The bone cement used for vertebroplasty must be sufficiently injectable. The introduction of granules reduces the amount of liquid required for liquefaction, implying that higher fluidity is achieved with the same amount of liquid. By employing β-tricalcium phosphate granules with an average diameter of 50 μm, changes in injectability are observed based on the paste preparation route and granular fraction. To obtain acceptable injectability, phase separation must be suppressed during injection, and sufficient capillary pressure to combine powder and liquid must work evenly throughout the paste. To achieve this, the granules should be evenly distributed. Reduced injection rates are observed for dry mixing and excessive granular content, owing to phase separation. All these correspond to conditions under which the clustered granules weakened the capillary pressure. The injected ratio of the paste formed by wet mixing displayed an inverted U-type shift with the granular fraction. The mixture of granules and powder resulted in an increase in the solid volume fraction, and a decrease in the liquid limit. This resulted in the enhancement of the liquidity, owing to the added liquid. It is inferred that the addition of granules improves the injectability, provided that the capillary pressure in the paste is maintained.

Abstract
1. Introduction
2. Experimental
    2.1 Preparation of Granules
    2.2 Measurement of Vpl
    2.3 Preparation of Paste
    2.4 Evaluation of Injectability
3. Results and Discussion
4. Conclusions
References

• Da Hye Mun(School of Advanced Materials Engineering, The Center of Biomedical Materials and Biotechnology, Andong National University)
• Sang Cheon Lee(Department of Maxillofacial Biomedical Engineering and Institute of Oral Biology, School of Dentistry, Kyung Hee University)
• Kyung-Sik Oh(School of Advanced Materials Engineering, The Center of Biomedical Materials and Biotechnology, Andong National University) Corresponding Author