What MICROPARTICLE means: Particles between 0.1 and 100 m in size. A m is a micrometer, which is one-millionth of a meter. Man-made microparticles include ceramics, glass, polymers and metals. In biological systems, microparticles are small membrane- bound vesicles derived from cells circulating in the bloodstream. Microparticles are generally 1000 times larger than nanoparticles.