White Paper: How To Scientifically Test Seal Integrity Of Soft Gel Capsules And The Dome Strength Of Empty Hard Shells

By Walter Friesendorf, Pharmatron, Inc.

Hardness testing is generally considered the exclusive providence of tablet manufacturing and related QC/QA activities. However, this basic form of force testing has proven to be a useful and often overlooked tool for qualifying and quantifying the seal integrity of soft gelatin capsules. Measuing the moisture content of dried and cured or aged soft gels provides little, if any, scientific insight to the strength or integrity of the seal.

To test seal's integrity we'll perform a burst test, which is virtually the same as a traditional tablet hardness test. A burst test requires the capsule to be positioned so the force is applied to the capsule's diameter and not the length. The seal must be oriented vertically or perpendicular (in the Y axis) to the testers tongue, which is in the X axis. (The tongue is the flat portion of the testing jaw that the test sample sits on as the slide depresses the sample against the anvil/pressing jaw) The force or hardness it took to burst the sample will be recorded along with the dimension where the test sample failed. This is the result of the test. The starting diameter (D1) was 7.35mm. A force of 15.7Kp casued the capsule to rupture its seal. The dimension at which the rupture event took place was 3.01mm.