The objective of the testing was to assess tablet strength by diametrical compression using a 36mm diameter cylindrical probe.
Tablets are the most widely used dosage forms due to their convenience in administration, compactness and ease of manufacturing. They need to be strong enough to resist chipping (when spun in a hopper) and withstand the stresses of packaging, shipping, and tablet handling by the pharmacist and patient. Tablet hardness affects the ease with which a drug is dissolved in the digestive system, thereby affecting the distribution of the dose at the required rate. Formulating tablets strong enough to undergo subsequent processing and transport and capable of breaking down in the body delivering the required dose at the desired rate is therefore important. Tablet strength testing is necessary for Research & Development of new formulations and for Quality Control. For instance, measuring tablet strength for chewable tablets can be a vital quality control parameter for patient acceptance and their safety.
The diametric crushing test is a common method widely used to measure the force required to cause tablet failure. The area under the curve for the force applied versus tablet deformation curve can be calculated to give Work done to Hardness 1(energy required to crush tablet).
Note: The penetration distance can be modified; however, the target distance chosen should be such that the probe does not touch the base of the fixture base table, otherwise the instrument will be overloaded. Hardness values will increase relative to the increased penetration depths. Consequently, for comparison purposes, penetration distances must always be reported.
Note: When optimising test settings the hardest sample is best tested first in order to predict the maximum testing range for subsequent samples.
Storage, handling and packaging are variable conditions that need to be standardized upon sample testing and reporting of results.
The following is a typical CT3 Texture Pro Plot. The graph shows the Load vs. Time of diametrical compression of a tablet.
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The graph in Figure 1 shows the hardness of a tablet. The area under the graph is Hardness Work Done (energy required to crush tablet), a measure of tablet toughness.
When a trigger force of 100g is detected the test commences. The probe proceeds to deform the sample to a deformation distance of 3mm. The maximum peak in Figure 1 represents the force required to cause the initial breaking of the sample followed by further crumbling of the tablet.
Click to enlarge
The graph in Figure 2 shows the load verses distance for the hardness of a tablet.
Tests obtained from 10 tablets of the same batch give the following mean Hardness and Hardness Work Done values below: