Precipitation of lysozyme nanoparticles from dimethyl sulfoxide using carbon dioxide as antisolvent

The protein lysozyme has been precipitated as amorphous nanoparticles from a DMSO solution using dense carbon dioxide as antisolvent, by applying the so-called gas antisolvent recrystallization technique in a 400-mL precipitator. The objective is to investigate the possibility of tuning the particle properties by changing the key process parameters, namely, antisolvent addition rate, initial solute concentration, and temperature. It is shown that none of these operating parameters has a major effect on the average particle size or the particle size distribution. The former is mostly between 200 and 300 nm and exhibits no evident trend. The latter is always unimodal and rather narrow and exhibits increasing agglomeration at higher temperature and initial solute concentration. Up to 75% of the protein activity measured in the starting crystalline material is retained by the precipitated amorphous nanoparticles. The present experimental results compare well with data about the same system obtained in a different experimental setup, which were previously reported in the literature, thus pointing at the reproducibility and robustness of GAS antisolvent recrystallization. Moreover, these are consistent with the theoretical understanding of gas antisolvent recrystallization as achieved by using a recently developed model of the process.