Abstract
Microneedle permits transdermal biosensing and drug delivery with minor pain. However, accurate microneedle transdermal positioning with minimal skin deformation remains a significant technical challenge due to inhomogeneous skin topology and discontinuous force applied to the microneedle. Here, we introduce bioinspired rotation microneedles for in vivo accurate microneedle positioning as inspired by honeybees' stingers. We demonstrate the benefits of rotation microneedles in alleviating skin resistance through finite element analysis, full-thickness porcine validations, and mathematical derivations of microneedle-skin interaction stress fields. The max penetration force was mitigated by up to 45.7% and the force attenuation rate increased to 2.73 times in the holding stage after penetration. A decrease in max skin deflection and a faster deformation recovery introduced by rotation microneedles implied a more precise penetration depth. Furthermore, we applied the rotation microneedles in psoriasis mice, a monogenic disorder animal model, for minimally invasive biological sample extraction and proinflammatory cytokine monitoring. An ultrasensitive detection method is realized by using only one microneedle to achieve cytokine mRNA level determination compared to commonly required biopsies or blood collection. Thus, rotation microneedles permit a simple, rapid, and ultraminimal-invasive method for subcutaneous trace biological sample acquisition and subsequent point-of-care diagnostics with minimal damage to both microneedles and skins.
Highlights
Microneedles have actively been studied for painless drug delivery [1–3] and biomarker diagnostics [4–6] through the transdermal route
We systematically addressed the effect of the application of rotation on skin resistance during microneedle insertion in the level of mechanism, including insertion force, skin deformation, and penetration accuracy
We define insertion force as the overall axial force applied to the microneedle tip due to skin resistance
Summary
Microneedles have actively been studied for painless drug delivery [1–3] and biomarker diagnostics [4–6] through the transdermal route. Microneedles can perforate the skin effectively, especially the rigid barrier of the stratum corneum (SC), the outermost 10–20 μm layer of the skin, without causing obvious pain [7, 8]. To effectively generate microchannels for clinical applications, microneedles should have an appropriate combination of mechanical strength and hardness to bear the skin resistance during insertion. Due to the extremely small size and limited material strength, microneedles are broken under the insertion force, leaving debris that causes potential injury to other organs [11, 12]. Studies have attempted to reduce insertion force by altering the microneedle structures such as changing the shape [13–15], sharpening the tip [16, 17], optimizing the diameter [11, 18], or using bioinspired
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