In order to improve the interfacial bonding between hydroxyapatite (HAP) and poly-l-lactic acid (PLLA), 2-Carboxyethylphosphonic acid (CEPA), a phosphonic acid coupling agent, was introduced to modify HAP nanoparticles. After this. the PLLA scaffold containing CEPA-modified HAP (C-HAP) was fabricated by selective laser sintering (frittage). The specific mechanism of interfacial bonding was that the PO₃²⁻ of CEPA formed an electrovalent bond with the Ca²⁺ of HAP on one hand, and on the other hand, the –COOH of CEPA formed an ester bond with the –OH of PLLA via an esterification reaction. The results showed that C-HAP was homogeneously dispersed in the PLLA matrix and that it exhibited interconnected morphology pulled out from the PLLA matrix due to the enhanced interfacial bonding. As a result, the tensile strength and modulus of the scaffold with 20% C-HAP increased by 1.40 and 2.79 times compared to that of the scaffold with HAP, respectively. In addition, the scaffold could attract Ca²⁺ in simulated body fluid (SBF) solution by the phosphonic acid group to induce apatite layer formation and also release Ca²⁺ and PO₄³⁻ by degradation to facilitate cell attachment, growth and proliferation.

Background: Fe ₃ O ₄ nanoparticles are highly desired for constructing endogenous magnetic microenvironment in scaffold to accelerate bone regeneration due to their superior magnetism. However, their random arrangement easily leads to mutual consumption of magnetic poles, thereby weakening the magnetic stimulation effect. Methods: In this study, magnetic nanochains are synthesized by magnetic-field-guided interface co-assembly of Fe ₃ O ₄ nanoparticles. In detail, multiple Fe ₃ O ₄ nanoparticles are aligned along the direction of magnetic force lines and are connected in series to form nanochain structures under an external magnetic field. Subsequently, the nanochain structures are covered and fixed by depositing a thin layer of silica (SiO ₂ ), and consequently forming linear magnetic nanochains (Fe ₃ O ₄ @SiO ₂ ). The Fe ₃ O ₄ @SiO ₂ nanochains are then incorporated into poly l-lactic acid (PLLA) scaffold prepared by selective laser sintering technology. Results: The results show that the Fe ₃ O ₄ @SiO ₂ nanochains with unique core–shell structure are successfully constructed. Meanwhile, the orderly assembly of nanoparticles in the Fe ₃ O ₄ @SiO ₂ nanochains enable to form magnetic energy coupling and obtain a highly magnetic micro-field. The in vitro tests indicate that the PLLA/Fe ₃ O ₄ @SiO ₂ scaffolds exhibit superior capacity in enhancing cell activity, improving osteogenesis-related gene expressions, and inducing cell mineralization compared with PLLA and PLLA/Fe ₃ O ₄ scaffolds. Conclusion: In short, the Fe ₃ O ₄ @SiO ₂ nanochains endow scaffolds with good magnetism and cytocompatibility, which have great potential in accelerating bone repair.