Effect of halloysite nanotubes on poloxamer 407-containing calcium phosphate cement for bone repair applications

Owing to the associated biocompatibility, bioactivity, and osteoconductivity, calcium phosphate cements (CPCs) are widely used for bone repair and augmentation. Despite these advantages, commercially available CPCs often exhibit insufficient strength and injectability for clinical applications. In this study, we aimed to address these limitations by incorporating halloysite nanotubes (HNTs) and poloxamer 407 into CPCs. HNTs, known for their high mechanical strength, modulus, specific surface area, and aspect ratio, were added to improve the mechanical properties of the CPCs. To enhance injectability and minimize leakage from the bone defects, poloxamer 407 was incorporated into the CPCs. The incorporation of HNTs significantly enhanced the compressive strength of the cement, achieving a maximum improvement of 6.8 MPa, which corresponds to a 16.9% increase. Injectability decreased over time for all pastes during the poloxamer 407 sol-gel transition. HNT incorporation did not negatively affect cell viability or induce cytotoxicity, and enhanced cell adhesion and spreading were observed on the CPC surfaces, as demonstrated by in vitro studies using MC3T3-E1 cells. Alkaline phosphatase activity assays indicated improved osteogenic differentiation with HNTs. These results suggest that incorporating up to 3 wt% HNTs into CPCs optimizes their mechanical properties and biological performance, making them suitable for load-bearing applications in bone tissue engineering. Nevertheless, future in vivo studies are necessary to validate these findings and establish the clinical utility of HNT-reinforced CPCs incorporating poloxamer 407.