Nanoparticles formed from mixtures of proteins and synthetic polymers are of interest for applications such as protein delivery. Ge et al. examined the surface evolution of particles comprising conjugates of bovine serum albumin (BSA) and poly(methyl methacrylate) (PMMA). They first added 51 acryloyl groups to each denatured BSA molecule and then initiated radical polymerization at each site. Nanoparticles varying in BSA content from 4 to 82% by weight resulted from injection of an acetonitrile solution of these conjugates into phosphate-buffered saline. At the highest BSA content, the nanoparticles were well dispersed but the otherwise uniform surface of PMMA was covered with islands of BSA (as shown above). These islands grew over 2 weeks' time from surface patches to surface bumps in the buffered saline, but were unchanged if the nanoparticles remained in acetonitrile. The authors present a model in which PMMA, which is better solvated in acetonitrile, forms the main shell at the outset; over time in the aqueous medium, the more hydrophilic BSA then migrates to the surface.
Nano. Lett. 11, 10.1021/nl201303q (2011).