Advances in DLC coatings by hybrid PSII and PECVD as a barrier to corrosion in simulated body fluid*

In this study, diamond-like carbon (DLC) films were deposited on biomedical AISI316L stainless steel by hybrid plasma source ion implantation (PSII) and plasma-enhanced chemical vapour deposition (PECVD). Potentiodynamic polarization tests and Electrochemical Impedance Spectroscopy (EIS) have been employed to investigate the corrosion performance of different DLC films in Tyrode's simulated body fluid (pH = 7.4). The corrosion resistance of the DLC films by PECVD deteriorated rapidly after 24 h of immersion, but those made by hybrid PSII and PECVD offered more effective barrier for AISI316L stainless steel during 72 h of immersion. The test results demonstrated that the DLC film by hybrid PSII and PECVD possessed less corrosion current density, greater corrosion resistance, and more positive breakdown potential in simulated body fluid.     

Nanostructured diamondlike carbon thin films for medical applications

Diamondlike carbon (DLC) is an amorphous form of carbon that may contain a high fraction of sp³-hybridized carbon atoms. DLC thin films possess high hardness values, low coefficient of friction values, chemical inertness, and compatibility with human cells. The cardiovascular, orthopedic, ophthalmic, biosensor, and microelectromechanical system (MEMS) device applications for diamondlike carbon thin films are reviewed. Finally, processing of nanostructured diamondlike carbon thin films for medical applications is presented.     

不锈钢基体预处理对合成类金刚石碳膜的影响

本文研究了在射频等离子体增强化学气相沉积工艺中不同的预处理方法对不锈钢基底上类金刚石碳膜生长的影响。所沉积的碳膜的结构和形貌分别用激光Raman光谱和扫描电子显微镜进行了分析，薄膜与基底的结合力通过划痕实验进行了表征。实验结果表明，通过采用合适的过渡层能显著提高类金刚石碳膜与基底的结合力，而通过化学腐蚀的方法对提高结合力的帮助不大。     

Synthesis and characterisation of nanostructured hardystonite coating on stainless steel for biomedical application

Here, nanostructured hardystonite bioceramic (Ca₂ ZnSi₂ O₇) was synthesised from tetraethyl orthosilicate, zinc nitrate hexahydrate, and calcium nitrate tetrahydrate via sol–gel method, dried at 60–120°C, and finally calcinated at 1300°C. X‐ray diffraction (XRD) analysis confirmed the formation of hardystonite bioceramic. Afterwards, electrophoretic method was utilised to coat the hardystonite ceramic on 316L stainless steel (SS). Methanol solution was used as suspension solvent. The best deposition procedure was carried out by electrophoretic device in the voltage of 50 V for 5 min. XRD analysis was employed for phase characterisation and scanning electron microscopy was utilised for microstructural and morphological characterisations of the coatings. Chemical composition of the coating was evaluated by energy‐dispersive X‐ray spectroscopy. The hardystonite coating improved the corrosion resistance of the substrate, so the corrosion current density in the coated samples was less than the uncoated ones (nine times). In order to assess the bioactivity of the coating, simulated body fluid was used. The main results of the coated sample bioactivity demonstrated that the nanostructured hardystonite coating could amend the in vitro SS bioactivity. Therefore, SS coated with nanostructured hardystonite may be a promising candidate to be applied as bioactive hard tissue implants.Inspec keywords: bioceramics, stainless steel, X‐ray diffraction, corrosion protective coatings, X‐ray chemical analysis, sol‐gel processing, calcium compounds, current density, nanofabrication, zinc compounds, scanning electron microscopy, corrosion resistance, calcination, crystal microstructure, nanostructured materials, prosthetics, nanomedicine, electrophoretic coatings, electrophoretic coating techniquesOther keywords: X‐ray diffraction analysis, electrophoretic method, XRD analysis, phase characterisation, microstructural characterisations, morphological characterisations, energy‐dispersive X‐ray spectroscopy, coated sample bioactivity, nanostructured hardystonite coating, zinc nitrate hexahydrate, sol–gel method, 316L stainless steel, tetraethyl orthosilicate, calcium nitrate tetrahydrate, suspension solvent, deposition procedure, scanning electron microscopy, chemical composition, corrosion resistance, corrosion current density, bioactive hard tissue implants, temperature 1300.0 degC, voltage 50.0 V, time 5.0 min, temperature 60 degC to 120 degC, Ca₂ ZnSi₂ O₇      

Study of adhesion of carbon nitride thin films on medical alloy substrates

The adhesion improvement of biocompatible thin films on medical metal alloy substrates commonly used for joint replacement implants is studied. Diamond-like carbon (DLC) and carbon nitride (CN) thin films are, because of their unique properties such as high hardness, wear resistance and low friction coefficient, candidates for coating of medical implants. However, poor adhesion on substrates with high thermal expansion coefficient limits their application. We deposited CN films by pulsed DC discharge vacuum sputtering of graphite target on CoCrMo and Ti6Al4V substrates. Surface nitridation of the substrate, changing the deposition parameters and use of interlayer led to improved adhesion properties of the films. Argon and nitrogen gas flow, thickness of the film and frequency of the deposition pulses had significant influence on the adhesion to the substrate. Properties of deposited films were analyzed using Scanning Electron Microscopy, Raman spectroscopy and tribology tests.     

Hydrogen induced microstructural variation in diamond and diamond like carbon thin films

Hydrogen plays a crucial role in the growth of micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films grown by plasma assisted chemical vapour deposition (PACVD) processes. It selectively etches graphite phase and helps in stabilizing the diamond phase. The presence of various hydrocarbon species in the plasma and their reaction with atomic, excited or molecular hydrogen on the substrate surface decide the mechanism of diamond nucleation and growth. Several mechanisms have been proposed but the process is still not well understood. Control of hydrogen and other deposition parameters in the PACVD process leads to deposition of yet another class of materials called diamond like carbon. By varying the concentration of hydrogen it is possible to produce purely amorphous carbon films on the one hand and amorphous hydrogenated carbon films (with as high as 60% hydrogen) on the other. Very hard, optically transparent and electrically insulating films characterize the diamond like behaviour. The proportion of hydrogen and its bonding with carbon or hydrogen in the film can be varied to obtain very hard to very soft films which could be optically transparent or opaque. The microstructure of these films have been investigated by a large number of techniques. The results show interesting situations. This paper reviews the work on the role of hydrogen on the growth, structure and properties of MCD and DLC thin films.     

In-situ investigation on the deformation and damage behaviour of diamond-like carbon coated thin films under uniaxial loading

In the present work, the failure behaviour of diamond-like carbon (DLC) coatings on thin steel substrate under uniaxial tensile loading is analyzed in-situ in scanning electron microscopy as well as ex-situ using focused ion beam cross section and transmission electron microscopy. Aim of the work is to find correlations between the failure behaviour of the coating system, the adhesion and the stress-strain behaviour of a DLC coating system under tensile loadings conditions. Therefore thin amorphous DLC films were coated onto thin stainless steel foils using a plasma assisted chemical vapour deposition technique. It is found from the in-situ investigations that at increasing strains cracks were formed in the coating, with decreasing spacing at higher strains. By comparing uncoated steels foils with coated systems the stress-strain behaviour of a DLC coating was determined. The DLC coating, although already strongly cracked, bears loads up to a total strain of 15%. Cross section analyses with a focused ion beam and microscopy techniques supported these investigations. During straining the formation of two deformation bands adjacent to the Cr adhesion layer was observed. This deformation bands also indicate a high interfacial adhesion.     

Electrochemical performance of diamond-like carbon thin films

Diamond-like carbon (DLC) thin films used in this study were intended for their electrochemical properties. The DLC films were deposited by a filtered cathodic vacuum arc (FCVA) process on p-type silicon (100) substrates biased at different pulse voltages (0-2000 V). The chemical bonding structures of the DLC films were characterized with micro-Raman spectroscopy and the electrochemical properties were evaluated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The DLC films showed high impedance, high polarization resistance and high breakdown potential in a 0.5 M H₂SO₄ aqueous solution, which were attributed to the high sp³ content and uniformity of the films. The excellent chemical inertness of the DLC films made them promising corrosion resistant coating materials.     

Dissolution effect and cytotoxicity of diamond-like carbon coatings on orthodontic archwires

Nickel–titanium (NiTi) has been used for implants in orthodontics due to the unique properties such as shape memory effect and superelasticity. However, NiTi alloys are eroded in the oral cavity because they are immersed by saliva with enzymolysis. Their reactions lead corrosion and nickel release into the body. The higher concentrations of Ni release may generate harmful reactions. Ni release causes allergenic, toxic and carcinogenic reactions. It is well known that diamond-like carbon (DLC) films have excellent properties, such as extreme hardness, low friction coefficients, high wear resistance. In addition, DLC film has many other superior properties as a protective coating for biomedical applications such as biocompatibility and chemical inertness. Therefore, DLC film has received enormous attention as a biocompatible coating. In this study, DLC film coated NiTi orthodontic archwires to protect Ni release into the oral cavity. Each wire was immersed in physiological saline at the temperature 37 °C for 6 months. The release concentration of Ni ions was detected using microwave induced plasma mass spectrometry (MIP-MS) with the resolution of ppb level. The toxic effect of Ni release was studied the cell growth using squamous carcinoma cells. These cells were seeded in 24 well culture plates and materials were immersed in each well directly. The concentration of Ni ions in the solutions had been reduced one-sixth by DLC films when compared with non-coated wire. This study indicated that DLC films have the protective effect of the diffusion and the non-cytotoxicity in corrosive environment.     

TiO2 /chondroitin‐4‐sulphate nanocomposite coating on Ti–6Al–4V for implants and prostheses applications

Nano‐titania, chondroitin‐4‐sulphate, and titania/chondroitin‐4‐sulphate nanocomposite were separately deposited on Ti–6Al–4V alloys by repetitive spin coating. Surface characterisation techniques were used to find out the crystalline nature, chemical bonding, surface homogeneity, and elemental composition. Biological studies of nanocomposite‐coated alloys revealed the formation of stable hydroxyapatite (Ca/P = 1.678), superior corrosion resistance, and ∼12 mm zone of inhibition against Staphylococcus sp. However, the cell line studies revealed the better response on polymer‐coated alloy than the uncoated and composite‐coated alloy. It has been found that the nanocomposite coating can synergistically increase the thickness of the pre‐existing passive layer and thereby improve the corrosion resistance of Ti–6Al–4V implant in simulated body fluid. The nanocomposite coatings improved the corrosion resistance of the bare Ti–6Al–4V implant specimens by decreasing the i _corr. The formation of hydroxyapatite on nanocomposite‐coated alloy may have ability to inhibit the release of toxic substance to the adjacent tissues. In addition, the in vitro cell line study confers that the nanocomposite‐coated Ti–6Al–4V induces cell attachment and proliferation, and it eventually help to new bone cell formation than the uncoated one. Overall, this nanocomposite coating can be applied in orthopedic applications for effective biomimic bone regeneration.Inspec keywords: titanium compounds, nanocomposites, titanium alloys, aluminium alloys, vanadium alloys, nanomedicine, biomedical materials, prosthetics, X‐ray diffraction, Fourier transform spectra, infrared spectra, scanning electron microscopy, fluorescence, corrosion resistance, polymer films, calcium compounds, cellular biophysics, boneOther keywords: chondroitin‐4‐sulphate nanocomposite coating, implants, prostheses, nano‐titania, repetitive spin coating, surface characterisation, X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray fluorescence, TiAlV, TiO₂ , effective biomimic bone regeneration, orthopaedic applications, bone cell formation, osteoblast cells, cell proliferation, cell attachment, simulated body fluid solution, composite‐coated alloy, polymer‐coated alloy, Staphylococcus sp, corrosion resistance, hydroxyapatite, elemental composition, surface homogeneity, chemical bonding, crystalline nature     

镁合金表面类金刚石膜的研究进展

类金刚石碳(DLC)膜具有高硬度、低摩擦系数、强化学惰性及生物相容性好等优异性能,镁合金表面制备DLC膜可极大地改善基体的使用性能。综述了采用不同制备技术在镁基体表面获得的多种DLC膜系的抗磨损及耐腐蚀性能,并展望了DLC膜表面改性镁合金的医用前景,指出镁合金表面制备DLC膜是其表面改性技术中具有前景的一个研究方向。     

High thermal stability and low power dissipation PCM with nanoscale oxygen‐doped SS thin film

To improve thermal stability and reduce power dissipation of phase‐change memory (PCM), the oxygen‐doped Sn₁₅ Sb₈₅ (SS) thin film is proposed by magnetron sputtering in this study. Comparing to undoped Sn15Sb85(SS), the oxygen‐doped‐SS thin film has superior thermal stability and better data retention. Meanwhile, the electrical conductivity of crystallisation oxygen‐doped‐SS thin film is also lower than that of SS, which means its less power consuming in PCM. The electrical conductivity ratio between amorphous and crystalline states for oxygen‐doped SS reaches up to two orders of magnitude. After oxygen doping, the root‐mean‐square surface roughness from amorphous (0.29 nm) to crystalline (0.46 nm) state for oxygen‐doped‐SS thin films becomes smaller. The switching time of amorphisation process for the oxygen‐doped‐SS thin film (∼2.07 ns) is shorter than Ge₂ Sb₂ Te₅ (GST) (∼3.05 ns). X‐ray diffractometer is recorded to investigate the change of crystalline structure. Thus, the authors infer that oxygen‐doped SS is a promising phase‐change thin film for PCM.Inspec keywords: sputter deposition, antimony compounds, X‐ray diffraction, phase change memories, thin films, surface roughness, doping, electrical conductivity, amorphisation, crystallisation, thermal stability, amorphous state, crystal structure, nanostructured materials, nanofabrication, oxygenOther keywords: oxygen doping, low power dissipation, high thermal stability, phase‐change memory, magnetron sputtering, nanoscale oxygen‐doped Sn15Sb85 thin film, electrical conductivity, crystallisation, crystalline state, amorphous state, root‐mean‐square surface roughness, amorphisation process, X‐ray diffractometry, crystalline structure, Sn₁₅ Sb₈₅      

In‐situ fabrication of zirconium–titanium nano‐composite and its coating on Ti‐6Al‐4V for biomedical applications

In this study, nanocomposite powder consisting of zirconia and titania (Zr–Ti) have been synthesised by sol–gel method, with the aim of protecting Ti‐6Al‐4V surface. A simple and low cost electrophoretic deposition (EPD) technique has been employed for coating the nanocomposite material on Ti‐6Al‐4V. The prepared nanocomposite powder was characterised for its functional groups, phase purity, surface topography by Fourier transform infrared spectroscopy, powder X‐ray diffraction and scanning electron microscopy. Further, the biocompatibility nature of the composite powder was studied by [3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyltetrazolium bromide] colorimetric assay and fluorescence analysis with MG63 osteoblast cell lines. The electrochemical behaviour of composite coating was investigated by potentiodynamic polarization and electrochemical impedance method. The results obtained from the electrochemical techniques indicate more corrosion resistance behaviour with increase of R _ct value with the corresponding decrease in R _dl values. From the above findings, the composite coating acts as a barrier layer against corrosion by preventing the leaching of metal ions from a dense and defect free coating. A scratch test analyser was used to assess the integrity of the coating; the lower traction force value of composite coating with increase in load has confirmed the presence of thick adherent layer on the substrate.Inspec keywords: zirconium compounds, titanium compounds, titanium alloys, aluminium alloys, vanadium alloys, nanofabrication, nanocomposites, nanoparticles, sol‐gel processing, electrophoretic coating techniques, surface topography, Fourier transform infrared spectra, X‐ray diffraction, scanning electron microscopy, X‐ray chemical analysis, fluorescence, cellular biophysics, biomedical materials, electrochemical impedance spectroscopy, corrosion resistance, corrosion protection, corrosion protective coatings, adhesionOther keywords: in‐situ fabrication, zirconium‐titanium nanocomposite powder, biomedical applications, zirconia, titania, sol‐gel method, electrophoretic deposition, EPD, functional groups, phase purity, surface topography, Fourier transform infrared spectroscopy, powder X‐ray diffraction, scanning electron microscopy, energy dispersive X‐ray analysis, biocompatibility, 3‐(4, 5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide colorimetric assay, acridine range fluorescence analysis, MG63 osteoblast cell lines, electrochemical behaviour, composite coating, potentiodynamic polarization, electrochemical impedance spectroscopy, corrosion resistance, barrier layer, leaching, defect free coating layer, scratch test analysis, adherent layer, TiAlV‐ZrO₂ ‐TiO₂      

Investigation of graphene‐on‐metal substrates for SPR‐based sensor using finite‐difference time domain

In this study, the authors investigated the effects of a single layer graphene as a coating layer on top of metal thin films such as silver, gold, aluminum and copper using finite‐difference time domain method. To enhance the resolution of surface plasmon resonance (SPR) sensor, it is necessary to increase the SPR reflectivity and decrease the full‐width‐half maximum (FWHM) of the SPR curve so that there is minimum uncertainty in the determination of the resonance dip. Numerical data was verified with analytical and experimental data where all the data were in good agreement with resonance angle differing in <10% due to noise present in components such as humidity and temperature. In further analysis, reflectivity and FWHM were compared among four types of metal with various thin film thicknesses where graphene was applied on top of the metal layers, and data was compared against pure conventional metal thin films. A 60 nm‐thick Au thin film results in higher performance with reflectivity of 92.4% and FWHM of 0.88° whereas single layer graphene‐on‐60 nm‐thick Au gave reflectivity of 91.7% and FWHM of 1.32°. However, a graphene‐on‐40 nm‐thick Ag also gave good performance with narrower FWHM of 0.88° and reflection spectra of 89.2%.Inspec keywords: graphene, surface plasmon resonance, finite difference time‐domain analysis, reflectivity, metallic thin films, silver, gold, aluminium, copper, chemical sensors, biological techniquesOther keywords: graphene‐on‐metal substrates, SPR‐based sensor, finite‐difference time domain, metal thin films, surface plasmon resonance sensor, SPR curve, resonance angles, reflectivity, C, Ag, Au, Al, Cu     

Investigation into the antibacterial property and bacterial adhesion of diamond-like carbon films

Diamond-like carbon films have unique properties for biological and medical applications due to their excellent biocompatibility, chemical inertness, and superior mechanical properties. In order to attend biomedical applications, there is an increasing interest in developing antibacterial coatings. In this paper, we investigated the bactericidal properties of diamond-like carbon films produced using plasma enhanced chemical vapor deposition. The films were deposited over 316L stainless steel substrates using a pulsed directly current discharge of methane gas. Diamond-like carbon structural quality was evaluated using Raman scattering spectroscopy. The bacterial adhesion and bactericidal activity of the coating was evaluated against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Salmonella typhimurium ATCC 14028 and Staphylococcus aureus ATCC 25923. These tests show diamond-like carbon bactericidal activity ranged between 25 and 55%, depending on the kind of bacteria. The bacterial adhesion on diamond-like carbon surface was influenced by its structure, chemical bonds and hydrogen content. The low surface roughness did not have decisive effect on its antibacterial performance.     

Design and fabrication of drug‐eluting polymeric thin films for applications in ophthalmology

To study the development, characterisation, and drug release of one‐ and two‐layered thin films based on organic polymers [poly(D,L‐lactide‐co ‐glycolide) lactide:glycolide (65:35), poly(D,L‐lactide‐co ‐glycolide) lactide:glycolide (75:25), and polycaprolactone] and dexamethasone. To examine their applicability for intraocular lenses (IOLs) and function in intraocular drug delivery systems. Four series of thin films, single and double‐layer, were prepared by the spin‐coating method on a silicon substrate. The films were studied using atomic force microscopy and spectroscopic ellipsometry. The release rate of dexamethasone was studied for a period of ten weeks. Series A and C demonstrated the formation of large dexamethasone aggregates. The monolayer films of series C and D formed pores, in agreement with previous findings. The spectroscopic ellipsometry study demonstrated that the samples were transparent. The drug release study demonstrated that dexamethasone was released during the first 6 weeks at a desirable rate. The films exhibited properties suitable for use in intraocular drug delivery systems. The single‐layer thin films demonstrated a sufficient encapsulation of dexamethasone and appropriate release of the therapeutic substance. Further studies are necessary to investigate the possibility of developing the films directly on the surface of the IOL.Inspec keywords: eye, ellipsometry, spin coating, biomedical materials, polymer films, encapsulation, atomic force microscopy, drug delivery systems, aggregation, drugs, monolayers, ophthalmic lenses, polymer blendsOther keywords: IOL, intraocular drug delivery systems, spin‐coating method, atomic force microscopy, dexamethasone aggregates, monolayer films, organic polymers, spectroscopic ellipsometry, drug release, drug‐eluting polymeric thin films, ophthalmology, one‐layered thin films, two‐layered thin films, poly(D,L‐lactide‐co‐glycolide), polycaprolactone, intraocular lenses, dexamethasone release rate, dexamethasone encapsulation, time 6.0 week, Si     

常温生长类金刚石薄膜的实验研究

利用射频等离子体增强化学气相沉积(RFPECVD)工艺在常温下实现在不锈钢、硅片、玻璃等基底上大面积沉积类金刚石(DLC)膜.薄膜表面光滑致密,与衬底的结合力较高.用Raman,FTIR,SEM,EDX研究了薄膜的形貌、结构与组分.用栓-盘摩擦磨损试验机测试了薄膜的摩擦系数.通过优化沉积参数,所沉积的DLC膜在与100Cr6钢球对磨时摩擦系数低于0.01.在摩擦过程中DLC膜的磨损机制借助SEM进行了研究.     

Electrophoretic deposition of hydroxyapatite‐shrimp crusts nanocomposite thin films for bone implant studies

Hydroxyapatite‐shrimp crusts nanocomposite thin films were deposited on titanium substrates by electrophoretic technique, under different preparation conditions, for bone implant applications. Fourier transform infrared spectrometer, atomic force microscope, X‐ray diffraction (XRD), optical microscope, and scanning electron microscope were employed to characterise the synthesised films. Vickers’ micro‐hardness measurements revealed a value of 502 HV for the hydroxyapatite films and 314.55 HV for the nanocomposite films. XRD results confirmed the polycrystalline nature of the hydroxyapatite and hydroxyapatite‐shrimp nanocomposite films. The in‐vitro bioactivity test of the synthesised films in simulated body fluid showed very low dissolution rate. Antibacterial activity of synthesised films was investigated against E. coli bacteria.Inspec keywords: electrophoretic coating techniques, thin films, nanocomposites, antibacterial activity, bone, prosthetics, nanomedicine, calcium compounds, bioceramics, nanofabrication, Fourier transform infrared spectra, atomic force microscopy, X‐ray diffraction, optical microscopy, scanning electron microscopy, Vickers hardness, microhardness, microorganisms, dissolvingOther keywords: Ti, Ca₁₀ (PO₄)₆ (OH)₂ , E. coli bacteria, antibacterial activity, dissolution rate, simulated body fluid, in‐vitro bioactivity test, polycrystalline nature, Vickers microhardness measurements, XRD, scanning electron microscopy, optical microscopy, X‐ray diffraction, atomic force microscopy, Fourier transform infrared spectrometer, bone implant applications, titanium substrates, hydroxyapatite‐shrimp crust nanocomposite thin films, electrophoretic deposition     

Surface adsorption and wetting properties of amorphous diamond-like carbon thin films for biomedical applications

Diamond-like carbon (DLC) thin films have unique properties for biological and medical applications due to their excellent bio-compatibility, chemical inertness, and superior mechanical properties. It is important to understand the surface properties of DLC thin films for these applications. In this work, we showed that after DLC deposition, NiTi surfaces became much smoother by choosing suitable deposition conditions. Adsorption and wetting properties of DLC films were studied. The adsorption properties of DLC films were unusual in that a hysteresis was found in the adsorption/desorption isotherms, which cannot be interpreted using the conventional theory of capillary condensation in pores. The model proposed in this work for this unusual hysteresis characteristic is that the hysteresis results from the non-wetting property of DLC surfaces in the nano-scale. The nano-sized droplets formed on the DLC surfaces may require significantly higher energy to evaporate than the formation energy. Argon plasma treatment resulted in a small decrease of the contact angles. After oxygen plasma treatment, the wetting contact angles reduced significantly due to the increase of carbon-oxygen sites on the surfaces, suggesting that the low concentration of carbon-oxygen sites on the surfaces of DLC films contributed to the adsorption hysteresis observed in this work.     

Vibrational and AFM studies of adsorption of glycine on DLC and silicon-doped DLC

A better understanding of protein adsorption onto surfaces of materials is required to control biocompatibility and bioactivity. Diamond-like carbon (DLC) is known to have excellent biocompatibility. Various samples of a-C:H and silicon-doped a-C:H thin films (Si-DLC) were deposited onto silicon substrates using plasma-enhanced chemical vapour deposition (PECVD). Subsequently, the adsorption of the simplest amino acid glycine onto the surfaces of the thin films was investigated to elucidate the mechanisms involved in protein adhesion. The physicochemical characteristics of the surfaces, before and after adsorption of glycine, were investigated using Raman spectroscopy and atomic force microscopy (AFM). The Raman study highlighted a slight decrease in the I _D/I _G ratio with increasing the silicon dopant levels. Following exposure to glycine solutions, the presence of bands at ~1735 and ~1200 cm⁻¹ indicates that the adsorption of glycine onto the surfaces has taken place. Glycine was bound to the surfaces via both deprotonated carboxyl and protonated amino groups whilst, as the silicon content in the DLC film increased the adsorption of glycine decreased. AFM analysis showed that the surface roughness increased following exposure to glycine. These results show that at low silicon doping the adsorption of the amino acid was enhanced whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore, doping of DLC may provide an approach to control the protein adsorption.