Bovine erythrocytes are poor surrogates for human when exposed to sublethal shear stress

Animal blood products are routinely used as surrogates for human tissue in haemocompatibility testing of rotary blood pumps. Bovine blood is particularly attractive due to the animal's large blood volume; however, bovine red blood cells (RBC) differ substantially from those of human, both in biophysical properties and molecular composition. We aimed to determine whether differences also exist in the sensitivity of bovine RBC to a standardised shear stress protocol. Fresh blood from healthy human and bovine donors was exposed to discrete combinations of shear stress using a Couette shearing system, prior to assessment of cellular deformability and mechanical sensitivity. Each sample was exposed to 25 sublethal shear stress combinations (ranging 60-100 Pa × 5-300 s). While bovine RBC exhibited decreased maximal elongation in the absence of conditioning shear, overall deformability at lower shears was ~1.8-fold greater than human. When exposed to any conditioning shear stresses >80 Pa (or 60-70 Pa beyond 5 s), human RBC were significantly rigidified, with greater magnitudes and prolonged exposure compounding this effect. Significantly larger shears were required to rigidify bovine RBC; the most extreme shear condition (100 Pa × 300 s) resulted in approximately three-times more rigidification of human RBC than bovine (137% and 47% respectively). Bovine RBC have superior resilience to mechanical stress when compared with human. Using bovine blood in ex vivo evaluation of rotary blood pumps may thus misrepresent and overestimate device-blood success, and may also have flow-on effects for eventual users. Fresh human blood during early-phase ex vivo testing is thus recommended, given shear-inducing blood pumps are designed for humans - not cattle.