Normal contact of elastic spheres with two elastic layers as a model of joint articulation.

An analytical model of two elastic spheres with two elastic layers in normal, frictionless contact is developed which simulates contact of articulating joints, and allows for the calculation of stresses and displacements in the layered region of contact. Using various layer/layer/substrate combinations, the effects of variations in layer and substrate properties are determined in relation to the occurrence of tensile and shear stresses as the source of crack initiation in joint cartilage and bone. Vertical cracking at the cartilage surface and horizontal splitting at the tidemark have been observed in joints with primary osteoarthritis. Deep vertical cracks in the calcified cartilage and underlying bone have been observed in blunt trauma experiments. The current model shows that cartilage stresses for a particular system are a function of the ratio of contact radius to total layer thickness (a/h). Surface tension, which is observed for a/h small, is alleviated as a/h is increased due to increased load, softening and/or thinning of the cartilage layer. Decreases in a/h due to cartilage stiffening lead to increased global compressive stresses and increased incidence of surface tension, consistent with impact-induced surface cracks. Cartilage stresses are not significantly affected by variations in stiffness of the underlying material. Tensile radial strains in the cartilage layer approach one-third of the normal compressive strains, and increase significantly with cartilage softening. For cases where the middle layer stiffness exceeds that of the underlying substrate, tensile stresses occur at the base of the middle layer, consistent with impact induced cracks in the zone of calcified cartilage and subchondral bone. The presence of the superficial tangential zone appears to have little effect on underlying cartilage stresses.     

Fracture toughness and fatigue crack propagation rate of short fiber reinforced epoxy composites for analogue cortical bone

Third-generation mechanical analogue bone models and synthetic analogue cortical bone materials manufactured by Pacific Research Laboratories, Inc. (PRL) are popular tools for use in mechanical testing of various orthopedic implants and biomaterials. A major issue with these models is that the current third-generation epoxy-short fiberglass based composite used as the cortical bone substitute is prone to crack formation and failure in fatigue or repeated quasistatic loading of the model. The purpose of the present study was to compare the tensile and fracture mechanics properties of the current baseline (established PRL "third-generation" E-glass-fiber-epoxy) composite analogue for cortical bone to a new composite material formulation proposed for use as an enhanced fourth-generation cortical bone analogue material. Standard tensile, plane strain fracture toughness, and fatigue crack propagation rate tests were performed on both the third- and fourth-generation composite material formulations using standard ASTM test techniques. Injection molding techniques were used to create random fiber orientation in all test specimens. Standard dog-bone style tensile specimens were tested to obtain ultimate tensile strength and stiffness. Compact tension fracture toughness specimens were utilized to determine plane strain fracture toughness values. Reduced thickness compact tension specimens were also used to determine fatigue crack propagation rate behavior for the two material groups. Literature values for the same parameters for human cortical bone were compared to results from the third- and fourth-generation cortical analogue bone materials. Tensile properties of the fourth-generation material were closer to that of average human cortical bone than the third-generation material. Fracture toughness was significantly increased by 48% in the fourth-generation composite as compared to the third-generation analogue bone. The threshold stress intensity to propagate the crack was much higher for the fourth-generation material than for the third-generation composite. Even at the higher stress intensity threshold, the fatigue crack propagation rate was significantly decreased in the fourth-generation composite compared to the third-generation composite. These results indicate that the bone analogue models made from the fourth-generation analogue cortical bone material may exhibit better performance in fracture and longer fatigue lives than similar models made of third-generation analogue cortical bone material. Further fatigue testing of the new composite material in clinically relevant use of bone models is still required for verification of these results. Biomechanical test models using the superior fourth-generation cortical analogue material are currently in development.     

High-Performance Dye-Sensitized Solar Cells Based on Morphology-Controllable Synthesis of ZnO–ZnS Heterostructure Nanocone Photoanodes

High-density and well-aligned ZnO–ZnS core–shell nanocone arrays were synthesized on fluorine-doped tin oxide glass substrate using a facile and cost-effective two-step approach. In this synthetic process, the ZnO nanocones act as the template and provide Zn²⁺ ions for the ZnS shell formation. The photoluminescence spectrum indicates remarkably enhanced luminescence intensity and a small redshift in the UV region, which can be associated with the strain caused by the lattice mismatch between ZnO and ZnS. The obtained diffuse reflectance spectra show that the nanocone-based heterostructure reduces the light reflection in a broad spectral range and is much more effective than the bare ZnO nanocone and nanorod structures. Dye-sensitized solar cells based on the heterostructure ZnO–ZnS nanocones are assembled, and high conversion efficiency (η) of approximately 4.07% is obtained. The η improvement can be attributed primarily to the morphology effect of ZnO nanocones on light-trapping and effectively passivating the interface surface recombination sites of ZnO nanocones by coating with a ZnS shell layer.     

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO₃ (001) and DyScO₃ (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca₂Nb₃O₁₀^- nanosheets were used, prepared by delamination of their layered parent compound HCa₂Nb₃O₁₀. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.     

Synthesis of Coral-Like Tantalum Oxide Films via Anodization in Mixed Organic-Inorganic Electrolytes

We report a simple method to fabricate nano-porous tantalum oxide films via anodization with Ta foils as the anode at room temperature. A mixture of ethylene glycol, phosphoric acid, NH₄F and H₂O was used as the electrolyte where the nano-porous tantalum oxide could be synthesized by anodizing a tantalum foil for 1 h at 20 V in a two–electrode configuration. The as-prepared porous film exhibited a continuous, uniform and coral-like morphology. The diameters of pores ranged from 30 nm to 50 nm. The pores interlaced each other and the depth was about 150 nm. After calcination, the as-synthesized amorphous tantalum oxide could be crystallized to the orthorhombic crystal system. As observed in photocatalytic experiments, the coral-like tantalum oxide exhibited a higher photocatalytic activity for the degradation of phenol than that with a compact surface morphology, and the elimination rate of phenol increased by 66.7%.     

Kinetic competence of enzymic intermediates: fact or fiction?

A number of enzymatic reactions involve intermediates that are not normally released during the reaction. Whether such an intermediate when added to the enzyme reacts as fast or faster than the normal substrates, and thus is "kinetically competent", depends on the degree to which the equilibrium constant for forming the intermediate from the substrates is different on the enzyme surface and in solution, as well as on the relative affinities of the enzyme for substrate and intermediate. Similar values for these equilibrium constants require that the intermediate react slowly, while a far more favorable value for intermediate formation on the enzyme allows the intermediate to react at up to the diffusion-limiting rate. When one intermediate is formed from two substrates, it may react much more rapidly than when two intermediates are formed from two substrates, or one from one. Comparison of the kinetics of the putative intermediate(s) and the substrate(s) can reveal a great deal about the mechanism of the catalytic reaction and the kinetic barrier that normally keeps the intermediate(s) on the enzyme.     

Yeast cell adhesion on oligopeptide modified surfaces

Self-assembling oligopeptides are novel materials with potential bioengineering applications; this paper explores the use of one of these oligopeptides, EAK 16 II, for modifying the surface properties of cell-supporting substrates. To characterize the surface properties, thermodynamic measurements of liquid contact angle and surface free energy were correlated to atomic force microscopy (AFM) observations. A critical concentration of 0.1 mg/ml was found necessary to completely modify the surface properties of the substrate with EAK 16 II. Adhesion of a yeast cell, Candida utilis, was modified by the coating of EAK 16 II on both hydrophobic (plastic) and hydrophilic (glass) surfaces: Cell coverage was slightly enhanced on the glass substrate, but decreased significantly on the plastic substrate. This indicates that the yeast cell adhesion was mainly determined via hydrophobic interactions between the substrate and the cell wall. However, on the EAK 16 II modified glass substrate, surface roughness might be a factor in causing a slightly larger cell adhesion than that on bare glass. The morphology of adhered cells was also obtained with AFM imaging, showing a depression at the center of the cell on all substrates. Small depressions on the oligopeptide-coated surfaces and plastic substrate may indicate good water-retaining ability by the cell. There was no apparent difference in cell adhesion and morphology among cells obtained from lag, exponential and stationary growth phases.     

Terraced self assembled nano-structures from laminarin

The formation of self assembled nano-structures from the biopolymer laminarin dried onto mica is reported. The observed structures are composed of stacked terraced layers decreasing in size away from the mica surface. The layers display a high degree of dimensional regularity as observed using atomic force microscope imaging (AFM). The width of the layers is linearly dependent upon the number of layers in the structure and decreases with layer number away from the mica substrate. The thickness of the layers is uniform throughout the structure. A pore is contained in the central region of each structure with more than one layer. We postulate that these structures have potential use as templates in microelectronic devices and sensors where the central pore has the potential to immobilise functional materials.     

Sensing and modulation of invadopodia across a wide range of rigidities

Recent studies have suggested that extracellular matrix rigidity regulates cancer invasiveness, including the formation of cellular invadopodial protrusions; however, the relevant mechanical range is unclear. Here, we used a combined analysis of tissue-derived model basement membrane (BM) and stromal matrices and synthetic materials to understand how substrate rigidity regulates invadopodia. Urinary bladder matrix-BM (UBM-BM) was found to be a rigid material with elastic moduli of 3-8 MPa, as measured by atomic force microscopy and low-strain tensile testing. Stromal elastic moduli were ∼6-fold lower, indicating a more compliant material. Using synthetic substrates that span kPa–GPa moduli, we found a peak of invadopodia-associated extracellular matrix degradation centered around 30 kPa, which also corresponded to a peak in invadopodia/cell. Surprisingly, we observed another peak in invadopodia numbers at 2 GPa as well as gene expression changes that indicate cellular sensing of very high moduli. Based on the measured elastic moduli of model stroma and BM, we expected to find more invadopodia formation on the stroma, and this was verified on the stromal versus BM side of UBM-BM. These data suggest that cells can sense a wide range of rigidities, up into the GPa range. Furthermore, there is an optimal rigidity range for invadopodia activity that may be limited by BM rigidity.     

Electrochemical properties of biocompatible material hardness modifications on titanium and steel under mechanical loads]

Friction corrosion may appear between different implant components or between implant and hard tissue. The sliding micro movements induce fretting wear corrosion and have been recently reported as a cause of joint prostheses failure. A surface coating is desirable, that retains the mechanical properties of the substrate, offers good biocompatibility and improves the fretting corrosion resistance. In this study it could be demonstrated that tantalum and niobium coatings fulfill the requirements. On titanium substrates the coating decreases the abrasion against PMMA, an orthopedic relevant material. Furthermore, in the case of medical steel substrates the biocompatibility and the corrosion properties are improved. The better abrasion-resistance is minimizing the release of allergological critical particles like nickel and chromium.     

Locally Addressable Electrochemical Patterning Technique (LAEPT) applied to poly(L-lysine)-graft-poly(ethylene glycol) adlayers on titanium and silicon oxide surfaces

The protein-resistant polycationic graft polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), was uniformly adsorbed onto a homogenous titanium surface and subsequently subjected to a direct current (dc) voltage. Under the influence of an ascending cathodic and anodic potential, there was a steady and gradual loss of PLL-g-PEG from the conductive titanium surface while no desorption was observed on the insulating silicon oxide substrates. We have implemented this difference in the electrochemical response of PLL-g-PEG on conductive titanium and insulating silicon oxide regions as a biosensing platform for the controlled surface functionalization of the titanium areas while maintaining a protein-resistant background on the silicon oxide regions. A silicon-based substrate was micropatterned into alternating stripes of conductive titanium and insulating silicon oxide with subsequent PLL-g-PEG adsorption onto its surfaces. The surface modified substrate was then subjected to +1800 mV (referenced to the silver electrode). It was observed that the potentiostatic action removed the PLL-g-PEG from the titanium stripes without inducing any polyelectrolyte loss from the silicon oxide regions. Time-of-flight secondary ions mass spectroscopy and fluorescence microscopy qualitatively confirmed the PLL-g-PEG retention on the silicon oxide stripes and its absence on the titanium region. This method, known as "Locally Addressable Electrochemical Patterning Technique" (LAEPT), offers great prospects for biomedical and biosensing applications. In an attempt to elucidate the desorption mechanism of PLL-g-PEG in the presence of an electric field on titanium surface, we have conducted electrochemical impedance spectroscopy experiments on bare titanium substrates. The results showed that electrochemical transformations occurred within the titanium oxide layer; its impedance and polarization resistance were found to decrease steadily upon both cathodic and anodic polarization resulting in the polyelectrolyte desorption from the titanium surface.     

Stress analysis of cemented glenoid prostheses in total shoulder arthroplasty

Glenoid component loosening is the most-frequently encountered problem in the total shoulder arthroplasty. The purpose of the study was to investigate whether failure of the glenoid component is caused by stresses generated within the cement mantle, implant materials and at the various interfaces during humeral abduction, using 3-D FE analyses of implanted glenoid structures. FE models, one total polyethylene and the other, metal backed polyethylene, were developed using CT-scan data and submodelling technique, which was based on an overall solution of a natural scapula model acted upon by all the muscles, ligaments and joint reaction forces. Material interfaces were assumed to be fully bonded. Based on the FE stress analysis, the following observations were made. (1) The submodelling technique, which required a large-size submodel and the use of prescribed displacements at cut-boundaries located far away from the glenoid, was crucial for evaluations on glenoid component. (2) Total polyethylene results in lower-peak stresses (tensile: 10 MPa, Von-Mises: 8.31 MPa) in the cement as compared to a metal-backed design (tensile: 11.5 MPa, Von-Mises: 9.81 MPa). The maximum principal (tensile) stresses generated in the cement mantle for both the designs were below its failure strength, but might evoke crack initiation. (3) The cement-bone interface adjacent to the tip of the keel seemed very likely to fail for both the designs. In case of metal-backed design, this interface adjacent to the tip of the keel appears even more likely to fail. (4) High metal-cement interface stresses for a moderate load might indicate failure at higher load. (5) It appears that both the designs were vulnerable to failure in some ways or the other. A part of the subchondral bone along the longitudinal axis of the glenoid cavity should be preserved to strengthen the glenoid structure and to reduce the use of cement.     

Characterization of cluster-assembled nanostructured titanium oxide coatings as substrates for protein arrays

Protein microarray technologies are rapidly expanding to fulfill current needs of proteome discovery for disease management. Nanostructured materials have been shown to present interesting features when used in biological settings: nanostructured titanium oxide film (ns-TiOx), synthesized by supersonic cluster beam deposition (SCBD), has recently emerged as a biocompatible substrate in different biological assays. The ns-TiOx surface is characterized by a morphology at the nanoscale that can be tuned to modulate specific biomolecule–material interactions. Here we present a systematic characterization of ns-TiOx coatings as protein binding surfaces, comparing their performances with those of most common commercial substrates in protein and antibody microarray assays. Through a robust statistical evaluation of repeatability in terms of coefficient of variation (CV) analysis, we demonstrate that ns-TiOx can be used as reliable substrate for biochips in analytical protein microarray application.     

不同处理方法对钛瓷结合强度影响的研究

目的:观察微弧氧化表面处理方法在钛瓷结合方面的作用。方法:将试样分为三组,微弧氧化组,预氧化组,光滑组:对各组钛试件表面进行瓷粉烧结。根据ISO 9693标准,对钛瓷间的三点弯曲结合强度进行测试,并对钛瓷结合界面和瓷剥脱面进行SEM和EDX观察与分析。结果:处理方法不同,钛表面形貌及相结构也不同。钛试样微弧氧化组,预氧化组,光滑组与瓷的结合强度分别是:42.40±4.35Mpa,34.28±2.84Mpa和28.58±2.74Mpa,微弧氧化组的钛瓷结合强度与不进行微弧氧化处理组的钛瓷结合强度相比在统计学上有显著差异(P<0.05);预氧化组的钛瓷结合强度大于光滑组(P<0.05),但明显小于微弧氧化组(P<0.01);未进行微弧氧化处理组的钛瓷界面间可见有明显裂隙;而微弧氧化组的钛瓷界面瓷与钛基体结合紧密,无任何气泡、孔隙存在。结论:钛表面微弧氧化处理后可有效提高钛瓷的结合强度。     

Cellular architecture and migration behavior of fibroblast cells on polyhydroxyoctanoate (PHO): A natural polymer of bacterial origin

Biodegradable and biocompatible novel materials of natural origin are gaining more and more attention in recent years. These so called biopolymers, characterized by their biointegrity and biocompatibility, find completely new and promising applications in biomedical sciences. The presented work focuses on the medium chain length elastomeric polyhydroxyalkanoate biopolymer—polyhydroxyoctanoate (PHO). This biopolymer is fully biodegradable without formation of harmful byproducts.We investigated PHO's physical properties with nanoindentation technique and scratch testing to determine Young's modulus and friction coefficient. Further, the work focused on the impact of PHO, used as growth substrate, on the physiology and morphology of mouse embryonic fibroblast cells (MEF 3T3). Application of fluorescent staining protocols and advanced microscopic techniques allowed to study the morphological changes in the cytoskeletons of cells grown on PHO and also gave an insight into their migration strategies on the polymer surface. We found that PHO exhibits no cellular cytotoxicity, similarly to a glass substrate. MEF cells spread better on glass surface than on each tested PHO substrate though there was almost no difference between PHO substrates cast from different solvents. However, a detailed analysis of actin and microtubule cytoskeletal architecture reveals changes in the density of actin and microtubular networks. Migration of MEF cells on PHO substrates was slower than on the glass substrate. To elucidate the molecular mechanisms of observed changes in cytoskeletal architecture and migration parameters can be of special interest for future medical application of PHO polymer.     

Growth strategy of heterotrophic bacterial population along successional sequence on spoil of brown coal colliery substrate

The bacterial population of brown coal colliery spoil (Sokolov coal mining district, Czechia) was characterized by measuring viable bacterial biomass, the culturable to total cell ratio (C:T), colony-forming curve (CFC) analysis and species and/or biotype diversity. Bacterial representatives that differed in colony-forming growth (fast and/or slow growers) were used for growth-strategy investigation of heterotrophic bacteria. Spoil substrates from the surface (0–50 mm) and the mineral (100–150 mm) layers were sampled on 4 sites undergoing spontaneous succession corresponding to 1, 11, 21 and 43 years after deposition (initial, early, mid and late stages). The bacterial biomass of the surface layer increased during the initial and early stages with a maximum at mid stage and stabilized in the late stage while mineral layer biomass increased throughout the succession. The maxima of C:T ratios were at the early stage, minima at the late stage. Depending on the succession stage the C:T ratio was 1.5–2 times higher in the mineral than the surface layer of soil. An increase in the fraction of nonculturable bacteria was associated with the late succession stage. CFC analysis of the surface layer during a 3-d incubation revealed that the early-succession substrate contained more (75 %) rapidly colonizing bacteria (opportunists, r-strategists) than successively older substrates. The culturable bacterial community of the mineral layer maintained a high genera and species richness of fast growers along the succession line in contrast to the surface layer community, where there was a maximum in the abundance of fast growers in the early stage. There was a balanced distribution of Grampositive and Gram-negative representatives of fast growers in both layers. A markedly lower abundance of slow growers was observed in the mineral in contrast to the surface layer. Gram-positive species dominated the slow growers at the surface as well as in the mineral layers. The growth strategy of the heterotrophic bacterial population along four successional stages on spoil of brown coal colliery substrate in the surface layer displayed a trend indicative of a r-K continuum in contrast to the mineral layer, where an r-strategy persisted. This research was funded by theCzech Science Foundation grant no. 526/03/1259 and by theResearch Plan of the Institute of Soil Biology, Academy of Sciences of the Czech Republic, project no. AV 0Z 6066 0521.     

Amino acid and lactate catabolism in trimethylamine oxide respiration of Alteromonas putrefaciens NCMB 1735

The nonfermentative Alteromonas putrefaciens NCMB 1735 grew anaerobically in defined media with trimethylamine oxide as external electron acceptor. All amino acids tested, except taurine and those with a cyclic or aromatic side chain, were utilized during trimethylamine oxide-dependent anaerobic growth. Lactate, serine, and cysteine (which are easily converted to pyruvate) and glutamate and aspartate (which are easily converted to tricarboxylic acid cycle intermediates) were metabolized at the fastest rate. Growth with lactate as growth-limiting substrate gave rise to the formation of 40 mol% acetate, whereas serine and cysteine were nearly completely oxidized to CO2. Molar growth yields with the latter substrates were the same and were 50% higher than with lactate. This showed that more ATP was formed when acetyl coenzyme A entered the tricarboxylic acid cycle than when it was converted via acetyl phosphate to acetate. Also, growth with formate as substrate indicated that the reduction of trimethylamine oxide to trimethylamine was coupled with energy conservation by a respiratory mechanism.     

Amino acid and lactate catabolism in trimethylamine oxide respiration of Alteromonas putrefaciens NCMB 1735.

The nonfermentative Alteromonas putrefaciens NCMB 1735 grew anaerobically in defined media with trimethylamine oxide as external electron acceptor. All amino acids tested, except taurine and those with a cyclic or aromatic side chain, were utilized during trimethylamine oxide-dependent anaerobic growth. Lactate, serine, and cysteine (which are easily converted to pyruvate) and glutamate and aspartate (which are easily converted to tricarboxylic acid cycle intermediates) were metabolized at the fastest rate. Growth with lactate as growth-limiting substrate gave rise to the formation of 40 mol% acetate, whereas serine and cysteine were nearly completely oxidized to CO2. Molar growth yields with the latter substrates were the same and were 50% higher than with lactate. This showed that more ATP was formed when acetyl coenzyme A entered the tricarboxylic acid cycle than when it was converted via acetyl phosphate to acetate. Also, growth with formate as substrate indicated that the reduction of trimethylamine oxide to trimethylamine was coupled with energy conservation by a respiratory mechanism.     

Micro-masonry for 3D Additive Micromanufacturing

Transfer printing is a method to transfer solid micro/nanoscale materials (herein called ‘inks’) from a substrate where they are generated to a different substrate by utilizing elastomeric stamps. Transfer printing enables the integration of heterogeneous materials to fabricate unexampled structures or functional systems that are found in recent advanced devices such as flexible and stretchable solar cells and LED arrays. While transfer printing exhibits unique features in material assembly capability, the use of adhesive layers or the surface modification such as deposition of self-assembled monolayer (SAM) on substrates for enhancing printing processes hinders its wide adaptation in microassembly of microelectromechanical system (MEMS) structures and devices. To overcome this shortcoming, we developed an advanced mode of transfer printing which deterministically assembles individual microscale objects solely through controlling surface contact area without any surface alteration. The absence of an adhesive layer or other modification and the subsequent material bonding processes ensure not only mechanical bonding, but also thermal and electrical connection between assembled materials, which further opens various applications in adaptation in building unusual MEMS devices.     

The response of stream macroinvertebrates to substrate size and heterogeneity

Manipulations of substrate size and components of heterogeneity were designed to test their independent effects and interactions on the abundance and species richness of stream macroinvertebrates. Two components of substrate heterogeneity, variation in size class proportions and number of size classes, had no independent effect on abundance or richness; and in general did not interact with median particle size. Median particle size, stream current, and detritus accounted for most of the significant variation in macroinvertebrates colonizing the experimental substrates. Rocks with high surface heterogeneity (roughness) were colonized by more individuals (but not taxa) than rocks with low surface heterogeneity.