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Within the scope of the European Horizon 2020 project ACDC – Artificial Cells with Distributed Cores to Decipher Protein Function, we aim at the development of a chemical compiler governing the three-dimensional arrangement of droplets, which are filled with various chemicals. Neighboring droplets form bilayers containing pores through which chemicals can move from one droplet to its neighbors. When achieving a desired three-dimensional configuration of droplets, we can thus enable gradual biochemical reaction schemes for various purposes, e.g., for the production of some desired macromolecules for pharmaceutical purposes. In this paper, we focus on geometric restrictions to possible arrangements of droplets. We present analytic results for the buttercup problem and a heuristic optimization method for the kissing number problem, which we then apply to find (quasi) optimum values for a bidisperse kissing number problem, in which the center sphere exhibits a larger radius.

We aim at planning and creating specific agglomerations of droplets to study synergic communication using these as programmable units. In this paper, we give an overview of preliminary obstacles for the various research issues, namely of how to create droplets, how to set up droplet agglomerations using DNA technology, how to prepare them for confocal microscopy, how to make a computer see droplets on photos, how to analyze networks of droplets, how to perform simulations mimicking experiments, and how to plan specific agglomerations of droplets.

We simulate the movement and agglomeration of oil droplets in water under constraints, like confinement, using a simplified stochastic-hydrodynamic model. In the analysis of the network created by the droplets in the agglomeration, we focus on the paths between pairs of droplets and compare the computational results for various system sizes.

Within the context of the European Horizon 2020 project ACDC, we intend to develop a probabilistic chemical compiler, to aid the construction of three-dimensional agglomerations of artificial hierarchical cellular constructs. These programmable discrete units offer a wide variety of technical innovations, like a portable biochemical laboratory that e.g. produces macromolecular medicine on demand. For this purpose, we have to investigate the agglomeration process of droplets and vesicles under proposed constraints, like confinement. This paper focuses on the influence of the geometry of the initialization and of the container on the agglomeration.

Anticancer drug development is a crucial step toward cancer treatment, that requires realistic predictions of malignant tissue development and sophisticated drug delivery. Tumors often acquire drug resistance and drug efficacy, hence cannot be accurately predicted in 2D tumor cell cultures. On the other hand, 3D cultures, including multicellular tumor spheroids (MCTSs), mimic the in vivo cellular arrangement and provide robust platforms for drug testing when grown in hydrogels with characteristics similar to the living body. Microparticles and liposomes are considered smart drug delivery vehicles, are able to target cancerous tissue, and can release entrapped drugs on demand. Microfluidics serve as a high‐throughput tool for reproducible, flexible, and automated production of droplet‐based microscale constructs, tailored to the desired final application. In this review, it is described how natural hydrogels in combination with droplet microfluidics can generate MCTSs, and the use of microfluidics to produce tumor targeting microparticles and liposomes. One of the highlights of the review documents the use of the bottom‐up construction methodologies of synthetic biology for the formation of artificial cellular assemblies, which may additionally incorporate both target cancer cells and prospective drug candidates, as an integrated “droplet incubator” drug assay platform., This review summarizes the recent progress of droplet technologies in anticancer drug development. Microfluidic‐formed droplets are utilized in both tumor spheroid formation and smart drug delivery. This work also highlights the current trend of using artificial cells materials for drug metabolism studies. Finally, a novel ‘droplet incubator’ concept as a prospective anticancer drug screening platform is introduced.

The bottom‐up construction of synthetic cells with user‐defined chemical organization holds considerable promise in the creation of bioinspired materials. Complex emulsions, droplet networks, and nested vesicles all represent platforms for the engineering of segregated chemistries with controlled communication, analogous to biological cells. Microfluidic manufacture of such droplet‐based materials typically results in radial or axisymmetric structures. In contrast, biological cells frequently display chemical polarity or gradients, which enable the determination of directionality, and inform higher‐order interactions. Here, a dual‐material, 3D‐printing methodology to produce microfluidic architectures that enable the construction of functional, asymmetric, hierarchical, emulsion‐based artificial cellular chassis is developed. These materials incorporate droplet networks, lipid membranes, and nanoparticle components. Microfluidic 3D‐channel arrangements enable symmetry‐breaking and the spatial patterning of droplet hierarchies. This approach can produce internal gradients and hemispherically patterned, multilayered shells alongside chemical compartmentalization. Such organization enables incorporation of organic and inorganic components, including lipid bilayers, within the same entity. In this way, functional polarization, that imparts individual and collective directionality on the resulting artificial cells, is demonstrated. This approach enables exploitation of polarity and asymmetry, in conjunction with compartmentalized and networked chemistry, in single and higher‐order organized structures, thereby increasing the palette of functionality in artificial cellular materials., Polarized artificial cells are created by 3D‐microfluidics. Multi‐material 3D‐printed microfluidics is used to create hierarchical droplet assemblies, where 3D‐channel geometries enable asymmetric and polarized patterning in droplet assemblies. These materials contain lipid‐bilayer‐segregated droplet networks and integrate patterned organic and inorganic components. Polarized patterning with magnetic microparticles bestows directional properties and motion in aqueous environments, with constructs exhibiting simple group‐level behaviors.

In article number https://doi.org/10.1002/advs.201901719, David Anthony Barrow, Oliver Kieran Castell, and co‐workers create polarized artificial cells from compartmentalized droplet networks and nanomaterials, using multi‐material, 3D‐printed fluidics. Polarized patterning with magnetic microparticles bestow directional properties and motion in aqueous environments, with artificial cells exhibiting simple group‐level behaviors.

The ability to make artificial lipid bilayers compatible with a wide range of environments, and with sufficient structural rigidity for manual handling, would open up a wealth of opportunities for their more routine use in real‐world applications. Although droplet interface bilayers (DIBs) have been demonstrated in a host of laboratory applications, from chemical logic to biosynthesis reaction vessels, their wider use is hampered by a lack of mechanical stability and the largely manual methods employed in their production. Multiphase microfluidics has enabled us to construct hierarchical triple emulsions with a semipermeable shell, in order to form robust, bilayer‐bound, droplet networks capable of communication with their external surroundings. These constructs are stable in air, water, and oil environments and overcome a critical obstacle of achieving structural rigidity without compromising environmental interaction. This paves the way for practical application of artificial membranes or droplet networks in diverse areas such as medical applications, drug testing, biophysical studies and their use as synthetic cells.

Computerized tomography scan (CT scan) imaging and finite element analysis were employed to investigate how the geometric composition of microneedles affects their mechanical strength and penetration characteristics. Simulations of microneedle arrays, comprising triangular, square and hexagonal microneedle base, revealed a linear dependence of the mechanical strength to the number of vertices in the polygon base. A laser-enabled, micromoulding technique was then used to fabricate 3 × 3 microneedle arrays, each individual microneedle having triangular, square or hexagonal base geometries. Their penetration characteristics into ex-vivo porcine skin, were investigated for the first time by CT scan imaging. This revealed greater penetration depths for the triangular and square-based microneedles, demonstrating CT scan as a powerful and reliable technique for studying microneedle skin penetration.

Microneedle technology offers a viable means of delivering biologically active pharmaceutical agents across the skin in a minimally invasive and virtually pain free manner. Previous work detailed the first successful transdermal delivery of a model peptide drug, polymyxin b, utilising a dissolving polymer-based microneedle system. The focus of this study was to examine the ability of a dissolving microneedle system to deliver a range of peptides of different sizes and properties. Analogue versions of 2 existing therapeutic peptides; pentagastrin and sincalide, were synthesised utilising Fmoc based solid phase peptide synthesis (SPPS) chemistry techniques and once successfully synthesised and purified, the peptide analogues were characterised using LC-MS. The peptide analogues were then incorporated into PVP/trehalose microneedle formulations. Skin permeation testing, in addition to skin penetration testing, was carried out to determine the effectiveness of the microneedle system to deliver the peptide analogues through porcine skin. The results obtained from these studies were then compared with the permeation results obtained utilising polymyxin B as the peptide drug cargo to evaluate the PVP/trehalose microneedle system's suitability to successfully deliver therapeutic peptides. Results indicated that the microneedle system successfully systemically delivered a higher overall percentage of the encapsulated peptides at an initially faster rate than peptide loaded control discs and in therapeutically relevant concentrations.

In this paper, a new type of microwave microfluidic sensor is proposed to detect and determine the dielectric properties of common liquids. The technique is based on perturbation theory, in which the resonant frequency and quality factor of the microwave resonator depend on the dielectric properties of the resonator. A microstrip split-ring resonator with two gaps is adopted for the design of the sensors (i.e., a double split-ring resonator). This resonator is both compact and planar, making it suitable for a lab-on-a-chip approach. Several types of solvents are tested with two types of capillaries to verify sensor performance. At 3 GHz, very good agreement is demonstrated between simulated and measured results.

We present a method of making low-loss split-ring resonators (SRRs) for microfluidic sensing at microwave frequencies using silver-coated copper wire. We show that a simple geometric modification and the use of square cross-section wire give greater electric field confinement in the capacitive region of the resonant sensor. We use a combination of theoretical analysis, finite-element simulations, and empirical measurements to demonstrate the subsequent increases in the sensitivity of these SRRs for complex permittivity measurements of some common solvents.

This paper presents a 2.45 GHz microwave cavity resonator with the novel dual function of both sensitive dielectric characterisation and directed, volumetric heating of fluids in a microfluidic chip. This method is shown to have a higher efficiency (> 90% for methanol) than previous microfluidic microwave heating methods and can regulate heating using real time cavity characterisation. The system is simple, robust and does not require on-chip integration of microwave waveguide structures. Furthermore, this method can be combined with miniaturised resonators (such as split rings) for localisation of heating within a microfluidic chip.

Herein, we demonstrate a method for simultaneously quantifying the electric and magnetic properties of liquid systems confined within a capillary. This is based upon an optimized perturbation of a microwave-frequency coaxial resonator, chosen to maximize the spatial separation of the two fields and to minimize the depolarization of the liquid. A capillary is passed through the center of the resonator so the sample occupies either maximum electric field (zero magnetic field) or maximum magnetic field (zero electric field) depending on whether an odd or even TEM mode is interrogated. This allows electric and magnetic effects to be distinguished at multiple discrete frequencies. We demonstrate this capability through the quantification of varying ionic content of saline solutions, which interact with both the electric and magnetic fields via several polarization mechanisms. The distinction of different cations and anions is also demonstrated.

A novel microfluidic biosensing platform based on Bipolar-Complementary Oxide Semiconductor (BiCMOS) technology is presented. The device relies on a quadruple electrode system and a microfluidic channel that are directly integrated into the back-end-of-line (BEOL) of the BiCMOS stack. For proof of concept repeatable electrical trapping of single SW620 (colon cancer) cells in the quadruple electrode system is initially demonstrated. Additionally, for the first time a microwave intermodulation technique is used for high sensitivity dielectric spectroscopy, which could pave the way to label-free monitoring of intracellular processes and manipulation such as electroporation.

A device for analysing the chemical composition of single- and multi-phase solvent flows using microfluidic dielectric spectroscopy is demonstrated in this work. An open-circuited, half-wavelength, coaxial resonator operating at microwave frequencies (i.e. harmonics of 600 MHz) was embedded in a compression-sealed polytetrafluoroethylene microfluidic chip for in situ characterization of solvent–solvent and solute–solvent mixtures of varying concentration, and an aqueous–organic segmented flow. Results are shown for a solvent mixture of acetonitrile in toluene as a test system, exhibiting a sensitivity limit of 400 nM. In addition to being highly sensitive, the measurement system is fast, robust and non-invasive, and can be readily miniaturized.

Herein we present a technique for performing complex permittivity measurements with an overmoded, evanescently perturbed coaxial resonator at microwave frequencies. The design of a noninvasive electromagnetic coupling structure, which allows transmission measurements to be taken from one end of a resonant section of coaxial cable, is discussed in detail. Quasi-spectral information was obtained through the exploitation of higher order resonances, and complex permittivity measurements of a number of common industrial solvents were taken at multiple discrete frequencies between 1 and 8 GHz. A combination of experimental and simulated results was used also to characterise the device behavior. The high stability of temporal measurements, coupled with the robustness of the design, make this device ideal for analytical chemistry and industrial process control.

Delivering apoptosis inducing peptides to cells is an emerging area in cancer and molecular therapeutics. Here, we have identified an alternative mechanism of action for the proapoptotic chimeric peptide D-NuBCP-9-r8. Integral to D-NuBCP-9-r8 is the Nur-77-derived D-isoform sequence fsrslhsll that targets Bcl-2, and the cell-penetrating peptide (CPP) octaarginine (r8) that is required for intracellular delivery. We find that the N-terminal phenylalanine of fsrslhsll acts in synergy with the cell-penetrating moiety to enhance peptide uptake at low nontoxic levels and cause rapid membrane blebbing and cell necrosis at higher (IC(50)) concentrations. These effects were not observed when a single phenylalanine-alanine mutation was introduced at the N-terminus of D-NuBCP-9-r8. Using primary samples from chronic lymphocytic leukemia (CLL) patients and cancer cell lines, we show that NuBCP-9-r8 induced toxicity, via membrane disruption, is independent of Bcl-2 expression. Overall, this study demonstrates a new mechanism of action for this peptide and cautions its use as a highly specific entity for targeting Bcl-2. For delivery of therapeutic peptides the work emphasizes that key amino acids in cargo, located several residues away from the cell-penetrating sequence, can significantly influence their cellular uptake and mode of action.

A contributing factor to the labored advance of molecularly imprinting as a viable commercial solution to molecular recognition needs is the absence of a standard and robust method for assessing and reporting on molecular imprinted polymer (MIP) performance. The diversity and at times inappropriateness of MIP performance indicators means that the usefulness of the literature back-catalogue, for predicting, elucidating or understanding patterns in MIP efficacy, remains largely inaccessible. We hereby put forward the case that the simple binding isotherm is the most versatile and useful method of assessing and reporting MIP function, allowing direct comparison between polymers prepared and evaluated in different studies. In this study we describe how to correctly plot and interpret a bound / free isotherm and show how such plots can be readily used to predict outcomes, retro-analyze data and optimize experimental design. We propose that by adopting the use of correctly constructed isotherms as the primary form of data representation researchers will enable inter-laboratory comparisons, promote good experimental design and encourage a greater collective understanding of molecular imprinting. Copyright © 2011 John Wiley & Sons, Ltd.

We report the first development of a novel, planar, microfluidic, graphitic carbon separations column utilizing an array of graphitic micropillars of diamond cross-section as the chromatographic stationary phase. 795 nm femtosecond laser ablation was employed to subtractively machine fluidic architectures and a micropillared array in a planar, graphitic substrate as a monolithic structure. A sample injector was integrated on-chip, together with fluid-flow distribution architectures to minimize band-broadening and ensure sample equi-distribution across the micro-pillared column width. The separations chip was interfaced directly to the ESI probe of a Thermofisher Surveyor mass spectrometer, enabling the detection of test-mixture analytes following their differential retention on the micro-pillared graphitic column, thus demonstrating the exciting potential of this novel separations format. Importantly, unlike porous, graphitic microspheres, the temperature and pressure resilience of the microfluidic device potentially enables use in subcritical H(2)O chromatography.

A microflow system for the investigation of multistep syntheses involving Pd-catalysed Heck reactions and Ru-catalysed ring-closing metathesis is described. A successful provision of reagent and catalyst delivery in a consecutive fashion allowed control over reaction parameters leading to fast optimisation. The performance of Heck reactions in multistep procedures was not as successful as in the single step coupling, whereas the ring-closing metathesis proved to be successful in the production of the desired compounds for further functionalisation.

Various Heck couplings have been carried out using segmented flow conditions to accelerate the reactions. Aryl iodides and aryl bromides as well as anilines in diazonium-type Heck reactions have been used successfully.

A cost effective methodology for pattering of Nano Imprint Lithography (NIL) templates incorporating different length scale features is proposed. The approach relies on selecting the optimum processing window of different technologies for cost effective micro- and nano-patterning. Very promising results were obtained when first fused silica templates were structured by F2 laser ablation at 157nm. It was demonstrated that nano-scale features and complex 3D micro-scale features could be machined with a Focused Ion Beam (FIB) over the existing topography produced by laser ablation. Thus, a large area (up to several square centimeters) of the NIL templates is easily patterned with micro- and even meso-scale features by laser ablation while nano- and micro-scale features could be introduced locally by FIB machining. Through S-FIL process such templates were validated and the nano- and micro-structures were accurately replicated in one imprinting step.

Capillary forces on the microscale are exploited to create a continuous flow liquid-liquid phase separator. Segmented flow regimes of immiscible fluids are generated and subsequently separated into their component phases through an array of high aspect ratio, laser machined, separation ducts (36 microm wide, 130 microm deep) in a planar, integrated, polytetrafluoroethylene (PTFE) microdevice. A controlled pressure differential across the phase separator architecture facilitates the selective passage of the wetting, organic, phase through the separator ducts, enabling separation of microfluidic multiphase flow streams. The reported device is demonstrated to separate water and chloroform segmented flow regimes at flow rates up to 0.4 ml min(-1). Separation efficiency is quantified over a range of flow rates and applied pressure differentials, characterising device behaviour and limits of operation. Experimental measurements and observations are supported by theoretical hydrodynamic and capillary pressure modelling. The influence of material properties and geometric design parameters on phase separation is quantified and optimisation strategies proposed. The novel ability of the membrane free device to separate an organic phase containing suspended microparticulates, from an aqueous phase, is also demonstrated.

A new microwave microstrip sensor is presented in this paper for microsphere detection and dielectric characterization within a microfluidic channel. This comprises a 2.5 GHz split ring resonator with a 35 µm gap. To validate the sensor, two sizes of polystyrene microspheres (of diameters 15 and 25 µm) were tested. Measurements of changes in resonant frequency and insertion loss of the odd mode were related to the dielectric contrast provided by the microspheres and their host solvent, here water. COMSOL Multiphysics® was used to model the sensor, and good agreements were found between the simulated and measured results.

Dissolving microneedles are especially attractive for transdermal drug delivery as they are associated with improved patient compliance and safety. Furthermore, microneedles made of sugars offer the added benefit of biomolecule stabilisation making them ideal candidates for delivering biological agents such as proteins, peptides and nucleic acids. In this study, we performed experimental and finite element analyses to study the mechanical properties of sugar microneedles and evaluate the effect of sugar composition on microneedle ability to penetrate and deliver drug to the skin. Results showed that microneedles made of carboxymethylcellulose / maltose are superior to those made of carboxymethylcellulose / trehalose and carboxymethylcellulose / sucrose in terms of mechanical strength and the ability to deliver drug. Buckling was predicted to be the main mode of microneedle failure and the order of buckling was positively correlated to the Young’s modulus values of the sugar constituents of each microneedle.

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media.

Crossflow membrane emulsification is a promising method to achieve very small and uniform emulsions. The droplet size produced is controlled mainly by the choice of membrane. Using microengineering technology it is currently possible to produce membranes with precision defined parameters (uniform pore size, shape and inter-pore distance). In the work presented here, individual pore behaviour was studied using micromachined membranes with wider inter-pore distances (100 ?m). It was found that the diameter of droplets increased during an initial period of operation. Also, interaction between droplets formed at adjacent pores was observed to enhance the reduction of mean droplet size and negatively correlated with inter-pore distance. A ‘push-to-detach’ mechanism was proposed to explain the behaviour observed. It was demonstrated that a micromachined membrane with pore diameter of 2 ?m and inter-pore distance of 20 ?m produced smaller droplets than for membranes with larger inter-pore distances. To facilitate the droplet detachment from the membrane and provide additional control over droplet detachment, the effects of membrane vibration were investigated. Preliminary results showed that smaller droplets could be produced by introducing low frequency (0–100 Hz) membrane vibrations without increasing their size distribution.

A numerical model for segmented flow in a microreactor has been developed. The model is based on computational fluid dynamics (CFD) which means that the flow field and mass transfer are described by a set of partial differential equations. A general purpose CFD code was extended in order to predict the internal flow patterns of fluid segments and the transfer of dissolved chemical species within segments and across fluid segment interfaces. The model has been validated by comparing predicted data with experimental microreactor titrations.

This paper describes the use of microfluidic microwave sensors for measuring the length, volume, speed and dielectric properties of different liquids in a segmented flow. The sensor is a variant of the split ring resonator, operating around 4 GHz, realized in a microstrip implementation. Changes of the resonant frequency and quality factor are performed when a segment enters the sensing region, in this case the gap regions. Two different geometries of resonators were used for the sensors, each with two gaps to accommodate a planar microfluidic channel. The segments consisted of mineral oil and water. Sensor simulations were performed using COMSOL Software, which compare favorably with the experimental measurements.

a Abstract Electrically insulative alumina and silica-based coatings up to 500 mm in thickness have been deposited on steel substrates using a sol-gel composite technology. Coatings are produced by spray depositing a ceramic paint consisting of fine ceramic powders dispersed in a sol-gel solution to form a coating. Coatings are then dried at 343 K and fired at 723 K to pyrolyze the organic components. A room temperature dielectric strength up to 5000 V has been achieved at coating thicknesses as low as AC 300 mm on a steel substrate. Coatings have been fabricated that pass a 'hi-pot' test of 1275 V for 1 s at operating temperatures AC as high as 673 K. These results have been achieved through control of coating microstructure and the elimination of surface porosity. This technology provides cost effective electrical insulation for a wide range of applications including low profile integrated heating elements based on inexpensive steel and aluminum substrate materials. 2001 Elsevier Science B.V. All rights reserved.

Silicon plays a major role in both the microelectronics industry and in the more recently emerging fields of microsystems technology and micro-electromechanical-systems (MEMS). Porous silicon is used increasingly in MEMS due to many of its properties of high specific area and luminescence. Patterned geometrical arrangements of porous silicon generated by electrochemical etching in hydrofluoric acid solutions usually requires silicon nitride or silicon carbide, as an etch mask. An alternative methodology is reported here, which using photopatterned films of a negative, imaging-type, chemically-amplified-resist (SU8) to produce patterned geometrical areas of nanoporous and macroporous silicon.

Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.

The manipulation of yeast cells and latex particles of diameters 1.3, 12 and in aqueous suspension in 1 and 3 MHz ultrasonic standing waves has been examined and compared in microgravity (0 g), 1 g and 1.8 g. The experiments were carried out during the 23rd ESA parabolic flight campaign. The suspended particles concentrated to form bands at half wavelength separation in the axial direction of a vertical tubular sample holder with a Bessel pressure amplitude distribution profile. At 1 g small ( latex) particles formed bands but these broke up within a few seconds. In contrast throughout 0 g bands of these particles formed and remained stable. The transition from 0 to 1.8 g during flight induced streaming which broke up the bands of latex. Bands formed with yeast cells were more stable at 1 g but, during transitions from 0 to 1.8 g, some bands broke up. Bands of the larger (12 and ) particles were stable at 0, 1 and 1.8 g and during all transitions between the fields. Thermal gradient convective flow rather than acoustic streaming was identified as the main source of flow in the sample holder at 1 g. The absence of thermal streaming at 0 g allowed manipulation of smaller particles in that situation. A frequency ramping technique appropriate for removal of particles from suspension in 1 g had a better performance in 0 g.

Various Heck couplings have been carried out using segmented flow conditions to accelerate the reactions. Aryl iodides and aryl bromides as well as anilines in diazonium-type Heck reactions have been used successfully.

Highly efficient molecular extractions in continuous flow microfluidic systems are demonstrated utilising the rapid mixing properties of biphasic segmented flow in conjunction with suspended micro-particulate adsorbents. A continuous flow technique providing potential for continual on-line sample enrichment, purification and clean-up in chemical synthesis, and sample preparation.

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.