Soft gelatin capsules and die roll engineering: a comprehensive review of die roll designs, global manufacturing...

Soft gelatin capsules (softgels) are among the most commercially significant oral dosage forms, offering hermetic liquid and semi-solid encapsulation with superior bioavailability. Central to their manufacture is the rotary die encapsulation process, in which precision die rolls simultaneously form, fill, and seal capsules from two gelatin ribbons. Despite its critical role in determining seam integrity, leakage resistance, and efficiency, a comprehensive peer-reviewed analysis of die roll design classifications has not been published previously. This review analyses seven principal designs: single-step (uni-lip), double-step (bi-lip), D-Step Outer (DS-O), D-Step Inner (DS-I), triple-step (tri-lip), Max Offset Seal (MOS), and blasted surface. For each design, the mechanistic basis, application domain, advantages, limitations, and quality implications are examined. Special attention is given to the MOS architecture for trailing-edge seam asymmetry in suspension fills, the DS-I configuration for moisture-sensitive active pharmaceutical ingredients, and the glass bead-blasted surface for universal pinhole leakage mitigation. A global survey of encapsulation machine and die roll manufacturers-including Changsung, Technophar, Schaefer Technologies, United Pharmatek, Joysun, SEC Softgel, Hedagel, SKY Softgel, CapPlus Technologies, and AIPAK/SaintyCo-is presented (Table 2). Five comparative tables and six annotated figure placeholders cover die roll specifications, process parameters, service life, troubleshooting, and advantages versus limitations. Regulatory considerations under ICH Q8/Q9/Q10, FDA 21 CFR 314.70, and GCC/SFDA frameworks are discussed. Future directions include digital twin simulation, AI-assisted die design, and additive manufacturing tooling. This review serves as an authoritative reference for die roll selection, optimisation, troubleshooting, and regulatory lifecycle management.