Editors' ChoiceDrug Delivery

Angling for a bug-inspired method of coating therapeutics onto microneedles

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Science Translational Medicine  22 Jan 2020:
Vol. 12, Issue 527, eaba2914
DOI: 10.1126/scitranslmed.aba2914

Abstract

Mimicking the microstructures on the surface of European true bugs may help optimize loading of therapeutics onto transdermal microneedle patches.

Microneedle patches hold promise as a method of painless transdermal drug or vaccine delivery, potentially obviating the need for the conventional needle and syringe. Recent trials have begun to illustrate the clinical potential of these arrays of tiny needles (typically <1 mm in height) in self-administered therapeutic delivery; however, the translation of microneedle-based technology has not been without its challenges. Cost-effectiveness and control over the amount of therapeutic being delivered are crucial. Mass-manufacturing strategies must be considered from the onset, both with respect to high-fidelity microneedle patch fabrication and how a therapeutic can be efficiently coated or encapsulated, ideally toward the tips of the microneedles.

Conventionally, therapeutics are loaded onto microneedle patches using dipping or spraying methods that are either too slow or result in excess waste of the valuable payload. Plamadeala and colleagues’ solution required some lateral thinking. Through a bioinspired approach, they looked at how the secretory systems of some European true bugs use oriented surface microstructures to transport liquids away from their bodies. Adopting a similar strategy, they designed a microneedle patch in which the walls of the pyramid-shaped microneedles were themselves covered in arrays of even tinier conical microstructures. When a therapeutic was loaded in solution at the base of these microneedles, the oriented microstructures caused the liquid to wick up toward the microneedle tip until the solvent evaporated, leaving a residue of the therapeutic behind that was ready for use.

The researchers used two-photon polymerization—a highly accurate method of three-dimensional printing—to create these intricate geometries with multiscale features. They showed that they could accurately replicate their microneedle patch design in a medical-grade epoxy, suggesting that these patches could eventually be mass-manufactured. These patches maintained their integrity upon insertion into human skin and appeared to be reasonably effective at penetrating the skin in model systems. However, further preclinical assessment—including delivery of various agents—will be necessary to determine whether these researchers have truly debugged therapeutic loading onto microneedles.

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