(182x) Protein Corona Formation on Pegylated Particles for Drug Delivery

Particles used for drug delivery are often modified with poly(ethylene glycol) (PEG) to increase the circulation time of the particle and efficiently ‘hide’ from the immune system to avoid off-target accumulation. The addition of PEG is thought to succeed at this by preventing the formation of a protein corona on the surface of the particle, thus making it harder to detect by the body as a foreign object. PEG will swell in water and this hydrated layer is thought to act as an anti-fouling surface, preventing the binding of proteins to the surface. Previous measurements of the size of the protein corona on pegylated particles have supported this, showing little to no protein corona formation on the surface of the particles after incubation in blood plasma.

However, previously reported protein corona measurements on particles are done after washing the particles and then measuring them in pure water using dynamic light scattering. In our lab, we have developed a technique using nanoparticle tracking analysis (NTA) to measure the size of the particle in pure blood plasma, without the need for washing. Measuring the size of the particles by this method has surprising results with protein coronas on pegylated particles that are almost 50% of the size of the particle. This large protein corona is observed on particles that were modified with several different molecular weights of PEG and for both polystyrene particles and poly(lactic-co-glycolic acid) particles. A dilution study was done comparing the size of the particles measured at different plasma concentrations until the concentration was dilute enough for comparison to DLS measurements. At low plasma concentration, size results are consistent with DLS measurements, however a logarithmic trend is apparent in the particle size with plasma concentration. This suggests that the protein corona observed in pure plasma is a ‘soft’ corona made of loosely bound proteins. As the solution is diluted, these protein diffuse off the surface making the protein corona smaller. By washing a pegylated particle, most of this soft corona is removed, leaving behind a surface without any protein corona. By using this novel application of NTA to measure the size of the protein corona on drug delivery particles, the full protein corona can be measured in conditions it would experience in the body.