Monitoring human health is of considerable significance in biomedicine. In particular, the ion concentrations in blood are important reference indicators related to many diseases. Microneedle array-based sensors have enabled promising breakthroughs in continuous health monitoring due to their minimally invasive nature. In this study, we developed a microneedle sensing-array integrated system to continuously detect subcutaneous ions to monitor human health status in real time based on a fabrication strategy for assembling planar microneedle sheets to form 3D microneedle arrays. The limitations of preparing 3D microneedle structures with multiple electrode channels were addressed by assembling planar microneedle sheets fabricated via laser micromachining; the challenges of modifying closely spaced microneedle tips into different functionalized types of electrodes were avoided. The microneedle sensing system was sufficiently sensitive for detecting real-time changes in Ca2+, K+, and Na+ concentrations, and it exhibited good detection performance. The in vivo results showed that the ion-sensing microneedle array successfully monitored the fluctuations in Ca2+, K+, and Na+ in the interstitial fluids of rats in real time. By using an integrated circuit design, we constructed the proposed microneedle sensor into a wearable integrated monitoring system. The integrated system could potentially provide information feedback for diseases related to physiological ion changes.
Microneedle systems have been widely used in health monitoring, painless drug delivery, and medical cosmetology. Although many studies on microneedle materials, structures, and applications have been conducted, the applications of microneedles often suffered from issues of inconsistent penetration rates due to the complication of skin-microneedle interface. In this study, we demonstrated a methodology of determination of transdermal rate of metallic microneedle array through impedance measurements-based numerical check screening algorithm. Metallic sheet microneedle array sensors with different sizes were fabricated to evaluate different transdermal rates. In vitro sensing of hydrogen peroxide confirmed the effect of transdermal rate on the sensing outcomes. An FEM simulation model of a microneedle array revealed the monotonous relation between the transdermal state and test current. Accordingly, two methods were primely derived to calculate the transdermal rate from the test current. First, an exact logic method provided the number of unpenetrated tips per sheet, but it required more rigorous testing results. Second, a fuzzy logic method provided an approximate transdermal rate on adjacent areas, being more applicable and robust to errors. Real-time transdermal rate estimation may be essential for improving the performance of microneedle systems, and this study provides various fundaments toward that goal.
Background A variety of implantable microparticles have been developed to detect, diagnose and treat a wide range of diseases, but undesirable bio-fouling caused by biological substances including proteins, bacteria and cells adhesion, can easily lead to the risk of complications such as inflammation. Although most modification techniques have achieved biofouling resistance, the fragility of coatings in fluids and the particles agglomeration often caused by modification limit their applications. Here, we report deliverable microparticles coated with nano-forest like structure (NFMPs) that are exceptionally dispersed and resistant to biofouling. Methods The nano-forest-like microspheres were formed by the combined modification of tree-trunk like nanospikes and dendritic ‘liquid-like’ molecular brush coatings on the conventional microspheres surface. Its structure and surface characteristics were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), static contact angles (CAs), slide angles (SAs). Compared the dispersibility of nanospike-modified hydrophobic microspheres with conventional hydrophobic microspheres in water to determine nanospike-induced abnormal dispersion. Furthermore, the nano-forest-like microparticles were incubated with proteins, bacteria and cells to verify their anti-biofouling properties, and its anti-adhesion mechanisms were explored through activity tests and anti-biofouling performance tests of nanoforest structure-modified planar structures. Results The ‘liquid-like’ coating is reliably biocompatible and induces microparticles to exhibit long-term and robust resistance against proteins, bacterial and cells adhesion. While the microparticles were aggregated in water due to their increased hydrophobicity caused by the coating, the tree-trunk-like nanospikes induced specific dispersion of the microparticles. Conclusion Based on these results, our research introduces a unique modification technology for deliverable microparticles with exceptional dispersibility and anti-biofouling properties, which will facilitate the development of deliverable devices or materials to reduce inflammation or infection.
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