Characterization of PFC- MPs
It has been well established that oxygen carrying properties of PFC-MPs stem from the PFC substitutions, [18,19] therefore in this report we focused on studying the composition of microfluidic generated MPs while confirming the presence of PFC molecules(Figure 1). Figure 1B shows the TGA spectrum of crosslinked non-PFC-MPs and PFC-MPs. The weight loss in both spectra begins at approximately 90°C and continues until 130°C which is likely associated with loss of absorbed water in the crosslinked MPs. Based on these data both MPs were able to absorb water correlating to ~25% via hydrophilic moieties in chitosan.[20] Another major mass loss stage is observed between 280-400°C, which is related to thermal decomposition of chitosan.[21] Overall, around 43.1% w/w of PFC-MPs and 52.82% w/w of non-PFC-MPs were lost when heated above 400°C, suggesting higher thermal stability of PFC-MPs compared to non-PFC-MPs. Carbon–fluorine (C-F) bonds in PFC molecules are strongly polarized, which accounts for their thermal stability.[22] Next, XPS was used to provide a quantitative analysis from the outer 10 nm of MP surfaces. XPS spectra showed carbon (C1s at 284.7 eV) and oxygen (O1s at 531.5 eV) as well as fluorine (F1s at 688.6 eV) on surface of PFC-MPs (Figure 1C),suggesting the presence of PFC molecules on the surface of MPs. This is expected since the particles were crosslinked while still in the oil phase. We tried Fourier-transform infrared spectroscopy (FTIR) as well(Figure S2) ; however, due to PFC abundance being lower than the detection threshold (2 wt%), we could not detect C-F bonds.