固化纤维在多孔生物陶瓷内的隧道条纹效应

为使制备的多孔生物陶瓷满足生物学和结构要求,将经固化处理的纤维纱线与羟基磷灰石料浆同步织入模具,在陶瓷初坯烧结的低温区设置多次恒温.结果表明,纤维表面条纹结合涂层对陶瓷的蚀刻作用清晰印刻于隧道内表面,烧结体内隧道连通,无块状颗粒堵塞,成型完整,内壁呈细条纹.该方法制备的多孔生物陶瓷为组织细胞生长、迁移、黏附提供了有利的空间,X射线衍射分析验证样品未因制作工艺引入异质成分.     

Fabrication of 1-dimensional porous hydroxyapatite and evaluation of its osteoconductivity

Porous HA ceramics with 1-dimensional pore channels were fabricated to obtain controllable microstructure. 1-dimensional porous HA was objected to find out the optimum condition of bone ingrowth and also to facilitate the observation of osteocondutive behavior in porous HA. The porous structure was formed by burnt-out of polymeric fibers and the size of pores was determined by the diameter of polymeric fibers. The porosity could be varied by the thickness of HA slurry coated on polymeric fiber and by the thickness of HA tapes inserted between fiber layers. As result, 1-dimensional porous HA ceramics of this study have the uniform interconnection size (50-500 microm) and the linearly open pore structure. The compressive strength of 1-dimensional porous HA was 6-10 MPa similar to that of human cancellous bone. On the in vivo test, oteon-like osteoconduction in pore channel of 1-dimensional porous HA was observed, like what had been found in cortical bones. This osteon-like new bone grew from the surface to the center of pore channels. The 1-dimensional porous HA ceramics prepared in this study were very useful as a model system to observe bone ingrowth in the porous HA implants.     

Engineering the surface texture and shape of channels in ceramic substrates

Ceramic/ceramic joining can transform surface channels on a ceramic subcomponent into an interior channel. Interior channels have a number of potential uses in advanced ceramic applications, including application as conduits of a variety of fluids, such as fuel, medicine, or cooling fluids. For cooling fluids in particular, the surface texture and shape of the channel can greatly affect its heat transfer and fluid flow characteristics. This paper explores means of “engineering” the surface textures and shapes of such channels, including the fabrication of channels with circular and non-circular cross-sections as well as channels with smooth or textured walls (and channels with a combination of smooth and textured regions). The microstructure of the channels is analyzed using laser scanning confocal microscopy (LSCM). Although LSCM has been used extensively in biological studies, this study is one of the first studies to apply LSCM as a tool to characterize three-dimensional shapes and textures in ceramic materials.     

Miniaturized electrochemical flow cells

Several novel types of miniaturized electrochemical flow cells are described. The flow cells are fabricated in fluorinated ethylene propylene using a novel technique where channels with inner diameters down to 13 microm are integrated with electrodes. The channel is formed by shrinking and simultaneous melting of a heat shrink/melt tubing around a channel template (a tungsten wire) and electrodes followed by removal of the channel template. The technique allows incorporation of different electrode materials of different sizes. The electrode configuration consists of one or two working electrodes inside the channel and a counter electrode located in the channel outlet reservoir. Electrode configurations with different channel and working electrode sizes, different electrode materials including carbon fibers, glassy carbon rods, poly(tetrafluoroethylene)/carbon composite material, and platinum wires, and different arrangements have been assembled. Hydrodynamic voltammograms in dual-electrode (generator-collector) experiments indicate good potential control for cells with 25-microm channels, while there is some iR drop in cells with 13-microm channels. Cells prepared with a cylindrical working electrode tangent and perpendicular to a flow channel show a flow rate dependence consistent with thin-layer cell behavior. Electrode areas can be made in the range of 10(-10)-10(-8) m2.     

高性能SiBN(C)陶瓷纤维的热稳定性能及透波性能

SiBN(C)陶瓷纤维因其优异的性能(高温稳定性、高温抗蠕变和高温抗氧化性能等)被认为是高温高性能陶瓷基复合材料的理想增强体。研究了SiBN(C)陶瓷纤维的热稳定性能及微观结构, 探索了SiBN(C)陶瓷纤维在1 100~1 500 ℃的抗氧化过程, 并研究了C含量对SiBN(C)陶瓷纤维介电性能的影响。结果表明: SiBN(C) 陶瓷纤维在高温热处理至1 600 ℃的N₂气氛下仍然呈现无定形结构;HT-TGA结果表明该SiBN(C)陶瓷纤维具有良好的高温热稳定性, 该陶瓷纤维的热失重率(1 450 ℃, N₂气氛)仅为1.5wt%; 同时SiBN(C)纤维也表现出优良的高温抗氧化性能, SiBN(C)陶瓷纤维在1 400 ℃, 空气中处理5 h后, 纤维致密且无裂纹, XRD分析表明SiBN(C)陶瓷仍然呈现无定形结构, 1 500 ℃处理5 h后, SiBN(C)陶瓷纤维开始出现皮芯结构, 并且出现微晶现象; XRD、SEM和EDX等测试手段表明氧化后样品的表面主要以SiO₂微晶形式存在; 介电性能研究表明当C含量低至0.1wt%时, SiBN(C)陶瓷纤维的介电常数为2.1, 介电损耗为0.001 7(频率为10 GHz)。性能评价说明该SiBN(C)陶瓷纤维可满足高温透波材料对增强体的要求。      

Hydroxyapatite scaffolds processed using a TBA-based freeze-gel casting/polymer sponge technique

A novel freeze-gel casting/polymer sponge technique has been introduced to fabricate porous hydroxyapatite scaffolds with controlled “designer” pore structures and improved compressive strength for bone tissue engineering applications. Tertiary-butyl alcohol (TBA) was used as a solvent in this work. The merits of each production process, freeze casting, gel casting, and polymer sponge route were characterized by the sintered microstructure and mechanical strength. A reticulated structure with large pore size of 180–360 μm, which formed on burn-out of polyurethane foam, consisted of the strut with highly interconnected, unidirectional, long pore channels (~4.5 μm in dia.) by evaporation of frozen TBA produced in freeze casting together with the dense inner walls with a few, isolated fine pores (<2 μm) by gel casting. The sintered porosity and pore size generally behaved in an opposite manner to the solid loading, i.e., a high solid loading gave low porosity and small pore size, and a thickening of the strut cross section, thus leading to higher compressive strengths.     

Analysis of the elastic properties of an interpenetrating AlSi12-Al2O3 composite using ultrasound phase spectroscopy

An interpenetrating composite fabricated by squeeze-casting a eutectic aluminium-silicon alloy into a porous alumina preform is studied in this work. The preform was fabricated by pyrolysis of cellulose fibres used as pore forming agent, pressing of the green ceramic body and subsequent sintering of alumina particles. The resulting preform had both micropores within the ceramic walls and macropores between those walls, which were infiltrated by the liquid metal. Composites with alumina contents varied in the range of 18-65 vol.% were studied. Three longitudinal and three shear elastic constants of the composites were determined using ultrasound phase spectroscopy on rectangular parallelepiped samples. Complete stiffness matrix of one sample was determined by modifying the sample geometry by cutting at the corners of the sample and subsequent ultrasonic measurements. All composites exhibit a moderately anisotropic behavior, which can be attributed to a non-random pore orientation distribution caused by uni-axial pressing of the preforms prior to sintering. The experimental results are compared with several theoretical micromechanical models.     

微管式固体氧化物燃料电池阳极微结构及其性能

利用相转化纺丝法制备了NiO-YSZ中空纤维, 在其外表面负载YSZ膜1450℃共烧后形成YSZ/NiO-YSZ双层中空纤维。阳极孔结构通过芯液(N-甲基砒咯烷酮(NMP)+乙醇)中溶剂NMP的含量来控制。 当NMP含量从0、30wt%、50wt%、70wt%增加到100wt%时, 阳极的孔结构由指状孔/海绵孔/指状孔三明治结构逐渐成为贯通的指状孔结构, 电解质膜致密性、还原后的双层中空纤维的机械强度、阳极电导率逐渐减小, 而孔隙率则增加。多孔的阴极Ag涂敷于致密的电解质膜外表面构成微管SOFC。H₂/空气微管SOFC的浓差极化随着指状孔长度的增加而减小, 当NMP含量为70wt%时, 输出性能最佳, 最大功率密度为662 mW/cm² (800℃), 此时极化阻抗最小。     

Fabrication of Metallized Nanopores in Silicon Nitride Membranes for Single‐Molecule Sensing

The fabrication and characterization of a metallized nanopore structure for the sensing of single molecules is described. Pores of varying diameters (>10 nm) are patterned into free‐standing silicon nitride membranes by electron‐beam lithography and reactive ion etching. Structural characterization by transmission electron microscopy (TEM) and tomography reveals a conical pore shape with a 40° aperture. Metal films of Ti/Au are vapor deposited and the pore shape and shrinking are studied as a function of evaporated film thickness. TEM tomography analysis confirms metalization of the inner pore walls as well as conservation of the conical pore shape. In electrical measurements of the transpore current in aqueous electrolyte solution, the pores feature very low noise. The applicability of the metallized pores for stochastic sensing is demonstrated in real‐time translocation experiments of single λ‐DNA molecules. We observe exceptionally long‐lasting current blockades with a fine structure of distinct current levels, suggesting an attractive interaction between the DNA and the PEGylated metallic pore walls.     

Multichannel mould processing of 3D structures from microporous coralline hydroxyapatite granules and chitosan support materials for guided tissue regeneration/engineering

A three-dimensional composite material was produced from microporous coralline origin hydroxyapatite (HA) microgranules, chitosan fibers and chitosan membrane. Cylindrical HA microgranules were oriented along channel direction within multichannel mould space and aligned particles were supported with fibers and a chitosan membrane. The positive replica of mould channels was clasp fixed to produce thicker scaffolds. Light microphotographs of the developed complex structure showed good adhesion between the HA particles, the fibers and the supporting membrane. The composite material showed 88% (w/w) swelling in one hour and preserved the complex structure of the original material upon long-term incubation in physiological medium. MEM extract test of HA chitosan complex showed no cell growth inhibition and cell viability assay (MTS) indicated over 90% cell viability.     

羟基磷灰石内连通空心球陶瓷支架的形貌特征及力学性能

利用聚苯乙烯微球模板,采用负压抽滤注浆工艺制备了羟基磷灰石(hydroxylapatite,HA)内连通空心球陶瓷支架,分析了制备工艺对空心球陶瓷的形貌特征和力学性能的影响,并研究了孔隙率与压缩强度的关系.结果表明,空心球陶瓷支架具有连通球形孔及连通球体间隙的独特复合孔结构;当注浆2次,浆料固含量为0.5g/ml时支架的孔壁完整,表面形态有利于骨细胞生长;通过改变工艺参数,得到HA空心球陶瓷的孔隙率为61%～90%,压缩强度为1.1～6.9MPa,孔隙率P与压缩强度σf的关系符合ln(σf)=ln(σf0)-bP方程.     

Nanoindentation on porous bioceramic scaffolds for bone tissue engineering

We report nanoindentation mechanical properties measurements on porous ceramic scaffolds made for tissue engineering applications. The scaffolds have been made from tricalcium phosphate (TCP), hydroxyapatite (HA) nanopowder and mixed powders of HA (50 wt%) and TCP (50 wt%) using the polyurethane sponge method, which produces open porous ceramic scaffolds through replication of a porous polymer template. The scaffolds prepared by this method have a controllable pore size and interconnected pore structure. The crystal structures and morphology of porous scaffolds were determined by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. Nanoindentation measurements to a depth of 600 nm showed a Young's modulus value of 10.3 GPa for HA+TCP composite scaffolds and 1.5 GPa for TCP scaffolds. The hardness values were 240 MPa for HA+TCP composites and 21 MPa for TCP sample respectively. The results showed that the mechanical properties of the biodegradable scaffolds can be considerably enhanced with the addition of HA while maintaining the interconnected open pores and pore geometry desirable for bone tissue engineering.     

Poly(dimethylsiloxane)-based microchip for two-dimensional solid-phase extraction-capillary electrophoresis with an integrated electrospray emitter tip

A microchip in poly(dimethylsiloxane) (PDMS) for in-line solid-phase extraction-capillary electrophoresis-electrospray ionization-time-of-flight mass spectrometry (SPE-CE-ESI-TOF-MS) has been developed and evaluated. The chip was fabricated in a novel one-step procedure where mixed PDMS was cast over steel wires in a mold. The removed wires defined 50-microm cylindrical channels. Fused-silica capillaries were inserted into the structure in a tight fit connection. The inner walls of the inserted fused-silica capillaries and the PDMS microchip channels were modified with a positively charged polymer, PolyE-323. The chip was fabricated in a two-level cross design. The channel at the lower level was packed with 5-microm hyper-cross-linked polystyrene beads acting as a SPE medium used for desalting. The upper level channel acted as a CE channel and ended in an integrated emitter tip coated with conducting graphite powder to facilitate the electrical contact for sheathless ESI. An overpressure continuously provided fresh CE electrolyte independently of the flows in the different levels. Further studies were carried out in order to investigate the electrophoretic and flow rate properties of the chip. Finally, six-peptide mixtures, in different concentrations, dissolved in physiological salt solution was injected, desalted, separated, and sprayed into the mass spectrometer for analysis with a limit of detection in femtomole levels.     

Fabrication and functional characterization of engineered features on pyrolytic carbon

Engineered features on pyrolytic carbon (PyC) have been reported to improve the functional performance of the bio-implants. This paper is focused on the functional characterization of micro-features created on the surface of PyC. Two different types of micro-features (wide channels and arrayed holes) have been created by micro-electrical discharge machining (micro-EDM). Two other micro-features (fine channels and micro-pillars) have been created by micromilling process. Coliform bacterial strain was isolated from a sample of water and grown on all four textured. Cell growth was carried out on an unmachined surface to see the behavior of the isolated bacterial strain on the textured/non-textured surfaces. The samples were examined under SEM before and after wash to see cell growth and cell adhesion capability of the textures. The wide channels by micro-EDM show the maximum cell growth but poor cell adhesion. 184% higher cell growth has been observed on the wide channels in comparison with unmachined surface. The fine channels by micro-milling show comparatively lower growth but the cell adhesion on this surface was found excellent. 71% cells remain unwashed after washing of the surface having fine channel textures. It means that the channels structure shows the maximum cell growth and adhesion independent of machining process.     

Benefits and limitations of porous substrates as biosensors for protein adsorption

Porous substrates have gained widespread interest for biosensor applications based on molecular recognition. Thus, there is a great demand to systematically investigate the parameters that limit the transport of molecules toward and within the porous matrix as a function of pore geometry. Finite element simulations (FES) and time-resolved optical waveguide spectroscopy (OWS) experiments were used to systematically study the transport of molecules and their binding on the inner surface of a porous material. OWS allowed us to measure the kinetics of protein adsorption within porous anodic aluminum oxide membranes composed of parallel-aligned, cylindrical pores with pore radii of 10-40 nm and pore depths of 0.8-9.6 μm. FES showed that protein adsorption on the inner surface of a porous matrix is almost exclusively governed by the flux into the pores. The pore-interior surface nearly acts as a perfect sink for the macromolecules. Neither diffusion within the pores nor adsorption on the surface are rate limiting steps, except for very low rate constants of adsorption. While adsorption on the pore walls is mainly governed by the stationary flux into the pores, desorption from the inner pore walls involves the rate constants of desorption and adsorption, essentially representing the protein-surface interaction potential. FES captured the essential features of the OWS experiments such as the initial linear slopes of the adsorption kinetics, which are inversely proportional to the pore depth and linearly proportional to protein concentration. We show that protein adsorption kinetics allows for an accurate determination of protein concentration, while desorption kinetics could be used to capture the interaction potential of the macromolecules with the pore walls.     

Pore structure of porous ceramics synthesized from water-based slurry by freeze-dry process

A unique porous ceramic with complex pore structure was synthesized by the freeze-dry process. A water-based ceramic slurry was frozen while controlling the growth direction of ice, and sublimation of the ice were generated by drying it at a reduced pressure. By sintering this green body, a porous ceramic with complex pore structure was obtained, where macroscopically aligned open pores exceeding 10 m in size contained minute pores of about 0.1 m in their internal walls. Wide control of the porosity was possible by changing the concentration of the starting slurry. The pore size distribution as well as the microstructure were substantially affected by the freezing and sintering temperatures. Optimization of the synthesis conditions was investigated in order to obtain the desired pore structure.     

Hydrogen peroxide sensing with horseradish peroxidase-modified polymer single conical nanochannels

Inspired from the funtioning and responsiveness of biological ion channels, researchers attempt to develop biosensing systems based on polymer and solid-state nanochannels. The applicability of these nanochannels for detection/sensing of any foreign analyte in the surrounding environment depends critically on the surface characteristics of the inner walls. Attaching recognition sites to the channel walls leads to the preparation of sensors targeted at a specific molecule. There are many nanochannel platforms for the detection of DNA and proteins, but only a few are capable of detecting small molecules. Here, we describe a nanochannel platform for the detection of hydrogen peroxide, H(2)O(2), which is not only a toxic waste product in the cellular systems but also a key player in the redox signaling pathways. The sensor is based on single conical nanochannels fabricated in an ion tracked polymer membrane. The inner walls of the channel are decorated with horseradish peroxidase (HRP) enzyme using carbodiimide coupling chemistry. The success of the HRP immobilization on the channel surface is confirmed by measuring the pH-dependent current-voltage (I-V) curves of the system. The reported HRP-nanochannel system detects nanomolar concentrations of H(2)O(2) with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the substrate. The immobilized HRP enzyme is thus capable of inducing redox reactions in a subfemtoliter volume of single nanochannels. We demonstrate that functioning of the designed biosensor is reversible and can be used multiple times to detect H(2)O(2) at various concentrations.     

High thermal stability thick wall mesoporous titania thin films

Mesoporous TiO₂ thin films were prepared by using tetrabutyl titanate as the inorganic precursor and triblock copolymer (Pluronic F127) as the structure directing agent. The obtained mesostructured TiO₂ thin film exhibits a high thermal stability, which can sustain 600 °C thermal treatment. The small angle XRD and wide angle XRD patterns indicate that the samples have mesoporous channel and are composed of anatase. The corresponding TEM images show that the homogeneous mesostructure and very thick pore walls (about 9–13 nm) are formed in the obtained thin films, which could be responsible for the high thermal stability of the framework. In addition, the samples have narrow pore diameter distribution and a mean pore size of 7.4 nm.     

Effect of polyvinyl alcohol additive on the pore structure and morphology of the freeze-cast hydroxyapatite ceramics

Porous hydroxyapatite (HAP) ceramics with different morphologies were fabricated by the freeze casting method. The morphologies of HAP ceramics were modified by adjusting the concentration of polyvinyl alcohol (PVA) additive in the HAP slurries. HAP ceramics without PVA additive were composed of non-interconnected macroscopic lamellar pores and porous ceramic walls. With PVA additive, the HAP ceramics were made up of small lamellar pores or three-dimensional reticulate pores and porous ceramic walls. PVA additive had no effect on the phase composition of HAP ceramics. The open porosity and pore connectivity were improved because of the addition of PVA.     

Hydroxyapatite implants with designed internal architecture

Porous hydroxyapatite (HA) has been used as a bone graft material in the clinics for decades. Traditionally, the pores in these HAs are either obtained from the coralline exoskeletal patterns or from the embedded organic particles in the starting HA powder. Both processes offer very limited control on the pore structure. A new method for manufacturing porous HA with designed pore channels has been developed. This method is essentially a lost-mold technique with negative molds made with Stereolithography and a highly loaded curable HA suspension as the ceramic carrier. Implants with designed channels and connection patterns were first generated from a Computer-Aided-Design (CAD) software and Computer Tomography (CT) data. The negative images of the designs were used to build the molds on a stereolithography apparatus with epoxy resins. A 40 vol% HA suspension in propoxylated neopentyl glycol diacrylate (PNPGDA) and iso-bornyl acrylate (IBA) was formulated. HA suspension was cast into the epoxy molds and cured into solid at 85 °C. The molds and acrylate binders were removed by pyrolysis, followed by HA green body sintering. With this method, implants with six different channel designs were built successfully and the designed channels were reproduced in the sintered HA implants. The channels created in the sintered HA implants were between 366 m and 968 m in diameter with standard deviations of 50 m or less. The porosity created by the channels were between 26% and 52%. The results show that HA implants with designed connection pattern and well controled channel size can be built with the technique developed in this study. © 2001 Kluwer Academic Publishers