Ultrananocrystalline Diamond Coatings Research Articles

A Biocompatible Ultrananocrystalline Diamond (UNCD) Coating for a New Generation of Dental Implants.

Implant therapy using osseointegratable titanium (Ti) dental implants has revolutionized clinical dental practice and has shown a high rate of success. However, because a metallic implant is in contact with body tissues and fluids in vivo, ions/particles can be released into the biological milieu as a result of corrosion or biotribocorrosion. Ultrananocrystalline diamond (UNCD) coatings possess a synergistic combination of mechanical, tribological, and chemical properties, which makes UNCD highly biocompatible. In addition, because the UNCD coating is made of carbon (C), a component of human DNA, cells, and molecules, it is potentially a highly biocompatible coating for medical implant devices. The aim of the present research was to evaluate tissue response to UNCD-coated titanium micro-implants using a murine model designed to evaluate biocompatibility. Non-coated (n = 10) and UNCD-coated (n = 10) orthodontic Ti micro-implants were placed in the hematopoietic bone marrow of the tibia of male Wistar rats. The animals were euthanized 30 days post implantation. The tibiae were resected, and ground histologic sections were obtained and stained with toluidine blue. Histologically, both groups showed lamellar bone tissue in contact with the implants (osseointegration). No inflammatory or multinucleated giant cells were observed. Histomorphometric evaluation showed no statistically significant differences in the percentage of BIC between groups (C: 53.40 ± 13% vs. UNCD: 58.82 ± 9%, p > 0.05). UNCD showed good biocompatibility properties. Although the percentage of BIC (osseointegration) was similar in UNCD-coated and control Ti micro-implants, the documented tribological properties of UNCD make it a superior implant coating material. Given the current surge in the use of nano-coatings, nanofilms, and nanostructured surfaces to enhance the biocompatibility of biomedical implants, the results of the present study contribute valuable data for the manufacture of UNCD coatings as a new generation of superior dental implants.

Influence of surface termination of ultrananocrystalline diamond films coated on titanium on response of human osteoblast cells: A proteome study

Successful osseointegration, i.e. the fully functional connection of patient's bone and artificial implant depends on the response of the cells to the direct contact with the surface of the implant. The surface properties of the implant which trigger cell responses leading to its integration into the surrounding bone can be tailored by surface modifications or coating with thin layers. One potential material for such applications is ultrananocrystalline diamond (UNCD). It combines the exceptional mechanical properties of diamond with good biocompatibility and possibility of coating as thin uniform films on different substrates of biological interest. In the current work we firstly deposited UNCD films on titanium-coated substrates and applied oxygen or ammonia plasma to modify their surface properties. The as-grown and modified UNCD exhibited relatively smooth surfaces with topography dominated by rounded features. The modifications induced oxygen- or amino-terminated surfaces with increased hydrophilicity. In addition, the UNCD coatings exhibited very low coefficient of friction when diamond was used as a counterpart. As-grown and modified UNCD samples were applied to study the responses of human osteoblast MG63 cells triggered by surfaces with various terminations assessed by proteomic analysis. The results revealed that the coating of Ti with UNCD as well as the plasma modifications resulting in O- or NH2-terminated UNCD induced upregulation of proteins specific for cytoskeleton, cell membrane, and extracellular matrix (ECM) involved in the cell-ECM-surface interactions. Proteins from each of these groups, namely, vimentin, cadherin and fibronectin were further studied immunocytochemically and the results confirmed their increased abundance leading to improved cell-to-surface adhesion and cell-to-cell interactions. These findings demonstrate the potential of implant coating with UNCD and its surface modifications for better osseointegration and bone formation.

Tribological performance and wear mechanism of smooth ultrananocrystalline diamond films

• HFCVD is used to synthesize UD-MCD, UD-UNCD, UD-MCD/UD-UNCD, BD-MCD, BD-UNCD, BD-MCD/BD-UNCD films on WC-Co substrates. • Growth mechanism of UNCD with high carbon concentration and low gas pressure in hydrogen-rich chemistry are illustrated. • Undoped and boron doped UNCD coatings are firstly applied on WC-Co micro drills to improve the surface smoothness. • Both boron doping and middle layer MCD contribute to the strong adhesive level of UD-MCD/UD-UNCD and BD-MCD/BD-UNCD. • The UD-MCD/UD-UNCD, BD-UNCD and BD-MCD/BD-UNCD coated PCB micro drills show superior cutting performances. 5G printed circuit boards (PCBs), composed of glass fiber, epoxy resin and ceramic, are a kind of difficult-to-machine material. The manufacture of massive high-quality micro holes on 5G PCBs raise high requirements on the tool life and machining precision of PCB micro drills. Chemical vapor deposition (CVD) diamond coatings can be used as effective protective films on PCB micro drills. The surface smoothness and coating-substrate adhesion of diamond coated micro drills are two important factors affecting the drilling performances. Different from previously reported microcrystalline diamond (MCD) or nanocrystalline diamond (NCD) coating types on cutting tools, undoped (UD-) and boron doped (BD-) ultrananocrystalline diamond (UNCD) coatings with higher surface smoothness are firstly applied on PCB micro drills to reduce the friction and cutting resistance and improve the cutting performances while machining PCBs. Moreover, different from the usual argon-rich gas atmosphere for UNCD synthesis, the synthesis mechanisms of UD-UNCD and BD-UNCD with hydrogen-rich atmosphere adopting HFCVD method are clarified. Sufficiently high renucleation rate of diamond crystallites, long mean free path of reactive precursor species and high removal rate of non-diamond carbon phases lead to the successful synthesis of UNCD films. UDMCD, UD-UNCD, UD-MCD/UD-UNCD, BD-MCD, BD-UNCD, and BD-MCD/BD-UNCD, were synthesized on PCB micro drills using HFCVD. The tribological performances and wear mechanisms of these different diamond coatings were studied systematically. The dominant wear mechanism causing tool wear and fracture of diamond coated micro drills in high-speed machining PCBs is abrasive wear. The degree of abrasive wear while machining PCBs are mainly determined by the surface smoothness, surface roughness and coefficient of friction of diamond coatings. The top layer UNCD with tiny grain size leads to the improvement of surface smoothness and tribological properties, which enhance the chip evacuation capacity and reduce the tool wear. Besides, both boron doping and middle layer MCD can contribute to the strong coating-substrate adhesion. Therefore, BD-MCD/BD-UNCD coated micro drill exhibits the best cutting performances while machining PCBs.

Novel Biocompatible Ultrananocrystalline Diamond Coating Technology for a New Generation of Medical Implants, Devices, and Scaffolds for Developmental Biology

A new biomaterial paradigm for a new generation of implantable medical devices, prostheses, and scaffolds for stem cells growth and differentiation for developmental biology is provided by a novel multifunctional/biocompatible/body fluid corrosion-resistant ultra-nanocrystalline diamond (UNCD) film developed and patented in recent years. The UNCD coating provides a unique combination of multi functionalities, including biocompatibility, bioinertnes to chemical attack by body fluids, and surface chemistry, based on Carbon (C) atoms (element of life), to enable a new generation of implantable medical devices, prostheses, and scaffolds for tissue engineering, to impact the quality of life of people. This review article includes the following topics: 1) Brief description of the synthesis and properties of UNCD films and comparison with other diamond film technologies. 2) Brief description of key medical devices and prostheses under development, based on UNCD coatings. 3) Demonstration of UNCD as an outstanding scaffold for growing stem cells and induces differentiation for developmental biology, to treat specific medical conditions.Topics discussed include: • UNCD-coated microchip (artificial retina) is implantable on the eye’s retina to restore partial vision to people. Who are blind by retinitis pigmentosa, produced by genetically induced degeneration of the retina photoreceptors (The Argus II device, developed by a team of researchers and doctors from universities, national laboratories and the second Sight was currently implanted commercially in the USA and Europe,and it was selected by TIME magazine as one of the top 25 inventions for 2013). • UNCD- coated intraocular device for the treatment of glaucoma (intraocular pressure associated optical neuropathy that could lead to blindness). • UNCD-coated metal dental implants with order of magnitudelonger life and superior performance than current implants. • UNCD- coated prostheses (hips, knees and other metal-basedimplants); • New generation of Li-ion batteries (LIBs) for defibrillator/ pacemakers, with ≥ 10 × longer life and safer than current LIBs. • Description of UNCD-based scaffolds

Ultrananocrystalline diamond coatings for the dental implant: electrochemical nature

Titanium (Ti) and its alloys are currently used as biomaterials for dental implants. However, titanium and its alloys suffer electrochemical corrosion in the oral environment. Ultrananocrystalline diamond (UNCD) coating is a promising coating material with exceptional biocompatibility, excellent osseointegration, high wear resistance and extreme resistance to chemical attack for producing a new generation of long-life dental implants. The main objective of this work was to investigate the basic electrochemical behavior of UNCD-coated samples of commercially pure titanium (Cp-Ti/Ti-2) and titanium alloy (Ti–6Al–4V/Ti-5) at three different pH conditions of artificial saliva. All titanium and titanium alloy samples of four groups were used: (a) control Ti-2, (b) UNCD-coated Ti-2, (c) control Ti-5 and (d) UNCD-coated Ti-5. For each group, electrochemical analysis was performed at pH 3, 6·5 and 9·0. In the electrochemical tests, the evolution of potential was higher in the UNCD-coated Ti-2 and UNCD-coated Ti-5 than in the uncoated samples. Potentiodynamic (Ecorr, Icorr) and impedance measurements also showed improvement in the electrochemical behavior of both UNCD-coated titanium samples for all three pH conditions. These preliminary findings indicate that UNCD coatings could be considered for the next generation of the dental implants, to improve their performance.

Evaluation of the Adhesion of Ultrananocrystalline Diamond Coatings on WC-Co Substrates

In order to improve the cutting performance and lifetime of WC-Co hard metal tools, the issues related to synthesis and adherence of micro- and nanocrystalline CVD diamond coatings on these tools has been frequently discussed in the literature. However, there are few studies focused on ultrananocrystalline diamond (UNCD) coatings. In this study, we report the results of the characterization of UNCD coatings with different thicknesses with the purpose of evaluating their adhesion to WC-9%Co substrates. The structure and morphology of the UNCD coatings as a function of their thicknesses were investigated by Raman spectroscopy, atomic force microscopy (AFM) and field emission gun scanning electron microscope (FEG-SEM) analysis. The UNCD coating-substrate adhesion was evaluated by means of indentation tests with a load of 1000N.

Influence of seeding pre-treatments on mechanical properties of ultrananocrystalline diamond films on silicon and Si3N4 substrates

Ultrananocrystalline diamond (UNCD) films on silicon and Si3N4 substrate were prepared by microwave plasma chemistry vapor deposition method using argon-rich CH4/H2/Ar plasmas. The influence of the nucleation density on the development of morphology of UNCD films and their mechanical properties has been investigated by varying pretreatments. Their morphology and topography have been characterized by scanning electron microscopy and surface profilometer. The influences of pretreatments on mechanical properties of the deposited UNCD films are investigated by using nano-indentation and nano-scratch tests. It was found that grain size, hardness, and elastic modulus are less dependent on nucleation density change, which is caused by different pre-treatments. Changes in grain size are more dependent on deposition temperature and plasma atmosphere. As compared to the nucleation density pretreated by the suspension of diamond (0.25μm) powder mixed with nano-diamond (3–5nm), nucleation density is obviously enhanced by pretreatments with W powder (0.25μm) or Ti powder (0.25μm) mixed with nano-diamond (3–5nm). It was also observed that there is no difference in nanohardness and elastic modulus with different substrates (Si and Si3N4 substrates). But the UNCD's adhesion on Si3N4 substrate is obviously higher than that on Si substrate. The determined hardness was about 54–58GPa for all samples under investigation, the elastic modulus 542–667GPa, and the elastic recovery 74–81%. The scratch tests proved a strong adhesion of the UNCD coatings and their protective effect on silicon substrates and Si3N4 substrates. Detailed experimental results and mechanisms for UNCD film deposition in argon-rich plasma are discussed.

In vitro and in vivo evaluation of ultrananocrystalline diamond as an encapsulation layer for implantable microchips

Thin ultrananocrystalline diamond (UNCD) films were evaluated for use as hermetic and bioinert encapsulating coatings for implantable microchips, where the reaction to UNCD in vitro and in vivo tissue was investigated. Leakage current tests showed that depositing UNCD coatings, which were conformally grown in (1% H2) Ar/CH4 plasma, on microchips rendered the surface electrochemically inactive, i.e. with a very low leakage current density (2.8×10−5Acm−2 at −1V and 1.9×10−3Acm−2 at ±5V) ex vivo. The impact of UNCD with different surface modifications on the growth and activation of macrophages was compared to that of standard-grade polystyrene. Macrophages attached to oxygen-terminated UNCD films down-regulated their production of cytokines and chemokines. Moreover, with UNCD-coated microchips, which were implanted subcutaneously into BALB/c mice for up to 3months, the tissue reaction and capsule formation was significantly decreased compared to the medical-grade titanium alloy Ti–6Al–4V and bare silicon. Additionally, the leakage current density, elicited by electrochemical activity, on silicon chips encapsulated in oxygen-terminated UNCD coatings remained at the low level of 2.5×10−3Acm−2 at 5V for up to 3months in vivo, which is half the level of those encapsulated in hydrogen-terminated UNCD coatings. Thus, controlling the surface properties of UNCDs makes it possible to manipulate the in vivo functionality and stability of implantable devices so as to reduce the host inflammatory response following implantation. These observations suggest that oxygen-terminated UNCDs are promising candidates for use as encapsulating coatings for implantable microelectronic devices.

Mechanical properties of ultrananocrystalline diamond films modified by hydrogen concentration in deposition atmosphere

Ultrananocrystalline diamond (UNCD) films on silicon were prepared by microwave plasma chemical vapor deposition method using argon-rich CH4/H2/Ar plasmas. The grains with different sizes were obtained by deposition in different atmosphere and the sizes of grain were measured after the deposition by X-ray diffraction (XRD). The influences of the grain size on the development of the morphology of ultrananocrystalline diamond (UNCD) films and their mechanical properties have been investigated by variation of hydrogen content from 5% to 20% in the deposition atmosphere. Their morphology and topography have been characterized by scanning electron microscopy (SEM) and surface profilometer. The influences of the hydrogen concentration on the mechanical properties of the deposited UNCD films are investigated by using nano-indentation and nano-scratch tests. It was found that the grain size, growth rate and surface roughness are increased with the increase of the hydrogen concentration. This changes the morphology of the films from granular to needle-like clusters. It can also be seen that the elastic modulus is increased with the addition of hydrogen; the hardness increased monotonically from 5% to 15% hydrogen, then decreased for 20% hydrogen with the maximum at 15% hydrogen; and the elastic recovery is 72–78%. Hardness and toughness are all decisive for protecting nature of the coatings. The scratch tests proved a strong adhesion of the UNCD coatings up to 45mN and their protective effect on silicon substrates. The hydrogen has significant influence on the mechanical properties. Detailed experimental results and failure mechanisms for UNCD film deposition in argon-rich plasma are discussed. The deposited highly smooth UNCD film is also expected to be applicable in medical implants, surface acoustic wave (SAW) devices and micro-electromechanical systems (MEMS).

Development of ultrananocrystalline diamond (UNCD) coatings for multipurpose mechanical pump seals

The reliability and performance of silicon carbide (SiC) shaft seals on multipurpose mechanical pumps are improved by applying a protective coating of ultrananocrystalline diamond (UNCD). UNCD exhibits extreme hardness (97 GPa), low friction (0.1 in air) and outstanding chemical resistance. Consequently, the application of UNCD coatings to multipurpose mechanical pump seals can reduce frictional energy losses and eliminate the downtime and hazardous emissions from seal failure and leakage. In this study, UNCD films were prepared by microwave plasma chemical vapor deposition utilizing an argon/methane gas mixture. Prior to coating, the SiC seals were subjected to mechanical polishing using different grades of micron-sized diamond powder to produce different starting surfaces with well-controlled surface roughnesses. Following this roughening process, the seals were seeded by mechanical abrasion with diamond nanopowder, and subsequently coated with UNCD. The coated seals were subjected to dynamic wear testing performed at 3600 RPM and 100 psi for up to 10 days during which the seals were periodically removed and inspected. The UNCD-coated seals were examined using Raman microanalysis, scanning electron microscopy, optical profilometry, and adhesion testing before and after the wear testing. These analyses revealed that delamination of the UNCD films was prevented when the initial SiC seal surface had an initial roughness >0.1 μm. In addition, the UNCD surfaces showed no measurable wear as compared to approximately 0.2 μm of wear for the untreated SiC surfaces.

Nanoporous ultrananocrystalline diamond membranes

Micro- and nanoporous membranes have a wide range of applications in many fields, including medical diagnostics, drug delivery, and hemodialysis. Ultrananocrystalline diamond coatings are becoming more and more significant in medical applications because of the highest degree of biocompatibility, unmatched by other materials. The pores ranging in diameter from 100 to 2000 nm have been fabricated in a 1-μm-thick ultrananocrystalline diamond film on silicon wafers using e-beam and optical lithography, reactive ion etching, and laser writing.

Structural and optical properties of ultrananocrystalline diamond / InGaAs/GaAs quantum dot structures

The combination of the unique properties of ultrananocrystalline diamond (UNCD) films and of semiconductor quantum dot (QD) structures could significantly improve the performance of different electronic and optoelectronic devices, where e.g. good thermal management and advanced mechanical parameters are required. In the current work quantum dot InGaAs/GaAs heterostructures have been grown by molecular beam epitaxy (MBE) with different densities between 1.6×1010cm−2 and 1.6×1011cm−2 controlled by the substrate temperature in the range between 490 and 515°C. These structures were overgrown with UNCD by microwave plasma chemical vapor deposition (MWCVD) using methane/nitrogen mixtures at 570°C. Scanning electron microscopy (SEM) reveals that without ultrasonic pretreatment the diamond nucleation density on QD structures is low and only separate islands of UNCD are deposited, while after pretreatment thin closed films are formed. From the cross-section SEM images a growth rate of ca. 3nm/min is estimated which is very close to that on silicon at the same deposition conditions. The UNCD coatings exhibit a morphology consisting of two types of structures as shown by atomic force microscopy (AFM). The first one includes nodules with diameters between 180 and 350nm varying with the density of the underlying QDs; the second is formed by a kind of granular substructure of these nodules with diameters of about 40nm for all QD densities. The optical properties were investigated by photoluminescence (PL) spectroscopy before and after the deposition of UNCD. The PL signals of QD structures overgrown with UNCD, although with decreased intensity, remain almost unchanged with respect to the peak positions and widths, revealing that the UNCD/QD structures retain the optical properties of uncoated InGaAs/GaAs quantum dots.

Ultrananocrystalline Diamond Film as a Wear-Resistant and Protective Coating for Mechanical Seal Applications

Mechanical shaft seals used in pumps are critically important to the safe operation of the paper, pulp, and chemical process industry, as well as petroleum and nuclear power plants. Specifically, these seals prevent the leakage of toxic gases and hazardous chemicals to the environment and final products from the rotating equipment used in manufacturing processes. Diamond coatings have the potential to provide negligible wear, ultralow friction, and high corrosion resistance for the sliding surfaces of mechanical seals, because diamond exhibits outstanding tribological, physical, and chemical properties. However, diamond coatings produced by conventional chemical vapor deposition (CVD) exhibit high surface roughness (Ra ≥ 1 μm), which results in high wear of the seal counterface, leading to premature seal failure. To avoid this problem, we have developed an ultrananocrystalline diamond (UNCD) film formed by a unique CH4/Ar microwave plasma CVD method. This method yields extremely smooth diamond coatings with surface roughness Ra = 20–30 nm and an average grain size of 2–5 nm. We report the results of a systematic test program involving uncoated and UNCD-coated SiC shaft seals. Results confirmed that the UNCD-coated seals exhibited neither measurable wear nor any leakage during long-duration tests that took 21 days to complete. In addition, the UNCD coatings reduced the frictional torque for seal rotation by five to six times compared with the uncoated seals. This work promises to lead to rotating shaft seals with much improved service life, reduced maintenance cost, reduced leakage of environmentally hazardous materials, and increased energy savings. This technology may also have many other tribological applications involving rolling or sliding contacts.