Calcium phosphate cements composed of β-tricalcium phosphate (β-TCP) and phosphoric acid were modified by addition of 5, 10, 12.5, 15 and 20 wt.% phytic acid (IP6) related to the β-TCP content and compared to a reference containing 0.5 M citric acid monohydrate solution as setting regulator. The hydration reaction of these cements was investigated by isothermal calorimetry and in-situ X-ray diffraction at 23 °C and 37 °C. The cements were further characterized with respect to their injectability, rheology, zeta potential and time-resolved compressive strength development.

Injectability was strongly improved by IP6 addition, while the maximum effect was already reached by the addition of 5 wt.% IP6. This could be clearly related to an increase of the negative zeta potential leading to a mutual repulsion of cement particles. A further increase of the IP6 content had a detrimental effect on initial paste viscosity and shifted the gelation point to earlier time points. IP6 was further proven to act as a retarder for the cement setting reaction, whereas the effect was stronger for higher IP6 concentrations. Additionally, IP6 favoured the formation of monetite instead of brushite and a better mechanical performance compared to the IP6 free reference cement.

Statement of Significance

Calcium phosphate cements (CPCs) are clinically applied for bone repair due to their excellent biocompatibility and bone regeneration capacity. A deep understanding of the setting mechanism is the prerequisite for the targeted fabrication and application of such bone cements, whereas setting characteristics are usually adjusted by additives. Here, novel injectable CPC formulations were developed by modifying a cement composed of β-tricalcium phosphate and phosphoric acid with phytic acid (IP6). A detailed investigation of the setting mechanism of the IP6 modified CPCs is provided, which demonstrated the effectiveness of IP6 as setting regulator to adjust the reaction time and kind of setting product. Additionally, the high surface charge of cement particles after IP6 addition was effective in dispersing cement particles leading to low viscous cement pastes, which can be directly applied through a syringe for minimal invasive surgery.

中文翻译：

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植酸改性的磷酸钙水泥的水化机理

通过添加与β-TCP含量有关的5、10、12.5、15、20和60 wt％的植酸（IP6）来改性由β-磷酸三钙（β-TCP）和磷酸组成的磷酸钙水泥。含0.5 M柠檬酸一水合物溶液作为调节剂的参比样品。通过等温量热法和在23°C和37°C下进行原位X射线衍射研究了这些水泥的水合反应。关于水泥的可注射性，流变性，ζ电势和时间分辨的抗压强度的发展，进一步进行了表征。

加入IP6大大改善了可注射性，而加入5 wt。％IP6已达到最大效果。这显然与负zeta电位增加有关，导致水泥颗粒相互排斥。IP6含量的进一步增加对初始糊状粘度有不利影响，并使胶凝点移动到更早的时间点。IP6被进一步证明可作为水泥固化反应的阻滞剂，而IP6浓度较高时效果更强。另外，与不含IP6的参比水泥相比，IP6有利于形成透钙磷石而不是透钙磷石，并具有更好的机械性能。

重要声明

磷酸钙水泥（CPC）由于其出色的生物相容性和骨骼再生能力而在临床上用于骨修复。对凝结机理的深入了解是有针对性地制造和应用此类骨水泥的前提，而凝结特性通常由添加剂来调节。在这里，通过用植酸（IP6）改性由β-磷酸三钙和磷酸组成的水泥，开发了新型可注射CPC制剂。详细研究了IP6修改的CPC的设置机制，证明了IP6作为设置调节器来调节反应时间和设置产品种类的有效性。此外，