In vivo quantification of protein release from IPN hydrogel. NIR dye-labeled BSA were mixed with different concentrations (0, 3, and 5% polymer weight) of IPN nanoparticles (1 mg BSA/100 µl nanoparticles) at room temperature and then implanted subcutaneously on the back of a mouse. (A) In vivo images represent the fluorescence intensities of different implantation sites at specified time points (0, 1, 3, and 5 days). (B) Quantification of the percentages of accumulative release of NIR-BSA from different concentration of IPN nanoparticles up to day 5.