Electrophoretic coating of multilayered apatite composite on alumina ceramics

Tailoring Copper-Doped Bioactive Glass/Chitosan Coatings with Angiogenic and Antibacterial Properties

Implant coatings are frequently applied to modulate tissue response and delivery of drugs. Copper (Cu)-containing coatings on dental implant abutments have been proposed to improve soft tissue integration and reduce the risk for peri-implant infections. However, precise control over Cu loading and release kinetics remains a major challenge. In this study, we introduced a bottom-up coating deposition method based on nanoparticle assembly to allow for local release of Cu ions from implant surfaces. We first doped mesoporous bioactive glass (MBG) nanoparticles with various amounts of Cu. Subsequently, we suspended these Cu-doped MBG (Cu-MBG), Cu-free MBG nanoparticles, or mixtures thereof in chitosan solution and prepared a series of composite coatings on commercially pure titanium disks as model surfaces for transmucosal components of bone implants through electrophoretic deposition (EPD). By changing the Cu-MBG:MBG ratio of the composite coatings, we controlled the Cu release kinetics without changing other coating properties. Human gingival fibroblasts proliferated on the composite coatings except for coatings with the highest amount of Cu, which inhibited their proliferation. The migration rate of human umbilical vein endothelial cells cultured on the composite coatings was highest on coatings containing equal amounts of Cu-MBG and Cu-free MBG. Antibacterial tests confirmed that Cu-containing coatings reduced the growth of Porphyromonas gingivalis up to fivefold compared with uncoated implants. In conclusion, our data indicate that the EPD method is suitable to deposit nanoparticle-based coatings onto dental implants, which enhance endothelial cell migration and reduce bacterial growth.

Nanostructured Hydroxyapatite Coatings for Improved Adhesion and Corrosion Resistance for Medical Implants

Hydroxyapetite (HA) coating on medical implant has been used in commercial application for several decades. The coating, commercially made by thermal spray method, functions as a intermediate layer between human tissues and the metal implant. The coating can speed up early stage healing after operation but the life span is much limited by low interfacial bond strength, which comes from the dissolution of amorphous HA in human body fluid during its service. This amorphous phase is formed in coating process under high temperature. To overcome these problems, we have developed a novel room temperature electrophoretic deposition process to fabricate nanostructured HA coating. This nanostructured HA coating significantly improved coating's bond strength up to 50-60 MPa, 2-3 times better than the thermal sprayed HA coating. The nanostructured HA coating also has corrosion resistance 50-100 times higher than the conventional HA coating. X-ray diffraction shows that all the HA coating is fully crystalline phase. It is expected that the implants with the nanostructured HA coating will have much longer service life. Other benefits derived from this process include room temperature deposition, the ability to control the coating microstructure and phases, and low cost for production.

Electrophoretic deposition of biomaterials

Electrophoretic deposition (EPD) is attracting increasing attention as an effective technique for the processing of biomaterials, specifically bioactive coatings and biomedical nanostructures. The well-known advantages of EPD for the production of a wide range of microstructures and nanostructures as well as unique and complex material combinations are being exploited, starting from well-dispersed suspensions of biomaterials in particulate form (microsized and nanoscale particles, nanotubes, nanoplatelets). EPD of biological entities such as enzymes, bacteria and cells is also being investigated. The review presents a comprehensive summary and discussion of relevant recent work on EPD describing the specific application of the technique in the processing of several biomaterials, focusing on (i) conventional bioactive (inorganic) coatings, e.g. hydroxyapatite or bioactive glass coatings on orthopaedic implants, and (ii) biomedical nanostructures, including biopolymer-ceramic nanocomposites, carbon nanotube coatings, tissue engineering scaffolds, deposition of proteins and other biological entities for sensors and advanced functional coatings. It is the intention to inform the reader on how EPD has become an important tool in advanced biomaterials processing, as a convenient alternative to conventional methods, and to present the potential of the technique to manipulate and control the deposition of a range of nanomaterials of interest in the biomedical and biotechnology fields.

Magnesium-sputtered titanium for the formation of bioactive coatings

Osteoconductive coatings may improve the clinical performance of implanted metallic biomaterials. Several low-temperature coating methods have been reported where a supersaturated solution is used to deposit typically apatitic materials. However, due to the very low solubility of apatite, the concentration of calcium and phosphate ions attainable in a supersaturated solution is relatively low ( approximately 1-2mM), thus coating formation is slow, with several solution changes required to form a uniform and clinically relevant coating. In order to avoid this problem, we present a novel method where substrates were initially sputter coated with pure magnesium metal and then immersed in differing phosphate solutions. In this method, upon immersion the implant itself becomes the source of cations and only the anions to be incorporated into the coating are present in solution. These ions react rapidly, forming a continuous coating and avoiding problems of premature non-localized precipitation. The different coatings resulting from varying the phosphate solutions were then characterized in terms of morphology and composition by microscopy and chemical analyses. Upon immersion of the sputter-coated metals into ammonium phosphate solution, it was found that a uniform struvite (MgNH(4)PO(4).6H(2)O) coating was formed. Upon subsequent immersion into a calcium phosphate solution, stable coatings were formed. The coated surfaces also enhanced both osteoblastic cellular adhesion and cell viability compared to bare titanium. The concept of sputter-coating a reactive metal to form an adherent inorganic metal coating appears promising in the field of developing rapid-forming low-temperature bioceramic coatings.

Zirconia toughened alumina ceramic foams for potential bone graft applications: fabrication, bioactivation, and cellular responses

Zirconia toughened alumina (ZTA) has been regarded as the next generation orthopedic graft material due to its excellent mechanical properties and biocompatibility. Porous ZTA ceramics with good interconnectivity can potentially be used as bone grafts for load-bearing applications. In this work, three-dimensional (3D) interconnected porous ZTA ceramics were fabricated using a direct foaming method with egg white protein as binder and foaming agent. The results showed that the porous ZTA ceramics possessed a bimodal pore size distribution. Their mechanical properties were comparable to those of cancellous bone. Due to the bio-inertness of alumina and zirconia ceramics, surface bioactivation of the ZTA foams was carried out in order to improve their bioactivity. A simple NaOH soaking method was employed to change the surface chemistry of ZTA through hydroxylation. Treated samples were tested by conducting osteoblast-like cell culture in vitro. Improvement on cells response was observed and the strength of porous ZTA has not been deteriorated after the NaOH treatment. The porous 'bioactivated' ZTA ceramics produced here could be potentially used as non-degradable bone grafts for load-bearing applications.

Electrophoretic deposition of zirconia-Bioglass composite coatings for biomedical implants

Composite bilayer coatings on Ti6Al4V substrates were prepared by electrophoretic deposition, a simple and fast low temperature coating technique. Biocompatible yttrium-stabilized zirconia (YSZ) in the form of nanoparticles and bioactive Bioglass (45S5) in the form of microparticles were chosen as coating materials. The first layer consisted of 5 microm of YSZ, deposited with the intention to avoid any metal tissue contact. The second layer consisted of 15-microm thick 45S5-YSZ composite, supposed to react with the surrounding bone tissue and to enhance implant fixation. The adsorption of YSZ nanoparticles on 45S5 microparticles in organic suspension was found to invert the surface charge of the 45S5 particles from negative to positive. This enabled cathodic electrophoretic deposition of 45S5, avoiding uncontrolled anodization (oxidation) of the substrate. The coatings were sintered at 900 degrees C for 2 h under argon flow. The characterization was performed using SEM, EDX, and nanoindentation (cross section). Potential applications in the orthopedics field are discussed.

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.

Calcium phosphates formation on CaTiO3 coated titanium

In this study, performance of calcium phosphate formation of CaTiO3 coating film on Ti in Hanks' balanced saline solution (HBSS) was investigated. CaTiO3 thin films with a thickness of 50 nm were deposited on Ti using radiofrequency (RF) magnetron sputtering. The temperature of Ti substrate was adjusted to room temperature (RT) and 873 K. Thereafter, the specimens deposited at RT were annealed at 873 K in air for 7.2 ks. The films were characterized by grazing incident angle X-ray diffractometry (GI-XRD) and X-ray photoelectron spectroscopy (XPS). After immersion in HBSS for 60 d, on CaTiO3 coated Ti, the formation of hydroxyapatite (HAP) was observed. Furthermore, HAP layer formed was thicker on the specimen on which CaTiO3 film was deposited at RT and annealed than that prepared at 873 K. The major difference between both specimens was the chemical properties of the outermost surface. In summary, CaTiO3 thin film deposited at RT and followed by annealing at 873 K for 7.2 ks in air enhances calcium phosphate formation ability on Ti.

Hydrothermal crystallization of carbonate-containing hydroxyapatite coatings prepared by radiofrequency-magnetron sputtering method

Carbonate-containing hydroxyapatite (HA) films were prepared by low-temperature hydrothermal annealing from carbonate-containing calcium phosphate amorphous coatings on titanium substrates. The biocompatibility of the carbonate-containing HA layers was estimated by in vitro tests using simulated body fluid (SBF). Precursory amorphous coatings were deposited with rf-magnetron sputtering apparatus, using calcium phosphate glass target in Ar/CO2 atmosphere. The carbonate-containing HA coatings were successfully formed by the annealing at above 130 degrees C for 20 h. On the basis of SEM observation, about 2-microm thickness films coated rigidly were durable enough for the hydrothermal treatment. The coating layer was revealed to consist of single phase of PO4(-) and OH- partially carbonated HA by XRD and IR analyses. Overgrowing of bone-like apatite layers on the carbonate-containing HA surfaces in the SBF implied that the obtained films acquired a sufficient osteoconductivity, while it was still unclear that activity was enhanced, compared to pure HA coatings. The low-temperature hydrothermal annealing method was effective for preparation of rigid HA coatings on titanium as well as modification of their chemical compositions.

SiO2-CaO-K2O coatings on alumina and Ti6Al4V substrates for biomedical applications

Alumina and Ti6Al4V alloys are widely used for orthopedics and dental applications due to their good mechanical properties and biocompatibility. Unfortunately they can not provide a satisfactory osteointegration when implanted. In fact, both alumina and Ti6Al4V are not bioactive and thus they can only guarantee a morphological fixation with the surrounding tissues without a suitable chemical anchorage. Aiming to impart bioactive properties to these materials a coating can be proposed. At this purpose, a bioactive glass belonging to the SiO2-CaO-K2O system was selected and prepared. This glass, named SCK, possess a thermal expansion coefficient matching with the alumina (8.5x 10(- 6)/ degrees C) and Ti6Al4V (9 x 10(- 6)/ degrees C) ones and thus is a good candidate to produce coatings on both of them. Simple and low-cost enameling and glazing techniques were used to realize the coatings. Structural, morphological and compositional characterizations of the coatings were carried out by means of X-ray diffraction, optical and scanning microscopy and compositional analyses. The in vitro properties of the coatings were investigated by soaking them in a simulated body fluid (SBF) in order to study the precipitation, on their surfaces, of a biologically active layer of hydroxylapatite (HAp).

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.

Fluoroapatite glass-ceramic coatings on alumina: structural, mechanical and biological characterisation

The aim of this work was to realise bioactive coatings on full density alpha-alumina substrates. An SiO2-CaO-based glass (SC) and an SiO2-Al2O3-P2O5-K2O-CaO-F--based glass-ceramic (SAF) were used for this purpose. Specifically, SAF is a fluoroapatite containing glass-ceramic and previous studies have shown that it is a highly bioactive biomaterial. Furthermore, these fluoroapatite crystals possess a needle-shaped morphology which mimics that of hydroxylapatite found in human hard tissues, particularly in teeth. SAF is a very viscous glass-ceramic and for this reason an intermediate, less viscous, SC layer was interposed in direct contact with alumina aiming to obtain a good coating adhesion. Moreover, this intermediate layer strongly lowers the Al3+ diffusion and thus minimises both compositional changes in the SAF outer layer and the risk of detrimental modifications of the nature of the crystalline phases. A complete characterisation of the coated samples was performed by means of X-ray diffraction, optical and scanning microscopy. Coating adhesion on alumina was tested by comparative shear tests while biocompatibility was investigated on alumina. bulk SAF and on the realised coatings. For this purpose, cytotoxicity, adhesion and proliferation of human osteoblast-like cells were cultured onto the three materials. Results showed that the interposition of the SC layer was successful in allowing a good softening and spreading of the SAF outer layer and in avoiding the crystallisation of undesired crystalline phases maintaining the good bioactive properties of the bulk one. In vitro results on the coatings showed osteoblast-like cell behaviour similar to bulk fluoroapatite glass-ceramic and better respect to alumina substrates, being a promising index of bone material integration and of its in vivo possible applications.