Injection of calcium phosphate pastes: prediction of injection force and comparison with experiments

Abstract

Calcium phosphate ceramics suspensions (ICPCS) are used in bone and dental surgery as injectable bone substitutes. This ICPCS biomaterial associates biphasic calcium phosphate (BCP) granules with hydroxypropylmethylcellulose (HPMC) polymer. Different ICPCS were prepared and their rheological properties were evaluated in parallel disks geometry as a function of the BCP weight ratio (35, 40, 45 and 50 %). The suspensions show a strongly increased viscosity as compared to the suspending fluid and the high shear rate part of the flow curve can be fitted with a power law model (Ostwald-de Waele model). The fitting parameters depend on the composition of the suspension. A simple device has been used to characterize extrusion of the paste using a disposable syringe fitted with a needle. The injection pressure of four ICPCS formulations was studied under various conditions (needle length and radius and volumetric flow rate), yielding an important set of data. A theoretical approach based on the capillary flow of non-Newtonian fluids was used to predict the necessary pressure for injection, on the basis of flow curves and extrusion conditions. The extrusion pressure calculated from rheological data shows a quantitative agreement with the experimental one for model fluids (Newtonian and HPMC solution) but also for the suspension, when needles with sufficiently large diameters as compared to the size of particles, are used. Depletion and possibly wall slip is encountered in the suspensions when narrower diameters are used, so that the injection pressure is less than that anticipated. However a constant proportionality factor exists between theory and injection experiments. The approach developed in this study can be used to correlate the rheological parameters to the necessary pressure for injection and defines the pertinent experimental conditions to obtain a quantitative agreement between theory and experiments.

Extrusion-Based 3D Printing of Calcium Magnesium Phosphate Cement Pastes for Degradable Bone Implants

“…Furthermore, it was demonstrated that the viscosity decreased with increasing shear rate (see Figure 1 B). As expected for a long-chain and unbranched molecule, HPMC in H 2 O was a shear-thinning material, which is consistent with the results of the rheological studies by Fatimi et al [ 22 ]. Increasing entanglement of polymer chains with storage time resulted in an increase in viscosity.…”

Critical review: Injectability of calcium phosphate pastes and cements

“…This increases P PS (Eq. 4) and has been demonstrated to reduce [35,79] and even eliminate [76,[80][81][82] [80]. Contrastingly, Wang et al [83] reported that the viscous gel produced with the addition of modified starch to CPC reduced injectability.…”

“…11 to obtain key parameters from the rheometry of a CPC (i.e. biphasic CaP and HPMC aqueous solution)[81]. The parameters were used with the Hagan-Poiseuille equation to estimate the extrusion pressure for the CPC.…”

Extent and mechanism of phase separation during the extrusion of calcium phosphate pastes

“…However, Montufar et al did find needle geometry had an effect on the injectability of CPC. Burguera et al [ 16 ] and Fatimi et al [ 42 ] also found needle geometry had a significant effect on the extrusion of CPC, however both studies used a more viscous liquid phase (hydroxypropyl methylcellulose-water solution) and no phase separation was exhibited.…”