A Quiet Excipient, Everywhere in Tablets
Microcrystalline cellulose (often abbreviated MCC) is one of the most widely used excipients worldwide in the manufacture of solid oral dosage forms.
Invisible to the patient, it is nonetheless present in an overwhelming proportion of the tablets and capsules on the market. Its versatility — acting at once as a diluent, binder, and disintegrant — combined with its excellent compressibility, has made it a cornerstone of modern pharmaceutical formulation.
Origin and Discovery
Microcrystalline cellulose is not a new molecule but a purified derivative of cellulose, the most abundant polymer in the plant kingdom and a key component of plant and wood cell walls. Cellulose itself was first identified as early as 1838 by the French chemist Anselme Payen.
Microcrystalline cellulose, by contrast, is a mid-20th-century innovation. It was developed in the 1950s by researcher Orlando A. Battista and his collaborator Patricia Smith at the American Viscose Corporation (later part of the FMC group). The product was launched commercially in the early 1960s under the now-iconic Avicel brand, which remains a reference name in the pharmaceutical and food industries today.
Manufacturing: From Wood Pulp to Pharmaceutical Powder
Microcrystalline cellulose is obtained from wood pulp (or other α-cellulose-grade plant fibers). The process relies on controlled acid hydrolysis: a dilute mineral acid selectively attacks the amorphous regions of the cellulose fibers, while the more resistant crystalline regions remain intact.
This yields a so-called 'hydrocellulose' made up of microcrystals, which is then neutralized, washed, and spray-dried into a fine, free-flowing powder. The resulting degree of polymerization is markedly lower than that of the starting cellulose, which gives the product its specific properties.
Physicochemical Properties and Grades
MCC is chemically inert, physiologically harmless, and non-allergenic. It stands out for its excellent compressibility: under pressure, its particles deform plastically and form numerous interparticle bonds, producing hard, cohesive tablets even at low compression forces.
It also offers good flow properties (particularly in granular grades) and a water-absorption capacity that promotes tablet disintegration. It is available in several standardized grades (PH-101, PH-102, PH-200, PH-112, and others) differing in particle size, density, and moisture content. These variants explain the many microcrystalline cellulose references found in a raw-material catalog.
Use in Pharmaceutical Formulation
Microcrystalline cellulose fulfills several essential functions in the formulation of solid oral dosage forms:
- Diluent / filler: it adds bulk to tablets and capsules containing low doses of active ingredient.
- Binder: it ensures tablet cohesion, particularly in direct compression processes, which it has played a major role in popularizing by removing the need for a granulation step.
- Disintegrant: its ability to absorb water helps the tablet break apart in the digestive tract, releasing the active ingredient.
- Spheronization aid: used in producing granules and microgranules (pellets) via extrusion-spheronization.
It is precisely thanks to excipients such as MCC that poorly compressible active ingredients like paracetamol can be turned into tablets with good hardness and stability.