Influence of deposition parameters on chemical properties of calcium phosphate coatings prepared by using electrostatic spray deposition

The Anatase Phase of Nanotopography Titania with Higher Roughness Has Better Biocompatibility in Osteoblast Cell Morphology and Proliferation

Previous studies have concluded that surface-modified titanium oxide (titania, TiO2) surface properties promote osteoblast cell morphology and proliferation. To screen a suitable structured titania coating with the best biocompatibility to be used in dental implants, five titania films (two amorphous, one rutile, and two anatases) with different surfaces were successfully synthesized on polished titanium by radio frequency (RF) magnetron sputtering. We applied atomic force microscopy (AFM) and X-ray diffraction (XRD) to depict the formulations. Furthermore, MC3T3-E1, the mouse osteoblast precursor cell, was used to assess cell proliferation and observe morphologic changes at the film surface. The data indicated that the overall number of MC3T3-E1 cells on anatase films was significantly higher as compared with cells on rutile and amorphous films. Meanwhile, the actin filaments of the cells grown on the anatase phase films were well defined and fully spread. In addition, the film with higher roughness had enhanced biocompatibility than that with lower roughness. The results showed that the crystal phase and titania coated roughness had a greater influence on the biocompatibility of nanostructured titania film. The higher the roughness of the anatase phase was, the better bioactivity for the morphology and proliferation of osteoblast. This is a good surface-modified biological material and may have a good application prospect in dental implants.

Calcium orthophosphate deposits: Preparation, properties and biomedical applications

Since various interactions among cells, surrounding tissues and implanted biomaterials always occur at their interfaces, the surface properties of potential implants appear to be of paramount importance for the clinical success. In view of the fact that a limited amount of materials appear to be tolerated by living organisms, a special discipline called surface engineering was developed to initiate the desirable changes to the exterior properties of various materials but still maintaining their useful bulk performances. In 1975, this approach resulted in the introduction of a special class of artificial bone grafts, composed of various mechanically stable (consequently, suitable for load bearing applications) implantable biomaterials and/or bio-devices covered by calcium orthophosphates (CaPO4) to both improve biocompatibility and provide an adequate bonding to the adjacent bones. Over 5000 publications on this topic were published since then. Therefore, a thorough analysis of the available literature has been performed and about 50 (this number is doubled, if all possible modifications are counted) deposition techniques of CaPO4 have been revealed, systematized and described. These CaPO4 deposits (coatings, films and layers) used to improve the surface properties of various types of artificial implants are the topic of this review.

A silver ion-doped calcium phosphate-based ceramic nanopowder-coated prosthesis increased infection resistance

BACKGROUND

Despite progress in surgical techniques, 1% to 2% of joint arthroplasties become complicated by infection. Coating implant surfaces with antimicrobial agents have been attempted to prevent initial bacterial adhesion to implants with varying success rates. We developed a silver ion-containing calcium phosphate-based ceramic nanopowder coating to provide antibacterial activity for orthopaedic implants.

QUESTIONS/PURPOSES

We asked whether titanium prostheses coated with this nanopowder would show resistance to bacterial colonization as compared with uncoated prostheses.

METHODS

We inserted titanium implants (uncoated [n = 9], hydroxyapatite-coated [n = 9], silver-coated [n = 9]) simulating knee prostheses into 27 rabbits' knees. Before implantation, 5 × 10(2) colony-forming units of Staphylococcus aureus were inoculated into the femoral canal. Radiology, microbiology, and histology findings were quantified at Week 6 to define the infection, microbiologically by increased rate of implant colonization/positive cultures, histologically by leukocyte infiltration, necrosis, foreign-body granuloma, and devitalized bone, and radiographically by periosteal reaction, osteolysis, or sequestrum formation.

RESULTS

Swab samples taken from medullary canals and implants revealed a lower proportion of positive culture in silver-coated implants (one of nine) than in uncoated (eight of nine) or hydroxyapatite-coated (five of nine) implants. Silver-coated implants also had a lower rate of colonization. No cellular inflammation or foreign-body granuloma was observed around the silver-coated prostheses.

CONCLUSIONS

Silver ion-doped ceramic nanopowder coating of titanium implants led to an increase in resistance to bacterial colonization compared to uncoated implants.

CLINICAL RELEVANCE

Silver-coated orthopaedic implants may be useful for resistance to local infection but will require in vivo confirmation.

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.

Electrohydrodynamic deposition of nanotitanium doped hydroxyapatite coating for medical and dental applications

Nano-sized titanium containing hydroxyaptite has been prepared, the particle size of nanoTiHA was shown to be 12-20 nm in width and 30-40 nm in length, smaller than that of nanoHA. X-ray diffraction analysis revealed the phase purity of nanoTiHA produced. Antimicrobical assays demonstrated that nanoTiHA has excellent growth inhibitory properties, and is able to inhibit the growth of all bacterial strains tested, both Gram-negative and Gram-positive species, including multi-antibiotic resistant EMRSA 15 and EMRSA 16 'superbugs'. Biocidal activity against all four Staphylococcus spp was also shown at the concentration tested. Nanostuctured TiHA coating was successfully deposited onto Ti surfaces using EHDA spraying under optimized processing conditions with the thickness of the coating being further controlled by the spraying time. All of the nanoTiHA coated Ti surfaces were able to support human osteoblast (HOB) cell attachment and growth. The coating thickness did not significantly influence the proliferation of HOB cells on nanoTiHA coatings, while the ability of nanoTiHA coating to support HOB cell differentiation was demonstrated from the alkaline phosphatase activity. Our study showed that nanoTiHA has excellent anti-bacterial properties and the thin nanoTiHA coating was also able to support the attachment, growth and differentiation of HOB cells. Therefore, nanoTiHA coating could pave the way for the development of the next generation of dental and orthopedic implants by offering anti-infection potential in addition to osteoconductivity.

The anatase phase of nanotopography titania plays an important role on osteoblast cell morphology and proliferation

The surface properties of biomaterials play a vital role in cell morphology and behaviors such as cell adhesion, migration, proliferation and differentiation. Three different crystal phases of titania film (rutile, anatase and amorphous titania) with similar roughness were successfully synthesized by DC reactive magnetron sputtering. The surface roughness of each film was about 8-10 nm. Primary rat osteoblasts were used to observe changes in morphology and to evaluate cell behavior at the film surface. The number of the osteoblasts on anatase film was significantly higher than rutile and amorphous films after 36 and 72 h incubation. More importantly, synthesis of alkaline phosphatase was significantly greater by osteoblasts cultured on anatase film than on rutile and amorphous films after 7 and 14 days. In addition, the cells grown on the anatase phase film had the largest spreading area; the actin filaments in cells with regular directions were well defined and fully spreaded. The results indicate that the anatase phase of titania with nanoscale topography yield the best biological effects for cell adhesion, spreading, proliferation and differentiation. There are strong therapeutic prospects for this biomaterial film for osteoblast proliferation, with possible applications for orthopedic and dental implant.

Characterization andin vitro evaluation of biphasic calcium pyrophosphate–tricalciumphosphate radio frequency magnetron sputter coatings

The objective of this study was to characterize the physicochemical, dissolution, and osteogenic properties of radio frequency magnetron sputtered dicalcium pyrophosphate/tricalciumphosphate (Pyro/TCP) and hydroxylapatite (HA) coatings. Therefore Pyro/TCP and HA coatings were deposited on grit-blasted titanium discs. The results showed that the deposited coatings were amorphous and changed into a crystalline structure after IR heat-treatment of 550 degrees C for HA and 650 degrees C for Pyro/TCP. Heat-treated HA coatings appeared to be stable during immersion in simulated body fluid (SBF), that is no changes in the XRD pattern were observed. Also, no dissolution of the coating was observed by scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) revealed that the Ca/P ratio of the HA coatings remained constant during SBF immersion. On the other hand, the heat-treated Pyro/TCP coatings showed a surface reaction of calcium pyrophosphate into a beta-tricalcium phosphate phase during SBF immersion. This was confirmed by EDS analysis. Rat bone marrow-derived osteoblast-like cells cultured on the heat-treated substrates showed that cell proliferation and differentiation occurred on both types of bioceramic coatings. No significant differences for proliferation and early differentiation were observed between cells cultured on heat-treated Pyro/TCP and HA at individual time points. However, osteocalcin expression, a late marker for osteoblast-like cell differentiation, was significantly increased after 12 days of culture on HA-coatings. These results were confirmed by SEM observations and suggest increased osteogenic properties for HA-coatings over Pyro/TCP-coatings. Additional research is necessary to obtain conclusive evidence on the in vivo osteogenic capacity of Pyro/TCP coatings.

In vitro and in vivo reactivity of porous, electrosprayed calcium phosphate coatings

The dissolution and/or precipitation behaviour of porous calcium phosphate (CaP) coatings, deposited using electrostatic spray deposition (ESD), was investigated (a) in vitro after soaking in simulated body fluid (SBF) for several time periods (2, 4, 8, and 12 weeks), and (b) in vivo after subcutaneous implantation of CaP-coated implants in the back of goats for identical time periods. Physical and chemical properties of coatings were characterized before and after in vitro/vivo testing by means of scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and energy dispersive spectroscopy. Moreover, part of the explants was prepared for light microscopical evaluation of the tissue response. In vitro, all apatitic ESD-coatings induced the formation of homogeneous and adherent CaP precipitation layers. Amorphous CaP, however, displayed a delayed precipitation of poorly adherent CaP layers, whereas heterogeneous calcification was observed on top of beta-TCP-coated substrates, indicating that beta-TCP and amorphous CaP coatings exhibit a poor ability of inducing calcification in SBF as compared to crystalline apatitic coatings. In vivo, no adverse tissue reactions (toxic effects/inflammatory cells) were observed using light microscopy, and all coatings became surrounded by a dense, fibrous tissue capsule after implantation. All ESD-coatings degraded gradually at a dissolution rate depending on the chemical phase (order of relative solubility: amorphous CaP approximately carbonate apatite>beta-TCP>carbonated hydroxyapatite), thereby enabling synthesis of CaP coatings with a tailored degradation rate.

Mechanical properties of porous, electrosprayed calcium phosphate coatings

Mechanical properties of calcium phosphate coatings (CaP), deposited using the electrostatic spray deposition (ESD) technique, have been characterized using a range of analytical techniques, including tensile testing (ASTM C633), fatigue testing (ASTM E855), and scratch testing using blunt and sharp scratch styli. Moreover, a simple explantation procedure was successfully introduced using ESD-coated, threaded dental implants to characterize the mechanical performance of CaP coatings qualitatively under conditions that mimic clinical situations as close as possible. Generally, all analysis techniques revealed that ESD coatings need to be crystallized in order to ensure interfacial adhesion to the substrate and sufficient mechanical strength of the superficial reticular structure. Crystalline carbonated hydroxyapatite coatings (CHA, heat-treated at 700 degrees C) were resistant to fatigue as well as to plastic ploughing deformation by means of various scratch styli, and the fragile surface structure of ESD coatings was maintained to a large extent after unscrewing CHA-coated dental implants from femoral condyles of goat cadavers. From these experiments, it was concluded that interfacial adhesion of crystalline CHA ESD coatings to the titanium substrate was sufficient, but that mechanical strength of the superficial architecture of ESD coatings need to be optimized for applications where high shear and compressive stresses are imposed onto the rather fragile coating surface of reticular ESD morphologies.