Interconnectivity and permeability of supercritical fluid-foamed scaffolds and the effect of their structural properties on cell distribution

This study aims to investigate interconnectivity and permeability of scCO₂-foamed scaffolds and the influence of structural scaffold properties on cell distribution. Supercritical fluid technology was utilized to fabricated scaffolds from 37 kDa, 53 kDa and 109 kDa PLGA (85:15). Pore size, pore size distribution and porosity were quantified by MicroCT, and window sizes were measured using SEM. A novel interconnectivity algorithm allowed the quantification of scaffold interconnectivity in three space dimensions. To determine the permeability of porous materials direct perfusion experiments were performed, where a known flow rate was applied to measure the pressure differential across the scaffolds. The permeability was calculated using Darcy's law. Largest pore sizes, porosities, interconnectivities and permeabilities were obtained for scaffolds fabricated from 37 kDa PLGA. These scaffolds showed a heterogeneous pore structure and distribution, whereas homogeneous pore structure, smallest pore sizes, porosities, interconnectivities and permeabilities were observed for scaffolds fabricated from 109 kDa PLGA. The distribution of 3T3 fibroblasts through scCO₂-foamed scaffolds was investigated by MicroCT and MTT staining. Cells were further visualized by fluorescent imaging. Uniform cell distribution was observed on scaffolds fabricated from 109 kDa PLGA and an average of 10% of the total scaffold volume was covered with cells that had adhered onto them.     

A comparative study on the corrosion behavior of porous and dense NiTi shape memory alloys in NaCl solution

The corrosion behaviors of porous and dense NiTi shape memory alloys with the same nominal composition were investigated in a 0.9% aqueous NaCl solution using electrochemical methods. The study clarified the role of the porous structure in influencing the corrosion behavior of the porous NiTi alloys, which exhibited porosity values ranging from 35.5% to 63.8%. The results indicated that the porous NiTi alloy was more susceptible to localized corrosion than was the dense NiTi alloy. However, the porous NiTi alloy sample with a higher porosity did not suffer more serious corrosion than the one with a lower porosity. Furthermore, the potential distribution exists on the pore wall of the porous NiTi alloys as a result of current flow within the pore electrolyte. Thus, the role of potential distribution inside the pore and porous structure in the corrosion behavior of the porous NiTi alloys is an important factor.     

Detection of open or closed porosity in low-κ dielectrics by solvent diffusion

The presence of open porosity in a porous interlayer dielectric (ILD) can seriously degrade the ultimate performance and reliability of a device. A simple method for detecting the open porosity in ILDs would facilitate the design of materials with pore morphologies compatible with the required specifications of a particular device. The measurement of effective diffusion coefficients in a low-κ ILD over a range of porosities is shown to permit the detection of open porosity. An example illustrating the simplicity of this method is presented using toluene solvent in a well-characterized porous organosilicate material. The result using this method is consistent with available data in the literature.     

Performance Modeling of MANET Interconnectivity

The proliferation of mobile wireless computing devices and the increasing usage of wireless networking have motivated substantial research in mobile ad hoc networks (MANETs). In addition, much has also been done to link autonomous MANETs to the Internet, and as MANETs become more prevalent, the need to interconnect multiple MANETs becomes increasingly important too. However, direct interconnection of MANETs has rarely been studied. In this paper, we first report an experimental study on the performance of interconnected MANETs running two different routing protocols, viz., the Ad hoc On-Demand Distance Vector (AODV) and Optimized Link State Routing (OLSR) protocols, which represent the two major categories, and show that with the use of multiple gateways, it is possible to viably interconnect multiple networks running different MANET routing protocols. We then follow with a simulation study to evaluate the performance in large networks, which not only validates the scalability of the proposed scheme, but also helps to identify various problems that were not apparent in small experimental networks.     

Debating big data: A literature review on realizing value from big data

Big data has been considered to be a breakthrough technological development over recent years. Notwithstanding, we have as yet limited understanding of how organizations translate its potential into actual social and economic value. We conduct an in-depth systematic review of IS literature on the topic and identify six debates central to how organizations realize value from big data, at different levels of analysis. Based on this review, we identify two socio-technical features of big data that influence value realization: portability and interconnectivity. We argue that, in practice, organizations need to continuously realign work practices, organizational models, and stakeholder interests in order to reap the benefits from big data. We synthesize the findings by means of an integrated model.     

Role of the pore interconnectivity on the dielectric,switching and tunability properties of PZTN ceramics

The influence of phase interconnectivity in porous Pb_0.988(Zr_0.52Ti_0.48)_0.976Nb_0.024O₃ ceramics on the structural, dielectric and tunability properties is reported. Porous ceramics with the same porosity level, but with different types of pore interconnectivity (0−3) and (3-3) type have been prepared by using dry and wet mixing of perovskite powder with starch porosity former agent. By comparison to the dense sintered ceramic (predominantly tetragonal), high porosity tends to favour the formation of monoclinic phase on the expense of the tetragonal one. A strong decrease of the effective permittivity with respect with the dense ceramic in both the porous structures was found, with lower values for the (3-3) connectivity. To describe the observed role of the phase interconnectivity on the dielectric properties, Finite Element Modeling calculations were performed. The local boundary conditions for such specific configurations generate a local field inhomogeneity, with a broad field distribution and decrease of the average field, which is more pronounced in the (3-3) porous configuration. As result, a strong decrease of the effective permittivity, switching polarization, loop area and rectangularity factor are predicted for this configuration, and confirmed by high-field experiments (tunability ε(E) and P(E) ferroelectric loops). This study shows that not only the pore amount, but the pore interconnectivity has a major role on the electrical properties and well-designed phase interconnectivity may provide useful functional properties.     

Fabrication and characterization of honeycomb β-tricalcium phosphate scaffolds through an extrusion technique

In this study, for the first time honeycomb β-tricalcium phosphate (β-TCP) scaffolds were fabricated through an extrusion technique. The physicochemical properties and cell behaviors of the honeycomb β-TCP scaffolds were investigated. The results showed that scaffolds were characterized by ordered channel-like macropores and unidirectional interconnection. The pore structure and mechanical strength could be tailored by changing the parameters of extrusion molds. The pore size of scaffolds was in the range of 400–800 µm approximately, while their compressive strength parallel to the pore direction and porosity ranged from 14 to 20 MPa and 60–70%, respectively. The in vitro cell behavior demonstrated that cells could well attach on the surfaces and grow into the inner channel-like pores of thescaffolds; the scaffolds with higher porosity showed better cell proliferation but poorer cell differentiation. The honeycomb scaffolds fabricated by extrusion technique are potential candidate for bone tissue engineering.     

Preparation of highly interconnected porous hydroxyapatite scaffolds by chitin gel-casting

In this study, a simple and effective method for producing highly interconnected porous hydroxyapatite (HA) scaffolds was developed by combining gel-casting, particle-leaching and extrusion techniques. Chitin (CT) sol was used to disperse HA particles and wax spheres were introduced as porogens for their excellent deformability. In extrusion process, the accumulated wax spheres in point-to-point contact can transform into surface-to-surface contact by means of the extrusion pressure. Thus, the obtained porous HA scaffolds exhibited an interconnected channel network after leaching out of the porogens. The results showed that the scaffolds prepared by different size of wax spheres exhibited nearly the same volumetric porosity of about 86%, while the compressive strengths decreased as the pore size increased. Therefore, the method developed can be used to effectively tailor the pore size of HA scaffolds while maintaining a high porosity. The highly porous HA scaffolds with excellent interconnectivity are expected to be a promising bone substitute in clinical practice.     

Enhancement of the Pore Interconnectivity and Porosity of Calcium Phosphate Scaffolds by Acid-Etching Method

Porous hydroxyapatite(HA)–tricalcium phosphate(TCP) ceramic scaffolds were prepared using a screw-type extrusion method with polymer beads. HA and dicalcium phosphate dehydrates(DCPD) were added at various ratios to obtain different HA/TCP ratios in sintered ceramic scaffolds. To further enhance the pore interconnectivity and porosity,the developed porous ceramic scaffolds were etched with acid solutions. The maximum porosity(~85%) was observed in the Ca-P scaffold with the lowest HA(~7%) content. On the other hand, the maximum compressive strength was noted in the scaffolds with the highest HA content(~85%). X-ray diffraction showed that the extent of the b-TCP to a-TCP phase transformation increased with decreasing HA/DCPD ratio. All HCl-etched scaffolds were observed to generate micropores,which improved the interconnectivity, while biomineralization was found to be the same for both the HCl-etched and nonetched scaffolds. In particular, hydrochloric acid etching is a promising method for improving the interconnectivity and porosity of the ceramic scaffolds.     

Artificially controlling of inner structure to porous hydroxyapatite ceramic by using solidified coated fibers

Porous hydroxyapatite (HA) ceramic was fabricated by 3D fiber network. These fibers as channel underprops were treated by surface coating with acidic macromolecule glue. The solidified coated fibers in ceramic block could form run-through channels and also etch stripes on channel walls for cell attachment. The channels formed in sintering process by fibers volatilization may be directed artificially according to beforehand design of structure for ceramic block. The results showed that the pore characteristics and the inner structure of the sample made from this technique have settled for essential requests of porous bioceramic. The channels in sintered scaffold shown in SEM (scanning electron microscopy) micrographs have directional connection, equal distribution, intact configuration and existence of thin stripes on inner walls. All of these characteristics have met requests for tissue cell developing, transplanting and attaching. The samples have appropriate interconnectivity and reasonable structure with equable pore-arranging and uniform size of pore. XRD (X-ray diffraction) patterns of sample indicated no major change of the crystalline structure.