Implantation of a scaffold into the body in a safe and convenient manner remains a challenge in the repair of patient bone defect. In the present study, a strategy for fabrication of the redox-sensitive nanofibers with a core−shell structure that can deliver the growth factors in a tunable manner is presented. Poly(ethylene oxide) (PEO) and bone morphogenetic protein 2 (BMP-2) forms the inner core region, and a mixture of poly(epsilon-caprolactone) (PCL) and redox-responsive c-6A PEG−PCL nanogel with −S−S− bond forms the outer shell. The redox-sensitive shell of the nanofibers can respond the change of the GSH (glutathione) concentration and thus regulate the BMP-2 release behavior in vitro and in vivo. In vitro cytotoxicity results indicated that the redox-sensitive nanofiber had good osteoinduction. The in vivo results demonstrated that the nanofibers exhibited a capacity of prompting new bone generation in the bone defect. Therefore, the redox-responsive nanofiber in the present study may be of great potential for application in bone reconstruction.

Bulk metallic glass (BMG) possesses high strength, hardness and elastic deformation limit [1][2][3] and has long been regarded as a potential structural material. However, monolithic BMGs usually exhibit poor ductility and strain hardening ability during room temperature deformation due to highly localized shear bands, which significantly limits the range of possible applications. In order to overcome the limited plastic deformability of BMGs, Zr-, Cu-and Ti-based BMG composites with enhanced compression plasticity have been prepared by ex-situ or in situ methods. [4][5][6][7][8][9] Recent works also show that impressive improvements in plasticity can be achieved for some Zr-, [10] Pd-, [11] Pt- [12] and Cu-Zr- [13][14][15][16][17][18][19][20][21] based have exhibited large compressive plastic strain. Moreover, these Cu-Zr based alloys are free of nocuous elements like Ni, Be and might be more suitable for biomedical and structural applications. The presence of samll nanocrystals, and the deformation-induced nanocrystallization have been given for factors contributing to the intrinsic ductility of these Cu-Zr based BMGs. [13][14][15][16][17][18][19][20][21] For example, it was considered that the large plasticity and strain hardening-type phenomena observed in Cu 47.5 Zr 47.5 Al 5 BMG were attributed to the chemical heterogeneities and Cu-rich nanocrystals with the size of about 5 nm. [15][16] The excellent plasticity of Cu 50 Zr 50 and Zr 65 Al 7.5 Cu 27.5 alloy is also thought to be related with the presence of small nanocrystals. [13][14]20] Besides, the recent work of Kumar et al [17] shows that the heterogeneities observed in Cu 47.5 Zr 47.5 Al 5 alloy BMGs [15][16] were merely caused by transition electron microscope (TEM) during sample preparation and the deformation-induced nanocrystallization in the shear bands during compression was the main reason for the enhanced plasticity. Kim et al also claimed that some Cu-Zr based BMGs can display excellent plasticity due to the deformation-induced nanocrystallization during quasistatic compression. [21] And they also proposed that the plasticity of Cu-Zr containing glassy matrix was concerned with the activation energy for crystallization. [22] It is obvious that the origin of enhanced plasticity for Cu-Zr based alloys under quasistatic compression is still unclear and it is of great importance to clarify it. It should be noted that the geometrical imperfections in the compression specimen (i.e. miscut or non-orthogonal specimens) have great effects on the measured plastic strain during the compression test. [23] Thus, the three point bending test is better to evaluate the plasticity of BMGs. [24] Then, in this paper, a series of Cu 46 Zr 47 Al 7 alloys with different microstructures, including full glassy structure, marginal BMG containing small in-situ precipitated nanocrystals and BMG composite containing large CuZr crystals were prepared. Both compression and bending tests were undertaken to evaluate their plasticity. The effect of the nanocrystals on the pl...

Ti 5 bulk metallic glass (BMG) alloy samples in both rod and plate geometry were prepared. Different free volume states were obtained through thermal treatment. The plastic deformation ability of the BMGs was investigated through both a three-point bending test and compression test. The three-point bending results reveal the important role of free volume content on the formation of multiple shear bands, as the shear band propagation can be efficiently stopped due to the existence of the stress gradient from the surface to the neutral plane. In compression, the sample size rather than free volume controls the shear banding behavior.

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Due to the absence of long-range order, bulk metallic glasses (BMGs) exhibit unique properties, such as high strength, high hardness, large elastic limit, good soft magnetic properties, and high corrosion resistance. [1,2] However, there is a fatal weakness that prevents wide application of BMGs: that is almost zero plasticity under tension and limited plasticity under compression. [3][4][5] Therefore, improving the plasticity of metallic glass is currently the subject of extensive study. Recent research has shown that impressive improvements in plasticity can be achieved for some Zr-, [6] Pd-, [7] Pt-, [8] Cu-Zr-. [9][10][11][12][13] Ti-based bulk metallic glasses (BMGs) under compression, in which the enhanced plasticity was attributed to the presence of small nanocrystals, [9][10][11] stress-induced nanocrystallization, [12,13] and a high Poisson ratio. [6][7][8] However, the mechanism is still not fully understood. The excellent plasticity of a Ti-based BMG sample with 1 mm diameter [14] and a Cu-based BMG [15] under compression were attributed to an increase in free volume introduced by high cooling rate and minor alloying, respectively. Moreover, many earlier investigations have shown that annealing imparts severe brittleness to the BMGs. [16][17][18][19][20][21] This is attributed to various factors including reduction in free volume, [16][17][18][19] precipitation of crystalline phases [20] and phase separation. [21] Of these mechanisms, the most prominent is the reduction in free volume that occurs during structural relaxation of metallic glasses, whereby free volume gets redistributed and annihilated, resulting in the loss of ductility. [16] There have also been several reports that the ductility of thermally embrittled amorphous ribbon samples could be recovered by thermal treatment [22][23][24] or neutron-irradiation. [25] Furthermore, Nagel et al. demonstrated that the annihilated free volume can be restored by heat treatment above the glass transition temperature (T g ). [26] Thus, detailed understanding of the effect of the free volume on the mechanical properties of BMGs, in particular ductility is still important from the applications point of view. In this paper, Cu 46 Zr 47 Al 7 BMG alloys with different free volume states were obtained through thermal treatments such as annealing and quenching. We demonstrate that the ductility of BMGs is closely related to the free volume and the ductility of thermally embrittled BMGs can be restored by thermal treatments.A Cu 46 Zr 47 Al 7 alloy (in at.%) was used in the current investigation. Plate with dimensions of 50 mm  20 mm  1.5 mm was prepared by arc melting, and the as-cast sample had the fully glassy structure. [27] The glass transition temperature T g and the onset temperature T x of the amorphous alloy have been reported to be about 696 and 769 K, respectively, at a heating rate of 0.33 k s À1 . [28] Different free volume states were achieved by different thermal treatment processes. The as-cast samples were sealed in an evacuated quartz capsul...