Thermal stability of porous A-type carbonated hydroxyapatite spheres

Porous A-type carbonated hydroxyapatite (CHAp) spheres were synthesized in the high-pressure hydrothermal system by the template-directed method. The thermal stability of porous A-type CHAp spheres was first studied via calcining in the wide temperature range from 393 K up to 1173 K, analyzed by FT-IR, XRD and SEM. The results showed that the decomposition of porous A-type CHAp spheres went through two stages, owing to the release of the carbonate from the OH⁻ channel and the collapse of apatite-type structure above 973 K, consecutively. The nanoparticles in situ replaced the flakelets of porous CHAp spheres and packed closely into new regular porous Ca₃(PO₄)₂ spheres.     

Faster synthesis of A-type carbonated hydroxyapatite powders prepared by high-temperature reaction

Synthesis of A-type carbonated hydroxyapatite (CHA) materials has typically involved heating of a hydroxyapatite composition for 24 h or greater. In this study, a hydroxyapatite powder was heated at 800, 900 or 1000 °C for 1, 8 or 16 h in dry CO₂. Samples heated for 8 and 16 h at 900/1000 °C were fully-carbonated A-type CHAs. After only one hour at 1000 °C, the carbonate content approached 95% of the theoretical maximum. Preparing compositions with more than 95% of the theoretical maximum with reduced thermal energy (1000 °C for 1 h, or 900 °C for 8 h) results in powders with higher surface areas and a reduced level of sintering, compared to powders prepared with typical thermal treatments reported for A-type CHAs, such as 1000 °C for 16 h. As far as the authors are aware, these are the shortest heating times reported for the preparation of fully-carbonated A-type CHAs which is significant for future applications of such powders, particularly in applications beyond medical devices such as chromatography, remediation and carbon capture.     

Template-directed one-step synthesis of flowerlike porous carbonated hydroxyapatite spheres

Flowerlike porous carbonated hydroxyapatite (CHAp) spheres were first synthesized by the template-directed self-assembly method in a high-pressure system. The product was characterized via Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that flowerlike porous CHAp spheres were obtained, that the average granularity of porous CHAp spheres is about 20 μm, that the average aperture is about 1 μm, and that the average thickness of flakes is about 50 nm. Great amounts of OH channels, high special surface area and regular spherical shape imply potential applications.     

Preparation of porous hydroxyapatite

The aim of the paper was to obtain a porous hydroxyapatite (HA) biomaterials relating to the manufacture of artificial implants. The technique of impregnating a body of porous polyurethane foam with slurry containing HA powder, water and additives was applied and proved to be more successful. The process of preparations was discussed and the porous HA with desired properties was obtained at last.     

Preparation of porous hydroxyapatite scaffolds

In this work, the sintering and grain growth of hydroxyapatite green bodies are analyzed in order to identify the optimum heat treatments for the preparation of porous hydroxyapatite scaffolds. Sintering in air at temperatures ranging between 1100 and 1200 °C yields dense materials with narrow grain-size distributions. The scaffolds are formed by the infiltration of polymer foams with hydroxyapatite slurries or by robocasting, a novel rapid-prototyping technique. Examples of the microstructures achieved with each approach are presented. It is observed that both techniques can be used to fabricate scaffolds with adequate pore size to promote bone ingrowth.     

Preparation of porous scaffold from hydroxyapatite powders

Hydroxyapatite (HA) powder was prepared by wet chemical method. The hydroxyapatite phase was stable up to 1250 °C without decomposition to beta-tricalcium phosphate. Interconnected porous hydroxyapatite scaffold resembling trabecular bone structure was developed from polymeric replica sponge method. The prepared scaffold has 60 vol.% porosity having a major fraction of ~ 50–125 μm pore diameter. The pore content, pore morphology, pore interconnectivity of scaffold and their compressive strength were dependent on the solid loading and binder content. In-vitro bioactivity and bioresorbability confirmed the feasibility of the developed scaffolds.     

Preparation and structure of carbonated calcium hydroxyapatite substituted with heavy rare earth ions

Calcium hydroxyapatite (CaHap) particles substituted five types of heavy rare earth ions (Ln: Y³⁺, Gd³⁺, Dy³⁺, Er³⁺ and Yb³⁺) were synthesized using a precipitation method and characterized using various means. These Ln ions strongly affected the crystal phases and the structures of the products. With increasing Ln/(Ln + Ca) in the starting solution ([X_Ln]), the length and the crystallinity of the particles first increased and then decreased. The rare earth metal-calcium hydroxyapatite (LnCaHap) solid solution particles were obtained at [X_Y] ≤ 0.10 for substituting Y system and at [X_Ln] ≤ 0.01–0.03 for substituting the other Ln systems. LnPO₄ was mixed with LnCaHap at higher [X_Ln] for all Ln systems. A series of yttrium-calcium hydroxyapatite (YCaHap) solid solutions with [X_Y] = 0–0.10 were investigated using XRD, TEM, ICP-AES, IR and TG–DTA in detail.     

Preparation of porous hydroxyapatite with interconnected pore architecture

Since pore connectivity has significant effects on the biological behaviors of biomedical porous hydroxyapatite (PHA), the preparation of PHA with interconnected pore architecture is of great practical significance. In the present study, PHA with highly interconnected architecture was prepared via a simple burnout route with rod-like urea as the porogen. Microscopy and porosimetry data showed that the as-prepared PHA had open and interconnected pore structure with the average fenestration size of about 120 μm. Open pores occupied up to 98% of the total porosity. The compressive strength and modulus of the as-prepared PHA were respectively 1.3–7.6 MPa and 4.0–10.4 GPa.     

Preparation of highly porous hydroxyapatite from cuttlefish bone

Hydroxyapatite structures for tissue engineering applications have been produced by hydrothermal (HT) treatment of aragonite in the form of cuttlefish bone at 200°C. Aragonite (CaCO₃) monoliths were completely transformed into hydroxyapatite after 48 h of HT treatment. The substitution of CO₃ ²⁻ groups predominantly into the PO₄ ³⁻ sites of the Ca₁₀(PO₄)₆(OH)₂ structure was suggested by FT-IR spectroscopy and Rietveld structure refinement. The intensity of the ν₃PO₄ ³⁻ bands increase, while the intensity of the ν₂CO₃ ²⁻ bands decrease with the duration of HT treatment resulting in the formation of carbonate incorporating hydroxyapatite. The SEM micrographs have shown that the interconnected hollow structure with pillars connecting parallel lamellae in cuttlefish bone is maintained after conversion. Specific surface area (S _BET) and total pore volume increased and mean pore size decreased by HT treatment.     

Hydrothermal synthesis and nanostructure of carbonated calcium hydroxyapatite

The influence of precursor concentration, pressure, temperature and time of hydrothermal synthesis on the development of calcium hydroxyapatite structure has been analyzed. The obtained results show that it is possible to adjust the conditions of hydrothermal synthesis from solutions of relatively high concentrations to obtain calcium hydroxyapatite nanopowders of well-defined structure. The relationship between the synthesis and the lattice parameters, as well as the crystallite size and the microstructure of synthesized hydroxyapatite has been established. The synthesized powders are preferentially carbonated hydroxyapatite of the B type in the form of agglomerates that accommodate two-modal size pores of 1.5–10 and 50–200 nm. The structure of calcium hydroxyapatite particles consists of crystallites 8–22 nm in size, bound within prime particles, which size is between 10 and 63 nm, that in turn form bigger agglomerates 200 nm in size, which further cluster building up agglomerates 5–20 μm in size.     

Synthesis of carbonated hydroxyapatite nanospheres through nanoemulsion

This study investigated the nanoemulsion technique as a means to synthesize carbonated hydroxyapatite (CHAp) nanospheres which could be used to produce composite tissue engineering scaffolds. CHAp nanospheres were successfully synthesized by mixing an acetone solution of Ca(NO₃)₂ · 4H₂O with an aqueous solution of (NH₄)₂HPO₄ and NH₄HCO₃. Four reaction temperatures, namely, 4, 25, 37 and 55 °C, were investigated and no surfactant was added in all nanoemulsion processes. Wet slurries of CHAp from the nanoemulsions were freeze-dried to obtain dry powders. X-ray diffraction (XRD) results showed that the as-synthesized CHAp nanoparticles were mainly in an amorphous state. After calcination at 900 °C, the apatite became well crystallized. Fourier transform infrared (FTIR) spectroscopy showed that the CHAp was B-type substitution. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the CHAp particles were spherical in shape and that their sizes were in the nanometer range. The successful synthesis of CHAp nanospheres is a critical step forward in our efforts to fabricate bone tissue engineering scaffolds using the selective laser sintering technology.     

碳酸羟基磷灰石粉体的热处理研究

以沉淀法制备了碳酸根质量分数为8.5%的碳酸羟基磷灰石(carbonated hydroxyapatite, CHA),研究热处理工艺参数对其热稳定性和碳酸根替代的影响.通过XRD、FTIR和C/S碳硫仪等测试手段表征了CHA粉体的特性.结果表明,随热处理温度的升高,碳酸根的含量减少,而碳酸根的A型替代与B型替代之比则呈现先降后升的趋势.与湿N2气氛相比,湿CO2气氛能减少碳酸根的损失,提高热稳定性.与干CO2气氛相比,湿CO2气氛有利于生成以B型替代为主的CHA.热处理过程中CO2分压越高,碳酸根的损失量越少,热稳定性越好.     

非均相悬浮法制备多孔羟基磷灰石微球

为了获得具有吸附和生物学功能的多孔羟基磷灰石(HA)微球,以自制的纳米羟基磷灰石(HA)粉体为原料,用非均相悬浮法制备了HA/明胶微球,将微球在1 250℃下焙烧,成功制备了直径100~500μm的多孔HA微球.采用光学显微镜、SEM分析、XRD分析和BET氮吸附法研究了微球形貌、尺寸、物相组成、比表面积和孔径,测定了微球对水中F-离子的吸附性能.结果表明:微球具有良好球形形貌和相互贯通的纳米微孔;尺寸比较均匀,分散性良好;微球的主要结晶相为羟基磷灰石;BET表面积为1.867 0~2.089 5 m~2/g,孔径6.53~6.85 nm;对氟离子的平衡吸附容量为1.909~1.940 mg/g.通过控制m(HA)/m(明胶)比例、油温、搅拌速度和搅拌时间,可以在一定范围内控制微球直径和比表面积.     

羟基磷灰石基多孔复合支架的制备及其表征

研究利用造孔剂法制备高度贯通的多孔羟基磷灰石(HA)支架,孔隙率约为78%,并利用聚己内酯(PCL)分别复合纳米HA(nHA)或微纳米生物玻璃(nBG)粉末对其进行涂覆改性,粉末的添加量均为10%~40%(质量分数)。4种类型支架分别记为HA、PCL/HA、nHA-PCL/HA和nBG-PCL/HA。实验结果发现,nHA-PCL/HA和nBG-PCL/HA复合支架最大抗压强度分别为1.41~1.98 MPa和1.35~1.78MPa。4类支架矿化实验显示,浸泡21d后nBG-PCL/HA表面促进生成较多的磷灰石矿化物;细胞实验结果显示细胞在4类支架上均生长良好,说明支架具有良好的生物相容性。支架在实验犬背部肌肉组织内植入2个月的组织学检测显示,4种支架内均有新骨形成,尤其是nHA-PCL/HA和nBG-PCL/HA孔内有更多的新生骨组织,说明这两种支架表面复合涂层中的生物活性纳米颗粒对诱导新骨生成具有积极的促进作用。     

孔径可控的多孔羟基磷灰石的制备工艺研究

采用添加造孔剂法,选择合适的造孔剂聚甲基丙烯酸甲酯（PMMA）,通过严格筛分,可烧结制得孔径可控的多孔基磷灰石陶瓷,气孔率可从20％到50％变化。并对烧结多孔体中孔的结构、孔径分布与特征,影响气孔率和力学性能的因素进行了研究与讨论。     

骨组织工程用多孔HA生物材料的制备

用PVB、NH4HCO3和(NH4)2CO3粒子作造孔剂,制备了骨组织工程用多孔HA生物材料.讨论了烧结工艺和造孔剂含量等对材料结构的影响.研究表明,较佳的烧结工艺为1200℃烧结4h,烧结后样品主要是HA相.造孔剂PVB、(NH4)2CO3、NH4HCO3含量分别为10vol%、15vol%和20vol%时,多孔HA陶瓷拥有大于100μm和5～50 μm的贯通孔,具有较好的孔连通性与孔结构,有利于细胞和组织的生长以及营养输送;其最大孔隙率为50.3%,抗压强度为6.33MPa.     

Preparation of highly interconnected porous hydroxyapatite scaffolds by chitin gel-casting

In this study, a simple and effective method for producing highly interconnected porous hydroxyapatite (HA) scaffolds was developed by combining gel-casting, particle-leaching and extrusion techniques. Chitin (CT) sol was used to disperse HA particles and wax spheres were introduced as porogens for their excellent deformability. In extrusion process, the accumulated wax spheres in point-to-point contact can transform into surface-to-surface contact by means of the extrusion pressure. Thus, the obtained porous HA scaffolds exhibited an interconnected channel network after leaching out of the porogens. The results showed that the scaffolds prepared by different size of wax spheres exhibited nearly the same volumetric porosity of about 86%, while the compressive strengths decreased as the pore size increased. Therefore, the method developed can be used to effectively tailor the pore size of HA scaffolds while maintaining a high porosity. The highly porous HA scaffolds with excellent interconnectivity are expected to be a promising bone substitute in clinical practice.     

Bactericidal property and biocompatibility of gentamicin-loaded mesoporous carbonated hydroxyapatite microspheres

Implant-associated infection is a serious problem in orthopaedic surgery. One of the most effective ways is to introduce a controlled antibiotics delivery system into the bone filling materials, achieving sustained release of antibiotics in the local sites of bone defects. In the present work, mesoporous carbonated hydroxyapatite microspheres (MCHMs) loaded with gentamicin have been fabricated according to the following stages: (i) the preparation of the MCHMs by hydrothermal method using calcium carbonate microspheres as sacrificial templates, and (ii) loading gentamicin into the MCHMs. The MCHMs exhibit the 3D hierarchical nanostructures constructed by nanoplates as building blocks with mesopores and macropores, which make them have the higher drug loading efficiency of 70–75% than the conventional hydroxyapatite particles (HAPs) of 20–25%. The gentamicin-loaded MCHMs display the sustained drug release property, and the controlled release of gentamicin can minimize significantly bacterial adhesion and prevent biofilm formation against S. epidermidis. The biocompatibility tests by using human bone marrow stromal cells (hBMSCs) as cell models indicate that the gentamicin-loaded MCHMs have as excellent biocompatibility as the HAPs, and the dose of the released gentamicin from the MCHMs has no toxic effects on the hBMSCs. Hence, the gentamicin-loaded MCHMs can be served as a simple, non-toxic and controlled drug delivery system to treat bone infections.     

Fabrication of mesoporous carbonated hydroxyapatite microspheres by hydrothermal method

Mesoporous carbonated hydroxyapatite microspheres (MCHMs) have been converted from calcium carbonate microspheres (CCMs) by hydrothermal method. After soaking the CCMs in disodium hydrogen phosphate solutions, carbonated hydroxyapatite nanoparticles are formed via a dissolution-precipitation reaction. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) reveal that the as-obtained samples are calcium deficient hydroxyapatite with B-type CO₃²⁻ substitution. The transmission electron microscopy (TEM) indicates that the MCHMs are composed of many nanoparticles within the whole microspheres. These nanoparticles aggregate to form mesopores with a pore size of 4.5-14.0 nm among them. The formation mechanism of MHAMs has been discussed.     

微波水热转化制备多孔羟基磷灰石微球

提出对球形碳酸钙进行精细化加工来制备羟基磷灰石的方法。通过与Na2HPO4-(NH4)2HPO4混合溶液在微波加热条件下进行阴离子交换反应,对粒度约15μm的球形碳酸钙进行水热转化并利用ESEM、XRD和EDS等手段对反应产物进行表征。反应15min后,碳酸钙转化为羟基磷灰石主相,无其它磷酸钙盐相存在,产物保留了原料的球形骨架结构,其显微结构为约0.2μm的细小颗粒聚集体,孔径约为100nm。EDS分析表明产物的表面组成为[Ca9.04Mg0.40Na1.16][(PO4)5.22(CO3)0.61](OH)3.12,属部分CO32-离子取代的羟基磷灰石。结果表明,在微波加热下碳酸钙能在较短时间内不经其它磷酸盐中间态而直接转化成单一的羟基磷灰石相。