Capsules are an important dosage form in the modern pharmaceutical and health supplement industries, and their synthesis methods directly impact product quality and production efficiency. Capsules are generally categorized into two main types: hard capsules and soft capsules, and their synthesis processes differ significantly.
Hard capsule synthesis primarily involves the selection and molding of the capsule shell material. The capsule shell is typically made from a specific mixture of gelatin, glycerin, and water. The gelatin provides toughness, while the glycerin acts as a plasticizer to prevent brittle cracking. During production, the mixture is injected into a mold and dried to form a hollow capsule shell. Subsequently, drug powder or granules are filled into the shell using automated filling equipment and sealed. Controlling the thickness and uniformity of the capsule shell is crucial for hard capsule synthesis to ensure that the disintegration time meets pharmacopoeial standards.
Soft capsules are synthesized using either the drop-casting method or the compression method. The drop-casting method involves injecting the drug solution and gelatin solution separately into two nozzles, forming spherical capsules in a cooling liquid. The compression method utilizes rotary compression to compress the drug and gelatin mixture into soft capsules. Soft capsule shells typically contain a higher proportion of glycerin or other plasticizers to enhance flexibility. Furthermore, soft capsules are often used to encapsulate oily liquids or fat-soluble ingredients, so sealing and content stability are key priorities during synthesis.
Quality control during capsule synthesis includes shell solubility testing, microbial limit testing, and verification of drug content uniformity. With technological advancements, plant-based shells (such as hydropropyl methylcellulose) are gradually replacing traditional gelatin to meet vegetarian or religious requirements. Mastering the core technologies of capsule synthesis methods will help enhance product competitiveness and meet the diverse demands of the international market.
