Liposomes have been widely used as a delivery vehicle for small molecules; however, it remains difficult to achieve high levels of encapsulation for many macromolecular drugs within liposomes and many drug formulations leak from liposomes too quickly to maintain useful drug delivery kinetics. While drug delivery by micro- and nanoparticles can encapsulate proteins and small-molecule drugs, this still typically yields very low total mass encapsulated drug per mass of particles, typically on the order of ˜10 μg drug/mg particles. In addition, the organic solvents used in polymer particle synthesis and hydrophobic/acidic environment within these particles can lead to destruction of therapeutics. (See Zhu et al. Nat. Biotechnol. 2000 18:52-57.)
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