Kazutoshi Fujihara

Electrospun Nanofibers: Solving Global Issues

Energy and environment will head the list of top global issues facing society for the next 50 years. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. The route toward these nano-objects is based primarily on electrospinning: a highly versatile method that allows the fabrication of continuous fibers with diameters down to a few nanometers. The mechanism responsible for the fiber formation mainly includes the Taylor Cone theory and flight-instability theory, which can be predicted theoretically and controlled experimentally. Moreover, the electrospinning has been applied to natural polymers, synthetic polymers, ceramics, and carbon. Fibers with complex architectures, such as ribbon fiber, porous fiber, core-shell fiber, or hollow fiber, can be produced by special electrospinning methods. It is also possible to produce nanofibrous membranes with designed aggregate structure including alignment, patterning, and two-dimensional nanonets. Finally, the brief analysis of nanofibers used for advanced energy and environmental applications in the past decade indicates that their impact has been realized well and is encouraging, and will continually represent a key technology to ensure sustainable energy and preserve our environment for the future.

Performance study of braided carbon/PEEK composite compression bone plates

In addition to unidirectional laminates and short fiber reinforcements for compression bone plate developments in the literature, we have proposed using a textile structure, i.e. braid preform, for this purpose. In the present paper, the influence of braiding angles and plate thicknesses on the bending performance of the braided composite bone plates is investigated. As a result, the influence of the braiding angle, varied in a certain range, on the plate bending properties is not significant when the plate thickness is thin. This influence becomes higher with an increase in the plate thickness. A 10 degrees braiding angle has been seen to be appropriate for all the cases under consideration. The present study indicates that the braided composite plate with 2.6mm thickness can be suitable for forearm treatment whereas the braided composite plate of 3.2mm thickness is applicable to femur or tibia fixation.

Relationship between the molecular orbital structure of the dyes and photocurrent density in the dye-sensitized solar cells

Through a combined experimental and theoretical investigation we have shown that the efficiency of charge injection in dye-sensitized solar cells constituted from dyes having a single carboxylic group is determined by the extent to which the lowest unoccupied molecular orbital (LUMO) of the dye falls on its anchoring group. This conclusion was brought by calculating the LUMO surface of three indoline dyes and comparing the conversion efficiency of dye-sensitized solar cells fabricated using those dyes. The Ruthenium based N3 dye was used as standard both in the calculation and experiment.

Giant strain in PbZr0.2Ti0.8O3 nanowires

The authors report a giant reversible piezoelectric strain of ∼4.2% achieved with single-crystalline PbZr0.2Ti0.8O3 nanowires of ∼70nm in diameter, which is nearly 300% greater than the nominal values reported for ceramic perovskite single crystals. The giant strain arises from the reversible switching of ferroelastic domains. In the nanowires, there is a competition between surface tension, which forces in-plane polarization, and applied electric field, which stabilizes out-of-plane polarization, through the entire voltage cycle, the result of which is the reversible movement of ferroelastic domains.

Strain distribution analysis of braided composite bone plates

Abstract Bone plates made of braided composites have low elastic modulus compared to conventional metal bone plates. This low elastic modulus of ensures only a part of load is transferred through bone plate and the remaining load is borne by the bone itself, thus creating a small movement at fracture. The movement induced by external loading gives stimulus to the damaged bone tissue and encourages callus formation. It is necessary to calculate magnitudes of strains induced in bone plate system subjected to loading. The results from stress–strain curves of the composite indicate that at 1% strain, there is no danger of fibre and matrix separation. The suitability of a braided carbon–epoxy composite for bone plate application is studied.

Fabrication of a new composite orthodontic archwire and validation by a bridging micromechanics model.

A new technique based on tube shrinkage is proposed for the fabrication of composite archwires. Compared with a traditional pultrusion method, this new technique can avoid any fiber damage during the fabrication and can provide the archwire with a required curvature in its final clinical usage. The present paper focuses on the technique development and mechanical design and validation in terms of constituent materials by using a micromechanics bridging model. Prototype archwire has been fabricated using fiberglass and an epoxy matrix, with a wire diameter of 0.5mm and a 45% fiber volume fraction. Tensile and three-point bending tests have shown that the mechanical performance of the prototype composite archwire is comparable to that of a clinical Ni-Ti archwire. Another purpose of the present paper is to provide an efficient procedure for a critical design of composite archwires. For this to be possible, the ultimate load especially flexural load carrying ability of the composite archwire must be assessed from the knowledge of its constituent properties. However, difficulty exists in doing this, which comes from the fact that the failure of the utmost filament of the composite archwire subjected to initially the maximum bending stress does not imply its ultimate failure. Additional higher loads can still be applied and a progressive failure process is generated. In this paper, the circular archwire was discretized into a number of parallel laminae along its axis direction, and the bridging micromechanics model combined with the classical lamination theory has been applied to understand the progressive failure process with reasonable accuracy. Only the constituent fiber and matrix properties are required for this understanding. Nevertheless, the ultimate bending strength cannot be obtained only based on a stress failure criterion. This is because neither the first-ply nor the last-ply failure corresponds to the ultimate failure. An additional critical deflection (curvature) condition must be employed also. By using both the stress failure and the critical deflection conditions, the predicted load-deflection up to the ultimate failure agrees well with the measured data. Thereafter, different mechanical performances of composite archwires can be tailored before fabrication by choosing suitable constituent materials, their contents, and the archwire diameters. Several design examples have been shown in the paper.

Modified Halpin-Tsai Equation for Clay-Reinforced Polymer Nanofiber

In this paper, two sets of electrospun fibers—nylon-6 and montmorillonite (MMT)-reinforced nylon-6—are being investigated for their tensile modulus. Results show that a reduction of fiber diameter close to nano-scale range reveals increasing modulus due to greater alignment of polymeric molecules and increased influence of surface stresses as a result of increased surface-to-volume ratio. However, addition of MMT caused a reduction of modulus in spite its very high modulus. This anomalous phenomenon may well be attributed to the effect of small fiber radius for containing the MMT platelets width. By expressing the matrix modulus as a function of fiber diameter and by introducing a proportionality constant, we obtained a semi-empirical micromechanical model within the framework of the Halpin-Tsai equation—hence the modified Halpin-Tsai model. The result suggests that the fibers be shrunk for increasing its modulus without reinforcement. However, for cases where fillers are required to fulfill non-mechanical purposes (such as medical purposes), the modified Halpin-Tsai model is useful for informing the designer of the threshold weight or volume fraction of the inclusion to maintain the modulus above the required level.

Recent Advances In Tissue Engineering Applications Of Electrospun Nanofibers

that information on circul ating low molecular weight peptides can be correlated to certain disease states. Exploitation of the uni fo m1, small pores and surface functi onali za tion propertie enabled by porou silicon particles to extract and enabl e analys is of these peptides as suggested by Liotta et al (to diagnose the early stages of disease by analys i of the low molecular weight proteome using porous silicon particulates) is, in our opinion, feas ible and potentially quite powerful. Recent research on the penetration, loading, and adsorption of proteins into porous silicon, the use of porous silicon as a size-exclusion matrix for resolving protein sizes, and exceptional capacity to tune the pore size indi cate the potential for clinical use of porous silicon in proteomics. . . Furthermore, novel, contro llably dual-s ided, symmetric hydrophobi c and hydrophilic particul ates of porous _s ilicon have been conceived and are being fabri cated (see Figure 3 for an SEM image of the porous silicon surface) . They are prepared from a polysilicon precursor and are precisely size monodisperse on the sca le of one micron (d iameter and thickness). These particulates may enable unidirectional fl ow of transported drugs, proteins/peptides, nucleic ac ids, etc. They may also fac ilitate controllably different intraparti cle surface chemistries, and therefore potenti ally di fferent types of antibodie , proteins, etc., present on the same particle.

Flexural Failure Behavior of Laminated Composites Reinforced with Braided Fabrics

The failure behavior and ultimate strength of laminated textile composites subjected to bending is analyzed. Each ply in the laminate is a braided fabric reinforced lamina, with a different braiding angle if necessary. The overall load shared by the lamina in the laminate is determined by means of the classical lamination theory. After discretizing the lamina into small elements, the internal stresses generated in the constituent fiber and matrix materials of the lamina are calculated based on a general micromechanics model, the bridging model. A stress failure criterion is applied to check the lamina failure status, by comparing the internal stresses with their critical values. Unlike an in-plane load situation where the ultimate failure of the laminate corresponds to its last-ply failure, the ultimate bending strength of the laminate generally occurs before its last-ply failure. Thus, the only use of a stress-failure criterion is no longer sufficient. A critical deflection condition must be employed also. Application to several laminated beams made of 8 layers of diamond braided HTA (T300) carbon fabrics and R57 epoxy matrix subjected to four-point bending has been made. The predicted ultimate strengths of the laminates agree well with our experimental measurements.

Effects of surface treatment and weave structure on interlaminar fracture behaviour of plain glass woven fabric composites: Part II. Report of the 2nd round robin test results

This paper reports the second part of the results from the round robin test program proposed by the Society of Interfacial Materials Science (SIMS) to characterise the interlaminar fracture behaviour of E-glass woven fabric reinforced vinylester composites. Special emphasis was placed on the study of loading direction (i.e. weft and warp directions) effect on interlaminar shear strength and fracture toughness. Ten laboratories worldwide participated in this test (Table 1). Each laboratory was supplied with composite laminates and conducted the tests according to its own procedure. The results showed that although there were large variations in absolute magnitude between laboratories, a general trend was established with higher interlaminar fracture resistance in the weft direction than in the warp direction for a given silane agent. The larger number of strands running in the warp direction with rougher, more undulating areas perpendicular to the direction of crack propagation was mainly responsible for this result. The results also confirmed the previous finding that the mode I interlaminar fracture toughness increased with increasing silane agent concentration.