Microsphere
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.
Microparticles are particles between 0.1 and 100 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.
Although the generally accepted definition of 0.1 to 100 m complements the size definition of nanoparticles, there are other ways to define the size.
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