Characterization of sonochemically prepared proteinaceous microspheres

Aqueous suspensions of albumin and haemoglobin microspheres can be synthesized using high-intensity ultrasound. The particle size distributions are Gaussian with mean diameters of a few micrometers. These microspheres can contain either nonaqueous liquids (i.e. microcapsules) of air (i.e. microbubbles). The chemical processes involved in the synthesis and some physical properties of the microspheres have been elucidated. Yields and size distributions of albumin microbubbles as a function of experimental parameters indicate that the microspheres are held together primarily by disulphide cross-linking of cysteine residues between protein molecules. The primary oxidizing agent is superoxide (HO₂), which is generated from water and oxygen during acoustic cavitation. Physically, the protein within the microsphere shell is not significantly denatured; the heme held within haemoglobin, for example, is fully retained. Optical, scanning electron, and transmission electron microscopy reveals spherical particles with diameters between 1 and 3 μm, and an approximate shell thickness of roughly 30 nm.