Materials science: the key to revolutionary breakthroughs in micro-fluidic devices

In microfluidics, valves and pumps that can combine specifications like precise flow control, provision of precise reagent quantities, minimal sample carryover, and low-cost manufacture, while also being inherently compatible with microfluidic system fabrication, are beyond the current state of the art. Actuators in micro-fluidics made using stimuli-responsive materials are therefore of great interest as functional materials since actuation can be controlled without physical contact, offering improvements in versatility during manifold fabrication, and control of the actuation mechanism. Herein we review the potential use of novel approaches to valving and pumping based on stimuli-responsive polymers for controlling fluid movement within micro-fluidic channels. This has the potential to dramatically simplify the design, fabrication and cost of microfluidic systems. In particular, stimuli-responsive gels incorporating ionic liquids (ILs) produce so-called ‘ionogels’ that have many advantages over conventional materials. For example, through the tailoring of chemical and physical properties of ILs, robustness, acid/ base character, viscosity and other critical operational characteristics can be finely adjusted. Therefore, the characteristics of the ionogels can be tuned by simply changing the IL and so the actuation behaviour of micro-valves made from these novel materials can be more closely controlled

Electromechanical properties of suspended Graphene Nanoribbons

Graphene nanoribbons present diverse electronic properties ranging from semiconducting to half-metallic, depending on their geometry, dimensions and chemical composition. Here we present a route to control these properties via externally applied mechanical deformations. Using state-of-the-art density functional theory calculations combined with classical elasticity theory considerations, we find a remarkable Young's modulus value of ~7 TPa for ultra-narrow graphene strips and a pronounced electromechanical response towards bending and torsional deformations. Given the current advances in the synthesis of nanoscale graphene derivatives, our predictions can be experimentally verified opening the way to the design and fabrication of miniature electromechanical sensors and devices based on ultra-narrow graphene nanoribbons.Comment: 12 pages, 6 figure

Growth of catalyst-free high-quality ZnO nanowires by thermal evaporation under air ambient

ZnO nanowires have been successfully fabricated on Si substrate by simple thermal evaporation of Zn powder under air ambient without any catalyst. Morphology and structure analyses indicated that ZnO nanowires had high purity and perfect crystallinity. The diameter of ZnO nanowires was 40 to 100 nm, and the length was about several tens of micrometers. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The growth of the ZnO nanostructure was explained by the vapor-solid mechanism. The simplicity, low cost and fewer necessary apparatuses of the process would suit the high-throughput fabrication of ZnO nanowires. The ZnO nanowires fabricated on Si substrate are compatible with state-of-the-art semiconductor industry. They are expected to have potential applications in functional nanodevices

3D printing: Principles and pharmaceutical applications of selective laser sintering

Pharmaceutical three-dimensional (3D) printing is a modern fabrication process with the potential to create bespoke drug products of virtually any shape and size from a computer-aided design model. Selective laser sintering (SLS) 3D printing combines the benefits of high printing precision and capability, enabling the manufacture of medicines with unique engineering and functional properties. This article reviews the current state-of-the-art in SLS 3D printing, including the main principles underpinning this technology, and highlights the diverse selection of materials and essential parameters that influence printing. The technical challenges and processing conditions are also considered in the context of their effects on the printed product. Finally, the pharmaceutical applications of SLS 3D printing are covered, providing an emphasis on the advantages the technology offers to drug product manufacturing and personalised medicine

Moisture-triggered physically transient electronics

Physically transient electronics, a form of electronics that can physically disappear in a controllable manner, is very promising for emerging applications. Most of the transient processes reported so far only occur in aqueous solutions or biofluids, offering limited control over the triggering and degradation processes. We report novel moisture-triggered physically transient electronics, which exempt the needs of resorption solutions and can completely disappear within well-controlled time frames. The triggered transient process starts with the hydrolysis of the polyanhydride substrate in the presence of trace amounts of moisture in the air, a process that can generate products of corrosive organic acids to digest various inorganic electronic materials and components. Polyanhydride is the only example of polymer that undergoes surface erosion, a distinct feature that enables stable operation of the functional devices over a predefined time frame. Clear advantages of this novel triggered transience mode include that the lifetime of the devices can be precisely controlled by varying the moisture levels and changing the composition of the polymer substrate. The transience time scale can be tuned from days to weeks. Various transient devices, ranging from passive electronics (such as antenna, resistor, and capacitor) to active electronics ( such as transistor, diodes, optoelectronics, and memories), and an integrated system as a platform demonstration have been developed to illustrate the concept and verify the feasibility of this design strategy

Computer Aspects of Solid Freeform Fabrication: Geometry, Process Control, and Design

Solid Freefonn Fabrication (SFF) is a class of manufacturing technologies aimed at the production of mechanical components without part-specific tooling or process planning. Originally used for creating modelsfor visualization, many industrial users of SFF technologies are realizing the greater potentialofSFF as legitimate manufacturing processes for producing patterns and, in some cases, functional.parts. Thus, SFF is becoming an important aspect of the product realization process in these industries. Solid Freefonn Fabrication arose from the dream of "push-button" prototyping, in which solid reproductions of three-dimensional geometric models are created automatically under computer control. Perhaps more than any other class of manufacturing technologies, computer software development has been an integral part of the emergence of SFF. As SFF technologies evolve toward the ability to create functional parts, computer issues gain more importance. This paper discusses three aspects of software design for SFF: processing of geometric data, global and local control of SFF processes, and computer-based analysis and design for SFF manufacturing. The discussion of geometric processing issues focuses on accuracy and completeness of input models, and the algorithms required to process such models. The interplay between the physics of SFF processing and the desired output geometry is discussed in terms of the development of model-based control algorithms for SFF. These two areas, geometric processing and control, are necessary for the practical implementation of any SFF technology. However, for SFF to realize its potential as an alternative for manufacturing functional parts, engineers must be provided with analysis and design tools for predicting mechanical properties, ensuring dimensional accuracy, choosing appropriate materials, selecting process parameter values, etc. For each of these three different but related areas of software design, the state-of-theart is assessed, contemporary research is summarized, and future needs are outlined.Mechanical Engineerin