Improving the Observation and Evaluation of Tablets and Tableting Machines

Malfunctions in the tableting process can cause defects in tablets, most often due to the properties of the principal agent. The cause is most often the properties of the principal agent in the medicine. For example, if distributed on the surface of the tablet, this agent will come into direct contact with the metal surfaces of the tableting machine’s punch and die, possibly changing the characteristics of this agent. This is a typical tableting malfunction caused by the inclusion of an inappropriate amount of binding agent.
This defect can be classified according to the amount of binding agent as follows.

Insufficient binding agent
This can cause capping (in which the top or bottom surface of the tablet comes off) and lamination (in which the main body of the tablet comes off).

Excessive binding agent
This can cause defects such as sticking (in which a part of the material affixes to the contact surface of the punch and comes off), picking (in which a small amount of material affixes to the contact surface of the punch, causing patchy strips in tablets), and binding (in which vertical scratches occur on the sides of tablets).

This is another typical problem in tableting and includes decreased hardness (in which tablets are softer than intended due to uneven distribution) and delayed dissolution (in which the dissolution property decreases, which is the opposite problem of decreased hardness). These quality-characteristic errors cause tablets to dissolve with unintended timing in the gastrointestinal tract after the patient takes the medicine, causing it to be absorbed by this tract too early or too late. Hence, the internal medicine does not have its intended effect.

The first countermeasure against these tableting defects and problems when taking medicine is to ensure the hole in the die is filled with the appropriate amount of material. Changes to the characteristics can also be avoided by distributing the binding agent on the surface of the tablet (the die side), preventing the principal agent in the medicine from coming into contact with the die. Sufficient consideration must also be given to the response to water during tablet storage and when taking the medicine.
As such, tablet quality assurance requires that the causes and problems of tablet defects be investigated and eliminated through observation of the outer appearance of tablets. Therefore, clear magnified observation and evaluation through quantitative measurement of the outer appearance and cross sections of tablets are very important.

The VHX Series 4K digital microscope provides a depth of field that is at least 20 times larger than optical microscopes, capturing fully focused images of the entire tablet, even if it is contained in a PTP (press through package).
Imaging tablets through PTP can be difficult due to the light reflections; but by using the ring-reflection removal function, users can clearly observe the surface irregularities on tablets.
This tool is useful for capturing defects and identifying the process in which the tablets were scratched or chipped.

Observation of a tablet in a PTP using the VHX Series 4K digital microscope

Observation of tablet cross sections is vital in investigating the density of tablets and the distribution of ingredients during tableting. However, most tablets consist of a single light color, which makes it easy for glare to occur. Therefore, using conventional microscopes was time-intensive and difficult to determine the optimal lighting conditions.
The VHX Series 4K digital microscope is equipped with a Multi-lighting function that automatically acquires data captured with omnidirectional lighting at the press of a button. The operator just has to select the optimal image from all those that have been acquired, eliminating the time and effort that were conventionally wasted on repeated lighting condition determination. The optimal images for observation of microscopic surface irregularities can now be easily obtained even when observing low-contrast tablet cross sections.
Furthermore, lighting data is saved even after images are recorded, so observation under the same lighting conditions can be performed immediately with no need to determine its conditions again. This allows operators to view samples under the same lighting conditions while minimizing the risk for error.

Observation of a tablet cross section with the omnidirectional lighting of the VHX Series 4K digital microscope

To reduce the occurrences of defective products in the mass production of tablets, it is important to understand the status of tableting machines. Wear on the surface of the punch tip—which acts as a mold and continually contacts the materials, compressing them inside the die—may lead to poor stamping of text information such as the medicine name and dosage, so it is necessary to check the status of punch tips through periodic observation. However, the surfaces of these tips are small, and the surface irregularities used to stamp text have microscopic shapes, so it was difficult to observe these shapes in three dimensions.
The VHX Series digital microscope can capture microscopic shapes and surface conditions while changing the focus position, allowing for observation with 3D images and accurate measurements.
The 3D-displayed stamping surface of the punch tip can be rotated in any direction for efficient observation of microscopic shape changes and surface conditions. Accurate 2D/3D measurements can be easily captured and recorded, making it possible to find trends in wear.

During tableting, the tableting machine’s die molds the sides of the tablet. Scratches on the die are projected onto the sides of the tablet, so checking the internal surfaces of the die is vital to maintaining quality. However, it is very difficult to observe the surface conditions of deep parts at high magnifications and in a non-destructive manner.
The VHX Series 4K digital microscope is equipped with a Multi-lighting function that automatically acquires image capturing data with omnidirectional lighting at the press of a button. Observation can be performed immediately simply by selecting the optimal image, eliminating the hassle of determining the conditions. This product uses a free-angle observation system with XYZ motorized stage to enable tilted observation with easy field-of-view alignment, rotation, and oblique axis motion. Observation from various angles with high-resolution images is possible even for the inner surfaces of small die holes.
Using the high-resolution, fully-focused images captured at any angle or magnification allows users to take accurate sub-micrometer 3D measurements of the subtle surface irregularities on tablets.