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Microparticles (yeast cells) in flowing suspensions have been concentrated in bands in pressure nodal planes of a standing wave chamber driven at resonant frequencies ranging from its thickness fundamental of 0.66 MHz to its 15th harmonic. An outlet laminar flow expansion chamber preserves particle order for many centimeters downstream from the transducer. The 10 mm outlet width has the potential to facilitate the separation of concentrated microparticles from the clarified inter-band suspending phase, while the high frequencies utilised will allow manipulation of smaller microparticles.

Biomicroelectromechanical systems (bio-MEMS) are MEMS which are designed for medical or biological applications. As with other MEMS, bio-MEMS frequently, have to be packaged to provide an interface to the macroscale world of the user. Bio-MEMS can be roughly divided in two groups. Bio-MEMS can be pure technical systems applied in a biological environment or technical systems which integrate biological materials as one functional component of the system. In both cases, the materials which have intimate contact to biological matter have to be biocompatible to avoid unintentional effects on the biological substances, which in case of medical implants, could harm the patient. In the case of biosensors, the use of nonbiocompatible materials could interfere with the biological subcomponents which would affect the sensor's performance. Bio-MEMS containing biological subcomponents require the use of "biocompatible" technologies for assembly and packaging; e.g., high temperatures occurring, for instance, during thermosonic wire bonding and other thermobonding processes would denature the bioaffinity layers on biosensor chips. This means that the use of selected or alternative packaging and assembly methods, or new strategies, is necessary for a wide range of bio-MEMS applications. This paper provides an overview of some of the strategies, technologies, and applications in the field of bio-MEMS packaging. It includes the following: strategies for the partitioning of subsystems within integrated microsystems for (bio)chemical analysis/synthesis; methods for microassembly of bio-MEMS; technologies for bonding of polymer bio-MEMS components; packaging of miniature medical devices; packaging of biosensors for in vitro applications; packaging of micropumps as a bio-MEMS component. The applications discussed are derived from different fields to demonstrate the plethora of bio-MEMS considerations. In commercial production, packaging is possibly the major cost factor of bio-MEMS-based products, and its development requires special attention.

Summary Background The skin represents an accessible somatic tissue for therapeutic gene transfer. The superficial lipophilic layer of the skin, the stratum corneum, however, constitutes a major obstacle to the cutaneous delivery of charged macromolecules such as DNA. Objectives To determine whether silicon-based microneedles, microfabricated via a novel isotropic etching/BOSCH reaction process, could generate microchannels in the skin of sufficient dimensions to facilitate access of lipid : polycation : pDNA (LPD) nonviral gene therapy vectors. Methods Scanning electron microscopy was used to visualize the microconduits created in heat-separated human epidermal sheets after application of the microneedles. Following confirmation of particle size and particle surface charge by photon correlation spectrocopy and microelectrophoresis, respectively, the diffusion of fluorescent polystyrene nanospheres and LPD complexes through heat-separated human epidermal sheets was determined in vitro using a Franz-type diffusion cell. In-vitro cell culture with quantification by flow cytometry was used to determine gene expression in human keratinocytes (HaCaT cells). Results The diffusion of 100 nm diameter fluorescent polystyrene nanospheres, used as a readily quantifiable predictive model for LPD complexes, through epidermal sheets was significantly enhanced following membrane treatment with microneedles. The delivery of LPD complexes either into or through the membrane microchannels was also demonstrated. In both cases considerable interaction between the particles and the epidermal sheet was observed. In-vitro cell culture was used to confirm that LPD complexes mediated efficient reporter gene expression in human keratinocytes in culture when formulated at the appropriate surface charge. Conclusions These studies demonstrate the utility of silicon microneedles in cutaneous gene delivery. Further studies are required to elucidate fully the influence of the physicochemical characteristics of gene therapy vectors, e.g. particle diameter and surface charge, on their diffusion through microchannels and to quantify gene expression in vivo.

Microchip based Solid-Phase-Extraction (SPE) manifold cartridges were fabricated by Deep Reactive Ion Etching (DRIE) of silicon and packaged in a polymeric housing. Restraining pillars within the manifold system allowed 5 micron packing material to be incorporated. Computational Fluid Dynamics (CFD) simulations of fluid flow around restraining pillars and experimental packing demonstrated that neither pillar geometry nor layout were critical for effective packing but were influential on sample absorption and elution.

The use of ultrasonic technologies to trap and filter desired particulates from a suspending media has been well documented to date. Recent advancements in microsystems and micro-fluidic technology have enabled the design of a miniaturised ultrasonic particle separation unit. The automated microsystem enables contact-less microprocessing operations to be conducted on small volumes of fluid suspensions in remote environments. Furthermore, the protocol for particle separation is simplified and reduces the need for operator handling. The microfabricated ultrasonic separator sub-system is combined with micro-fluidic components (valves, pumps, flow sensors) manifold systems and surface mount interface electronics to monitor and control the system's function. The operational function of the system utilises two reservoirs; (i) a pre-process reservoir containing crude sample extract, and (ii) a second reservoir holding wash media. During operation, a crude sample is channelled into the membrane-less filter system and manipulated by ultrasonic sound waves. Wash media is subsequently pumped into the filter, replacing or diluting the support media of the original sample. The sample is then removed, when desired, into a post-processing reservoir. The system has been developed for space micro-gravity operations and other configurations are applicable to other terrestrial processing applications.

Herein we present a device for performing non-contact dielectric spectroscopy upon liquids in a microfluidic environment. The device is comprised of a compression-sealed, micromilled polytetrafluoroethylene (PTFE) chip with an embedded GHz-frequency coaxial resonator. The resonator is overmoded, allowing dielectric measurements at six discrete frequencies between 1 and 8 GHz. A novel electromagnetic coupling structure allows transmission measurements to be taken from one end of the resonator, which yields a large dynamic range; provides coupling to all modes, and allows easy integration with the fluidic circuitAn optimised microchannel design maximises sensitivity and repeatability. A simple ‘fingerprint’ method for identifying solvents is demonstrated, whereby a sample is characterised by air-referenced changes in centre frequency and bandwidth of the first six modes of the device. Complex permittivity values are also obtained from these measurements according to a perturbation theory-based inversion, and are quantified for a variety of common solvents. A combination of experimental and simulated results is used to characterise the device behaviour, limits of operation and measurement uncertainty. The error of the fingerprint method is five orders of magnitude lower than the measured changes in frequency, and the uncertainty of the complex permittivity values is < 2%. The high stability of temporal measurements, coupled with the robustness of the design, make this device ideal for analytical chemistry and industrial process control.

The stratum corneum (SC) represents a significant barrier to the delivery of gene therapy formulations. In order to realise the potential of therapeutic cutaneous gene transfer, delivery strategies are required to overcome this exclusion effect. This study investigates the ability of microfabricated silicon microneedle arrays to create micron-sized channels through the SC of ex vivo human skin and the resulting ability of the conduits to facilitate localised delivery of charged macromolecules and plasmid DNA (pDNA). Microscopic studies of microneedle-treated human epidermal membrane revealed the presence of microconduits (10-20 microm diameter). The delivery of a macromolecule, beta-galactosidase, and of a 'non-viral gene vector mimicking' charged fluorescent nanoparticle to the viable epidermis of microneedle-treated tissue was demonstrated using light and fluorescent microscopy. Track etched permeation profiles, generated using 'Franz-type' diffusion cell methodology and a model synthetic membrane showed that >50% of a colloidal particle suspension permeated through membrane pores in approximately 2 hours. On the basis of these results, it is probable that microneedle treatment of the skin surface would facilitate the cutaneous delivery of lipid:polycation:pDNA (LPD) gene vectors, and other related vectors, to the viable epidermis. Preliminary gene expression studies confirmed that naked pDNA can be expressed in excised human skin following microneedle disruption of the SC barrier. The presence of a limited number of microchannels, positive for gene expression, indicates that further studies to optimise the microneedle device morphology, its method of application and the pDNA formulation are warranted to facilitate more reproducible cutaneous gene delivery.

The aim of the current work is to develop a new, high frequency (12 MHz) system where microfabrication techniques are employed to construct a high Q, resonant chamber with resulting high values for the standing wave acoustic pressure amplitude. The long-term goal is to develop a microfabricated acoustic cavity for the manipulation of nanoparticles (in suspension) which is gravity and orientation free in functionality and independent of particulate concentration. This will provide a generic technology for a diversity of fields of application.