Excimer laser deposition of hydroxyapatite thin films

Substituted Hydroxyapatite, Glass, and Glass-Ceramic Thin Films Deposited by Nanosecond Pulsed Laser Deposition (PLD) for Biomedical Applications: A Systematic Review

The deposition of thin films of bioactive materials is the most common approach to improve the bone bonding ability of an implant surface. With this purpose, several wet and plasma assisted deposition methods were proposed in the scientific literature. In this review, we considered films obtained by nanosecond Pulsed Laser Deposition (PLD). Since hydroxyapatite (HA) has composition and structure similar to that of the mineral component of the bone, the initial studies focused on the selection of experimental conditions that would allow the deposition of films that retain HA stoichiometry and crystallinity. However, biological apatite was found to be a poorly crystalline and multi-substituted mineral; consequently, the attention of researchers was oriented towards the deposition of substituted HA, glass (BG), and glass-ceramic (BGC) bioactive materials to exploit the biological relevance of foreign ions and crystallinity. In this work, after a description of the nanosecond ablation and film growth of ceramic materials, we reported studies on the mechanism of HA ablation and deposition, evidencing the peculiarities of PLD. The literature concerning the PLD of ion substituted HA, BG, and BGC was then reviewed and the performances of the coatings were discussed. We concluded by describing the advantages, limitations, and perspectives of PLD for biomedical applications.

Bio-inspired citrate-functionalized apatite thin films crystallized on Ti-6Al-4V implants pre-coated with corrosion resistant layers

In this paper the crystallization of a bioinspired citrate-functionalized apatite (cit-Ap) thin film (thickness about 2μm) on Ti-6Al-4V supports pre-coated with bioactive and corrosion resistant buffer layer of silicon nitride (Si3N4), silicon carbide (SiC) or titanium nitride (TiN) is reported. The apatitic coatings were produced by a new coating technique based on the induction heating of the implants immersed in a flowing calcium-citrate-phosphate solution at pH11. The influence of the buffer layers and the surface roughness of the substrate on the chemical-physical features and adhesion of the cit-Ap films were investigated. The best plasticity, compactness and adherence properties have been found in the Ap layer grown on Si3N4, followed by the Ap grown on SiC and TiN, respectively. The adhesion property was likely related to the roughness of the buffered substrates, whereas the compactness and plasticity were closely related to the operating conditions during the Ap crystallization (flow rate of the solution and increase of temperature) rather than to the nature of the buffer layer.

Hydroxylapatite nanoparticles: fabrication methods and medical applications

Hydroxylapatite (or hydroxyapatite, HAp) exhibits excellent biocompatibility with various kinds of cells and tissues, making it an ideal candidate for tissue engineering, orthopedic and dental applications. Nanosized materials offer improved performances compared with conventional materials due to their large surface-to-volume ratios. This review summarizes existing knowledge and recent progress in fabrication methods of nanosized (or nanostructured) HAp particles, as well as their recent applications in medical and dental fields. In section 1, we provide a brief overview of HAp and nanoparticles. In section 2, fabrication methods of HAp nanoparticles are described based on the particle formation mechanisms. Recent applications of HAp nanoparticles are summarized in section 3. The future perspectives in this active research area are given in section 4.

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.

Calcium phosphate composite layers for surface-mediated gene transfer

In this review, the surface-mediated gene transfer system using calcium phosphate composite layers is described. Calcium phosphate ceramics are osteoconductive bioceramics used typically in orthopedic and dental applications. Additionally, calcium phosphate particles precipitated by a liquid-phase process have long been used as a safe and biocompatible transfection reagent in molecular biology. Recently, calcium phosphate composite layers immobilizing DNA were fabricated on the surfaces of base materials through a biomimetic process using supersaturated solutions. These composite layers possess useful characteristics of both osteoconductive bioceramics and transfection reagents; they thus provide a biocompatible surface to support cell adhesion and growth, and can stimulate the cell effectively via surface-mediated gene transfer. By modifying the fabrication conditions, physicochemical and biological properties of the composite layers can be varied. With such an approach, these composite layers can be designed to have improved affinity for cells and to exhibit increased gene transfer efficiency over that of conventional lipid transfection reagents. The composite layers with the increased gene transfer efficiency induced specific cell differentiation and tissue regeneration in vivo. These composite layers, given their good biocompatibility and the potential to control cell behavior on their surfaces, have great potential in tissue engineering applications.

Surface characteristics of a novel hydroxyapatite-coated dental implant

Purpose

This study evaluated the surface characteristics and bond strength produced using a novel technique for coating hydroxyapatite (HA) onto titanium implants.

Methods

HA was coated on the titanium implant surface using a super-high-speed (SHS) blasting method with highly purified HA. The coating was performed at a low temperature, unlike conventional HA coating methods. Coating thickness was measured. The novel HA-coated disc was fabricated. X-ray diffraction analysis was performed directly on the disc to evaluate crystallinity. Four novel HA-coated discs and four resorbable blast medium (RBM) discs were prepared. Their surface roughnesses and areas were measured. Five puretitanium, RBM-treated, and novel HA-coated discs were prepared. Contact angle was measured. Two-way analysis of variance and the post-hoc Scheffe's test were used to analyze differences between the groups, with those with a probability of P<0.05 considered to be statistically significant. To evaluate exfoliation of the coating layer, 7 sites on the mandibles from 7 mongrel dogs were used. Other sites were used for another research project. In total, seven novel HA-coated implants were placed 2 months after extraction of premolars according to the manufacturer's instructions. The dogs were sacrificed 8 weeks after implant surgery. Implants were removed using a ratchet driver. The surface of the retrieved implants was evaluated microscopically.

Results

A uniform HA coating layer was formed on the titanium implants with no deformation of the RBM titanium surface microtexture when an SHS blasting method was used.

Conclusions

These HA-coated implants exhibited increased roughness, crystallinity, and wettability when compared with RBM implants.

Liquid-phase laser process for simple and area-specific calcium phosphate coating

Simple, mild, and area-specific calcium phosphate (CaP) coating techniques are useful for the production and surface modification of biomaterials. In this study, an area-specific CaP coating technique for polymer substrates was successfully developed using a liquid-phase laser process. In the proposed method, Nd-YAG laser light (355 nm, 30 Hz, and 1-3 W) irradiated an ethylene-vinyl alcohol copolymer (EVOH) substrate immersed in a supersaturated CaP solution for various periods of time (up to 30 min). The CaP-forming ability increased with an increase in the laser power and irradiation period. At the optimal laser power (3 W), a continuous CaP layer formed within 30 min on the laser-irradiated surface of the EVOH substrate. The formation of CaP was attributed to laser absorption by the EVOH substrate, which promoted the surface modification of EVOH and an increase in the temperature of the solution near the surface of the substrate. The resulting CaP coating showed better cell adhesion property than the naked EVOH substrate. The proposed CaP coating technique is simple (quick and single step) and area specific. Furthermore, the present process is carried out under mild conditions, that is, at normal pressures and temperatures in a safe aqueous medium. These are significant advantages of the proposed CaP coating technique.

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.

Control of proliferation and differentiation of osteoblasts on apatite-coated poly(vinyl alcohol) hydrogel as an artificial articular cartilage material

One of the key challenges in employing biomaterials is determining how to fix them into the surrounding tissue. To enhance the interaction with surrounding bone, amorphous hydroxyapatite (HA) was coated onto the surface of the bio-inert poly(vinyl alcohol) hydrogel (PVA-H), as an artificial cartilage material, by a pulsed laser deposition technique. Next we examined the binding effects of the HA thin film (300 nm thick) to the underlying bone using osteoblast proliferation and differentiation. A mouse osteoblast cell line, MC3T3E1, was cultured on the HA-coated and noncoated PVA-H with a water content of 33% or 53% for 3 weeks. Cell proliferation, alkaline phosphatase (ALP) activity, and levels of osteocalcin were evaluated for biocompatibility and differentiation. HA coating enhanced the cell proliferation, the ALP activity, and the levels of osteocalcin on both low and high water-content PVA-Hs. The cell growth rates on the PVA-H were lower than on tissue culture dishes even after the HA coating was added; however, osteoblastic differentiation was highly promoted by the HA coating on low water content PVA-H. These results suggested that the HA coating on the PVA-H enhanced the affinity between the bone and the PVA-H as an artificial cartilage material in surface replacement arthroplasty.

Pulsed laser deposition of hydroxyapatite thin films on Ti-6Al-4V: effect of heat treatment on structure and properties

Hydroxyapatite (HA) is an attractive biomaterial that has been widely used as a coating for dental and orthopedic metal implants. In this work, HA coatings were deposited on Ti-6Al-4V substrates by laser ablation of HA targets with a KrF excimer laser. Deposition was performed at ambient temperature under different working pressures that varied from 10(-4) to 10(-1) torr of oxygen. The as-deposited films were amorphous. They were annealed at 290-310 degrees C in ambient air in order to restore the crystalline structure of HA. The coatings morphology, composition and structure were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction techniques. Mechanical and adhesive properties were examined using nanoindentation and scratch tests, respectively. The stability of the HA coatings was tested under simulated physiological conditions. This study reveals that the combination of pulsed laser deposition and post-deposition annealing at 300 degrees C have the potential to produce pure, adherent, crystalline HA coatings, which show no dissolution in a simulated body fluid.

Effect of substrate temperature on mechanical properties of calcium phosphate coatings

The effect of substrate temperature and processing parameters on mechanical properties of nanoscale calcium phosphate coatings are being studied in order to refine the processing technique for Functionally Graded Hydroxyapatite (FGHA) coatings. Coatings were deposited on titanium substrates with a set substrate temperature of 450, 550, 650, or 750 degrees C in an Ion Beam Assisted Deposition (IBAD) system using a sintered hydroxyapatite (HA) target. Mechanical properties of the coatings deposited with a set substrate temperature such as, bonding/adhesion strength to the substrate, nanohardness, and Young's Modulus as well as coating thickness were evaluated and compared with commercial plasma spray HA coatings. It is concluded that depositing FGHA coatings would better be started at 550-650 degrees C to maintain superior properties of the film at the interface. It can also be concluded that the residual stresses caused by different Coefficient of Thermal Expansions (CTEs) between the substrate and coatings are not the only factor controlling the bonding strength and mechanical properties of these samples. Other parameters such as the nature of the interface layers and their bonding to each other as well as the density and grain structure of the coatings must be taken into consideration for an appropriate evaluation of mechanical properties of calcium phosphate coatings deposited on heated substrate.

Preparation and Characterization of Anodized Titanium Surfaces and Their Effect on Osteoblast Responses

In this study, titanium (Ti) surface was modified by anodizing with a mixture of β-glycerophosphate sodium and calcium (Ca) acetate, and the anodized surfaces were characterized by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. In vitro osteoblast response to anodized oxide was also evaluated. The anodic oxide produced was observed to have interconnected pores (0.5–2 μm in diameter) and intermediate roughness (0.60–1.00 μm). In addition, anodic oxide was observed to have amorphous and anatase oxide. Calcium and phosphorus ions were deposited on the Ti oxide during anodization. Osteoblast differentiation, as indicated by alkaline phosphatase production, was enhanced on anodized surfaces. It was thus concluded from this study that Ca phosphate can be deposited on Ti surfaces by anodization. It was also concluded that the phenotypic expression of osteoblast was enhanced by the presence of Ca phosphate and higher roughness on anodized Ti surfaces.

Biological stability and osteoconductivity in rabbit tibia of pulsed laser deposited hydroxylapatite coatings

A comparative study of the biological stability and the osteoconductivity of hydroxylapatite (HA) coatings produced by pulsed laser deposition (PLD) and plasma spraying (PS) was conducted. Three different implant groups were used: grit-blasted titanium rods coated with HA-PLD (2-microm-thick), grit-blasted titanium rods coated with HA-PS (50-microm-thick), and uncoated. Implantation took place into the proximal tibia of 12 mature New Zealand White rabbits for 24 weeks. Samples were evaluated using descriptive histology and histomorphometry. While HA-PS implants showed considerable instability and reduction in thickness after 24 weeks, but no statistical difference to the titanium group, the HA-PLD group showed a significant higher amount of bone apposition (Scheffé test, p<0.05) than the other two groups, without signs of degradation or dissolution. Remarkably, after 6 months, the almost intact thin pulsed laser deposited coating could be observed by electron microscopy in extended areas.

Control of phase composition in hydroxyapatite/tetracalcium phosphate biphasic thin coatings for biomedical applications

Biphasic calcium phosphates comprising well-controlled mixtures of nonresorbable hydroxyapatite and other resorbable calcium phosphate phases often exhibit a combination of enhanced bioactivity and mechanical stability that is difficult to achieve in single-phase materials. This makes these biphasic bioceramics promising substrate materials for applications in bone tissue regeneration and repair. In this paper we report the synthesis of highly crystalline, biphasic coatings of hydroxyapatite/tetracalcium phosphate with control over the weight fraction of the constituent phases. The coatings were produced by pulsed laser deposition using ablation targets of pure crystalline hydroxyapatite. The fraction of tetracalcium phosphate phase in the coatings was controlled by varying the substrate temperature and the partial pressure of water vapor in the deposition chamber. A systematic study of phase composition in the hydroxyapatite/tetracalcium phosphate biphasic coatings was performed with X-ray diffraction. Tetracalcium phosphate in the coatings obtained at high substrate temperature is not formed by partial conversion of previously deposited hydroxyapatite. Instead, it is produced by nucleation and growth of tetracalcium phosphate itself from the ablation products of the hydroxyapatite target or by accretion of tetracalcium phosphate grains formed during ablation. This finding was confirmed by formation of calcium oxide, not tetracalcium phosphate, after annealing of pure hydroxyapatite coatings at high temperatures of 700-850 degrees C.

Review paper: surface modification for bioimplants: the role of laser surface engineering

Often hard implants undergo detachment from the host tissue due to inadequate biocompatibility and poor osteointegration. Changing surface chemistry and physical topography of the surface influences biocompatibility. At present, the understanding of biocompatibility of both virgin and modified surfaces of bioimplant materials is limited and a great deal of research is being dedicated to this aspect. In view of this, the current review casts new light on research related to the surface modification of biomaterials, especially materials for prosthetic applications. A brief overview of the major surface modification techniques has been presented, followed by an in-depth discussion on laser surface modifications that have been explored so far along with those that hold tremendous potential for bioimplant applications.

Laser-induced crystallization of calcium phosphate coatings on polyethylene (PE)

Calcium phosphate (CaP) coatings are used for obtaining a desired biological response. Usually, CaP coatings on metallic substrates are crystallized by annealing at temperatures of at least 400-600 degrees C. For polymeric substrates, this annealing is not possible due to the low melting temperatures. In this work, we present a more suitable method for obtaining crystalline coatings on polymeric substrates, namely laser crystallization. We were successful in obtaining hydroxyapatite coatings on polyethylene. Because of the UV transmission characteristics of the CaP coatings, the use of a low wavelength (157 nm) F(2) laser was necessary for this. As a result of the laser treatment, the CaP coating broke up into islands. The cracks between the islands became larger and the surface became porous with increasing laser energy. The mechanism behind the formation of this morphology did not become clear. However, the fact that crystalline CaP coatings can be obtained on polymeric substrates in an easy way, possibly allows for the development of new products.

Biocompatible Mn2+-doped carbonated hydroxyapatite thin films grown by pulsed laser deposition

Mn(2+)-doped carbonated hydroxyapatite (Mn-CHA) thin films were obtained by pulsed laser deposition on Ti substrates. The results of the performed complementary diagnostic techniques, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy investigations indicate that the films are crystalline with a Ca/P ratio of about 1.64-1.66. The optimum conditions, when nearly stoichiometric crystalline thin films were deposited, were found to be 10 Pa oxygen pressure, 400 degrees C substrate temperature, and postdeposition heat treatment in water vapors at the same substrate temperature. The films were seeded with L929 fibroblast and hFOB1.19 osteoblast cells and subjected to in vitro tests. Both fibroblast and osteoblast cells have a good adherence on the Mn-CHA film and on the Ti or polystyrene references. Proliferation and viability tests showed that osteoblast cells growth on Mn-CHA-coated Ti was enhanced as compared to uncoated pure Ti surfaces. Caspase-1 activity was not affected significantly by the material, showing that Mn-CHA does not induce apoptosis of cultured cells. These results demonstrate that Mn-CHA films on Ti should provoke a faster osteointegration of the coated implants as compared to pure Ti. (c) 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 353-358, 2004.

Osteoblast response to phospholipid modified titanium surface

The objective of this study was to evaluate the effect of different phospholipid coatings on osteoblast responses in vitro. Commercially available phospholipids [phosphatidylcholine (PC), phosphatidyl-serine (PS) and phosphatidylinositol (PI)] were converted to their Ca-PL-PO(4) and were coated on commercially pure titanium (Ti) grade 2 disks. Using uncoated Ti surfaces as controls, cell responses to phospholipid-coated surfaces were evaluated using the American Type Culture Collection (Manassas, VA, USA) CRL-1486 human embryonic palatal mesenchyme cells (HEPM), an osteoblast precursor cell line, over a 14-day period. Total protein synthesis and alkaline phosphatase specific activity at 0, 7, and 14 days were measured. It was observed that Ti surfaces coated with PS exhibited enhanced protein synthesis and alkaline phosphatase specific activity compared to other phospholipids and uncoated surfaces. These results indicate the possible usefulness of PS-coated Ti surfaces for inducing enhanced bone formation and are very encouraging for bone and dental implantology.

In vitro osteoblast response to anodized titanium and anodized titanium followed by hydrothermal treatment

In this study, Titanium (Ti) surfaces were modified using anodization. The electrolyte used for anodization was a mixture of calcium glycerophosphate and calcium acetate. The anodized surfaces were divided into three groups. Hydrothermal treatments were performed on two of the anodized groups for either 2 or 4 h. In vitro osteoblast response to anodized oxide and the hydrothermal treated oxide after anodization was evaluated in this study. Calcium and phosphorus ions were deposited on the Ti oxide during anodization. Anodized surfaces following a 4-h hydrothermal treatment were observed to promote the growth apatite-like crystals as compared with anodized surfaces after a 2-h hydrothermal treatment. Cellular function and onset of mineralization, as indicated by protein production and osteocalcin production, respectively, also were observed as enhanced on hydrothermal-treated surfaces. It was thus concluded from this study that calcium phosphate and apatite-like crystals could be deposited on Ti surfaces using anodization and a combination of anodization and hydrothermal treatment. It was also concluded that the phenotypic expression of osteoblast was enhanced by the presence of calcium phosphate or apatite-like crystals on anodized or hydrothermally treated Ti surfaces.

Characterization of calcium phosphate coatings deposited by Nd:YAG laser ablation at 355 nm: influence of thickness

Calcium phosphate coatings were deposited by pulsed laser ablation with a radiation of 355 nm from a Nd:YAG laser. All the coatings were obtained at the same conditions, but deposition was stopped after different number of pulses to get coatings with different thickness. The influence of thickness in the structural and mechanical properties of the coatings was investigated. Coatings structure was characterised by scanning electron microscopy, grazing incidence X-ray diffractometry and Raman spectroscopy. The mechanical properties were evaluated by scratch test. The morphology of the coatings is dominated by the presence of droplets. The coatings are composed mainly of hydroxyapatite, alpha tricalcium phosphate and amorphous calcium phosphate. Thinner coatings withstand higher loads of failure in the scratch test.

Influence of thickness on the properties of hydroxyapatite coatings deposited by KrF laser ablation

The growth of hydroxyapatite coatings obtained by KrF excimer laser ablation and their adhesion to a titanium alloy substrate were studied by producing coatings with thicknesses ranging from 170 nm up to 1.5 microm, as a result of different deposition times. The morphology of the coatings consists of grain-like particles and also droplets. During growth the grain-like particles grow in size, partially masking the droplets, and a columnar structure is developed. The thinnest film is mainly composed of amorphous calcium phosphate. The coating 350nm thick already contains hydroxyapatite, whereas thicker coatings present some alpha tricalcium phosphate in addition to hydroxyapatite. The resulting coating to substrate adhesion was evaluated through the scratch test technique. Coatings fail under the scratch test by spallating laterally from the diamond tip and the failure load increases as thickness decreases, until not adhesive but cohesive failure for the thinnest coating is observed.

Ion-beam-sputtering/mixing deposition of calcium phosphate coatings. I. Effects of ion-mixing beams

Ion-beam-sputtering/mixing deposition was used to produce thin calcium phosphate coatings on titanium substrate from the hydroxyapatite target. The mixing beam could be either Ar(+) or N(+) ions. It was found that as-deposited coatings were amorphous. No distinct peak of the hydroxyl group was observed in FTIR spectra of the coatings, but new spectral peaks, brought about during the deposition process, were present for CO(3)(2-). Scanning electron microscopy revealed that the deposited coatings had a uniform and dense structure. The calcium-to-phosphorous ratio of these coatings varied between 2.0 and 3.0. Compared with the calcium phosphate coatings produced by Ar(+) beam-mixing deposition, the calcium phosphate coatings produced by N(+) beam-mixing deposition exhibited a higher dissolution rate in the physiologic saline solution and showed a lower proliferation rate of osteoblast cells.

The study of surface transformation of pulsed laser deposited hydroxyapatite coatings

Hydroxyapatite (HA) coatings generally exhibit very good biocompatibility owing to their compositional resemblance to the natural hard tissue and to bioactive properties that are directly related to surface transformations in physiological fluids. In this study, two types of porous HA coatings produced with pulsed laser deposition were tested with respect to their dissolution/reprecipitation in a semidynamic simulated physiological solution. Coatings with higher porosity produced with a 355-nm wavelength laser exhibited significant reprecipitation earlier than those produced with a 266-nm wavelength laser. The dissolution of the non-HA phases played a major role in the reprecipitation of HA-like material as indicated by X-ray diffraction (XRD). The coatings' Ca/P ratio became closer to the theoretical value of HA. The newly formed HA had imperfect crystal structure and/or small crystal size as suggested by XRD. The reprecipitation resulted in a very dense morphology as shown by scanning electron microscopy, suggesting a mechanically strong structure after reprecipitation. Despite undergoing dissolution and reprecipitation, the coatings showed sufficient stability in the solution, as XRD and energy-dispersive X-ray studies indicated no significant loss of the coatings. The stability of these HA coatings and their ability to cause reprecipitation of HA in the simulated physiological solution showed the potential of these coatings for clinical applications.

Structural and morphological study of pulsed laser deposited calcium phosphate bioceramic coatings: influence of deposition conditions, laser parameters, and target properties

Calcium phosphate (CaP) bioceramics, especially hydroxyapatite (HA), have been used as coatings on implants owing to their biocompatible properties. The commercial practice for applying HA coating, plasma spraying, has some disadvantages which limit the long-term stability of the implants. Pulsed laser deposition (PLD) is being investigated as an alternative technique. The purpose of this research was to systematically study the effect of various parameters of the PLD process on the properties of CaP coatings. In this study, three types of HA targets and two laser wavelengths were used to make six categories of coatings. Predominantly crystalline HA coatings were produced under all six categories at optimum conditions, although small amounts of minor phases sometimes were found. Sufficient coating/substrate bond strength was also obtained. A wide variety of coating morphologies was obtained, from rather dense and uniform to rough and porous. The important factors that affected the morphology included target properties, vacuum level, deposition temperature, and laser wavelength and energy density. PLD's ability to produce both amorphous and crystalline, and both smooth/dense and rough/porous coatings may be a unique advantage.

Ion-beam-assisted deposition (IBAD) of hydroxyapatite coating layer on Ti-based metal substrate

A hydroxyapatite layer was formed on the surface of a Ti-based alloy by ion-beam-assisted deposition. The deposition methodology comprised of an electron beam vaporizing a pure hydroxyapatite target, while an Ar ion beam was focused on the metal substrate to assist deposition. All deposited layers were amorphous, regardless of the current level of the ion beam. The bond strength between the layer and the substrate increased steadily with increasing current, while the dissolution rate in a physiological saline solution decreased remarkably. These improvements were attributed to an increase in the Ca/P ratio of the layer. Without ion beam assistance, the Ca/P ratio was much lower than the stoichiometric HAp (Ca/P = 1.67). With ion-beam assistance, the Ca/P ratio of the layer increased presumably due to the high sputtering rate of P compared to that of Ca from the layer being coated.

XPS, EDX and FTIR analysis of pulsed laser deposited calcium phosphate bioceramic coatings: the effects of various process parameters

Many techniques have been used to produce calcium phosphate, especially hydroxyapatite (HA), coatings on metallic implant surfaces for improved biocompatibility. Although some techniques have produced coatings used clinically, the long-term stability of the coating/implant is still questionable. As a new technique for making HA coatings, pulsed laser deposition (PLD) shows some advantages in controlling the coatings' crystal structure and composition. In this study, three types of HA target and two wavelengths of laser were used to produce calcium phosphate coatings. Despite PLDs ability to improve the crystal structure by incorporating water vapor into the deposition process, the characterization with EDX and XPS showed that coatings had different Ca/P ratios from that of the pure HA targets, which almost assured the presence of non-HA phases. FTIR spectra also showed differences in phosphate bands of coatings and targets although the difference in data collecting modes might have been a factor. The observed differences might be related to the differences between the surface and bulk chemistries of the coatings. Nevertheless, when evaluating the suitability of the PLD technique for making HA coatings, the possibility of the formation of non-HA phases cannot be excluded, although it may not necessarily be a negative factor.

Calcium phosphate coatings for medical implants

In surgical disciplines where bone has to be repaired, augmented or improved, bone substitutes are essential. Although bone banks, such as Eurotransplant, are founded to supply such substitutes, natural bone is not always adequate. For example, frequently these so-called bone grafts resorb after implantation (1). Further, they cannot be used for joint and tooth replacement, and recently worries have been raised about the transfer of infectious diseases. Therefore, interest has dramatically increased in the use of synthetic materials for replacement of lost or damaged bone tissue. The generic name of these tissue alternatives is biomaterials. A special class of these biomaterials is composed of metallic devices with coatings to improve bone bonding. These specialized coatings used to improve the metallic implant are the topic of this paper.

Characterization of hydroxyapatite film with mixed interface by Ar+ ion beam enhanced deposition

Ar+ ion beam enhanced deposition (IBED) was used to produce a hydroxyapatite (HA) film on polished titanium substrates. In this study, the HA ceramic target was sputtered by an argon-ion beam with an energy of 1.5 KeV, and the sputtered film was intermittently bombarded by energetic argon-ions at 60 KeV. An effective Ca-Ti mixed layer produced by the energetic argon-ion bombardment was confirmed by using Auger electron spectroscopy. The characteristics of the deposited films were evaluated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. XRD analysis revealed that the as-deposited film was amorphous, and a hydroxyapatite-type structure was obtained from the post-heat treatment of the deposited films. SEM observations showed that no distinct difference in surface morphology was found between the as-deposited and heat-treated samples for Ar+ IBED films, suggesting a strongly bonded HA film on the titanium substrate. In comparison with the HA target, some chemistry alterations were brought about in the deposited films, such as the incorporation of CO3, the loss of the OH groups and some distortion of the phosphate lattice.

Structural characterization of pulsed laser-deposited hydroxyapatite film on titanium substrate

Pure, crystalline hydroxyapatite (HA) films with thicknesses of roughly 10 microns have been deposited on titanium substrate using the pulsed laser deposition (PLD) technique. Experimental results indicate that the structure and properties of the PLD-HA films varied with deposition parameters. The PLD process used in the present study did not induce significant amounts of calcium phosphate phases other than apatite, or significant changes in the behaviour of hydroxyl or phosphate functional groups. Broad face scanning electron microscopy showed that HA coating was comprised of numerous essentially spheroidal-shaped particles of different sizes, while the lateral morphology indicated that columnar and dome-shaped structures both existed in the film. Many pinholes and crevices observed on coating surfaces were linked to the original substrate surface crevices/craters. The adhesion strength of the coating, mostly in the range of 30-40 MPa, was found to be closely related to the fractography of the tested specimen. The fracture surfaces of specimens with higher bond strengths were usually accompanied by a higher degree of deformation and coating-substrate debonding, while the fracture of specimens with lower bond strengths occurred more frequently within HA coatings in a more brittle manner. The energy dispersive spectroscopy-determined Ca/P ratios of raw HA powder (1.78) and sintered HA target for PLD (1.79) were very close, indicating that the sintering process used in the present study essentially did not change the Ca/P ratio of HA. After the PLD process, the Ca/P ratio of the HA film increased to 1.99. Cross-sectional scanning electron microscopy-energy dispersive spectroscopy point analysis indicated that the value of the Ca/P ratio was significantly higher in the region near the surface, particularly near the coating-substrate interface, than in the coating interior.

Atomic force microscopic study of the surface morphology of apatite films deposited by pulsed laser ablation

Atomic force microscopy (AFM) has been used to study the surface morphology of apatite films deposited on metallic and polyethylene substrates by laser ablation using KrF and transversely excited atmospheric CO2 lasers. The films are found to consist of a smooth apatite coating with macroparticles scattered on the surface. A wide variety of macroparticles, differing in size, shape and roughness, were found and analysed employing the high spatial resolution of AFM (< 1 nm). We have investigated the correlation between the apatite film morphology and the deposition conditions. Of particular importance are laser fluence, gas pressure, the nature of the target and the substrate temperature. We have explained these dependencies on the basis of a theoretical model which includes evaporation and a cluster-type laser ablation mechanism.