Abstract
Arrays of microneedles (MNAs) are integrated in an out-of-plane fashion with a base plate and can serve as patches for the release of drugs and vaccines. We used soft-lithography and micromolding to manufacture ceramic nanoporous (np)MNAs. Failure modes of ceramic npMNAs are as yet poorly understood and the question remained: is our npMNA platform technology ready for microneedle (MN) assembly into patches? We investigated npMNAs by microindentation, yielding average crack fracture forces above the required insertion force for a single MN to penetrate human skin. We further developed a thumb pressure-actuated applicator-assisted npMNA insertion method, which enables anchoring of MNs in the skin by an adhesive in one handling step. Using a set of simple artificial skin models, we found a puncture efficiency of this insertion method a factor three times higher than by applying thumb pressure on the npMNA base plate directly. In addition, this new method facilitated zero MN-breakage due to a well-defined force distribution exerted onto the MNs and the closely surrounding area prior to bringing the adhesive into contact with the skin. Owing to the fact that such parameter space exists, we can conclude that npMNAs by soft lithography are a platform technology for MN assembly into a patch.
Highlights
Adopting miniaturization technology has been key to successfully applying novel devices in the life-sciences industry
While our findings suggest that for all the tested npMNA configurations an optimized parameter space for the applicator design being used on human skin can exist, we suggest that the mechanical optimization of these mechanical boundary conditions should benefit from the use of simplified skin models in order to find the best match between applicator design and a specific npMNA geometry, which must take the variations in npMNA base plate thickness, base plate diameter, total number of needles and their density in an array, MN length, and the resulting MN tip sharpness due to variations in the production process more carefully into account
Single microneedle crack-fracture forces were measured by means of a microindenter reaching values 10× higher than the required insertion force for a single microneedle to penetrate human skin
Summary
Adopting miniaturization technology has been key to successfully applying novel devices in the life-sciences industry. Such miniaturized devices are explored for the manipulation of tiny amounts of fluids, coined microfluidics. This fairly new research discipline presents us with the possibility of fabricating microneedle arrays for use in drug delivery via the skin. To bring any of these minimally invasive devices to market-entry, one has to develop suitable models that allow clinical researchers to benchmark these emerging microneedle techniques against the state of the art, i.e., the hypodermic needle, and amongst each other to define the best possible method of drug delivery for a specific medical need
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