Screening Mesenchymal Stem Cell Attachment and Differentiation on Porous Silicon Gradients

The profound effects that nanoscale surface topography exerts on cell behavior are highly relevant to the development of advanced biomaterials and to advances in tissue engineering and regenerative medicine. Here, an asymmetric anodization procedure is used to produce n‐type porous silicon (pSi) gradients with pore sizes ranging from tens to hundreds of nanometers in diameter and changes in the ridge nanoroughness from a few to tens nanometers. Rat mesenchymal stem cells (rMSCs) adhere poorly at the regions with small pore size but high ridge roughness. Cell adhesion is increased gradually towards the large pore size but low ridge roughness end of the pSi gradients. Surface topography influences cell differentiation, but not cell proliferation. Osteogenesis of rMSCs is enhanced by porous topography with a ridge roughness lower than 10 nm, while adipogenesis of rMSCs is enhanced on the entire pSi gradient compared with flat Si substrates. The results demonstrate that the gradient format allows in‐depth screening of surface parameters that are important for the control of mammalian cell behavior, thereby advancing the development of new and improved biomaterials for orthopaedic and tissue engineering applications.     

Clathrin sheets on the protoplasmic surface of ventral membranes of osteoclasts in culture

Physical cell-shearing resulted in various degrees of disruption of the basolateral (upper) membranes, cytoskeletons or cell organelles and exposed the protoplasmic surface of ventral (adhesion) membranes of osteoclasts that were attached to the underlying substratum, such as coverslips, mica or synthetic apatite plates. Freeze-dried replicas of the ventral membranes left behind on the substratum after cell-shearing provided three-dimensional information on the ultrastructure of the protoplasmic membrane surface of cultured osteoclasts. An extensive area of the protoplasmic surface and various amounts of cytoskeletal structures attached to the adherent ventral surface of the plasma membrane were visible. In particular, the most characteristic finding of the present study is that numerous clathrin sheets displaying various sizes, shapes and curvature were revealed on the ventral membrane. The polygon substructures of the clathrin lattices appeared to be composed of hexagons with a few pentagons interspersed. They were seen at the peripheral membranes where they were situated at the sites of close contact with the underlying substratum. In addition, clathrin lattices were never observed on the basolateral (upper) membranes. In favourable stereo views, most cytoskeletons were not in direct contact with the clathrin sheets. However, a few observations indicated possible remnants of cytoskeletons attached to clathrin lattices. Podosomes did not have a direct structural relationship to clathrin lattices. Although it is generally accepted that cytoskeletal podosomes in motile cells, such as osteoclasts, play a major role in cell adhesion, the present study indicates that membrane-associated clathrin might also function during attachment to the substrate. In this regard, clathrin is thought to be required for receptor-mediated endocytosis, but whether it might also function in cell attachment is still a matter for debate. This type of clathrin-related adhesion appears to be a previously unrecognized site of cell/substrate adhesion in osteoclasts. To assess this possible function, we focused on clathrin and related cytoskeletal elements on the ventral membranes of cultured osteoclasts.     

Aperture-Adjustable and Repairable Metal-Based MOFs Catalysis Membrane for Water Purification

Precise adjustment of the pore size, damage repair, and efficient cleaning is all challenges for the wider application of inorganic membranes. This study reports a simple strategy of combining dry-wet spinning and electrosynthesis to fabricate stainless-steel metal–organic framework composite membranes characterized by customizable pore sizes, targeted reparability, and high catalytic activity for membrane cleaning. The membrane pore size can be precisely customized in the range of 14–212 nm at nanoscale, and damaged membranes can be repaired by targeted treatment in 120 s. In addition, advanced oxidation processes can be used to quickly clean the membrane and achieve 98% flux recovery. The synergistic actions of the membrane matrix and the selective layer increase the adsorption energy of active sites to oxidant, shorten the electron transfer cycle, and enhance the overall catalytic performance. This study can provide a new direction for the development of advanced membranes for water purification and high-efficiency membrane cleaning methods.     

Constrained Order in Nanoporous Alumina with High Aspect Ratio: Smart Combination of Interference Lithography and Hard Anodization

With only two matched processing steps, the fabrication of thick nanoporous alumina membranes with mono‐oriented, perfect hexagonal packing of pores, and precise control of all structural parameters over large areas is demonstrated. The cylindrical pores are uniform in shape and widely tunable in their dimensions and spatial distribution, with aspect ratios as high as 500. In brief, electropolished aluminum is first patterned using three‐beam interference lithography in a single step and then anodized in a hard regime. The periodic concavities in the aluminum surface guide the pore nucleation, and the self‐ordering phenomenon guarantees the maintenance of the predefined arrangement throughout the entire layer. In contrast to other methods, the interpore distance can be easily adjusted, the porous layer is not limited in thickness, no prefabricated stamps are involved, and the periodic pattern can be easily reproduced without risk of degradation. The approach overcomes the time, cost, and scale limitations of other existing processes. These membranes are well‐suited for the templated fabrication of perfectly ordered arrays of highly uniform 1D nanostructures. Thus, the application fields of these functional membranes are diverse: magneto‐optical and opto‐electronic devices, photonic crystals, solar cells, fuel cells, and chemical and biochemical sensing systems, to name a few.     

Formation of Embryoid Bodies with Controlled Sizes and Maintained Pluripotency in Three‐Dimensional Inverse Opal Scaffolds

Embryoid bodies (EBs) are aggregates of cells derived from embryonic stem (ES) cells, which can serve as a good model system to investigate molecular and cellular interactions in the earliest stages of embryo development. Current methods for producing EBs mainly rely on the use of hanging drops or suspensions in non‐tissue culture treated plates, microwells, and spinner flasks. The capability of these methods is limited in terms of size uniformity and distribution as well as scalability. Here, a new platform based on three‐dimensional alginate inverse opal scaffolds with uniform pores is presented, where uniform EBs with controllable sizes could be produced in the pores and then recovered after disintegration of the scaffolds. The size of the EBs could be readily controlled by varying the culture time and/or by using scaffolds with different pore sizes. The EBs maintained their viability and undifferentiated state, and they were able to differentiate into specific lineages upon stimulation.     

Sub‐10 nm Wide Cellulose Nanofibers for Ultrathin Nanoporous Membranes with High Organic Permeation

There are increasing requirements for highly efficient and solvent‐resistant nanoporous membranes in various separation processes. Traditional membranes usually have a poor solvent resistance and a thick skin layer leading to a low permeation flux. Currently, the major challenge lies in fabrication of ultrathin few‐nanometers‐pore membranes for fast organic filtration. Herein, a facile approach is presented to prepare ultrafine cellulose nanofibers for fabrication of ultrathin nanoporous membranes. The obtained nanofibers have a uniform diameter of 7.5 ± 2.5 nm and are homogeneously dispersed in aqueous solutions that are favorable to the fabrication of ultrathin nanoporous membranes. The resulting cellulose nanoporous membranes have an adjustable thickness down to 23 nm and pore sizes ranging from 2.5 to 12 nm. They allow fast permeation of water and organics during pressure‐driven filtration. Typically, the 30 nm thick membrane has high fluxes of 1.14 and 3.96 × 10⁴ L h^?1 m^?2 bar^?1 for pure water and acetone respectively. Furthermore, the as‐prepared cellulose nanofibers are easily employed to produce a novel syringe filter with sub‐10 nm pores that have a wide application in fast separation and purification of nanoparticles on few‐nanometers scale.     

Use of Elastic,Porous, and Ultrathin Co-Culture Membranes to Control the Endothelial Barrier Function via Cell Alignment

Porous membranes used in co-culture enable the in vitro partitioning of cellular microenvironments, while still permitting physical and biochemical crosstalk between cells. Thus, features of the co-culture membrane are crucial for recapitulating the physiological functions of co-cultured cells. This study presents elastic, porous, and ultrathin membranes (EPUMs), which enhance cell–cell interactions and control cell alignment with surface topology created by stretching the membranes. The EPUM is fabricated using poly(lactide-co-caprolactone) as the base material, and the porous feature is endowed by a vapor-induced phase separation process induced by the presence of hygroscopic salt. Owing to its elastic property, the membrane can be stretched, and the deformed porous structures on the membrane surfaces act as nanostructured topographical cues, resulting in cell alignment. By co-culturing human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) on the opposite sides of the membrane, rapid endothelialization occurs through the membranes, as compared to the commercial membranes. Furthermore, the stretched membranes induce the alignment of hMSCs and HUVECs and ultimately exhibit enhanced endothelial barrier function. The co-culture membrane developed in this study may provide an effective tool for recapitulating endothelial basement membranes with a controllable endothelial barrier function.     

Infiltrating Semiconducting Polymers into Self‐Assembled Mesoporous Titania Films for Photovoltaic Applications

Interpenetrating networks of organic and inorganic semiconductors are attractive for photovoltaic cells because electron transfer between the two semiconductors splits excitons. In this paper we show that films of titania with a uniform distribution of pore sizes can be made using a block copolymer as a structure‐directing agent, and that 33 % of the total volume of the film can be filled with a semiconducting polymer.     

Lithium Extraction by Emerging Metal–Organic Framework-Based Membranes

Lithium is mainly extracted from brine and ores; however, current lithium mining methods require large amounts of chemicals, discharge many wastes, and can have serious environmental repercussions. Metal–organic framework (MOF)-based membranes have shown great potential in lithium extraction due to their uniform pore sizes, high porosities, and rich host–guest chemistry compared to other materials. In this review, the processes and disadvantages of current lithium extraction technologies are introduced. The structure features and corresponding design strategy of MOFs suitable for Li⁺ ion separations are presented. Following, recent advances of polycrystalline MOF membranes, mixed matrix membranes, and MOF channel membranes for lithium-ion separation are discussed in detail. Finally, opportunities for future developments and challenges in this emerging research field are presented.     

利用微运动分析仪研究MEMS器件的运动特性

介绍了一种计算机控制的微运动分析仪（MMA）,用来研究微机电系统（MEMS）中可动部件的运动特性。它采用了2种光学无损测量方法：计算机微视觉方法用于面内运动测量;相移干涉方法用于离面运动测量。这个高度集成的系统包括了高性能成像系统、驱动电路、数据采集和分析软件。MMA利用频闪照明方法冻结器件的快速运动,可以测量1Hz～10MHz频率的三维运动特性,达到了nm级分辨力。通过研究一个微加工多晶硅微谐振器的运动特性来说明MMA的强大功能。     

Evaluation of Packaging Effect on MEMS Performance: Simulation and Experimental Study

The thermal cure required for die attach during microelectro-mechanical systems (MEMS) packaging causes thermal mismatch that induces undesirable stresses and strains in surface micromachined structures, which may adversely affect the performance and reliability of the packaged component. Understanding the influence of the packaging process is, therefore, critical for successful device design. This paper analyzes the influence of the die attach process on the electromechanical behavior of doubly-anchored surface micromachined beams. A number of different adhesive materials were considered, and the results of parametric studies on the effects of die attach on the pull-in behavior of beams of various lengths, widths, and anchor types are presented. An upward shift in pull-in voltage of the studied devices was observed in both simulation and experiment; modelled and measured data were found to correlate closely.     

Design of Lange-couplers and single-sideband mixers usingmicromachining techniques

This paper reports on the design and performance of micromachined Lange-couplers and single-sideband mixers (SSB) on thin dielectric membranes at Ku-band. The micromachined Lange-coupler results in a 3.6±0.8 dB coupling bandwidth from 6.5 to 20 GHz. The Lange-coupler and an interdigital filter are used in a 17-GHz SSB. The SSB mixer requires 1-2 mW of local oscillator (LO) power without dc bias and achieves a 30 dB upper-sideband (USB) image rejection for an IF frequency of 1 GHz and above. The micromachined membrane technology can be easily scaled to millimeter-wave monolithic microwave integrated circuits (MMIC's) to meet the low-cost requirements in automotive or portable communication systems     

Surface Segregation and Self-Assembly of Block-Copolymer Separation Layers on Top of Homopolymer Substructures in Asymmetric Ultrafiltration Membranes from a Single Casting Step

Surface segregation in blended polymer films has attracted much interest in fundamental research as well as for practical applications. A variety of methodologies have been proposed for controlling surface segregation. They often require long annealing times, however, to achieve thermodynamic equilibrium. Here, a strategy and proof-of-principle experiments are described to control surface segregation of thin block-copolymer (BCP) layers on top of a homopolymer in a single casting step from blended BCP/homopolymer solutions. The surface coverage by the minor constituent BCP (2–10 wt%) is accomplished despite almost identical surface energies of BCP and homopolymer constituents. Immersing this casted solution into water for nonsolvent induced phase separation (NIPS), a nonequilibrium process, affords solidified bilayer ultrafiltration membranes composed of a thin porous surface layer of self-assembled BCP atop an asymmetric porous homopolymer substructure. Key to successful BCP surface segregation is the choice of a binary solvent system based on careful considerations of solvent surface energies and polymer-solvent interaction parameters. Furthermore, stabilizing the BCP micellar structure by a divalent metal additive is also essential. The approach provides a cost-effective method for fabricating bilayer-type asymmetric ultrafiltration membranes with uniform BCP self-assembly based selective top surface pore layers in a single casting step.     

Pattern transfer of microstructures between deeply etched surface for MEMS applications

Photolithography plays a vital role in micromachining process however; coating a thin and uniform resist layer on a non-planar surface is a challenging task for micro-electro-mechanical system (MEMS). Conventional spin coating of photoresist (PR) over an un-even surface would deliver streaks all over the wafer surface. Spray coating of PR is a promising technique when compared to other candidates. This paper presents an efficient pattern transfer of microstructures between the bulk micromachined cavities over silicon and glass wafers using an uncommon photoresist mixture being spray coated. The method is simple and highly cost effective. Finally we implemented this technique for a MEMS application to prove the feasibility of spray coating for microstructure fabrication.     

Acoustically actuated flextensional Si/sub x/N/sub y/ and single-crystal silicon 2-D micromachined ejector arrays

We propose using two-dimensional (2-D) micromachined droplet ejector arrays for environmentally benign deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics used in IC manufacturing. Direct deposition of these chemicals will reduce waste as well as production cost. The proposed device does not harm heat or pressure sensitive fluids and they are chemically compatible with the materials used in IC manufacturing. Each element of the 2-D ejector array consists of a flexurally vibrating circular membrane on one face of a cylindrical fluid reservoir. The membrane has an orifice at the center. A piezoelectric transducer generating ultrasonic waves, located at the open face of the reservoir, actuates the membranes. As a result of this actuation, droplets are fired through the membrane orifice. Ejector arrays were built with either Si/sub x/N/sub y/ or single-crystal silicon membranes using two different fabrication processes. We show that single-crystal silicon membranes are more uniform in their thickness and material quality than those of Si/sub x/N/sub y/ membranes. The single-crystal silicon membrane-based devices showed thickness and material uniformity across all the membranes of an array. This improvement eliminated nonuniform membrane resonance frequencies across an array as observed with Si/sub x/N/sub y/ membrane-based devices. Therefore, it should be possible to repeatably build devices and to predict their dynamic characteristics. Using the fabricated devices, we demonstrated water ejection at 470 kHz, 1.24 MHz, and 2.26 MHz. The corresponding droplet diameters were 6.5, 5, and 3.5 /spl mu/m, respectively.     

Hydrothermally Robust Molecular Sieve Silica for Wet Gas Separation

A major challenge in silica membranes for gas separation is to maintain a robust pore structure in the presence of steam. In this work, use of a carbonized template is proposed to reduce damage to the pore structure by inhibiting silica migration along the membrane pore surface. This departs from the conventional wisdom of creating hydrophobic surfaces to achieve hydrostability. The carbonized‐template molecular sieve silica (CTMSS) membranes can then be applied to clean‐energy systems such as hydrogen separation and carbon dioxide sequestration, and membrane reactors where steam is present.     

Ultra-high-resolution scanning electron microscopy of vaccinia virus and its recombinant carrying the gag gene of human immunodeficiency virus type 1.

FL cells infected with vaccinia virus or its recombinant carrying the gag gene of human immunodeficiency virus type 1 (HIV-1) were examined by ultra-high-resolution scanning electron microscopy. Virions, whether located extracellularly or intracellularly, had a brick-shaped or watermelon appearance as a whole. Extracellular virions observed on the surface of infected cells had variable surface ultrastructures depending on the manner in which particular virions were wrapped in cell membranes. Most of the intracellular naked virions adherent to the inner face of cell surface membranes clearly exhibited ridgy, rod-shaped or globular surface structures on their surface. HIV-like particles with a diameter of about 100 nm and virions of vaccinia virus were both observed distinctly on the surface of FL cells infected with the recombinant virus.     

Flexible,Mechanically Stable,Porous Self-Standing Microfiber Network Membranes of Covalent Organic Frameworks: Preparation Method and Characterization

Covalent organic frameworks (COFs) show advantageous characteristics, such as an ordered pore structure and a large surface area for gas storage and separation, energy storage, catalysis, and molecular separation. However, COFs usually exist as difficult-to-process powders, and preparing continuous, robust, flexible, foldable, and rollable COF membranes is still a challenge. Herein, such COF membranes with fiber morphology for the first time prepared via a newly introduced template-assisted framework process are reported. This method uses electrospun porous polymer membranes as a sacrificial large dimension template for making self-standing COF membranes. The porous COF fiber membranes, besides having high crystallinity, also show a large surface area (1153 m² g⁻¹), good mechanical stability, excellent thermal stability, and flexibility. This study opens up the possibility of preparation of large dimension COF membranes and their derivatives in a simple way and hence shows promise in technical applications in separation, catalysis, and energy in the future.     

Hydroxyapatite/Mesoporous Graphene/Single‐Walled Carbon Nanotubes Freestanding Flexible Hybrid Membranes for Regenerative Medicine

Freestanding flexible membranes based on biocompatible calcium phosphates are of great interest in regenerative medicine. Here, the authors report the first synthesis of well‐aligned biomimetic hexagonal bars of hydroxyapatite (HAp) on flexible, freestanding mesoporous graphene/single‐walled carbon nanotubes (MG/SWCNT) hybrid membranes. The chemical composition and surface morphology of the HAp coating resemble those of biological apatite. Nitrogen doping and oxygen plasma etching of the MG/SWCNT membranes increase the density of nucleation sites and yield more uniform coatings. This novel membrane favors the attachment and proliferation of human fetal osteoblast (hFOB) osteoprogenitor cells. When soaked in simulated body fluid, enhanced in vitro biomineralization occurs on the hybrid membranes. This hybrid membrane holds great promise in biomedical applications such as patches and strips for spine fusion, bone repair, and restoration of tooth enamel.     

Characterization of novel mono- and bifacially activesemi-transparent crystalline silicon solar cells

This paper presents the latest cell results for semi-transparent mono- as well as bifacially active POWER (Polycrystalline Wafer Engineering Result) solar cells of different cell sizes on Cz and multicrystalline silicon substrates. Top efficiencies of 10.4% for monofacial and 12.9% for bifacial cells are reported. Attention has been paid to apply a fully industrially compatible production process. It uses dicing saw based mechanical texturization of the front and rear side of the silicon wafer and screen printing metallization. In the POWER solar cell concept, perpendicular grooves on the front and rear side create holes with a variable diameter at their crossing points. This results in a partial optical transparency of the solar cell. In this study, holes of 200 μm diameter lead to a transparency of 16-18% on average for the total cell area. The cell characteristics for the different cell types are compared by means of illuminated and dark current-voltage (I-V), spectral response, and Laser Beam Induced Current (LBIC) measurements. While bifacial POWER cells need a more elaborate production process, they reveal better I-V characteristics and a higher efficiency as compared to monofacial cells. This is mainly explained by a better surface passivation due to an active emitter and a passivating silicon nitride ARC both on the front and rear surface