A new insight for an old system: protein-PEG colocalization in relation to protein release from PCL/PEG blends.

Quantification of protein-polymer colocalization in a phase-separated polymer blend gives important insights into the protein release mechanism. Here, we report on the first visualization of protein-poly(ethylene glycol) (protein-PEG) colocalization in poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG) blend films using a combined application of confocal Raman mapping and confocal laser scanning microscopy (CLSM) imaging. The degree of protein-PEG colocalization was further quantified via a novel image processing technique. This technique also allowed us to characterize the 3-D protein distribution within the films. Our results showed that the proteins were homogeneously distributed within the film matrix, independent of PEG content. However, the degree of protein-PEG colocalization was inversely proportional to PEG content, ranging from 65 to 94%. This quantitative data on protein-PEG colocalization was used along with in vitro PEG leaching profile to construct a predictive model for overall protein release. Our prediction matched well with the experimental protein release profile, which is characterized by an initial burst release and a subsequent slower diffusional release. More importantly, the success of this predictive model has highlighted the influence of protein-PEG colocalization on the protein release mechanism.