Fabrication of porous alumina–zirconia ceramics by gel-casting and infiltration methods

Porous alumina–zirconia ceramics were obtained by infiltrating porous alumina ceramics, which were prepared by tert-butyl alcohol (TBA)-based gel-casting method. Back scattering images of the fracture surface and energy dispersive spectroscopy were performed to obtain composition profiles on the fracture surface and across sections of the sintered composites. The porosity, pore size distribution and compressive strength were also investigated. The results show that the content of zirconia can be adjusted effectively by infiltration times and it decreases with increasing distance from the surface of the samples. The porosity and compressive strength can also be controlled by the infiltration times. With increases of the infiltration times from 1 to 3 cycles, the open porosity decreases slightly from 62.43% to 56.62%, while the compressive strength of the porous alumina–zirconia ceramics increases from 13.57 ± 1.21 to 26.87 ± 2.01 MPa, indicating that the porous ceramics with high porosity and high strength can be prepared by TBA-based gel-casting method combined with the infiltration process.     

Design and fabrication of porous ZrO2/(ZrO2 + Ni) sandwich ceramics with low thermal conductivity and high strength

3Y–ZrO₂/(3Y–ZrO₂ + Ni) sandwich ceramics were fabricated through cold isostatic pressing and pressureless sintering. Porous 3Y–ZrO₂ ceramics with large connecting open pores and permeability were used as interlayers for insulation, whereas outer metal–ceramic layers were used as bearing loads. Microstructures and properties of the porous ZrO₂ and ZrO₂/(ZrO₂ + Ni) sandwich ceramics were investigated in detail. The ZrO₂/(ZrO₂ + Ni) sandwich ceramics exhibited better mechanical properties than the monolithic porous ZrO₂ ceramics at the same low thermal conductivity (approximately 0.85 W/m K). The mechanical properties of the sandwich ceramics were influenced by metal toughening and sintering-induced residual thermal stress.     

Fabrication of porous titanium scaffold with controlled porous structure and net-shape using magnesium as spacer

This paper reports a new approach to fabricating biocompatible porous titanium with controlled pore structure and net-shape. The method is based on using sacrificial Mg particles as space holders to produce compacts that are mechanically stable and machinable. Using magnesium granules and Ti powder, Ti/Mg compacts with transverse rupture strength (~ 85 MPa) sufficient for machining were fabricated by warm compaction, and a complex-shape Ti scaffold was eventually produced by removal of Mg granules from the net-shape compact. The pores with the average size of 132–262 μm were well distributed and interconnected. Due to anisotropy and alignment of the pores the compressive strength varied with the direction of compression. In the case of pores aligned with the direction of compression, the compressive strength values (59–280 MPa) high enough for applications in load bearing implants were achieved. To verify the possibility of controlled net-shape, conventional machining process was performed on Ti/Mg compact. Compact with screw shape and porous Ti scaffold with hemispherical cup shape were fabricated by the results. Finally, it was demonstrated by cell tests using MC3T3-E1 cell line that the porous Ti scaffolds fabricated by this technique are biocompatible.     

Synthesis of aligned porous poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite microspheres

We synthesized poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite microspheres with an aligned porous structure and evaluated their potential applications in bone tissue engineering. A range of HA particles (0, 5, 10 and 20 wt.% in relation to the PCL polymer) were added to a PCL solution in order to improve the biocompatibility of the porous PCL/HA composite microspheres. All the synthesized microspheres showed that the HA particles were distributed well in the PCL matrix, while preserving their aligned porous structure. The average size of the PCL/HA composite microspheres increased from 62 ± 7 to 179 ± 95 μm with increasing HA content from 0 to 20 wt.%. The incorporation of the HA particles to the PCL polymer led to a considerable improvement in in vitro bioactivity, which was assessed by immersing the PCL/HA composite microspheres in simulated body fluid (SBF). A number of apatite crystals could be precipitated on the surface of the aligned porous PCL/HA composite microspheres after soaking in the SBF for 7 days.     

Effects of binder system and processing parameters on formability of porous Ti/HA composite through powder injection molding

Porous titanium-hydroxyapatite (Ti/HA) composite is a developed composite material suitable for bio-medical applications. Powder injection molding (PIM) with space holder method is used to produce porous Ti/HA with mechanical properties, similar to human bone, and pores helps to initiate tissue growth. However, the differences in physical and mechanical properties of these composites are the main challenges during debinding and sintering. Therefore, the main objective is to determine effects of binder systems and processing parameters on formability of Ti/HA composite. In PIM, a binder system is necessary to produce green and ultimately sintered part. There are two binder systems and variation of sintering temperature has been used. Results revealed that Polyethylene glycol (PEG)-based binder system is applicable with NaCl space holder and optimum sintering parameters, including temperature, heating rate, and holding time of 1300 °C, 10 °C/min, and 5 h, respectively. The fabricated porous Ti/HA exhibits average porosity, pore size distribution, compressive strength, and roughness values of 55%, 60 μm to 170 μm, 370 MPa, and 0.323 μm, respectively. FESEM results showed that the pores are interconnected. It may be an appropriate material for future bio-medical applications.     

Electrohydrodynamic forming of porous ceramic capsules from a preceramic polymer

Porous polymeric near-spherical capsules, ~ 3.6 mm in diameter, were prepared using an electrodydrodynamic process. These capsules were pyrolysed to porous ceramics, ~ 3 mm in diameter. The ceramic capsules had interconnected pores of ~ 1.3 μm in size, and large cells with a mean size of 28 μm. The larger pores resemble the cells in a typical ceramic foam and were evenly distributed throughout the structure. A large proportion of the ceramic capsules contained 65–70% porosity, and their compressive strength was 0.2–0.4 MPa.     

Influence of preparation method on hydroxyapatite porous scaffolds

Hydroxyapatite (HA) is extensively used in medical applications as an artificial bone because of its similarity to the natural components of human bones and for its excellent biocompatibility. The porous structure of HA ceramics is more generally used as a scaffold. Many techniques, which are performed under fluid system, have been applied to fabricate HA porous scaffolds. In this work, polymeric sponge technique was employed in the preparation of HA slurry appropriated for porous ceramic fabrication. Effort for strength improvement was made on porous HA ceramic in several aspects. The effect of HA/water, binder/plasticizer ratios and dispersant content on the rheological properties of HA suspension in combination with the addition of SiC and SiO₂ on the compressive strength of porous bodies were investigated and discussed.     

Porous structure to improve microwave absorption properties of lamellar ZnO

The novel porous ZnO nanoflakes were fabricated by a facile two-step method containing preparation of precursor ZnCO₃ and subsequently calcination of ZnCO₃. The as-prepared products were analyzed by X-ray diffraction, scanning electron microscopy, and thermalgravimetric analysis. The results reveal that the porous ZnO nanoflakes were in the diameter and thickness of several to tens micrometers and 100–500 nm, respectively. The microwave absorption properties of porous ZnO nanoflakes were investigated by the network analyzer, which exhibit the minimal reflection loss of ?34.5 dB at 10.7 GHz with only thickness of 1.5 mm. The effective absorption (below ?10 dB) bandwidth can be tuned between 7.0 GHz and 17.1 GHz by tuning absorber thickness of 1.0–2.2 mm. Thus, the porous lamellar ZnO could be used as a promising absorbing material with the features of high efficiency absorption, wide-band and light weight.     

Mechanical properties of sinter-hardened Cr–Si–Ni–Mo based steel foam

Highly porous sinter-hardenable Cr–Si–Ni–Mo based steel foam for automotive applications was produced by space holder method. Steel powders were mixed with binder (polyvinylalcohol) and space holder (carbamide), and compacted. Carbamide in the green compacts was removed by water leaching at room temperature. The green specimens were then sintered at temperatures between 1100 °C and 1250 °C for sintering times of 15, 30 and 45 min. In addition, the steel foams were sinter-hardened to enhance mechanical properties. Sinter-hardening combines sintering and heat treatment in one step by increasing the post-sintering cooling rate. This reduces the cost of operation and makes powder metallurgy more competitive. Effects of sinter-hardening process parameters on compressive strength, Young’s modulus, hardness and energy absorption of the steel foams were investigated.     

In vivo osteocompatibility of lotus-type porous nickel-free stainless steel in rats

The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.     

Ultrafine porous fibers electrospun from cellulose triacetate

Ultrafine porous cellulose triacetate (CTA) fibers were prepared by electrospinning with methylene chloride (MC) and a mixed solvent of MC/ethanol (EtOH) and their intra- and inter-fiber pore structures was investigated. Ultrafine porous CTA fibers electrospun with MC had isolated circular shape pores with a narrow size distribution in the range of 50–100 nm. In the case of ultrafine CTA fibers electrospun with MC/EtOH (90 / 10 v/v), they had interconnected larger pores in the range of 200–500 nm. These porous structures were induced by phase separation resulting from the rapid evaporation of solvent during the electrospinning process. However, non-porous corrugated fibers were obtained from MC/EtOH (85 / 15 v/v) and MC/EtOH (80 / 20 v/v) due to their lower vapor pressure. The pore sizes in ultrafine CTA fibers electrospun with MC showed a bimodal distribution centered at ∼17 and ∼64 nm. CTA fibers electrospun with MC/EtOH (90 / 10 v/v) showed the greatest porosity due to their larger intra-fiber pores and fiber diameter.     

Fabrication and characterization of porous Co–Cr–Mo/58S bioglass nano-composite by using NH4HCO3 as space-holder

In the present study, Co–Cr–Mo/58S porous nano-composites were successfully fabricated by the use of space-holder and powder metallurgy techniques. The cold compacted Samples were heated at 175 °C for 2 h and then was raised to 1250 °C and held for 2 h. Scanning electron microscope (SEM) and optical microscope (OM) images of porous samples showed interconnected, isolated pores and appropriate range of pore sizes. The results of compressive strength and Young's modulus were in the range of 33–566 MPa and 0.19–4.46 GPa, respectively. In particular, the compressive strength and Young's modulus at the porosity of 38.5% were found to be similar to those of bone. The SEM images, pH values and Fourier-transform infrared spectroscopy (FTIR) results showed that apatite crystallites were formed on the surface of sample with 38.5% porosity during immersion in simulated body fluid which revealed bioactivity of this sample. In vitro cytocompatibility of the sample with 38.5% porosity was evaluated and cell growth was examined. SEM images revealed that cells grew on the surface and inside the pores. The present investigation has shown that this porous nano-composite is a promising biomaterial for bone tissue engineering by virtue of its porous structure, appropriate mechanical properties, bioactivity and biocompatibility.     

Fabrication of three-dimensional poly(ε-caprolactone) scaffolds with hierarchical pore structures for tissue engineering

The physical properties of tissue engineering scaffolds such as microstructures play important roles in controlling cellular behaviors and neotissue formation. Among them, the pore size stands out as a key determinant factor. In the present study, we aimed to fabricate porous scaffolds with pre-defined hierarchical pore sizes, followed by examining cell growth in these scaffolds. This hierarchical porous microstructure was implemented via integrating different pore-generating methodologies, including salt leaching and thermal induced phase separation (TIPS). Specifically, large (L, 200–300 μm), medium (M, 40–50 μm) and small (S, < 10 μm) pores were able to be generated. As such, three kinds of porous scaffolds with a similar porosity of ~ 90% creating pores of either two (LS or MS) or three (LMS) different sizes were successfully prepared. The number fractions of different pores in these scaffolds were determined to confirm the hierarchical organization of pores. It was found that the interconnectivity varied due to the different pore structures. Besides, these scaffolds demonstrated similar compressive moduli under dry and hydrated states. The adhesion, proliferation, and spatial distribution of human fibroblasts within the scaffolds during a 14-day culture were evaluated with MTT assay and fluorescence microscopy. While all three scaffolds well supported the cell attachment and proliferation, the best cell spatial distribution inside scaffolds was achieved with LMS, implicating that such a controlled hierarchical microstructure would be advantageous in tissue engineering applications.     

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.     

Microstructure,mechanical property and corrosion behavior of interpenetrating (HA + β-TCP)/MgCa composite fabricated by suction casting

The novel interpenetrating (HA + β-TCP)/MgCa composites were fabricated by infiltrating MgCa alloy into porous HA + β-TCP using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composites have been evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical testing, electrochemical and immersion tests. It was shown that the composites had compact structure and the interfacial bonding between MgCa alloy and HA + β-TCP scaffolds was very well. The ultimate compressive strength of the composites was about 500–1000 fold higher than that of the original porous scaffolds, and it still retained quarter-half of the strength of the bulk MgCa alloy. The electrochemical and immersion tests indicated that the corrosion resistance of the composites was better than that of the MgCa matrix alloy, and the corrosion products of the composite surface were mainly Mg(OH)₂, HA and Ca₃(PO₄)₂. Meanwhile, the mechanical and corrosive properties of the (HA + β-TCP)/MgCa composites were adjustable by the choice of HA content.     

In situ synthesized low modulus biomedical Zr-4Cu-xNb alloys

In order to develop new biomaterials for hard tissue replacements, the Zr-4Cu-xNb (x = 0, 0.3, 0.6 and 0.9) biomedical alloys with required properties were designed and prepared using vacuum arc melting method for the first time. Phase analysis and microstructure observation showed that all the as-cast Zr-4Cu-xNb samples consisted of α-Zr and Zr₃Cu. In addition, the lamellar eutectoid is found near the grain boundary. These alloys exhibited moderate compressive strength (1150–1300 MPa), yield stress (750–1000 MPa), favorable plastic strain (19%–27%), high elastic energy (11 MJ/m³–16 MJ/m³) and low Young's modulus (25 GPa–31 GPa). This good combination of mechanical properties indicates them potential biomedical materials for biological hard tissue replacements.     

用冰模板法制备羟基磷灰石多孔陶瓷

使用水基羟基磷灰石(HA,Ca5(PO4)3OH)浆料,用冰模板法制备定向层状多孔HA陶瓷,研究了浆料中HA陶瓷颗粒含量和冷端温度的影响.结果表明:随着浆料中HA陶瓷颗粒含量的提高,浆料的粘度值增大,层状多孔结构的层厚度相应增加,孔道层间距减小甚至消失,多孔材料的抗压强度从1.4 MPa提高到5.7 MPa,孔隙率从7...     

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200 °C for 60 min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600 °C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400 °C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.     

Novel,simple and reproducible method for preparation of composite hierarchal porous structure scaffolds

Demand to develop a simple and adaptable method for preparation the hierarchical porous scaffolds for bone tissue regeneration is ever increasing. This study presents a novel and reproducible method for preparing the scaffolds with pores structure spanning from nano, micro to macro scale. A macroporous Sr-Hardystonite (Sr–Ca₂ZnSi₂O₇, Sr–HT) scaffold with the average pore size of ~ 1200 μm and porosity of ~ 95% was prepared using polymer sponge method. The struts of the scaffold were coated with a viscous paste consisted of salt (NaCl) particles and polycaprolactone (PCL) to provide a layer with thickness of ~ 300–800 μm. A hierarchical porous scaffold was obtained with macro, micro and nanopores in the range of 400–900 μm, 1–120 μm and 40–290 nm, after salt leaching process. These scales could be easily adjusted based on the starting foam physical characteristics, salt particle size, viscosity of the paste and salt/PCL weight ratio.     

Fabrication and technological properties of nanoporous spinel/forsterite/zirconia ceramic composites

In this work, nanoporous spinel/forsterite/zirconia ceramic composites were fabricated at 1600 °C for 2 h. The influence of zirconia content (up to 10 mass%) on the technological properties, nanopores formation, phase compositions, microstructure and thermal diffusivity of nanoporous ceramic composites was investigated. Nanospinel and nanoforsterite powders were synthesized via a modified co-precipitation and sol–gel techniques, respectively. Results indicated that apparent porosity of the fired nanoporous ceramic composites is mostly in the range 14.26–56.14% with the average pores diameter 35.8 nm. Using of nanopowders (spinel and forsterite) as the staring materials were achieved high mechanical (cold crushing strength ∼ 235–164 MPa) and elastic (Young’s modulus ∼ 123.6–4.5 GPa) properties of the prepared nanoporous ceramic composites. Microstructure analysis exhibited all of the crystalline phases and pores of the nanoporous ceramic composites are in the nanosize (35–40 nm). These nanoporous ceramic composites are promising porous ceramic materials for using in advanced applications due to their excellent combination properties.