Fabrication of injectable and expandable PMMA/PAASf bone cements

The volume of polymethyl methacrylate (PMMA) bone cement shrank by 3.82%-7.08% during solidification. Such volume shrinkage generated a residual stress that induces minor cracking in bone-cement interface and affected the long-term stability and mechanical property of vertebral body. In this study, injectable and expandable PMMA/sodium polyacrylate short fiber (PAASf) composite bone cements were fabricated, and water absorption and swelling properties of PAASf were taken into account. Effects of PAASf volume fraction in PMMA/PAASf bone cements on absorption ratios of simulated body fluid (SBF) and volume expansion ratios were investigated. When the volume fraction of PAASf was lower than 30%, PMMA/PAASf bone cements were stable and did not fall apart after expansion in SBF, and the maximum volume expansion ratio was 33.4%. When PAASf content increased from 10 vol% to 30 vol%, solidification time of PMMA/PAASf bone cements increased and their injection and mechanical properties decreased, although the PMMA/PAASf bone cements (9:1) still satisfy the requirements for clinical application. The absorption expansion mechanism of PMMA/PAASf bone cements in SBF in the first stage of expansion (global expansion before solidification) and in the second stage of expansion (local surface expansion after solidification) was analyzed through micro-computed tomography and SEM. Cytotoxicity of PMMA bone cement and PMMA/PAASf bone cements were compared, and results suggested that their cytotoxicity did not significantly vary. These findings indicated that injectable and expandable PMMA/PAASf bone cements can be used in clinical treatments.