Space Holder Technique Research Articles

Antimicrobial activity of porous metal injection molded (MIM) 316L stainless steel by Zn, Cu and Ag electrodeposition

Porous 316L stainless steel samples were functionalized with electrodeposited zinc, copper, and silver coatings for antimicrobial activity against gram-positive bacteria Staphylococcus aureus (S. aureus). Porous stainless steel samples were created by combining metal injection molding (MIM) with a powder space holder (PSH) technique using sodium chloride (20 wt%) as a space holder material. Galvanostatic (0.10 A) electrodeposition was used for zinc, copper, and silver deposition, and antimicrobial activity of functionalized samples was evaluated using a touch test protocol with S. aureus. All electrodeposited samples completely prevented the growth of S. aureus. These results confirm that metal depositions only in the pores of the porous 316L were sufficient to inhibit the growth of S. aureus completely.

Compressive Properties and Energy Absorption Behavior of 316L Steel Foam Prepared by Space Holder Technique

The effect of porosity and pore size on the quasi-static compression properties and energy absorption characteristics of the steel foam was investigated in this paper. The 316L steel foams were prepared through powder metallurgy using urea as the space holder. The macrostructure of steel foam and microstructure of the pore walls were characterized, and the quasi-static compression experiments were conducted on the specimens in the axial direction at a strain rate of 10-3 s-1. The results show that the increase in porosity decreases the yield strength and plastic modulus of the steel foam but increases the densification strain of the steel foam. The yield strength of the steel foam decreases significantly when the pore size is 2.37 mm. However, the pore size has little effect on the plastic modulus. Moreover, the energy absorption per volume of the steel foam decreases with increasing porosity at the same strain. The effect of porosity on energy absorption efficiency is greater than that of pore size.

Type-A Gelatin-Based Hydrogel Infiltration and Degradation in Titanium Foams as a Potential Method for Localised Drug Delivery.

A gelatin-based hydrogel was infiltrated and degraded-released in two different titanium foams with porosities of 30 and 60 vol.% (Ti30 and Ti60 foams) and fabricated by the space holder technique to evaluate its potential to act as an innovative, alternative, and localised method to introduce both active pharmaceutical ingredients, such as antibiotics and non-steroidal anti-inflammatory drugs, and growth factors, such as morphogens, required after bone-tissue replacement surgeries. In addition, the kinetic behaviour was studied for both infiltration and degradation-release processes. A higher infiltration rate was observed in the Ti60 foam. The maximum infiltration hydrogel was achieved for the Ti30 and Ti60 foams after 120 min and 75 min, respectively. Further, both processes followed a Lucas-Washburn theoretical behaviour, typical for the infiltration of a fluid by capillarity in porous channels. Regarding the subsequent degradation-release process, both systems showed similar exponential degradation performance, with the full release from Ti60 foam (80 min), versus 45 min for Ti30, due to the greater interconnected porosity open to the surface of the Ti60 foam in comparison with the Ti30 foam. In addition, the optimal biocompatibility of the hydrogel was confirmed, with the total absence of cytotoxicity and the promotion of cell growth in the fibroblast cells evaluated.

Experimental Analysis and Parametric Optimization on Compressive Properties of Diamond-Reinforced Porous Al Composites.

The present study aims to optimize the compressive properties of porous aluminum composites fabricated using the powder metallurgy (PM) space holder technique. These properties were optimized by taking into consideration different processing factors such as sintering temperature, compaction pressure, and sintering time. The experimental design was formulated using L9 orthogonal array by employing these three parameters at three levels. The density, porosity, plateau stress, and energy absorption capacity were determined and analyzed. The impact of individual input parameters was evaluated using the Taguchi-based S/N ratio and analysis of variance (ANOVA). The main effect plots outlined the optimum parameter levels to achieve maximum values for compressive properties (plateau stress and energy absorption capacity). The results revealed that the sintering temperature and time significantly impact compressive properties. The ANOVA analysis exhibited similar results, with maximum contribution from sintering temperature. Further response optimization of compressive properties concluded that the maximum values could be achieved at optimum parameters, i.e., a sintering temperature of 590 °C, compaction pressure of 350 MPa, and sintering time of 90 min. Further, confirmation tests on the optimized parameters revealed improved results and some minor errors and deviations indicating that the selected parameters are vital for controlling the compressive properties of the aluminum composites.

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Effect of Mg Powder's Particle Size on Structure and Mechanical Properties of Ti Foam Synthesized by Space Holder Technique.

Titanium foam has been the focus of special attention for its specific structure and potential applications in purification, catalyst substrate, heat exchanger, biomaterial, aerospace and naval industries. However, the liquid-state foaming techniques are difficult to use in fabricating Ti foam because of its high melting temperature and strong chemical reactivity with atmospheric gases. Here, the fabrication of Ti foams via the powder metallurgy route was carried out by utilizing both magnesium powders and magnesium particles as spacer holders, and Ti powders as matrix metal. The green compacts containing Ti powder, Mg powder and Mg particles were heated to a certain temperature to remove the magnesium and obtain the Ti foam. The results show that the porosities of the obtained Ti foam are about 35-65%, and Young's modulus and yield strength are found to be in the ranges of 22-126 MPa and 0.063-1.18 GPa, respectively. It is found that the magnesium powders play a more important role than the magnesium particles in the deformation and the densification of the green compact during the pressing, and the pore structure of Ti foam depends on the amount and the size of the magnesium spacer holders after sintering.

Characterization of Cr-Mo Alloyed Steel Foams Produced by Evaporative and Leachable Space Holder Techniques

Steel foams have attracted a lot of attention in both academia and industry with unique properties such as low density, high strength-to-weight ratio, operating temperature, good energy absorption, electrical conductivity, and large specific surface. The development of production methods will increase the use of steel foam. In this paper, Cr-Mo alloyed steel foams having porosities in the range of 46.8-71.3% were produced by evaporative and leachable space holder techniques in powder metallurgy. The effect on the properties of removing the carbamide used as a space holder material from the porous structure by different methods was compared. Microstructural evaluations of the pore wall, pore size, pore wall thickness, and the compressive deformation behavior of steel foam were evaluated. Steel foams produced by both routes have a rather similar macropore structure but differences in pore wall structure such as micropore ratio and pore wall thickness. The differences increase with increasing porosity content. The mechanical properties are higher in foams produced by the evaporative route as compared to the leachable route at similar porosity due to its stronger cell wall. The compressive stress and energy absorption of the leachable and evaporative process are in the range of 15-84 and 102 MPa and 1.91-6.03 and 2.98-7.83 J/mm2, respectively.

B4C‐Reinforced Al–Zn Foams Having Superior Energy Absorption Efficiency

The low density of the aluminium foam and high energy absorption make them favourable for automobile, aerospace, and defence industries. However, the melt route for foam fabrication has challenges in achieving homogeneous distribution of pores. Hence, we have adopted the space holder technique using the powder metallurgy methodology to overcome such a challenge. In the current study, we fabricated Al–Zn alloy foams reinforced with varying volume fractions of B4C particles using NaCl as a space holder implemented by hot pressure‐assisted sintering and dissolution. X‐ray computed tomography revealed a homogeneous distribution of pores. The quasistatic compression studies showed that the samples containing a higher volume fraction of pores exhibited higher energy absorption efficiency in the fabricated foam. The maximum energy absorption efficiency (η) achieved was ≈93% for the pristine Al alloy foam with ≈50% porosity, which is ≈11% higher than the η value of 9 vol% B4C samples with similar porosity. Additionally, B4C particles delay the sudden collapse of cell walls and stabilize the compression behaviour. Adding B4C improves the η and strength at higher relative density. This fabrication methodology would help us develop foams with a homogenous pore distribution and regular geometry, achieving highly desirable mechanical properties.

Ti64/20Ag Porous Composites Fabricated by Powder Metallurgy for Biomedical Applications.

We present a novel Ti64/20Ag highly porous composite fabricated by powder metallurgy for biomedical applications and provide an insight into its microstructure and mechanical proprieties. In this work, the Ti64/20Ag highly porous composites were successfully fabricated by the space holder technique and consolidated by liquid phase sintering, at lower temperatures than the ones used for Ti64 materials. The sintering densification was evaluated by dilatometry tests and the microstructural characterization and porosity features were determined by scanning electron microscopy and computed microtomography. Permeability was estimated by numerical simulations on the 3D real microstructure. Mechanical properties were evaluated by simple compression tests. Densification was achieved by interparticle pore filling with liquid Ag that does not drain to the large pores, with additional densification due to the macroscopical deformation of large pores. Pore characteristics are closely linked to the pore formers and the permeability was highly increased by increasing the pore volume fraction, mainly because the connectivity was improved. As expected, with the increase in porosity, the mechanical properties decreased. These results permitted us to gain a greater understanding of the microstructure and to confirm that we developed a promising Ti64/20Ag composite, showing E of 7.4 GPa, σy of 123 MPa and permeability of 3.93 × 10−11 m2. Enhanced adaptability and antibacterial proprieties due to Ag were obtained for bone implant applications.

Self-lubrication of porous metal injection molded (MIM) 17-4PH stainless steel by impregnated paraffin wax

Paraffin impregnation into the internal pore structure of porous 17-4PH was used as a lubricant storage. Porous 17-4PH specimens were fabricated by metal injection molding (MIM) combined with powder space holder (PSH) technique for samples with three different porosities. Sodium chloride was used as a space holder material. Paraffin impregnation was achieved by immersing the 17-4PH specimens into melted paraffin wax. Dynamic coefficient of friction (COF) of porous and non-porous specimens was measured in dry sliding and paraffin-lubricated conditions. Significant COF reduction in paraffin-lubricated results was observed with the porous samples compared to the non-porous reference samples. The lowest COF value was observed for specimens with 20 and 30 wt% porosity.

An effective process to reinforced open cell 316LSS foams with MWCNT for improving biocompatibility

316L stainless steel and stainless steel-MWCNT composite foam were synthesized by space holder technique using spherical urea particles. The influence of MWCNT content on the microstructure, mechanical and corrosion behaviour of the foam was studied. Stainless steel composite foam samples containing 0, 0.5, 1 and 1.5 wt%. MWCNT were fabricated. The micro-hardness and corrosion resistance increased with increase in MWCNT concentration. However the mechanical properties show optimum value at 0.5 wt% MWCNT. To sum up, the MWCNT was an effective reinforcement for enhancing the mechanical and bio-corrosion resistance of stainless steel composite foam samples, making it a suitable candidate for engineering and bio-medical applications.

Synthesis titanium foam by space holder technique

Synthesis titanium foam by space holder technique

Approach to the Fatigue and Cellular Behavior of Superficially Modified Porous Titanium Dental Implants.

In this work, the fatigue and cellular performance of novel superficially treated porous titanium dental implants made up using conventional powder metallurgy and space-holder techniques (30 vol.% and 50 vol.%, both with a spacer size range of 100–200 µm) are evaluated. Before the sintering stage, a specific stage of CNC milling of the screw thread of the implant is used. After the consolidation processing, different surface modifications are performed: chemical etching and bioactive coatings (BG 45S5 and BG 1393). The results are discussed in terms of the effect of the porosity, as well as the surface roughness, chemical composition, and adherence of the coatings on the fatigue resistance and the osteoblast cells’ behavior for the proposed implants. Macro-pores are preferential sites of the nucleation of cracks and bone cell adhesion, and they increase the cellular activity of the implants, but decrease the fatigue life. In conclusion, SH 30 vol.% dental implant chemical etching presents the best bio-functional (in vitro osseointegration) and bio-mechanical (stiffness, yield strength and fatigue life) balance, which could ensure the required characteristics of cortical bone tissue.

Uniform porous and functionally graded porous titanium fabricated via space holder technique with spark plasma sintering for biomedical applications

Porous materials with low stiffness and high strength are sought as implant materials to prevent stress shielding and fracture during in vivo use. This study proposes a powder metallurgy-based space holder technique to fabricate porous titanium with mechanical performance suitable for implant materials. Mixed powders of titanium and sodium chloride were sintered at low temperature using spark plasma sintering, and then the sodium chloride was dissolved in water. As a result, uniform porous titanium (UP-Ti) with a wide range of microstructures: porosity from 26% to 80% and average pore size from 75 μm to 475 μm was successfully fabricated. Also, functionally graded porous titanium (FGP-Ti) was successfully fabricated, in which porous titanium with high porosity and dense titanium were placed at the inside and surface, respectively. The stiffness of UP-Ti was comparable to that of natural bones, but its strength was lower than that of natural bones, which would be insufficient for use as an implant. In contrast, the mechanical performance of FGP-Ti was improved, compared with UP-Ti with the porosity comparable to the average porosity of FGP-Ti: its strength was higher than that of natural bones and its stiffness was comparable to that of natural bones. These results imply that porous titanium, especially functionally graded porous titanium, is a candidate metal for implants used to replace heavily loaded natural bone.

Influence of Femtosecond Laser Modification on Biomechanical and Biofunctional Behavior of Porous Titanium Substrates.

Bone resorption and inadequate osseointegration are considered the main problems of titanium implants. In this investigation, the texture and surface roughness of porous titanium samples obtained by the space holder technique were modified with a femtosecond Yb-doped fiber laser. Different percentages of porosity (30, 40, 50, and 60 vol.%) and particle range size (100–200 and 355–500 μm) were compared with fully-dense samples obtained by conventional powder metallurgy. After femtosecond laser treatment the formation of a rough surface with micro-columns and micro-holes occurred for all the studied substrates. The surface was covered by ripples over the micro-metric structures. This work evaluates both the influence of the macro-pores inherent to the spacer particles, as well as the micro-columns and the texture generated with the laser, on the wettability of the surface, the cell behavior (adhesion and proliferation of osteoblasts), micro-hardness (instrumented micro-indentation test, P–h curves) and scratch resistance. The titanium sample with 30 vol.% and a pore range size of 100–200 μm was the best candidate for the replacement of small damaged cortical bone tissues, based on its better biomechanical (stiffness and yield strength) and biofunctional balance (bone in-growth and in vitro osseointegration).

Production of MWCNT-Reinforced Aluminum Foams Via Powder Space-Holder Technique and Investigation of their Mechanical Properties

Production of MWCNT-Reinforced Aluminum Foams Via Powder Space-Holder Technique and Investigation of their Mechanical Properties

Fabrication and characterization of wollastonite-titanium porous scaffold for pharmaceutical application: Representative volume element simulation

The use of modern methods for the fabrication of porous scaffolds has led to the construction of complex composite scaffolds with a very similar bone structure. One of these useful methods is called the space holder method which uses the NaCl microparticles as space agents. In this study, the novel calcium silicate bioceramic (Wollastonite: WS) particles are used as the based ceramic with the addition of various amounts of titanium particle (TiO2-TiNP). The combination of WS-TiNP with various amounts of Ti-NP (pure WS (S1), WS-5 wt% TiO2 (S2), WS-10 wt% TiO2 (S3), and WS-15 wt% TiO2 (S4)) composed with NaCl space agent under 200 MPa using space holder technique is performed. The materials characterization is performed using Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis for morphological and phase analysis. After analyzing the mechanical features such as compressive strength and fracture toughness, the biological properties such as biodegradation rate and bioactivity are evaluated after 28 days of soaking in phosphate buffer saline (PBS) and simulated body fluid (SBF), respectively. As the porosity value affects the mechanical performance the Abaqus software was utilized to predict the atomic structure of the porous bio-composite WS-TiNP. The obtained results indicate that the compressive strength and porosity increased and decrease from 5.2 to 8.5 MPa and 62% to 45%, respectively. Also, the Abaqus models and experimental data have an error of 18% to evaluate the influence of the porosity on the compressive strength. The observation indicate that the sample with 10 wt% TiO2 has a potential for pharmaceutical and maxilla facial application.

A fuzzy analysis for porous bioceramic-magnetite nanoparticles-zirconia scaffold prepared by space holder technique with poly vinyl pyrrolidone (PVP) coating: Investigation of mechanical and biological properties

Many efforts were made to make the biodegradable implants for bone repair in the last two decades. In this study, coral aragonite were successfully used to replace broken bones as these materials can make strong chemical bonds with soft tissues and bone. Among them, calcium-based ceramics have been important in terms of their ability to form the strong chemical bonds with tissues and bones. In this research, the porous scaffold is made from marine coral (calcium carbonate) composed of the magnetite nanoparticles (MNPs) and zirconia nanoparticles by space holder method under hot system pressing with a uniaxial hydraulic press. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis are performed to evaluate the phase, structure, and morphology of samples. The biological investigation of sample performed using phosphate buffer saline (PBS) and simulated body fluid (SBF) test was used to evaluate the ability of apatite formation and biodegradation on the porous scaffolds. The sample without any reinforcement shows a compressive strength of about 1.3–1.4 MPa at a strain rate of 10% and a fracture strength of 1.7 MPa. Moreover, the sample with MNPs reinforcement shows higher compressive strength than the sample containing zircon nanoparticles with 7.4 MPa at the strain of about 32 MPa. The porosity results of the samples examined under SEM images show that the porosity reduced from 65% to 58%, and the pore size was about 100–200 μm. A fuzzy logic modeling is also used to predict the outputs for any set of input values using the experimental data in this study. The results show that the developed model is a precise one, and the fuzzy modeling method can be used in similar studies.

Fabrication of Ti Fiber-Reinforced Porous Ti with Mechanical Biocompatibility via Powder Metallurgy-Based Space Holder Technique

Titanium (Ti) and its alloys have been used for artificial bones because of their high mechanical performance and corrosion resistance. It has been reported that natural bones surrounding a Ti-based artificial bone are damaged due to the stress shielding effect, which is caused by the higher stiffness (Young’s modulus) of artificial bone than that of natural bone. To develop implant materials with lower Young’s modulus and higher strength which are desirable mechanical properties for artificial bones, Ti fiber-reinforced porous Ti was fabricated in this study. As a result, the Ti fiber-reinforced porous Ti with the porosity of 60% and the fiber volume fraction of 3% to 20% was successfully fabricated via the space holder technique with spark plasma sintering. Tensile testing showed that the porous Ti exhibited Young’s modulus and strength comparable to the natural bones.

Effect of the Processing Parameters on the Porosity and Mechanical Behavior of Titanium Samples with Bimodal Microstructure Produced via Hot Pressing.

Commercially pure (c.p.) titanium grade IV with a bimodal microstructure is a promising material for biomedical implants. The influence of the processing parameters on the physical, microstructural, and mechanical properties was investigated. The bimodal microstructure was achieved from the blends of powder particles with different sizes, while the porous structure was obtained using the space-holder technique (50 vol.% of ammonium bicarbonate). Mechanically milled powders (10 and 20 h) were mixed in 50 wt.% or 75 wt.% with c.p. titanium. Four different mixtures of powders were precompacted via uniaxial cold pressing at 400 MPa. Then, the specimens were sintered at 750 °C via hot pressing in an argon gas atmosphere. The presence of a bimodal microstructure, comprised of small-grain regions separated by coarse-grain ones, was confirmed by optical and scanning electron microscopies. The samples with a bimodal microstructure exhibited an increase in the porosity compared with the commercially available pure Ti. In addition, the hardness was increased while the Young’s modulus was decreased in the specimens with 75 wt.% of the milled powders (20 h).