Post-deposition heat treatments for ion beam sputter deposited calcium phosphate coatings

A review on bovine hydroxyapatite; extraction and characterization

High rate of bone grafting surgeries emphasizes the need for optimal bone substitutes. Biomaterials mimicking the interconnected porous structure of the original bone with osteoconductive and osteoinductive capabilities have long been considered. Hydroxyapatite (HA), as the main inorganic part of natural bone, has exhibited excellent regenerative properties in bone tissue engineering. This manuscript reviews the HA extraction methods from bovine bone, as one of the principal biosources. Essential points in the extraction process have also been highlighted. Characterization of the produced HA through gold standard methods such as XRD, FTIR, electron microscopies (SEM and TEM), mechanical/thermodynamic tests, and bioactivity analysis has been explained in detail. Finally, future perspectives for development of HA constructs are mentioned.

A facile chemical process to form an ultrathin hydroxyapatite layer with a customizable silver-releasing function on a titanium implant

Silver-containing hydroxyapatite (Ag/HAp) layer on a bioinert material provides both bioactive and antibacterial properties; however, the Ag release duration needs to be customized to a patient's age and metabolism for minimizing the toxic effects. Herein, we present a facile chemical process to produce an ultrathin Ag/HAp layer on a Ti implant with a customized Ag-releasing profile. The process involves the following steps: preparation of a slurry-type reagent by mixing calcium phosphate powder with an aqueous AgNO₃ solution, burying a Ti substrate in the slurry, and heating the slurry in air. An HAp layer, approximately 50 nm thick, with Ag particle deposits was obtained using this process. The Ag-particle content can be varied by adjusting the concentration of AgNO₃ solution used for slurry preparation, resulting in different Ag-release profiles in a physiological solution. For instance, Ag release was retained for up to 30 days when 100 mM AgNO₃ was used, whereas the release lasted 15 days when 10 mM AgNO₃ was used. The duration of the antibacterial activity varied accordingly, but Ag-release-derived cytotoxicity was not observed irrespective of the AgNO₃ concentration. In addition, differentiation of osteoblast-like cells was facilitated owing to the formation of the HAp layer. Thus, the chemical process presented in this study allows the production-at a clinical site-of an Ag/HAp layer customized to the patient's needs.

Endowing Orthopedic Implants' Antibacterial, Antioxidation, and Osteogenesis Properties Through a Composite Coating of Nano-Hydroxyapatite, Tannic Acid, and Lysozyme

There is a substantial global market for orthopedic implants, but these implants still face the problem of a high failure rate in the short and long term after implantation due to the complex physiological conditions in the body. The use of multifunctional coatings on orthopedic implants has been proposed as an effective way to overcome a range of difficulties. Here, a multifunctional (TA@HA/Lys)_n coating composed of tannic acid (TA), hydroxyapatite (HA), and lysozyme (Lys) was fabricated in a layer-by-layer (LBL) manner, where TA deposited onto HA firmly stuck Lys and HA together. The deposition of TA onto HA, the growth of (TA@HA/Lys)_n, and multiple related biofunctionalities were thoroughly investigated. Our data demonstrated that such a hybrid coating displayed antibacterial and antioxidant effects, and also facilitated the rapid attachment of cells [both mouse embryo osteoblast precursor cells (MC3T3-E1) and dental pulp stem cells (DPSCs)] in the early stage and their proliferation over a long period. This accelerated osteogenesis in vitro and promoted bone formation in vivo. We believe that our findings and the developed strategy here could pave the way for multifunctional coatings not only on orthopedic implants, but also for additional applications in catalysts, sensors, tissue engineering, etc.

Investigation of Coatings, Corrosion and Wear Characteristics of Machined Biomaterials through Hydroxyapatite Mixed-EDM Process: A Review

Together, 316L steel, magnesium-alloy, Ni-Ti, titanium-alloy, and cobalt-alloy are commonly employed biomaterials for biomedical applications due to their excellent mechanical characteristics and resistance to corrosion, even though at times they can be incompatible with the body. This is attributed to their poor biofunction, whereby they tend to release contaminants from their attenuated surfaces. Coating of the surface is therefore required to mitigate the release of contaminants. The coating of biomaterials can be achieved through either physical or chemical deposition techniques. However, a newly developed manufacturing process, known as powder mixed-electro discharge machining (PM-EDM), is enabling these biomaterials to be concurrently machined and coated. Thermoelectrical processes allow the migration and removal of the materials from the machined surface caused by melting and chemical reactions during the machining. Hydroxyapatite powder (HAp), yielding Ca, P, and O, is widely used to form biocompatible coatings. The HAp added-EDM process has been reported to significantly improve the coating properties, corrosion, and wear resistance, and biofunctions of biomaterials. This article extensively explores the current development of bio-coatings and the wear and corrosion characteristics of biomaterials through the HAp mixed-EDM process, including the importance of these for biomaterial performance. This review presents a comparative analysis of machined surface properties using the existing deposition methods and the EDM technique employing HAp. The dominance of the process factors over the performance is discussed thoroughly. This study also discusses challenges and areas for future research.

Influence of nano-hydroxyapatite coating implants on gene expression of osteogenic markers and micro-CT parameters. An in vivo study in diabetic rats

This study evaluated the response of a nano-hydroxyapatite coating implant through gene expression analysis (runt-related transcription factor 2 (Runx2), alkaline phosphatase (Alp), osteopontin (Opn), osteocalcin (Oc), receptor activator of nuclear factor-kappa B (Rank), receptor activator of nuclear factor-kappa B ligand (Rank-L), and osteoprotegerin (Opg)). Three-dimensional evaluation (percent bone volume (BV/TV); percent intersection surface (BIC); bone surface/volume ratio (BS/BV); and total porosity (To.Po)) were also analyzed. Mini implants were surgically placed in tibias of both healthy and diabetic rats. The animals were euthanized at 7 and 30 days. Evaluating all factors the relative expression of Rank showed that NANO surface presented the best results at 7 days (diabetic rats). Furthermore the levels of Runx2, Alp, Oc, and Opn suggest an increase in osteoblasts proliferation, especially in early stages of osseointegration. %BIC in healthy and diabetic (7 days) depicted statistically significant differences for NANO group. BV/TV, BS/BV and To.Po demonstrated higher values for NANO group in all evaluated time point and irrespective of systemic condition, but BS/BV 30 days (healthy rat) and 7 and 30 days (diabetic rat). Microtomographic and gene expression analyses have shown the benefits of nano-hydroxyapatite coated implants in promoting new bone formation in diabetic rats.

Development of Robust Chitosan–Silica Class II Hybrid Coatings with Antimicrobial Properties for Titanium Implants

The purpose of this study was to develop robust class II organic–inorganic films as antibacterial coatings on titanium alloy (Ti6Al4V) implants. Coating materials were prepared from organic chitosan (20–80 wt.%) coupled by 3-glycydoxytrimethoxysilane (GPTMS) with inorganic tetraethoxysilane (TEOS). These hybrid networks were imbedded with antimicrobial silver nanoparticles (AgNPs) and coated onto polished and acid-etched Ti6Al4V substrates. Magic-angle spinning nuclear magnetic resonance (13CMAS-NMR), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and the ninhydrin assay, confirmed the presence and degree of covalent crosslinking (91%) between chitosan and GPTMS. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) identified surface roughness and microtopography on thin films and confirmed homogeneous distribution of elements throughout the coating. Cross-hatch and tensile adhesion testing demonstrated the robustness and adherence (15–20 MPa) of hybrid coatings to acid-etched titanium substrates. Staphylococcus aureus and Escherichia coli cultures and their biofilm formation were inhibited by all hybrid coatings. Antibacterial effects increased markedly for coatings loaded with AgNPs and appeared to increase with chitosan content in biofilm assays. These results are promising in the development of class II hybrid materials as robust and highly adherent antibacterial films on Ti6Al4V implants.

Exploring the mechanism behind improved osteointegration of phosphorylated titanium implants with hierarchically structured topography

Titanium (Ti) and its alloys have been frequently used in dental and orthopedic implants, but the undesired oxide layer easily formed on the surface tends to be the cause of implant failure for Ti-based implants. To address this problem, we herein prepared a phosphorylated Ti coating (TiP-Ti) with a micro/nano hierarchically structured topography on commercially pure Ti implants by a hydrothermal method to improve its osteointegration capacity. The surface morphology, chemical composition, and biological activity were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact-angle measurement, and protein adsorption assay. Osteointegration of TiP-Ti implants in rat tibia was investigated by biomechanical testing, micro-CT and histological analyses. We further explored the proposed mechanism which improves osteointegration of TiP-Ti implants by proliferation, adhesion, and differentiation assays of rat bone marrow mesenchymal stem cells (BMSCs). Our results demonstrated that the improved osteointegration mainly benefited from the better spread and adhesion of BMSCs on the micro/nano hierarchically structured TiP-Ti surfaces compared to hydroxyapatite coated Ti (HA-Ti), the positive control, and untreated Ti (untreated-Ti), the negative control. In conclusion, TiP-Ti surface is a promising candidate implant surface design to accelerate the osteointegration of Ti-based implants in biomedical applications.

Titanium-Tissue Interface Reaction and Its Control With Surface Treatment

Titanium (Ti) and its alloys are widely used for medical and dental implant devices-artificial joints, bone fixators, spinal fixators, dental implant, etc. -because they show excellent corrosion resistance and good hard-tissue compatibility (bone formation and bone bonding ability). Osseointegration is the first requirement of the interface structure between titanium and bone tissue. This concept of osseointegration was immediately spread to dental-materials researchers worldwide to show the advantages of titanium as an implant material compared with other metals. Since the concept of osseointegration was developed, the cause of osseointegration has been actively investigated. The surface chemical state, adsorption characteristics of protein, and bone tissue formation process have also been evaluated. To accelerate osseointegration, roughened and porous surfaces are effective. HA and TiO2 coatings prepared by plasma spray and an electrochemical technique, as well as alkalinization of the surface, are also effective to improve hard-tissue compatibility. Various immobilization techniques for biofunctional molecules have been developed for bone formation and prevention of platelet and bacteria adhesion. These techniques make it possible to apply Ti to a scaffold of tissue engineering. The elucidation of the mechanism of the excellent biocompatibility of Ti can provide a shorter way to develop optimal surfaces. This review should enhance the understanding of the properties and biocompatibility of Ti and highlight the significance of surface treatment.

Ion-substituted calcium phosphate coatings by physical vapor deposition magnetron sputtering for biomedical applications: A review

Coatings based on ion-substituted calcium phosphate (Ca-P) have attracted great attention in the scientific community over the past decade for the development of biomedical applications. Among such Ca-P based structures, hydroxyapatite (HA) has shown significant influence on cell behaviors including cell proliferation, adhesion, and differentiation. These cell behaviors determine the osseointegration between the implant and host bone and the biocompatibility of implants. This review presents a critical analysis on the physical vapor deposition magnetron sputtering (PVDMS) technique that has been used for ion-substituted Ca-P based coatings on implants materials. The effect of PVDMS processing parameters such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment on the surface properties of ion-substituted Ca-P coatings is elucidated. Moreover, the advantages, short comings and future research directions of Ca-P coatings by PVDMS have been comprehensively analyzed. It is revealed that the topography and surface chemistry of amorphous HA coatings influence the cell behavior, and ion-substituted HA coatings significantly increase cell attachment but may result in a cytotoxic effect that reduces the growth of the cells attached to the coating surface areas. Meanwhile, low-crystalline HA coatings exhibit lower rates of osteogenic cell proliferation as compared to highly crystalline HA coatings developed on Ti based surfaces. PVDMS allows a close reproduction of bioapatite characteristics with high adhesion strength and substitution of therapeutic ions. It can also be used for processing nanostructured Ca-P coatings on polymeric biomaterials and biodegradable metals and alloys with enhanced corrosion resistance and biocompatibility. STATEMENT OF SIGNIFICANCE: Recent studies have utilized the physical vapor deposition magnetron sputtering (PVDMS) for the deposition of Ca-P and ion-substituted Ca-P thin film coatings on orthopedic and dental implants. This review explains the effect of PVDMS processing parameters, such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment, on the surface morphology and crystal structure of ion-substituted Ca-P and ion-substituted Ca-P thin coatings. It is revealed that coating thickness, surface morphology and crystal structure of ion-substituted Ca-P coatings via PVDMS directly affect the biocompatibility and cell responses of such structures. The cell responses determine the osseointegration between the implant and host bone and eventually the success of the implants.

Investigation of Realizing Both Antibacterial Property and Osteogenic Cell Compatibility on Titanium Surface by Simple Electrochemical Treatment

Recently, the problem of infection on implanted devices caused by the formation of biofilms has been recognized. Surface treatment to prevent the initial stages of bacterial adhesion and subsequent bacterial growth is the only possible solution against such infection. In this study, simple electrochemical treatment was used for introducing silver, an antibiotic agent, on the titanium surface. A porous oxide layer containing small amounts of silver was formed on the metal of the substrate. This was done by microarc oxidation using the electrolyte with silver nitrate. The porous oxide layer was almost amorphous with a small fraction of anatase phase. The samples prepared using the electrolyte containing 0.04 mM or a higher concentration of silver nitrate showed an excellent antibacterial effect against both E. coli and S. aureus. However, the proliferation of osteoblast-like cells in the samples was not affected when a concentration of 0.5 mM or lower was used. Moreover, samples containing silver showed no harmful effects on the process of bone differentiation. Furthermore, the calcification process of the cells on the samples treated with and without silver were more promoted than that on untreated Ti. Thus, we found that it is possible to use this optimum concentration of silver to realize the conflicting biofunctions: its antibacterial property and osteogenic cell compatibility.

Influence of Post-deposition Heating Time and the Presence of Water Vapor on Sputter-coated Calcium Phosphate Crystallinity

Extensive research suggested that calcium phosphate (CaP) coatings on titanium implants are essential for early bone response. However, the characterization of CaP crystallinity and the means to control coating crystallinity are not well-established. In this study, the effect of a 400°C heat treatment for 1, 2, or 4 hours, and in the presence or absence of water vapor, on CaP crystallinity was investigated. Scanning electron microscopy indicated dense as-sputtered coatings. Increase in coating crystallinity was observed to be consistent with the increasing number of PO4 peaks observed as a result of different heat treatments. In addition, x-ray diffraction analyses indicated amorphous as-sputtered coatings, whereas crystalline CaP coatings in the range of 0-85% were observed after different post-deposition heat treatments. It was concluded that the presence of water vapor and post-deposition heat treatment time significantly affect the crystallinity of CaP coatings, which may ultimately affect bone healing.

Surface functionalization of polymer substrates with hydroxyapatite using polymer-binding peptides

Material-binding peptides are used as non-covalent bond linkers for surface functionalization because they bind to materials under mild conditions without affecting the properties of the materials and are functionalized by conjugating with other molecules. In the present study, the surface functionalization of polyetherimide (PEI) with hydroxyapatite (HAp) was examined using two types of PEI-binding peptides conjugated with other sequences. One peptide consisted of PEI-binding peptide p1 (TGADLNT) and a triasparate sequence for the biomimetic mineralization of HAp in simulated body fluids (SBFs), while the other consisted of p1 and HAp-binding peptide (HABP, CMLPHHGAC) for the immobilization of HAp and amorphous calcium phosphate (ACP) nanoparticles. The results obtained revealed deposits of HAp on PEI films treated with the peptide consisting of p1 and triasparate. HAp and ACP nanoparticles were immobilized on PEI films treated with peptides consisting of p1 and HABP, and immersion of the resultant substrates in SBFs completely covered the surfaces of PEI films with HAp.

Effect of Roughness on in Situ Biomineralized CaP-Collagen Coating on the Osteogenesis of Mesenchymal Stem Cells

Because of its outstanding osteo-conductive property, a calcium phosphate (CaP) coating has been used as an implant coating for bone tissue engineering. Nevertheless, the issues, such as harsh fabrication conditions, long-term stability and biocompatibility, and the requirement for expensive instruments, still exist in current coating techniques. To address these issues, the CaP coatings doped with collagen (CaP-Col) were in situ generated on polyelectrolyte multilayers (PEMs) by incubating PEMs in a mixture of the collagen, phosphate, and calcium ions. The resulting coatings have controllable physical properties (chemical composition, crystallinity, and roughness) and good stability before and after incubation with cell culture medium. We also found that both the cellular viability and osteogenesis of mesenchymal stem cells (MSCs) were closely related to the roughness of PEMs/CaP-Col, one of the easily ignored physical factors in current coating designs but very critical. The existed roughness window (between 18 ± 1.2 and 187 ± 7.3 nm) suitable for MSC proliferation on PEMs/CaP-Col coating and the optimal roughness (∼98 ± 3.5 nm) for MSC osteogenesis further demonstrated that the roughness was a critical factor for bone formation. Therefore, we envision that our exploration of the effects of surface roughness on MSC behaviors would provide better guidance for the future design of material coating and eventual medical success.

Calcium orthophosphate coatings, films and layers

In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the interfaces, the surface properties of the implants are of the paramount importance in determining both the biological response to implants and the material response to the physiological conditions. Hence, a surface engineering is aimed to modify both the biomaterials, themselves, and biological responses through introducing desirable changes to the surface properties of the implants but still maintaining their bulk mechanical properties. To fulfill these requirements, a special class of artificial bone grafts has been introduced in 1976. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide an adequate bonding to bones. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings, films and layers used to improve the surface properties of various types of artificial implants are the topic of this review.

Hydroxyapatite Coatings Produced by Right Angle Magnetron Sputtering for Biomedical Applications

Hydroxyapatite coatings have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered coatings are usually non-stoichiometric and amorphous which can cause some serious problems such as poor adhesion and excessive coating dissolution rate. A versatile right-angle radio frequency magnetron sputtering (RAMS) approach has been developed to deposit HA coatings on various substrates at low power levels. Using this alternative magnetron geometry, as-sputtered HA coatings are nearly stoichiometric, highly crystalline, and strongly bound to the substrate, as evidenced by analyses using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). In particular, coatings deposited on oriented substrates show a polycrystalline XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. Post deposition heat treatment under high temperature does not result in a marked improvement in the degree of crystallinity of the coatings. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.

Biosynthesis of Calcium Hydroxylapatite Coating on Sputtered Ti/TiN Nano Multilayers and their Corrosion Behavior in Simulated Body Solution

Titanium/titanium nitride (Ti/TiN) nanoscale multilayered films were deposited onto 316L stainless steel substrates by reactive magnetron sputtering using a Ti target. Coatings characterized by X-ray diffraction showed that the stack possesses centered cubic structure. The X-ray photoelectron spectroscopy survey spectra on the etched surfaces of the stack film on steel exhibited the characteristic Ti2p, N1s, and O1s peaks at the corresponding binding energies 454.5, 397.0, and 530.6 eV, respectively. Platelet adhesion experiments were carried out to examine the interaction between blood and the materials in vitro. The results indicated that the smoothness and lower isoelectric point contribute to better hemocompatibility of the Ti/TiN nanoscale multilayered coating. The biomediated synthesis of calcium hydroxylapatite (HA) was carried out on coated substrates using calcium-depositing bacteria. The observation of low corrosion current density ( Icorr) for the calcium HA-coated Ti/TiN specimens in simulated body fluid confirmed their highly resistive nature under the testing condition.

The effect of a nanothickness coating on rough titanium substrate in the osteogenic properties of human bone cells

This study evaluated the effect of a bioactive ceramic coating, in the nanothickness range, onto a moderately rough surface on the osteogenic behavior of human bone cells. The cells were harvested from the mandibular mental region and were cultured over Ti-6Al-4V disks of different surfaces: as-machined (M), alumina-blasted/acid etched (AB/AE), and alumina-blasted/acid-etched + 300-500 nm thickness amorphous Ca- and P-based coating obtained by ion beam-assisted deposition (Nano). The culture was then evaluated regarding cell viability, adhesion, morphology, immunolocalization of osteopontin (OPN) and alkaline phosphatase (ALP). The results showed that the surface treatment did not interfere with cell viability. At 1 day, AB/AE and Nano showed higher adhesion than the M surface (p < 0.001). Higher adhesion was observed for the M than the Nano surface at 7 days (p < 0.005). The percentage of cells showing intracellular labeling for OPN at day 1 was significantly higher for the Nano compared to M surface (p < 0.03). The percentage of ALP intracellular labeling at 7 days was significantly higher for the AB/AE compared to the M surface (p < 0.0065); no differences were detected at 14 days. Our results suggest that the presence of a thin bioactive ceramic coating on a rough substrate did not favor the events related to in vitro osteogenesis. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Functional Coatings or Films for Hard-Tissue Applications

Metallic biomaterials like stainless steel, Co-based alloy, Ti and its alloys are widely used as artificial hip joints, bone plates and dental implants due to their excellent mechanical properties and endurance. However, there are some surface-originated problems associated with the metallic implants: corrosion and wear in biological environments resulting in ions release and formation of wear debris; poor implant fixation resulting from lack of osteoconductivity and osteoinductivity; implant-associated infections due to the bacterial adhesion and colonization at the implantation site. For overcoming these surface-originated problems, a variety of surface modification techniques have been used on metallic implants, including chemical treatments, physical methods and biological methods. This review surveys coatings that serve to provide properties of anti-corrosion and anti-wear, biocompatibility and bioactivity, and antibacterial activity.

Osteoblast proliferation on hydroxyapatite coated substrates prepared by right angle magnetron sputtering

The preparation of hydroxyapatite (HA) coatings via a versatile right-angle magnetron sputtering (RAMS) approach for use as a biomaterial has recently been reported. RAMS coatings show some advantages over conventionally sputtered films in that room temperature deposition yields nanocrystalline and nearly stoichiometric HA coatings under appropriate conditions, thereby avoiding the troublesome post deposition annealing treatment. In this article, we present an exploratory study of the biocompatibility of RAMS HA coatings deposited on metallic substrates. RAMS HA coatings with a thickness around 500nm were prepared on various substrates. X-ray diffraction (XRD) analysis showed that the as-deposited HA coatings were polycrystalline with some strongly preferred orientations. Atomic force microscopy (AFM) results showed that the coatings were rather smooth with surface roughness on the order of 10 nm. X-ray photoelectron spectroscopy (XPS) confirmed that the surface chemistry was nearly stoichiometric. To study the biocompatibility of these coatings, murine pre-osteoblastic MC3T3-E1 cells were seeded onto various substrates. Cell density counts using fluorescence microscopy showed that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. Additionally, in preliminary studies the influence of Zn, Mg, and Al incorporation in the HA crystal lattice on the in vitro behavior was also evaluated. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.

Crystallographically engineered, hydrothermally crystallized hydroxyapatite films: an in vitro study of bioactivity

The aim of this study was to evaluate the bioactivity of hydroxyapatite films composed of hexagonal single crystals that display {1010} and {0001} crystallographic faces. The effect of engineered [0001] crystallographic orientation was investigated in parallel. Films were deposited by triethyl phosphate/ethylenediamine-tetraacetic acid doubly regulated hydrothermal crystallization on Ti6Al4V substrates (10, 14, 24 h). Bioactivity was investigated by analysis of MC3T3-E1 pre-osteoblast spreading using scanning electron microscopy and quantitative analysis of cell metabolic activity (Alamar Blue) (0-28 days). Scanning electron microscopy and X-ray diffraction were used to evaluate the ability of films to support the differentiation of MC3T3-E1 pre-osteoblasts into matrix-secreting, mineralizing osteoblasts. Results demonstrated that all films enabled MC3T3-E1 cells to spread, grow, and differentiate into matrix-secreting osteoblasts, which deposited biomineral that could not be removed after extraction of organic material. Differences in [0001] HA crystallographic orientation were not, however, found to significantly affect bioactivity. Based on these results, it is concluded that these hydrothermal hydroxyapatite films are non-toxic, bioactive, osteoconductive, and biomineral bonding. The lack of a relationship between reported hydroxyapatite crystallographic face specific protein adsorption and bulk HA bioactivity are discussed in terms of crystallographic texture, surface roughness, assay robustness, and competitive protein adsorption.

Production and characterization of HA and SiHA coatings

Plasma sprayed hydroxyapatite (HA) coatings on metallic prostheses have been used clinically in dentistry and orthopedics since the mid 1980s. The coating properties are dependent on the spraying parameters. Since silicon-substituted hydroxyapatite (SiHA) has been shown to offer improved bioactivity over phase pure HA, SiHA coatings have the potential for enhanced performance in clinical application. In this study, phase pure HA and 0.8 wt% SiHA powders were synthesized with similar particle size distribution and morphology. The powders were plasma sprayed onto Ti-6Al-4V substrates at 37 kW and 40 kW plasma gun input power respectively. Four kinds of samples were prepared, HAC 37, HAC 40, SiHAC 37 and SiHAC 40. Materials characterization showed that the coatings were of relatively high phase purity. In vitro cell culture demonstrated that human osteoblast cells grew well on all samples, with the highest cell growth observed on SiHA coatings produced under the lower plasma gun input power.

Physico/chemical characterization and in vivo evaluation of nanothickness bioceramic depositions on alumina-blasted/acid-etched Ti-6Al-4V implant surfaces

The objective of this study was to physico/chemically characterize and evaluate the in vivo performance of two nanothickness ion beam assisted depositions (IBAD) of bioceramic coatings on implants in a beagle model. Alumina-blasted/acid-etched (AB/AE) Ti-6Al-4V implants were subjected to two different IBAD depositions (IBAD I and IBAD II), which were physico/chemically characterized by SEM, EDS, XPS, XPS + ion-beam milling (depth profiling), XRD, AFM, and ToF-SIMS. A beagle dog tibia model was utilized for histomorphometric and biomechanical (torque) comparison between AB/AE, IBAD I, IBAD II, and plasma-sprayed hydroxyapatite (PSHA) coated implants that remained in vivo for 3 and 5 weeks. The coatings were characterized as amorphous Ca-P with high Ca/P stoichiometries with thicknesses of an order of magnitude difference (IBAD I = 30-50 nm and IBAD II = 300-500 nm). The histomorphometric and biomechanical testing results showed that the 300-500 nm thickness deposition (IBAD II) and PSHA positively modulated bone healing at early implantation times.

A novel nano-porous alumina biomaterial with potential for loading with bioactive materials

Nano-porous alumina, with the potential for being loaded with bioactive materials, has been proposed as a novel material for coating implants. In this study, the shear strength of the interface between such nano-porous anodic aluminium oxide (AAO) coatings and titanium substrates, their biocompatibility, and their potential for pore loading have been investigated. An interface shear strength in excess of 29 MPa was obtained which is comparable with that of conventional plasma sprayed hydroxyapatite implant coatings. The viability and differentiation of MG63 osteoblastic cells co-cultured on the coating was found to be broadly comparable to that of similar cells co-cultured on conventional bioinert implant materials such as titanium and fully dense alumina. Extensive pore loading with silica nano-particles of different sizes and in different combinations was demonstrated throughout the thickness of AAO layers 1 microm and 60 microm thick. This work has demonstrated, that with suitable choice of pore filling materials, this novel coating might simultaneously combat infection, encourage bone regeneration, and secure fixation of the implant to bone.

Effects of calcium phosphate coating to SLA surface implants by the ion-beam-assisted deposition method on self-contained coronal defect healing in dogs

The aim of this study was to evaluate the healing of self-contained coronal defects on a sand-blasted, large-grit, acid-etched (SLA) surface implant, which had a calcium phosphate (CaP) coating applied by ion-beam-assisted deposition (IBAD). We also evaluated the effect of heating the coating to different temperatures. The CaP-coated SLA implants exhibited a slightly larger bone healing capacity in the self-contained coronal defect than SLA implants, indicating that combining SLA surface implants and a CaP coating by the IBAD method had synergistic effects on bone healing. There was no difference in the healing capacity between 350 degrees C and 450 degrees C heat treatment of the coating layer.

Basic research methods and current trends of dental implant surfaces

Among dental implant design alterations, surface modifications have been by far the most investigated topic. Regarding implant surface research, the lack of hierarchical approaches relating in vitro, in vivo, clinical trials, and ex vivo analyses has hindered biomaterials scientists with clear informed rationale guidelines for implant surface design. This manuscript provides a critical hierarchical overview of the in vitro, laboratory in vivo, clinical, and ex vivo methodologies used to investigate the performance of novel biomaterials aiming to allow dental professionals to better evaluate the past, present, and future dental implant surface research. This manuscript also contains an overview of the commercially available surface texture and chemistry modifications including novel nanotechnology-based fabrication processes. Over the last decade, surface texturing has been the most utilized parameter for increasing the host-to-implant response. Recently, dental implant surfaces utilizing reduced length scale physico/chemical features (atomic and nanometric) have shown the potential to synergistically use both texture and the inclusion of bioactive ceramic components on the surface. Although surface modifications have been shown to enhance osseointegration at early implantation times, information concerning its long-term benefit to peri-implant tissues is lacking due to the reduced number of controlled clinical trials. Given the various implants/surfaces under study, the clinician should ask, founded on the basic hierarchical approach described for the in vitro, laboratory in vivo data, as well as the results of clinical studies to effectiveness before use of any dental implant.

Corrosion resistance evaluation of a Ca- and P-based bioceramic thin coating in Ti-6Al-4V

The objective of this study was to physico/chemically characterize and determine the corrosion resistance of a Calcium-Phosphate (Ca-P) based bioceramic thin coating processed by a sputtering process on titanium alloy (Ti-6Al-4V). The samples utilized in this study were uncoated and coated disks of 10 mm diameter by 3 mm thickness. The coating was characterized by SEM, XPS + ion beam milling (IBM), thin-film mode XRD, and atomic force microscope (AFM) (n = 3). Coated and uncoated Ti-6Al-4V disk surfaces were tested in Phosphate Buffered Saline (PBS) at 25 degrees C through an area of 0.79 cm(2). A three-electrode cell set-up was used with a saturated calomel electrode (SCE) and a platinum wire as reference and counter electrodes. After 3, 17, and 25 days of immersion, electrochemical impedance spectroscopy (EIS) experiments were performed (n = 3). The EIS tests were carried out in potentiostatic mode at the open circuit potential (OCP). The frequency range considered was from 100 kHz to 10 mHz, using 10 mV root mean square as the amplitude of the perturbation signal. A potentiodynamic polarization scan using a frequency response analyzer potentiostat, was acquired following 3 days of immersion in PBS. The potentiodynamic polarization scans (n = 3) were carried out with a scan rate of 1 mV/s ranging from -0.8V(SCE) to 3.0V(SCE).

RESULTS

The physico/chemical characterization showed an amorphous Ca- and P-based coating of approximately 400-700 nm thickness with Ca-P nanometer size particles embedded in a Ca-P matrix. The Bode phase angle diagrams showed highly capacitive results at low and medium frequencies for both surfaces tested. The polarization curves showed low current densities at the corrosion potential (E (corr)), in the order of 10(-8)A/cm(2), typical of passive materials with protective surface films. Coated sample current densities were comparable to the uncoated samples.

CONCLUSION

Coated and uncoated samples were stable in the test solution with a protective film maintained throughout the 25 day immersion test period.

Preparation of hydroxyapatite-nanocrystal-coated stainless steel, and its cell interaction

Calcined nanocrystals of hydroxyapatite (HAp) having spherical or rod-shaped morphologies were coated through covalent linkage on a type 316L stainless steel substrate, which was chemically modified by the graft polymerization of gamma-methacryloxypropyl triethoxysilane (MPTS) at 70-110 degrees C. The grafting of poly(MPTS) on the substrate was confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR). In order to coat the substrate with the HAp crystals through covalent linkage, the reactionbetween the alkoxysilyl groupsin the poly (MPTS) grafted on the substrate and the OH groups on the HAp crystals was conducted at 80 degrees C. The poly(MPTS)-grafted substrate was strongly coated with the HAp nanocrystals, although the HAp crystals adsorbed physically on the original substrate without poly(MPTS) grafting were removed by ultrasonic treatment. Human umbilical vein endothelial cells (HUVEC) adhered in larger numbers on the HAp-coated stainless steel substrate as compared with the original substrate after 24 h of initial incubation. The number of HUVEC adhered on the rod-shaped HAp-coated substrate was not significantly different from that on the spherical HAp-coated substrate under the present conditions.

CaTiO(3) coating on titanium for biomaterial application--optimum thickness and tissue response

The objectives of this study were to determine the optimum thickness of a CaTiO(3) film for biomaterial applications and to investigate the biocompatibility and bone formation of titanium with a CaTiO(3) film. First, CaTiO(3) films of 10, 20, 30, and 50 nm in thickness were deposited on titanium substrates using radiofrequency magnetron sputtering followed by annealing at 873 K in air for 7.2 ks. The optimum thickness of the CaTiO(3) film for bone formation was determined by comparison with its performance regarding calcium phosphate formation in Hanks' balanced saline solution (HBSS). Regarding calcium phosphate formation, the performance of the specimen with a 50-nm-thick CaTiO(3) film was superior to those of specimens with other thicknesses. A titanium prism with a CaTiO(3) film of 50-nm in thickness was surgically inserted in both soft and hard rat tissues. The biocompatibility of CaTiO(3)-deposited titanium and bone formation on it was investigated by histological observations. A slight inflammatory reaction was observed around the titanium with the 50-nm-thick CaTiO(3) film, while no severe response, such as degeneration and necrosis, was observed in either soft or hard rat tissue. New bone formation on the titanium plate with the CaTiO(3) film was more active than that without the film. The 50-nm-thick CaTiO(3) film has biocompatibility and can facilitate new bone formation in vivo, and, consequently, it is an excellent surface modification method for biomaterial applications.

Osteoblast proliferation on hydroxyapatite thin coatings produced by right angle magnetron sputtering

Right angle magnetron sputtering (RAMS) was used to produce hydroxyapatite (HA) film coatings on pure titanium substrates and oriented silicon wafer (Si(0 0 1)) substrates with flat surfaces as well as engineered surfaces having different forms. Analyses using synchrotron XRD, AFM, XPS, FTIR and SEM with EDS showed that as-sputtered thin coatings consist of highly crystalline hydroxyapatite. The HA coatings induced calcium phosphate precipitation when immersed in simulated body fluid, suggesting in vivo bioactive behavior. In vitro experiments, using murine osteoblasts, showed that cells rapidly adhere, spread and proliferate over the thin coating surface, while simultaneously generating strong in-plane stresses, as observed on SEM images. Human osteoblasts were seeded at a density of 2500 cells cm(-2) on silicon and titanium HA coated substrates by RAMS. Uncoated glass was used as a reference substrate for further counting of cells. The highest proliferation of human osteoblasts was achieved on HA RAMS-coated titanium substrates. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.

In vitro andin vivo biological responses of plasma-sprayed hydroxyapatite coatings with posthydrothermal treatment

This study was undertaken to evaluate the effect of post-hydrothermal treatment on the biological responses of the plasma-sprayed hydroxyapatite (HA)-coated Ti-6Al-4V implant system both in vitro and in vivo. After hydrothermal treatment, the HA coating (HAC) shows the high mechanical strength and indices-of-crystallinity, denser microstructure, lower concentrations of amorphous and impurity phases, when compared with the as-sprayed HAC. The in vitro cell-culture studies, using UMR106 osteoblast-like cell, demonstrated no signifiacnt cell growth on both surface of as-sprayed and hydrothermal-treated HACs during 10-day culture. The in vivo studies, using the transcortical implant model in the femora of goats, evaluated the histological responses of two coatings. After 6 week of implantation, using backscattered electron images, no substantial histological variations in the extents of new bone apposition and new bone healing between the two HACs were observed. However, the as-sprayed HAC, owing to the dissolution induced the granular particles dissociated from the HAC, showed the statically lower extent of new bone apposition than hydrothermal-treated HAC at 12 weeks. The results suggest that hydrothermal treatment could be used to improve the mechanical strength, crystallinity, and phase composition of HAC, which are important factors of long-term fixation and stability of implant. Besides, the treated HAC could also achieve the initial fixation of implant in clinical use.

Effect of post-deposition heating temperature and the presence of water vapor during heat treatment on crystallinity of calcium phosphate coatings

In this study, radiofrequency sputtered calcium phosphate (CaP) coatings were evaluated after 1h post-deposition heat treatment at either 350 degrees C, 400 degrees C, 450 degrees C, 500 degrees C or 600 degrees C in the presence or absence of water vapor. X-ray diffraction analyses indicated the as-sputtered coatings to be amorphous. With different post-deposition heat treatments used, in this study, crystallinity of CaP coatings was observed to be in the range of 0-68%. The 400 degrees C and 450 degrees C heat-treated CaP coatings in the absence of water vapor were poorly crystalline, exhibiting a crystallinity of 2+/-1%. In comparison to heat treatments at 450 degrees C in the absence of water vapor, the presence of water vapor at 450 degrees C heat treatment resulted in a significant increase in coating crystallinity. However, this effect was not observed at higher temperatures. A coating crystallinity of 60-68% was observed for coatings heat treated at 450 degrees C in the presence of water vapor, and at 500 degrees C and 600 degrees C in the presence or absence of water vapor. In addition, increases in the degree of coating crystallinity were observed to be consistent with the increasing number of PO(4) peaks observed as a result of different post-deposition heat treatments. It was concluded that the presence of water vapor at 450 degrees C post-deposition heat treatment significantly affect the crystallinity of CaP coatings, whereas an increase to temperature higher than 450 degrees C and in the presence of water vapor has no significant effect on crystallinity.

Quantitative analysis of osteoblast behavior on microgrooved hydroxyapatite and titanium substrata

The effects of implant surface topography and chemistry on osteoblast behavior have been a research focus because of their potential importance in orthopedic and dental applications. This work focused on the topographic effects of hydroxyapatite (HA) and titanium (Ti) surface that had identical micropatterns to determine whether there was synergistic interaction between surface chemistry and surface topography. Surface microgrooves with six different groove widths (4, 8, 16, 24, 30, and 38 microm) and three different groove depths (2, 4, and 10 microm) were made on single crystalline silicon wafers using microfabrication techniques. Ti and HA thin films were coated on the microgrooves by radio-frequency magnetron sputtering. After that, human osteoblast-like cells were seeded and cultured on the microgrooved surfaces for up to 7 days. The cells' behavior was examined using scanning electron microscopy after cells were fixed and dehydrated. Statistical analysis was based on quantitative data of orientation angle, evaluating the contact guidance, and form index, describing cell shape or cell morphology changes. The contact guidance and cell shape changes were observed on the HA and Ti microgrooves. No difference in orientation angle between HA and Ti microgrooves was found. This might suggest that surface chemistry was not a significant influence on cell guidance. However, the form index analysis indicated an interaction between topographic effects and surface chemistry. Thus, conclusions about surface topographic effects on cell behavior drawn from one type of material cannot simply be applied to another type of material.

Osteoblast precursor cell attachment on heat-treated calcium phosphate coatings

The influence of properties of calcium phosphate (CaP) coatings on bone cell activity and bone-implant osseointegration is not well-established. This study investigated the effects of characterized CaP coatings of various heat treatments on osteoblast response. It was hypothesized that heat treatments of CaP coatings alter the initial osteoblast attachment. The 400 degrees C heat-treated coatings were observed to exhibit poor crystallinity and significantly greater phosphate or apatite species compared with as-sputtered and 600 degrees C heat-treated coatings. Similarly, human embryonic palatal mesenchyme (HEPM) cells, an osteoblast precursor cell line, seeded on 400 degrees C heat-treated coatings, exhibited significantly greater cell attachment compared with Ti surfaces, as-sputtered coatings, and 600 degrees C heat-treated coatings. The HEPM cells on Ti surfaces and heat-treated coatings were observed to attach through filopodia, and underwent cell division, whereas the cells on as-sputtered coatings displayed fewer filopodia extensions and cell damage. Analysis of the data suggested that heat treatment of CaP coatings affects cell attachment.

Growth of calcium phosphate on poling treated ferroelectric BaTiO3 ceramics

Barium titanate (BaTiO3; BTO) is ferroelectric and piezoelectric after poling treatment. In this study, the bioactivity of BTO was investigated after a poling treatment by examining the formation of crystal growth on specimen surfaces in vitro. Negatively charged BTO surfaces showed calcium phosphate (Ca-P) crystal growth, while deposition of sodium chloride was observed on the positively charged BTO surfaces. After 30 days immersion in Eagle's MEM, the thickness of Ca-P crystal on negatively charged BTO surfaces increased to 0.8-0.9 microm. These data indicate that incorporating selectively polarized BTO on implant surfaces is a promising means for improving the bioactivity of implant materials.

Solution deposition of hydroxyapatite on titanium pretreated with a sodium ion implantation

Titanium surfaces were treated by exposing them to a beam of sodium ions. Sodium titanate was shown to be incorporated within the oxidic titanium surface. The ion-implanted surfaces were examined for their reactivity by immersion in a simulated body fluid, which showed the formation of surface-bound hydroxyapatite. The surface was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and optical and electron microscopy. The surface hydroxyl concentration was determined using the nuclear reaction (1)H((15)N, alpha gamma)(12)C. Surface-related parameters that may affect hydroxyapatite nucleation are discussed in terms of the electrical double layer.

Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: a review

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.