Micro and Nanosystems - Volume 3, Issue 4, 2011

Nature through evolution of life over billion years has evolved biological systems and materials with high performance and unique properties from the macro to the nanoscale. These materials created by unique biologically mediated self-assembled processes and adaptability optimized through evolution have many remarkable properties including sophistication, multifunction, hierarchical organizations, hybridisation. Biologically inspired design of materials, processes and systems refereed as “biomimetics” is at the frontier between biological and material sciences, chemistry, physics, engineering and biotechnology and represent one of the most promising scientific and technological challenges in this century. Elucidating these properties, their building principles and functions is emerging multidisciplinary research field with perspective to build a bridge between biology and technology and solve today's most critical problems such as energy, health and sustained environment. The potential of these materials has inspired scientists and engineers to synthetise numerous new materials and devices using a biomimetic or bio-inspired approach. Successful examples include cat eye reflectors, gecko-like fasteners, self-cleaning lotus leaf-like surfaces, low-weight wood-like composite materials, butterfly-like antireflective coatings and opal effect pigments, self-repair plastics, bionic medical implants, and tissue repair. In this context the focus of this special issue on Bio-inspired Micro and Nanosystem is to show some recent advances on several specific aspects based on the physical, chemical, biological and biotechnological approaches. The issue is composed of selected contributions from recognised experts in this field presenting some of the most outstanding examples of nature's creations used for inspirational design of new materials and devices. Bioinspiration is a highly promising method in the design of emerging MEMS/NEMS with enhanced tribological properties and the paper by Ille C. Gebeshuber et al. introduces a new way to analyse best practice biological materials, structures and processes that were established via the biomimicry innovation method, by relating them to four main areas relevant for MEMS and related microsystems development: dynamic, mechanic, surface and structure related functions. Diatoms, single-cell photosynthetic algae (Bacillariophyta), are one of the most outstanding examples of 3-d micro to nano structured materials generated in nature showing unique optical, photonic, mechanical and sorting properties. A new multidisciplinary research field called diatom nanotechnology has recently emerged and review by M. D. Kurkuri et al. highlights some of recent applications based on the integration of micro and nanostructures including sensing/biosensing, drug delivery and chemical-free pest control.....

Tribology deals with parts in relative motion, and related friction, adhesion, lubrication and wear phenomena. With our devices getting smaller and smaller, our understanding of tribology on the small scale has to increase. Microand nanotribology denotes tribology performed with micro- and nanotechnological instruments. This field is still in a developmental stage, and establishing the relation and interdependence between tribological knowledge and understanding on the macro-, micro- and nanoscales is a hot topic of research. Because of scaling and other issues, we cannot directly translate long-established tribological facts to small-scale technologies. However, we can immediately benefit from input concerning established ‘best practice’ systems in nature: organisms. Biological micro- and nanosystems show interesting tribological features, and furthermore can teach us novel aspects and possible approaches concerning our emerging technology that would not readily come to mind - here lies their enormous innovation potential. This manuscript introduces a new way to analyse best practice biological materials, structures and processes that were established via the biomimicry innovation method, by relating them to four main areas relevant for MEMS and related microsystems development: dynamic, mechanical, surface and structure related functions. Four representative examples for each of these four areas are presented, along with generated process and product ideas, in the concept stage or already on the market. Furthermore, this manuscript introduces reasons for a balanced mixture of problem-oriented and solution-oriented biomimetics innovation methods regarding tribology in technical micro- and nanotribological devices that ensures maximum benefit regarding revenue, innovation and sustainability.

The unique morphologies and properties of the diatom silica shell with its intricate, hierarchically organized three dimensional (3-D) structures with nanoscale dimensions have attracted considerable interest in materials science and nanotechnology in recent years. This review highlights recent emerging applications from diatom nanotechnology research with particular emphasis on applications based on the integration of micro and nanostructures including sensing/ biosensing, drug delivery and chemical-free pest control.

In medicine, objects that need to be removed later - such as stents - are commonly placed in patients, with the time of removal dependent on progress of the patient. In these cases biodegradable materials that last for a specific time may not be suitable. We propose a new class of nanostructured materials that can hold their form as long as wanted, Triggered, Nanostructured Biodegradables (TNBs), that can be disintegrated to micro- or nanoscaled components when externally triggered on command to do so. DNA nanotensegrity microstructures, metastable foams, nanobots and other bioinspired disintegratable scaffold structures are given as potential examples.

The design of a microfluidic nanoporous reflective interferometric (RIfS) sensor is presented. The key element of the sensor is a highly ordered nanoporous structure of anodic aluminium oxide (AAO) integrated into a microfluidic chip and combined with an optical fibre spectrophotometer and notebook computer. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at 50V for 40 minutes. The performance of the microfluidic RIfS for sensing of surface binding reaction of alkanethiols (mercapto undecanoic acid) on gold is evaluated showing excellent sensitivity. The results show potential for development and application of interferometric label-free biosensing elements for a wide range of biomedical applications.

This study is motivated by the need to develop a semi analytical model for predicting the stratified two-fluid flow with a curved interface in a rectangular microchannel under the combined effect of pressure and electroosmosis. With the non-slip boundary conditions at the wall and the matching condition at the curved interface, the fully developed Navier-Stokes equation and Poisson-Boltzmann equation are solved using separate variable method. Part of parameters in the distributions of velocity and electric potential is calculated using the least-square method. Details of the analytical treatment of the two-fluid flow with curved interface are presented. The results show that the analysis can be employed for concave, convex and planar interface. The validity of the two-fluid model with curved interface is evaluated by comparing its prediction with available numerical data and with the results of exact analytical solutions for laminar flows with planar interface, comparison of the electric potential distribution and velocity distributions shows excellent agreement with data in the literature. Finally, the effects of interface shape on the electric potential distribution, electroosmotic velocity distribution, and flow rates are discussed, the results show that the interface shape influences the two-fluid flow in microchannel significantly.

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In this work we have successfully fabricated & assembled free Gold nanoparticles (diameter 8-10nm) into micron size structured network (with unbroken lengths often more than few microns) by the bottom up method through the process of PEGylation. This was done using only a solid metallic Au target, MEG (Mono Ethylene Glycol) (combined with DI water with fixed proportion) and a pulsed excimer laser (λ=248nm). The Au networked structure formed in liquid medium is mechanically as well as thermally stable and can be transferred unchanged into a solid substrate which can span a large surface area. The nanochains show a broad optical absorption covering almost the complete visible spectrum. NMR analysis was carried out to understand the formation mechanism of these chains. The process reported does not use any precursor, reducing agent or surfactant and thus can be described as one pot synthesis route and the complete synthesis can be done well within few minutes and instantly br ready to use as there is no further processing is required. It is also biocompatible (as Gold, PEG are non toxic materials for living beings) so can be functionalised and used inside the body for various purposes. This method can be used in mass production of such network structures.

For silicon direct bonding SOI accelerometers, due to the stress in device layer, there is vertical deformation in proof-mass, which can make the accelerometers fail to work. In the light of mechanics theory and by dividing the proof - mass into several continuous varied cross-section beams, utilizing symmetric continuous conditions of the beams, and combining deformation compatibility, a vertical deformation mechanics model of proof-mass is proposed. The validity of the model is demonstrated by measuring the experimental structures with SOI device layer 50 μm and oxide layer 5 μm. The model could hopefully be helpful in further exploration on deformation of MEMS structure.

This paper reviews the most recent advances in the formulation of materials for H2 storage. A revision of the goals for such materials, with relevance to the transportation issues is given. The objectives are indeed stringent as for gravimetric and volumetric density, as well as for the stability to repeated loading cycles. The attention will be particularly focused on micro- and nanoporous sorbents, where a proper design of pore size is important to optimize capacity and the energetics of the sorbent/sorbate interaction. Furthermore, the same parameter, together with particle size is important to minimize mass transfer limitations and to improve diffusion kinetics. The latter may be increased also by functionalization, e.g. with metallic nanoparticles. Examples will be provided mainly pointing to carbon based materials, to novel inorganic compounds and to metal organic frameworks or coordination polymers. These different subjects will be considered from the points of view of the synthesis/functionalization, of their performance, predominantly under practically relevant conditions. Some references will be also given regarding theoretical issues, e.g. in the case of graphene-like materials. Finally the research issues to be rapidly solved to propose a convenient material to the fuel cells market will be addressed.

Electromagnetic vacuum fluctuations underlie the van der Waals and Casimir forces, which dominate much of the dynamics at the nanoscale. Here we propose a means to harness these forces to transmit intense, high-frequency mechanical pressure and power between surfaces across pure vacuum. Potentially large power densities (P>108 W/m2) should be sufficient to acoustically probe or heat bulk samples; to melt, vaporize and chemically alter surfaces. Power deposition can be made highly local, perhaps down to tens of square nanometers, thereby permitting new kinds of nanoscale microscopy, lithography, machining, and chemical manufacturing. Tests of this Hamaker hammer effect appear possible using inexpensive, off-the-shelf technology.

A planar micro spark gap switch was designed and fabricated on a quartz (or glass) wafer using the surface micromachining based on non-silicon surface micromachining technology. It consists of two arc main electrodes and a thin strip, a triggered electrode. The gap distance between two main electrodes is 800μm. The switch is integratable for its micron size and its cost is reduced profiting from MEMS technology. The designed switch has been optimized and tested. By decreasing spark gap length of the main gap and increasing discharge density of the triggering gap, it gives out a pulse current with peak of 7173.91A and 74ns rise time. The pulse peak current is about 3 times larger than that of the schottky diode one-shot switch reported and the pulse rise time is less than it.