Showing papers in "Journal of Functional Biomaterials in 2013"

Self-Setting Calcium Orthophosphate Formulations

Abstract: In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Keeping an Eye on Decellularized Corneas: A Review of Methods, Characterization and Applications

Abstract: The worldwide limited availability of suitable corneal donor tissue has led to the development of alternatives, including keratoprostheses (Kpros) and tissue engineered (TE) constructs. Despite advances in bioscaffold design, there is yet to be a corneal equivalent that effectively mimics both the native tissue ultrastructure and biomechanical properties. Human decellularized corneas (DCs) could offer a safe, sustainable source of corneal tissue, increasing the donor pool and potentially reducing the risk of immune rejection after corneal graft surgery. Appropriate, human-specific, decellularization techniques and high-resolution, non-destructive analysis systems are required to ensure reproducible outputs can be achieved. If robust treatment and characterization processes can be developed, DCs could offer a supplement to the donor corneal pool, alongside superior cell culture systems for pharmacology, toxicology and drug discovery studies.

Antimicrobial, mechanical and thermal studies of silver particle-loaded polyurethane.

Abstract: Silver-particle-incorporated polyurethane films were evaluated for antimicrobial activity towards two different bacteria: Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Distributed silver particles sourced from silver nitrate, silver lactate and preformed silver nanoparticles were mixed with polyurethane (PU) and variously characterized by field emission scanning electron microscopy (FESEM), fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD) and contact angle measurement. Antibacterial activity against E.coli was confirmed for films loaded with 10% (w/w) AgNO3, 1% and 10% (w/w) Ag lactate and preformed Ag nanoparticles. All were active against S. aureus, but Ag nanoparticles loaded with PU had a minor effect. The apparent antibacterial performance of Ag lactate-loaded PU is better than other Ag ion-loaded films, revealed from the zone of inhibition study. The better performance of silver lactate-loaded PU was the likely result of a porous PU structure. FESEM and FTIR indicated direct interaction of silver with the PU backbone, and XRD patterns confirmed that face-centred cubic-type silver, representative of Ag metal, was present. Young’s modulus, tensile strength and the hardness of silver containing PU films were not adversely affected and possibly marginally increased with silver incorporation. Dynamic mechanical analysis (DMA) indicated greater thermal stability.

Epoxy Cross-Linked Collagen and Collagen-Laminin Peptide Hydrogels as Corneal Substitutes

Abstract: A bi-functional epoxy-based cross-linker, 1,4-Butanediol diglycidyl ether (BDDGE), was investigated in the fabrication of collagen based corneal substitutes. Two synthetic strategies were explored in the preparation of the cross-linked collagen scaffolds. The lysine residues of Type 1 porcine collagen were directly cross-linked using l,4-Butanediol diglycidyl ether (BDDGE) under basic conditions at pH 11. Alternatively, under conventional methodology, using both BDDGE and 1-Ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as cross-linkers, hydrogels were fabricated under acidic conditions. In this latter strategy, Cu(BF4)2·XH2O was used to catalyze the formation of secondary amine bonds. To date, we have demonstrated that both methods of chemical cross-linking improved the elasticity and tensile strength of the collagen implants. Differential scanning calorimetry and biocompatibility studies indicate comparable, and in some cases, enhanced properties compared to that of the EDC/NHS controls. In vitro studies showed that human corneal epithelial cells and neuronal progenitor cell lines proliferated on these hydrogels. In addition, improvement of cell proliferation on the surfaces of the materials was observed when neurite promoting laminin epitope, IKVAV, and adhesion peptide, YIGSR, were incorporated. However, the elasticity decreased with peptide incorporation and will require further optimization. Nevertheless, we have shown that epoxy cross-linkers should be further explored in the fabrication of collagen-based hydrogels, as alternatives to or in conjunction with carbodiimide cross-linkers.

Tissue engineering of the corneal endothelium: a review of carrier materials.

Abstract: Functional impairment of the human corneal endothelium can lead to corneal blindness. In order to meet the high demand for transplants with an appropriate human corneal endothelial cell density as a prerequisite for corneal function, several tissue engineering techniques have been developed to generate transplantable endothelial cell sheets. These approaches range from the use of natural membranes, biological polymers and biosynthetic material compositions, to completely synthetic materials as matrices for corneal endothelial cell sheet generation. This review gives an overview about currently used materials for the generation of transplantable corneal endothelial cell sheets with a special focus on thermo-responsive polymer coatings.

Incorporation of Exogenous RGD Peptide and Inter-Species Blending as Strategies for Enhancing Human Corneal Limbal Epithelial Cell Growth on Bombyx mori Silk Fibroin Membranes

Abstract: While fibroin isolated from the cocoons of domesticated silkworm Bombyx mori supports growth of human corneal limbal epithelial (HLE) cells, the mechanism of cell attachment remains unclear. In the present study we sought to enhance the attachment of HLE cells to membranes of Bombyx mori silk fibroin (BMSF) through surface functionalization with an arginine-glycine-aspartic acid (RGD)-containing peptide. Moreover, we have examined the response of HLE cells to BMSF when blended with the fibroin produced by a wild silkworm, Antheraea pernyi, which is known to contain RGD sequences within its primary structure. A procedure to isolate A. pernyi silk fibroin (APSF) from the cocoons was established, and blends of the two fibroins were prepared at five different BMSF/APSF ratios. In another experiment, BMSF surface was modified by binding chemically the GRGDSPC peptide using a water-soluble carbodiimide. Primary HLE were grown in the absence of serum on membranes made of BMSF, APSF, and their blends, as well as on RGD-modified BMSF. There was no statistically significant enhancing effect on the cell attachment due to the RGD presence. This suggests that the adhesion through RGD ligands may have a complex mechanism, and the investigated strategies are of limited value unless the factors contributing to this mechanism become better known.

A Novel Glass Polyalkenoate Cement for Fixation and Stabilisation of the Ribcage, Post Sternotomy Surgery: An ex-Vivo Study.

Abstract: This study investigates the use of gallium (Ga) based glass polyalkenoate cements (GPCs) as a possible alternative adhesive in sternal fixation, post sternotomy surgery. The glass series consists of a Control (CaO–ZnO–SiO2), and LGa-1 and LGa-2 which contain Ga at the expense of zinc (Zn) in 0.08 mol% increments. The additions of Ga resulted in increased working time (75 s to 137 s) and setting time (113 to 254 s). Fourier Transform Infrared (FTIR) analysis indicated that this was a direct result of increased unreacted poly(acrylic acid) (PAA) and the reduction of crosslink formation during cement maturation. LGa samples (0.16 wt % Ga) resulted in an altered ion release profile, particularly for 30 days analysis, with maximum Ca2+, Zn2+, Si4+ and Ga3+ ions released into the distilled water. The additions of Ga resulted in increased roughness and decreased contact angles during cement maturation. The presence of Ga has a positive effect on the compressive strength of the samples with strengths increasing over 10 MPa at 7 days analysis compared to the 1 day results. The additions of Ga had relatively no effect on the flexural strength. Tensile testing of bovine sterna proved that the LGa samples (0.16 wt % Ga) are comparable to the Control samples.

Design and in vitro biocompatibility of a novel ocular drug delivery device.

Abstract: The capsule drug ring (CDR) is a reservoir and delivery agent, which is designed to be placed within the capsular bag during cataract surgery. Prototypes were manufactured by hot melt extrusion of Bionate II®, a polycarbonate urethane. The devices have been optimized using Avastin® as the drug of interest. In vitro biocompatibility was assessed with human lens epithelial cell (B-3), mouse macrophage (J774A.1) and mouse fibroblast (L-929) cell lines. Cell migration and proliferation were assessed after in vitro culture. Pro-inflammatory cytokines (i.e., MIP-1β, MIP-1α, MCP-1, IL-1β, TNF and TGF-β1) were quantified using cytometric bead array (CBA). Preliminary in vivo biocompatibility and pharmacokinetics testing has been performed in rabbits.

Study on reinforcing and toughening of graphene oxide to cement-based composites

Abstract: Nano-graphene oxide(GO) aqueous was prepared by oxidizing graphite according to Hummers method and ultrasonic dispersion.The effects of GO on the concrete properties doped with polycarbonate superplasticizer(PCs) were investigated by measuring the fluidity,viscosity and setting time of cement pastes,pore structure of hardened cement paste,folding strength and compression strength of mortar in the presence of PCs.The results indicated that nano-graphene oxide could make lightly decrease of fluidity and setting time,could make hardened cement paste become dense,could decrease larg pore number and could remarkably increase folding and compression strength of mortar.The results of XRD and SEM testing showed that the GO could lead and promote cement hydration to produce more crystal products with regular shape,which hinted the template role of GO for cement hydration.Therefore,research on the effect of nano-graphene oxide on cement composite microstructure is important to reinforcement and toughening of concrete and prolongs concrete life.

Preparation and characterization of high specific area activated carbon by KOH/NaOH activation from abandoned capsicum straw

Abstract: The active carbon with high specific surface area was prepared from capsicum straw by using KOH/NaOH as the activation agent.Studied the activation temperature,activation time,carbonization temperature and KOH/NaOH/C on the adsorption properties through orthogonal test,and the optimum conditions are that the activation temperature of 700℃,the activation time of 80min,and the carbonization temperature of 450℃,KOH/NaOH/C for 3∶1∶1.Microstructure of the sample showed that the activated carbon developed possesses a large apparent surface area(SLangmuir=3270.478m2/g) and average pore size diameter of 3.590nm,larger than the single-KOH activated samples(SLangmuir=3159.200m2/g,D=2.672nm).The morphology and structure of active carbon were observed by SEM and FT-IR,the chemical composition is similar with the sample by KOH/NaOH activation or single-KOH/NaOH activation.The capsicum straw activated charcoal had enriched and developed cellular pore structure,but the sample by KOH/NaOH activation was found more mesopore and some measure of macropore.

Dynamic sorption and hygroexpansion of wood by humidity cyclically changing effect

Abstract: In order to investigate dynamic sorptive and hygroexpansive behavior of wood under cyclic relative humidity condition,poplar(populus euramericana Cv)specimens,in the size of 20mm(T)×20mm(R)×4mm(L)and 20mm(T)×20mm(R)×10mm(L),were exposed to sinusoidally relative humidity between 45%-75%at 25℃for 1,6,and 24h.Moisture changes and radial and tangential dimensional changes measured during the cycling gave the following results.Moisture and dimensional changes of the specimens were generally sinusoidal but lagged behind the imposed humidity.The phase lag decreased and the amplitude increased with increasing cyclic periods,while specimen thickness had an opposite effect on the phase lag and amplitude.Under dynamic conditions,the specimens showed sorption hysteresis and swelling hysteresis as well,and moisture sorption coefficient and humidity expansion coefficient of them were in positively correlation with cyclic period, but inversely related to specimens thickness.The dynamic sorption model proposed by aprevious study based on softwood obtained good agreement with experiment results in this study for hardwood species and different specimen thickness.

Cultivation of Human Microvascular Endothelial Cells on Topographical Substrates to Mimic the Human Corneal Endothelium

Abstract: Human corneal endothelial cells have a limited ability to replicate in vivo and in vitro. Allograft transplantation becomes necessary when an accident or trauma results in excessive cell loss. The reconstruction of the cornea endothelium using autologous cell sources is a promising alternative option for therapeutic or in vitro drug testing applications. The native corneal endothelium rests on the Descemet’s membrane, which has nanotopographies of fibers and pores. The use of synthetic topographies mimics the native environment, and it is hypothesized that this can direct the behavior and growth of human microvascular endothelial cells (HMVECs) to resemble the corneal endothelium. In this study, HMVECs are cultivated on substrates with micron and nano-scaled pillar and well topographies. Closely packed HMVEC monolayers with polygonal cells and well-developed tight junctions were formed on the topographical substrates. Sodium/potassium (Na+/K+) adenine triphosphatase (ATPase) expression was enhanced on the microwells substrate, which also promotes microvilli formation, while more hexagonal-like cells are found on the micropillars samples. The data obtained suggests that the use of optimized surface patterning, in particular, the microtopographies, can induce HMVECs to adopt a more corneal endothelium-like morphology with similar barrier and pump functions. The mechanism involved in cell contact guidance by the specific topographical features will be of interest for future studies.

Study on preparation and properties of capric-myristic acid/diatomite form-stable phase change energy storage materials

Abstract: Capric acid-myristic acid eutectic mixture/diatomite form-stable phase change energy(FSPCM) storage materials were prepared by using vacuum impregnation method.Capric acid was mixed with myristic acid to prepare binary fatty acid eutectic,which was selected as energy storage element material and diatomite was selected as supporting material.The structure,microstructure,thermal properties and thermal stability of FSPCM were characterized by infrared spectroscope,scanning electronic microscope,differential scanning calorimeter and thermogravimetric analysis apparatus,respectively.It was shown that the CA-MA was well adsorbed into the porous of diatomite,and they were physical interaction in nature between CA-MA and diatomite.The maximum absorption of CA-MA in the FSPCM was determined as 45wt% without melted PCM seepage from the FSPCM when FSPCM change from solid to liquid state.The melting temperature and latent heat of the FSPCM is 22.75℃ and 67.03J/g,respectively.The freezing temperature and latent heat of the FSPCM is 14.52℃ and 66.85J/g,respectively,and FSPCM have a good thermal stability.So the FSPCM was applied to building field.

Use of an Ophthalmic Viscosurgical Device for Experimental Retinal Detachment in Rabbit Eyes

Abstract: To investigate the temporary tamponade effects of an ophthalmic viscosurgical device (OVD) for experimental retinal tears, we performed vitrectomy in four rabbit eyes and created a posterior vitreous detachment and artificial retinal tear to produce retinal detachment. The retina was flattened with liquid perfluorocarbon (PFC), the area peripheral to the tear was photocoagulated, an OVD was applied to the retinal tear surface below the PFC and the PFC was removed by aspiration. In the control group, PFC was removed without application of OVD. At one, three and seven days postoperatively, funduscopy and optical coherence tomography (OCT) were performed to examine the sealing process of the retinal tear. In OVD-treated eyes, the OVD remained on the retinal surface, and the retinal tear was patched for ≥ 3 days postoperatively. By seven days postoperatively, the OVD on the retinal surface had disappeared, and the retina was reattached. In control eyes, the edge of the retinal tear was rolled, and retinal detachment persisted. In OVD-treated eyes, the border of the retinal tear was indistinct, and the defect area was significantly decreased. These results show that application of an OVD effectively seals retinal tears and eliminates retinal detachments.

Study on high-temperature phase change composites of NaNO_3-LiNO_3/expanded graphite by saturated water solution method

Abstract: The NaNO3-LiNO3/expanded graphite high-temperature phase change composite were prepared by saturated water solution method,with agitating the suspension in a water bath at a temperature of 90℃ and then drying it in an electric heating drying oven at a temperature of 120℃ over 24 hour.The composites with EG amount of 10%,20% and 30% were prepared in the similar method.The morphology,phase change temperature and latent heat,thermal conductivity and endothermic and exothermic behavior during thermal cycling of EG composites were characterized by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),Hot Disk thermal constants analyzer and self-designed automatic cycle equipment.The results show that the composites are uniform and well dispersed with the NaNO3-LiNO3 eutectic adsorbed during the graphite laminar,and the thermal storage performance of the eutectic does not weaken with added EG.At increasing graphite amount,the thermal conductivity of the composite is found to progressively increase with intensifications up to 10 but the effective latent heat is found to reduce.The composite with lower graphite amount displays better thermal stability behavior.It is proven that saturated water solution method is a simple and efficient technique for improving the salt thermal conductivity.It is necessary to optimal selection and design between heat storage and thermal conductivity in practical applications.

Influence regularities of chemical admixtures on creep

Abstract: The influence law of naphthalene based plasticizer,polycarboxylic superplasticizer,retarding component and shrinkage reducing component on creep characteristics of concrete with same mix proportion were studied by the self-made creep loading device and the influence mechamism were analyzed by testing non-evaporable water of paste with same water-binder ratio with concrete and internal relative humidity of loaded concrete specimensThe results indicate that: compared with naphthalene based plasticizer,polycarboxylic superplasticizers could significantly reducing creep of concrete,and this effect of early-strength polycarboxylic superplasticizer is the best;shrinkage reducing components could also reduce creep,the incorporation of retarding component have an adverse effect on creep;polycarboxylic superplasticizers and shrinkage reducing component reduce creep by decreasing the internal moisture transmission and diffusion to external environment;early-strength polycarboxylic superplasticizer make concrete have more hydration products,which have certain advantages on increasing strength and lower creep;incorporation of retarding component slows hydration and reduce the total hydration product contents,therefore strength reduced and creep increased

Thermal conductivity anisotropy of expanded graphite/LiCl-NaCl phase change material

Abstract: Expanded graphite/LiCl-NaCl composite phase-change materials were successfully prepared by aqueous solution method.The morphology of the samples was analyzed by SEM,which shows the composites are uniform and well dispersed with the LiCl-NaCl eutectic adsorbed during the graphite laminar.The thermal conductivities of the samples under different forming pressure were tested by hot-disk thermal constants analyzer,which shows the thermal conductivity is enhanced progressively with increasing pressure and EG amount,and it has anisotropy.The two main factors that lead to the thermal conductivity anisotropy are forming pressure and expanded graphite content.Within a certain range,thermal conductivity and its anisotropy increased with the forming pressure,but beyond a certain range,both thermal conductivity and its anisotropy did not change significantly.Under certain expanded graphite content,thermal conductivity and its anisotropy varied slightly,but above certain content,they increased with the expanded graphite content.Forming pressure and expanded graphite content had coupling effect on the thermal conductivity of EG/LiCl-NaCl composite phase-change materials.The formula to calculate the thermal conductivity in the horizontal direction and the vertical direction were given by the degree of orientation Φ.

Preliminary investigation of the dissolution behavior, cytocompatibility, effects of fibrinogen conformation and platelet adhesion for radiopaque embolic particles.

Abstract: Experimental embolic particles based on a novel zinc-silicate glass system have been biologically evaluated for potential consideration in transcatheter arterial embolization procedures. In addition to controlling the cytotoxicity and haemocompatibility for such embolic particles, its glass structure may mediate specific responses via dissolution in the physiological environment. In a 120 h in-vitro dissolution study, ion release levels for silicon (Si4+), sodium (Na+), calcium (Ca2+), zinc (Zn2+), titanium (Ti4+), lanthanum (La3+), strontium (Sr2+), and magnesium (Mg2+), were found to range from 0.04 to 5.41 ppm, 0.27–2.28 ppm, 2.32–8.47 ppm, 0.16–0.20 ppm, 0.12–2.15 ppm, 0.16–0.49 ppm and 0.01–0.12 ppm, respectively for the series of glass compositions evaluated. Initial release of Zn2+ (1.93–10.40 ppm) was only evident after 120 h. All compositions showed levels of cell viabilities ranging from 61.31 ± 4.33% to 153.7 ± 1.25% at 25%–100% serial extract dilutions. The conformational state of fibrinogen, known to induce thrombi, indicated that no changes were induced with respect of the materials dissolution by-products. Furthermore, the best-in-class experimental composition showed equivalency to contour PVA in terms of inducing platelet adhesion. The data generated here provides requisite evidence to continue to in-vivo pre-clinical evaluation using the best-in-class experimental composition evaluated.

Adsorption of methyl orange from aqueous solutions onto protonated cross-linked chitosan

Abstract: The adsorption of methyl orange onto protonated cross-linked chitosan was studied.Effect of adsorbent dosage,initial concentration of methyl orange,pH,adsorption time,etc on the adsorption of methyl orange was investigated.The adsorption was higher than 90% with the adsorbent concentration of 3.6g/L when the dye concentration was low than 200mg/L.The pseudo-second order kinetic model can described the whole absorption process well.The isotherm absorption equilibrium conformed to the Langmuir model.The protonated cross-linked chitosan shown a good adsorption towards methyl orange in a wide range of pH,which would enhanced the utility value of chitosan.

Investigation on pyrolitic carbon-coated microcrystalline graphite as anode material for Li-ion batteries

Abstract: The phenolic resin carbon-coated microcrystalline graphite,as anode materials for lithium-ion battery,was prepared by being coated with phenolic resin carbon by immersion method,following with carbonization.The influences of the content of phenolic resin carbon on the structure and electrochemical performances of microcrystalline graphite were investigated.The results show that the process improved the surface morphology of microcrystalline graphite without destructing its crystal structure.With the proper coating content(4%),the initial coulombic efficiency increased to 81.4%,and the deintercalation capacity remained 257.9 mAh/g at the current density of 0.5C after 50 cycles.The high rate charge/discharge performance is improved dramatically.

Study on natural aging properties of bamboo fibers/polylactic acid composites

Abstract: The interface of bamboo fiber(BF)/polylactic acid(PLA) composites was regulated by hydroxide and isocyanate,BF/PLA composites was prepared by injection molding process.Natural aging properties of BF/PLA composites was studied by the methods of Fourier transform infrared spectroscopy,X-ray diffraction,gel permeation chromatography and scanning electron microscopy.The results showed that with the synergistic effect of the water,light,heat and oxygen,the PLA molecules in the composites were continuously hydrolyzed,the molecular chains were fractured,the molecular weight was decreased,the certain crystalline state of PLA was gradually transformed into the amorphous state,the degree of crystallinity was reduced,PLA strength was decreased,the bond strength between PLA and BF was continuously decreased,the bonding interface between the two materials was destroyed,the mass of composites reduced and the mechanical properties of composites decreased in the process of natural aging.There are obviously cracks in the surface of composites,and the tensile strength and impact strength were reduced by 69.6% and 75.8% after aging for 137 days.The natural aging of BF/PLA composites was serious and need to adopt certain technical means to further improve the composites outdoor use performance.

Synthesis and characterization of a novel amphoteric super absorbent resin based on corn straw

Abstract: Super absorbent resins were synthesized by graft copolymerization reaction of acrylic acid(AA) and acrylic amide(AM) and acryloyl-oxyethyl trimethyl ammonium chloride(DAC) onto the pretreatment corn straw(PTCS) by radical polymerization in aqueous solution.The factors,which influenced absorbency of super absorbents,such as weight ratio of monomers and pretreatment corn straw(PTCS),the amount of initiator and cross-linker,temperature,time and neutralization degree of AA,were investigated.The molecular structure of the product was confirmed by Fourier transform infrared spectroscopy(FT-IR) and the morphological features were evidenced by scanning electron microscopy(SEM).The experimental results showed that when the mass of the PTCS,AA,AM,DAC were 1,5,2,0.5g,respectively;the ratio of K2S2O8 to monomer was 1.0%;the ratio of MBA to monomer was 0.1%;neutralization degree of AA was 75%;temperature was 60℃ and time was 3h,the super absorbent resin reached the best water absorbency of 235.9g/g in distilled water and 31.3g/g in 0.9wt% NaCl solution.

Preparation and electrical properties of insulating aluminum oxide thin films by sol-gel process

Abstract: Aluminum oxide thin films were prepared on various substrates by the sol-gel spin-coating process from a stable coating sol using 2-ethoxyethanol as solvent,aluminum isopropoxide as precursor and acetylacetone as chelating agent.The microstructure and the surface morphology of sol-gel films were characterized by X-ray diffraction(XRD),field emission scanning electron microscope(FESEM) and metallurgical microscope.The results indicate that the thin films obtained are uniform,dense,crack-free and amorphous in structure.The J-E and J-t curves were measured to study the electrical properties of the films.When electric field strength is 0.5 MV/cm,the leakage current density is about 9.0×10-6A/cm2.The breakdown electric field Eb of the films is in the range of 2.0-3.0 MV/cm.

Varied thickness of aragonite plates in nacreous layer and microstructure investigation

Abstract: The microstructural characteristic of nacreous layer in freshwater cultured pearls was investigated by field emission-scanning electronic microscope(FE-SEM).It is shown that the thickness of aragonite platelets varied in all specimens.Furthermore,the further from the center of pearl,the greater the thickness of aragonite platelets.In addition,it was discovered that the thickness of aragonite sheets are obviously different in nacreous layer nearly out surface region of pearls with different color,at the same time,the "terraced" structure and morphology are also different on pearls surface.The more compact "terraced" structure is,the thinner the thickness of aragonite platelets near the surface of pearl is.

Design and emulation of combined-shaped electromagnetic stealthy cloak made of metamaterials

Abstract: Based on the method of coordinate transformation,the distributions of the electromagnetic parameters in the elliptical and trapezoidal transformed spaces were derivedAimed at combined target,the electromagnetic stealthy cloak made of metamaterials was designedOn the condition that TE wave of 400MHz entered normally into the domain,the stealthy characteristic of stealthy cloak was emulatedThe result of emulation showed that few waves penetrate into the interior of the target model because of the stealthy cloakBesides,the electromagnetic field outside the cloak had no obvious changeSo the excellent stealthy characteristic of the cloak was verifiedThe entire phenomenons were in accordance with the predicted results in theoryTherefore,metamaterials designed by coordinate transformation,have the capacity of controlling the path of electromagnetic wave's transmission and making little influence to the external electromagnetic field theoretically

Theoretic and experimental study of chain-formation mechanism for MRF

Abstract: Comprehensive theoretical and experimental analyses of chain-formation process for magnetorheological fluid(MRF) are performed in this paper.Firstly,the physical model for the chain-formation process has been established.The Monte Carlo method has been used to simulate the chain-formation process under the gradient magnetic field.Secondly,we study the chain-formation process of MRF under the magnetic field by experiment.Numerical and experimental studies show that: when the magnetic field direction is parallel to the level of magnetorheological fluid and the external magnetic field is zero,magnetic particles are disordered.when the magnetic field strength increases gradually,the magnetic particles form smaller chains,mesh and even columnar structure along the direction of magnetic field;When there is a certain angle between the magnetic field direction and magnetorheological fluid level,with the increase of magnetic field,in the vertical direction of the level,magnetic particles form the small chains and then become the large chains along the magnetic field,finally,all are in the arrangement of chains or columnar chain.The results of this study can provide a theoretical basis for optimizing MRF parameters and design of high-performance MRF devices.

Research on the dispersion uniformity and stability of nano-ATO

Abstract: The efficient dispersion and long-term stability of nano-ATO are the key factors to prepare nano transparent insulation material.Influences of the value of pH,type and content of dispersants,surface characteristics of particles,dispersing technology,and viscosity on the dispersion stability are discussed.The dispersion effect is characterized by methods of sedimentation,spectrophotometry and scanning electron microscope.The results show that the dispersion effect can reach the optimal state by using compound dispersant with its dosage being 5%of particles mass,and adopting dispersion ways of combining ultrasound and ball milling.The stability of particles can be effectively improved by increasing the sphericity of particles and the viscosity of dispersion medium.The value of pH has a little impact on dispersion stability.The nano-ATO dispersion paste and nano transparent insulation coating with high uniformity and long-term stability is obtained by optimizing dispersion process.

Reviews on the magnetic particles of magnetorheological fluids

Abstract: The magnetic particles of Magnetorheological fluid demand high coercive force,low specific gravity and high stability in a wide temperature range.Based on hereinbefore,this article summarizes the characteristics of various magnetic particles,development process and preparations including chemical and physical methods.It illustrates the relation between kinds of preparations and the structure and function of the magnetic particles.Besides,the effect of magnetic particles on magnetorheological fluids was analyzed.Finally it points the shortage of magnetorheological fluids nowadays and make a view on the preparations,function,structure and the process.

Study on principle of the shielding effectiveness of woven fabrics containing stainless steel fibers and simulation

Abstract: According to the theory of electromagnetic shielding,principle of shielding effectiveness for textile containing metal fibers was briefly introduced.Based on this theory,a three-dimensional simulation model was established using the multi-physics coupled software COMSOL.Simulation test of several 304 austenitic stainless steel filament were done on different radius of stainless steel filament,different stainless filament distance,different polarization direction of EM wave and different radiation frequency.The result shows that fabric shielding effectiveness are effected significantly by different polarization direction,different radius and difference distance.These findings provide a theoretical proof in optimizing the designing of anti-electromagnetic radiation fabric made of metallic fiber fabric.

Citrate-linked keto- and aldo-hexose monosaccharide cellulose conjugates demonstrate selective human neutrophil elastase-lowering activity in cotton dressings.

Abstract: Sequestration of harmful proteases as human neutrophil elastase (HNE) from the chronic wound environment is an important goal of wound dressing design and function. Monosaccharides attached to cellulose conjugates as ester-appended aldohexoses and ketohexoses were prepared on cotton gauze as monosccharide-citrate-cellulose-esters for HNE sequestration. The monosaccharide-cellulose analogs demonstrated selective binding when the derivatized cotton dressings were measured for sequestration of HNE. Each monosaccharide-cellulose conjugate was prepared as a cellulose citrate-linked monosaccharide ester on the cotton wound dressing, and assayed under wound exudate-mimicked conditions for elastase sequestration activity. A series of three aldohexose and four ketohexose ester cellulose conjugates were prepared on cotton gauze through citric acid-cellulose cross linking esterification. The monosaccharide portion of the conjugate was characterized by hydrolysis of the citrate-monosaccharide ester bond, and subsequent analysis of the free monosaccharide with high performance anion exchange chromatography. The ketohexose and aldohexose conjugate levels on cotton were quantified on cotton using chromatography and found to be present in milligram/gram amounts. The citrate-cellulose ester bonds were characterized with FTIR. Ketohexose-citrate-cellulose conjugates sequestered more elastase activity than aldohexose-citrate-cellulose conjugates. The monosaccharide cellulose conjugate families each gave distinctive profiles in elastase-lowering effects. Possible mechanisms of elastase binding to the monosaccharide-cellulose conjugates are discussed.