![]() Anatomical principle of the barrier and routes of fluid transfer cannot explain the extraordinary accuracy of fluids and substances needed to enter or leave the brain firmly. Many hydrophilic substances are effectively prevented from the entry into the brain via blood, while others like neurotransmitters are extremely hindered from getting out of the brain. Despite this, CSF and ISF exhibit very similar compositions, but differ significantly from blood plasma. Microvessels within the parenchyma are sufficiently close to every cell where diffusion areas for solutes are tiny. The ISF and CSF provide water and solutes influx and efflux from cells to these targeted fluids in a quite precise way. This constitutes a formidable challenge that normal organisms surpass daily. The skull is a rigid box thereby the sum of volumes occupied by the parenchyma with its ISF, related connective tissue, the vasculature, the meninges and the CSF must be relatively constant according to the Monroe-Kellie dogma. The current view assumes that choroidal plexuses secrete the major part of Cerebrospinal Fluid (CSF), while the Blood-Brain Barrier (BBB) has a much less contribution to fluid production, generating Interstitial Fluid (ISF) that drains to CSF. ![]() There are specific mechanisms concerned with fluid secretion of the controlled composition of the brain, and others responsible for reabsorption eventually to blood and the extracellular fluid whatever their composition is. This regulation tends to act as barrier to prevent free exchange of materials between the brain and blood. ![]() These fluids transport all substances required for cells and remove the unwanted materials. Regulation of composition, volume and turnover of fluids surrounding the brain and damp cells is vital. The review concludes with some of the key challenges and opportunities faced by this next-generation wearable sensing technology. Successive content will focus on microneedle technologies which have been integrated with electrochemical biosensors for the quantification of various metabolites, electrolytes and other miscellaneous entities known to be present in the dermal interstitial fluid. We look briefly at microneedle technologies used to extract dermal interstitial fluid for subsequent analysis. An introduction to interstitial fluid is provided placing emphasis on sampling methods that have been employed to extract and/or sample tissue fluid for analysis. ![]() The integration of a biosensor with a microneedle platform opens the possibility for minimally invasive bio-chemical detection or continuous monitoring within the dermal interstitial fluid. This article explores recent advances in the development of electrochemical biosensors on microneedle platforms towards on-device sensing of biomarkers present in dermal interstitial fluid. ![]()
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