How to Measure the Physical Properties of Pharmaceutical Products

One field becoming increasingly significant to the pharmaceutical industry is that of texture analysis, which is being used to uphold quality standards, whilst providing essential product data and benchmarking statistics. Instruments such as Stable Micro Systems’ TA.XTplus texture analyser may be supplied with a range of optional probes and attachments, which are fitted to the body of the machine in order to perform various tests on different products during research and development, production and quality control.

Typical Texture Analysis Tests for Pharmaceutical Products

How to Measure Tablet Hardness

Conventional testing measured only the point force at which tablets snap, but crush (diametral compression using a cylinder probe) testing using a Texture Analyser - particularly for controlled-release products provides valuable information about the likely performance of the tablet. Whilst capable of breaking up readily at a controlled rate inside the body, they must be strong enough to withstand further manufacturing procedures (such as coating and packing), transportation and handling. Formulation and processing variables can be assessed using such tests.

Tablet Strength Test and typical graph

Tablet Strength Test and typical graph

How to Measure Tablet Coating Adhesion

Coating formulation is of primary concern because it can have a crucial effect on the performance of the tablet and the release of the active ingredients in it. Dyes and other inorganic materials can act as stress concentrators, encouraging cracking, edge splitting peeling, which can have a profound detrimental effect if the tablet has been coated with an entero-insoluble or sustained release film. It is now possible to perform tests using a Tablet Coating Adhesion Rig to ascertain the adhesive strength of the coating to the tablet surface. This enables manufacturers to assess the impact of changes in coating formulation.

Tablet Coating Adhesion Rig and typical graph

Tablet Coating Adhesion Rig and typical graph

How to Measure Tablet Disintegration

A thorough analysis of disintegration behaviour is vital for the formulation of new fast-melt tablets (FMTs) to ensure reliable and consistent drug release. The tablet or wafer has to be resilient enough to endure manufacturing and shipping, yet release sufficient disintegrants to deliver an optimum dissolution rate. The Tablet Disintegration Rig facilitates reliable assessment of the mechanical properties of FMTs. The rig closely replicates the in vivo conditions of the human mouth, enabling manufacturers to examine water absorption and the disintegration of associated particles.

Tablet Disintegration Rig and typical graph

Tablet Disintegration Rig and typical graph

How to Measure Mucoadhesion

The swelling and disintegration properties of gel coatings, which are designed to adhere to the intestine or other mucosae, determine the time taken for the dissipation of the gel and the subsequent release of active ingredients. Using a cylinder probe, manufacturers can track changes in sample thickness over specified immersion times, whilst penetration tests provide information on the movement of the penetration front and the increase in gel layer thickness. Mucoadhesive testing measures the adhesion of polymeric devices to a mucosal surface in conditions similar to those in the body.

Mucoadhesion test and typical graph

Mucoadhesion test and typical graph

How to Measure Hard Capsule Strength

The hard capsule is an ideal pharmaceutical form for producing several types of products because it can function either as a simple edible package to deliver its coated particulate contents to the start of the GI tract or it can be converted by coating into a complex delivery system. The brittleness, hardness and flexibility of hard gel capsules impacts their ability to be filled and to withstand variable storage conditions.

The Capsule/Loop Tensile Rig measures the force required to split one half of a hard gel capsule. This allows manufacturers to investigate the effects of certain fillings on the capsule shell and identify changes that may impact their stability and long-term performance.

Prior to testing, the filling of the capsule is removed and the empty shell is mounted to a separating rod fixture on the texture analyser. Vertical movement of the upper rod is then applied until the capsule is split apart, while the force required to do so is recorded. This test highlights three important parameters; elastic stiffness, 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. If the texture of a capsule is compromised, it may not be able to withstand handling and storage, resulting in fillings leaking from the capsule.

Capsule/Loop Tensile Rig and typical comparative graphs

Capsule/Loop Tensile Rig and typical comparative graphs

How to Measure Soft Capsule Bursting Strength

A TA.XTPlus Texture Analyser can used for determining the bursting point of soft gelatin capsules and this is useful for measuring the points of weakness in the gelatin film and/or in the seals of the capsules during manufacture.

One traditional method involves taking a strip of gelatin film, making a dumbbell shaped piece for testing, placing the wide ends in the upper and lower jaws of a texture analyser and measuring the forces to stretch the film to a given distance and/or to rupture the film. Low speeds of 1 to 2mm/s are frequently used for gelatin film.

The most common test of soft gel capsules is the bursting test which is a way to determine the weak point in the capsule using a small diameter cylinder probe. When the probe descends into the gel capsule the force is driven perpendicular to the line of force and the seal is tested. Some say the seal is the strongest point and they want to test the bursting point of the film and thus have the capsule seal in a vertical orientation so that the probe applies the force directly against the seal line. The maximum force provides the measure of rupture force and the distance at this point indicates the elasticity of the capsule.

Typical capsule burst test using a 2mm cylinder probe

Typical capsule burst test using a 2mm cylinder probe

For a full summary of typical texture analysis tests that can be performed on pharmaceutical products:

This information has been sourced, reviewed and adapted from materials provided by Stable Micro Systems Ltd.

For more information on this source, please visit Stable Micro Systems Ltd.

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