The rheological behavior of a fast-setting calcium phosphate bone cement and its dependence on deformation conditions.

Calcium phosphate cements are osteoconductive biomaterials that are widely used for bone repair and regeneration applications, including spinal fusion, vertebroplasty, khyphoplasty, cranioplasty and periodontal surgeries. The flow and deformation behavior (rheology) and injectability of the calcium phosphate bone cements to the treatment site are governed by the setting kinetics of the cement during which the initially flowable, viscous cement paste transforms into a rigid elastic solid. Here time-dependent development of the linear viscoelastic properties of a brushite-forming calcium phosphate cement are characterized and linked to the mechanism and kinetics of the setting reaction and to the injectability window available during the surgical applications of the cement. The setting kinetics is shown to be a function of the deformation conditions that are utilized in rheological characterization, emphasizing the intimate relationships between setting kinetics, particle to particle network formation and deformation history. Furthermore, the preshearing of the calcium phosphate cement prior to injection and temperature are shown to alter the kinetics of the setting reaction and thus to provide additional degrees of freedom for the tailoring of the rheological behavior and injectability of the calcium phosphate cement.