Novel pH-sensitive nanogels based on poly(ethylene glycol)-b-poly(L-glutamate-g-tyramine) (PEG-b-P(LGA-g-Tyr)) copolymer were developed for efficiently delivering and releasing proteins into HeLa cells. The core–shell nanogels were in situ fabricated through the enzyme-catalyzed oxidative coupling of tyramine moieties in the core of the self-assembled PEG-b-P(LGA-g-Tyr) micelles in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The stable nanogels have spherical morphology with an average diameter of about 125 nm under physiological condition. The pH-dependent size shrink of the nanogels was observed by dynamic light scattering (DLS). Fluorescein isothiocyanate conjugate bovine serum albumin (FITC-BSA) was in situ incorporated into the nanogels with an entrapment efficiency of 69.9% during the enzyme-catalyzed crosslinking reaction. In vitro protein release profiles at pH 7.4 and pH 6.8 showed a burst effect followed by a continuous release phase. The FITC-BSA loaded nanogels exhibited pH-sensitive protein release. A significantly fast FITC-BSA release was observed at endosomal pH than at physiological pH. The cumulative release of FITC-BSA from the nanogels at pH 7.4 and pH 6.8 were 24.2% and 40.3%, respectively. Cell Counting Kit-8 (CCK-8) assay showed that these nanogels were non-toxic up to a concentration of 2.0 mg mL−1. Confocal laser scanning microscopy (CLSM) studies revealed that FITC-BSA loaded nanogels efficiently delivered and released proteins into HeLa cells. We are convinced that these enzymatically crosslinked nanogels with excellent biocompatibility and pH-responsibility have a promising potential for protein delivery system.

Novel core–shell-structured Pluronic-based nanocapsules with thermally responsive properties were successfully prepared using a modified emulsification/solvent evaporation method. The nanocapsules were constructed through the cross-linking reaction between p-nitrophenyl-activated Pluronic F127 and hyaluronic acid (HA) (named Pluronic F127/HA) or poly(ε-lysine) (PL) (named Pluronic F127/PL) at the organic/aqueous interface. The formation, size, and thermal responsiveness of the nanocapsules were characterized by 1H NMR, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The resultant shell-cross-linked nanocapsules exhibit a larger volume transformation (26 times change in volume for Pluronic F127/HA and 31 times for Pluronic F127/PL) over a temperature range of 4–37 °C because of the temperature-dependent dehydration of cross-linked Pluronic F127 polymer chains. The nanocapsules are about 72 ± 4 nm (polydispersity index [PDI] = 0.08) for Pluronic F127/PL (69 ± 5 nm, PDI = 0.10 for Pluronic F127/HA) at 37 °C with narrow size distribution and expand to about 226 ± 23 nm (PDI = 0.34) for Pluronic F127/PL (206 ± 20 nm, PDI = 0.3) for Pluronic F127/HA at 4 °C with broad size distribution in aqueous solutions. The nanocapsules were used to encapsulate and control the release of doxorubicin hydrochloride (DOX·HCl) in aqueous solution. DOX·HCl was physically encapsulated in the nanocapsules using a soaking–freeze-drying–heating procedure. The release curve and release kinetics disclosed that the thermally responsive hollow nanocapsules are good carries for drug delivery.