Core−Shell Structure of PLA−PEG Nanoparticles Used for Drug Delivery

Small-angle neutron scattering (SANS) has been used to study the internal structure of poly(lactic acid)−poly(ethylene glycol) (PLA(d)−PEG) block copolymer assemblies, which are being investigated as particulate drug carriers. Three PLA(d)−PEG copolymers with a fixed PEG of 5 kDa and a fully deuterated PLA(d) block of either 3, 15, or 45 kDa were synthesized by the ring opening polymerization of d8-d,l-lactide, using stannous octoate as a catalyst. These copolymers assembled to form nanoparticles in aqueous media, following precipitation from a water miscible organic solvent. The hydrodynamic radius of the PLA(d)−PEG nanoparticles increased with the molecular weight of the PLA(d) block. SANS data obtained at three different solvent contrasts were analyzed simultaneously using core−shell models, which assumed a homogeneous core of uniform scattering length density and a simple functional form for the scattering length density profile of the shell. The thickness and structure of the stabilizing PEG layer we...