The present invention provides for methods of preparing silk nanoparticles and microparticles, methods of encapsulating an active agent into the silk nano- and microparticles and compositions comprising these silk particles. In particular, the silk spheres are prepared from phase separation of silk and polyvinyl alcohol (PVA), without exposure to an organic solvent. The method employs a chemical, PVA, which is an FDA-approved ingredient in drug formulations. Different parameters can be adjusted to control the size and shape of the silk spheres during the fabrication process. The silk particle compositions of the present invention may also encapsulate active agents or chemicals. Such compositions allow the active agents to be controllably and sustainably released to the target organs or tissues. The silk composition entrapping active agents also provides for a long-term storage medium for the active agents so entrapped. The silk nano- and microparticles of the present invention are thus suitable for a variety of biomedical and pharmaceutical applications, such as drug delivery or tissue engineering.
