Bone streaming potentials and currents depend on anatomical structure and loading orientation

Bone streaming potentials (SPs) and streaming currents (SCs) may be a remodeling signal to cells, and might also be used to probe bone pore structure and fluid flows. For SPs or SCs to serve as either a remodeling signal or as a probe for pore structure, they must depend on bone structure. This study was undertaken to address two related questions. First, will differences in Haversian and laminar bone structure and fluid flow direction produce measurable differences in SP and SC? Second, do differences in SP or SC relate to differences in macroscopic bone impedance or large pore structure? SPs and SCs were measured across Haversian and laminar bone specimens with fluid flow driven in different directions by sinusoidal four-point bending. Data were grouped by bone type and flow direction (Haversian tissue, laminar tissue with radial flow, and laminar tissue with tangential flow) and flow direction alone (tangential and radial). SPs were larger for Haversian tissue and for laminar tissue with radial flow than for laminar tissue with tangential flow. SP and SC magnitude, and impedance were larger for radial than tangential flow. No difference in SC magnitude, SP or SC kinetics, or macroscopic bone impedance was observed between Haversian tissue, laminar tissue with radial flow, and laminar tissue with tangential flow. Thus, since laminar tissue with tangential flow had more vascular connections in the direction of fluid flow, SP was smallest for greatest vascular connectivity. The relation between SP or SC and impedance was inconclusive.