Controlling the drug release rate from biocompatible polymers with micro-patterned diamond-like carbon (DLC) coating

During the past year, we have witnessed the evolution of an intense public controversy regarding late thrombosis following implantation of drug eluting stent (DES) in patients with obstructive coronary artery disease. To overcome the problem, DES should possess sufficient biocompatibility and non-thrombogenicity with a controlled drug release system. A new DES composed of biocompatible polymers coated with antithrombogenic diamond-like carbon (DLC) coating was proposed. In this study, the drug release profile of the newly proposed drug eluting system was thoroughly investigated. Three polymers were selected as base drug-reservoir materials: hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC), hydrophobic poly (ethylene-co-vinyl acetate) (EVA) and less hydrophobic polyurethane (PU). The three polymers are currently used or studied for biomedical materials, while MPC and DLC were already confirmed as excellent biocompatible materials with antithrombogenicity. After coating the lattice-like patterned DLC on both polymers containing drug, samples were soaked in 2 ml of medium of phosphate-buffered saline with 10% ethanol. The drug release rate was measured by a spectrophotometer. The percentile cover area of patterned DLC on polymers was varied from 0% (without DLC) to 100% (fully covered). The sample without DLC coating presented an initial burst of the drug release from the polymer matrix, whereas the DLC-coated samples inhibited the initial burst release from polymers within the first five days of the experiments. It was found that the drug eluting profiles could be effectively controlled by changing the cover area of micro-patterned DLC coatings on polymers, which may be applicable to the next-generation DES system that eventually prevents late thrombosis.     

Biaxial elastic modulus of very thin diamond-like carbon (DLC) films

The biaxial elastic modulus of very thin diamond-like carbon (DLC) films was measured by the recently suggested free overhang method. The DLC films of thickness ranging from 33 to 1100 nm were deposited on Si wafers by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) or by the filtered vacuum arc (FVA) process. Because the substrate was partially removed to obtain sinusoidal free overhang of the DLC film, this method has an advantage over other methods in that the measured value is not affected by the mechanical properties of the substrate. This advantage is more significant for a very thin film deposited on a substrate with a large difference in mechanical properties. The measured biaxial elastic moduli were reasonable values as can be judged from the plane strain modulus of thick films measured by nanoindentation. The biaxial elastic modulus of the film deposited by r.f.-PACVD was 90±3 GPa and that of the film deposited by FVA process was 600±50 GPa. While the biaxial elastic modulus of the film deposited by FVA is independent of the film thickness, the film deposited by r.f.-PACVD exhibited decreased elastic modulus with decreasing film thickness when the film is thinner than 500 nm. Although the reason for the different behavior could not be clarified at the present state, differences in structural evolution during the initial stage of film growth seem to be the reason.     

Instability of diamond-like carbon (DLC) films during sliding in aqueous environment

The instability of diamond-like carbon (DLC) film deposited on Ti-6Al-4V alloy substrate using the r.f.-PACVD method was investigated under sliding conditions in an aqueous environment. Significant adhesive wear was observed when tested in this environment, while normal abrasive wear occurred in an ambient air of relative humidity about 25%. A critical test was performed to elucidate the reason for the instability which limits the biomedical applications of the DLC coating. By employing a multi-step coating process, it was shown that the instability is closely related to the penetration of water molecules to the interface via through-film defects or pinholes. These results suggest that the stability of DLC film in aqueous environment can be improved by controlling the through-film defects in the DLC coating layer.     

Effect of diamond-like carbon (DLC) on the properties of the NiTi alloys

NiTi alloy has found wide application in the biomedical field due to its unique shape memory effect, superelasticity and biocompatibility. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, NiTi alloys were coated with diamond-like carbon (DLC) fabricated by plasma immersion ion implantation and deposition (PIIID) to improve their corrosion resistance and blood compatibility without sacrificing their shape memory effect and superelasticity. The structure of the films and the depth profiles between the films and substrate were studied using Raman spectroscopy and XPS, respectively. The phase transformation temperature, superelasticity, anticorrosion behavior and Ni ions release of the coated and uncoated sample were investigated by DSC, tensile tests, potentiodynamic polarization and AAS, respectively. The hemocompatibilty of the coated and uncoated samples was measured using clotting time and platelet adhesion. The results shows that the films is DLC accompanying with the formation of the mixing layer, and the DLC films can markedly improve the corrosion resistance and the hemocompatibility, obviously increase the ratio of albumin-to-fibrinogen and effectively block the Ni ions release of the NiTi alloys without sacrificing its superelasticity and changing its phase transformation temperature. The research results suggest DLC films prepared by PIIID could improve the in vivo performance of NiTi alloys implanted into the human body.     

Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC)-coated Si probe

Atomic force microscope (AFM) equipped with diamond-like carbon (DLC)-coated Si probe has been used for scratch nanolithography on Si surfaces. The effect of scratch direction, applied tip force, scratch speed, and number of scratches on the size of the scratched geometry has been investigated. The size of the groove differs with scratch direction, which increases with the applied tip force and number of scratches but decreases slightly with scratch speed. Complex nanostructures of arrays of parallel lines and square arrays are further fabricated uniformly and precisely on Si substrates at relatively high scratch speed. DLC-coated Si probe has the potential to be an alternative in AFM-based scratch nanofabrication on hard surfaces.     

Relationship between static friction and surface wettability of orthodontic brackets coated with diamond-like carbon (DLC), fluorine- or silicone-doped DLC coatings

In orthodontics, it is important to reduce the static friction between brackets and wires in order to enable easy tooth movement. The goal of the present study was to deposit diamond-like carbon (DLC), fluorine-doped DLC (F-DLC), and silicon-doped DLC (Si-DLC) coatings onto the slot surface in stainless steel orthodontic brackets using the plasma-enhanced chemical vapor deposition (PECVD) method and to characterize the frictional property between the coated bracket and wire under dry and wet conditions.In order to characterize DLC-, F-DLC- or Si-DLC-coated surface, XPS, the surface roughness and surface wettability of three deferent surfaces were measured. A nanoindentation test and a scratch test were performed in order to measure the hardness and adhesiveness, respectively, of DLC-, F-DLC- or Si-DLC coatings. The static friction between DLC-, F-DLC-, Si-DLC-coated brackets and 0.019 × 0.025-in stainless steel (SS) orthodontic wires was measured for several angulations under dry and wet conditions using a universal testing machine equipped with a custom-made friction-testing device.The F 1s or Si 2p and Si 2s peaks were observed for F-DLC (27.8 at.%:F) or Si-DLC (26.8 at.%:Si), respectively. There were no significant differences in the surface roughness of the slot surface of the bracket among the four types of specimens. The F-DLC was significantly hydrophobic and Si-DLC was significantly hydrophilic as compared to DLC. Doping the DLC with fluorine or silicon caused the surface hardness to decrease significantly.The results of the present study indicate that DLC, F-DLC and Si-DLC coatings provided a significant reduction in static friction. Among the coatings examined herein, F-DLC-coated bracket exhibited the significantly lowest static friction between the bracket and wire under the wet condition, which was lower than that under the dry condition. The F-DLC coating is highly promising as a means of promoting effective tooth movement and shortening treatment time for orthodontic treatments.     

The influence of nitrogen on the dielectric constant and surface hardness in diamond-like carbon (DLC) films

In this work a carbon target was sputtered by a methane/argon/nitrogen plasma in order to produce nitrogenated diamond-like carbon films (a-C:H:N). As the N₂ content in the sputtering gas was increased, the deposition rate increased markedly. Rutherford backscattering spectrometry (RBS) was used to investigate the chemical composition of the films. This nitrogen incorporation modifies the chemical bonding structure of the films, as shown by the analysis of the Raman spectra, including the occurrence of two extra peaks at approximately 2200 and 690 cm⁻¹. Electrical properties were measured through capacitance–voltage (C–V) curves. The hardness of the films decreased with the N content as shown by measurements performed by indentation method. A correlation among the Raman studies, the N content in the films, the dielectric constant and the surface hardness is presented.     

Corrosion performance of diamond-like carbon (DLC)-coated Ti alloy in the simulated body fluid environment

DLC coatings have been deposited onto substrate of Ti alloy (Ti-6Al-4V) using r.f. PACVD (plasma-assisted chemical vapor deposition) with C₆H₆, and mixture of C₆H₆ and SiH₄ as the process gases. Three kinds of DLC coatings were prepared as a function of diverse bias voltage and Si incorporation. Corrosion performance of DLC coatings was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analyses (atomic force microscopy and scanning electron microscopy). The electrolyte used in this test was a 0.89% NaCl solution of pH 7.4 at temperature 37°C. The porosity and protective efficiency of DLC coatings were obtained using potentiodynamic polarization test. Moreover, the delamination area and volume fraction of water uptake of DLC coatings as a function of immersion time were calculated using electrochemical impedance spectroscopy. This study provides the reliable and quantitative data for assessment of the effect of Si incorporation and an increase of bias voltage on corrosion performance. In conclusion, electrochemical measurements showed that DLC coatings with Si addition and an increase of bias voltage could improve corrosion resistance in the simulated corrosive environment of the body fluid by a 0.89% NaCl solution. This could be attributed to the formation of a dense and low-porosity coating, which impede the penetration of water and ions.     

Study of photoconductivity in thin amorphous diamond-like carbon (a:DLC) films prepared by r.f. glow discharge technique

Thin a:DLC films were deposited by r.f. plasma system in which methane (CH₄) was admitted. Photoconductivity measurements were performed on an Al-a:DLC-Cu sandwich structure and an Al-a:DLC-Al planar structure. The photocurrent was measured in a wide interval of temperatures. The photocurrent signal of the sandwich device is about 100 times higher than the dark current measured under He-Ne laser incident light (2.5 mW) at 160 K. A photocurrent response time of τ_o ≈ 8 ms was measured at this temperature. In the planar device, under the same conditions, the photocurrent signal was twice the dark current. The maximum mobility-lifetime product of a:DLC (sandwich device) was about 2 × 10⁻¹⁰ cm²/V.     

溶胶——凝胶镀膜技术综述(连载2)

2.2 过渡金属烷氧基化合物化学 多数金属的烷氧基化合物化学活性都比Si(OR)4大得多，这些金属原子的电负性较Si小。因此，它们所带的部分正电荷较硅原子大，此外，它们在氧化物中的配位数N高于它们各自的氧化态Z。配位数的增大，对化学反应活性起着主要作用。……     

溶胶--凝胶镀膜技术综述(连载7)

第二节 玻璃基板的清洗 要使镀膜牢固地附着在基板上,首先要保证玻璃表面的清洁,镀液才能在玻璃表面润湿。一般来讲,基板清洗方法的选择取决于镀膜方法与产品用途。基板的表面状态对镀膜的结构及物理性质都有很大影响。所以,象真空镀膜,化学气相沉积等都有自己独特的清洗方法。谈到基板的清洗,一般是指     

溶胶--凝胶镀膜技术综述(连载4)

第二章 氧化物镀膜材料、结构与性质 第一节 氧化物镀膜的材料1 形成均匀氧化物镀膜的基本条件 为加工出具有一定光学性质的氧化物膜,所选用的镀膜溶液必须具有特定的物理和化学性质,即:     

溶胶--凝胶镀膜技术综述(连载3)

2　溶胶向凝胶的转化一般采用升高温度或加入电解质的办法 ,促使溶胶向凝胶转化。升高温度 ,由于蒸发作用 ,胶粒间液体的量降低 ,同时也会使热骚动加剧 ,胶粒间碰撞机会增多 ,胶粒表面的 Si— OH发生聚合反应 ,使胶粒联在一起。加入电解质 ,调整胶体溶液的 p H值 ,减小胶粒间的电斥力 ,诱发胶粒间的碰撞 ,促使胶粒聚集形成凝胶。一般是加入酸 ,使溶液 p H值降低到5～ 6。溶胶在不断地转化为凝胶。这种胶粒的不断聚集 (微凝胶 )漫延到整个溶胶体系。然而 ,二氧化硅和溶剂的局部浓度保持不变 ,溶胶和凝胶之间具有图 7[12 ]　导致溶胶和凝胶…     

溶胶--凝胶镀膜技术综述(连载8)

第四章 镀膜溶液的配制 及镀膜工艺设备 第一节 镀膜溶液的配制 正如前所述,镀膜溶液的成膜物质主要是某些元素的烷氧基化合物及一些无机盐类。成膜物质的选择原则已在第二章中作了介绍。表19列出几种常用成膜物质的物理性质。     

溶胶--凝胶镀膜技术综述(连载5)

第三节　常见氧化物膜目前研究最多的氧化物膜可谓二氧化硅和二氧化钛膜 ,这两种薄膜也是接受呈色离子、制备彩色镀膜常用的基体膜 ,所以 ,有必要将它们单独列出 ,加以讨论。1　二氧化钛膜在所有高折射率材料中 ,由钛的化合物制备的氧化物膜具有特殊的实际意义。因此 ,对二氧化     

溶胶--凝胶镀膜技术综述(连载6)

3 其它金属氧化物膜 前面曾经提到,所有高价金属,如果它们的化合物能够溶于有机溶剂,并在干燥过程中没有析晶倾向,这些金属均可用来浸镀氧化物膜。镀液的配制合适与否是很关键的因素。一种镀液的各种化学成分的最佳比例应该通过系统的实验来决定,不能单独作为成膜物质形成氧化物膜的元素,可以加到其它氧化物基体膜中,从而得到高质量的镀膜。可以单独作为成膜物质,并具有优良的光学和机械性质的氧化物膜的例子列于表6。     

Synthesis of poly(styrene-co-maleimide) and poly(octadecene-co-maleimide) nanoparticles and their utilization in paper coating

Aqueous polymer dispersions comprising of poly(styrene-co-maleimide) (SMI) or poly(octadecene-co-maleimide) (OMI) nanoparticles were synthesized by thermal imidization of the corresponding maleic anhydride copolymer precursors with ammonia using an organic solvent free process. Different reaction parameters such as temperature, time, agitation speed and stirrer geometry, and molar ratio of ammonia-to-anhydride were investigated in order to find optimal conditions. The obtained copolymer nanoparticles exhibited glass transition temperatures (T_g's) between 140 and 170 °C with particle sizes ranging from 50 to 230 nm. The compositional analysis was conducted by recording ¹H NMR and ATR-FTIR spectra. In addition, SMI dispersions were successfully spray dried and analyzed by SEM. Finally, the polymer dispersion's utility as auxiliary organic pigment in paper coating formulations was evaluated.     

Synthesis of poly(styrene-co-maleimide) and poly(octadecene-co-maleimide) nanoparticles and their utilization in paper coating

Aqueous polymer dispersions comprising of poly(styrene-co-maleimide) (SMI) or poly(octadecene-co-maleimide) (OMI) nanoparticles were synthesized by thermal imidization of the corresponding maleic anhydride copolymer precursors with ammonia using an organic solvent free process. Different reaction parameters such as temperature, time, agitation speed and stirrer geometry, and molar ratio of ammonia-to-anhydride were investigated in order to find optimal conditions. The obtained copolymer nanoparticles exhibited glass transition temperatures (T_g's) between 140 and 170 °C with particle sizes ranging from 50 to 230 nm. The compositional analysis was conducted by recording ¹H NMR and ATR-FTIR spectra. In addition, SMI dispersions were successfully spray dried and analyzed by SEM. Finally, the polymer dispersion's utility as auxiliary organic pigment in paper coating formulations was evaluated.