Bone cell–material interactions on metal-ion doped polarized hydroxyapatite

The objective of this work is to study the influence of Mg²⁺ and Sr²⁺ dopants on in vitro bone cell–material interactions of electrically polarized hydroxyapatite [HAp, Ca₁₀(PO₄)₆(OH)₂] ceramics with an aim to achieve additional advantage of matching bone chemistry along with the original benefits of electrical polarization treatment relevant to biomedical applications. To achieve our research objective, commercial phase pure HAp has been doped with MgO, and SrO in single, and binary compositions. All samples have been sintered at 1200 °C for 2 h and subsequently polarized using an external d.c. field (2.0 kV/cm) at 400 °C for 1 h. Combined addition of 1 wt.% MgO/1 wt.% SrO in HAp has been most beneficial in enhancing the polarizability in which stored charge was 4.19 μC/cm² compared to pure HAp of 2.23 μC/cm². Bone cell–material interaction has been studied by culturing with human fetal osteoblast cells (hFOB) for a maximum of 7 days. Scanning electron microscope (SEM) images of cell morphology reveal that favorable surface properties and dopant chemistry lead to good cellular adherence and spreading on negatively charged surfaces of both Sr²⁺ and Mg²⁺ doped HAp samples over undoped HAp. MTT assay results at 7 days show the highest viable cell densities on the negatively charged surfaces of binary doped HAp samples, while positive charged doped HAp surfaces exhibit limited cellular growth in comparison to neutral surfaces.     

The interplay of cell–cell and cell–substrate adhesion in collective cell migration

Collective cell migration often involves notable cell–cell and cell–substrate adhesions and highly coordinated motion of touching cells. We focus on the interplay between cell–substrate adhesion and cell–cell adhesion. We show that the loss of cell-surface contact does not significantly alter the dynamic pattern of protrusions and retractions of fast migrating amoeboid cells (Dictyostelium discoideum), but significantly changes their ability to adhere to other cells. Analysis of the dynamics of cell shapes reveals that cells that are adherent to a surface may coordinate their motion with neighbouring cells through protrusion waves that travel across cell–cell contacts. However, while shape waves exist if cells are detached from surfaces, they do not couple cell to cell. In addition, our investigation of actin polymerization indicates that loss of cell-surface adhesion changes actin polymerization at cell–cell contacts. To further investigate cell–cell/cell–substrate interactions, we used optical micromanipulation to form cell–substrate contact at controlled locations. We find that both cell-shape dynamics and cytoskeletal activity respond rapidly to the formation of cell–substrate contact.     

Inelastic behaviour of collagen networks in cell–matrix interactions and mechanosensation

The mechanical properties of extracellular matrix proteins strongly influence cell-induced tension in the matrix, which in turn influences cell function. Despite progress on the impact of elastic behaviour of matrix proteins on cell–matrix interactions, little is known about the influence of inelastic behaviour, especially at the large and slow deformations that characterize cell-induced matrix remodelling. We found that collagen matrices exhibit deformation rate-dependent behaviour, which leads to a transition from pronounced elastic behaviour at fast deformations to substantially inelastic behaviour at slow deformations (1 μm min⁻¹, similar to cell-mediated deformation). With slow deformations, the inelastic behaviour of floating gels was sensitive to collagen concentration, whereas attached gels exhibited similar inelastic behaviour independent of collagen concentration. The presence of an underlying rigid support had a similar effect on cell–matrix interactions: cell-induced deformation and remodelling were similar on 1 or 3 mg ml⁻¹ attached collagen gels while deformations were two- to fourfold smaller in floating gels of high compared with low collagen concentration. In cross-linked collagen matrices, which did not exhibit inelastic behaviour, cells did not respond to the presence of the underlying rigid foundation. These data indicate that at the slow rates of collagen compaction generated by fibroblasts, the inelastic responses of collagen gels, which are influenced by collagen concentration and the presence of an underlying rigid foundation, are important determinants of cell–matrix interactions and mechanosensation.     

Preparation of DNA–cyclodextrin–silica composite by sol–gel method and its utilization as an environmental material

A DNA–cyclodextrin–silica composite was prepared by the sol–gel method. This composite possessed the bi-functions of double-stranded DNA, such as intercalation into DNA, and cyclodextrin, such as inclusion into its intramolecular cavity. Therefore, we demonstrated the accumulation of harmful compounds from an aqueous multi-component solution using a DNA–cyclodextrin–silica composite column. As a result, the DNA–cyclodextrin–silica composite column can effectively accumulate not only planar structure-containing harmful compounds, such as dioxin and polychlorobiphenyl (PCB) derivatives, but also non-planar structure containing compounds, such as bisphenol A and diethylstilbestrol, from an aqueous multi-component solution. The accumulated amount of these harmful compounds was more than 90%. Additionally, the DNA–cyclodextrin–silica composite column was recycled by the application of methanol. Therefore, the DNA–cyclodextrin–silica composite may have the potential to be used as an environmental material for the accumulation of harmful compounds from industrial or experimental waste.     

Injectable collagen/α-tricalcium phosphate cement: collagen–mineral phase interactions and cell response

A bone inspired material was obtained by incorporating collagen in the liquid phase of an α-tricalcium phosphate cement, either in solubilized or in fibrilized form. This material was able to set in situ, giving rise to a calcium deficient hydroxyapatite (CDHA)/collagen composite. The morphology and distribution of collagen in the composite was shown to be strongly affected by the collagen pre-treatment. The interactions between collagen and the inorganic phase were assessed by FTIR. A red shift of the amide I band was indicative of calcium chelation by the collagen carbonyl groups. The rate of CDHA formation was not affected when diluted collagen solutions (1 mg/ml) were used, whereas injectability improved. The presence of solubilized collagen, even in low amount (1 %), increased cell adhesion and proliferation on the composites. Still in the absence of osteogenic medium, significant ALP activity was detected both in the inorganic and the collagen-containing cements. The maximum ALP activity was advanced in the collagen-containing cement as compared to the inorganic cement.     

Quantitative imaging and measurement of cell–substrate surface deformation by digital holography

Quantitative phase microscopy by digital holography (DH-QPM) is introduced to study the cell–substrate interactions and migratory behavior of adhesive cells. A non-wrinkling elastic substrate, collagen-coated polyacrylamide (PAA) has been employed and its surface deformation due to cell adhesion and motility has been visualized as certain tangential and vertical displacement and distortion. The surface deformation on substrates of different elasticity and thickness has been quantitatively imaged and the corresponding cellular traction force of motile fibroblasts has been measured from phase profiles by DH-QPM. DH-QPM is able to yield quantitative measures directly and provide efficient and versatile means for quantitatively analyzing cellular motility.     

A novel heat-resistant Al–Si–Cu–Ni–Mg base material synergistically strengthened by Ni-rich intermetallics and nano-AlN_p microskeletons

In this work, nano-AlN particle(nano-AlN_p) microskeletons were introduced into an Al–Si–Cu–Ni–Mg alloy by Al–8 AlN master alloy in which the nano-AlN_p reinforcements connect with each other to form three-dimensional networks. It is found that these nano-AlN_p microskeletons mainly distribute in the binary Al–Si eutectic zones resulting in flaky eutectic Si phases being modified to particulates. Meanwhile,the microskeletons strengthen the matrix synergistically with semi-continuous Ni-rich intermetallics in three dimensions. The tensile mechanical properties, micro-hardness and thermal expansion properties of the alloy at different temperatures are significantly improved. Especially, the ultimate tensile strength(UTS) at 350℃ increases from 85MPa to 106MPa, rising by 24.7%, which is ascribed to nano-AlN_p microskeletons assisting intermetallics with undertaking mechanical loading, and to the modification of eutectic Si phases to reduce the stress concentration at elevated temperatures.     

Aligned collagen–GAG matrix as a 3D substrate for Schwann cell migration and dendrimer-based gene delivery

The development of artificial off-the-shelf conduits that facilitate effective nerve regeneration and recovery after repair of traumatic nerve injury gaps is of fundamental importance. Collagen–glycosaminoglycan (GAG) matrix mimicking Schwann cell (SC) basal lamina has been proposed as a suitable and biologically rational substrate for nerve regeneration. In the present study, we have focused on the permissiveness of this matrix type for SC migration and repopulation, as these events play an essential role in nerve remodeling. We have also demonstrated that SCs cultured within collagen–GAG matrix are compatible with non-viral dendrimer-based gene delivery, that may allow conditioning of matrix-embedded cells for future gene therapy applications.     

Elastic–plastic material response of fatigue crack surface profiles due to overload interactions

The deformation caused by single and periodic overloads on the crack surface profile is studied using finite element fatigue crack closure simulations in a material with linear kinematic hardening. Differential surface profiles (difference of crack surface displacements before and after overloads), Δu_y, are found useful in understanding the role and the interaction between overloads. Three parameters, ΔK_OL/ΔK, ΔK and R, are found necessary to characterize deformation response of a single overload on the crack surface profile. The simulation procedure and results are discussed based on experimental and numerical studies reported in literature on overload interactions.The deformation occurred on the crack surface due to an applied single overload (hump) inhibits reversed plastic deformations by acting like a spring. Therefore, a second single overload leads to a larger deformation response even if this second overload is applied outside the overload plastic zone of the first single overload. This second deformation response is found equivalent to the response of a single overload with a higher K_min value.     

Microwave–material interaction phenomena: Heating mechanisms,challenges and opportunities in material processing

Efforts to use microwaves in material processing are gradually increasing. However, the phenomena associated with the processing are less understood; popular mechanisms such as dipolar heating and conduction heating have been mostly explored. The current paper reviews most of the significant phenomena that cause heating during microwave–material interaction and heat transfer during microwave energy absorption in materials. Mechanisms involved during interaction of microwave with characteristically different materials – metals, non-metals and composites (metal matrix composites, ceramic matrix composites and polymer matrix composites) have been discussed using suitable illustrations. It was observed that while microwave heating of metal based materials is due to the magnetic field based loss effects, dipolar loss and conduction loss are the phenomena associated with the electric field effects in microwave heating of non-metals. Challenges in processing of advanced materials, particularly composites have been identified from the available literature; further research directions with possible benefits have been highlighted.     

Three-dimensional performance surfaces–a tool for analysing and estimation of production system performances

This paper presents a new method to describe, analyse and estimate production system performances. Work-in-process (units), lead time (number of time units spent in the production system for each unit) and throughput (number of produced units per time unit) are basic performance measures, also used in this article. It is essential for industry to know about relations between system parameters and system performances in existing systems, and in not yet implemented system alternatives. Different performances are achieved by adjusting system parameters. Trade-offs between system parameters and its different performances are necessary to stay efficient and competitive in today's market. Queuing theory and simulation can help the decision makers to estimate system performances of existing and not yet implemented systems. When the complexity increases queuing theory becomes cumbersome, very difficult and eventually impossible to use. A single simulation presents limited information. Multiple simulations are necessary to ensure that the best alternative is chosen. A high number of simulations demand a lot of computer time and resources. Reduction of runs is desirable even with cheaper computer equipment. Currently, traditional two-dimensional charts are the only tools to present and analyse system performances. This article presents a new surrogate model for easier estimation and presentation of system performances, their internal relations, and relations to the system parameters. With the new surrogate model, system performances based on simulations are presented as positions in a three-dimensional environment. Parametric curves and surfaces of Bezier type are generated and adapted to these positions. System performances of other system alternatives can then be estimated without explicit simulation. The number of simulation calculations can thereby be moderated. The method is illustrated with a small production line system.     

Dyakonov–Tamm waves guided jointly by an ordinary,isotropic, homogeneous,dielectric material and a hyperbolic,dielectric, structurally chiral material

The planar interface of an ordinary, isotropic, homogeneous, dielectric material and a hyperbolic, dielectric, structurally chiral material can support the propagation of one or multiple Dyakonov–Tamm waves, at a specified frequency and along a specified direction in the interface plane. When multiple Dyakonov–Tamm waves can exist, they differ in phase speed, propagation length, degree of localization to the interface, and spatial profiles of the associated electromagnetic fields. Dependence on the relative permittivity scalar of the isotropic partnering material suggests exploitation for optical sensing of analytes in fluids.     

The properties and physicochemical interactions in iron–fluor-oligomer systems

We explore the efficiency of fuel pumps by modifying the friction surfaces with fluor-oligomeric films, analyze the peculiarities of interaction between the fluor-oligomer and iron, and investigate the influence of fluor-oligomer on the corrosive properties of iron. After processing the surfaces of precise friction pairs with fluor-oligomer, the average cyclic delivery of fuel pumps increases by up to 18%, and the elevated efficiency persists for 40 hours of operation. The fluor-oligomer lowers wear as compared with the control version, especially at higher rotation speeds. The positive effect is explained by the chemical interaction between iron and the fluoroligomer film as follows from the data obtained by the M?ssbauer spectroscopy, the X-ray diffraction analysis, and electrochemical technique. Even extremely thin fluor-oligomeric films (down to 2 μg · cm^–2 ) may sufficiently improve the corrosion resistance of iron.     

Comparisons between drum–buffer–rope and material requirements planning: a case study

Drum–Buffer–Rope (DBR) is an alternative approach to manufacturing planning and control that is not as formally tested as Material Requirements Planning (MRP) systems which have traditionally been around for years. Yet, some reports indicate very good performance for DBR and the associated use of synchronous manufacturing principles. But how do these systems compare and relate to one another? Based on our experiences of studying a Bearing Manufacturing Company that actually made the transition from an MRP system to a DBR system, we conduct simulation-based experiments in this paper with the objective of providing a more formal comparison between these two systems than what has been offered in prior literature. To our knowledge, this is the only study of its kind that uses a real-world setting to evaluate key differences and convergence points between comprehensive MRP and DBR systems. Our results show that even though the MRP and DBR systems position inventory differently and provide different dynamic responses to customer demand, there are several operating policies that can be implemented in either system. While the DBR performance in our simulation model was clearly superior to a nominal MRP implementation, we show that even within the constraints of the structural design of MRP system, policy modification based on DBR principles can significantly reduce these performance differences. This finding has an important implication for practising managers who need not necessarily switch from a MRP system to a DBR type of a system (as was done by our case-study firm) in order to take advantage of attractive features of the DBR system. Future researchers can use our study to understand more fully how these Structural Design and Operating Policy differences can be further exploited to implement unique systems that combine the best features of both DBR and MRP systems.     

Ground temperature monitoring and its recent change in Qinghai–Tibet Plateau

It is very important to analyze the change of the active layer and the permafrost thermal regime for Qinghai–Tibet Plateau. Formerly, there is only few data of monitoring to analyze the response of the active layer and the permafrost to climate change in Qinghai–Tibet Plateau. The monitoring data of the permafrost thermal regime with seven sites from 1995 to 2000 make it possible to analyze this response relationship.The monitoring data is used to analyze the recent change in the thickness of active layer, the subsurface temperature, the near permafrost surface temperature, and the permafrost temperature at the depth of 6 or 8 m. The results show that their changes have a better accordance with air temperature change. The climate change has an impact on the change of the active layer and the thermal regime of the permafrost. The change of the active layer and the thermal regime of the permafrost can indirectly explain some features of climate change.     

Solute–solute and solute–solvent interactions in transition metal alloys: Pt–Ti system

Abstract

The activity of Ti in solid Pt has been measured as a function of composition at 1573 K using a metal oxide–gas equilibration technique under controlled oxygen partial pressures. Thin foils of Pt were equilibrated with TiO_x at constant oxygen chemical potentials. Oxygen partial pressures were established using Ar–H₂–H₂O gas mixtures of controlled composition. A solid state cell, based on yttria doped thoria as the solid electrolyte, independently determined the chemical potential of oxygen in the gas phase. The concentration of Ti in solid Pt was determined using spectrophotometric methods. The activities of Ti were computed from the oxygen potentials established by the gas phase coupled with independent data on the thermodynamic properties of titanium oxides. The excess chemical potential of titanium in solid Pt at 1573 K in J mol^-1 can be represented as Δμ^E_Ti = —83 940 — 214 140 (1 — X _Ti )² with an error of ±2800 J mol^-1. The activity coefficient of Ti at infinite dilution determined from this study and that of other elements of the first transition series in solid Pt obtained from previous work confirm the trend predicted by both Miedema’s model and Engel–Brewer theory. The attractive interaction between the solute and the solvent (Pt) increases with decreasing atomic number of the solute. The self-interaction parameters of the first transition series elements in solid Pt indicate an increase in solute–solute repulsion with decrease in 3d electron concentration of the solute. The standard Gibbs energy of formation of TiPt₃ is —282·57 ± 4 kJ mol^-1 at 1573 K. The large negative values of the Gibbs energy of formation of phases in the system Pt–Ti indicate that Pt is not phase compatible with nitrides and carbides of Ti at high temperatures.     

Synergy of cell–cell repulsion and vacuolation in a computational model of lumen formation

A key step in blood vessel development (angiogenesis) is lumen formation: the hollowing of vessels for blood perfusion. Two alternative lumen formation mechanisms are suggested to function in different types of blood vessels. The vacuolation mechanism is suggested for lumen formation in small vessels by coalescence of intracellular vacuoles, a view that was extended to extracellular lumen formation by exocytosis of vacuoles. The cell–cell repulsion mechanism is suggested to initiate extracellular lumen formation in large vessels by active repulsion of adjacent cells, and active cell shape changes extend the lumen. We used an agent-based computer model, based on the cellular Potts model, to compare and study both mechanisms separately and combined. An extensive sensitivity analysis shows that each of the mechanisms on its own can produce lumens in a narrow region of parameter space. However, combining both mechanisms makes lumen formation much more robust to the values of the parameters, suggesting that the mechanisms may work synergistically and operate in parallel, rather than in different vessel types.     

Electrochemical properties of magnesium doped LiFePO4 cathode material prepared by sol–gel method

Magnesium doped Li_1?2xMg_xFePO₄/C (x = 0.00, 0.01, 0.03, 0.05) cathode materials were synthesized by sol–gel method, and the effect of magnesium doping as well as its content on the electrochemical properties for lithium batteries was also investigated_. Their morphology was studied with field emission scanning electron microscope and Li_1?2xMg_xFePO₄ materials showed the olivine phase without impurities. The thin carbon layer of Li_1?2xMg_xFePO₄/C was confirmed by high resolution transmission electron microscopy. The magnesium doped Li_1?2xMg_xFePO₄/C particles were smaller than those undoped. The Li_1?2xMg_xFePO₄/C materials showed better cycling behavior than undoped LiFePO₄, especially at high C-rate in which Li_0.94Mg_0.03FePO₄/C composition exhibited the best electrochemical properties.     

Microwave curing of carbon–epoxy composites: Penetration depth and material characterisation

Microwave heating has several major advantages over conventional conductive heating when used to cure carbon–epoxy composites, especially in speed of processing. Despite this and many other well-known advantages, microwave heating of carbon–epoxy composites has not taken off in industry, or even academia, due to the problems associated with microwave energy distribution, arcing, tool design and (ultimately) part quality and consistency, thus leading to a large scepticism regarding the technique/technology for heating such type of materials. This paper presents some evidence which suggests that with the correct hardware and operating procedure/methodology, consistent and high quality carbon–epoxy laminates can be produced, with the possibility of scaling up the process, as demonstrated by the micro- and macro-scale mechanical test results. Additionally, the author proposes a methodology to practically measure the maximum microwave penetration depth of a carbon–epoxy composite material.     

On the sol–gel synthesis and characterization of strontium ferrite ceramic material

A simple oxalate based sol–gel process has been described to produce a highly stable anion deficient strontium ferrite for separation of oxygen from air. The method involves metal nitrates and oxalic acid precursors with ethanol and water as solvents, gel formation, digestion for 4 h, drying at 150 °C for 24 h, and finally decomposition at 800 °C in air. The resulting material (i) exhibits a single perovskite-type cubic (SrFeO_3?ξ; ξ ～ 0.13) phase with a_o = 3.862 ± 0.002 Å, (ii) contains both the Fe⁴⁺ and Fe³⁺ species in 2.8:1 ratio, (iii) undergoes Fe⁴⁺ → Fe³⁺ reduction upon heating at 650 °C in rare gas ambient and transition to an orthorhombic phase with a ～ a_o√2, b ～ 4a_o, c ～ a_o√2, which reverts back to cubic phase with oxygen uptake at elevated temperatures, and (iv) acts as filter for air with excellent oxygen permeation, typical flux density value being 2.45 ml/cm² min at 1000 °C.