Capsules are a widely used dosage form in medication and supplements, consisting of an outer shell that encloses active ingredients. Their popularity stems from factors such as ease of swallowing, portability, and the ability to mask unpleasant tastes or odors.
Understanding Capsule Varieties
Capsules fall into two main categories: hard-shelled and soft-shelled. Hard-shelled capsules have a two-piece design, with a body and a cap that fit together. They commonly encapsulate dry ingredients like powders, granules, or pellets. Their shells are typically made from gelatin or plant-based cellulose materials like hydroxypropyl methylcellulose (HPMC).
Soft-shelled capsules, or softgels, feature a single, sealed construction. They are suited for encapsulating liquids, suspensions, or semi-solid formulations. Softgel shells are typically made from gelatin combined with plasticizers like glycerin or sorbitol, which provide flexibility.
The Hard Capsule Manufacturing Process
Empty hard-shelled capsules are created using a precise, multi-step dipping process. Raw materials such as gelatin or plant-based polymers are dissolved in demineralized water, heated to approximately 60-70 degrees Celsius, to form a viscous solution. Colorants and opacifying agents may be added for desired appearance.
Stainless steel pins, shaped to form capsule halves, are then dipped into this solution. As the pins are withdrawn, they are rotated to ensure an even coating and to remove any excess material, which helps in achieving uniform thickness and size. The coated pins then pass through drying ovens, where controlled temperature and humidity solidify the material into rigid shells.
Once dried, capsule halves are mechanically stripped from the pins and trimmed. The two halves, a smaller body and a larger cap, are then joined to form the empty hard capsules, ready for filling.
The Soft Capsule Manufacturing Process
Soft-shelled capsules are manufactured through an integrated process where the shell is formed and filled simultaneously, typically using the rotary die encapsulation method. The process begins with preparing a warm, liquid gelatin mass by mixing gelatin with water, plasticizers like glycerin or sorbitol, and sometimes colorants or opacifiers. This mixture is heated to around 60°C until fully dissolved and homogenous.
This liquid gelatin is then spread onto cooling drums, forming two continuous, pliable ribbons. These ribbons are fed into the rotary die machine, where they converge. As the ribbons meet, the fill material is accurately injected between them through a filling wedge.
Rotating dies simultaneously press, cut, and seal the capsule, shaping it while encapsulating the fill material. After encapsulation, softgels are transferred to drying tumblers and then spread onto drying trays for several days. This allows excess water to evaporate, achieving final hardness and stability.
Filling and Final Preparation
For hard capsules, empty shells are separated into cap and body components by specialized machinery. The body of the capsule is then precisely filled with a measured amount of the active ingredient, such as powder, granules, or pellets. After filling, the cap is rejoined with the body, and the capsule is securely closed.
Following filling, both hard and soft capsules undergo further preparation to ensure cleanliness and integrity. Capsules are typically passed through polishing machines, which use rotating brushes and vacuum systems to remove residual powder or dust. This cleaning enhances appearance and meets hygiene standards. A visual inspection, manual or automated, identifies and removes capsules with defects in shape, integrity, or appearance.
Quality Control and Assurance
Rigorous quality control and assurance measures are implemented throughout manufacturing to ensure capsule safety, quality, and efficacy. In-process checks continuously monitor parameters like capsule weight, dimensions, and fill volume accuracy.
Finished capsules undergo comprehensive tests. Disintegration and dissolution testing verify the capsule shell breaks down and releases contents appropriately, ensuring active ingredients are available for absorption. Content uniformity testing confirms each capsule contains the correct and consistent amount of active pharmaceutical ingredient, which is crucial for patient safety and therapeutic effect.
Stability testing assesses how capsules maintain quality over time, establishing their shelf life. Microbial testing ensures the absence of harmful microorganisms, upholding product safety standards. Adherence to Good Manufacturing Practices (GMP) and other regulatory standards is maintained throughout all production stages.