ICMCTF2011 Session DP: Symposium D Poster Session

Due to carbon nanotubes (CNTs) unique properties and potential applications in a variety of biomedical and biological systems and devices, significant progress has been made in the effort to overcome some of the fundamental and technical barriers toward bioapplications. Recently, the investigation of CNTs in biomedical applications has primarily focused on preventing nonspecific protein adsorption and identifying particular proteins by surface modification and promoting cell growth as a culture medium by utilizing their uniquely individual shapes and electrical properties. CNTs have no toxicity and maintain their intrinsic cytoimmunity function. Recently, however, tissue compatibility of CNTs need further improvement. There have been few studies of hemocompatibility for CNTs.

In considering tissue compatibility and hemocompatibility improvement of CNTs, nano-thick carbon coatings, such as diamond-like carbon (DLC) and carbon nitride (CN_x), appear to have an advantage because promising studies of DLC supporting its biomedical applications. As a comparable to DLC in structural as well as mechanical and tribiological properties and probable positive effect on biocompatibility due to the presence of nitrogeon, however, CN_x has not been paid attention to biocompatibility so far, especially for the hemocompatibility investigations. CN_x coated CNTs should be a [app:ds:potential] biocompatible material for use to improve biocompatibility of CNTs, which is not only due to its excllent properties such as high chemical inertness and wear resistence, but also due to its chemical composition containing only carbon, hydrogen and nitrogen, which is biocompatible.

In this work, CN_x with different N concentration were coated on CNTs by chemical vapor deposition (CVD). This study compared and investigated cell adhesion and hemocompatibility on CNTs with and without CN_x coating using contact angle test, cells adhesion testing, platelet adhesion testing, and hemolytic rate testing. The results showed that the fibroblasts exhibited much better spindle-shape or polygon morphology with round nucleus on CNT with CN_x coating than those on CNTs without CN_x coating. Cell numbers on CNTs with CN_x coating were continuous to increase with incubation time. No toxicity reaction can be observed during culture. Blood tests showed that hemolytic rate and number and adhesion rate of platelet of on CNT with CN_x coating were lower than MWCNT without CN_x coating. This result indicated CN_x coated on CNTs possessed good tissue and blood compatibility. We believe that CN_x coated on CNTs can improve biocompatibility of CNTs due to wettability increasing.

A method of producing superhydrophilic surfaces on titanium substrates via sandblasting and dip-coating with colloidal silica nanoparticles is presented. The surface exhibits a high level of hydrophilic stability, as it stays superhydrophilic for an excess of 40 days and through multiple wetting-dewetting cycles. The combination of microscale roughness from the sandblasting and nanoscale roughness from the silica particles results in a micro-nano binary structure, which greatly enhances the hydrophilicity of the titanium samples. Due to the simplicity and ease of implementation of this method, this surface is suitable for potential use in a variety of applications, such as prosthetic dentistry and other biomedical fields.

References

[1] Knudson CB, Knudson W, Hyaluronan-binding proteins in development, tissue homeostasis, and disease. Faseb Journal 1993; 7(13): 1233-1241.

[2] Toh WS, Lee EH, Guo XM, Chan JKY, Yeow CH, Choo AB, Cao T. Cartilage repair using hyaluronan hydrogel-encapsulated human embryonic stem cell-derived chondrogenic cells. Biomaterials 2010; 31(27): 6968-6980.

In this study, an ionic silver was uniformly incorporated into Silica framework by sol-gel process, which introduce controlled Al ions to play a significant role in overall Silica matrix. The interaction between [AlO₄]^- tetrahedral structure and Ag⁺ result in uniform Ag⁺ distribution by electrostatic force, and then Ag⁺ embedded Al-O-Si structure is revealed. The Ag⁺ embedded Al-O-Si structure is then annealing by O₂ atmosphere range from the temperature 600 to 900 ^oC. We utilized as-prepared Ag-embedded silica to hybrid with Polyethylene(PE), which show excellent antibacterial behavior by reason of having the minimum inhibition concentration(MIC) value 350 ug/l against E.coil as well as slowly release silver ions into ethanol and H₂O. The UV-visible spectrum illustrates to be colorless pattern when Ag⁺ embedded Al-O-Si structure mix with polyethylene. These consequences provide prospective development in biomaterial, which obviously demonstrate the outstanding superiority in homogeneity and lower reactive temperature.

Titanium alloys known for their excellent physical properties and biocompatibility has therefore been considered as ideal metals for orthopedics and dental implants. In our previous studies, we had developed an anatase (A) rich and rutile (R) rich titanium dioxide (TiO₂) coating, respectively, on β-Ti alloy surface by using micro-arc oxidation (MAO) technique. It is also noticeable that the R rich TiO₂ coating not only achieved better in-vitro biocompatibility but also in-vivo osteogenesis performance. However, microscopical aspect on the interaction between osteoblast and TiO₂ layer was lack. A focused ion beam (FIB) technique was used in this study for cross-sectional sampling of the osteoblast cell that grown on the TiO₂ layer, followed by using energy dispersive spectrometer (EDS) and transmission electron microscope (TEM) for investigating how the TiO₂ coating influence osteoblast cell growth.

Experimental results revealed that the osteoblast adhered more tenaciously and grew conformably with a larger extent on the R rich TiO₂ specimen than on A rich TiO₂ and raw β-Ti specimens. In addition, the number of adhered and proliferated cells on R rich TiO₂ specimen was visually greater than that on both A rich TiO₂ and raw β-Ti specimens. By observing EDX profile along FIB-cut cross-section, the nitrogen and sulfur elements (as the biological feature of osteoblast cell) were both detected in the cell body and interior space of TiO₂ layer. This supports the hypothesis that the osteoblast cell could well grow into porous structure of MAO-TiO₂ coatings. Moreover, the well-conformal growth of the osteoblast cell on R rich TiO₂ specimen rather than A rich and raw β-Ti alloy specimens confirms that the R rich TiO₂ coating formed by MAO technique can serve as a novel surface modification technique for β-Ti alloy implants for orthopedics and dental implant applications.

Polyetheretherketone (PEEK) resembling human cancellous bone in biomechanical performance has been extensively used for implant materials. However, its bio-inertness and hydrophobic surface properties provide poor osseointegration. A surface modification method using arc ion plating (AIP) technique is developed to produce highly osteoblast compatible titanium dioxide (TiO₂) coatings onto PEEK substrate in this study. The TiO₂ modified PEEK was implanted into the femurs of New Zealand white rabbits to evaluate its in vivo performance. The osseointegration response and shear strength of the bone/implant interface using histological observation and push-pull testing are carried out in this research..

The results showed that utilizing AIP technique can successfully prepare TiO₂ coatings onto bullet-type PEEK substrates, for use as implant materials. After a long implantation period (4 weeks, 8 weeks and 12 weeks) of animal experiments, no signs of inflammation were detected in any of the substrates. The formation of newly regenerated bone occurred more prominently in TiO₂ modified PEEK based on microstructure observation of bone/implant interface. In addition, the shear strength of the bone/implant interface increases with increasing implantation period, what’s more important is that the TiO₂ modified PEEK exhibited superior bone bonding performance than the bare PEEK. It is also noticeable that the rutile-rich TiO₂ coatings achieved better osseointegration than anatase-rich coatings. Therefore, the AIP-TiO₂ can be considered to serve as a novel surface modification method for spinal interbody fusion PEEK cages.

Application of thin films in the biomedical field represents an attractive challenge due to the multiple situations where they may improve or even functionalize implant surfaces. Implant failure is a huge problem, which involves repeated surgeries and consequently considerable economical resources, this failure can be attributed to a variety of factors including: excessive wear and wear debris, corrosion process of the implant, bacterial biofilm formation, etc….

The aim of the present work is to study the electrochemical behavior of silver doped TiCN thin films deposited by DC unbalanced reactive magnetron sputtering, on simulated biological fluids.

The obtained Ag-Ti(C,N) based coatings were characterized in terms of composition and structure as well as in terms of corrosion in two different electrolytes that simulated biological conditions: NaCl 0,89% and phosphate buffer saline (PBS). Both solutions are isotonic to the human body, but PBS also contains phosphates. The electrochemical response was evaluated using potentyodynamical and electrochemical impedance spectroscopy (EIS), the latter as a function of immersion time.

The results showed that the electrochemical response depends not only on the amount of silver incorporated, but also on the Ti-C-N phases present. Without silver, the TiCN films showed similar response than the stainless steel substrate. Silver incorporation up 14 at% gave better corrosion resistance, but above this value, the TiCN films decomposed into a two phase material, where amorphous carbon nitride was predominant and then the corrosion resistance was decreased. Similar behavior was observed when the EIS spectra were analyzed as a function of the immersion time. However, it is important to note that the film dissolution, liberating Ag ions might be beneficial to promote an antibacterial response that inhibit bacterial attachment on the surface. This was studied using two bacterial strains Candida Albicans and Staphilococus Epidermis and evaluating the percentage of growth inhibition on each surface.

Ag(Au)-TiCN coatings were deposited onto Stainless Steel 316L aiming at the evaluation of silver ionization on antibacterial activity and adhesion of the Staphylococcus epidermidis. Samples were prepared by DC unbalanced reactive dual magnetron sputtering using two targets, Ti and Ti+Ag in an Ar, C₂H₂, N₂ atmosphere. Silver pellets were placed on the erosion zone of the Ti target in order to obtain a silver content between 0 to 9 at. %. Additionally, with the purpose of accelerates silver ion release to enhance the antibacterial effect of the films, Au pellets were added to the Ti-Ag target. Compositional depth profiling of the coatings have been obtained by GDOES. Phase formation will be analysed by XRD. Samples were in previous contact with the media used to perform biofilm formation (Tryptic Soy Broth). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the content of silver ions in the TSB medium. Moreover the surface chemical and morphological modifications of the coatings were analyzed by XPS, ARXPS and HR-SEM. Adhesion was assessed by epifluorescence microscopy and Biofilm activity was determined by measuring the amount of formazan salts formed after the biofilm reaction with XTT and the amount of total biomass formed was determined after crystal violet staining.

Titanium dioxide (TiO₂) has received great attentions because of its high reactivity under UV light irradiation (λ＜380 nm). When TiO₂ is doped with silver, its photocatalytic and bacteriacidal activities can be extended and enhanced in the visible light [1]. Reactive magnetron sputtering and cosputtering techniques were used to prepare various silver containing titania samples, which include two different types, Ag/TiO₂ double layer and Ag-TiO₂/TiO₂ multilayer. The as-deposited and annealed samples were characterized for composition, structure, morphology and photocatalytic characteristics. The results indicate the photocatalytic performance of the Ag/TiO₂ double-layered films is not proportional to the amount of silver on the surface of titania due to shielding effect. In the other hand, the Ag-TiO₂/TiO₂ multilayers exhibit improved photocatalytic activities under visible light. The SEM observation of surface morphology of the annealed multilayers reveals a unique three-dimentional net-like nanocomposite structure, which largely increases the specific surface area of the sample for catalytic reaction [2]. Furthermore, silver nanoparticles are uniformly distributed in the nanostructure, which could decrease the probability of e^－/h⁺ recombination and enhance antibacterial effect [3]. The Ag-TiO₂/TiO₂ multilayers exhibit excellent photocatalytic and bacteriacidal activities in the visible light.

In this study, the corrosive behavior of the mild steel (control metal), Ti (Ti6Al4V) and CoCrMo alloy were studied as a function of immersion time. The electrolytes were, 2.4% NaCl solution, ringer solution and bovine calf serum (biologically simulated synovial fluid) and in a controlled environment such as temperature (37^oC) and dissolved oxygen level. The open circuit potential (OCP), Potentiodynamic curve, and Electrochemical Impedance Spectroscopy (EIS) was employed in characterizing the corrosive behavior. The EIS results were modeled using Z-view software. In this study, it is hypothesized that CoCrMo alloy exhibits inferior corrosion resistance in bovine calf serum (BCS) compared with protein-free solutions due to a change in corrosion kinetics.

Thick polycrystalline diamond layers are used in the biomedical applications mostly because of such properties as the highest thermal conductivity, remarkable biocompatibility, chemical resistance, good optical properties and high electrical breakdown voltage. Nowadays one of the most popular separation technique is the electrophoresis, which uses an electric field for the separation of charged particles. Biomolecules, such as DNA or proteins, migrate inside the microchannels (forced by the electric field) and are separated due to the differences in electrical charges and molecular masses. The microchannels are filled by a buffer. In this paper properties of a diamond electrophoretic chip manufactured by replica method using a Si mould are presented. Electrophoretic separations were performed in small microchannels (40 wide and 250µm depth) built-in diamond film. The designed microstructure of the mould was made with use of the 4" diameter and 3mm thick silicon wafer. Standard photolithography, with the single mask was used for the pattern transfer on the photoresist layer and chemical solutions were used to etch SiO₂/Al layers. Plasma etching (Bosch process) with high aspect ratio (depth-to-width) was used to produce ridges on Si to be converted to deep trenches in deposited diamond. The 0.5 mm thick polycrystalline diamond film was grown on the Si mould by MPCVD (Microwave Plasma Chemical Vapor Deposition) method. After diamond deposition the Si has been etched away to produce the diamond plate with channel system on the substrate side. Bio-samples of extremely small volumes were introduced from lateral cross-channels to the central micro-fluidic channel, where the electrophoresis takes place. Joule heating is a major problem during the conventional electrophoresis processes. Small size of the microchannels and application of material with good thermal properties made it possible to minimize this phenomenon. Moreover in further investigations due to very high thermal conductivity of diamond we will be able to apply higher electrical field and provide biomedical investigations faster. The buffer temperature characteristics and Raman spectroscopy temperature measurements inside the microchannels are the main subject of this paper.

Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. The TiAlPt_xN coatings can improve the corrosion and wear resistance of materials for biomedical applications. The tribocorrosion behavior of TiAlPt_xN coatings and TiAlPt_xN/TiAlPt_x multilayers immersed in a corrosive environment was investigated. The coatings were deposited on 316L stainless steel and Ti6Al4V alloys by magnetron sputtering. The period size of multilayers was 350 nm and the total thickness was 4.2 microns. The corrosion was studied using open circuit potential (OCP) measurements and potentiodynamic polarization techniques in a Ringer ´s solution. Tribocorrosion tests were performed using a reciprocating ball- on- flat geometry where the sliding contact is fully immersed in a Ringer ´s solution. The counterbody was a 10 mm diameter alumina ball. The loads used were from 1 to 5 N, the oscillating frequencies were 1 and 5 Hz. The potentiodynamic polarizations and OCP measurements were performed during, and after the sliding test. The composite microhardness, nanohardness and the scratch resistance were measured as function of the Pt content in the films. The structure and composition of multilayers were studied by means of XRD and XPS techniques respectively. The surface topography and worn surface were studied by means of optical microscopy and profilometry. The microhardness, scratch resistance and wear depend of the Pt content within the multilayers. The wear mechanism and synergy effect of the tribocorrosion tests are reported.

Micro Arc Oxidation (MAO) has been considered as a new technique to form ceramic coatings on Titanium alloys for tribocorrosion resistances. A number of studies have been carried out for using of micro arc oxidation (MAO) technology for depositing ceramic coatings on titanium alloys. However, very few have focused on the behaviour of tribocorrosion of the MAO process parameters. In this study, the Cp-Titanium was coated by using Micro arc oxidation technique with different frequencies parametres and tribocorrosion behavior of coatings studied using different electrochemical test techniques including open circuit potential (OCP) measurement and potentiodynamic polarization tests under sliding contact in 1 M NaCl solution. Potentiodynamic polarization measurements were conducted to determine the tribocorrosion resistance of the samples and Scanning electron microscopy (SEM) was employed in order to characterize corrosive-wear damage. The results showed that which frequency parameter was the most significant factor affecting on the coatings’s tribocorrosion resistance.