bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increase in γ/α2 Lamellar Boundary Density and its Effect on Creep Resistance of TiAl Alloy
Authors: Maruyama Kouichi , Matsuda Jun , Zhu Hanliang 
Published: April 2011

ABTSRACTSeveral lamellar microstructures of a Ti-48 % Al alloy were made by changing heating rate in the α+γ dual phase field, and their creep properties were investigated at 1150 K. Average spacing and average length of α2 lamellae decrease with increasing heating rate. The decrease of α2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing the heating rate, since a high density of γ/α2 boundaries stabilizes lamellar microstructure during creep. On the other hand creep rate increases at high heating rate, since α2 lamellar length becomes shorter with increasing heating rate. A reduction of creep rate by one order of magnitude is achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α2 lamellae.
Effect of Molecular Interactions at Polymer-Mineral Interfaces on Mechanical Response
Authors: Bhowmik Rahul , Katti Kalpana S , Katti Dinesh R 
Published: April 2011

AbstractNanocomposites of polymer and hydroxyapatite are widely used as bone replacement materials. The mechanical responses of these nanocomposites are known to be influenced by molecular interactions at mineral polymer interface. Molecular modeling of these interactions is an area of current interest but force field parameters of such dissimilar molecules are not available for a common force field. Also, parameters for several commonly used force fields are not available in the literature for hydroxyapatite. Recently a unique force field was described in literature that represents the structure of hydroxyapatite reasonably well. Yet the applicability of this force field for studying the interaction between dissimilar materials (such as mineral and polymer) is limited as there is no accurate representation of polymer. CVFF is a commonly used force field for which parameters of many material systems are available. We have obtained the parameters of CVFF for monoclinic hydroxyapatite from the known potential energy function of apatites and from experimentally obtained infrared spectra. Validation of simulations is done by comparison of computationally obtained unit cell parameters, vibrational spectra and different atomic distances with experiments. This study represents molecular modeling of polymermineral interfaces with the known parameters of hydroxyapatite.
Nanoscale Characterisation of Salivary Pellicle
Authors: Dickinso Michelle E. , Mann Adrian B. 
Published: April 2011

AbstractSalivary pellicle is an organic biofilm formed by the physisorption of proteins and carbohydrates onto the surface of dental enamel exposed to the oral environment. The pellicle has several key roles in oral physiology including lubrication and reduction of friction between teeth during mastication, as well as chemical protection of the enamel against acidic solutions. However, pellicle proteins are known to react with dietary compounds to cause extrinsic staining on the tooth surface.In this study, nanoindentation and AFM have been used in vitro to examine the acquired salivary pellicle formed in vivo on dental enamel. The mechanical properties, growth, structure and morphology of pellicle grown in vivo on human enamel surfaces have been analysed. In addition, the effects of dietary agents such as polyphenols on the pellicle's morphology and properties have been studied.It was found that initial adsorption of proteins on the enamel surface occurred within 30 seconds of exposure to the oral cavity, with full growth achieved within 2 hours. Differences in the properties of the pellicles such as surface adhesion, and time dependent effects due to polyphenol interaction were measured using nanoindentation. It was seen that the polyphenol interaction has a significant effect on these properties. These results suggest that the stained pellicle is mechanically stiffer, but also less viscous and more fluid like. This could explain why traditional tooth brushing techniques do not efficiently remove this layer.
Nanomechanical Testing of Hydrated Biomaterials: Sample Preparation, Data Validation and Analysis
Authors: Kaufman Jessica D. , Klapperich Catherine M. 
Published: April 2011

AbstractImplants, tissue engineering scaffold materials, drug delivery and bio-micro electromechanical systems (BioMEMs) all use polymer or hydrogel materials. These applications require both mechanical performance and successful integration of the material into a biological environment. Mechanical strength, storage and loss moduli, wear resistance and surface adhesion properties are all critical in biomedical device design and can be determined using nanoindentation. The difficulty of obtaining large samples of specialized materials, and the complexity of testing soft materials in traditional materials testing apparatus, make nanoindentation an attractive alternative. Our previous research using nanoindentation to measure the surface mechanical properties of non-hydrated polymers led to improvement in nanoindentation testing protocols. One of the major challenges in using this technique for hydrogels and tissues is maintaining and controlling hydration of the materials during the test. Here we describe the design of a microfluidic platform for nanoindentation that facilitates continuous hydration of hydrogel samples and high throughput nanomechanical testing. Data from creep experiments on synthetic, hydrated poly-2-hydroxyethyl methacrylate (poly-HEMA) are presented. In addition, we show data to validate the materials properties determined from nanomechanical testing by complementary testing. Finally, the data is fitted to a phenomenological model for viscoelastic materials, specifically the three-element standard linear solid model used by Cheng et al. [1].
Computational Mechanics Routes to Explore the Origin of Mechanical Properties in a Biological Nanocomposite: Nacre
Authors: Katti Dinesh , Katti Kalpana 
Published: April 2011

ABSTRACTNacre, the inner layer of seashells, is a laminated nanocomposite consisting of micron sized pseudo hexagonal aragonitic calcium carbonate platelets with about 20 nanometer thick organic layer sandwiched between the platelets. This nanocomposite has been studied extensively as a model system for the design of new biomimetic nanocomposites. The nano and micro architecture of nacre has many features and nuances, which have been attributed as possible reasons for the exceptional mechanical properties. In our work, we have used computational mechanics routes to model and simulate observed macro response, to quantitatively evaluate the contribution of various components of the nano and micro architecture of nacre to the mechanical properties. We also describe our discovery of platelet interlocks and their impact on the mechanical response of nacre. Our experiments on tensile failure and scanning electron microscopy of nacre specimens, and simulations using finite element modeling, indicate that the interlocks function as a physical restraint against free relative movement of platelets. Hence, these interlocking features need to yield/break before the complete transfer of load can occur to an intervening organic. The observed interlocks play a critical role in the mechanical response of nacre. During failure the features observed in the microstructure of nacre, such as relative rotation between platelet layers, platelet penetration, and other geometrical abnormalities such as an elongated side etc., appear not to be accidents of nature; they seem to exist for a purpose. These abnormalities lead to high toughness and strength, which is necessary for protecting the organism within the seashell.
Shrinkage Of Bone
Authors: Lees Sidney 
Published: April 2011

ABSTRACTShrinkage of bone and other mineralized Type 1 collagen tissues when the tissue is dried has been observed for a long time. It is anisotropic with respect to the orientation of the bone structure. It is linearly dependent on the inverse wet tissue density (specific volume) in the radial direction but not in the axial direction. The volume fraction of water in the tissue has also been shown to be linearly dependent on the inverse and other wet density leading to a direct relation between the shrinkage and the volume fraction of water.Shrinkage may be determined on any scale, macroscopic to microscopic but volume fraction of water is closely related to the lateral spacing of the collagen molecules, that is on the scale of nm. The linear dependence of shrinkage on volume fraction shows the generalized packing model underlies bone structure and is due to the properties of collagen molecules assembled in sheets.
Influence of Protein Structures on Mechanical Response
Authors: Ghosh Pijush , Katti Dinesh R. , Katti Kalpana 
Published: April 2011

ABSTRACTIn biological nanocomposites such as bones, teeth and seashells, proteins play an important role in their mechanical response. Proteins in nacre, the inner layer of seashells have been shown to have exceptional mechanical properties. The secondary structures, β-sheets of protein when present close to each other in multiple numbers could take the shape of a planar β-sheath like structure or a β-barrel to form a domain. In natural proteins both these types of structures are commonly found. Effort has been made through this work to study the mechanical response of these β-planar sheath and β-barrel structures when subjected to external loads. Comparative study of the stress-deformation characteristics of these two types of structures has been made. The influence of shear force on the conformation of planar and barrel structure is investigated. Both these structures with almost similar number of amino acids have been extracted from one single spinach protein, Ferredoxin Reductase (1FNR). Steered molecular dynamics has been used to conduct these studies. The paper deals with the separation of the two domains from the main protein, simulation details and results comparing the responses.
Continuous force-displacement relationships for the human red blood cell at different erythrocytic developmental stages ofPlasmodium falciparummalaria parasite
Authors: Mills John P. , Qie Lan , Dao Ming , Tan Kevin S. W. , Lim Chwee Teck , Suresh Subra 
Published: April 2011

ABSTRACTPrior work involving either aspiration of infected cells into micropipette under suction pressure or deformation in laminar shear flow revealed that the malaria parasitePlasmodium (P.) falciparumcould result in significant stiffening of infected human red blood cells (RBCs). In this paper, we present optical tweezers studies of progressive changes to nonlinear mechanical response of infected RBCs at different developmental stages ofP. falciparum.From early ring stage to late trophozoite and schizont stages, up to an order of magnitude increase in shear modulus was found under controlled mechanical loading by combining experiments with three-dimensional computational simulations. These results provide novel approaches to study changes in mechanical deformability in the advanced stages of parasite development in the erythrocyte, and suggest a significantly greater stiffening of the red blood cell due toP. falciparuminvasion than that considered from previous studies.
Nanomechanics and Chemistry of Caries-Like Lesions in Dental Enamel
Authors: Dickinson Michelle E. , Mann Adrian B. 
Published: April 2011

ABSTRACTDental enamel lesions are formed by the demineralisation of dental enamel due to dietary and bacterial factors which lower the local pH. If progression of this demineralisation continues the enamel structure eventually fails giving rise to a cavity (carie). Fortunately, in the earliest stages this process is reversible and if the pH of the environment increases, ions such as calcium, phosphate and fluoride can diffuse back into the enamel to give an arrested lesion. Hence, the tooth's structural integrity is preserved. The use of artificially produced enamel caries allows the study of lesion formation under conditions of highly controlled demineralisation. This provides a fundamental insight into the process of caries formation in enamel. In this study human premolars have been treated with a lactic acid solution to create artificial “caries-like” lesions in the enamel on the buccal side of the teeth. In the test samples the lesions penetrated around 100 μm into the enamel structure, accounting for approximately one tenth of the thickness of the enamel. Cross sections through the lesion were characterized with nanoindentation, electron probe micro-analysis and time of flight secondary ion mass spectrometry. From the data obtained maps of both mechanical and chemical properties were plotted across the entire width of the lesions. The results show that the lesions have a significantly reduced hardness and elastic modulus in comparison to sound enamel. These changes in mechanical properties were found to correlate with a loss of calcium and phosphate from the structure. There was also evidence of a stronger, less demineralised layer of enamel close to the lesion's surface. This surface zone is suggestive of remineralisation within the lesion which is of importance with regards to preventing the lesion developing into a carie.
Biodegradable Poly[bis(ethyl alanato)phosphazene] - Poly(lactide-co-glycolide) Blends: Miscibility and Osteocompatibility Evaluations
Authors: Nair Lakshmi S. , Bender Jared D. , Singh Anurima , Sethuraman Swaminathan , Greish Yaser E. , Brown Paul W. , Allcock Harry R. , Laurencin Cato T. 
Published: April 2011

ABSTRACTWe have previously demonstrated that blending biodegradable glycine co-substituted polyphosphazenes with poly(lactide-co-glycolide) (PLAGA) results in novel biomaterials with versatile properties. The study showed that the degradation rate of polyphosphazene/PLAGA blends can be effectively controlled by varying the blend composition while at the same time the degradation products of polyphosphazenes effectively neutralized the acidic degradation products of PLAGA. In the present study, novel blends of hydrophobic, biodegradable polyphosphazene, poly[bis(ethyl alanato) phosphazene] (PNEA) and PLAGA (LA: GA; 85:15) were developed as candidates for bone tissue engineering applications. Two different blend compositions were developed by blending PNEA and PLAGA having weight ratios of 25:75 (Blend-1) and 50:50 (Blend-2) by the mutual solvent technique using dichloromethane as the solvent. The miscibility of the blends was determined using differential scanning calorimetry (DSC), fourier transform-infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Surface analysis of the blends by SEM revealed a smooth uniform surface for Blend-1, whereas Blend-2 showed evidence of phase separation. PNEA is not completely miscible with PLAGA, as evidenced from DSC and FT-IR measurements. The osteocompatibilities of Blend-1 and Blend-2 were compared to those of parent polymers by following the adhesion and proliferation of primary rat osteoblast cells on two dimensional (2-D) polymer and blend films over a 21 day period in culture. Blend films showed significantly higher cell numbers on the surface compared to PLAGA and PNEA films.
Rheology and Biocompatibility of Poly(lactide)-poly(ethylene oxide)-poly(lactide) Hydrogels
Authors: Agrawal Sarvesh K. , Chin Kyuong S. , Sanabria-Delong Naomi , Aamer Khaled A. , Sardinha Heidi , Tew Gregory N. , Roberts Susan C. , Bhatia Surita R. 
Published: April 2011

ABSTRACTWe report rheological data on hydrogels formed from triblock copolymers of poly(L-lactide) (PLLA) and poly(ethylene oxide) (PEO). We are able to create gels with elastic moduli greater than 10,000 Pa, which is an order of magnitude higher than previously achieved with related physically associated gels of similar chemistry. Moreover, the value of the elastic modulus strongly depends on PLLA block length, offering a mechanism to control the mechanical properties as desired for particular applications. Additionally, we have developed protocols for using these materials for cell encapsulation and present preliminary cell viability studies for encapsulated human liver cells (HepG2 cell line). Our results have implications for the design of new materials for soft tissue engineering, where native tissues have moduli in the kPa range.
Fabrication of Micro-Optical Devices by Holographic Interference of High Photosensitive Inorganic-Organic Hybrid Materials (Photo-HYBIRMER)
Authors: Kang Dong Jun , Kim Jin-Ki , Bae Byeong-Soo 
Published: April 2011

ABSTRACTSol-gel derived photosensitive inorganic-organic hybrid materials (Photo-HYBRIMER) containing a large quantity of photoactive molecules exhibit the large changes in both refractive index (over 10-2) and volume (over 30%) on UV exposure. The materials could be used for direct fabrication of micro-optical devices using holographic interference. With the change of the beam number for holographic interference (1-beam, 2-beam, 3-beam and 4-beam interference), various typed micro-optical devices (Fresnel-type lens, 1D- and 2D-typed diffraction gratings) could be easily fabricated. Importantly, the fabricated micro-optical devices exhibited the very homogeneous surface structures and good optical performance.
An efficient top-emitting electroluminescent device on metal-laminated plastic substrate
Authors: Tan L. W. , Hao X. T. , Ong K. S. , Li Y. Q. , Zhu F. R. 
Published: April 2011

ABSTRACTAn efficient flexible top-emitting organic light-emitting device (OLED) was fabricated on an aluminum-laminated polyethylene terephthalate substrate. A spin-coated light-emitting polymer layer was sandwiched between a silver anode and a multi-layered semitransparent cathode. The performance of polymer OLEDs was analyzed and compared with that of the devices having a conventional structure. An optical microcavity formed in the device enables to tune the emission color by varying the thickness of the active polymer layer. The OLEDs having a 110-nm-thick active polymer layer exhibited superior electroluminescence performance, with a turn-on voltage of 2.5V and a luminance efficiency of 4.56 cd/A at an operating voltage of 10V.
Prototyping of three-dimensional photonic crystal structures using electron-beam lithography
Authors: Subramania G. , Rivera J. M. 
Published: April 2011

ABSTRACTWe demonstrate the fabrication of a three-dimensional woodpile photonic crystal in the near-infrared regime using a layer-by-layer approach involving electron-beam lithography and spin-on-glass planarization. Using this approach we have shown that we can make structures with lattice spacings as small as 550 nm with silicon as well as gold thus allowing for fabrication of photonic crystals with omnidirectional gap in the visible and near-IR. As a proof of concept we performed optical reflectivity and transmission measurements on a silicon structure which reveal peaks and valleys expected for a photonic band gap structure. The approach described here can be scaled down to smaller lattice constants (down to ∼400 nm) and can also be used with a variety of materials (dielectric and metallic) thus enabling rapid prototyping full three-dimensional photonic bandgap based photonic devices in the visible.
Writing Laser Power Dependence of Second Harmonic Generation in an Optically Poled Azo-dye/polymer Film
Authors: Wang C. H. , Tai Oliver Y.-H. , Wang Yuxiao 
Published: April 2011

ABSTRACTThe time and power dependence of the optical poling process of an azo chromophore in the PMMA matrix at room temperature is investigated. A model previously proposed is used to account for the writing process of the optical poling of the chromophore/PMMA system. Theoretical predictions of the growth rate and the plateau SHG intensity are found to be in good agreement with the experimental result.
Phosphorescence Quantum Efficiency and Intermolecular Interaction of Iridium(III) Complexes in Co-Deposited Films with Organic Semiconducting Hosts
Authors: Kawamura Yuichiro , Goushi Kenichi , Brooks Jason , Brown Julie J. , Sasabe Hiroyuki , Adachi Chihaya 
Published: April 2011

ABSTRACTWe accurately measured the absolute photoluminescence (PL) quantum efficiency (ηPL) of organic solid-state thin films by using an integrating sphere. We measured the ηPL of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq3), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4, 4'-bis(carbazol-9-yl)-2, 2'-biphenyl [Ir(ppy)3:CBP] co-deposited film. Alq3 and Ir(ppy)3:CBP showed a ηPL = 20 ± 1% and 97 ± 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-N, C3'] (acetylacetonato) iridium(III) [Btp2Ir(acac)] with CBP, and the blue complex, bis[(4, 6-difluorophenyl)pyridinato-N, C2](picolinato)iridium(III) [FIrpic], with m-bis(N -carbazolyl)benzene. The maximum ηPL values for Btp2Ir(acac), and FIrpic were 51±1% (at 1.4mol%), and 99±1% (1.2mol%), respectively. These results suggest that the ηEL of red phosphorescent OLEDs using Btp2Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.
Synthesis of Dendridic NLO Chromophores for the Improvement of Order in Electro-optics
Authors: Sinness Jessica , Clot Olivier , Hammond Scott R. , Bhatambrekar Nishant , Rommel Harrison L. , Robinson Bruce , Jen Alex K-Y. , Dalton Larry 
Published: April 2011

ABSTRACTPrevious research in organic electro-optics has shown dramatic increases in the hyperpolarizablity of NLO chromophores. However, this large microscopic activity has not been translated to the macroscopic domain. The polymeric electro-optic (E-O) materials continue to lack the high noncentrosymmetric order of the poled chromophores within the matrix necessary for high E-O response (r33). This deficiency of order represents one major obstacle that must be overcome before E-O device commercialization can be achieved. This lack of order is partially due to the large dipole moments of high μβ chromophores, which cause the chromophores to align in a centrosymmetric fashion through intermolecular electrostatic interactions. However, quantum calculations show that when the aspect ratio between the width and length of the chromophore system is adjusted to be greater than 1.4:1 by adding bulky side groups around the center of the chromophore, it would prevent side on pairing of the chromophores. This would cause a decrease in the large areas of centrosymmetric aggregation and thus allow for easier poling of the system. Here we report the synthesis of a nanoscale NLO architecture in which dendritic moieties have been incorporated around the center of the chromophore to give a three dimensional structure in order to achieve the 1.4:1 aspect ratio and maximize the macroscopic order of the system.
Optical Switching Devices Using Redox Polymer Nanosheet
Authors: Matsui Jun , Abe Kenichi , Mitsuishi Masaya , Aoki Atsushi , Miyashita Tokuji 
Published: April 2011

ABSTRACTOptical switching devices, which control the current direction by light stimuli, were constructed using redox polymer nanosheet assemblies. Two kind of nanosheet-photodiode, which can operate by different light irradiation wavelength were assembled in a series so that each current direction becomes opposite. In the nanosheet photodiodes, one photodiode contains ruthenium complex as a sensitizer and the other contains anthracene. When 460 nm light was irradiated to the nanosheet assemblies, only the photodiode containing the ruthenium complex becomes active and an anodic photocurrent was observed. On the other hand, when 390 nm light was irradiated to the photodiode assemblies, only the photodiode containing the anthracene chromophore becomes active and a cathodic photocurrent was observed. This means that we can control the photocurrent direction by 460 nm and 390 nm irradiation as input signals.