Relevance of the setting reaction to the injectability of tricalcium phosphate pastes

Abstract

The aim of the present work was to analyze the influence of the setting reaction on the injectability of tricalcium phosphate (TCP) pastes. Even if the injection was performed early after mixing powder and liquid, powder reactivity was shown to play a significant role in the injectability of TCP pastes. Significant differences were observed between the injection behavior of non-hardening β-TCP pastes and that of self-hardening α-TCP pastes. The differences were more marked at low liquidto-powder ratios, using fine powders and injecting through thin needles. α-TCP was in general less injectable than β-TCP and required higher injection loads. Moreover, clogging was identified as a mechanism hindering or even preventing injectability, different and clearly distinguishable from the filter-pressing phenomenon. α-TCP pastes presented transient clogging episodes, which were not observed in β-TCP pastes with equivalent particle size distribution. Different parameters affecting powder reactivity were shown to affect also paste injectability. Thus, whereas powder calcination resulted in an increased injectability due to lower particle reactivity, the addition of setting accelerants, such as hydroxyapatite nanoparticles, tended to reduce the injectability of the TCP pastes, especially if adjoined simultaneously with a Na2HPO4 solution. Although as a general trend faster setting pastes were less injectable, some exceptions were found to this rule. For example, whereas in absence of setting accelerants fine TCP powders were more injectable than the coarse ones in spite of their shorter setting times, when setting accelerants were added this trend was inverted, and coarse powders were more injectable than the fine ones. after mixing powder and liquid, powder reactivity was shown to play a significant role in the injectability of TCP pastes. Significant differences were observed between the injection behavior of non-hardening β-TCP pastes and that of self-hardening α-TCP pastes. The differences were more marked at low liquid-to-powder ratios, using fine powders and injecting through thin needles. α-TCP was in general less injectable than β-TCP and required higher injection loads. Moreover, clogging was identified as a mechanism hindering or even preventing injectability, different and clearly distinguishable from the filter-pressing phenomenon. α-TCP pastes presented transient clogging episodes, which were not observed in β-TCP pastes with equivalent particle size distribution. Different parameters affecting powder reactivity were shown to affect also paste injectability. Thus, whereas powder calcination resulted in an increased injectability due to lower particle reactivity, the addition of setting accelerants, such as hydroxyapatite nanoparticles, tended to reduce the injectability of the TCP pastes, especially if adjoined simultaneously with a Na 2 HPO 4 solution. Although as a general trend faster setting pastes were less injectable, some exceptions were found to this rule. For example, whereas in absence of sett...

Robocasting of biomimetic hydroxyapatite scaffolds using self-setting inks

“…This second increase of the extrusion force can be associated with the setting reaction of the a-TCP, caused by formation of an entangled network of CDHA crystals, which has been described as a factor hindering the extrusion of a-TCP pastes. 13 This phenomenon was observed also in the a-TCP/ water suspension, but only aer a long induction time. The long induction period compared to what was found in a previous study with similar pastes 13 can be explained by the much higher L/P ratio used in the present work.…”

“…13 This phenomenon was observed also in the a-TCP/ water suspension, but only aer a long induction time. The long induction period compared to what was found in a previous study with similar pastes 13 can be explained by the much higher L/P ratio used in the present work. The fact that the increase in extrusion force associated with the hydrolysis of a-TCP was observed earlier for the gelatine-based ink suggests an accelerating effect in the setting reaction, as proposed by Bigi et al, 17,18 who claimed a nucleation effect of gelatine on the precipitation of CDHA.…”

“…The ability to extrude the ink is one of the critical aspects, especially when the reactivity of the particles can modify the rheological behaviour over time, and reduce considerably their printability. 13 Moreover, in addition to the basic requirements of ceramic inks for robocasting, such as low extrusion force without phase separation and shape retention aer extrusion, the additives used in self-setting inks should neither hamper cement reactivity nor compromise the material biocompatibility.…”

Influence of Si substitution on the reactivity of α-tricalcium phosphate

“…In this study, the external pattern method was employed [38]. The external pattern used in this work was β-TCP which is present in all samples and do not participate on the setting reaction, thus, its mass fraction is constant during all the process [5,39,40].…”

Self-Setting Calcium Orthophosphate Formulations

“…It is measured by the weight percentage of the formulation that could be injected without demixing from a standard syringe by either a hand or a force of 100 N maximum (Figure 8). The numerical values are calculated by the following equation [304]:…”