# Microparticles

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For the biological cell fragment, see Microvesicles.
IUPAC definition

Particle with dimensions between 1 × 10−7 and 1 × 10−4 m.

Note 1: The lower limit between micro- and nano-sizing is still a matter of debate.

Note 2: To be consistent with the prefix “micro” and the range imposed by the definition,
dimensions of microparticles should be expressed in μm.[1]

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 bloodstream 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 microparticles. Many applications are also listed in the microsphere article.

A recent study showed that infused, negatively charged, immune-modifying microparticles could have therapeutic use in diseases caused or potentiated by inflammatory monocytes. [2]

## References

1. ^
2. ^ Getts DR, Terry RL, Getts MT et al. (Jan 2014). "Therapeutic inflammatory monocyte modulation using immune-modifying microparticles.". Sci Transl Med. 6 (219): 219. doi:10.1126/scitranslmed.3007563. PMID 24431111.