Boris Stoeber

Clinical microneedle injection of methyl nicotinate: stratum corneum penetration.

Background/purpose: In recent years, microneedles were proposed as a method to painlessly deliver drugs past the stratum corneum. Microneedles have been fabricated in several designs, but limited studies have tested microneedle injections in humans. In this work, we compare microneedle injections with topical application (TA) to investigate if microneedles enhance in vivo drug delivery past the stratum corneum.

Arrays of hollow out-of-plane microneedles for drug delivery

Drug delivery based on MEMS technology requires an invasive interface such as microneedles, which connects the microsystem with the biological environment. Two-dimensional arrays of rigid hollow microneedles have been fabricated from single-crystal silicon using a combination of deep reactive ion etching and isotropic etching techniques. The fabricated needles are typically 200 /spl mu/m long with a wide base and a channel diameter of 40 /spl mu/m. The fabrication process allows creating either blunt needles or needles with sharp tips. Their shape and size make these needles extremely suitable for minimally invasive painless epidermal drug delivery. MEMS technology allows for batch fabrication and integration with complex microsystems. Fluid has been successfully injected 100 /spl mu/m deep into sample tissue through arrays of microneedles. Needle breakage did not occur during this procedure. Experiments have shown that the modified Bernoulli equation is a good model for liquid flowing through the narrow microneedle lumen.

Paper as a platform for sensing applications and other devices: a review.

Paper is a ubiquitous material that has various applications in day to day life. A sheet of paper is produced by pressing moist wood cellulose fibers together. Paper offers unique properties: paper allows passive liquid transport, it is compatible with many chemical and biochemical moieties, it exhibits piezoelectricity, and it is biodegradable. Hence, paper is an attractive low-cost functional material for sensing devices. In recent years, researchers in the field of science and engineering have witnessed an exponential growth in the number of research contributions that focus on the development of cost-effective and scalable fabrication methods and new applications of paper-based devices. In this review article, we highlight recent advances in the development of paper-based sensing devices in the areas of electronics, energy storage, strain sensing, microfluidic devices, and biosensing, including piezoelectric paper. Additionally, this review includes current limitations of paper-based sensing devices and points out issues that have limited the commercialization of some of the paper-based sensing devices.

Copper foil-type vibration-based electromagnetic energy harvester

This paper presents the modeling, simulation, fabrication and experimental results of a vibration-based electromagnetic power generator (EMPG). A novel, low-cost, one-mask technique is used to fabricate the planar coils and the planar spring. This fabrication technique can provide an alternative for processes such as lithographie galvanoformung abformung (LIGA) or SU-8 molding and MEMS electroplating. Commercially available copper foils of 20 µm and 350 µm thicknesses are used for the planar coils and planar spring, respectively. The design with planar coils on either side of the magnets provides enhanced power generation for the same footprint of the device. The harvesters overall volume is 1 cm3. Excitation of the EMPG, at the fundamental frequency of 371 Hz, base acceleration of 13.5 g and base amplitude of 24.4 µm, yields an open circuit voltage of 60.1 mV, as well as 46.3 mV load voltage and 10.7 µW power for a 100 Ω load resistance. At a matching impedance of 7.5 Ω the device produced a maximum power of 23.56 µW and a power density of 23.56 µW cm−3. The simulations based on the analytical model of the device show good agreement with the experimental results.

In vivo evaluation of a microneedle-based miniature syringe for intradermal drug delivery

A microfabrication process for miniature syringes is described. The MEMS syringes consist of a silicon plate with an array of hollow out-of-plane needles and a flexible poly-dimethylsiloxane (PDMS) reservoir attached to the back of the plate. The PDMS reservoir can be filled with a drug solution or microparticle suspension which is delivered into the skin simply by the pressure of a finger pushing on the miniature syringe. The efficiency of such a syringe for delivering a suspension of microparticles into skin tissue and a radiolabelled protein (albumin) solution into live mice is reported. Such microneedle devices could be used for the intradermal delivery of vaccination agents or for the systemic delivery of highly effective drugs.

Fluid injection through out-of-plane microneedles

In order to make frequent injections of insulin and other therapeutic agents more efficient, a new painless way to inject drug subcutaneously is investigated. Injecting such agents just under the stratum corneum is a painless and very effective way of drug delivery, since the nerve endings occur deeper under the skin, and the presence of a large number of capillaries help to absorb the drugs efficiently into the vascular system. The critical component for the successful development of this methodology is an array of robust, sharp, hollow microneedles. Arrays of needles that fulfill these requirements have been fabricated using a new fabrication process based on a combination of isotropic and anisotropic etching. Prototypes of these single crystal needles have been successfully tested by injection of fluid into chicken thighs. The flow characteristics of these needles have been modeled using the modified Bernoulli equation. This one-dimensional model has been validated through experimental results.

A microneedle-based glucose monitor: fabricated on a wafer-level using in-device enzyme immobilization

This paper presents a disposable minimally invasive self-calibrating continuous glucose monitor consisting of hollow out-of-plane microneedles to sample interstitial fluid from the epidermis, an integrated porous poly-Si dialysis membrane and an integrated enzyme-based flow-through glucose sensor. The proposed system can be fabricated on a wafer-level using standard MEMS technology and a novel in-device enzyme immobilization technique that allows wafer-level patterning of enzymes inside micro-scale flow channels after wafer bonding. This technique solves the compatibility issue of high temperature wafer bonding and temperature sensitive enzymes. A prototype of the glucose monitor is fabricated in order to demonstrate the high potential of out-of-plane microneedles for this application. Sampling of interstitial fluid through the microneedles results in a significant sensor response of the integrated glucose sensor.

Substrate‐Free Fabrication of Self‐Supporting ZnO Nanowire Arrays

Thin films composed of self-supporting ZnO nanowire arrays are fabricated via a hydrothermal approach without the presence of any substrates. The films can be transferred and bonded to an arbitrary substrate for device applications. As a demonstration, a piezoelectric converter is made which is able to generate electric charge under compressive forces.

Flow control in microdevices using thermally responsive triblock copolymers

Active and passive microflow control has been demonstrated using gel formation by dilute aqueous solutions of triblock copolymers at elevated temperatures. Solutions of a poly(ethylene oxide)/sub 106/-poly(propylene oxide)/sub 70/-poly(ethylene oxide)/sub 106/ polymer, which has the trade name Pluronic/spl reg/ F127, have been used as a sample system. Flow in a microchannel has been stopped in less than 33 ms by introducing heat with an integrated electric heater. Viscous heating under high shear rates also induces gel formation, which has been used for passive automated flow control in a microchannel.

Piezoelectric paper fabricated via nanostructured barium titanate functionalization of wood cellulose fibers.

We have successfully developed hybrid piezoelectric paper through fiber functionalization that involves anchoring nanostructured BaTiO3 into a stable matrix with wood cellulose fibers prior to the process of making paper sheets. This is realized by alternating immersion of wood fibers in a solution of poly(diallyldimethylammonium chloride) PDDA (+), followed by poly(sodium 4-styrenesulfonate) PSS (-), and once again in PDDA (+), resulting in the creation of a positively charged surface on the wood fibers. The treated wood fibers are then immersed in a BaTiO3 suspension, resulting in the attachment of BaTiO3 nanoparticles to the wood fibers due to a strong electrostatic interaction. Zeta potential measurements, X-ray diffraction, and microscopic and spectroscopic analysis imply successful functionalization of wood fibers with BaTiO3 nanoparticles without altering the hydrogen bonding and crystal structure of the wood fibers. The paper has the largest piezoelectric coefficient, d33 = 4.8 ± 0.4 pC N(-1), at the highest nanoparticle loading of 48 wt % BaTiO3. This newly developed piezoelectric hybrid paper is promising as a low-cost substrate to build sensing devices.