Nanospheres are polymeric matrix of spherical shape that ranges in size between 10- 200 nm in diameter. The drug is dissolved, entrapped, encapsulated or attached to the matrix of polymer. The nature of nanospheres can be amorphous or crystalline, and they potentiate to protect the drug from chemical and enzymatic degradation. In the matrix of this polymer, a drug will evenly distribute as well as physically and uniformly disperse and can enclose a variety of drugs, enzymes and, genes, providing a long circulation time. Nanospheres have the capability to convert poorly soluble, poorly absorbed and labile biologically active substance into promising deliverable drugs. This review focuses on the mechanism for synthesis of nano-based drug delivery systems, characterization, and application of biodegradable nanospheres and mainly on successful formulations based on biodegradable nanospheres.
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