A glycerine/water mixture flowing through a flexible tube represents blood flow through a vessel. An injury is produced (red arrow) by puncturing the vessel with a 22G needle. The magnetorheological (MR) suspension is infused downstream and flows to the injury site, where a pair of magnets (orange lines) have been mounted into transparent 3D printed magnet holders (blue lines), maintaining a fixed separation distance. The magnetic field traps the MR suspension, causing it to solidify. Eventually, enough of the MR suspension solidifies to form an obstruction, greatly diminishing the rate of blood loss.