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.     

Solid state reaction, sintering and Pb removal activity of hydroxyapatite/zirconia layered composite

In order to form a layered hydroxyapatite/zirconia ceramic, the solid state reaction and sintering were examined by the three processes of powder mixture, dry-pressing compaction and tape cast. The solid state reaction between hydroxyapatite and zirconia occurred in the thin width of 10–50 m at interface in a layered composite body. In both sintered layer composites from dry compaction and tape cast, the significant deformation of composite bodies was observed, depending on sintering temperatures. By selecting a sintering temperature of 1200°C, we fabricated a layer ceramic composite of hydroxyapatite/zirconia exhibiting the flat film shape. The tape cast process was useful to form a porous sintered composite of hydroxyapatite and zirconia. The porous composite showed the removal performance of aqueous lead from wastewater.     

Development of a Three-Dimensional Slurry Printing System Using Dynamic Mask Projection for Fabricating Zirconia Dental Implants

This study aims to develop a three-dimensional slurry printing system (3DSP) and to use a two-stage sintering process for the fabrication of zirconia dental implants. Solvent-soluble slurry which is composed of zirconia powder, visible light-curable resin, and methanol is prepared. During layer casting, the liquid slurry penetrates into the pores of the subjacent layers. The fresh layer and the subjacent layer tightly connect when the solvent dries. The mask pattern for the sliced layers is then exposed on a solvent-soluble slurry, for solidification and to form the green part that is embedded in the green block, layer-by-layer. The green block is immersed in a methanol solution, which causes the collapse of the un-exposed part. As a result, the rigid green part is obtained. Two-stage sintering is used to heat the rigid green part to 600°C to produce binder burnout and to 1450°C to sinter the zirconia dental implant part. The results show that sintered parts have an average flexural strength and micro-hardness of 539.1 MPa and 1556 HV, respectively. The zirconia dental implant is successfully fabricated using the 3DSP system developed. The proposed fabrication method using a 3DSP system is briefly described and it is proven that there is a good capacity to fabricate zirconia dental implants.     

Tape casting of AlN/glass composites for LTCC substrate

AlN/glass composite is low-fired substrate material for microelectronic packaging material. In this work, AlN/glass sheets were prepared by tape casting process. The dispersion, stabilization and the rheological properties of the slurry were studied. The optimum drying condition and mechanisms of debinding were also investigated. The results showed that powder size influenced the optimum content of dispersant and the viscosity of slurry. The slurry for tape casting exhibited a typical shear-thinning behavior. Smooth green tape without cracking was acquired after it was dried at solvent atmosphere. The binder was fully burned out at 600°C at low heating speed. The lamination with uniform microstructure was achieved by hot-pressed at 900°C.     

Ti Coatings with Macropores for Improved Implant Fixation Obtained by Electrophoretic Deposition of TiH2 Stabilized Emulsions

Current implant technology focuses on enhancing the fixation between implant and surrounding tissue in order to reduce the risk of implant loosening and subsequent failing. Modifying the implant's surfaces with a macroporous metallic coating can provide a mechanical anchorage by bone ingrowth and at the same time improves the loading capacity for antibacterial drugs or bone growth stimulating agents. In this work, pure Ti coatings with spherical macropores are applied on dense Ti6Al4V substrates by electrophoretic deposition of TiH2 stabilized emulsions, followed by drying, dehydrogenation, and subsequent vacuum sintering at 850 °C. The obtained Ti coatings exhibit a porous network with an open porosity varying from 50 to 65% and a mean spherical pore size changeable from 50 to 80 µm. The morphology of the coating is easily adapted by changing the powder particle size, the emulsion droplet size, and the deposition parameters. Since the coatings are produced in the frame of optimizing implant technology, a good adhesion between the substrate and the coating is a crucial prerequisite. Measurements show that the obtained tensile adhesion strength is >29 MPa.     

RETRACTED ARTICLE: Characteristics of porous zirconia coated with hydroxyapatite as human bones

Since hydroxyapatite has excellent biocompatibility and bone bonding ability, porous hydroxyapatite ceramics have been intensively studied. However, porous hydroxyapatite bodies are mechanically weak and brittle, which makes shaping and implantation difficult. One way to solve this problem is to introduce a strong porous network onto which hydroxyapatite coating is applied. In this study, porous zirconia and alumina-added zirconia ceramics were prepared by ceramic slurry infiltration of expanded polystyrene bead compacts, followed by firing at 1500°C. Then slurry of hydroxyapatite-borosilicate glass mixed powder was used to coat the porous ceramics, followed by firing at 1200°C. The porous structures without the coating had high porosities of 51–69%, high pore interconnectivity, and sufficiently large pore window sizes (300–500 μm). The porous ceramics had compressive strengths of 5·3∼36·8 MPa, favourably comparable to the mechanical properties of cancellous bones. In addition, porous hydroxyapatite surface was formed on the top of the composite coating, whereas a borosilicate glass layer was found on the interface. Thus, porous zirconia-based ceramics were modified with a bioactive composite coating for biomedical applications.     

Dense/Porous Layered Hydroxylapatite Ceramic for Orthopedic Device Coating Prepared by Tape Casting Technique

A possible surgical technique in the replacement of a traumatized hip joint by a prosthesis system is to connect the acetabular component of the implant directly with pelvis bone tissue, without use of bone cement. It is possible to improve the osteointegration process and to ensure a better connection with bone tissue by coating the outside implant surface with a biocompatible ceramic. The best choice for a bioceramic coating is porous hydroxylapatite because its surface shows bonding-osteogenesis properties much higher than other materials. Here, a double HAp layer has been made by tape casting technology. The first layer was a high porous HAp ceramic with high osteophilic-osteoconductive characteristics. Because the scale of porosity was relatively insensitive to slurry composition and sintering temperature such a microstructure was produced using a particular technique described here. The second layer was dense HAp ceramic that resulted a substrate able to improve the mechanical properties of the brittle porous HAp layer. Several microstructure-designed ceramic coatings having the porous part with a controlled porosity can be obtained by tape casting using the same technique.     

Hydroxyapatite coating on porous zirconia

Since hydroxyapatite has excellent biocompatibility and bone bonding ability, porous hydroxyapatite ceramics have been intensively studied. However, porous hydroxyapatite bodies are mechanically weak and brittle, which makes shaping and implantation difficult. One way to solve this problem is to introduce a strong porous network onto which hydroxyapatite coating is applied. In this study, porous zirconia and alumina-added zirconia ceramics were prepared by ceramic slurry infiltration of expanded polystyrene bead compacts, followed by firing at 1500 °C. Then a slurry of hydroxyapatite–borosilicate glass mixed powder was used to coat the porous ceramics, followed by firing at 1200 °C. The porous structures without the coating had high porosities of 51% to 69%, a high pore interconnectivity, and sufficiently large pore window sizes (300 μm–500 μm). The porous ceramics had compressive strengths of 5.3˜36.8 MPa and Young's moduli of 0.30˜2.25 GPa, favorably comparable to the mechanical properties of cancellous bones. In addition, porous hydroxyapatite surface was formed on the top of the composite coating, whereas a borosilicate glass layer was found on the interface. Thus, porous zirconia-based ceramics were modified with a bioactive composite coating for biomedical applications.     

水基流延浆料性能影响因素分析

水基流延法是在传统流延法上进行改进,采用水作溶剂制备片层陶瓷基板的一种方法。分子间作用力、静电力和空间位阻的共同作用,构成水基流延浆料的稳定机理;粉体的颗粒尺寸和粒径分布对流延生坯的性能具有重要影响;选择合适的添加剂种类和加入量能极大地改善水基流延浆料的流变性和稳定性,同时可提高流延生坯的可加工性;球磨工艺和真空除泡工艺的选择对于制得良好的水基流延浆料也很重要。     

Osteoblast attachment to hydroxyapatite micro-tube scaffolds

Tissue engineering offers a novel route for repairing damaged or diseased tissue by incorporating the patient’s own healthy cells or donated cells into temporary scaffolds that act as a matrix for cell cultivation. Tissue scaffolds that are biocompatible and are porous with interconnected porous channels for cell ingrowth with a suitable degradation rate would be advantageous. In this study hydroxyapatite micro-tubes produced using the biomimetic coating technique will be pressed into a tissue scaffold. A compaction and sintering study will be done to observe appropriate pressure and heat treatment to produce a mechanically stable scaffold material. The ideal pressure was found to be 2.5 MPa where the tube-like structure was maintained, high porosity was achieved and suitable strength was possible. Sintering between 1,000 and 1,100 °C was found to produce good results. The average porosity for the chosen pressure of 2.5 MPa was 68 %. The scaffold was observed with SEM, micro tomography (micro-CT), chemical analysis and degradation testing. Porous channels were established using micro-CT where the porous channels were roughly 100 µm. Chemical analysis showed constant release of calcium and phosphorous, and far below toxic levels of heavy metals from the die. Degradation testing showed high degradation compared to tested commercially available materials. Cell culturing was done on the scaffold to characterise the biological performance of the scaffolds. Cell culturing was done in a 7 and 24 day cell culture to examine cell morphology and cell ingrowth. The results showed cell ingrowth into a micro-tube and cell orientation in a longitudinal direction. SEM, confocal microscopy and histology were employed as characterisation tools for observing cell ingrowth.     

The influence of sintering temperature on the properties of compacted bovine hydroxyapatite

On the sintering characteristic of hydroxyapatite (HA), the resulting microstructure and properties are influenced not only by the characteristic and impurities of materials but also are found to be dependent on the thermal history during the fabrication process. This research is concerned with the effect of sintering temperature on the relative density, hardness, and phase purity after sintering process. Bovine HA (BHA) powder obtained from heated local cortical bovine bone at 900 °C for 2 h was uniaxially pressed at 156 MPa into green bodies using a 20 mm cylindrical dies. The compacted green body was pressurelessly sintered in air atmosphere at temperatures ranging from 1000 to 1400 °C, at a furnace ramp rate of 5 °C/min and dwell time of 2 h. The BHA starting powder was characterized using XRD and FTIR. SEM was also used for observing the microstructures of the starting material. The sintered BHA specimens were analyzed using Archimedes method for measuring density; XRD for phase stability; and Vickers method for hardness measurement. The analysis results show that the starting BHA powder and the sintered BHA specimens contain HA. The intensity of the three main peaks of HA decreases with increasing sintering temperature which may be due to decomposition of HA at high temperature. The density and hardness of BHA increases with increasing sintering temperature based on the results obtained.     

Combined reduction and sintering of preformed cuprous oxide strip

Abstract

A new method of making thin copper strip direct from cuprous oxide powder by an integrated powder technology route has been outlined. The proposed route consists of making, by a slurry method, a green cuprous oxide strip which is subsequently reduced with hydrogen to produce a porous copper strip. The strip is densified by hot rolling to produce a fully dense structure. The combined reduction and sintering behaviour of the green cuprous oxide strip is reported. The mechanism of reduction of the cuprous oxide with hydrogen at various temperatures is discussed, and the geometry of the reaction zone in the green oxide strip is described.

MST/183     

Effect of characteristics of (Sm,Ce)O2 powder on the fabrication and performance of anode-supported solid oxide fuel cells

Effect of characteristics of Sm_0.2Ce_0.8O_1.9 (SDC) powder as a function of calcination temperature on the fabrication of dense and flat anode-supported SDC thin electrolyte cells has been studied. The results show that the calcination temperature has a significant effect on the particle size, degree of agglomeration, and sintering profiles of the SDC powder. The characteristics of SDC powders have a significant effect on the structure integrity and flatness of the SDC electrolyte film/anode substrate bilayer cells. The SDC electrolyte layer delaminates from the anode substrate for the SDC powder calcined at 600 °C and the bilayer cell concaves towards the SDC electrolyte layer for the SDC powder calcined at 800 °C. When the calcinations temperature increased to 1000 °C, strongly bonded SDC electrolyte film/anode substrate bilayer structures were achieved. An open-circuit voltage (OCV) of 0.82–0.84 V and maximum power density of ～1 W cm^?2 were obtained at 600 °C using hydrogen as fuel and stationary air as the oxidant. The results indicate that the matching of the onset sintering temperature and maximum sintering rate temperature is most critical for the development of a dense and flat Ni/SDC supported SDC thin electrolyte cells for intermediate temperature solid oxide fuel cells.     

Highly porous hydroxyapatite bioceramics with interconnected pore channels using camphene-based freeze casting

We fabricated highly porous hydroxyapatite (HA) bioceramics using the camphene-based freeze casting method. In this method, HA/camphene slurries with various HA contents (10, 15, and 20 vol.%) were prepared by ball-milling at 60 °C and then cast into a mold at room-temperature. This method allowed the fabricated sample to have completely interconnected pore channels by removing the frozen camphene network via sublimation and dense HA walls by sintering the highly packed HA powder networks at 1250 °C for 3 h. As the initial HA content was increased from 10 to 20 vol.%, the porosity decreased from 75 to 56%, while the compressive strength remarkably increased from 0.94 to 17 MPa.     

流延法制备AlN陶瓷基板的研究

从颗粒尺寸、浆料流体类型、干燥条件、排胶机制等方面对流延法制备ＡｌＮ陶瓷基板展开了较为系统的研究．结果表明,颗粒尺寸的不同直接影响到浆料粘度及分散剂用量．适于ＡｌＮ流延成型的浆料流体类型属于假塑性流体．保持一定的溶剂气氛有利于获得表面平整光滑的流延素坯膜．二次排胶有利于排除ＡｌＮ流延素坯膜中的残余碳．烧结后基板的断口ＳＥＭ照片表明晶粒发育较为完善,无明显开气孔,断裂模式为沿晶断裂．     

Shape memory effect in porous volume NiTi articles fabricated by selective laser sintering

The shape memory effect in porous nickel titanium (NiTi) articles obtained by means of layered synthesis using selective laser sintering (SLS) technology was studied by measuring the temperature dependence of the electric resistivity of the material. For the porous NiTi samples synthesized from Ni and Ti powders, the interval of probable appearance of the shape memory effect falls within the temperature interval from −50 to 0°C. In a porous material synthesized by laser sintering from a commercial NiTi powder of the PV N55T45 grade, this effect falls in the interval from +25 to +50°C. Prospects for the use of porous NiTi articles as medicinal implants are discussed.     

VO_x-Cu浸渍复合阳极支撑的抗硫中温固体氧化物燃料电池的制备与性能

用流延法制备钇稳定氧化锆(YSZ)多孔体素坯,在流延素坯上丝网印刷沉积10Sc1CeSZ电解质,经共烧结得到多孔YSZ支撑致密10Sc1CeSZ薄膜电解质的约为5cm×5cm较大面积的双层膜。在电解质薄膜上依次印刷阻挡层Ce0.8Gd0.2O2(CGO)和阴极La0.6Sr0.4CoO3(LSC)。向多孔YSZ支撑体内浸渍偏钒酸铵、草酸的混合溶液和硝酸铜溶液多次后经低温煅烧后得到V2O5-CuO-YSZ复合阳极。用SEM对双层薄膜结构浸渍前后进行显微结构表征,结果表明流延法制备的多孔YSZ孔洞连通,丝网印刷制备的电解质层致密,电解质厚度约为7μm;浸渍后,催化剂均匀地分布在YSZ孔隙间。在800℃,分别以湿H2和含5.2×10-3体积分数的H2S湿合成气(40%H2,60%CO)为燃料进行电化学测试,开路电压分别为1.07和1.08V,最大功率密度均为37mW/cm2。电性能测试结果表明,该方法制备的固体氧化物燃料电池复合阳极具有抗硫化氢毒化和抗碳沉积的性能。     

Mechanical properties of hydroxyapatite–zirconia compacts sintered by two different sintering methods

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)–zirconia (ZrO₂) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO₂ powder have been ball milled to create mixtures containing 0–5 wt% ZrO₂ loadings. Compacts were microwave sintered at either 700, 1000 or 1200°C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700°C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000°C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200°C showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200°C, even with 0 wt% ZrO₂, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO₂, along with increasing open porosity. Nanosized ZrO₂ prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.     

In-situ hardening hydroxyapatite-based scaffold for bone repair

Musculoskeletal conditions are becoming a major health concern because of an aging population and sports- and traffic-related injuries. While sintered hydroxyapatite implants require machining, calcium phosphate cement (CPC) bone repair material is moldable, self-hardens in situ, and has excellent osteoconductivity. In the present work, new approaches for developing strong and macroporous scaffolds of CPC were tested. Relationships were determined between scaffold porosity and strength, elastic modulus and fracture toughness. A biocompatible and biodegradable polymer (chitosan) and a water-soluble porogen (mannitol) were incorporated into CPC: Chitosan to make the material stronger, fast-setting and anti-washout; and mannitol to create macropores. Flexural strength, elastic modulus, and fracture toughness were measured as functions of mannitol mass fraction in CPC from 0% to 75%. After mannitol dissolution in a physiological solution, macropores were formed in CPC in the shapes of the original entrapped mannitol crystals, with diameters of 50 μm to 200 μm for cell infiltration and bone ingrowth. The resulting porosity in CPC ranged from 34.4% to 83.3% volume fraction. At 70.2% porosity, the hydroxyapatite scaffold possessed flexural strength (mean ± sd; n = 6) of (2.5 ± 0.2) MPa and elastic modulus of (0.71 ± 0.10) GPa. These values were within the range for sintered porous hydroxyapatite and cancellous bone. Predictive equations were established by regression power-law fitting to the measured data (R² > 0.98) that described the relationships between scaffold porosity and strength, elastic modulus and fracture toughness. In conclusion, a new graft composition was developed that could be delivered during surgery in the form of a paste to harden in situ in the bone site to form macroporous hydroxyapatite. Compared to conventional CPC without macropores, the increased macroporosity of the new apatite scaffold may help facilitate implant fixation and tissue ingrowth.     

Porous alumina ceramics prepared by slurry infiltration of expanded polystyrene beads

To produce highly porous MgO-doped alumina (Al₂O₃) ceramics, expanded polystyrene (EPS) beads were packed as a pore former and well-dispersed alumina slurry was used to infiltrate the pore space in the EPS bead compacts. The alumina particle-EPS bead green compacts were then heated to 1550°C in air to burn out the pore former and subsequently densify the MgO-doped alumina struts. The porous Al₂O₃ ceramics were featured with uniformly distributed open pore structures with porosities ranging from 72 to 78% and a pore interconnectivity of about 96%. The macropore size and the pore window size could be controlled by adjusting the size of the EPS beads and the contacting area between the EPS beads. The compressive strengths of the porous Al₂O₃ ceramics were in the range of 5.5–7.5 MPa, similar to those of cancellous bones (2–12 MPa). The porous alumina ceramics were further made bioactive after the dip coating of a sol-gel derived 58 S bioglass powder, followed by sintering at 1200°C.