Development of low-cost, high-performance antibacterial reagents is of critical importance in the face of increasing occurrence of bacterial resistance against conventional antibiotics. In the present study, polyethylenimine (PEI)-modified graphene quantum dot (GQD) and ZnO nanoparticle nanocomposites, which were readily dispersed in water and exhibited markedly enhanced antimicrobial activity toward Escherichia coli, as compared to the PEI-free ZnO/ GQD counterparts, were prepared by a facile sol−gel method. This was largely ascribed to the reduced size of the nanoparticles and the enhanced adsorption of the nanocomposites onto the bacterial cell surfaces, as manifested by adsorption experiments and TEM characterization of the bacterial cells, as well as electron spin resonance measurements. The results highlight the significance of structural engineering of functional nanocomposites in the development of efficient antibacterial agents.

Background: Natural clay nanomaterials are an emerging class of biomaterial with great potential for tissue engineering and regenerative medicine applications, most notably for osteogenesis. Materials and Methods: Herein, for the first time, novel tissue engineering scaffolds were prepared by 3D bioprinter using nontoxic and bioactive natural attapulgite (ATP) nanorods as starting materials, with polyvinyl alcohol as binder, and then sintered to obtain final scaffolds. The microscopic morphology and structure of ATP particles and scaffolds were observed by transmission electron microscope and scanning electron microscope. In vitro biocompatibility and osteogenesis with osteogenic precursor cell (hBMSCs) were assayed using MTT method, Live/Dead cell staining, alizarin red staining and RT-PCR. In vivo bone regeneration was evaluated with micro-CT and histology analysis in rat cranium defect model. Results: We successfully printed a novel porous nano-ATP scaffold designed with inner channels with a dimension of 500 µm and wall structures with a thickness of 330 µm. The porosity of current 3D-printed scaffolds ranges from 75% to 82% and the longitudinal compressive strength was up to 4.32±0.52 MPa. We found firstly that nano-ATP scaffolds with excellent biocompatibility for hBMSCscould upregulate the expression of osteogenesisrelated genes bmp2 and runx2 and calcium deposits in vitro. Interestingly, micro-CT and histology analysis revealed abundant newly formed bone was observed along the defect margin, even above and within the 3D bioprinted porous ATP scaffolds in a rat cranial defect model. Furthermore, histology analysis demonstrated that bone was formed directly following a process similar to membranous ossification without any intermediate cartilage formation and that many newly formed blood vessels are within the pores of 3D-printed scaffolds at four and eight weeks. Conclusion: These results suggest that the 3D-printed porous nano-ATP scaffolds are promising candidates for bone tissue engineering by osteogenesis and angiogenesis.

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