A histomorphometric study on collagen-apatite composite as a graft material: the influence of gap size at the titanium–bone interface in animal model

The purpose of this study was to evaluate the healing process of collagen-apatite composite (CAC) at the titanium–bone interface in animal model. Small gaps (0.5 or 1.0 mm-sized wells) were prepared in the epoxy-resin block implants coated with pure titanium. The gaps were filled with CAC or demineralized freeze-dried bone (DFDB). The titanium-coated epoxy-resin block implants were inserted in the tibia of rabbit for 4 weeks or 8 weeks. The microscopic features of bony healing process in the grafted gaps were examined and analyzed. In the histomorphometric analysis, CAC group showed higher fraction of newly-formed bone than DFDB group in both 0.5 and 1.0 mm gap subgroup at 4-week specimen (P < 0.05). In the transmission electron microscopic examinations, osteoblasts of the newly-formed bone of CAC group showed more cellular activity than that of DFDB group. From the results, it was expected that CAC had more beneficial property on early bony healing process than DFDB at the titanium–bone interface.     

The effect of bone ingrowth depth on the tensile and shear strength of the implant–bone e-beam produced interface

New technologies, such as selective electron beam melting, allow to create complex interface structures to enhance bone ingrowth in cementless implants. The efficacy of such structures can be tested in animal experiments. Although animal studies provide insight into the biological response of new structures, it remains unclear how ingrowth depth is related to interface strength. Theoretically, there could be a threshold of ingrowth, above which the interface strength does not further increase. To test the relationship between depth and strength we performed a finite element study on micro models with simulated uncoated and hydroxyapatite (HA) coated surfaces. We examined whether complete ingrowth is necessary to obtain a maximal interface strength. An increase in bone ingrowth depth did not always enhance the bone–implant interface strength. For the uncoated specimens a plateau was reached at 1,500 μm of ingrowth depth. For the specimens with a simulated HA coating, a bone ingrowth depth of 500 μm already yielded a substantial interface strength, and deeper ingrowth did not enhance the interface strength considerably. These findings may assist in optimizing interface morphology (its depth) and in judging the effect of bone ingrowth depth on interface strength.     

An experimental study of the influence of fibre–matrix interface on fatigue tensile strength of notched composite laminates

The objective of this study was to investigate the effect of fibre–matrix interfacial adhesion on fatigue residual strength of polymer matrix composite laminates containing a circular hole. Composite laminates were manufactured using surface-treated and -untreated carbon fibres, and the interfacial adhesion was quantified by measuring the transverse flexural strength of the two material systems. Tensile–tensile cyclic fatigue experiments were conducted at three load levels. Residual strength of notched laminates, subjected to cyclic loading was then measured for the two composite systems. Damage mechanisms were analysed using C-scan and SEM fractography and correlated with notched residual strength.     

Implant–abutment connections: influence of the design on the microgap and their fatigue and fracture behavior of dental implants

Microgap between implant and abutment can produce biological and mechanical problems such as peri-implantitis and/or fatigue failures. The aim of this study was to evaluate microgap size and fatigue behavior of external and internal connections. In both systems the torque to tighten the abutment screw of single crown abutments was 45 Ncm. Fifty implants for each connection type were studied. One subgroup (n = 5) was used by the observation and evaluation of the microgap, other (n = 5) was tested for fracture strength and the other (n = 40) was subjected to dynamic loading. The internal connection presents a lower microgap than the external ones. From fatigue results, the external hexagon interface showed superior result compared to the internal hexagon interfaces. The tolerances in the internal connections are better and favour the fatigue behavior but this factor alone is not sufficient to improve the fatigue response in relation to the external connections when the screw is subjected at the same torque. The external system presents a higher value of the area than the internal and it produces a better load distribution. Microgaps and mechanical properties are very important for the long-term behavior of the dental implants and these aspects should be known by the implantologists.     

The influence of core properties on the perforation resistance of sandwich structures – An experimental study

The aim of this study is to investigate the perforation resistance of a range of foam-based sandwich structures. Nine foams, based on a crosslinked PVC, a linear PVC and PET, have been combined with thin glass fibre reinforced plastic skins to produce a range of lightweight sandwich structures, Initially, the mechanical properties of the different foams are characterised. Here, a new test geometry is used to evaluate the toughness characteristics and strengths of the foams under shear loading, a condition similar to that encountered during the impact perforation event.The influence of the plastic collapse stress of the foam in determining the failure thresholds of the front and rear composite skins is established. Here, an existing model has been used to successfully predict failure of the top surface composite skin in the sandwich structures. In addition, the force associated with perforating the lightweight core has been shown to be strongly dependent on the shear strength of the polymer foam. Finally, the perforation resistance of the sandwich structure has been shown to be closely linked to the Mode II work of fracture of the foam material. Here a unique relationship has been established between these two parameters, with all of the experimental points lying on one curve.     

Frigatebird behaviour at the ocean–atmosphere interface: integrating animal behaviour with multi-satellite data

Marine top predators such as seabirds are useful indicators of the integrated response of the marine ecosystem to environmental variability at different scales. Large-scale physical gradients constrain seabird habitat. Birds however respond behaviourally to physical heterogeneity at much smaller scales. Here, we use, for the first time, three-dimensional GPS tracking of a seabird, the great frigatebird (Fregata minor), in the Mozambique Channel. These data, which provide at the same time high-resolution vertical and horizontal positions, allow us to relate the behaviour of frigatebirds to the physical environment at the (sub-)mesoscale (10–100 km, days–weeks). Behavioural patterns are classified based on the birds’ vertical displacement (e.g. fast/slow ascents and descents), and are overlaid on maps of physical properties of the ocean–atmosphere interface, obtained by a nonlinear analysis of multi-satellite data. We find that frigatebirds modify their behaviours concurrently to transport and thermal fronts. Our results suggest that the birds’ co-occurrence with these structures is a consequence of their search not only for food (preferentially searched over thermal fronts) but also for upward vertical wind. This is also supported by their relationship with mesoscale patterns of wind divergence. Our multi-disciplinary method can be applied to forthcoming high-resolution animal tracking data, and aims to provide a mechanistic understanding of animals'' habitat choice and of marine ecosystem responses to environmental change.     

Effect of SiC nanoparticles on the wear behaviour of squeeze-cast AZ91–2.0Ca–0.3Sb alloy

The dry sliding wear behaviour of the AZ91–2.0Ca–0.3Sb alloy and the AZ91–2.0Ca–0.3Sb–xSiC_np nanocomposites have been investigated. The wear rate is lower for all the nanocomposites compared to the alloy. All the nanocomposites demonstrate the lower specific wear rates than the alloy. Among the nanocomposites, the one containing 2.0SiC_np exhibits the best tribological performance. The values of the coefficient of friction are lower for the nanocomposites than the alloy. The abrasion, adhesion, oxidation, and delamination are the dominant wear mechanisms. The 3D topography depicts that the addition of SiC_np to the AZ91–2Ca–0.3Sb alloy results in the reduced surface roughness during the wear tests, confirming the superior wear behaviour of the nanocomposites compared to the alloy.     

A study of Mg and Cu additions on the foaming behaviour of Al–Si alloys

Aluminium casting alloys containing Mg and Cu in addition to Si were investigated with respect to their potential to be foamed. The kinetics of foam expansion of different alloys was studied and the resulting structures were characterised. Of the stages of evolution of foams, namely (i) pore nucleation, (ii) foam growth in the semisolid state, (iii) further expansion in the fully liquid state, the latter two were explored. Expansion in the semisolid state could be related to the available liquid fraction. Mg-containing Al–Si alloys yielded a less coarse and more uniform pore structure than the other alloys investigated. However, achieving a high volume expansion required restriction to a narrow process window and led to the suggestion of AlMg4Si8 as a practical alloy.     

Effect of Zn addition on hot tearing behaviour of Mg–0.5Ca–xZn alloys

The influence of Zn addition (0, 0.5, 1.5, 4.0 and 6.0 wt.%) on hot tearing behaviour of Mg–0.5 wt.% Ca alloy was investigated using a constrained rod casting (CRC) apparatus. The effects of mould temperature and grain refinement on the hot tearing susceptibility (HTS) were studied. Hot tears were observed with 3D X-ray tomography and the tear volumes were quantified. Results show that the Zn addition increases the HTS of Mg–0.5Ca alloys. At a mould temperature of 250 °C, all alloys investigated except Mg–0.5Ca–6Zn alloy show severe HTS. An increase in the mould temperature from 250 °C to 450 °C did not reduce the HTS in Mg–0.5Ca–1.5Zn and Mg–0.5Ca–4Zn alloys. Among all the investigated alloys, Mg–0.5Ca–4Zn alloy exhibits severe HTS as it completely broke away from the sprue–rod junction. The HTS of alloys was well correlated with the susceptible temperature range (ΔT_s). An increase in ΔT_s increased the HTS. The hot tears propagated along the grain boundaries through liquid film rupture. Grain refinement by Zr addition improved the hot tearing resistance of Mg–0.5Ca–4Zn alloy as the fine grain structure facilitated the easy feeding of liquid into the last area of solidification and accommodated the developed strain more effectively.     

Effects of Li addition on the corrosion behaviour and biocompatibility of Mg(Li)–Zn–Ca metallic glasses

Magnesium alloys with suitable corrosion behaviour and good mechanical properties are desired for biodegradable materials. In the current study, novel Mg–Li-based metallic glasses (MGs) demonstrate potential clinical applications as implantable biodegradable materials. The amorphous structure of MGs provides suitable elastic modulus with human bone. The enhanced corrosion resistance of MGs realises a uniform corrosion process, as well as maintains a stable acid-based environment, and increases cell proliferation. A schematic model is proposed to illustrate the corrosion mechanisms of MGs. Adding Li significantly improves the corrosion resistance of MGs. Both the indirect cytotoxicity and direct cell culture assays are conducted using transfected osteoblasts (hFOB) cells. Results show that the novel Mg–Li–Zn–Ca MGs have good biocompatibility.     

Synthesis and characterization of core–shell nanoparticles and their influence on the mechanical behavior of acrylic bone cements

Core–shell nanoparticles consisting of polybutyl acrylate (PBA) rubbery core and a polymethyl methacrylate (PMMA) shell, with different core–shell ratios, were synthesized in order to enhance the fracture toughness of the acrylic bone cements prepared with them. It was observed by TEM and SEM that the core–shell nanoparticles exhibited a spherical morphology with ca. 120 nm in diameter and that both modulus and tensile strength decreased by increasing the PBA content; the desired structuring pattern in the synthesized particles was confirmed by DMA. Also, experimental bone cements were prepared with variable amounts (0, 5, 10 and 20 wt.%) of nanoparticles with a core–shell ratio of 30/70 in order to study the influence of these nanostructured particles on the physicochemical, mechanical and fracture properties of bone cements. It was found that the addition of nanostructured particles to bone cements caused a significant reduction in the peak temperature and setting time while the glass transition temperature (T_g) of cements increased with increasing particles content. On the other hand, modulus and strength of bone cements decreased when particles were incorporated but fracture toughness was increased.     

In vitro study on the influence of strontium-doped calcium polyphosphate on the angiogenesis-related behaviors of HUVECs

Angiogenesis is of great importance in bone tissue engineering, and has gained large attention in the past decade. Strontium-doped calcium polyphosphate (SCPP) is a novel biodegradable material which has been proved to be able to promote in vivo angiogenesis during bone regeneration. An in vitro culture system was developed in the present work to examine its influence on angiogenesis-related behaviors of human umbilical vein endothelial cells (HUVECs), including cell adhesion, spreading, proliferation and migration. The effects of microtopography, chemical property and the ingredients in the degradation fluid (DF) on cell behaviors were discussed. The results showed that cells attached and spread better on SCPP scaffold than on calcium polyphosphate (CPP), which might partially result from the less rough surface of SCPP scaffold and the less hydrogel formed on the surface. In addition, cell proliferation was significantly improved when treated with SCPP DF compared with the treatment with CPP DF. Statistical analysis indicated that Sr(2+) in SCPP DF might be the main reason for the improved cell proliferation. Moreover, cell migration, another important step during angiogenesis, was evidently stimulated by SCPP DF. The improved in vivo angiogenesis by SCPP might be assigned to its better surface properties and strontium in the DF. This work also provides a new method for in vitro evaluation of biodegradable materials' potential effects on angiogenesis.     

Does mixing affect the setting of injectable bone cement? An ultrasound study

Experimental calcium sulphate bone cement has been tested by ultrasounds to characterise its progressive setting through the evolution of several acoustic properties. The acoustic impedance z(t), the density ρ (t) and the speed of sound c(t) versus the curing time have been monitored during the viscous-to-solid transition of the cement as a function of different mixing conditions. Injectability tests were also performed and the results have been related to the acoustic properties measured previously. It has been observed that further mixing after cement’s constituency, and before the initial setting time of the cement, drastically affects both the characteristic setting times and the injectability of the cement.     

Effect of Al content on hot tearing behaviour of Mg–xAl–2Ca–2Sm alloys

Mg–xAl–2Ca–2Sm (x?=?3, 5, 9 and 15) alloys were tested using an ‘L’-shaped sand mould serving as a hot tearing testing system. The experimental results showed that the solidification range of the Mg–xAl–2Ca–2Sm alloys first decreased and then increased as the Al content was increased. Furthermore, by increasing the Al content, the dendritic arms of the α-Mg phase become more developed, and the hot tearing tendency of the Mg–xAl–2Ca–2Sm alloys increased. In addition, the variety of precipitated phases was seen to be affected by the Al content and the tendency for hot tearing depended on the precipitated phase. The tendency of the Mg–xAl–2Ca–2Sm alloys for hot tearing first decreased and then increased with increasing Al content.     

An empirical study of service postponement: locating the push–pull boundary

The purpose of this paper is to determine if service firms can profitably perform postponement. We develop a general model to identify the optimal location of the push–pull boundary, or extent of postponement. While previous literature discusses the benefit of applying postponement to the service industry this is the first paper to-date that mathematically models the benefit of service postponement. This paper illustrates how service companies can balance the trade-off between increased responsiveness and increased costs. The single-stage newsvendor model is iteratively applied to each stage of the service process to determine the optimal level of postponement. Two examples demonstrate the value of postponement and the impact of changes in service characteristics are investigated. Finally, this paper provides guidance for service industry professionals on policy-level decisions and applications of postponement.     

In vitro antimicrobial properties of silver–polysaccharide coatings on porous fiber-reinforced composites for bone implants

Biostable fiber-reinforced composite (FRC) implants prepared from bisphenol-A-dimethacrylate and triethyleneglycoldimethacrylate resin reinforced with E-glass fibers have been successfully used in cranial reconstructions in 15 patients. Recently, porous FRC structures were suggested as potential implant materials. Compared with smooth surface, porous surface allows implant incorporation via bone ingrowth, but is also a subject to bacterial attachment. Non-cytotoxic silver–polysaccharide nanocomposite coatings may provide a way to decrease the risk of bacterial contamination of porous FRC structures. This study is focused on the in vitro characterization of the effect porosity on the antimicrobial efficiency of the coatings against Staphylococcus aureus and Pseudomonas aeruginosa by a series of microbiological tests (initial adhesion, antimicrobial efficacy, and biofilm formation). Characterization included confocal laser scanning microscopy and scanning electron microscopy. The effect of porosity on the initial attachment of S. aureus was pronounced, but in the case of P. aeruginosa the effect was negligible. There were no significant effects of the coatings on the initial bacterial attachment. In the antimicrobial efficacy test, the coatings were potent against both strains regardless of the sample morphology. In the biofilm tests, there were no clear effects either of morphology or of the coating. Further coating development is foreseen to achieve a longer-term antimicrobial effect to inhibiting bacterial implant colonization.     

An empirical study of users’ hype cycle based on search traffic: the case study on hybrid cars

Many forms of technology cycle models have been developed and utilized to identify new/convergent technologies and forecast social changes, and among these, the technology hype cycle introduced by Gartner has become established as an effective method that is widely utilized in the field. Despite the popularity of this commonly deployed model, however, the currently existing research literature fails to provide sufficient consideration of its theoretical frame or its empirical verification. This paper presents a new method for the empirical measurement of this hype cycle model. In particular, it presents a method for measuring the hype of the users rather than the hype cycle generated by research activities or by the media by means of analyzing the hype cycle using search traffic analysis. The analytical results derived from the case study of hybrid automobiles empirically demonstrated that following the introductory stage and the early growth stage of the life cycle, the positive hype curve and the negative hype curve, the representative figures of the hype cycle, were present in the bell curve for the users’ search behavior. Based on this finding, this paper proposes a new method for measuring the users’ expectation and suggests a new direction for future research that enables the forecasting of promising technologies and technological opportunities in linkage with the conventional technology life cycle model. In particular, by interpreting the empirical results using the consumer behavior model and the adoption model, this study empirically demonstrates that the characteristics of each user category can be identified through differences in the hype cycle in the process of the diffusion of new technological products discussed in the past.     

A study on the influence of Mo, Al and Si additions on the microstructure of annealed dual phase Cr–Ta alloys

The effects of additions of 5 at.% Mo, Al and Si on the long-term annealed microstructures of a two phase Cr–Cr₂Ta alloy have been studied. Following 200 h at 1300 °C, the lamellar eutectic constituent of all the alloys disintegrated into discrete particles of the Laves phase embedded within a Cr-rich solid solution phase, along with the formation of fine Laves phase precipitates. One of the predominant differences between the three alloying additions was the extent of the C14 to C15 polytypic transformation of the Cr₂Ta-based Laves phase. With Mo and Al additions, the Cr₂Ta Laves phase transformed from C14 to either C15 or intermediate hexagonal polytypes following 200 h annealing at 1300 °C. In contrast, Si additions stabilised the C14 polytype, with no transformation to other polytypes observed after prolonged annealing at 1000, 1100 and 1300 °C.     

Effect of strain rate on the fracture behaviour of epoxy–graphene nanocomposite

In this study, epoxy-based nanocomposite was fabricated by the addition of graphene nanosheet via a solution casting method. To investigate the effect of strain rate on tensile properties of epoxy, tensile tests were done on standard samples at different strain rates (0.05–1 min^?1). The role of strain rate and presence of graphene on fracture behaviour of epoxy were also studied by investigation of the fracture surfaces of some samples by scanning electron microscopy (SEM). Finally, Eyring’s model was performed to clarify the role of strain rate on activation volume and activation enthalpy of epoxy. The results of tensile tests showed a maximum strength of epoxy–graphene nanocomposite at the graphene wt% of 0.1%. Tensile strength of epoxy obviously improved with increasing strain rate, but tensile strength of epoxy/graphene nanocomposite sample was less sensitive. Fracture micrographs showed that the mirror zone of the fracture surface of epoxy diminished by increasing strain rate or addition of graphene; and final fracture zone also became rougher. Finally, by investigation of the activation enthalpies, it was showed that much higher enthalpy was needed to fracture the nanocomposite sample, as the activation enthalpy changed from 41.54 for neat epoxy to 67.34 kJ mol^?1 for EP–0.1% GNS sample.