Layer-by-layer assembled polyaspartamide nanocapsules for pH-responsive protein delivery

• Nanocapsules were prepared via layer-by-layer assembly of two polyaspartamides.
• Nanocapsule shell was cross-linked by hydrazone bonds.
• Both of the polyaspartamides are water-soluble with a protein-like structure.
• A model protein was entrapped in the nanocapsule via electrostatic adsorption.
• The protein loaded nanocapsules exhibited pH-dependent release behavior.

Biodegradable shell cross-linked nanocapsules were prepared via layer-by-layer assembly of PADH (tertiary amine and hydrazide grafted polyaspartamide) and PACA (carboxyl and aldehyde grafted polyaspartamide) on silica spheres. Both of the polyaspartamide derivatives are water-soluble and biodegradable polymers with a protein-like structure, and obtained by aminolysis reaction of polysuccinimide. The latter is prepared by thermal polycondensation of aspartic acid. Dynamic light scattering and zeta potential measurements were used to analyze the layer-by-layer assembly process. Bovine serum albumin (BSA), as a model protein, was entrapped in the nanocapsules via electrostatic adsorption. Nanocapsules encapsulating BSA were prepared via layer-by-layer assembly on protein-entrapping amino-functionalized silica spheres, hydrazone cross-linking and silica core removal. The BSA release profiles exhibited a pH-dependent behavior. BSA release rate increased significantly as the ambient pH dropped from the physiological pH to acidic. Cell viability study suggests that the obtained polymeric nanocapsules have good biocompatibility. These kinds of novel composite nanocapsules may offer a promising delivery system for proteins.

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