Compressibility of porous magnesium foam: dependency on porosity and pore size

Mechanical properties of porous magnesium with the porosity of 35–55% and the pore size of about 70–400 μm are investigated by compressive tests focusing on the effects of the porosity and pore size on the Young's modulus and strength. Results indicated that the Young's modulus and peak stress increase with decreasing porosity and pore size. The mechanical properties of the porous magnesium were in a range of those of cancellous bone. Therefore, it is suggested that the porous magnesium is one of promising scaffold materials for hard tissue regeneration.

Modelling of porosity defects in high pressure die casting with a neural network

High Pressure Die Casting (HPDC) is a complex process that results in casting defects if configured improperly. However, finding out the optimal configuration is a non-trivial task as eliminating one of the casting defects (for example, porosity) can result in occurrence of other casting defects. The industry generally tries to eliminate the defects by trial and error which is an expensive and error -prone process. This paper aims to improve current modelling and understanding of defects formation in HPDC machines. We have conducted conventional die casting tests with a neural network model of HPDC machine and compared the obtained results with the current understanding of formation of porosity. While most of our findings correspond well to established knowledge in the field, some of our findings are in conflict with the previous studies of die casting.

Porous titanium with porosity gradients for biomedical applications

Highly porous titanium and titanium alloys with an open cell structure are promising implant materials due to their low elastic modulus, excellent bioactivity, biocompatibility and the ability for bone regeneration. However, the mechanical strength of the porous titanium decreases dramatically with increasing porosity, which is a prerequisite for the ingrowth of new bone tissues and vascularization. In the present study, porous titanium with porosity gradients, i.e. solid core with highly porous outer shell was successfully fabricated using a powder metallurgy approach. Satisfactory mechanical properties derived from the solid core and osseointegration capacity derived from the outer shell can be achieved simultaneously through the design of the porosity gradients of the porous titanium. The outer shell of porous titanium exhibited a porous architecture very close to
that of natural bone, i.e. a porosity of 70% and pore size distribution in the range of 200 - 500 μm. The peak stress and the elastic modulus of the porous titanium with a porosity gradient (an overall porosity 63%) under compression were approximately 152 MPa and 4 GPa, respectively. These
properties are very close to those of natural bone. For comparison, porous titanium with a uniform porosity of 63% was also prepared and haracterised in the present study. The peak stress and the elastic modulus were 109 MPa and 4 GPa, respectively. The topography of the porous titanium
affected the mechanical properties significantly.

Improving the quality of die castings by using artificial neural networks for porosity defect modelling

The aim of this work is to improve the quality of castings by minimizing defects and scrap through the analysis of the data generated by High Pressure Die Casting (HPDC) Machines using computational intelligence techniques. Casting is a complex process that is affected by the interdependence of die casting process parameters on each other such that changes in one parameter results in changes in other parameters. Computational intelligence techniques have the potential to model accurately this complex relationship. The project has the potential to generate optimal configurations for HPDC Machines and explain the relationships between die casting process parameters.

Influence of porosity on shape memory behavior of porous TiNi shape memory alloy

Porous Ti-50.5at.%Ni shape memory alloy (SMA) samples with a range of  porosities were prepared by spacer sintering. The porous structure of the alloy was examined using scanning electron microscopy (SEM). The phase constituents of the porous TiNi alloy were determined by X-ray diffraction (XRD). The shape memory behavior of the porous TiNi alloy was investigated using loading–unloading compression tests. Results indicate that the porous TiNi alloy exhibits superelasticity and the recoverable strain by the superelasticity decreases with the increase of porosity. After a prestrain of 7%, the superelastically recovered strains for the porous TiNi alloy samples with porosities of 46%, 59%, 69% and 77% are 2.0%, 1.8%, 1.5% and 1.3%, respectively. The pores in the TiNi alloy samples cause stress/strain concentration, as well as crack initiation, which adversely affect the shape memory behavior of the porous TiNi alloy.

Three-dimensional tissue scaffolds from interbonded poly(e-caprolactone) fibrous matrices with controlled porosity

In this article, we report on the preparation and cell culture performance of a novel fibrous matrix that has an interbonded fiber architecture, excellent pore interconnectivity, and controlled pore size and porosity. The fibrous matrices were prepared by combining melt-bonding of short synthetic fibers with a template leaching technique. The microcomputed tomography and scanning electron microscopy imaging verified that the fibers in the matrix were highly bonded, forming unique isotropic pore architectures. The average pore size and porosity of the fibrous matrices were controlled by the fiber/template ratio. The matrices having the average pore size of 120, 207, 813, and 994 mm, with the respective porosity of 73%, 88%, 96%, and 97%, were investigated. The applicability of the matrix as a three-dimensional (3D) tissue scaffold for cell culture was demonstrated with two cell lines, rat skin fibroblast and Chinese hamster ovary, and the influences of the matrix porosity and surface area on the cell culture performance were examined. Both cell lines grew successfully in the matrices, but they showed different preferences in pore size and porosity. Compared with two-dimensional tissue culture plates, the cell number on 3D fibrous matrices was increased by 97.27% for the Chinese hamster ovary cells and 49.46% for the fibroblasts after 21 days of culture. The fibroblasts in the matrices not only grew along the fiber surface but also bridged among the fibers, which was much different from those on two-dimensional scaffolds. Such an interbonded fibrous matrix may be useful for developing new fiber-based 3D tissue scaffolds for various cell culture applications.

Controlling morphology and porosity of porous siloxane membranes through water content of precursor microemulsion

Here we report a facile method for controlling the morphology and porosity of porous siloxane membranes through manipulation of the water content of precursor microemulsions. The polymerizable microemulsion precursors consisted of a methacrylate-terminated siloxane macromonomer (MTSM) as the oil phase, nonionic surfactant (Teric G9A8), water, and cosurfactant (isopropanol). Photo-polymerization of the oil phase in the parent microemulsion solutions resulted in polymeric solids, and subsequent removal of the extractable components yielded porous PDMS membranes. The pre-cured parent microemulsion solutions and post-cured polymers were characterized by small angle X-ray scattering (SAXS) while the nanostructures of extracted porous polymer membranes were characterized by SAXS, scanning electron microscopy (SEM) and mercury porosimetry. The results indicated that nano- and micro-structures of the membranes could be modulated by the water content of the precursor microemulsions. Further, in situ photo-rheometry was used to follow the microemulsion polymerization process. The rate of polymerization and the mechanical properties of the resulting PDMS membranes also depend on the water content of precursor microemulsions. This study demonstrates a simple approach to the fabrication of a variety of novel porous PDMS membranes with controllable morphology and porosity.

Experimental verification of theoretical prediction of fiber to fiber contacts in electrospun multilayer nano-microfibrous assemblies: effect of fiber diameter and network porosity

Average number of fiber-to-fiber contacts in a fibrous structure is a prerequisite to investigate the mechanical, optical and transport properties of stochastic nanomicrofibrous networks. In this research work, based on theoretical analysis presented for the estimation of the number of contacts between fibers in electrospun random multilayer nanofibrous assembles, experimental verification for theoretical dependence of fiber diameter and network porosity on the fiber to fiber contacts has been provided. The analytical model formulated is compared with the existing theories to predict the average number of fiber contacts of nanofiber structures. The effect of fiber diameters and network porosities on average number of fiber contacts of nano-microfiber mats has been investigated. A comparison is also made between the experimental and theoretical number of inter-fiber contacts of multilayer electrospun random nanomicrofibrous networks. It has been found that both the fiber diameter and the network porosity have significant effects on the properties of fiber-to-fiber contacts.

Control of porosity and pore size of metal reinforced carbon nanotube membranes

Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to incorporate them into macrostructures have already shown to substantially increase the membrane performance. In this paper we report on the fabrication and engineering of metal-reinforced carbon nanotube (CNT) Bucky-Paper (BP) composites with tuneable porosity and surface pore size. A BP is an entangled mesh non-woven like structure of nanotubes. Pure CNT BPs present both very high porosity (>90%) and specific surface area (>400 m2/g). Furthermore, their pore size is generally between 20–50 nm making them promising candidates for various membrane and separation applications. Both electro-plating and electroless plating techniques were used to plate different series of BPs and offered various degrees of success. Here we will report mainly on electroless plated gold/CNT composites. The benefit of this method resides in the versatility of the plating and the opportunity to tune both average pore size and porosity of the structure with a high degree of reproducibility. The CNT BPs were first oxidized by short UV/O3 treatment, followed by successive immersion in different plating solutions. The morphology and properties of these samples has been investigated and their performance in air permeation and gas adsorption will be reported.

Effect of back pressure during equal-channel angular pressing on deformation-induced porosity in copper

The effect of back pressure during equal channel angular pressing (ECAP) on deformation-induced porosity is investigated. While percolating porosity was found after 4 ECAP passes in the absence of back pressure, no percolation was detected when a back pressure of 200 MPa was applied. However, after ECAP with back pressure continued to 8 passes, percolating porosity did appear. The nature of the percolating porosity developed in severely deformed materials is discussed.

Evolution of nanoscale porosity during equal-channel angular pressing of titanium

Small-angle neutron scattering (SANS) analysis and transmission electron microscopy evidence suggest the occurrence of nanoscale porosity in commercial-purity titanium processed by equal-channel angular pressing (ECAP). SANS data were produced at two different facilities (GKSS, Germany; and Los Alamos, USA) and were analysed using three different methods. The results are consistent and yield a conclusive picture of the distribution of the scattering centres, which are believed to be associated with nanoporosity. Back pressure applied during ECAP tends to reduce the average pore size, which also depends on the processing route used. The results of the study strongly suggest that ECAP leaves a footprint in titanium in the form of a population of polydispersed nanovoids, which may play an important role in subsequent processing of the material.