media Plural form of medium, a (usually sterile) preparation made for the growth, storage, maintenance, or transport of microorganisms or other cells.

Met Methionine; one of over 20 naturally occurring amino acids.

metered dose inhaler (MDI) A device used to deliver a fixed volume or dose of an aerosol form of an active drug substance to the lungs and/or bronchi.

micelle A spherical arrangement (bubble) formed by a group of lipid molecules in an aqueous environment; hydrophobic ends of the molecules are turned inward and hydrophilic ends are turned outward. A molecular aggregate that constitutes a colloidal particle (a substance consisting of particles dispersed throughout another substance with particles too small for resolution with an ordinary light microscope, but that can pass through a semipermeable membrane).

microassays Assays usually run on very small samples, often using "microplates," and often automated. Microplates can have room for 96, 384, or even 1,536 tiny samples. Microassays measure small quantities of components even when the sample size is large.

microbial fermentation Processes involving the use of microorganisms, such as E. coli, to produce a protein or other substance.

microbial testing Analytical methods required by regulations to ensure sterility and to measure bioburden or identify microorganisms in controlled, classified environments.

microbiology The study of microscopic life such as bacteria, viruses, yeast, and protozoa.

microcarrier A microscopic particle (often a 200-µm polymer bead) that supports cell attachment and growth in suspension culture; alternative to microencapsulation. Cells anchor into tiny pores on the beads for protection.

microencapsulation In cell culture, trapping cells inside a thin protective membrane to provide anchorage and protect them from harsh conditions. Microspheres are often biodegradable.

microfiltration A method of sterile filtration, clarification, or cell harvesting that removes particles in the 0.1–10.0 µm range.

microheterogeneity In BioPharm, usually small differences in the amino acid sequence or structure of a polypeptide chain. For example, to produce a recombinant protein in E. coli, a Met must be added to one end of the protein sequence to act as a signal that initiates protein synthesis. In most cases, that Met is removed once the protein is made. Sometimes the Met is removed for only some of the molecules. The purified product is then a mixture of a protein with the native sequence and a protein with the native sequence plus the extra amino acid.

microinjection Manually using tiny needles to inject microscopic material (such as DNA) directly into cells or cell nuclei; video screens provide a magnified view.

micron A micrometer (µm), 1/1,000th of a meter's length.

microorganism A microbe; a free-living organism too small to be seen by the naked eye.

microspheres Tiny polymer spheres (usually biodegradable) measured in micrometers.

microtubules Cellular organelles common in microorganisms: thin tubes that make structures involved in cellular movement.

mistake-proofing Also called poke-yoke; the engineering concept of designing things to reduce the probability of errors and accidents caused by human error. Color-coding, directional plugs, are examples of mistake proofing. A basic concept in risk management and quality systems.

mitochondria Animal-cell organelles that reproduce using their own DNA. They metabolize nutrients to provide the cell with energy and are believed to have once been symbiotic bacteria. Chloroplasts are their plant-cell equivalents.

moiety One of the portions into which something is divided; a component, part, or fraction. In chemistry, a specific section of a molecule, usually complex, that has a characteristic chemical effect or property.