Membranes have been used extensively for the purification and separation of biological species. A persistent challenge is the purification of species from concentrated feed solutions such as extracellular vesicles (EVs) from biological fluids. Researchers from the Rochester Institute of Technology investigated a new method to isolate micro- and nano-scale species termed tangential flow for analyte capture (TFAC), which is an extension of traditional tangential flow filtration (TFF). Initially, EV purification from plasma on ultrathin nanomembranes was compared between both normal flow filtration (NFF) and TFAC. NFF resulted in rapid formation of a protein cake which completely obscured any captured EVs and also prevented further transport across the membrane. On the other hand, TFAC showed capture of CD63 positive small EVs (sEVs) with minimal contamination. The researchers explored the use of TFAC to capture target species over membrane pores, wash and then release in a physical process that does not rely upon affinity or chemical interactions. This process of TFAC was studied with model particles on both ultrathin nanomembranes and conventional thickness membranes (polycarbonate track-etch). Successful capture and release of model particles was observed using both membranes. Ultrathin nanomembranes showed higher efficiency of capture and release with significantly lower pressures indicating that ultrathin nanomembranes are well-suited for TFAC of delicate nanoscale particles such as EVs.
Tangential flow analyte capture (TFAC) technique for isolation of particles
A) Microfluidic devices are assembled through a layer stack process, in which channels and other featured are patterned into PDMS sheets. B) These layers are then formed into the device through thermal bonding or stacking and clamping. C) The sample is passed across the surface of the membrane and a transmembrane pressure generated by syringe pumps drives particle motion towards the membrane. Contaminating particles pass through pores or are swept downstream while the particles are retained on the membrane surface. D) The cleaning buffer is then passed through the input channel under the same flow condition as the capturing step to wash the channel and membrane surfaces of any remaining contaminants. E) The transmembrane pressure is then reversed, releasing the particles from the membrane where they are then swept downstream and collected.