The size of the particles that comprise a formulation is critical for several types of drug formulations, especially those that consist of a solid that is or will be suspended in a liquid, such as a lyophilized powder, aerosol, spray or liquid suspension. Particle size is also highly critical for oil-based formulations such as emulsions and emulsifiable concentrates.
Achieving a mean particle size of less than 2 µm is necessary primarily for the mode of application, the homogeneity of a formulation and the consistency of how a formulation is dispersed or taken up at the target site. Typically, the ideal particle size of a formulation is obtained through a milling process that breaks the larger particles into smaller particles, or a sonication process, which applies sound energy. Obtaining an acceptable particle size is also enhanced or restricted by the types of surfactants used within a formulation, and many of the formulation compositions created in the design phase are weeded out at this stage.
Hamilton's automation solution can aid in both wet and dry milling of particles by preparing the formulation samples with the addition of various size beads (e.g., glass or steel beads), capping sample tubes or plates and using on-deck shakers to vigorously mix components at specified time intervals to facilitate the particle milling process (shown below).
Hamilton’s automated systems can then decap sample vessels and aid in the liquid addition and sampling to dry-milled components to create a sample solution for particle size analysis, or simply pipette an aliquot from a wet-milled sample for particle size analysis. The graph below shows the particle size distribution from a pre- and post-milled formulation sample that was prepared and milled on a Hamilton liquid handler. The Hamilton milled formulation sample below was determined to have a mean particle size of 1.2 µm after the automated milling process.
Particle size reduction can also be achieved for emulsion and emulsion concentrate formulation sample types with Hamilton automation by integrating an automation-friendly sonicator instead of bead milling.