Testing: How Leak-Proof are Your Capsules?
Testing: How Leak-Proof are Your Capsules?
Claire Freeman
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Ametek Brookfield
Leaking gelatin capsules diminish consumer confidence in the product and the manufacturer. To prevent defective capsules from reaching the market, you must develop tests to identify them. One approach is to use a texture analyzer instrument that applies tensile and compressive forces to gelatin capsules to confirm they have sufficient wall strength to withstand external forces during manufacturing, storage, packaging, and transport.
When formulating a capsule drug product, it&#;s important to know whether the fill&#;both the API and excipients&#; is compatible with the gelatin shell, which comprises a mixture of water-soluble proteins. Any substances that contain aldehydes (e.g., formaldehyde) can cause the gelatin to cross-link, with lysine residue within and between gelatin strands. This stiffens the gelatin structure and slows its disintegration. Learning how a fill will interact with the gelatin shell&#;s water content is also important. A highly hygroscopic fill, for instance, may absorb water from the shell and cause it to become brittle and more prone to breakage.
A texture analyzer quantifies the mechanical strength of hard gelatin capsule shells so you can assess how different fills affect capsule strength and stability. It does so by imposing controlled mechanical conditions on a sample and then quantifying the resulting behavior. How the samples respond relates directly to their physical characteristics and provides a real-life indication of their internal structure.
A texture analyzer operates in tension or compression mode and can perform cyclic testing, in which it imposes a deformation action multiple times. The instrument measures load force, usually in grams, and associates it with capsule deformation. The results are then presented in a graphical format as force versus time or as force versus distance. Various textural parameters can be at work during deformation and it&#;s possible to observe them in the force-deformation curve that the test generates. In the last 40 years, many academic studies that used texture analysis have correlated these behaviors with their sensorial characteristics.
Capsule-Loop Tensile Test
Equipping the texture analyzer with a capsule-loop tensile fixture, as shown in the photo above, enables you to compare the mechanical strength of empty capsule shells. In practice, the fixture&#;s two thin rods are inserted into one half of the capsule shell, usually the cap. The lower rod is then anchored to the instrument base, while the upper rod is attached to the drive mechanism of the analyzer. The drive lifts the upper rod at a steady rate, typically between 0.1 and 1.0 millimeter per second, stretching the capsule shell a defined distance. In some cases, the test causes the shell to rupture.
Figure 1 shows that Sample A resisted stretching better than Sample B. That result is also reflected under the heading &#;Work done&#; in Table 1, which indicates Sample A was twice as resilient as Sample B.
Compression Test
A texture analyzer can also measure the compressive strength of a soft gelatin capsule (softgel) using two test methods. In the first, a probe 36 millimeters in diameter is used to quantify the seal strength (Figure 2) and in the second&#;a penetration test&#;a 2-millimeter cylindrical probe determines the softgel&#;s rupture point. The two tests not only identify weaknesses in the softgel&#;s strength, they simulate the circumstances under which the softgel could burst during packaging or transport. When measuring the seal strength of any capsule&#;hard or soft&#;use a compression probe whose diameter is larger than the capsule and orient the seal perpendicular to both the probe and the applied force. See the photo below. Table 2 lists the results of softgel hardness tests.
Gel Strength Test
Gelatin is used in many industries and in many different applications, and in nearly all cases, both the gelatin manufacturer and the end-user measure gel strength, which indicates its effectiveness. Gel strength depends largely on bloom strength. The photo on the next page shows a bloom jar with a gelatin sample ready to be tested.
Using a texture analyzer equipped with a standard bloom probe, bloom bottles, and a gelatin bath, you can perform simple tests and quickly and accurately determine gel strength, which is measured as the force required to deform the gel over a specified distance.
A texture analyzer can be used to quantify the gel strength of gelatin according to the British Standard Method, &#;Sampling and testing gelatin&#; (BS757: ) or by using standards from the Gelatin Manufacturers Institute of America (GMIA) or the Gelatine Manufacturers of Europe, which in adopted the GMIA standard. As a result, all current methods specify the use of a flat-faced cylindrical probe 12.7 millimeters in diameter with a sharp edge. (The European method specified a probe with a small radius instead of a sharp edge.)
This method can also be used with other capsule shell materials, such as HPMC. When testing samples with high mechanical strength, consider using a load cell with a larger capacity. Likewise, for samples with a highly elastic component, you may need to lengthen the test distance.
Additional reading:How to Choose Sesmic Sensor? 7 Key Factors to Consider
For more information, please visit Cell Instruments.
Conclusion
By identifying key characteristics that affect the finished product, texture analysis is an integral part of R&D, process optimization, and production. It helps guide your choices during the initial stages of development and provides at-line process control. By setting high and low limits of acceptance, texture analysis enables you to optimize manufacturing and reduce waste.
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How To Scientifically Test Seal Integrity Of Soft Gel ...
•White Paper: How To Scientifically Test Seal Integrity Of Soft Gel Capsules And The Dome Strength Of Empty Hard Shells
By Walter Friesendorf, Pharmatron
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.
Click Here To Download:•White Paper: How To Scientifically Test Seal Integrity Of Soft Gel Capsules And The Dome Strength Of Empty Hard Shells
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