ZIF-8 induced hydroxyapatite-like crystals enabled superior osteogenic ability of MEW printing PCL scaffolds

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Abstract Background In general, ZIF-8 tends to undergo ion responsive degradation in ionic solutions, which makes it difficult to maintain its original structure, thus restricting its direct application in biological settings. Methods ZIF-8 was synthesized using one-pot method and the ZIF-8/PCL scaffolds were built by a round mould or printed by melt electrowrittten (MEW) technology. Mineralization performance was evaluated by SEM with EDS-mapping and micro-CT scanning after soaking in simulated body fluid (SBF). The osteogenic activity in vivo or in vitro was assessed using different methods including micro-CT scanning, Alizarin red staining, and immunohistochemical staining. Results Herein, an abnormal phenomenon is reported that ZIF-8 can form large hydroxyapatite-like crystals when getting immersed directly in multi-ion simulated body fluid. The abnormal crystals showed the continuation of rapid growth in 14 days, with its volume increasing by more than ten times. As suggested by the release of Zn2+ and the emergence of new XRD diffraction peaks, ZIF-8 particles might gradually collapse and congregate through competitive coordination and re-nucleation. The above phenomenon is also observable on the surface of ZIF-8/PCL composite materials and MEW printing ZIF-8/PCL scaffolds. ZIF-8 increased the roughness of PCL by altering its surface topography, which significantly improved its biocompatibility and osteoinductivity both in vitro and in vivo. Notably, the capability of pro-biomineralization makes ZIF-8 also applicable in polylactic acid. Conclusions To sum up, the results shown in this study demonstrate that ZIF-8 can serve as a bioactive additive that enables the surface modification to synthetic polymers, which suggests its potential of application for in-situ bone regeneration.

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