Repair and regeneration of large bone defects is still a challenge, especially for defects which are the irregular and complex. Three-dimension (3D) printing, as an advanced fabrication technology, has been received considerable attentions due to its high precision, customized geometry and personalization. In this study, 3D porous polylactic acid/nano hydroxyapatite (PLA/nHA) composite scaffolds with enhanced osteogenesis and osteoconductivity were successfully fabricated by desktop fused deposition modeling technology. Morphological, composition and structural analysis revealed that nHA was successfully introduced into the PLA system and homogeneously dispersed in the printed PLA/nHA scaffolds. In vitro antibacterial experiment confirmed that the printed porous PLA/nHA scaffolds have good ability for loading and releasing vancomycin and levofloxacin. Meanwhile, MG-63 cells were used to evaluate the cytocompatibility of printed porous PLA/nHA scaffolds by proliferation and cellular morphological analysis. In addition, rabbit model was established to evaluate the osteogenesis and osteoconductivity of printed PLA/nHA scaffolds. All these results suggested that the 3D printed PLA/nHA scaffolds have great potential for repairing and regeneration of large bone defects.

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3D printing is an additive manufacturing (AM) technology that has developed rapidly in the past decades due to its advantages, such as freedom of design, mass customization, waste minimization, and the ability to manufacture complex structures, as well as fast prototyping. Various materials are used in 3D printing, including metals, polymers, ceramics, concrete, and their composites. The polymer's easy processing makes it stands out among many materials. As a thermoplastic polymer, polylactic acid (PLA) received more attention as an effective biomedical material due to its proven biodegradation and biocompatibility. Herein, the development of 3D-printing technology is summarized and various applications of 3D-printed PLA and their composites in orthopedics are introduced. Furthermore, the current limitations and future opportunities in 3D printing are also discussed to help guide the 3D-printing development and improve 3D-printing strategies in orthopedic.

Runoff and sediment yields from agricultural fields are major sources of nitrogen ͑N͒ entering lakes in China. Export of sediment and N can be impacted by soil and cropping management practices, but there is relatively little information on N leaving agricultural fields in lake basins in China. Sediment and surface runoff N from a series of field plots in two experimental lake basins were evaluated in situ under simulated rainfall conditions. Objectives of the study were to evaluate the effects of crop cover, slope, and fertilizer application on N in surface runoff and eroded soils. , indicating a problem in lake eutrophication due to high N concentration from agricultural surface runoff. The estimated mean annual export of total N was 6.0 and 14.7 kg ha -1 yr -1 for Baiyangdian and Taihu lake basins, respectively. The study showed that significantly more N ͑approximately ranging from 10% to 90% of total N͒ exported was associated with sediment, constituting a long-term source of potentially bioavailable N in lakes.

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The concentration of the heavy metals Cu, Cd, Pb and Zn in surface water and sediment samples taken from the length of the Xiangjiang River in China, revealed significant pollution in the vicinity of two industrial centres (Shuikoushan & Zhuzhou) . Additional insight into the potential adverse effects of these elevated concentrations was obtained from studies of the physiochemical forms (speciation) of these metals in the water column and in sediments .

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