Tablet hardness testing is a laboratory technique used by the pharmaceutical industry to determine the breaking point and structural integrity of a tablet and find out how it changes "under conditions of storage, transportation, packaging and handling before usage" [1] The breaking point of a tablet is based on its shape. [2] It is similar to friability testing, [1] but they are not the same thing.
Tablet hardness testers first appeared in the 1930s. [3] In the 1950s, the Strong-Cobb tester was introduced. It was patented by Robert Albrecht on July 21, 1953. [4] and used an air pump. The tablet breaking force was based on arbitrary units referred to as Strong-Cobbs. [3] The new one gave readings that were inconsistent to those given by the older testers. [3] Later, electro-mechanical testing machines were introduced. They often include mechanisms like motor drives, and the ability to send measurements to a computer or printer. [3]
There are 2 main processes to test tablet hardness: compression testing and 3 point bend testing. For compression testing, the analyst generally aligns the tablet in a repeatable way, [2] and the tablet is squeezed between a fixed and a moving jaw. The first machines continually applied force with a spring and screw thread until the tablet started to break. [3] When the tablet fractured, the hardness was read with a sliding scale. [3]
There are several devices used to perform this task:
According to the International System of Units, the units of measurement of tablet hardness mostly follow standards used in materials testing.