The environmental stability of boron-containing titanium alloys for biomedical applications

Musculoskeletal and craniofacial implants, and their interactions with the human body, are a very important area of medicine today. Aging populations and rapidly escalating health care costs make the study of implant-body interactions increasingly urgent. One of the major impediments to long-term durability of implant materials is the issue of aseptic loosening, i.e., inflammatory response against the prosthetic metal and metal debris produced by its corrosion. In this research summary, we discuss the corrosion behavior of a new class of boron-containing titanium alloys in physiologically relevant media. In addition, the suitability of these alloys from a mechanical perspective will also be discussed along with implications for alloy design.     

Plasma surface modification of titanium by TiB precipitation for biomedical applications

In order to improve the surface properties of titanium and expand its clinical application, many methods have been applied to modify its surface. In this work, properties of titanium were modified by boride microplasma surface alloying. Plasma surface alloying gives a wide range of layer thickness, which is controlled by the amount of the placed powder and process parameters. Formation of TiB phase precipitation was confirmed by XRD analysis. Additionally, the modified microstructure was observed by optical microscopy. The Vickers microhardness was significantly improved from 180 HV for original titanium substrate to 900 HV in obtained composite layer structure, with a smooth hardness reduction in the cross section profile. Strong heat penetration from microplasma melt-in technique led to substrate dissolution with formation of stable TiB phase dispersed in α-Ti matrix. The electrochemical treatment in phosphoric acid electrolyte resulted in developed surface formation, attractive for tissue fixing and growth. In vitro cytocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Lonza (CC-2538) were cultured on the disks of the materials and cell growth was examined. The results of the in vitro test suggest that TiB phase dispersed in α-Ti matrix displays good cytocompatibility, compared to that of microcrystalline titanium. Additionally, the SEM observation reveals a significant difference in morphological characteristics of the cells on developed and polished material, just after 1 day of cell culture. It can be concluded that, plasma alloying is an effective method to produce TiB phase dispersed in α-Ti matrix with high hardness, good cytocompatibility, which makes them potential candidates for biomedical applications.     

Mechanical properties and corrosion resistance of low rigidity quaternary titanium alloy for biomedical applications

Electrochemical corrosion of Ti-35Nb-5Ta-7Zr alloy fabricated by arc melting and heat treatment process was studied in 0.9% NaCl at (37±1) °C. Phase and microstructure of the fabricated alloy were investigated using X-ray diffractometer and scanning electron microscope. Mechanical properties such as yield strength and elastic modulus of the alloy were determined by tensile test. Potentiodynamic polarization technique and impedance spectroscopy were employed to study the corrosion behavior. The results of the study were compared with those obtained for Ti-6Al-4V commercial alloy. The result of the study supports feasibility of Ti-35Nb-5Ta-7Zr alloy for implant applications.     

Low energy helium ion texturization of titanium and relevance to biomedical applications

Helium irradiation of metals has long been studied in efforts to understand the damaging aspects associated with applications in fusion reactors and tritium storage. This work examines the possibility of using low energy helium ion bombardment as a method of producing a beneficial surface texturization to promote bone growth on orthopedic implants. Using 300 eV helium ions, two unique porous titanium surfaces were created when substrates were held at temperatures of roughly 450 °C and 600 °C. The surfaces were physically characterized by scanning electron microscopy (SEM) and scanning white light interferometry. A week long hFOB 1.19 cell culture was performed using an untreated titanium control to evaluate the suitability of these surfaces for orthopedic implants. Cell health and viability were evaluated by calcein AM live cell staining, MTT assay, and SEM. The results show that helium texturizations promote cellular activity and have no detrimental effect on cell health.     

Surface modification of titanium by pack cementation treatment using calcium phosphate powders for biomedical applications

The surface modification of commercially pure titanium by pack cementation treatment using hydroxyapatite (HAp) or tetracalcium phosphate (TTCP) powder was investigated for temperatures ranging from 773 K to 1073 K. An HAp phase was detected on the surface of the titanium substrates after pack cementation treatment at temperatures of 973 K and 1073 K. After treatment using HAp and TTCP powders, a reaction layer with small HAp particles and pores containing small HAp particles, respectively, was observed. Apatite crystallites with a network pattern formed on the pack-cementation-treated titanium substrates after the substrates were immersed in Kokubo solution for 43.2 ks; such rapid apatite formation suggests that pack cementation treatment improves the biocompatibility of titanium.     

Laser micromachining for biomedical applications

Laser micromachining is becoming a common method for fabrication of microstructured medical devices. Developments in pulsed laser technology have made it possible to achieve precision machining of sub-micrometer features with minimal damage to the surrounding material. Several aspects of laser micromachining, including machining methods, types of lasers used in micromachining, and laser-material interaction, are discussed in this article. Biomedical applications of laser micromachining are also reviewed. The ablation behavior of silicon was examined as a function of laser energy, aperture, and repetition rate. In vitro studies showed that microscale grooves on silicon substrates may be used to orient human aortic vascular smooth muscle cells. We anticipate that the use of laser micromachining for modifying medical and dental devices will become more significant over the coming years.     

Experimental and gas phase modeling of nanocrystalline diamond films grown on titanium alloys for biomedical applications

For biomedical applications, it is highly desirable to be able to deposit smooth adherent diamond films on various complex-shaped substrates using the hot filament chemical vapor deposition technique (HFCVD). The properties of these films are affected profoundly by process parameters such as filament temperature, gas composition, and pressure. In this study, we present an insight into the gas phase chemistry involved in HFCVD of smooth nanocrystalline diamond films using Ar/CH₄/H₂ precursor mixtures. Experimental results on the growth, surface morphology, and crystalline structure are also presented. It is evident that the addition of a noble gas such as argon has a considerable effect on the gas surface chemistry. Notably at high concentrations of inert gas dilution (>90 vol.% argon) there are significant changes in diamond crystallinity ranging from polycrystalline through microcrystalline, and at argon concentrations >98 vol.%, nanocrystalline facets are observed. Modeling of the gas phase chemistry showed that the relative concentrations of CH₃ and C₂H alter significantly in this region, and these in turn influence surface morphology and crystallinity of the deposited films.     

Bulk metallic glasses for biomedical applications

The selection criteria for biomaterials include the material’s properties and biocompatibility, and the ability to fabricate the desired shapes. Bulk metallic glasses (BMGs) are relative newcomers in the field of biomaterials but they exhibit an excellent combination of properties and processing capabilities desired for versatile implant applications. To further evaluate the suitability of BMGs for biomedical applications, we analyzed the biological responses they elicited in vitro and in vivo. The BMGs promoted cell adhesion and growth in vitro and induced improved foreign body responses in vivo suggesting their potential use as biomaterials. Because of the BMGs’ flexible chemistry, atomic structure, and surface topography, they offer a unique opportunity to fabricate complex implants and devices with a desirable biological response from a material with superior properties over currently used metallic biomaterials.     

Diamond-coated cutting tools for biomedical applications

Diamond coatings are attractive for cutting processes due to their high-hardness, low-friction coefficient; excellent wear resistance, and chemical inertness. The application of diamond coatings on cemented, tungsten carbide (WC-Co) burs has been the subject of much attention in recent years as a method to improve cutting performance and tool life. WC-Co burs containing 6% Co and 94% WC substrate, with an average grain size of 1–3 μm, were used in this study. To improve the adhesion between diamond and WC substrates, it is necessary to etch away the surface Co and prepare the surface for subsequent diamond growth. Hot filament chemical vapor deposition (HFCVD), with a modified vertical filament arrangement, has been used for the deposition of diamond films. Diamond film quality and purity has been characterized using scanning electron microscopy (SEM) and micro-Raman spectroscopy. The performance of diamond-coated WC-Co burs, uncoated WC-Co burs, and diamond-embedded (sintered) burs have been compared by drilling a series of holes into various materials such as human teeth, borosilicate glass, and acrylic teeth. Flank wear has been used to assess the wear rates of the burs when machining biomedical materials such as those just described. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appears on pp. 273–82 of the Proceedings.     

Fretting fatigue studies of titanium nitride-coated biomedical titanium alloys

Fretting fatigue is an adhesive wear mechanism caused by repetitive tangential micro-oscillation between two contacting materials pressed together under cyclic load. Bioimplants, such as hip joints and bone plates, are prone to undergo fretting fatigue failures during their service within the body. This article presents the fretting fatigue damage characterization of physical vapor deposition (PVD) TiN-coated biomedical titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) subjected to cyclic loads. The PVD TiN layer delayed the damage because of superior tribological properties compared with uncoated alloys. Delamination and abrasive wear damage of TiN at contact caused failure of the alloy. Friction coefficient curves of the PVD TiN-coated pair showed an irregular pattern caused by the influence of wear particulates and Ringer fluid at the contact.     

Stretchable diamond-like carbon microstructures for biomedical applications

Designing, fabricating, and evaluating stretchable electronics is a growing area of materials research. Electronic devices have traditionally been fabricated using rigid, inorganic substrates (e.g., silicon) with metallic components and interconnections. Conventional electronic devices may face limitations when placed in environments that are dominated by stretchable or three-dimensional structures, including those within the human body. This paper describes the use of pulsed laser deposition to create diamond-like carbon microstructures on polydimethylsiloxane. The viability of human epidermal keratinocyte cells on polydimethylsiloxane surfaces coated with arrays of diamond-like carbon islands was similar to that on unmodified polydimethylsiloxane surfaces, which are commonly used in medical devices. It is anticipated that stretchable electronic devices may be incorporated within novel medical devices and prostheses that interface with stretchable or three-dimensional structures in the human body.     

High-strength metastable beta-titanium alloys for biomedical applications

This investigation has shown that the strength of low-modulus metastable beta-titanium alloys can be increased by increasing their oxygen content and/or aging. Yield strength as high as 1,288 MPa along with reasonable ductility was obtained by aging Ti-35Nb-7Zr-5Ta-0.7O at 482°C for 8 h. Strengthening of these alloys is discussed in terms of ω-and α-phase precipitates. For more information, contact H.J. Rack, Clemson University, School of Materials Science and Engineering, Clemson, SC 29634-0907; (864) 656-5636; e-mail rackh@ces.clemson.edu.     

A comparative study of titanium nitrides, TiN, TiNbN and TiCN, as coatings for biomedical applications

A strategy used to reduce wear of the ultra high molecular weight polyethylene (UHMWPE) component of orthopedic joint implants has been to coat the metallic part with a hard ceramic layer. The advantage of this procedure is to reduce both wear and ion release of the metal while keeping a high mechanical resistance. In the present study, the performance of three titanium nitride coatings: TiN, TiNbN, and TiCN for biomedical applications was assessed in terms of their surface properties and cytotoxicity. The morphology, chemical composition, and wettability were determined through atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and contact angle measurement, respectively. The tribological behaviour of the coatings rubbing against UHMWPE in lubricated conditions was investigated using a pin-on-disk apparatus. Albumin adsorption on the three coatings was studied with a quartz crystal microbalance with dissipation (QCM-D) and AFM scratching. Cytotoxicity was determined both in direct or indirect contact of the cells with the coating materials. The results demonstrate that the three coatings have similar surface properties and are not cytotoxic. TiNbN seems to have the best tribological performance in the presence of albumin, although albumin adsorption is slightly higher on TiN.     

Military applications for β titanium alloys

Beta alloys are potentially useful for several types of nonaerospace military applications. The potential applications to be discussed in this article include armor, body armor, mortar barrels, and missile launch canisters. This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA.     

Polymer coatings for biomedical applications: a review

This review surveys some of the recent literature concerning the use of polymer coatings for a variety of biomedical applications. These have been grouped into six broad categories: orthopaedic materials, cardiovascular stents, antibacterial surfaces, drug delivery, tissue engineering and biosensors. These, to some extent overlapping, sections have been ordered such that the literature generally progresses from polymer coatings on metallic to non-metallic substrates. Polymer coatings can bestow a wide range of functionalities due to their various properties, such as antiwear characteristics, mechanical strength, corrosion protection, electrical conductivity, biocompatibility and surface chemistry. The review period is from 2011 to the present (mid-2013).     

Producing lower-cost titanium for automotive applications

Although titanium has attractive properties that can improve the performance and economy of automobiles, at its current cost, it cannot compete with steel in most applications for which it is suited. It is readily apparent that titanium cannot be considered a viable mass-market automotive materials alternative as long as it is produced with the Kroll process. A look at existing and new technologies (as well as some that have been found lacking) in terms of applicability toward high-volume, low-cost titanium production for automotive applications indicates other options. A.D. Hartman earned his B.S. in chemical engineering at the South Dakota School of Mines and Technology in 1983. He is currently a chemical engineer in the Thermal Treatment Technologies Division at the Albany Research Center, Department of Energy. S.J. Gerdemann earned his B.S. in engineering science at the University of Virginia in 1976. He is currently a chemical engineer in the Thermal Treatment Technologies Division at the Albany Research Center, Department of Energy. Mr. Gerdemann is a member of TMS. J.S. Hansen earned his B.S. in metallurgical engineering at Oregon State University in 1972. He is currently a metallurgist in the Thermal Treatment Technologies Division at the Albany Research Center, Department of Energy. For more information, contact P.C. Turner, Albany Research Center, Department of Energy, 1450 S.W. Queen Avenue, Albany, Oregon 97321; 541-967-5863; fax 541-967-5958; e-mail turner@alrc.doe.gov.     

High-velocity oxyfuel thermal spray coatings for biomedical applications

Plasma spraying is used to produce most commercially available bioceramic coatings for dental implants; however, these coatings still contain some inadequacies. Two types of coatings produced by the high- velocity oxyfuel (HVOF) combustion spray process using commercially available hydroxyapatite (HA) and fluorapatite (FA) powders sprayed onto titanium were characterized to determine whether this relatively new coating process can be applied to bioceramic coatings. Diffuse reflectance Fourier transform infrared (FTIR) spectroscopy, x- ray diffraction (XRD), and scanning electron microscopy (SEM) were used to characterize the composition, microstructure, and morphology of the coatings. The XRD and FTIR techniques revealed an apatitic structure for both HA and FA coatings. However, XRD patterns indicated some loss in crystallinity of the coatings due to the spraying process. Results from FTIR showed a loss in the intensity of the OH^∼ and F^∼ groups due to HVOF spraying; the phosphate groups, however, were still present. Analysis by SEM showed a coating morphology similar to that obtained with plasma spraying, with complete coverage of the titanium substrate. Interfacial SEM studies revealed an excellent coating-to-substrate apposition. These results indicate that with further optimization the HVOF thermal spray process may offer another method for producing bioceramic coatings.     

Laser transmission joint between PET and titanium for biomedical application

Laser transmission joint between biocompatible, dissimilar materials have the potential for application in biomedical and their encapsulation process. This process may involve photochemical reaction, and alter the chemical compositions of the interface and chemical bonds form at the interface. Understanding the laser joint at material interfaces is essential for the advancement in the laser joining application. This paper is devoted to laser transmission joint between 0.1 mm thick PET films and 0.1 mm thick Titanium. We have found processing conditions for successful joining of titanium with PET using near-infrared diode lasers. Laser joint samples were tested in microtester under tensile loading to determine joint strengths. The joint strength was found to be 65.46–90 MPa. The PET/titanium interfaces thus obtained were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) and microscopy techniques. The results give evidence for the formation of Ti–C chemical bonds in a sharp interfacial region between the two sides. These chemical bonds are believed to be responsible for the observed mechanical strength of the joints.     

汽车用铝合金开发近况

介绍了汽车车身用轻质材料铝合金的研究近况，包括材料选择和车体设计新概念等方面。为满足经济和环境保护等方面不断增长的要求，对乘用车在使用已成熟的和最新研究开发的铝合金方面的进展进行了讨论。介绍了一些改进的具有更高的强度和更好的成形性能的5系和6系铝合金，使用这些合金能减轻汽车质量和提高防撞性能。以铝合金在“多材料超轻汽车”概念中的应用到达显著的减重效果为例，介绍了多材料轻质设计方面的研究进展。