ICMCTF2017 Session DP: Symposium D Poster Session

In this study, a TNZT alloy composed of Ti-35Nb-7Zr-5Ta in at.% and pure niobium were comparatively tested for their ability to grow nano-scaffolds on the surface for biomedical applications such as implant devices. The TNZT alloy was made by vacuum arc melting; and then rolled into a plate where it was subsequently sectioned and cut. The TNZT and niobium samples were polished flat, ultrasonically cleaned, and underwent hydrothermal treatments to grow nano-scaffolds of oxides on the surface. The TNZT and niobium produced Nb₂O₅ nano-scaffolds from a hydrothermal reaction in varying alkaline solutions: KOH at 170°C and NaOH at 60°C. Oxide scaffolding was also created when samples were annealed in air at 900°C for 2 hours. The TNZT and niobium nano-scaffolds were characterized by scanning electron microscopy (SEM). The nano-scaffolds will be characterized by X-ray diffraction (XRD) and Raman spectroscopy and will be further examined in simulated body fluid to further assess their biocompatibility.

One of the main drawbacks observed from the usage of titanium alloys implants is premature failure due to excessive wear and corrosion. These often lead to a total revision arthroplasty and also may expose human body to noxious elements if they are present in the implant alloy composition. Recently, new deposition techniques and coating compositions have been emerged targeting higher mechanical, microstructural and tribocorrosion properties on the implant surfaces. Diamond-like carbon (DLC) appears as a considerable coating option in this case, since it has an amorphous structure chemically inert composed by two types of carbon hybridizations (sp² and sp³) that provides an extreme hardness, low friction coefficient, biocompatibility and still is a solid lubricant. The tribocorrosion behaviour of DLC films are influenced by the fraction between sp² and sp³ bonds contained in the coating microstructure. Nonetheless, not only the bonds fraction affects this behaviour, but also the adhesion between coating and substrate to avoid its detachment, which in turn is strongly related to the applied deposition technique. Moreover, carbide and nitride interlayers are often deposited over substrate to favoring the DLC coatings adhesion. Among the advanced DLC deposition techniques are the plasma immersion ion deposition (PIID) and the plasma enhanced magnetron sputtering (PEMS). Both are examples of the plasma enhancement during film vapor depositions that results in coatings with higher density and adhesion when compared to other conventional techniques. This work aims to investigate the tribocorrosion behaviour of DLC coatings with distinct carbide and nitride interlayers, obtained by PIID only and PEMS+PIID hybrid techniques, applied on Ti-6Al-4V alloy samples for biomedical applications. The tribocorrosion tests were performed under phosphate-buffered saline (PBS) solution on the DLC-coated samples and compared to a Ti-6Al-4V bare alloy sample. Besides tribocorrosion tests, it were performed X-ray diffraction (XRD) analysis, Raman spectroscopy, scanning electron microscopy (SEM), nanoindentation hardness and scratch tests to evaluate the microstructure, morphology, mechanical properties and adhesion of the DLC-coated samples. The tribocorrosion tests demonstrated that the applied deposition techniques and interlayers compositions affect not only the adhesion but also the main wear mechanism, which implies in significant wear rate disparities between the DLC-coated samples. Nevertheless, the results show that DLC coatings deposited by the plasma enhanced techniques could be promissory to improve tribocorrosion behaviour in Ti-6Al-4V alloy implants.

Advanced blood-contacting medical devices has been more intensive for reducing the mortality rate of cardiovascular diseases. Surface coating is one interesting method of improving the mechanical, physical and biocompatible properties of devices in direct contact with blood and tissue. Fluorine-incorporated hydrogenated amorphous carbon (a-C:H:F) has received much attention as a coating material because of outstanding blood compatible properties which suppress fatal failure of the devices. However, mechanical strength of a-C:H:F film is too low to apply for mechanical medical devices such as blood pump of ventricular assist device (VAD). Thus, fluorine-incorporated hydrogen-free amorphous carbon (a-C:F) films were newly synthesized with vacuum arc deposition method focused on both blood compatibility of a-C:H:F and excellent mechanical properties of hydrogen free tetrahedral amorphous carbon (ta-C). In this study, we evaluated the possible medical applications of new a-C:F films for frictional parts of blood pump in VAD.

The ta-C (control) and a-C:F films were deposited by filtered cathodic vacuum arc (FCVA) method using a graphite target and introducing C₃F₈ gas into the chamber. We synthesized these films by varying the pressure of C₃F₈ gas to control fluorine content in the films. The fluorine content of the film surfaces was measured by X-ray photoelectron spectroscopy. Carbon bonding structure was analyzed with Raman spectroscopy. Blood compatibility was evaluated by human platelets adsorption tests, and ball-on-disc tests were used to measure friction coefficient (f) for evaluating wear resistant properties. Finally, we applied a-C:F film on blood pump of ventricular assist device.

The fluorine content rate increased from 10 to 50 at.% with increase of C₃F₈ gas pressure. The shift of G peak position in the Raman spectra became lower with increase of fluorine content, and no peaks was identified at 50 at.% fluorine content as usual in a polymer-like film. The a-C:F films containing fluorine content reduced platelets adhesion than ta-C films. On the other hands, much fluorine doping in ta-C simultaneously degrade wear resistant ability. However, friction coefficient of a-C:F films with fluorine content of 10 and 30 at.% (f = 0.121, 0.138, respectively) were greater than or equal to ta-C (f = 0.138). We applied 10 at.% a-C:F on frictional parts of VAD, and consequently improved driving of VAD without frictional wear.

In conclusion, the fluorine-incorporated hydrogen-free amorphous carbon (a-C:F), which we newly developed by using FCVA method, is a promising candidate for frictional parts of blood-contacting medical devices.

The ankle joint consists of the tibia and fibula above, and the talus below. In the disabling conditions, total ankle replacement (TAR) is becoming an alternative to arthrodesis, i.e. fusion of the tibio-talar articulation, which implies long immobilization, loss of function, and a variable rate of success. This short comings of ankle fusion have led to the development of numerous ankle joint replacements. The conventional type of prosthesis is the three component prosthesis, have a free gliding core and give multi-axial motion, which designs the upper articulation allows for gliding and rotation and the lower articulation allows for flexion/extension. In spite of the increasing interest in TAR, the high failure rate associated with wear of the PE component that has related with their material property and surface roughness. The aim of this study was to verify the wear characteristics of total ankle joint prosthesis with their surface roughness.

The wear specimen of total ankle joint prosthesis was prepared with Ti-6Al-4V alloy and UHMWPE (ultra-high molecular weight polyethylene) for tibia-talus and bearing component, respectively. A wear test was carried out using a Force 5 (AMTI, Massachusetts, US) wear simulator which can be allowed to move in three axis to flexion-extension, internal-external axial rotation, as well as sinusoidal compressive load. All tests were performed following standard ISO 14243, wear rate was calculated with weight loss of UHMWPE bearing while the specimen has tested at certain cycles. The surface roughness by wear simulation cycles was measured using a SJ-411 surface roughness tester (Mitutoyo, Yokohama, Japan).

As based on the preliminary results, wear rate of UHMWPE bearing was 7.9 × 10^-6 mg/cycles. The surface roughness (Ra) of tibia-talus increased (0.05 to 0.1) with accumulation of simulation cycles while that of bearing component decreased (1.0 to 0.65).

Acknowledgement: This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number HI15C2149).

Keywords: Total Ankle Joint Prosthesis, Wear, Simulation, Surface Roughness, Biomaterials

Detection of compounds in liquids (such as sweat or saliva) and vapors (such as air in a workplace, a packaged food container, or the cockpit of a fighter jet) has broad reaching applications in industry, home, and battlefield. Analytical devices such as mass spectrometers or gas chromatographs can be used in these applications but they lack portability and the ability to operate continuously yet unobtrusively. Flexible sensor materials could be wearable or otherwise easily integrated into any of the environments suggested above. Mono- and few-layer TMDs are known to demonstrate extreme mechanical flexibility, accommodating up to 10% strain prior to rupture. In addition to convenient form factors afforded by their flexible nature, the high surface to volume ratio of ultrathin semiconducting materials allows detection of very low concentrations of adsorbed molecules via a measurable alteration of their electrical response (e.g., their current-voltage (IV) curve) as if they are “doped” by the presence of surface adsorbates. While the effects on adsorbate-surface relationships in graphene could be understood in context of decades of studies of p-based interactions dictating nanomaterial behavior, 2D TMD interactions are based on d-electron interactions and therefore respond much differently than carbon-based low-dimensional structures to adsorption events and other interactions with molecules. Non-covalent bonding on 2D TMD is only understood qualitatively. Measuring the response in materials with controlled densities of defects introducing localized metallic-like regions of exposed Mo plane-edge atoms and changing the 2D MoS₂ electronic band diagram systematically as predicted by simulations.will provide insight on charge transfer or redistribution in analyte-functional molecule-2D semiconductor interactions. We have demonstrated attachment of a binding peptide to a functional MoS₂ transistor, and observe a significant response in the I-V characteristic curve. Sensitivity to adsorbed molecules for semiconducting 2D TMDs such as MoS₂ is approximately two orders of magnitude higher than graphene based on the predicted minimum subthreshold swing (SS), defined as the inverse of the slope of a transistor IV curve in its steepest part (for a field effect transistor (FET), SS=d(V_gate-source)/d(I_drain). Smaller values of SS suggest higher sensitivity as a small change in surface potential gives rise to a significant change in current, thus enhancing sensitivity. For 2D MoS₂, the SS is around 60 mV/decade in contrast to 1000-5000 mV/decade minimum for graphene, suggesting >100 X higher sensitivity for TMD-based 2D sensors in comparison to graphene.

In this work we report the study of TiO₂-MgO composites as anticorrosive coatings on Mg substrates. Mg has been extensively studied in order to develop biodegradable implants, however, the fast degradation in the physiological fluid is its main disadvantage. Here, we propose the use of the biocompatible TiO2-MgO composite as a protective coating in order to modulate the corrosion resistance of Mg pieces. TiO₂-MgO composites were deposited on Mg substrates by the RF-sputtering technique, and the TiO₂/MgO ratio was changed through the sputtering power. XRD analysis showed that coatings with a high content of MgO present a cubic crystalline structure, while a decrease on the crystallinity was found as the TiO2 content is increased; finally, coatings with the highest content of TiO₂ are amorphous. XPS analysis showed the formation of Ti-O, Mg-O and Ti-Mg-O bonds; the rate between this bonds is related to the resistance against corrosion of the samples. Corrosion experiments were conducted by using the Hank´s solution as the corrosive media and Tafel curves were obtained by employing a potentiostat in the three electrode configuration. Values of corrosion current (i_corr) demonstrate that it is possible to improve the corrosion resistance of Mg by employing the TiO₂-MgO composite; even more, the TiO₂/MgO rate on the coatings permits to modulate the corrosion resistance, with the lowest resistance when the coating is only composed by MgO, and the highest resistance when only the TiO₂ is present.

This work is supported by PRODEP-SEP under project number UGTO-PTC-540.

Titanium and its alloys have been widely used for biomedical implant due to their desirable mechanical properties, corrosion resistance, and excellent biocompatibility. However, titanium and its alloys have an issue of their insufficient bioactivity. Recently, studies have shown that hydroxyapatite coated metal surface can improve both biocompatibility and bioactivity.

The objective of this work was to study nucleation and growth of bone-like apatite formation on Ti-6Al-4V in solution containing Mn, Mg, and Si ions after plasma electrolytic oxidation. Anodized alloys was prepared at 270V~300V voltages. And bone-like apatite formation was carried out in SBF solution for 1, 3, 5, and 7 days. The morphologies of PEO-treated Ti-6Al-4V alloy in containing Mn, Mg, and Si ions were examined by FE-SEM, EDS, and XRD (Supported by NRF: 2015H1C1A1035241 & NRF: No.2008-0062283 ; hcchoe@chosun.ac.kr).

Titanium and its alloys have been used in the fields of orthopedics and dentistry due to their abilities to exhibit high specific strength, high corrosion resistance, and chemical inertness particularly in biological circumstances. Despite these attractive properties, their passive films were somewhat bioinert in nature so that sufficient adhesion of bone cells to implant surface was delayed after surgical treatment. Recently, the Plasma electrolyte oxidation (PEO) of titanium metal has attracted a great deal of attention.

Silicon (Si) in particular has been found to be essential for normal bone and cartilage growth and development. Zinc (Zn) plays very important roles in bone formation and immune system regulation, and is also the most abundant trace element in bone. Manganese(Mn) is important in terms of protein synthesis, the manganese is insufficient, the generation of cartilage synthesis of the organic matrix is low is delayed, thickness and length decreased abnormal bone generation is performed. Si, Zn, and Mn has a beneficial effect on bone.

The objective of this work was research on i on r elease of Zn, Si, Mn-doped h ydroxyapatite f ilms f ormed on the Ti-6Al-4V a lloy by p lasma e lectrolytic o xidation. Anodized alloys was prepared at 270V~300V voltage in the solution containig Zn, Si, and Mn i ons. Ion release test was carried out using potentidynamic and AC impedance method in 0.9% NaCl solution. The surface characteristics of PEO treated Ti-6Al-4V alloy were investigated using XRD, FE-SEM, AFM and EDS(Supported by NRF: 2015H1C1A1035241 & NRF: No.2008-0062283 ; hcchoe@chosun.ac.kr [mailto:hcchoe@chosun.ac.kr] ).

CP-Ti and its alloys have over the past few decades become the premier choice as biocompatible dental and hip replacement implant materials. Although the Ti-6Al-4V alloy is an acceptable prosthetic biomaterial, recent studies indicated that the release and accumulation of Al and V ions could have harmful effects on the human body. In order to overcome these disadvantages of Ti-6Al-4V alloy, new β type Ti alloy made of non-toxic alloying elements such as Nb, Ta and Zr have been developed. Surface modification is generally essential to improve the chemical bonding between Ti implant and bone tissues. Thus, it has been shown that nano-scale porous as well as tubular oxide layers on titanium alloys can increase the bioactivity of an implant material. Also, it should be possible to control the nanotube size and morphology for biomedical implant use by controlling the applied voltage, alloying element, current density, anodization time and electrolyte. The aim of this study was surface modification of nanotube formed Ti-30Nb-xTa alloys with changes in anodization factors. The Ti-30Nb-xTa alloys with Ta contents of 0, 15 wt. % were melted by using a vacuum arc-melting furnace and, homogenized for 12h at 1000℃. The anodization was performed by changing of applied voltage from high to low (30 V to 10 V) and, from low to high (10 V to 30 V) for 1h. The electrolyte was composed of 1 M H₃PO₄ + 0.8 wt.% NaF. This study was evaluated the phase of Ti-30Nb-xTa alloys using an x-ray diffractometer (XRD), and the microstructure of the samples was investigated with field emission scanning electron microscopy (FE-SEM) and optical microscope (OM). For biocompatibility, fibroblast cell was cultured and contact angle was measured. (NRF: No.2008-0062283; hcchoe@chosun.ac.kr).

Particularly Silicon (Si) has been found to be essential for normal bone, cartilage growth and development. This hydroxyapatite, modified with the inclusion of small concentrations of silicon has been demonstrating to improve the osteoblast proliferation and the bone extracellular matrix production. Strontium-containing hydroxyapatite (Sr-HA) was designed as a filling material to improve the biocompatibility of bone cement. In vitro, the presence of strontium in the coating enhances osteoblast activity and differentiation, whereas it inhibits osteoclast production and proliferation.

The objective of this work was to study shapes of bone-like apatite formation on Sr and Si-doped hydroxyapatite surface of Ti-6Al-4V alloy after plasma electrolytic oxidation. Anodized alloys was prepared at 270V~300V voltages with various concentrations of Si and Sr ions. Bone-like apatite formation was carried out in SBF solution. The morphology of PEO, phase and composition of oxide surface of Ti-6Al-4V alloys were examined by FE-SEM, EDS, and XRD(Supported by NRF: 2015H1C1A1035241 & NRF: No.2008-0062283 ; hcchoe@chosun.ac.kr [mailto:hcchoe@chosun.ac.kr] ).

Most recently, to improve the biocompatibility, various processes that aim at coating an implant material with a bioactive nanoparticles such as synthetic hydroxyapatite have been proposed[1]. For this purpose, barrier and porous/tubular type of anodic oxide films could be formed by electrochemical anodization using a set of specific conditions including optimized potential, electrolyte composition, and temperature. Also, the chemical component of the electrolyte is essential in determining the type of morphology that is eventually formed, and the geometric morphology of TiO₂ oxide film is mutually important in direct contact with biological tissue in dental or surgical implants. In addition, the specific ions in the contact surface with the bone site plays a critical role in terms of adhesion and stability for long periods in the living body.

Despite magnesium has some advantages over the present biomaterials it has some handicaps for orthopedic applications, such as high corrosion rate, mechanical properties [1, 2]. To improve the corrosion resistance of magnesium a ceramic layer was produced on the Mg alloys by micro-arc oxidation (MAO) method. To provide a better corrosion resistance Ag ions added antibacterial HA nano particles were added to the electrolyte in the range of 1-15 g/lt. The coated alloys were characterized by using scanning electron microscopy and X-ray diffractometer. Also immersion tests, corrosion tests and anti-bacterial tests were done to compare the coatings.