Microparticles

Microparticles are particles between 0.1 and 100 $$\mu$$m in size. Commercially available microparticles are available in a wide variety of materials, including ceramics, glass, polymers, and metals. Microparticles encountered in daily life include pollen, sand, dust, flour, and powdered sugar.

Microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. For example, metal microparticles can be explosive in air.

Microspheres are spherical microparticles, and are used where consistent and predictable particle surface area is important.

In biological systems, microparticles are small membrane bound vesicles circulating in the blood derived from cells that are in contact with the bloodstram such as platelets and endothelial cells (see endothelial microparticle). Because they retain the signature membrane protein composition of the parent cell, microparticles carry useful information and can be detected and characterized by flow cytometry.

Alternative definitions for size
Although the generally accepted definition of 0.1 to 100 $$\mu$$m complements the size definition of nanoparticles, there are other ways to define the size.

Mathematical: as the term "micro" refers to $$10^{-6}$$, the range for micro would then be $$10^{-7.5}$$ to $$10^{-4.5}$$, or roughly 31.6 nm to 31.6 micrometers. However, general acceptance considers particles smaller than 100 nm nanoparticles.

Rounding: rules of rounding in mathematics provide an alternative for the definition. Anything larger than 0.5 $$\mu$$m and anything smaller than 0.5 mm is considered microparticles.

Convenient/popular: Very often particles with dimensions more than 100 nm are still called nanoparticles. The upper range may be between 300 to 700 nm, so this would give a size definition for microparticles of 0.3 to 300 $$\mu$$m or 0.7 to 700 micrometers.

Applications
Home pregnancy tests make use of gold micro particles. Many applications are also listed in the Microsphere article.

Mikropartikel Mikropartiklid Microparticule