Gravity-fed blood filtration on the bench

Retriever Medical is developing a gravity-fed, multi-filter system

intended to filter a patient's own (autologous) whole blood for reinfusion. An Earlier bench study by the same authors found no cell injury or clotting changes when pig and human blood were passed through.

The study checked two things: how reliably the filters keep particles of different sizes out of the final filtrate, and how fast fluid passes through.

• Three filters: stacked in sequence. with 2 mm, 250 micron and 40 micron pore sizes.
• Test particles: 2.3 mm stainless steel spheres, plus 355-425 micron (red) and 63-75 micron (green) fluorescent microspheres that glow under uv light.
• Blood analogue: a clear 50/50 water/glycerol mix, chosen to be thicker than whole blood so the test was harder and particles were easy to see.
• Five trials: five 100 cc samples were poured into the top of the device and drained by gravity, then the chambers were checked under UV light.

All five trials gave identical results. The steel spheres stayed above the 2 mm filter, both sizes or microspheres collected above the 250 micron filter, and only the smallest microspheres reached the 40 micron filter. No particles entered the collection chamber.

Each 100cc sample filtered in 4-7 seconds, a rate of more than 500cc per minute, even with a fluid thicker than whole blood. The authors conclude the device may prove useful for reinfusing autologous blood, which further study will need to confirm.