New PMMA-based composites for preparing spacer devices in prosthetic infections

Even though the systemic antibiotic therapy is usually applied after prosthetic infections surgical treatments, it is unable to reach the infection site in sufficient concentrations to eradicate bacteria. Delivering antibiotics locally with the use of custom made device (spacer or nail coating) might eradicate or reduce the infection and the risk of recolonization, providing a very high concentration of antibiotic. PMMA-based (Mendec Spine^®) composites with BaSO₄ were enriched with β-tricalcium phosphate (Porosectan-TCP) or only a slightly higher BaSO₄ concentration (Porosectan-BaSO₄) to obtain higher porosity. The aim of the study was to evaluate: (i) drug absorption capability and drug release kinetics in vitro soaking them with a combined solution of gentamicin and vancomycin, (ii) their in vitro and in vivo biocompatibility, and finally, (iii) they were tested preliminarily in an experimental model of bone infection. The simultaneous presence of β-TCP and BaSO₄ resulted in the formation of a texture of interconnecting channels with different diameters, from a few microns to several hundred microns, which totally filled the material. The porosity, determined by microcomputed tomography, was significantly higher in both tested plain composites (Porosectan-TCP: +17.3%; Porosectan-BaSO₄: +7.5%) in comparison to control composite material (Mendec Spine^®). The kinetics of antibiotic release from composites was rapid and complete, producing high drug concentrations for a short period of time. Both composites showed a good level of biocompatibility. The osteomyelitic model confirmed that both composites, soaked in antibiotic solution, were able to cure bone infection. These composites could be useful for preparing devices for prosthetic joint infections treatment also allowing the use of antibiotics solution at required concentrations.     

Functionally graded semiconductor layers for devices application

We report on various aspects of the application of functionally graded materials (FGM) for devices fabrication. The broad spectrum of problems ranging from design and technology of graded structures to its characterization is discussed. The main attention is focused on the application of FGM as an active area of a new photo-detector. The influence of various profile distributions of AIIIBV grading layers composition and layers configuration on the photo-detector spectral characteristics are discussed.     

Inverse design techniques for improving composite prosthetic devices

The design and performance of composite prosthetic devices can be improved by tailoring the material properties to achieve a prescribed response. An example of such a response would be displacements and stresses exhibited by healthy, undisturbed femoral bone. In this paper, an inverse design methodology, used in the Volumetrically Controlled Manufacturing (VCM) process, is developed and tested for improving the design of orthopedic prosthetic devices. First, a three-dimensional finite element (FE) model is developed based on available Computed Tomography (CT) data. The FE model is used to evaluate the response of the model subjected to a typical load. Second, as a part of the VCM process, the inverse design process is used to formulate a design problem that is in the form of a constrained least-squares problem. The intent is to find the material properties of the FE model to obtain a known displacement field on the stem-cancellous interface. Third, a solution methodology is developed to solve this constrained least squares problem using the finite element analysis for function evaluations and a gradient-based nonlinear programming (NLP) method to solve the design problem. Two test problems are solved to illustrate the developed methodology. The results indicate that material properties can be tailored to meet specific response requirements.     

Layered nanocomposites from gold nanoparticles for neural prosthetic devices

Treatments of neurological diseases, diagnostics of brain malfunctions, and the realization of brain-computer interfaces require ultrasmall electrodes that are "invisible" to resident immune cells. Functional electrodes smaller than 50 μm are impossible to produce with traditional materials due to high interfacial impedance at the characteristic frequency of neural activity and insufficient charge storage capacity. The problem can be resolved by using gold nanoparticle nanocomposites. Careful comparison indicates that layer-by-layer assembled films from Au NPs provide more than 3-fold improvement in interfacial impedance and 1 order of magnitude increase in charge storage capacity. Prototypes of microelectrodes could be made using traditional photolithography. Integration of unique nanocomposite materials with microfabrication techniques opens the door for practical realization of the ultrasmall implantable electrodes. Further improvement of electrical properties is expected when using special shapes of gold nanoparticles.     

Compositionally graded ferroelectric multilayers for frequency agile tunable devices

Recently, there has been significant interest toward the development of tunable dielectric materials for voltage-controlled, frequency-agile phase shifters and filters operating in the microwave regime. The fundamental challenge in designing materials systems for such tunable devices is the simultaneous requirement of high dielectric tunability (>40%) over a large temperature interval (−10 °C to +90 °C) coupled with low dielectric losses (between 3.0 dB and 4.0 dB in operational bandwidths ranging from several hundred MHz up to 30 or more GHz). We show that a high- and temperature-insensitive tunability can be realized in compositionally graded ferroelectrics and provide a brief review of the results of experimental and theoretical studies on the dielectric properties of Barium Strontium Titanate (Ba_1−x Sr _x TiO₃ or BST) multilayer heterostructures. Theoretically, we discuss the role of thermal stresses on the dielectric properties using a non-linear thermodynamic model coupled with basic electrostatic considerations to describe the interlayer interactions between the ferroelectric layers. We show that the thermal strains arising from the thermal expansion coefficient mismatch between the multilayered film and the substrate may have a significant effect on the dielectric permittivity and tunability of BST multilayers. Experimentally, compositionally graded BST multilayers (5 mol% MgO doped and undoped) were grown via metallo-organic solution deposition (MOSD) on Pt–Si substrates and electrically characterized. Optimum conditions were found to exist in BST multilayers consisting of three distinct layers of ~220 nm nominal thickness with compositions corresponding to Ba_0.60Sr_0.40TiO₃ (BST 60/40), BST 75/25, and BST 90/10. At room temperature, the BST heterostructure has a small-signal dielectric permittivity of 360 with a dissipation factor of 0.012 and a dielectric tunability of 65% at 444 kV/cm. These properties exhibit minimal dispersion as a function of temperature ranging from 90 °C to −10 °C. Our results also show that MgO doping improves dielectric loss (tan δ = 0.008), but results in a moderate dielectric tunability of 29% at 444 kV/cm. Electrical measurements at microwave frequencies display a decrease in the dielectric permittivity and tunability for both undoped and MgO-doped BST multilayers. At 10 GHz, the dielectric response, tunability, and the loss characteristics for graded undoped BST are 261, 25% (at 1,778 kV/cm), and 0.078, respectively, and 189 and 15% (at 1,778 kV/cm), and 0.039, respectively, for the MgO-doped graded BST.     

Anisotropic magnetostrictive metal-polymer composites for functional devices

New metal-polymer composites based on mechanochemically synthesized magnetostrictive Fe-Ga phase particles with dimensions of up to 2 μm dispersed and spatially oriented in a polymer matrix have been studied. The polymer matrix for spatial anisotropic stabilization of particles was represented by modified polyurethane (PU). An increase in the magnetostrictive effect was achieved by directed orientation of particles in a magnetic field applied during polymerization of the PU matrix. The spatial anisotropy of the composite has been studied by the methods of conversion Mössbauer spectroscopy with resonant X-ray detection and scanning electron microscopy. It is shown that the mechanochemical synthesis is an effective method of obtaining particles with microstress-enhanced magnetostriction. The use of these particles for the formation of a functional elastomer composite provides a material with significant magnetostrictive effect, which can be several-fold increased due to orientation of particles in an applied magnetic field. The obtained anisotropic magnetostrictive composite is a promising material for the creation of smart functional components of positioning systems, attenuators, and sensors.     

Utilization of wood for making large-size measuring devices

Summary Wood diameter-measuring caliper gauges are convenient to use, provide more efficient and accurate measurements as compared with the best metal gauges and micrometers, and the ambient air temperature virtually has no effect on measurement results.Wooden measuring equipment has a number of advantages as compared with metal equipment, providing the peculiarities of wood are taken into account. The use of such equipment should raise by 1–2 grades the accuracy in measuring articles according to GOST 2689-54.     

Functionally graded tricalcium phosphate/fluoroapatite composites

This study was conducted to prepare fluorine-substituted apatite (FA)/beta-tricalcium phosphate (β-TCP) composites to combine the biostability of FA with the bioresorbability of β-TCP. The FA was prepared for the first time by mixing hydroxyapatite (HA) with aluminium fluoride (coded as AF). On the other hand, the β-TCP was prepared from a mixture of HA and CaHPO₄ (calcium hydrogen phosphate). The dissolution behaviour of the composites was tested using a 10-wt.% citric acid solution. Scanning electron microscopy (SEM) indicated that β-TCP dissolved in the citric acid much faster than FA, resulting in macropores among the FA matrix. In addition to bulk FA/β-TCP composites, novel functionally gradient FA/β-TCP composites were also prepared by varying the particle size and the volume content of the β-TCP granules. The functionally gradient FA/β-TCP composites could be used to design implants.     

Advanced symmetrically graded ceramic and ceramic-metal composites

The potential of electrophoretic deposition as a shaping process of free-standing objects with a gradient in composition is investigated. The capability to produce relatively thick continuously graded ZrO₂-Al₂O₃ and WC-Co-Ti(C,N) discs was explored. After electrophoretic deposition, the dried deposits were cold isostatically pressed and pressureless sintered. In order to create a symmetric gradient profile along the thickness of the plates, a mathematical model for the EPD process was developed in order to predict the composition and slope of the gradient profile in the discs from the starting composition of the suspension, the EPD operating parameters and the powder-specific EPD characteristics. The sintered graded materials have a continuous variation in composition, microstructure and mechanical properties. In the illustrated ZrO₂-Al₂O₃ example, the ZrO₂ content increases from 0 vol% on the outer surface up to 25 vol% in the core. For the WC-Co-Ti(C,N) discs, the Ti(C,N) content decreases from 5 wt% on the outer edge to 0 wt% in the bulk of the material. In both materials, a hard outer rim and a tough core are obtained. Finally, the residual surface stresses of the densified graded ZrO₂-Al₂O₃ discs were investigated.     

Characterization of piezoelectric polymer composites for MEMS devices

Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (k). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low k value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2?C2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.     

功能梯度铁电铁磁复合材料弯曲模态下的磁电效应

基于磁致伸缩相与压电相的本构方程,应用弹性力学的方法,建立了功能梯度铁电铁磁复合材料弯曲模态下的磁电耦合静态力学模型。假设铁电和铁磁材料的物理参数均为沿厚度方向的线性或指数函数,分析计算了由PZT作为铁电材料和CoFe2O4作为铁磁材料的双层复合材料的磁电效应。结果表明,在弯曲模态下,磁电电压系数出现两个峰值。负梯度的铁电(或铁磁)材料提高磁电效应,正梯度的铁电(或铁磁)材料降低磁电效应。同号梯度的铁电铁磁材料对磁电效应的影响更大。     

Effective bulk moduli of two functionally graded composites

Summary. This paper considers the effective bulk moduli and the underlying elastic fields of a particle- and a fiber-reinforced composite whose matrix properties are graded linearly along the radial distance. The governing Fuchsian equations are first transformed into Riemann equations which, by means of change of the dependent variable, are further transformed into hypergeometric equations which are solved in terms of the hypergeometric function. This set of solutions provides an explicit dependence of the effective bulk behavior of the composites with arbitrary variations of the slope of the matrix moduli.     

分级竹丝复合材料的原理与性质

竹子是性能最好的生物质材料之一, 其生长迅速、材料来源广泛, 成本低廉。竹材的结构是由竹纤维为主组成维管束, 维管束和薄壁细胞组成竹材。维管束在竹青一侧分布密集, 选择竹青片为原料可制作高性能的竹丝。竹丝的均齐性好, 具有良好的静态、抗冲击和抗疲劳性能。采用浸胶和预压方法制作预压料, 经过预压料的铺层, 热压压制, 可制成性能优良的分级竹丝复合材料。该材料的性能可达到或超过玻璃钢, 用于风轮叶片和船舶等重要工程。      

Processing and compressive response of functionally graded composites

Use of hollow particles in composite materials provides a unique possibility of creating functionally graded composites (FGCs) where the gradient is present in the particle wall thickness. The present work is focused on developing a processing method for creating such FGCs using hollow particles. The processing method is based on co-curing slurries of various compositions to obtain the desired final composition and configuration of FGCs. The fabricated composites are characterized for compressive properties. In addition, the same types of particles are used to create FGCs containing volume fraction gradient. The compressive properties of both types of composites are compared and some distinct advantages are observed in the wall thickness variation approach, which include better possibilities of tailoring their physical and mechanical properties.     

Dimethylformamide: an effective dispersant for making ceramic-carbon nanotube composites

Carbon nanotube (CNT) and alumina dispersions were prepared separately in dimethylformamide (DMF) and ethanol by ultrasonication. The colloidal stability of the dispersions was monitored and a particle size analysis was performed to evaluate the size range of the agglomerates after different times. DMF was found to be a much more effective dispersant than ethanol for making stable, homogeneous CNT and composite dispersions. Alumina-CNT (4.65?vol%) nanocomposites were sintered in a spark plasma sintering (SPS) furnace. DMF dispersions produced homogeneously distributed and agglomerate-free CNT-alumina nanocomposites with higher electrical conductivity as compared to nanocomposites prepared using ethanol.