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Poly(aspartic acid) (PASP) hydrogels were prepared by crosslinking polysuccinimide (PSI) with diaminobutane followed by the mild hydrolysis of the resultant PSI gels to PASP hydrogels. The composition dependence of the gelation time and the stiffness of bulk PASP hydrogels were determined by rheometry and compression tests, respectively. The composition of the prepared PASP nanogels was chosen based on the results on bulk PASP hydrogels. Prior to nanogel preparation stability of DMSO-in-oil (inverse) emulsions was tested as a function of the chemical quality of apolar phase, the concentration of the precursor polymer and the concentration of the surfactant. PASP nanogels in the size of a few hundred nanometers were prepared by the hydrolysis of PSI nanogels synthesized in inverse emulsion. PASP nanogels showed pH-dependent swelling and strongly negative surface charge at physiological pH values, thus they can be further developed to meet the specific criteria of different bio-related applications. [ABSTRACT FROM AUTHOR]

Nanogels loaded with fluorescent dextran as a model drug are synthesized by the oxidation induced cross-linking of water soluble redox responsive thiolated poly(amino acid) in miniemulsion without the introduction of any cross-linker molecule. Two types of high energy methods, namely, ultrasonication and high pressure homogenization (HPH), are compared. Dynamic light scattering and transmission electron microscopy measurements confirm that spherical nanogels in 100-150 nm diameter range are prepared successfully by HPH method. Size and surface charge of the nanogels can easily be controlled by environmental pH. The release of encapsulated drug is triggered by the degradation of nanogels in reducing environment due to the cleavage of disulphide bonds. [ABSTRACT FROM AUTHOR]