microsuspension

A microsuspension is a liquid suspension that contains solid particles with diameters in the micrometer range, typically from about 0.1 to 10 μm. These particles are larger than those in true colloids or nanosuspensions but small enough that Brownian motion can help oppose rapid sedimentation, at least for a period, when the system is stabilized.

Stability in microsuspensions is achieved through stabilization techniques that prevent particle aggregation. Electrostatic stabilization uses surface charge to create repulsive forces between particles, often quantified by a sufficient zeta potential. Steric stabilization relies on adsorbed polymers or surfactants that create a physical barrier to clumping. Sometimes both mechanisms are employed together. Viscosity modifiers or gel-forming agents can further slow sedimentation and improve redispersibility after sampling.

Preparation methods commonly involve size reduction and dispersion steps. Wet milling, high-pressure homogenization, and bead milling are used to achieve the desired particle size distribution. Dry methods such as spray drying can produce powders that are reconstituted into microsuspensions. Choice of stabilizers, solvent, pH, and ionic strength is guided by the intended application and the physical-chemical properties of the solid.

Applications are widespread in pharmaceuticals for poorly soluble drugs, where a microsuspension can enable oral, topical, or ophthalmic delivery. They are also used in inks, pigments, and agrochemicals. Key considerations include physical stability (sedimentation, caking, Ostwald ripening), rheology, and ease of redispersion. Particle size distribution and stability are typically assessed by microscopy, laser diffraction, and sedimentation tests.