Singapore researchers have solved the pressing issue in materials science of fabricating hollow microspheres with holes of a specific size by controlling the out-diffusion of solvent as the polyurethane spheres form. The team can tune the size of the final holes produced from 75 to 210 nm by changing the diffusion time of encapsulated chloroform from the microspheres into methanol solution from 5 to 20 h.

These hollow particles might now encapsulate smaller guests for the controlled release of pharmaceuticals, inks, cosmetics and pigments and in the protection of active reagents.

• Facile Route to Synthesize Polyurethane Hollow Microspheres with Size-Tunable Single Holes
  M. Li, J. Xue,
  Langmuir 2011.
  DOI: 10.1021/la104860b