Wettability is a property of a solid, which determines how liquid spreads and interacts with it. Wettability is most typically measured with a water contact angle measurement where a drop of water is placed on the solid surface and the shape of the drop is analyzed. When the contact angle is below 90 degrees, the surface is said to be wettable, when the contact angle is over 90 degrees, the surface is non-wetting.
Wettability plays an important role in many industrial applications where solid, and liquid interact. In the pharmaceutical industry, the solid is often in the form of a powder. In pharmaceutical powders, wettability plays a pivotal role in formulation, storage, and the performance of dosage forms.
Wettability is important in the manufacture of pharmaceutical dosage forms
Wettability has a crucial role in the granulation process used in pharmaceutical manufacturing. In granulation, the particles are combined into larger granules. Granulation is done to improve the flowability of your formulation, make your formulation more compressible, or to improve the distribution of API (active pharmaceutical ingredient) in your formulation.
The most typical way for granulation is called wet granulation where the granulation liquid (ideally water) is spread over the particles to allow liquid bridges to form between them to enhance the formation of granules. A good wettability of the solid is required to get uniform liquid distribution and well-controlled granule growth. If the wettability is poor, the liquid film around the particle is not formed and necessary adhesion is not achieved. On the other hand, if the wetting is too good, an excessive water layer may lead to adhesion problems between particles. Also, hydrates may form on the surface which can have different adhesion properties than the original drug substance. Another aspect to consider is the wetting characteristics of all the powders involved, not just to active drug but the excipients as well.
The efficacy of the drug is dependent on wettability
The efficacy of the drug is the combination of drug dissolution, drug bioavailability, and in vivo performance which are all related to wettability. Improving the wettability of a drug leads to less agglomeration of drug particles in contact with the liquid. Thus, the dissolution rate is also increased because of the greater surface area available.
As wettability plays a crucial role in both the manufacturing as well as efficacy of drugs, contact angle measurements on pharmaceutical powders are important.
If you would like to learn more about powder wettability and measurement techniques, please register for the webinar through the link below.
