Formulation Factors Affecting Capsule Brittleness

By: ACG North America

Gelatin capsules are a popular dosage form for numerous reasons, including faster speed to market and improved patient compliance. Brittleness is one of the common challenges associated with capsule performance. Capsule manufacturers often implicate poor performance of a capsule to manufacturing processes or storage conditions. However, it is important to realize that formulation parameters play an important role in overall capsule performance, including its tendency to become brittle.

Here’s looking at 4 major formulation factors that may have an impact on brittleness of capsule:

  1. Type of gelatin used

Gelatin is the main component of hard shell capsules and is derived from the chemical degradation of collagen. It behaves very differently depending on whether its macromolecules are in the collagen-like helical or coiled conformation. In the former case, the gelatin exhibits properties suitable for use at ordinary temperatures. However, in the latter case, gelatin is a typical rigid-chain polymer and behaves as a brittle impractical material. It does so because of the absence of water. Information about the performance of gelatin in terms of brittleness can be obtained by analyzing glass transition temperature and polymer crystallinity. Higher the crystallinity, the higher is the tendency of the gelatin to become brittle.

  1. Pigments

Pigments cause opacity and create a protective barrier to harmful radiation. However, they also play a significant role on mechanical properties of capsules; higher the pigment content, the higher is brittleness. Therefore, it is critical to formulate the capsule with optimum pigment content.

  1. Molecular weight

It is well known that molecular weight and molecular weight distribution can markedly affect the mechanical properties of a polymer. It is important to use the polymer of an optimum molecular weight: high enough for delivering good mechanical properties, but not too high that renders processability difficult.

Subjecting gelatin to higher temperatures for a long duration can cause polymer chains to fragment, reducing the molecular weight and deteriorating the capsule performance in terms of brittleness.  Therefore, it is important that processes that need gelatin to be heated are performed in the shortest possible time.

  1. Use of plasticizers

Plasticizers are often used to reduce the stiffness of a polymer by reducing the cohesive intermolecular forces along the polymer. The amount and choice of the plasticizer contribute to the hardness of the final product and may even affect its dissolution or disintegration characteristics, as well as its physical and chemical stability. For hard gelatin capsules, water acts as a plasticizer. Therefore, at low relative humidity, these capsules lose moisture and become brittle. Softgels capsules are more elastic owing to plasticizers such as glycerol or sorbitol and propylene glycol used in combination with glycerol.

In conclusion, numerous formulation parameters can affect the mechanical properties of raw materials and the capsule itself.  Extensive experience in the field of capsule manufacturing is needed to identify core fundamental properties that affect capsule performance. Therefore, it is important for manufacturers to also be cognizant of and have a stringent check over these parameters to improve the hard gelatin capsule performance.

With over fifty years of industry expertise, ACG is an integrated processing, manufacturing and packaging solutions provider to the global pharmaceutical industry. It is the world’s second largest manufacturer of high quality empty hard capsules. ACG’s capsule range is designed to provide customized solutions to the pharmaceutical and nutraceutical industry. 



Official blog of: INTERPHEX New York -
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