Novel sol-gel derived calcium phosphate coatings on Mg4Y alloy

Calcium phosphates (CaPs) and silicon containing calcium phosphates (Si-CaPs) coatings on a biodegradable magnesium yttrium alloy (Mg4Y) were prepared by a sol-gel technique to improve the bioactivity of the alloy surface. The experimental results show that thick porous coatings comprised of nano-sized calcium phosphate particles can be prepared by heating the as dip coated substrates at 450 °C. The in vitro degradation results show that the coatings do not alter the degradation kinetics of the substrates significantly and the release of magnesium and yttrium ions at initial time points was very similar for both the coated and bare substrates. The cyto-compatibility studies using MC3T3-E1 osteoblasts show that the coated substrates were more bioactive than the uncoated substrates as the cells begin to grow and form a matrix on the coated substrates more easily than on the bare metal. These preliminary results collectively show the potential of use of sol-gel derived calcium phosphate coatings on magnesium based degradable scaffolds to improve their surface bioactivity.     

Corrosion resistance of biomimetic calcium phosphate coatings on magnesium due to varying pretreatment time

Calcium phosphate coatings were prepared on magnesium substrates via a biomimetic coating process. The effects of a magnesium hydroxide pretreatment on the formation and the ultimate corrosion protection of the coatings were studied. The pretreatment layer was found to affect the amount of defects present in the coatings. Corrosion resistance of the coatings was studied in vitro using two simulated body fluids, 0.8% NaCl and Hanks solution. In NaCl, the resistance to corrosion of all samples decreases with time as corrosion proceeded through cracks and other defects in the coatings. Samples with no pretreatment displayed the highest corrosion resistance as these samples had the fewest defects in the coating. However, in Hanks solution, corrosion resistance increased with time due to additional nucleation of calcium phosphate from the fluid on to the substrate. In this solution, additional pretreatment time was beneficial to the overall corrosion resistance.     

磷酸钙涂覆炭织物体外细胞毒性的评价

医用植人体的成功与否常常取决于器件植入后细胞与材料表面间的相互作用.采用生物体外测试法考察了声电化学法制备的磷酸钙涂层对炭织物的骨细胞附着、增殖能力的影响.借助MTS检测技术、扫描电子显微镜,选择人类成骨细胞(MG63)作为细胞模型,通过测定细胞与炭织物、磷酸钙涂覆炭织物、以及其各自的提取液作用后的存活能力,研究了细胞/材料的相互作用,并对基底材料的细胞毒性进行了评价.结果表明,炭织物、磷酸钙涂覆炭织物均不具有细胞毒性,且磷酸钙涂层可提高成骨细胞的附着和增殖.SEM图像显示,细胞形貌正常,与对照组相比较生长增殖情况相似.     

On the development of an apatitic calcium phosphate bone cement

Development of an apatitic calcium phosphate bone cement is reported. 100 μ Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na₂HPO₄ as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results showed the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nano-crystallite growth over particulate matrix surface. The structure has an apparent porosity of ∼ 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.     

Preparation and evaluation of osteoinductive porous biphasic calcium phosphate granules obtained from eggshell for bone tissue engineering

The synthetic bone graft substitutes currently used clinically are osteoconductive but not osteoinductive; their low success rate is thus their biggest disadvantage. The use of biomass raw materials for synthesizing calcium phosphate has gradually attracted increased research attention. In this study, hydroxyapatite powder was prepared through liquid-phase precipitation from eggshell, and porous biphasic calcium phosphate granules (EBGs) were then obtained using a pore former and sintering procedure. The EBGs were discovered to have high biocompatibility and no cytotoxicity. The results of animal experiments showed that the area of new bone growth was high, numerous Haversian canals could be observed, and almost all EBGs were surrounded by new bone tissue, which proved that the EBGs had excellent osteoinductivity. By contrast, numerous fat cells were found in the femoral defect area when a commercial bone graft was employed. Various biological inorganic ions (Mg, Sr, Na, and Fe) originally in the eggshell raw materials were incorporated into the EBGs, and the EBGs exhibited excellent osteogenic abilities. The developed approach provides an economical and feasible solution for the treatment of bone defects.     

Synthesis of calcium phosphate hydrogel from waste incineration fly ash and bone powder

Waste incineration fly ash and bone powder could be successfully recycled into calcium phosphate hydrogel, a type of fast proton conductor. Various properties of the intermediate and calcium phosphate hydrogel from them were characterized and compared with that from calcium carbonate reagent. It was found that the intermediate from the incineration fly ash and calcium phosphate glass was more brittle than that from bone powder and calcium carbonate reagent. The electric conductivity of crystallized hydrogel obtained from all raw materials increases exponentially with temperature. However, the crystallized hydrogel from incineration fly ash has lower electric conductivity and lower crystallinity than that from bone powder and the reagent. Moreover, the difference in electric conductivity between these crystallized hydrogels decreases with temperature. Compared with using the reagent as a raw material, bone powder provides a 25% reduction in the usage of H(3)PO(4) to acquire the crystallized hydrogel which has the highest conductivity. These experimental results suggest that the incineration fly ash and bone powder are useful calcium sources for the synthesis of calcium phosphate hydrogel.     

Nano-sized calcium phosphate (CaP) carriers for non-viral gene deilvery

Gene therapy has garnered much interest due to the potential for curing multiple inherited and/or increases in the acquired diseases. As a result, there has been intense activity from multiple research groups for developing effective delivery methods and carriers, which is a critical step in advancing gene delivery technologies. In order for the carriers to effectively deliver the genetic payloads, multiple extracellular and intracellular barriers need to be overcome. Although overcoming these challenges to improve the effectiveness is critical, the development of safe gene delivery agents is even more vital to assure its use in clinical applications. The development of safe and effective strategies has therefore been a major challenge impeding gene therapy progress. In this regard, calcium phosphate (CaP) based nano-particles has been considered as one of the candidate non-viral gene delivery vehicles, but has been plagued by inconsistent and low transfection efficiencies limiting its progress. There has been major research effort to improve the consistency and effectiveness of CaP based vectors. Currently, it is therefore thought that by controlling the various synthesis factors such as Ca/P ratio, mode of mixing, and type of calcium phosphate phase, such variability and inefficiency could be modulated. This review attempts to provide a comprehensive analysis of the current research activity in the development of CaP based ceramic and polymer-ceramic hybrid systems for non-viral gene delivery. Preliminary transfection results of hydroxyapatite (HA or NanoCaPs), amorphous calcium phosphate (ACP) and brushite phases are also compared to assess the effect of various CaP phases, and correspondingly, changes in the dissolution characteristic of the pDNA-CaP complex on the gene transfection efficiency.     

Comparison of calcium phosphate product values using measurement of plasma total calcium and serum ionized calcium

Calcium phosphate product (Ca x Pi) is a clinically relevant tool to estimate the cardiovascular risk of patients with renal failure. In reports, mostly total serum calcium has been used. As measurement of serum ionized calcium has some benefits and is being used increasingly, we estimated the respective levels of calcium phosphate product using both total (t-Ca x Pi) and ionized calcium (ion-Ca x Pi). Fifty-eight healthy individuals and 180 hemodialysis (HD) patients from 2 centers were studied. Diagnostic accuracies for corresponding values of the t-Ca x Pi and ion-Ca x Pi were calculated using a GraphROC program. Of HD patients, 64% had t-Ca x Pi <4.4 mmol(2)/L(2) regarded as a desirable goal, and 10% had values over 5.6 mmol(2)/L(2) associated with a high cardiovascular risk. Based on GraphROC analysis, t-Ca x Pi of 4.4 mmol(2)/L(2) corresponded to a value of 2.2 mmol(2)/L(2) of ion-Ca x Pi and, respectively, t-Ca x Pi of 5.6 mmol(2)/L(2) corresponded 2.8 mmol(2)/L(2) of ion-Ca x Pi. Owing to the good agreement between the results in the 2 centers, these values for risk levels can be used in both centers. When measurement of ionized calcium is used, Ca x Pi values of 2.2 and 2.8 mmol(2)/L(2) can be used instead of generally used values of 4.4 and 5.6 mmol(2)/L(2) with total calcium.     

In vivo estimation of calcium phosphate cements containing chondroitin sulfate in subcutis

Calcium phosphate cements using an equimolar mixture of tetracalcium phosphate and dicalcium phosphate dihydrate (TeDCPD) for the powder phase were experimentally developed for use in endodontic treatment. The fundamental cement is comprised of TeDCPD kneaded with modified McIlvain's buffer solution containing calboxymethyl cellulose sodium salt (CEM-1). In the liquid phase of the modified one (CEM-2), chondroitin sulfate (CS) was added in place of the salt. The final concentration of CS in CEM-2 is 1%. Another one (CEM-3) contained 2% CS finally in place of the salt. X-ray diffract meter (XRD) was used to examine the crystalline phases of the cements. The tissue compatibility of the cements was examined histologically in the subcutaneous tissue using rats. The XRD results showed no dibasic calcium phosphate phase to be traced in CS containing two cements after 1 day of kneading. There were more multinucleated giant cells appearing around CEM-1 than around CEM-2 or CEM-3 after 4 weeks. Fibroblasts, collagen fibers and small vessels infiltrated into the internal porous structure of CEM-3. Excluding CEM-3, two cements were encapsulated with a dense fibrous connective tissue layer. We conclude that CS, in the experimentally developed cement, contributed to biocompatibility and bioactivity of the cement.     

Release behaviors of drug loaded chitosan/calcium phosphate coatings on titanium

Implants with antibiotic drug loaded bioactive coatings have been increasingly applied in orthopedic operations. Here we report the drug release behavior of gentamycin loaded chitosan/calcium phosphate coatings on titanium. Chitosan/calcium phosphate coatings with different component ratios and surface topographies were prepared by electrochemical deposition method. Our results showed that the drug release from these coatings was controlled by their component ratio and surface topography, and the former ratio played a more significant role. The present coatings could provide an effective way to create both good bioactivity and antibacterial activity.     

Sol-gel prepared β-TCP/FHA biphasic coatings

β-tricalcium phosphate/fluoridated hydroxyapatite (β-TCP/FHA) biphasic coatings were prepared on titanium alloy substrate by means of sol-gel method. The coatings combine the initial dissolution of β-TCP with the long-term stability of FHA to create a high quality bioactive coating. Ca(NO₃)₂, P₂O₅ and HPF₆ were dissolved in ethanol respectively and mixed in designed sequence and Ca : P : F ratios to form a sol. After the sol was refluxed for 24 h, the as-refluxed sol was used for FHA coating. β-TCP powders were dispersed into the sols to form colloidal sols for β-TCP/FHA biphasic coatings. The as-refluxed sols with different Ca : P : F ratios only resulted in apatite coatings with low F content. Biphasic coatings were prepared with the colloidal sols. The β-TCP contents of the coatings could be tailored by varying the amount of the powders in the colloidal sols. The surface morphology of the coatings becomes rougher with increasing amount of the powders, which favors cell attachment. However, excessive amount of powders results in powder agglomeration, leading to more cracks in the coatings. Fine powders and good dispersion are essential factors for good biphasic coatings.     

In vitro biocompatibility study of calcium phosphate glass ceramic scaffolds with different trace element doping

Porous calcium phosphate based glass ceramics (CaO-P₂O₅-Na₂O) containing different trace elements (2.0 mol% Mg, Sr and Zn respectively) were prepared by coating polyurethane foams with sol-gel derived glass slurry. After heat treatment at suitable temperatures, main phase catena hexaphosphate (Ca₄P₆O₁₉) and minor phase calcium pyrophosphate (β-Ca₂P₂O₇) crystallized from the glass matrix. These scaffolds were soaked in simulated body fluid (SBF) to determine the solubility and apatite formation, and mouse MC3T3-E1 cells were used to investigate the bioactivity and biocompatibility. The Sr doped scaffold showed a higher degradability than those samples containing Zn or Mg, inducing the formation of an apatite layer with a high (Sr + Ca)/P molar ratio of 1.64, whereas only some discontinuous CaP layers and spare apatite agglomerates were found on the scaffolds doped with Mg ((Mg + Ca)/P = 1.12) and Zn ((Zn + Ca)/P = 1.55) respectively. In vitro cell culture, a high degree of cell adhesion and spreading was achieved on the samples containing Sr or Zn, while only a few cells adhered to the Mg doped sample. These results implied that the bioactivity and biocompatibility of the scaffolds were not only strongly associated with the apatite forming ability, but also related with the Ca/P molar ratios of the deposits.     

Micromorphological effect of calcium phosphate coating on compatibility of magnesium alloy with osteoblast

Abstract

Octacalcium phosphate (OCP) and hydroxyapatite (HAp) coatings were developed to control the degradation speed and to improve the biocompatibility of biodegradable magnesium alloys. Osteoblast MG-63 was cultured directly on OCP- and HAp-coated Mg-3Al-1Zn (wt%, AZ31) alloy (OCP- and HAp-AZ31) to evaluate cell compatibility. Cell proliferation was remarkably improved with OCP and HAp coatings which reduced the corrosion and prevented the H₂O₂ generation on Mg alloy substrate. OCP-AZ31 showed sparse distribution of living cell colonies and dead cells. HAp-AZ31 showed dense and homogeneous distribution of living cells, with dead cells localized over and around corrosion pits, some of which were formed underneath the coating. These results demonstrated that cells were dead due to changes in the local environment, and it is necessary to evaluate the local biocompatibility of magnesium alloys. Cell density on HAp-AZ31 was higher than that on OCP-AZ31 although there was not a significant difference in the amount of Mg ions released in medium between OCP- and HAp-AZ31. The outer layer of OCP and HAp coatings consisted of plate-like crystal with a thickness of around 0.1 μm and rod-like crystals with a diameter of around 0.1 μm, respectively, which grew from a continuous inner layer. Osteoblasts formed focal contacts on the tips of plate-like OCP and rod-like HAp crystals, with heights of 2–5 μm. The spacing between OCP tips of 0.8–1.1 μm was wider than that between HAp tips of 0.2–0.3 μm. These results demonstrated that cell proliferation depended on the micromorphology of the coatings which governed spacing of focal contacts. Consequently, HAp coating is suitable for improving cell compatibility and bone-forming ability of the Mg alloy.     

Synergistic effects of Mg-substitution and particle size of chicken eggshells on hydrothermal synthesis of biphasic calcium phosphate nanocrystals

Magnesium(Mg^2+))ion plays important roles in biomineralization of bone,teeth and calcium carbonate skeletons.Herein,chicken eggshells mainly comprising of Mg-calcite nanocrystals(Mg/(Mg+Ca)2.0 mol.%)were used to fabricate biphasic calcium phosphate(BCP),a mixture of hydroxyapatite(HA)and p-tricalcium phosphate(p-TCP)nanocrystals,through hydrothermal reactions at 200℃for 24 h.Our results indicated thatβ-TCP nanocrystals formed through the ion-exchange reactions of Mg-calcite,while HA nanocrystals were mainly produced by dissolution-reprecipitation reactions on the surfaces of eggshell samples in the hydrothermal system.Mg substitution in calcite resulted in formation ofβ-TCP nanocrystals instead of HA crystals through ion-exchange reactions.BCP samples with different compositions(28.6-77.8 wt.%β-TCP)were produced by controlling particle sizes of eggshells for hydrothermal reactions.The larger particles lead to the larger proportion ofβ-TCP in the BCP composition.Therefore,Mg substitution and particle size had synergetic effects on the hydrothermal synthesis of BCP using chicken eggshells through balance of ion-exchange and dissolution-reprecipitation reactions.Cell culture results showed that the BCP products were non-cytotoxic to MC3 T3-E1 cells,which may be used for bone substitute materials in future.     

Micropatterned TiO2 effects on calcium phosphate mineralization

The effects of implant surface topography and chemistry on biomineralization have been a research focus because of their potential importance in orthopedic and bone replacement applications. While a vast amount of research is focusing on chemical modified surfaces and rough surfaces, little attention has been paid to the well-defined micropatterned surface effects on calcium phosphate mineralization process due to the difficulties in preparing microfabricated biomaterial surfaces. This work focuses on the effects of microgrooved TiO₂ surfaces on the calcium phosphate mineralization process. Firstly, we developed a new process that can prepare microgrooved TiO₂ coatings on glass substrates using soft-lithography and sol–gel technology. Then microgrooved TiO₂ surfaces were used to induce Ca–P mineralization under biomimetic conditions. The results revealed that topography dominated the growth and distribution of mineralization at the initial days and then the effects of topography become weak with the extended immersion days.     

Hydrothermal-electrochemical CaTiO3 coatings as precursor of a biomimetic calcium phosphate layer

The hydrothermal-electrochemical method was used to coat Ti and Ti6Al4V with calcium titanate CaTiO₃. The film exhibited a plate-like structure with several isolated pinholes around 100 nm in diameter. These coated samples were treated by a biomimetic procedure, immersing them in a simulated body fluid (SBF) solution for 5, 10 and 28 days. Characterization was performed by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. The CaTiO₃-coated samples after the SBF treatment showed a significant increment in their calcium and phosphorous amounts as compared with SBF-treated samples with no previous CaTiO₃ coating; the latter exhibited only surface phosphate incorporation.     

A simple sol-gel technique for synthesis of nanostructured hydroxyapatite, tricalcium phosphate and biphasic powders

Hydroxyapatite (HAP), β-tricalcium phosphate (β-TCP) and biphasic calcium phosphate (BCP) nanocrystalline powders were prepared by a simple sol-gel approach. Because of the unique characteristic of the phosphorous source ((CH₃O)₃P) and the proper uses of calcic and phosphorous sources with Ca/P molar ratio between 1.4 and 1.67, three different kinds of nanostructured calcium phosphate powders were achieved by changing the ratio of calcic and phosphorous sources. For HAP and β-TCP, pure phases were prepared. For BCP, the proportion of HAP and β-TCP could be changed by thermal treatment.     

Development of a fully injectable calcium phosphate cement for orthopedic and dental applications

A study on the development of a fully injectable calcium phosphate cement for orthopedic and dental applications is presented. The paper describes its characteristic properties including results of biocompatibility studies. A conventional two-component calcium phosphate cement formulation (having a powder part containing dry mixture of acidic and basic calcium phosphate particles and a liquid part containing phosphate solution) is modified with a biocompatible gelling agent, to induce flow properties and cohesion. The quantity of the gelling agent is optimized to get a viscous paste, which is smoothly injectable through an 18-gauge needle, with clinically relevant setting parameters. The new formulation has a setting time of 20 min and a compressive strength of 11 MPa. The X-ray diffraction, Fourier transform infrared spectrometry, and energy dispersive electron microprobe analyses showed the phase to be hydroxyapatite, the basic bone mineral. Scanning electron microscopy revealed a porous structure with particle sizes of a few micrometers. The cement did not show any appreciable dimensional or thermal change during setting. The injectability is estimated by extruding through needle and the cohesive property is assessed by water contact method. The cement passed the in vitro biocompatibility screening (cytotoxicity and haemolysis) tests.     

Composite ceramics thermal barrier coatings of yttria stabilized zirconia for aero-engines

Composite ceramics thermal barrier coatings(TBCs) are widely used in the aero-engines field due to their excellent thermal insulation, which improves the service life and durability of the inherent hot components. The most typical, successful and widely used TBCs material is yttria stabilized zirconia(YSZ). In this paper, fabrication methods, coating structures, materials, failure mechanism and major challenges of YSZ TBCs are introduced and reviewed. The research tendency is put forward as well. This review provides a good understanding of the YSZ TBCs and inspires researchers to discover versatile ideas to improve the TBCs systems.     

Role of macropore size in the mechanical properties and in vitro degradation of porous calcium phosphate cements

The goal of the present study was to investigate the effect of macropore size on the compressive strength and in vitro degradation of porous calcium phosphate cements (CPCs). For this purpose, a series of porous CPCs with three different macropore sizes (200-300 μm, 300-450 μm and 450-600 μm) and comparable porosity were prepared by salting-out method, and the study of in vitro degradation behavior was carried out under a constant fluid flow environment. The results showed that the increase in macropore size of CPCs with invariant porosity resulted in a decrease in the compressive strength but an increase in the degradation rate of CPCs significantly, suggesting the possibility that the degradation rate and compressive strength of biomaterials can be regulated by varying the macropore size while maintaining the porosity unchanged.