Outstanding protein-repellent feature of soft nanoparticles based on poly(N-(2-hydroxypropyl) methacrylamide) outer shells

Abstract

The influences of the hydrophilic chain length, morphology and chemical nature have been probed with regard to the adsorption of model proteins onto the surface of soft nanoparticles (crew-cut micelles and polymersomes). The investigations were based on assemblies manufactured from PEO_m-b-PLA_n (poly(ethylene oxide)-b-poly(lactic acid)), which is a well-established block copolymer platform towards the manufacturing of drug delivery vehicles, and PHPMA_m-b-PDPA_n (poly([N-(2-hydroxypropyl)]methacrylamide)-b-poly[2-(diisopropylamino)ethyl methacrylate]), which is pH-responsive and therefore potentially able to target damaged cells in slightly acid microenvironments. Besides, protein adsorption onto PHPMA-stabilized nanoparticles has been seldom explored up-to-date. The morphologies were produced using two different approaches (nanoprecipitation and thin-film hydration) and afterwards, the protein-repelling property of the assemblies in model protein environments (BSA - bovine serum albumin, lysozyme and IgG - immunoglobulin G) was evaluated. We report that, regardless the morphology, PHPMA₃₅-b-PDPA₄₂ block copolymer assemblies are highly stable with negligible protein binding. On the other hand, PEO_m-b-PLA_n nanostructures are susceptible to protein adsorption and the phenomenon is protein-dependent. The nanoparticles are more susceptible to adsorption of the model positively charged biomacromolecule (lysozyme). The adsorption phenomenon is thermodynamically complex with simultaneous endothermic and exothermic processes involved. Although the experimental data highlight that qualitatively the morphology plays negligible effects on the event, fluorescence spectroscopy measurements evidenced that the binding is stronger onto the surface of nanoparticles stabilized by shorter hydrophilic shells. Nevertheless, the adsorption does not affect the secondary structure of the model proteins as confirmed by circular dichroism spectroscopy. Overall, by comparing soft nanoparticles stabilized by PEO and PHPMA, the latter is herein proved to be a better choice towards the manufacturing of non-fouling structures (either core-shell or hollow spheres) where even a reasonably short hydrophilic chain confers outstanding protein-repelling feature.