Particle science and powder technology is an important subject for a pharmacist to develop a finished product in numerous dosage form.

Crystal state

Materials in the solid state can be crystalline or amorphous (or a combination of both). Crystalline materials are those in which the molecules are packed in a defined order, and this same order repeats over and over again throughout the particle.

The processes by which a crystal forms are called nucleation and growth. Nucleation is the formation of a small mass onto which a crystal can grow. Growth is the addition of more solute molecules onto the nucleation site. In order to achieve nucleation and growth, it is necessary to have a supersaturated solution. 

A supersaturated solution is one where the amount o solute dissolved in the liquid is greater than the true solubility. 

If the crystallization conditions are changed in any way, it is possible that the molecules may start to form crystals with a different packing pattern to that which occurred when the original conditions were used. The change in conditions could be a different solvent, a change in the stirring, or different impurities being present.

In summary, a change in the packing arrangement o the same molecule, giving two different crystal forms, could result in significant changes in the properties o the solid.

Amorphous state

When a material is in the solid state but the molecules are not packed in a repeating long-range ordered fashion, it is said to be amorphous. Amorphous solids have very different properties rom the crystal form o the same material. For example, crystals have a melting point (the break-up o the crystal lattice), whereas the amorphous form does not (as it does not have a crystal lattice to break).

Amorphous forms have a characteristic temperature at which there is a major change in properties. This is called the glass transition temperature (Tg). If the sample is stored below the Tg, the amorphous form will be brittle, described as being in the glassy state. If the sample is above its Tg, it becomes rubbery. The Tg, although not well understood, is a point at which the molecules in the glass exhibit a major change in mobility. The lack o mobility when the sample is glassy allows the amorphous form to exist or a longer time.

Crystallization occurs when the absorbed water has plasticized the sample to such an extent that the Tg has dropped below room temperature and allowed sufficient molecular mobility that the molecules are enable to align and crystallize.

Dry powder inhalers

Dry powder inhalers often have a micronized drug, which has to be small enough to be inhaled, mixed with a larger carrier particle which is often lactose. The carrier particle is there to make the powder suitable or handling and dosing, as micronized particles have poor ow properties. The shape and surface properties of the drug and/ or carrier particles can be critical parameters in controlling the dose of drug that is delivered. It may be necessary to adjust the sur ace roughness o carrier particles.

Source: Aulton's Pharmaceutics