A Needle-Free Transdermal Patch for Sampling Interstitial Fluid

OBJECTIVE: Modern diagnostics is pivoting towards less invasive health monitoring in dermal interstitial fluid, rather than blood or urine. However, the skin's outermost layer, the stratum corneum, makes accessing the fluid more difficult without invasive, needle-based technology. Simple, minimally invasive means for surpassing this hurdle are needed. METHODS: To address this problem, a flexible, Band-Aid-like patch for sampling interstitial fluid was developed and tested. This patch uses simple resistive heating elements to thermally porate the stratum corneum, allowing the fluid to exude from the deeper skin tissue without applying external pressure. Fluid is then transported to an on-patch reservoir through self-driving hydrophilic microfluidic channels. RESULTS: Testing with living, ex-vivo human skin models demonstrated the device's ability to rapidly collect sufficient interstitial fluid for biomarker quantification. Further, finite-element modeling showed that the patch can porate the stratum corneum without raising the skin's temperature to pain-inducing levels in the nerve-laden dermis. CONCLUSION: Relying only on simple, commercially scalable fabrication methods, this patch outperforms the collection rate of various microneedle-based patches, painlessly sampling a human bodily fluid without entering the body. SIGNIFICANCE: The technology holds potential as a clinical device for an array of biomedical applications, especially with the integration of on-patch testing.