 1.14–1.23, p < 0.00001) and higher risk for short-term mortality (RR = 0.43, 95% CI 0.38–0.48, p < 0.00001). There was no statistically significant difference between the PCI and CABG groups in the risk for late mortality (RR = 1.05, 95% CI 0.97–1.14, p = 0.25), myocardial infarction (RR = 1.05, 95% CI 0.46–2.36, p = 0.91) or stroke (RR = 1.02, 95% CI 0.64–1.61, p = 0.95). This meta-analysis showed that in ESKD patients requiring dialysis, CABG was superior to PCI in regard to cardiovascular death and need for repeat revascularization and inferior to PCI in regard to short term mortality. However, this meta-analysis has limitations and needs confirmation with large randomized controlled trials.     

Effect of cation stoichiometry on the transport properties of calcium ruthenium oxide ceramics

Seebeck coefficient and electrical resistivity have been determined on a series of compounds having the general composition Ca _n Ru_1−n O _y . From property and structural considerations, these compounds have been divided into two categories: one group resembling Ca₂RuO₄ and the second category exhibiting properties similar to CaRuO₃. While the former is an antiferromagnetic insulator, the latter is a paramagnetic metal. The Seebeck coefficient remains relatively unchanged within the members of the two groups, irrespective of the molar ratios of the cations. Even between the two groups of compounds, the Seebeck coefficient exhibits minimal difference even as the cation ratio (Ru/Ca) of the compounds is varied from 0.35 (n = 0.74) to 1.94 (n = 0.34). The resistivity, however, varies by nine orders of magnitude as the cation ratio is varied in the same range. Consequently, the resulting power factor (s ²σ, where s is the Seebeck coefficient and σ is the electrical conductivity), which is a measure of the usefulness or thermopower conversion efficiency of a thermoelectric material, is found to vary by nine orders of magnitude.     

Hybrid organic–inorganic materials based on polypyrrole and 1,3-dithiole-2-thione-4,5-dithiolate (DMIT) containing dianions

The synthesis of hybrid materials by electropolymerization of pyrrole and inorganic complexes based on the DMIT ligand (1,3-dithiole-2-thione-4,5-dithiolate), e.g. [NEt₄]₂[M(DMIT) _n ] (M = Ni, Pd or Pd, n = 2; M = Sn, n = 3], in acetonitrile solution is reported. Spectroscopic data showed that DMIT-containing anions, [M(DMIT) _n ]²⁻, were inserted into the polypyrrole framework without chemical modification during the electropolymerization process. Cyclic voltammetry showed that materials obtained were electroactive, undergoing redox processes related to both the conducting polymer and the counteranions. The electrochemical results also suggest that, in the case of the transition metal containing films, the counteranions are not trapped in the PPy matrix but undergo anion exchange during the redox cycle of PPy. However, an opposite behaviour was observed with the film with [M(DMIT) _n ]²⁻. The films exhibit good thermal stabilities and have conductivity values expected for semiconductors. This study of these hybrid materials highlights the importance of targeting specific materials for specific applications.

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Compositional dependence of some physical properties of ZnO–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Six glasses of the chemical composition 10ZnO–xPbO–(90−x) P₂O₅ were prepared. With an increase in PbO content a non-monotonous step like increase in the density, in the glass transition temperature, and in the refractive index was observed. From the Raman and IR spectra studied the evidence is given for the phosphate network depolymerization as PbO content increases. Increase in PbO content leads also to an increase in refractive index (n) up to n = 1.74, for x = 55, and to an increase in the glass transition temperature (T _g) from T _g = 270 °C (x = 30) to T _g = 360 °C (x = 55).

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Rapid synthesis of gold nanostructures by a microwave–polyol method with the assistance of CnTAB (n = 10, 12, 14, 16) or C16PC

Gold nanostructures have been synthesized by a microwave(MW)–polyol method with the assistance of such cationic surfactants as alkyltrimethyl ammonium bromide (C_nTAB: n = 10–16, even numbers) or cetylpryridinium chloride (C₁₆PC). Although major products were spherical aggregates for C_nTAB (n = 10, 12, 14), triangular, pentagonal, and hexagonal nanoplates were preferentially synthesized using C₁₆TAB. Spherical spike-ball structures were prepared through C₁₆PC. These results indicated that the morphology of gold nanostructures prepared by the MW–polyol method depends both on the chain length of hydrophobic alkyl group and on the hydrophilic head group.     

Electronic structures of relaxed BiOX (X = F, Cl, Br, I) photocatalysts

For photocatalysts BiOX (X = F, Cl, Br, I), the atomic sites have been relaxed and the electronic structures have been calculated via the density functional theory (DFT) with or without the adoption of Bi 5d states. BiOF exhibits a direct band gap while the other three species present the indirect feature. The consideration of Bi 5d states results in apparent expansion of the gaps, which are closer to the experimental results. The transition positions are almost independent of the incorporation of Bi 5d states, and the conduction-band bottom flattens with the increase in X atomic number. Both O 2p and X np (n = 2, 3, 4 and 5 for X = F, Cl, Br and I, respectively) states dominate the valence-bands while Bi 6p states contribute most to the conduction-bands. The density peak of the localized X np states in the valence-band shifts towards the valence-band top with the increasing X atomic number, along with certain changes in the valence and conduction bandwidths. Atomic and bond populations, as well as the spatial distribution of orbital density have also been investigated.     

Enhancement of thermal stability of TiO2 nanowires embedded in anodic aluminum oxide template

Titania (TiO₂) nanowires with diameters of 20, 50, and 80 nm were successfully synthesized via the template-assistant method. The TiO₂ nanowires embedded in anodic aluminum oxide template have extremely high crystallization and anatase-to-rutile phase transition temperatures than that of the free-state TiO₂ powders, and the thermal stability of embedded TiO₂ nanowires depends on the diameter of the templates. The growth and nucleation activation energy of rutile in 20 nm nanowires are determined to be _boxclose E_{\rm{g}}  = 2.8 ± 0.2 eV and E_n E_{\rm{n}}  = 2.7 ± 0.2 eV, respectively, much higher than that of the free-state TiO₂ powders with E_g E_{\rm{g}}  = 1.6 ± 0.2 eV and E_n E_{\rm{n}}  = 1.9 ± 0.2 eV. The pressure induced by the difference of thermal expansion coefficient between the TiO₂ and aluminum oxide acts as an effective barrier that prevents phase transition, resulting in the enhancement of the TiO₂ structural stability.     

Evolution of atomic and electronic structure of magnetic Gd-doped gold clusters

The evolution of atomic and electronic structure of small Au _n (n = 1–16, and 55) clusters doped with a Gd atom has been investigated using density functional theory within generalized gradient approximation for the exchange–correlation energy. Pure gold neutral clusters with n up to 15 are planar. However, with the doping of a Gd atom, the atomic structure of gold clusters changes, and there is a transition from planar-like structures to three dimensional structures at n = 10. The electronic structure of Gd-doped gold clusters shows a sharp increase in the highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap for certain sizes giving rise to their magic behavior. All clusters are magnetic with large magnetic moments ranging from 6 to 8 μ_B primarily due to the localized 4f electrons on Gd. This makes such clusters with large HOMO–LUMO gaps magnetic superatoms. The main interaction between gold and gadolinium atoms in the clusters is due to hybridization between Au-6s and Gd-5d6s orbitals. Our results indicate the emergence of a wheel structure for Gd@Au₇, a symmetric cage structure at n = 15 for Gd@Au₁₅ and n = 16 for Gd@Au₁₆ ⁺ and Eu@Au₁₆ corresponding to an electronic shell closing at 18 valence electrons leaving aside the f electrons on Gd while for Gd-doped Au₅₅ corresponding to 58 valence electrons, a Au₉Gd@Au₄₆ core–shell structure is obtained in which the Gd atom connects the core of Au₉ with the Au₄₆ shell. The binding energy shows odd–even oscillations with enhancement due to Gd doping compared with pure gold clusters. Such magnetic clusters of gold could have multifunctional biological applications in drug delivery, sensor, imaging, and cancer treatment.     

Synthesis of lamellar mesostructured calcium phosphates using n-alkylamines as structure-directing agents in alcohol/water mixed solvent systems

Lamellar mesostructured calcium phosphates constructed by ionic bonds were prepared by using n-alkylamines (n-C _n H_2n+1NH₂, n = 8–18) at room temperature in the mixed solvent systems of aliphatic alcohol (C _n H_2n+1OH, n = 1–4) and water, and the synthetic conditions were investigated in detail. The mixed solvent systems suppressed the formation of crystalline calcium phosphates like brushite (CaHPO₄·2H₂O) and monetite (CaHPO₄) at low temperatures, successfully affording pure lamellar mesostructured calcium phosphates. Other crystalline phases such as hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) were not formed under the conditions with the Ca/P molar ratios in the range of 0.7–1.0 in the starting mixtures. The Ca/P molar ratio of the lamellar mesostructured calcium phosphates was ca. 1.0, calculated by ICP and ³¹P MAS NMR data. Interestingly, the kind of alcohols strongly influenced the solubilities of calcium phosphate species and n-alkylamines, and then lamellar mesostructured phases were obtained with some morphological variation.     

Synthesis and optical properties of metal (M) atom-doped polycarbosilane (PCS) with extended conjugation (M = Al,Dy, Er and Eu)

Optical properties of metal atom-doped polycarbosilane (PCS) which originated from σ-conjugation effect were studied. Al, Dy, Er and Eu were introduced into PCS by one-pot method to yield polyaluminocarbosilane (PACS), polydysprosiumcarbosilane (PDCS), polyerbiumcarbosilane (PErCS) and polyeuropiumcarbosilane (PECS), respectively. Effects of oxidation curing and ultraviolet (UV) radiation on the photoluminescence (PL) properties of the samples were investigated. PL spectra show strong blue light-emissions and the intensity of PCS is enhanced by adding metal atoms. PACS with extended σ-conjugation exhibits an obvious PL red-shift, high intensity, high quantum yield and excellent oxidation resistance as compared with those of others. As treated under UV lamp for 3 h in air, PACS retains good UV resistance performance, owing to the AlOx (x = 4, 5, or 6) groups which effectively extend the σ-conjugation. The obtained results are expected to have important applications in active sources for electroluminescence (EL) devices, especially suitable for blue emission.