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Polycaprolactone (PCL) is widely used in bone tissue engineering due to its biocompatibility and mechanical strength. However, PCL is not biologically active and shows poor hydrophilicity, making it difficult for new bones to bind tightly to its surface. Magnesium (Mg), an important component of natural bone, exhibits good osteo-inductivity and biological activity. Therefore, porous PCL/Mg scaffolds, including pure PCL, PCL/5%Mg, PCL/10%Mg, and PCL/15%Mg, were prepared to elucidate whether the porous structure of scaffolds and the bioactivity of PCL may be enhanced via 3D printing and incorporation of Mg powder. Compared with the control group (pure PCL only), the hydrophilicity of composite PCL/Mg scaffolds was greatly increased, resulting in the scaffolds having decreased water contact angles. Tests for adhesion and proliferation of rat bone marrow mesenchymal stem cells (rBMSCs) indicated that the PCL/10%Mg scaffold showed superior compatibility. Furthermore, as indicated by alkaline phosphatase (ALP) activity and semiquantitative analysis of alizarin red staining, PCL/10%Mg scaffolds exhibited significantly stronger osteogenic activity than the other scaffolds. Animal experiments demonstrated that PCL/10%Mg scaffolds displayed pro-osteogenic effects at an early stage (4 weeks) and produced more new bone mass 8–12 weeks following implantation, compared with the control group. Visceral and blood parameter analyses indicated that PCL/10%Mg scaffolds did not exert any noticeable toxic effects. PCL/10%Mg composite scaffolds were found to promote bone defect repair at an early stage with good cytocompatibility. This finding revealed a new concept in designing bone tissue materials, which showed potential as a clinical treatment for bone defects.

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