Mechanical and in vitro performance of apatite–wollastonite glass ceramic reinforced hydroxyapatite composite fabricated by 3D-printing

In situ hydroxyapatite/apatite–wollastonite glass ceramic composite was fabricated by a three dimensional printing (3DP) technique and characterized. It was found that the as-fabricated mean green strength of the composite was 1.27 MPa which was sufficient for general handling. After varying sintering temperatures (1050–1300°C) and times (1–10 h), it was found that sintering at 1300°C for 3 h gave the greatest flexural modulus and strength, 34.10 GPa and 76.82 MPa respectively. This was associated with a decrease in porosity and increase in densification ability of the composite resulting from liquid phase sintering. Bioactivity tested by soaking in simulated body fluid (SBF) and In Vitro toxicity studies showed that 3DP hydroxyapatite/A–W glass ceramic composite was non-toxic and bioactive. A new calcium phosphate layer was observed on the surface of the composite after soaking in SBF for only 1 day while osteoblast cells were able to attach and attain normal morphology on the surface of the composite.     

Development of bioactive zirconium–tin alloy by combination of micropores formation and apatite nuclei deposition

In previous studies, Zr gained apatite‐forming ability by various methods; however, it took more than 7 days in simulated body fluid (SBF) to gain apatite‐forming ability. In this study, the authors developed the method to achieve apatite‐forming ability in Zr alloy within 1 day in SBF by a combination with apatite nuclei that promote apatite formation in SBF. First, Zr–Sn alloy was soaked in concentrated sulphuric acid, and pores in micro‐level were formed on the surface of Zr–Sn alloy. To attain apatite forming ability in Zr–Sn alloy, second, apatite nuclei were formed in the micropores. To evaluate apatite‐forming ability, thus‐obtained Zr–Sn alloy with apatite nuclei was soaked in SBF; hydroxyapatite formation was observed on the whole surface of the Zr–Sn alloy plates. From this result, it was clarified that higher apatite‐forming ability was attained on the apatite nuclei‐treated Zr–Sn alloy with micropores in comparison with that without micropores. When adhesive strength of formed hydroxyapatite film with respect to Zr–Sn alloy plates was measured, high‐adhesive strength of the formed apatite film was attained by forming micropores and subsequently precipitating apatite nuclei in the fabrication process because of an interlocking effect caused by hydroxyapatite formed in the micropores.Inspec keywords: precipitation, zirconium alloys, calcium compounds, bioceramics, tin alloys, adhesion, thin filmsOther keywords: apatite forming ability, micropore formation, hydroxyapatite film, bioactive zirconium‐tin alloy, apatite nuclei‐treated zirconium‐tin alloy, zirconium‐tin alloy plates, simulated body fluid, concentrated sulphuric acid, hydroxyapatite formation, adhesive strength, precipitating apatite nuclei, time 1.0 d, ZrSn, Ca₁₀ (PO₄)₆ (OH)₂      

Biomimetic apatite formation on Ultra-High Molecular Weight Polyethylene (UHMWPE) using modified biomimetic solution

Modifications were performed on a biomimetic solution (SBF), according to previous knowledge on the behavior of ions present in its composition, in order to obtain apatite coatings onto Ultra-High Molecular Weight Polyethylene (UHMWPE) without having to use polymer pre-treatments that could compromise its properties. UHMWPE substrates were immersed into a 30% H₂O₂ solution for a 24-h period and then submitted to a biomimetic coating method using standard SBF and two other modified SBF solutions. Apatite coatings were only obtained onto UHMWPE when the modified SBF solutions were used. Based on these results, apatite coatings of biological importance (calcium-deficient hydroxyapatite—CDHA, amorphous calcium phosphate—ACP, octacalcium phosphate—OCP, and carbonated HA) can be obtained onto UHMWPE substrates, allowing an adequate conciliation between bonelike mechanical properties and bioactivity.     

Biomimetic formation of hydroxyapatite investigated by analytical techniques with high resolution

Morphology, phase and chemical compositions of atmospheric plasma-sprayed (APS) hydroxyapatite (HAp) coatings were investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), proton-induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS). The study involved as-sprayed coatings and coatings incubated in simulated body fluid (rSBF) for up to 56 days. The results obtained using combined contributions from three complementary analytical techniques confirm that secondary Ca-deficient defect hydroxyapatite precipitated by a biomimetic process from the simulated body fluid onto the HAp coating surface after a prolonged induction time. Owing to its sensitivity proton-induced X-ray emission (PIXE) provides information on in vitro resorption of calcium phosphate ceramics and dynamic dissolution/precipitation events occurring during the incubation process.     

Biomimetic formation of crystalline bone-like apatite layers on spongy materials templated by bile salts aggregates

Since the trabecular bone exhibit sponge-like bicontinuity there is a growing interest in the synthesis of spongy-like sieves for the construction of bio-active implantable materials. Here, we propose a one step sol–gel method for the synthesis of bicontinuous pore silica materials using different bile salts aqueous mixtures as templates. The influences of the type and amount of bile salt on the synthesis processes are investigated and correlated with the final material morphology. As a final point, their structural properties are interrelated with their ability to induce a bone-like apatite layer in contact with simulated body fluid (SBF). We have confirmed that under specific template conditions, the synthesized material has an open bio-active macropore structure that is blanched in a 3D-disordered sponge-like network similar than those existed in trabecular bone.     

Effects of ions dissolved from bioactive glass-ceramic on surface apatite formation

Non-bioactive glass-ceramic A-W(Al) containing apatite and wollastonite in a MgO–CaO–SiO₂–Al₂O₃ glassy matrix did not form an apatite layer on its surface in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma and also in the fluids with small amounts of the calcium and silicate ions added individually, but formed the apatite layer in the fluid with the calcium and silicate ions added simultaneously. This indicates that the calcium and silicate ions dissolved from bioactive glass-ceramic A-W containing the apatite and wollastonite in a MgO–CaO–SiO₂ glassy matrix play a cooperative and important role in forming an apatite layer on its surface in the body, to give the glass-ceramic bioactivity. The calcium ion might increase the degree of the supersaturation of the surrounding body fluid, and the silicate ion might provide favourable sites for nucleation of the apatite on the surfaces of glass-ceramic.     

Nanostructured bioactive glass coating on porous hydroxyapatite scaffold for strength enhancement

Many attempts have been focused on preparing highly porous scaffolds with appropriate mechanical strength. This paper has developed a new route to enhance the compressive strength of porous HA (hydroxyapatite) scaffold (porosity: ∼ 83%, mean pore size:∼ 800 μm). Briefly this route included nanostructure coating of bioactive glass on struts of porous HA. Coating microstructure consisted of the grains with the range between 91 and 320 nm and micron size pores that could be detected by SEM observation. This simple method improved the compressive strength of highly porous HA from 0.22 to 1.49 MPa. The obtained scaffolds provided good mechanical support while maintaining bioactivity so they could be used as tissue engineering scaffolds for low-load bearing applications.     

Preparation of hydroxyapatite coating on CoCrMo implant using an effective electrochemically-assisted deposition pretreatment

A hydroxyapatite (HA) coating is efficiently generated on CoCrMo implant alloys by employing an electrochemically-assisted deposition (ECAD) pretreatment followed by chemical immersion in a supersaturated calcification solution. CoCrMo was electrochemically treated in a calcium- and phosphate-containing solution for short time. A thin layer about 200 nm thicknesses, consisting mainly of amorphous calcium phosphate, was formed on the surface of the CoCrMo after the ECAD pretreatment. After the chemical immersion for 2 h, a layer of octacalcium phosphate was formed on the surfaces. A layer of HA was formed after 72 h immersion. The effectiveness of these treatments was demonstrated by comparison with the alkaline treated CoCrMo. Results showed that the ECAD pretreatment highly enhanced the capability of formation of HA on the CoCrMo surface, while only a small amount of CaP islands were formed on CoCrMo through traditional chemical treatment. A tensile test showed that the coating tightly bonded to the substrate. This work has explored an effective ECAD pretreatment to activate CoCrMo implant surface for generating HA coating.     

Chitosan reinforced apatite–wollastonite coating by electrophoretic deposition on titanium implants

A novel bioactive porous apatite–wollastonite/chitosan composite coating was prepared by electrophoretic deposition. The influence of synthesis parameters like pH of suspension and current density was studied and optimized. X-ray diffraction confirmed crystalline phase of apatite–wollastonite in powder as well as composite coating with coat crystallinity of 65%. Scanning electron microscope showed that the porosity had interconnections with good homogeneity between the phases. The addition of chitosan increased the adhesive strength of the composite coating. Young’s modulus of the coating was found to be 9.23 GPa. One of our key findings was sheet-like apatite growth unlike ball-like growth found in bioceramics. Role of chitosan was studied in apatite growth mechanism in simulated body fluid. In presence of chitosan, dense negatively charged surface with homogenous nucleation was the primary factor for sheet-like evolution of apatite layer. The results suggest that incorporation of chitosan with apatite–wollastonite in composite coating could provide excellent in vitro bioactivity with enhanced mechanical properties.     

制备生物活性羟基磷灰石陶瓷粉末的新工艺

为开发制备含CO32-的羟基磷灰石(HA)新工艺,以Ca(OH)2-H3PO4为原料,依据中和法原理,用CaCO3代替部分Ca(OH)2,采用不同于常规的反应温度和加料操作制备HA.通过控制反应体系终点pH值、反应时间和反应温度制得含CO32-的羟基磷灰石,并用XRD和IR技术分析了生成物的组成和结构.研究结果表明:采用本文工艺生成的沉淀物不经陈化,易于过滤分离;制备较佳工艺条件为:反应体系终点pH值控制在微酸性条件(pH=6),反应温度≥75℃,沉淀反应时间约3 h.     

Biomimetic hydroxyapatite coating on glass coverslips for the assay of osteoclast activity in vitro

The osteoclast (OC) is the cell type responsible for the resorption of bone. The activity of this cell is important in the aetiology of a large number of skeletal pathologies, and also for the biocompatibility and osseointegration of orthopaedic implant materials. OC mediated acid hydrolysis of calcium phosphate from the bone matrix offers a prime means of studying the biology and activity of this cell type. We have developed a method of coating glass coverslips with a hydroxyapatite (HA)-like mineral, using a biomimetic approach. Hydroxylation followed by formation of a self assembled monolayer (SAM) using the surfactant triethoxysilylpropyl succinic anhydride (TESPSA), allowed biomimetic deposition of HA-like mineral from a simulated body fluid (SBF). The biocompatibility of the TESPSA SAM-HA coated glass coverslips was tested by culturing human mature OC present in samples of giant cell tumour of bone (GCT). Parameters of OC activity were assayed, including F-actin ring formation, release of calcium and formation of osteoclastic resorption pits, confirming that OC were able to attach to and resorb the coated surface. This approach for the preparation of HA coatings on glass coverslips could have wide applicability for the study of osteoclast behaviour in vitro. Gerald J. Atkins and Peter Majewski share senior author status.     

Influence of strontium for calcium substitution in bioactive glasses on degradation,ion release and apatite formation

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO₂–P₂O₅–CaO–Na₂O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.     

Hyaluronic acid stimulates the formation of calcium phosphate on CoCrMo alloy in simulated physiological solution

The behaviour of CoCrMo alloy has been studied in two simulated physiological solutions—NaCl and Hanks’ solutions—each containing the sodium salt of hyaluronic acid. Hyaluronic acid is a component of synovial joint fluid, so the behaviour of orthopaedic alloys in its presence needs to be assessed. Electrochemical methods, X-ray photoelectron spectroscopy and scanning electron microscopy have been used to analyse the composition, thickness and morphology of any layers formed on the alloy. The addition of hyaluronic acid shifts the corrosion potential and increases the value of polarization resistance. The presence of hyaluronic acid in simulated Hanks’ physiological solution stimulates the formation of a calcium phosphate layer, opening up the possibility for tailoring the surface properties of CoCrMo alloy. The viability of human osteoblast-like was determined using the Alamar^® Blue Assay, while the osteogenic activity was evaluated by alkaline phosphatase activity. The presence of hyaluronic acid affects the alkaline phosphatase activity.     

Direct cytotoxicity evaluation of 63S bioactive glass and bone-derived hydroxyapatite particles using yeast model and human chondrocyte cells by microcalorimetry

In this study, the cytotoxicity evaluation of prepared 63S bioactive glass and bone-derived hydroxyapatite particles with yeast and human chondrocyte cells was carried out using isothermal micro-nano calorimetry (IMNC), which is a new method for studying cell/biomaterial interactions. Bioactive glass particles were made via sol–gel method and hydroxyapatite was obtained from bovine bone. Elemental analysis was carried out by XRF and EDXRF. Amorphous structure of the glass and completely crystalline structure of HA were detected by XRD analysis. Finally, the cytotoxicity of bioactive glass and bone-derived HA particles with yeast and cultured human chondrocyte cells was evaluated using IMNC. The results confirmed the viability, growth and proliferation of human chondrocyte cells in contact with 63S bioactive glass, and bone-derived HA particles. Also the results indicated that yeast model which is much easier to handle, can be considered as a good proxy and can provide a rapid primary estimate of the ranges to be used in assays involving human cells. All of these results confirmed that IMNC is a convenient method which caters to measuring the cell-biomaterial interactions alongside the current methods.     

玻璃基生物骨水泥内部纳米羟基磷灰石的形成研究

以CaO-SiO2-P2O5系统生物玻璃和磷酸铵调和液混合制得玻璃基生物骨水泥(GBC),利用XRD、FTIR和SEM对GBC的产物晶相、化学组成和内部显微结构进行了分析,并对其力学性能进行了测试。实验结果表明,随着浸泡时间的增加GBC中的玻璃相逐步向羟基磷灰石(HAP)微晶转化,生成的磷灰石为弱结晶度的类骨状碳酸羟基磷灰石微晶,这些微晶主要分布于玻璃粉末的界面之间,端面尺寸在30～50nm,这表明GBC中所生成的HAY晶体与人体骨有很大的相似性,因而会具有良好的生物活性。对力学性能测试的结果表明,随着浸泡时间的增加GBC的抗压强度逐步增加,在30天时可达到80MPa。因而GBC不仅具有良好的生物活性,而且具有一定的力学强度。     

Ti合金表面沉积羟基磷灰石-牛血清蛋白生物活性涂层

通过仿生生长方法,将预处理后的钛片浸入到添加有牛血清蛋白的模拟体液中,使钙磷盐和牛血清蛋白(BSA)共沉积到钛合金的表面,制备生物活性涂层.利用SEM、XRD、红外光谱等对涂层进行了表征,结果表明:BSA通过化学作用和钙磷盐共沉积到基体的表面,并且BSA具有细化涂层晶粒的作用.     

Induction of hydroxycarbonate apatite formation on polyethylene or alumina substrates by spherical vaterite particles deposition

Hydroxycarbonate apatite (HCA) layers were formed on polyethylene (PE) or alumina substrates by depositing spherical sub-micron vaterite particles and then immersing in simulated body fluid (SBF). HCA formation on vaterite‐coated PE was faster than that on coated alumina (3 days for PE and 7 days for alumina). The adsorption of phosphate ions on the vaterite particles in SBF was studied by monitoring changes in the concentration of phosphorous in SBF and the surface charges of vaterite during the SBF immersion. The phosphorous concentration of SBF in which a vaterite-coated PE was immersed for 1 h was lower than that in which a vaterite-coated alumina was immersed. Zeta potential of the vaterite surface deposited on PE drastically decreased after 1 h immersion in SBF. The vaterite particles deposited on each substrate immediately adsorbed phosphate ions in SBF. The amount of ions adsorbing on the vaterite surfaces deposited on PE was larger than that on alumina. This was attributed to differences in the surface charges between PE (? 16 mV) and alumina (+ 38 mV). The phosphate adsorption was predominantly electrostatic therefore related to the surface charge of vaterite particles. The surface charges of substrates may affect the charge of vaterite particles.     

Nano-scale hydroxyapatite formation on silica fiber by using carbon nanofibers as templates

Nano-scale hydroxyapatite particle network with uniform morphology and good crystallinity was fabricated on silica fiber by using carbon nanofibers as templates and with a methanol solution of Ca(NO3)2 x 4H2O-H3PO4. Field emission scanning electron microscopy, coupled with X-ray diffraction analysis confirmed the template effect and the existence of hydroxyapatite on silica fiber. It was clearly verified that by tuning the formation of carbon nanofibers on silica fiber, it was possible to control the properties of the resulting hydroxyapatite on silica fiber. In addition, the formation mechanism of hydroxyapatite on silica fiber via the template route was proposed.     

The effect of residual glassy phase in a bioactive glass-ceramic on the formation of its surface apatite layerin vitro

A bioactive glass containing (in wt%) SiO₂ 48, P₂O₅ 9.5, Na₂O 20 and CaO 22.5 was transformed into a glass-ceramic through a heat treatment. The apatite formation on the surface of this glass-ceramic was examined in a simulated physiological solution. The data from X-ray diffraction, infrared reflection spectroscopy, scanning electron microscopy together with energy-dispersive X-ray analysis and composition imaging of backscattered electrons showed that the formation of the surface apatite layer depends on the relative amount of residual glassy phase in the glass-ceramic. The apatite layer was found to formin vitro on its surface if the glass-ceramic contained a residual glassy phase in a relative proportion more than a limiting volume. It lay on a layer rich in silica. However, only, a silica-rich layer was developed within the surface region of the glass-ceramic during the interaction with solution if the glass was almost completely crystallized. It is proposed that the apatite formation on the surface of the glass-ceramic is mainly caused by its residual glass. The residual glass facilitating apatite formation is considered to provide a negatively charged surface developed during its corrosion in the surrounding solution. The negatively charged surface attracts calcium ions and creates a solution within the glass — solution interface that is highly supersaturated with respect to hydroxyapatite. This leads to the formation of apatite on the surface of the glass-ceramic.