Best Practice: Testing Softgel Capsules

Softgel capsules are widely used in medicines, as well as vitamin and mineral supplements. The active ingredients are packaged inside a capsule or microcapsule to provide protection from the surrounding environment. At an appropriate time after the consumer places the capsule into their mouth, the ingredients are released by rupture, dissolution, melting, or diffusion. The rate at which these processes occur largely depends on the strength of the capsule wall.   

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Texture analyzers are used to test materials in compression or tension. The strength of the capsule wall is quantified using the texture analyzer in a penetration test with a 2-mm-diameter cylinder probe (shown in Figure 1) and a 4.5-kg load cell. This method determines the film strength (i.e., rupture point) of the softgel capsule. This same method is also used to detect points of weakness in a gelatine film or seal during the manufacturing process, simulating circumstances whereby a capsule might burst during packaging and transport.

The texture analyzer can also quantify the elasticity of the softgel capsule shell by measuring the deformation of the wall at a defined compressive load. Seal strength can be determined using a compression probe with a diameter larger than the capsule diameter (e.g., a 36-mm cylinder probe). The seal is positioned perpendicular to the probe and the force to break the seal is measured.  

Test settings
When optimizing test settings, the hardest sample is tested first to predict the maximum force range that will be required. This ensures that the load cell selected for the texture analyzer has sufficient measurement range to test all capsules. Typical settings for a compression test are a probe speed of 1.0 mm/s, a target distance of 8 mm, and a trigger force of 10 g; this is the threshold force that the probe detects before the texture analyzer begins to record test data.

Figure 2 is a typical graph from a compression test, which can be used to calculate the rupture force and elasticity of a softgel capsule. In Figure 2, the probe penetrates the sample to a deformation distance of 8 mm. The energy required to deform the sample to this defined deformation distance, as measured by the instrument, is the &#;work done hardness.&#; If the capsule cracks or splits open during the test, the measured force will suddenly drop off. The peak load equates with the rupture force required to break the capsule wall and indicates the capsule wall&#;s hardness. Harder samples will give a higher peak load and a higher work done hardness.

The elasticity of the capsule can be quantified by measuring the deformation distance at hardness (i.e., at the peak load). Elastic samples will have a higher deformation distance compared to brittle samples.

Multiple samples can be tested on the texture analyzer, and the software used with the instrument can calculate average values with standard deviations. These statistical data enable the quality assurance group to set control limits for acceptable product coming from manufacturing. As an example, test data obtained from 10 softgel capsules of the same batch are shown in Table I. 

Mean peak load
"Hardness"
(+/- SD)
(g)

Mean work done
Hardness 1
(+/- SD)
(mJ)

About the Authors
Chris Freeman, ,  is senior product manager, Texture Analyzers, and Claire Freeman, PhD, is laboratory tech specialist, Ametek (GB) Limited, both at Brookfield Technical Centre, Stadium Way, Harlow, Essex CM19 5GX England, : (44) .  

The 6D(SG) Soft Gelatin Capsule Tester is the soft gel variant of the world renowned model 6D tablet hardness tester. It is capable of measuring any shape liquid and cream filled Soft Gelatin Capsules for deflection and burst strength.

For more information, please visit Cell Instruments.

The 6D(SG) Soft Gelatin Capsule Tester is the soft gel variant of the world renowned model 6D tablet hardness tester. It is capable of measuring any shape liquid and cream filled Soft Gelatin Capsules for deflection and burst strength. The 6D(SG) uses a combination of precision potentiometer and load cell technology to precisely determine the diameter and force applied to each capsule. The instrument's accuracy is east to maintain and you can calibrate or verify the instrument yourself in a matter of minutes using NIST traceable weights and gauge blocks. The operator can test individual samples or batches of up to 100 capsules. In semi automated mode a programmable delay gives you time to place the capsule in the correct position.

The 6D (SG) has an option of three depression tests and a burst test. The four tests, described below, can be administered to either the length or width of the capsule with the width being the most informative axis for testing soft gels. Hard shell capsule dome and force to lock tests require applying a force along the length of the sample.

FOUR TYPES of VARIABLE INPUT CAPSULE TESTS

• The Fixed Distance Depression Test measures the force required to depress a test sample by a select number of millimeters. Example: A test sample measuring 23.09mm (D1) required a force of 1.3 Kp to depress it 3mm to 20.09mm (D2). The 3mm setting is the test variable chosen by the operator for this particular test.

• The Percentage Distance Depression Test measures the force required to depress a test sample by a given percentage of a chosen dimension. Example: A test sample measuring 9.74mm (D1) required 10.8 Kp of force to compress it 25% to 7.30mm (D2). The 25% setting is the selected test variable.

• The Fixed Force Depression Test measures the amount of depression a specified force has on the test sample. Example: A selected force of 6kp depressed a 9.81mm (D1) test sample to 8.31mm (D2). In test types #1 and #2 we are interested in knowing the force (Kp) required to satisfy the test's objective. In this test we are interested in the resultant size in millimeters of D2 when the selected force of 6 Kp is applied to the test sample.

• The Burst Test is virtually the same as a tablet hardness test. The tester first measures the test sample's beginning dimension, D1. Next the force or hardness it takes to burst the sample will be recorded along with the D2 dimension at the point where the test sample failed. Example: A 7.35mm (D1) test sample required a force of 15.7kp to cause it to burst. The dimension at which the burst event took place was 3.01mm (D2).

Using one or more of the above tests enables you to perform the follow types of tests.

Hard Shell Capsule Tests

• Cap dome test
• Body dome test
• Force to lock-empty
• Force to lock-filled
• Burst- liquid filled

Soft Shell Capsule Tests

• Seam integrity-burst x axis test
• Seam integrity-burst y axis test
• Fixed distance depression test
• Fixed percentage depression test
• Fixed force test

Sample test reports are available upon request.

Features:

• Strain Gauge S Beam Load Cell
• Large LED Character Display
• Simple User Menu
• Manual or Automatic Mode
• Easy Calibration
• Calibration Verification Function
• RS232 Data Output Port
• Debris Receptacle

Options:

• Snap-in Special Jaws
• Grooved platform for ease of oblong tablet alignment
• Plain Paper Printer
• TabStat data gathering and statistical software
• 21 CFR Part 11 PH21 software
• Calibration Kit
• Handheld keypad or flat standard or dustproof & spill proof keyboard
• Mechanical Tablets - 5, 10, 15 & 20 Kp
• Tablet Hardness version
• Complete Validation Protocol and Service Contracts

Contact us to discuss your requirements of gelatin capsule tester. Our experienced sales team can help you identify the options that best suit your needs.