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One of the important challenges in bone tissue engineering is the development of biodegradable bone substitutes with appropriate mechanical and biological properties for the treatment of larger defects and those with complex shapes. Recently, magnesium phosphate (MgP) doped with biologically active ions like strontium (Sr 2+ ) have shown to significantly enhance bone formation when compared with the standard calcium phosphate-based ceramics. However, such materials can hardly be shaped into large and complex geometries and more importantly lack the adequate mechanical properties for the treatment of load-bearing bone defects. In this study, we have fabricated bone implants through extrusion assisted three-dimensional (3D) printing of MgP ceramics modified with Sr 2+ ions (MgPSr) and a medical-grade polycaprolactone (PCL) polymer phase. MgPSr with 30 wt % PCL (MgPSr-PCL30) allowed the printability of relevant size structures (>780 mm 3 ) at room temperature with an interconnected macroporosity of approximately 40%. The printing resulted in implants with a compressive strength of 4.3 MPa, which were able to support up to 50 cycles of loading without plastic deformation. Notably, MgPSr-PCL30 scaffolds were able to promote in vitro bone formation in medium without the supplementation with osteo-inducing components. In addition, long-term in vivo performance of the 3D printed scaffolds was investigated in an equine tuber coxae model over 6 months. The micro-CT and histological analysis showed that implantation of MgPSr-PCL30 induced bone regeneration, while no bone formation was observed in the empty defects. Overall, the novel polymer-modified MgP ceramic material and extrusion-based 3D printing process presented here greatly improved the shape ability and load-bearing properties of MgP-based ceramics with simultaneous induction of new bone formation.

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The aim of this study was to develop a novel double network scaffold composed of polycaprolactone fumarate (PCLF) and eggshell membrane (ESM) (ESM:PCLF) by using the vacuum infiltration method. Compared to ESM, the mechanical properties of double network scaffold were significantly improved, depending on the solvents applied for double network scaffold formation; acetic acid and dichloromethane. Noticeably, the toughness and strength of double network scaffold prepared using acetic acid were significantly improved compared to ESM (26.6 and 25 times, respectively) attributed to the existence of hydrophilic functional groups in acetic acid which made ESM flexible to absorb further PCLF solution. To assess the effect of double network formation on the biological behavior of ESM, the attachment, proliferation and spreading of PC12 cells cultured on the ESM:PCLF scaffolds were evaluated. Results revealed that the number of cells attached on double network ESM:PCLF scaffold were nearly similar to ESM and significantly higher than that of on the tissue culture plate (2.6 times) and PCLF film (1.7 times). It is envisioned that the offered ESM:PCLF double network scaffold might have great potential to develop the constructs for nerve regeneration.