The IUPAC defines a microsphere as a “microparticle of spherical shape without membrane of any distinct outer layer”, with a note that quality, sphericity, uniformity, particle size, and particle size distribution (PSD) vary wildly. Microscopic glass beads produced in New York in 1914 are perhaps the earliest example of synthetically produced particles which would fit that description. By 1922, enormous quantities of glass microspheres with high refractive indices were commissioned to produce movie screen coatings.
Hollow glass microspheres were developed as an offshoot of these glass beads during the ‘50s. Sometimes described as micro-balloons or glass bubbles, these hollow particles offered a significantly reduced density to solid glass microspheres, combined with enhanced functionality. This initiated the rapid growth and acceleration of microsphere technology. During the ‘60s, microspheres were used as fillers for the booming plastics industry.
Today, ceramic microspheres are available for industrial applications, improving composite thermosets’ durability, strength, and toughness. Some ceramic microspheres even serve biomedical applications, such as minimally invasive implantation and bone defect filling. Likewise, glass-based microspheres have been used in pharmaceuticals, specifically as novel delivery systems for biodegradable radiation.