Space Holder Method Research Articles

A novel open-porous magnesium scaffold with controllable microstructures and properties for bone regeneration.

The traditional production methods of porous magnesium scaffolds are difficult to accurately control the pore morphologies and simultaneously obtain appropriate mechanical properties. In this work, two open-porous magnesium scaffolds with different pore size but in the nearly same porosity are successfully fabricated with high-purity Mg ingots through the titanium wire space holder (TWSH) method. The porosity and pore size can be easily, precisely and individually controlled, as well as the mechanical properties also can be regulated to be within the range of human cancellous bone by changing the orientation of pores without sacrifice the requisite porous structures. In vitro cell tests indicate that the scaffolds have good cytocompatibility and osteoblastic differentiation properties. In vivo findings demonstrate that both scaffolds exhibit acceptable inflammatory responses and can be almost fully degraded and replaced by newly formed bone. More importantly, under the same porosity, the scaffolds with larger pore size can promote early vascularization and up-regulate collagen type 1 and OPN expression, leading to higher bone mass and more mature bone formation. In conclusion, a new method is introduced to develop an open-porous magnesium scaffold with controllable microstructures and mechanical properties, which has great potential clinical application for bone reconstruction in the future.

Enhanced in vitro bioactivity of porous NiTi–HA composites with interconnected pore characteristics prepared by spark plasma sintering

Porous NiTi possesses suitable mechanical characteristics for orthopaedic implants. However, its poor bioactivity is a major challenge in the clinical application. Composite structures of porous NiTi and hydroxyapatite (HA) can be used to promote the bone ingrowth and integration of the implant with the surrounding tissue. But the differences in physical and mechanical properties of these composites are the main problem during sintering. Hence, we report a rapid fabrication of porous NiTi–HA composites using spark plasma sintering (SPS) with space holder method. Effect of HA on pore characteristics, mechanical properties and in vitro bioactivity (corrosion behaviors, ion release and apatite formation ability) of the porous NiTi–HA was investigated. Results showed that interconnected pore characteristics and 29%–37% porosity could be achieved by adding HA from 3 to 10wt.%. Compression test revealed that porous NiTi–HA possessed not only low elastic modulus of 5.6–8.1GPa (close to that of human bone) but also high compressive strength. Furthermore, the addition of HA could improve the bioactivity of porous NiTi significantly. The bioactivity mechanism and a relationship of HA concentration in the NiTi matrix are also discussed. The combination of interconnected pore characteristics, low elastic modulus, high strength and good bioactivity might make this material a candidate for hard tissue implants.

The Effect of Different Composition of Stainless Steel (SS316L) Foam via Space Holder Method

Stainless Steel materials (SS316L) generally known as a highly wear performance and resistant to corrosion. The purpose in this study is to produce the stainless steel foam and physical properties of sintered 316L stainless steel materials produced by powder metallurgy (P/M) method. In this paper, the method is based on using spherical urea as space holder was investigated. Then, the foams will be given to consider the properties of SS316L foam after sintering process. Powder metallurgy process needs to go through the mixing, pressing, sintering and analysis. The selected compositions of SS316L were varied from 50 wt % to 60 wt % SS316L, respectively while the remaining percentages are foaming agent. The SS316L powders were cold-pressed with 8 tons pressure and sintered at 1200°C via tube furnace. The SS316L foams were then characterised using Scanning Electron Microscopy (SEM) for morphological characterisation of the samples after sintering process. Lastly, porosity and density were tested for this sample. As a result, the composition with 60 wt % SS316L is provided higher bulk density and lower porosity which are 4.34 g/cm3 and 69.03 %, respectively.

スペースホルダー法により作製した金属多孔質焼結体フィルターの研究

スペースホルダー法により作製した金属多孔質焼結体フィルターの研究

Preparation of nanostructure bioactive diopside scaffolds for bone tissue engineering by two near net shape manufacturing techniques

Diopside has been recently investigated as a bioceramic with high mechanical and bioactivity properties, excellent biocompatibility, and appropriate degradation rate. This study has focused on fabrication of novel nanostructure diopside scaffolds by two near net shape manufacturing techniques (space holder and gelcasting methods) and comparison of their properties. The obtained scaffolds were characterized by means of X-ray Diffraction, transmission electron microscopy, scanning electron microscopy, Archimedes method, image analysis, and compression tests. The results demonstrated that both the space holder and gel casting methods led to fabrication of highly porous scaffolds with 82–85% total porosity. The prepared scaffolds were highly interconnected and had appropriate pore size (200–800µm) and compressive strength (0.98±0.11–1.33±0.13MPa). Therefore, the prepared nanostructure diopside scaffolds would be appropriate structure for use as bone substitute in bone tissue engineering.

Effect of fluidity on the manufacturing of open cell magnesium alloy foams

Abstract The effect of fluidity on open cell AZ31 metal foam samples fabricated using a solid state space holder method was investigated. Granule was fabricated by plaster powder and perlite powder. Granules were sieved which compacted layer by layer in casting mold. Preforms which made by granules were then heated to 200 °C, 300 °C, 400 °C, 500 °C under a rough (mechanical) vacuum before pressure infiltration with AZ31 Mg alloy. Samples were infiltrated using vacuum pressure values range of 8–14 KPa. The conditions of pressure and temperature were performed in order to get different fluidity on manufacturer of open cell AZ31 metal foam specimen quantity. It is found that the fluidity plays significant role to determine the open cell AZ31 alloy foam. The fluidity is affected by preheat temperature and infiltration vacuum pressure. The macrostructure, the distribution of the pores, microstructure, infiltration length, and porosity were investigated.

Fabrication and characterization of nanostructure diopside scaffolds using the space holder method: Effect of different space holders and compaction pressures

Diopside (CaMgSi2O6) ceramic with its biodegradable and bioactive characteristics can be a very good candidate in making tissue engineering scaffolds; however, few studies have been conducted in this area. In this study, for the first time, 3D macroporous nanostructure diopside scaffolds were fabricated using the space holder technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to analyze the composition, particle size, microstructure, pore size distribution, pore morphology, and pore interconnectivity of the diopside scaffolds. Immersion test in simulated body fluid (SBF) was employed to evaluate the degradation and in vitro bioactivity of the scaffolds. The results showed the successful fabrication of highly porous diopside scaffolds (53–85% porosity) with macropore sizes in the range of 150–600μm and compressive strength in the range of 0.98–8.17MPa. The prepared scaffolds with appropriate mechanical strength and pore size could satisfy the criteria required for an ideal scaffold in tissue engineering applications.

Ultrafine-grained porous titanium and porous titanium/magnesium composites fabricated by space holder-enabled severe plastic deformation

Compaction of powders by equal channel angular pressing (ECAP) using a novel space holder method was employed to fabricate metallic scaffolds with tuneable porosity. Porous Ti and Ti/Mg composites with 60% and 50% percolating porosity were fabricated using powder blends with two kinds of sacrificial space holders. The high compressive strength and good ductility of porous Ti and porous Ti/Mg obtained in this way are believed to be associated with the ultrafine grain structure of the pore walls. To understand this, a detailed electron microscopy investigation was employed to analyse the interface between Ti/Ti and Ti/Mg particles, the grain structures in Ti particles and the topography of pore surfaces. It was found that using the proposed compaction method, high quality bonding between particles was obtained. Comparing with other powder metallurgy methods to fabricate Ti with an open porous structure, where thermal energy supplied by a laser beam or high temperature sintering is essential, the ECAP process conducted at a relatively low temperature of 400°C was shown to produce unique properties.

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

Abstract 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.

Development of tantalum scaffold for orthopedic applications produced by space-holder method

In the present study, production of tantalum porous scaffolds using the space holder technique was performed. The effect of size and content of sodium chloride particles, used as space holder, as well as compacting pressure on foam structure and mechanical properties have been investigated. The morphological characterization was carried out by means of scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and micro-CT technique. The relationship between the elastic modulus and yield strength of the tantalum porous scaffold and the pore structure was evaluated. Space holder technique allows obtaining tantalum open-cell structure (70% of porosity) and modulus of elasticity similar to cancellous bone, with reproducible processability into three-dimensional structures and reasonable manufacturing costs.

Specific surface areas of porous Cu manufactured by Lost Carbonate Sintering: Measurements by quantitative stereology and cyclic voltammetry

Open-cell porous metals have many applications due to high surface area to volume ratios. Porous metals manufactured by the space holder methods have distinctively different porous structure from commercial open-cell metal foams, but very little research has been conducted to characterise the surface area of this class of materials. This paper measured the geometric, electroactive and real surface areas of porous Cu samples manufactured by the Lost Carbonate Sintering process by quantitative stereology and cyclic voltammetry. A cyclic voltammetry (peak current) procedure has been developed and successfully applied to the measurement of electroactive surface areas of the porous Cu. For porous Cu samples with pore sizes 75–1500 μm and porosities 0.5–0.8, the volumetric and gravimetric specific geometric, electroactive and real surface areas are in the ranges of 15–90 cm−1 and 5–45 cm2/g, 200–400 cm−1 and 40–130 cm2/g, and 1000–2500 cm−1 and 400–800 cm2/g, respectively, varying with pore size and porosity. The geometric, electroactive and real surface areas are found to result from the contributions from primary porosity, primary and secondary porosities, and surfaces of metal particles, respectively. The measurement methods adopted in this study can provide vital information of surface areas at different length scales, which is important for many applications.

The compression behaviors of titanium/carbamide powder mixtures in the preparation of biomedical titanium scaffolds with the space holder method

Titanium has been widely used as a preferred metallic biomaterial for bone tissue engineering scaffolds. So far, a number of techniques have been developed to produce porous-structured titanium, including the space holder method. However, a number of technological challenges are still present, such as the difficulties in controlling the geometry changes of space-holding particles during the compaction of titanium/space holder powder mixtures. In this research, a series of experiments were performed to investigate the compression behaviors of titanium/carbamide powder mixtures and determine maximum compacting pressures, considering the specific net energy expended during the process, the at-pressure relative density of powder compacts and the yield pressure derived from the load–displacement plots of powder compression cycles. The results showed that the titanium and carbamide powders exhibited dissimilar compression behaviors and titanium/carbamide powder mixtures exhibited intermediate compression behaviors of the monolithic titanium and carbamide powders. The yield pressures of titanium/carbamide powder mixtures, obtained from the Heckel plots and used as a measure for the appropriate compacting pressures, decreased with increasing volume fraction of carbamide in the mixture. The rule of mixtures was found to be applicable to predict the compression behaviors and the appropriate compacting pressures of titanium/carbamide powder mixtures. However, limitations of this model were recognized in the case of compacting mixtures with large volume fractions of carbamide space-holding particles (x>50%) and at high pressures (P>300MPa).

Effect of pore sizes on the microstructure and properties of the biomedical porous NiTi alloys prepared by microwave sintering

Biomedical porous NiTi alloys with tailored pore sizes at the same porosity levels (∼50%) were prepared by microwave sintering technique and space holder method. The effects of pore sizes on the microstructure, macrohardness, compressive strength, elastic modulus, superelasticity and corrosion resistance of the porous NiTi alloys were investigated. The results showed that the porosities of the porous NiTi alloys mainly depended on the weight ratio of the NH4HCO3 space holder agents, while the pore sizes mainly depended on the particle sizes of the space holder agents. The porous NiTi alloys mainly consisted of the predominant NiTi phase and the secondary phases Ti2Ni and Ni3Ti. With increasing the pore sizes of the porous NiTi alloys, the Ti2Ni phase and Ni3Ti phase increased, while the NiTi phase decreased. The hardness, compressive strength and elastic modulus of the porous NiTi alloys presented “S” type variation tendency with the pore sizes, respectively. The superelasticity of the porous NiTi alloys could reach ∼4% under the pre-strain of 5% as the pore sizes smaller than 294μm. Moreover, partial shape memory effect was observed for all pore size levels under the experiment conditions. The increase of the pore sizes had adverse effects on the corrosion resistance of the porous NiTi alloys in Hank’s solution.

Biomedical porous TiNbZrFe alloys fabricated using NH4HCO3 as pore forming agent through powder metallurgy route

Porous Ti59.38Nb26.6Zr8.7Fe5.32 (wt-%, referred to as TNZF) alloys with high strength and low modulus were successfully fabricated by space holder method through adding ammonium hydrogen carbonate (NH4HCO3). Results show that the fabricated porous TNZF alloys are of β type titanium alloy with adjustable pore characteristics and mechanical properties. Varied amount of NH4HCO3 exerts significant effects on phase constituents, pore characteristics and mechanical properties of the porous alloys. Fracture mechanism of the porous alloys, which is different from the typical brittle fracture as a result of high porosity, exhibits transgranular fracture accompanied with cleavage steps. Strain increased even under low stress during the compressive deformation, demonstrating that the porous alloys possess certain ductility. The porous TNZF alloys with a porosity of 39–53%, an average pore size of 300–800 μm and a compressive modulus of 7–16 GPa and a compressive strength of 117–204 MPa can well meet the requirements of biomedical implant materials.

Characterization of mesoporous nanostructured cobalt ferrite foams fabricated by microwave and conventional sintering routes

Cobalt ferrite nanopowders with an average particle size of 50 nm were synthesized by a modified Pechini type sol–gel method. Obtained powder was subjected for fabrication of magnetic foams by using microwave and conventional sintering approaches coupled by space holder method. Carbamide was used as space holder material. Samples were characterized by X-ray diffraction, stereomicroscope, scanning and transmission electron microscope, nitrogen gas adsorption–desorption, and vibration sample magnetometer analyses. The results revealed that microwave sintering offered magnetic foams with surface area of 5.21 m2/g which is four times greater than the samples obtained by conventional sintering. Such a mesoporous nanostructure was achieved only after 5 min of microwave sintering which yielded monolith foams with sufficient strength and grain growth suppression of nanostructure. Moreover, magnetic studies indicated that magnetic parameter of squareness ratio for microwave sintered foams is twice greater than that of conventionally sintered foams.

In vitro bioactivity investigation of alkali treated Ti6Al7Nb alloy foams

Biocompatible Ti6Al7Nb alloy foams with 70% porosity manufactured by space holder method were activated via alkali treatment using 5M NaOH solution at 60°C. The interconnected pore structures enabled formation of homogenous sodium rich coating on the foam surfaces by allowing penetration of alkali solution throughout the pores which had average size of 200μm. The resulted coating layer having 500nm thickness exhibited porous network morphology with 100nm pore size. On the other hand, heat treatment conducted subsequent to alkali treatment at 600°C in air transformed sodium rich coating into crystalline bioactive sodium titanate phases. Although the coatings obtained by additional heat treatment were mechanically stable and preserved their morphology, oxidation of the samples deteriorated the compressive strength significantly without affecting the elastic modulus. However, heat treated samples revealed better hydroxyapatite formation when soaked in simulated body fluid (SBF) compared to alkali treated foams. On the other hand, untreated surfaces containing bioactive TiO2 layer were observed to comprise of Ca and P rich precipitates only rather than hydroxyapatite within 15 days. The apatite formed on the treated porous surfaces was observed to have flower-like structure with Ca/P ratio around 1.5 close to that of natural bone.

Three-dimensional real structure-based finite element analysis of mechanical behavior for porous titanium manufactured by a space holder method

In this study, porous titanium samples were manufactured by a space holder method with sodium chloride. Each porous titanium sample contained two types of pores based on their sizes: macropores and micropores. Macropores were those emerged from removing the space holder, whereas micropores were voids created during powder compaction. The porous titanium exhibited low elastic modulus close to that of the human bone. Computed tomography (CT) was employed to examine the porous structure of the Ti samples. The CT results were then used in finite element simulations for analysis of the mechanical behavior of the porous titanium. The CT-based finite element model was found to give better results compared to the unit-cell finite element model in terms of agreement with the experimental data. The CT model combined with the strain hardening behavior of Ti having micropores prescribed to the matrix allowed for accurate predictions of elastic modulus, yield strength, and flow stress. These results signify the importance of taking into account pores at different scales as well as their morphology and distribution at least at macroscale.

Modeling of metallic foam morphology using the Representative Volume Element approach: Development and experimental validation

This paper focuses on the development of an algorithm capable of generating morphologically-representative foam structures using the Representative Volume Element (RVE) approach. Stereology, a sampling method based on direct observations of the foam cross-sections, is used to characterize the pore size and shape distributions. Using the morphology generation algorithm, the smallest RVEs corresponding to the numerically-convergent foam morphologies are calculated for different foam porosities. To validate the foam generation algorithm, the pore size and shape distributions of the numerically-generated foams are compared to those of the titanium foams manufactured by the space holder method.

A new approach to the fabrication of porous magnesium with well-controlled 3D pore structure for orthopedic applications

A new approach to the fabrication of porous magnesium by using the titanium wire space holder (TWSH) method has been developed. Since the entangled titanium wire structure is used as the space holder, the porous structure is pipe-like and interconnected, and the pore size is identical and equals to the diameter of the titanium wire. In particular, the pore size, porosity, and porous morphology of the porous magnesium can be exactly and individually controlled. When the porosity is in the range of 54.2–43.2%, the compressive yielding strength is in the range of 4.3–6.2MPa, and the Young's modulus is in the range of 0.5–1.0GPa.

Production of ultra-thin porous metal paper by fibre space holder method

The fibre space holder (FSH) method combines powder metallurgy and lost-foam casting with the aim of producing novel ultra-thin materials with micro-porous structures. A fabric, used as a spaceholder, is coated with metal powder (stainless steel, copper, nickel or titanium) in a water-soluble polymer binder. During sintering, the spaceholder is removed by a high temperature treatment to obtain the final porous metal sheet. This new material combines the advantages of fabric and porous metal. Its large specific surface area, minimum thickness of <30 μm, maximum porosity of >95% and strong liquid absorbency make it suitable for various application, in particular electrodes in hydrogen fuel cells and medical applications. The metal sheet can be further functionalised by coating with nanopowders.