Morphological regulation and crystal growth of hydrothermal-electrochemically deposited apatite

Velvet antler polypeptide combined with calcium phosphate coating to protect peripheral nerve cells from oxidative stress

Functionalizing biomaterial substrates with biological signals shows promise in regulating cell behaviors through mimicking cellular microenvironment. Calcium phosphate (CaP) coating is an excellent carrier for immobilizing biological molecules due to its non-toxicity, good biocompatibility, biodegradability, and favorable affinity to plenty of molecules. In this study, we reported the adhesion, the viability and proliferation behaviors after oxidative stress injury of Schwann cells RSC96 on CaP immobilized with the Velvet Antler Peptide (VAP) isolated from velvet antler through coprecipitation process in modified Dulbecco's phosphate-buffered saline (DPBS) containing VAP. This approach provided well retention of functional molecules up to 28 days, and supported the adhesion and proliferation of RSC96 after oxidative stress injury without cytotoxicity. The simple and reproducible method of coprecipitation suggests that CaP is an ideal carrier to functionalize materials with biological molecules for peripheral nerve repair-related applications.

Bioactive-hybrid-zirconia implant surface for enhancing osseointegration: an in vivo study

Background

Zirconia is characterized by a hard, dense, and chemically inert surface which requires additional surface treatments in order to enhance osseointegration. The proposed hypothesis of the study was that combination of a nano-porous surface infiltrated with a bioactive material may enhance osseointegration of zirconia implants.

Methods

Custom-made zirconia implants (3.7 mm × 8 mm) were designed, milled, and sintered according to manufacturer recommendations. All implants received selective infiltration etching (SIE) technique to produce a nano-porous surface. Surface porosities were either filled with nano-hydroxy apatite particle- or platelet-rich plasma while uncoated surface served as a control (n = 12, α = 0.05). New surface properties were characterized with mercury porosimetry, XRD analysis, SEM, and EDX analysis. Implants were inserted in femur head of rabbits, and histomorphometric analysis was conducted after healing time to evaluate bone–implant contact percentage (BIC%).

Results

Selective infiltration etching produced a nano-porous surface with interconnected surface porosities. Mercury porosimetry revealed a significant reduction in total porosity percent after application of the two coating materials. XRD patterns detected hexagonal crystal structure of HA superimposed on the tetragonal crystal phase of zirconia. Histomorphometric analysis indicated a significantly higher (F = 14.6, P < 0.001) BIC% around HA–bioactive–hybrid surface (79.8 ± 3%) and PRP-coated surface (71 ± 6 %) compared to the control (49 ± 8%).

Conclusions

Bioactive–hybrid–zirconia implant surface enhanced osseointegration of zirconia implants.

Corrosion resistance of a novel SnO2-doped dicalcium phosphate coating on AZ31 magnesium alloy

A SnO₂-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition. The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 μm. The surface of the coating became smooth with an increase additive amount of the SnO₂ nanoparticles. The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO₂ were reduced compared to the coating without SnO₂ and the bare AZ31 substrate, indicating an improvement in the corrosion resistance of the SnO₂-doped coating.

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A thick and dense SnO₂-doped DCPA coating forms via hydrothermal deposition.

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The DCPA coating doped with 10 g L⁻¹ SnO₂ exhibits the best corrosion resistance.

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SnO₂ provided heterogeneous nucleation sites for the deposition of Ca²⁺ and HPO₄²⁻.

In vivo Study on the Corrosion Behavior of Magnesium Alloy Surface Treated with Micro-arc Oxidation and Hydrothermal Deposition

OBJECTIVE

To study the corrosion behavior of magnesium alloy surface treated with micro-arc oxidation and hydrothermal deposition in living animals.

METHODS

A magnesium oxide (MgO) layer was prepared on Mg alloy using micro-arc oxidation technology, and then a composite coating composed of magnesium hydroxide, hydroxyapatite, and MgO was coated on the MgO layer using the hydrothermal deposition method for 2 h and 24 h. Male 3-month-old white New Zealand rabbits (n = 48) weighting 2200-2300 g, were divided into four groups randomly. The prepared Mg alloy samples with composite coatings were implanted into the femoral medullary cavity of rabbits. For the Mg group, bare Mg samples without any treatment were implanted; for the MgO group, bare Mg samples undergoing MAO treatment were implanted; for the HT2h group, samples of the MgO group undergoing hydrothermal treatment (HT) for 2 h were implanted; and for the HT24h group, samples of group MgO undergoing HT for 24 h were implanted. Then the in vivo corrosion behaviors of implants were evaluated by X-ray observation, micro-CT analysis and serum Mg2+ examination.

RESULTS

The X-ray showed that samples implanted in animals were decreased as time went by. The micro-CT showed that on the fourth week, the residual volume percentages (RVP) of samples of the Mg, MgO, HT2h, and HT24h groups were 72.81% ± 2.10%, 71.68% ± 1.49%, 81.14% ± 1.54%, and 82.04% ± 0.89%, respectively; on the eighth week, the RVP of four groups were 29.45% ± 1.06%, 41.82% ± 1.13%, 53.92% ± 0.37%, and 62.53% ± 2.06%, respectively; while on the 12th week, RVP were 8.45% ± 0.49%, 9.97% ± 0.75%, 37.09% ± 0.89%, 46.71% ± 1.87%. The RVP of the HT2h group and the HT24h group were higher than for the Mg group and the MgO group for all three time points (P < 0.05); the RVP for HT24h was higher than for HT2h at 8 and 12 weeks, and the differences were significant, indicating that the degradation of Mg alloy slowed down after composite coating. In addition, the composite-coated Mg alloy by 24-h hydrothermal treatment exhibited a slower degradation than that treated by 2 h. Serum Mg2+ concentration results showed that on the second week, the Mg2+ concentrations of the Mg, MgO, HT2h, and HT24h groups were 2.24 ± 0.10 mmol/L, 2.12 ± 0.07 mmol/L, 2.06 ± 0.11 mmol/L, and 2.15 ± 0.12 mmol/L, respectively. On the fourth week, these concentrations were 1.99 ± 0.33 mmol/L, 2.18 ± 0.06 mmol/L, 2.17 ± 0.09 mmol/L, and 2.13 ± 0.14 mmol/L, respectively. On the eighth week, the concentrations were 2.22 ± 0.09 mmol/L, 2.20 ± 0.17 mmol/L, 2.06 ± 0.11 mmol/L, and 2.14 ± 0.07 mmol/L, respectively. On the 12th week, the concentrations were 2.18 ± 0.04 mmol/L, 2.20 ± 0.08 mmol/L, 2.09 ± 0.02 mmol/L, and 2.16 ± 0.11 mmol/L.

CONCLUSION

The combination of micro-arc oxidation and hydrothermal deposition can greatly improve the anti-corrosion behavior of Mg alloy, and Mg alloy coated with this composite coating is a promising biomaterial with a satisfactory degradation rate.

Biodegradable/biocompatible coated metal implants for orthopedic applications

Biocompatible metals have been suggested as revolutionary biomaterials for bone-grafting therapies. Although metals and their alloys are widely and successfully used in producing biomedical implants due to their good mechanical properties and corrosion resistance, they have a lack in bioactivity. Therefore coating of the metal surface with calcium phosphates (CaP) is a benign way to achieve well bioactivity and get controlled corrosion properties. The biocompatibility and bioactivity calcium phosphates (CaP) in bone growth were guided them to biomedical treatment of bone defects and fractures. Many techniques have been used for fabrication of CaP coatings on metal substrates such as magnesium and titanium. The present review will focus on the synthesis of CaP and their relative forms using different techniques especially electrochemical techniques. The latter has always been known of its unique way of optimizing the process parameters that led to a control in the structure and characteristics of the produced materials.

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.

Mineral substituted hydroxyapatite coatings deposited on nanoporous TiO2 modulate the directional growth and activity of osteoblastic cells

The biocompatibility of anodized titanium was improved by electrophoretically deposited mineral substituted HAP.

Syntheses of single-crystal apatite particles with preferred orientation to the a- and c-axes as models of hard tissue and their applications

Hydroxyapatite [Ca10(PO4)6(OH)2; HAp] is the mineral component of vertebrate hard tissues and an important raw material for biomaterials. The HAp crystal belongs to a hexagonal system and has two types of crystal plane with different atomic arrangements: positively charged calcium ions are mainly present in the a(b)-planes, while negatively charged phosphate ions and hydroxyl groups are mainly present in the c-planes. In vertebrate long bone surfaces, HAp crystals have a c-axis orientation, which leads to the development of the a(b)-plane; while in tooth enamel surfaces, they have an a(b)-axis orientation, which leads to the development of the c-plane. However, it is not clear why the orientations of long bone and tooth enamel are in different crystal planes. In order to clarify this question, we have synthesized single-crystal apatite particles with preferred orientation to the a- and c-axes as models for bone and teeth enamel. This review first describes the syntheses process of single-crystal apatite particles with preferred orientation to a(b)- and c-axes and then discusses specific protein adsorption to the crystal surface of the resulting plate- and fiber-shaped apatite particles with different surface charges. In addition, porous apatite-fiber scaffolds (AFSs) fabricated using the fiber-shaped apatite particles and their application to tissue engineering of bone are described on the basis of the three-dimensional cell culture of mesenchymal stem cells derived from rat bone marrow using the AFS settled into a radial-flow bioreactor.

Calcium phosphate deposition rate, structure and osteoconductivity on electrospun poly(l-lactic acid) matrix using electrodeposition or simulated body fluid incubation

Mineralized nanofibrous scaffolds have been proposed as promising scaffolds for bone regeneration due to their ability to mimic both nanoscale architecture and chemical composition of natural bone extracellular matrix. In this study, a novel electrodeposition method was compared with an extensively explored simulated body fluid (SBF) incubation method in terms of the deposition rate, chemical composition and morphology of calcium phosphate formed on electrospun fibrous thin matrices with a fiber diameter in the range ~200-1400 nm prepared using 6, 8, 10 and 12 wt.% poly(l-lactic acid) (PLLA) solutions in a mixture of dichloromethane and acetone (2:1 in volume). The effects of the surface modification using the two mineralization techniques on osteoblastic cell (MC3T3-E1) proliferation and differentiation were also examined. It was found that electrodeposition was two to three orders of magnitude faster than the SBF method in mineralizing the fibrous matrices, reducing the mineralization time from ~2 weeks to 1h to achieve the same amounts of mineralization. The mineralization rate also varied with the fiber diameter but in opposite directions between the two mineralization methods. As a general trend, the increase of fiber diameter resulted in a faster mineralization rate for the electrodeposition method but a slower mineralization rate for the SBF incubation method. Using the electrodeposition method, one can control the chemical composition and morphology of the calcium phosphate by varying the electric deposition potential and electrolyte temperature to tune the mixture of dicalcium phosphate dihydrate and hydroxyapatite (HAp). Using the SBF method, one can only obtain a low crystallinity HAp. The mineralized electrospun PLLA fibrous matrices from either method similarly facilitate the proliferation and osteogenic differentiation of preosteoblastic MC3T3-E1 cells as compared to neat PLLA matrices. Therefore, the electrodeposition method can be utilized as a fast and versatile technique to fabricate mineralized nanofibrous scaffolds for bone tissue engineering.

Development of a,b-plane-oriented hydroxyapatite ceramics as models for living bones and their cell adhesion behavior

In vertebrate bones and tooth enamel surfaces, the respective a,b-planes and c-planes of hydroxyapatite (HAp) crystals are preferentially exposed. However, the reason why the HAp crystals show different orientations depending on the type of hard tissues is not yet understood. To clarify this question, appropriate ceramic models with highly preferred orientation are necessary. In the present study, dense HAp ceramic models which have the same orientation as living bones were fabricated using composite powders of c-axis-oriented single-crystal apatite fibers (AF) and wet-synthesized apatite gels (AG). The results of crystalline identification and ultrastructural observation showed that the resulting HAp ceramics maintained the c-axis orientation of the AF particles, and their high a,b-plane orientation degrees could be maintained with small additive amounts of AG; however, when the AG content was over 30 mass%, this value decreased. The influence of orientation degree on the surface characteristics was investigated by evaluating the surface zeta-potential and wettability. These results show that increasing the a,b-plane orientation degree shifted the surface charge from negative to positive, and decreased the surface wettability. Initial cell-attachment assays were performed on these resulting ceramics using MC3T3-E1 cells as models of osteoblasts. The results show that the cell-attachment efficiency decreased with increasing a,b-plane orientation degree.

Synthesis of dental enamel-like hydroxyapatite through solution mediated solid-state conversion

An ordered dental enamel-like structure of hydroxyapatite (HAp) was achieved through a solution mediated solid-state conversion process with organic phosphate surfactant and gelatin as the mediating agent. Transmission electron microscopy (TEM) tests demonstrated uniform sizes in the obtained apatite nanorods which arranged in parallel to each other along the c-axis and formed organized microarchitectural units over 10 microm in size. The sizes of the synthetic hydroxyapatite nanorods were similar to that observed in enamel from human teeth. The formation and regulation of the orientation and size of HAp nanorods might lead to a better understanding of the biomineralization process for the preparation of high performance biomaterials.

Preparation of nanometer-scale rod array of hydroxyapatite crystal

Fabrication of nano- or micro-structured scaffolds to mimic structural and three-dimensional details of natural bone or teeth has been the subject of much interest, and this study proposes a new strategy for self-assembling one-dimensional hydroxyapatite (HAp) nanorods into organized superstructures. A nanometer-scale rod array of HAp having preferred orientation to the c-axis was successfully prepared simply by soaking calcium-containing silicate glass substrates in Na(2)HPO(4) aqueous solution at 80 degrees C for various periods. Those HAp rods grew perpendicularly to the glass surface, and the crystallites covered the glass surface uniformly, resulting in a "dental enamel-like" rod array structure consisting of "pine-leaf-like" structure units.

Sonoelectrochemical deposition of calcium phosphate coatings on carbon materials--effect of electrolyte concentration

Calcium phosphate was deposited on carbon materials using a sonoelectrochemical method in an electrolyte containing calcium and phosphate ions. The effect of electrolyte concentration on sonoelectrochemically deposited calcium phosphate coatings was investigated and the underlying deposition mechanisms were discussed. The morphology, size and composition of the crystalline deposits changed with the electrolyte concentration. A mixture of plate, sphere and needle-like deposits was obtained at Ca(2+) ion concentrations greater than 16 mM, however needle-like hydroxyapatite (HA) was obtained at lower Ca(2+) concentrations. Analysis revealed that the sonoelectrochemical deposition of calcium phosphate consists of two processes-nucleation and crystal growth. The results suggest that the homogeneous nucleation of calcium phosphates in solution, followed by their absorption onto the carbon surface may account for the mechanism of coating observed at higher ionic concentrations. At lower concentrations, heterogeneous nucleation occurs on the surface of the carbon fibres, followed by the development of islands of crystal growth. The lower ionic concentration was shown to favour the generation of hydroxyapatite on carbon-based materials.

Sonoelectrochemical deposition of calcium phosphates on carbon materials: effect of current density

Calcium phosphate (CaP) coatings on carbon fabric substrate were produced by sonoelectrodeposition at different current densities (5, 8, 13, 20 and 34 mA/cm2). The surface morphology and chemical composition of the coatings were characterized by SEM, Raman and FTIR spectra. The results showed that at 5 mA/cm2 current density, the coating exhibits plate-like morphology, indicating an octacalcium phosphate (OCP) phase was pre-formed in the deposits and then converted into hydroxyapatite (HA). When the current density was increased to 8 mA/cm2 and higher, the coatings exhibited needle-like morphology corresponding to a HA phase. Furthermore, the sonoelectrodeposited CaP coating exhibited denser and more uniform structures with smaller crystal sizes as the current density increased. Cathodic reaction mechanisms of CaP coatings on carbon in the sonoelectrochemical processes are proposed to explain the different kinds of calcium phosphate obtained.

Apatite formation on titanium substrates by electrochemical deposition in metastable calcium phosphate solution

An apatite layer was successfully formed on titanium substrates by electrochemical deposition in a metastable calcium phosphate solution, which had 1.5 times the ion concentrations of a normal simulated body fluid, but did not contain MgCl(2).6H(2)O, at 41 degrees C for 40 or 60 min at 13 mA. The current did not produce large effects on the crystalline size of the apatite, but the thickness of the apatite layer could be controlled by deposition conditions such as electrolyte temperature, current and deposition time. It is expected that the present electrochemical deposition will be useful to rapidly coat apatite on metallic materials.

Calcium phosphate formation on titanium by low-voltage electrolytic treatments

Electrochemical treatments are expected to be effective for the coating of calcium phosphate ceramics to a titanium substrate. In the present study, two types of chronoamperometry with a step potential and a cyclic wave potential at low voltage (up to 2.0 V) and low current density were performed in Hanks' solution to modify the surface characteristics of titanium. Titanium oxide film formed by self-passivation, that formed as reconstructed film during electrochemical treatments, and a calcium phosphate layer precipitated through treatments were characterised by X-ray photoelectron spectroscopy. The thickness and compositions of the surface films and layers were quantified from the XPS results. Calcium phosphate formation during immersion in Hanks' solution for 1.0 Ms was evaluated by scanning electron microscopy with energy-dispersive X-ray spectrometry. The results confirmed that the electrolytic treatments in this study were effective to accelerate calcium phosphate formation on titanium in Hanks' solution in spite of their lower voltage than conventional methods. The results also suggested that the hydroxyl group in the surface oxide film might contribute to the formation of calcium phosphate. This technique is a promising process for the treatment of thin titanium materials.

An electrodeposition method of calcium phosphate coatings on titanium alloy

Calcium phosphates coatings were deposited onto titanium alloy discs via en electrodeposition method. Titanium alloy discs were blasted with calcium phosphate particles, then etched in a mixture of nitric and fluoric acids and rinsed in demineralized water. The titanium alloy disc (cathode) and platinum mesh (anode) were immersed in a supersaturated calcium phosphate electrolyte buffered at pH 7.4 and connected to a current generator. The microstructure, chemical composition and crystallinity of the electrodeposited coatings were studied as function of time 10-120 min, temperature 25-80 degrees C, current density 8-120 mA/cm(2), magnesium and hydrogen carbonate amounts (0.1-1 mM). Uniform calcium phosphate coatings were obtained in 30 min but coating thickness increased with deposition time. Raising the temperature of electrolyte resulted in more uniform coatings as ionic mobility increased. Low current density was preferable due to hydrogen gas evolving at the cathode, which disturbed the deposition of calcium phosphate crystals on titanium. The amounts of magnesium and hydrogen carbonate ions affected both the homogeneity and morphology of the coatings. This study showed that the electrodeposition method is efficient for coating titanium with osteoconductive calcium phosphate layers.

Corrosion resistance and bioactivity of titanium after surface treatment by three different methods: ion implantation, alkaline treatment and anodic oxidation

The paper compares the effects of various surface modifications, ion implantation, alkaline treatment and anodic oxidation, upon the corrosion resistance and bioactivity of titanium. The chemical composition of the surface layers thus produced was determined by XPS, SIMS and EDS coupled with SEM. The structure of the layers was examined by TEM, and their phase composition by XRD. The corrosion resistance was determined by electrochemical methods after the samples were exposed to the test conditions for 13 h. The bioactivity of titanium was evaluated in a simulated body fluid at a temperature of 37 degrees C after various exposure time.