microcapillary

Microcapillary refers to a capillary with a very small inner diameter, typically in the micrometer range, used in two primary contexts: biology and microfluidics. In physiology, microcapillaries are the smallest blood vessels that form networks between arterioles and venules, facilitating exchange between blood and surrounding tissues. Their walls are mainly a single layer of endothelial cells, sometimes with pericytes, and they may be continuous, fenestrated, or sinusoidal depending on tissue. The narrow lumens slow blood flow and enable efficient diffusion of oxygen, carbon dioxide, nutrients, and waste products. In many tissues, red blood cells pass through these vessels in single file, and local regulation of flow is achieved by precapillary sphincters and local signaling.

In laboratory and engineering contexts, microcapillaries describe tiny tubes or channels used to handle small liquid volumes. Capillary action allows fluids to rise or fill narrow tubes automatically, which is useful for sampling, chromatography, and microanalysis. Microcapillary channels and tubes are commonly fabricated from glass or polymer and have smooth inner surfaces to minimize adsorption. They are key components of microfluidic systems that manage laminar flow, mixing, and separation, and they underpin techniques such as capillary electrophoresis and point‑of‑care diagnostics.

Physical principles governing microcapillaries include capillary rise (Jurin’s law) and capillary flow in narrow channels (Lucas–Washburn type behavior). Performance depends on surface properties, contact angle, liquid viscosity, and surface tension. Limitations include fragility, susceptibility to clogging, and variability in biological or fabricated systems. See also: capillary action, capillary tube, microfluidics, capillaries.