Centrifugal Method

Centrifugal method is a commonly used method for exosome extraction, and the exosomes obtained are large in size but low in purity.¹⁹ Moreover, the centrifugal force induced by the high speed of the centrifugation can cause changes in the exosome structure and size. The centrifugation methods can be summarized as follows: differential centrifugation, density gradient centrifugation, and ultrafiltration centrifugation.

Differential ultracentrifugation is one of the most classic exosome extraction methods. In the process of centrifugation, low and high-speed alternating centrifugation are used to obtain vesicles with a similar diameter and size. The operation of this method is relatively simple, but the it takes a long time. Repeated centrifugation also destroys the exosomes, which results in low exosome purity and poor treatment.²⁰

Ultrafiltration centrifugation is a relatively new extraction method, which uses an ultrafiltration membrane with a different molecular weight cutoff (MWCO) to selectively separate the sample, so that exosomes can be obtained at the end of the process.²¹ This method is simple and efficient and has little effect on the biological activity of exosomes, but the purity of the exosomes obtained is low.

The sucrose density gradient centrifugation method uses a sucrose solution that forms a density layer from low to high after a centrifugation at 100 000 × g, so that the exosomes in the sample can be aggregated in the density range of 1.13 ~ 1.19 g/mL. This enables the obtention of sediments rich in exosomes with high purity; however, the preparation work is complicated and the method is time consuming.²²