Physical characterisation specialist Stable Micro Systems has developed an innovative test method for the pharmaceutical industry.
The Capsule Tensile Rig measures the force required to split one half of a hard gel capsule. This allows manufacturers to investigate the effects of fillings on the mechanical strength of the capsule shell and identify changes that may affect their stability and long-term performance.
The simplified manufacturing process of hard gelatine capsules and their ability to withstand higher filling temperatures is attractive to many manufacturers. Yet, the introduction of certain types of liquid, such as hydrophilic solvents, to hard capsules can often affect the mechanical properties of the shell, causing it to become brittle or to soften. If the texture of a capsule is compromised, it may not be able to withstand handling and storage, resulting in leakage of the fillings.
As effects are likely to be progressive, only displaying very small changes initially, compressive tests are often limited in their ability to distinguish the anomalies. Stable Micro Systems" Capsule Tensile Rig is designed to help manufacturers identify subtle degradation, providing valuable information which can be used to avoid subsequent capsule failure.
Prior to testing, the filling of the capsule is removed and the empty shell is mounted to a separating rod fixture on the TA.XTPlus texture analyser. Vertical movement of the upper rod is then applied until the capsule is split apart, while Exponent software records the force required to do so. This test highlights three important parameters; elastic stiffness (if a linear region on the graph is present), tensile force and elongation at break point. A reduction in elastic stiffness and tensile strength occurs when capsules become softer and therefore show a tendency to fail.