Microcrystalline Cellulose

Microcrystalline cellulose (MCC), often known as Avicel, is the most common of cellulose (Fig.1) powder used in tablet formulation. It exists in two grades, pH 101 (powder) and pH 102 (granules), and possesses good flow properties with excellent direct compression characteristics.

Fig. 1: The chemical structure of cellulose.
Fig. 1: The chemical structure of cellulose.

Microcrystalline cellulose is insoluble in water and alcohol. Despite being insoluble in water, promotes rapid penetration of water into tablet matrix through capillary action. This process causes disintegration by breaking hydrogen bonds between cellulose microcrystal bundles. The existence of hydrogen bonds responsible for the mechanical strength and disintegration of microcrystalline cellulose tablets.

The Function of MCC

The function of MCC in tablet formulation is: it acts as a diluent (bulking agent) and a disintegrating agent and a compression aid. As a diluent, it is a somewhat unique diluent in that while producing cohesive compacts. It is, however, a relatively expensive material when used as a diluent in high concentration and is thus typically combined with other materials. As in the case of starch, microcrystalline cellulose is often added to tablet formulation for several possible functions. The function of microcrystalline cellulose in tablet formulation is twofold: it acts as both a diluent and a disintegrating agent. As a diluent, it helps produce cohesive compacts, but it’s relatively expensive in high concentrations, so it’s often combined with other materials. Additionally, microcrystalline cellulose serves as a disintegrating agent and compression aid, providing high compactibility-compressibility, good flow behavior, improved blending, and potentially enhanced disintegration in drug formulations.

Microcrystalline cellulose can play a unique role in granulation. Usually regarded as a direct compression filler–binder because of its high compactibility. However, microcrystalline cellulose is sometimes also added extragranularly, often at a level of 10–25%, to enhance the compactibility of the running mix when the granulation itself lacks sufficient compactibility. Furthermore, despite losing compactibility after wet granulation, microcrystalline cellulose can be added intragranularly as a granulation aid, typically at levels between 5% and 20%. It’s hydrophilicity and water holding capacity contribute to the improvement of both the granulation and drying processes. It’s presence intragranularly promotes rapid, even wetting and drying, aiding in avoiding overrunning the granulation endpoint during high shear mixing. Additionally, it reduces the tendency toward uneven distribution of soluble colorants (and other soluble components) that can result from migration during granulation drying. Based on specific data from preformulation studies and other constraints, improved initial formulations may be utilized.

Microcrystalline cellulose formation

The name indicates that the particles have both crystalline and amorphous regions, depending on the relative position of the cellulose chains within the solid. The degree of crystallinity may differ depending on the source of the cellulose and the preparation procedure. The degree of crystallinity will affect the physical and technical properties of the particles, e.g. in terms of hygroscopicity and powder compactability. Microcrystalline cellulose is prepared by hydrolysis of cellulose followed by spray-drying. The particles thus formed are aggregates of smaller cellulose fibres. Depending on the preparation conditions, aggregates of different particle size can be prepared which have different flowabilities.

Reference:

  • Aulton, M. (2018). Aulton’s pharmaceutics, the design and manufacture of medicines. Edinburgh. : Elsevier.
  • Khar, R.,Vyas, S., Ahmad, F., & Jain, G. (2016). Lachman/Lieberman’s The Theory and Practice of Industrial Industrial Pharmacy. New Delhi, ND: CBS Publishers & Distributors Pvt Ltd.