Novel hollow microneedle technology for depth-controlled microinjection-mediated dermal vaccination: a study with polio vaccine in rats.

PURPOSE: The aim of the study was to develop a cheap and fast method to produce hollow microneedles and an applicator for injecting vaccines into the skin at a pre-defined depth and test the applicability of the system for dermal polio vaccination. METHODS: Hollow microneedles were produced by hydrofluoric acid etching of fused silica capillaries. An electromagnetic applicator was developed to control the insertion speed (1-3 m/s), depth (0-1,000 µm), and angle (10°-90°). Hollow microneedles with an inner diameter of 20 µm were evaluated in ex vivo human skin and subsequently used to immunize rats with inactivated poliovirus vaccine (IPV) by an intradermal microinjection of 9 µL at a depth of 300 µm and an insertion speed of 1 m/s. Rat sera were tested for IPV-specific IgG and virus-neutralizing antibodies. RESULTS: Microneedles produced from fused silica capillaries were successfully inserted into the skin to a chosen depth, without clogging or breakage of the needles. Intradermal microinjection of IPV induced immune responses comparable to those elicited by conventional intramuscular immunization. CONCLUSIONS: We successfully developed a hollow microneedle technology for dermal vaccination that enables fundamental research on factors, such as insertion depth and volume, and insertion angle, on the immune response.

Limits of miniaturization: assessing ITP performance in sub-micron and nanochannels.

The feasibility of isotachophoresis in channels of sub micrometer and nanometer dimension is investigated. A sample injection volume of 0.4 pL is focused and separated in a 330 nm deep channel. The sample consists of a biomatrix containing the fluorescently-labeled amino acids glutamate and phenylalanine, 20 attomoles of each. Isotachophoretic focusing is successfully demonstrated in a 50 nm deep channel. Separation of the two amino acids in the 50 nm deep channel however, could not be performed as the maximum applicable voltage was insufficient. This limit is imposed by bubble formation that we contribute to cavitation as a result of the mismatch in electro-osmotic flow, so called electrocavitation. This represents an unexpected limit on the miniaturization of ITP. Nonetheless, we report the smallest isotachophoretic separation and focusing experiment to date, both in terms of controlled sample injection volume and channel height.

Single-electrolyte isotachophoresis using a nanochannel-induced depletion zone.

Isotachophoretic separations are triggered at the border of a nanochannel-induced ion-depleted zone. This depletion zone acts as a terminating electrolyte and is created by concentration polarization over the nanochannel. We show both continuous and discrete sample injections as well as separation of up to four analytes. Continuous injection of a spacer compound was used for selective analyte elution. Zones were kept focused for over one hour, while shifting less than 700 µm. Moreover, zones could be deliberately positioned in the separation channel and focusing strength could be precisely tuned employing a three-point voltage actuation scheme. This makes depletion zone isotachophoresis (dzITP) a fully controllable single-electrolyte focusing and separation technique. For on-chip electrokinetic methods, dzITP sets a new standard in terms of versatility and operational simplicity.

Stimulus-sensitive hydrogels and their applications in chemical (micro)analysis.

In this tutorial review the use of stimulus-sensitive hydrogels as sensors and actuators for (micro)analytical applications is discussed. The first part of the article is aimed at making the reader familiar with stimulus-sensitive hydrogels, their chemical composition and their chemo-physical behavior. The prior art in the field, that comprises a number of sensors ranging from metal ion-sensitive sensors to antigen-sensitive sensors and a few actuators, is also treated in this part. The second part of the article focusses on the use of stimulus-sensitive hydrogels for microsensors and microactuators as well as their application in micro total analysis systems. The benefits of stimulus-sensitive hydrogels, their miniaturisation and the use of 365 nm UV-photolithography as a fast economical manufacturing technique are discussed.