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Published in Tom Bell, Katsuya Akamatsu, Stainless Steel 2000, 2020
The microstructure formed at 520°C is similar to those obtained by plasma nitriding indicating that the equilibrium precipitation of CrN and α-ferrite is controlled by essentially the same thermodynamic and kinetic factors, i.e. all the beneficial effects of implantation have been lost. At 520°C the substitutional atoms possess sufficient mobility to allow nucleation and growth of precipitates such as CrN, preventing the formation of an amorphous zone. Precipitation of CrN depletes the austenite of chromium, favouring the formation of ferrite and CrN in a lamellar structure. In the outermost layer, however, the collision cascades set up by continuous implantation enhance the mobility of the substitutionals, making possible the precipitation of other nitrides such as (Cr,Fe)2N1−x.
Polyphosphazenes as Biomaterials
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
Meng Deng, Cato T. Laurencin, Harry R. Allcock, Sangamesh G. Kumbar
Inspired by the hierarchical structures that enable bone function, Deng (2010) recently developed a mechanically competent 3D scaffold mimicking the bone marrow cavity, as well as, the lamellar structure of bone by orienting electrospun polyphosphazene-polyester blend nanofibers in a concentric manner with an open central cavity. The 3D biomimetic scaffold exhibited a similar characteristic mechanical behavior to that of native bone. Compressive modulus of the scaffold was found to be within the range of human trabecular bone. To our knowledge this is the first mechanically competent 3D electrospun nanofiber scaffold with mechanical properties in the middle range of human trabecular bone. The potential of this scaffold for bone repair was further investigated by monitoring the cellular activity and mechanical performance over time using in vitro culture. These blend nanofiber matrices supported PRO adhesion, proliferation, and showed an elevated pheno-type expression compared to PLAGA nanofibers. This biomimetic scaffold supported the robust PRO growth throughout the scaffold architecture and maintained osteoblast phenotype expression in vitro, which resulted in a similar cell-matrix organization to that of native bone and maintenance of structure integrity. When combined with the desirable polymer blend properties, the concentric open macrostructures of nanofibers that structurally and mechanically mimic the native bone can be a potential scaffold design for accelerated bone healing.
Preparation and properties of modified nano-montmorillonite viscosity reducers
Published in Journal of Dispersion Science and Technology, 2022
Huijun Zhao, Jing Jia, Xiaofei Lv, Pengfei Yu, Xiang Ding
The electron microscope images of 50, 5, and 1 μm were selected for comparative analysis. The results of Na-MMT, MMT-CTAB, and MMT-OTAC by scanning electron microscope are shown in Figure 6. It can be seen that after CTAB and OTAC modification, the montmorillonite layer had a certain degree of aggregation, little particle sense, and a gradually apparent layered structure. Therefore, it is concluded that the aggregation mode between montmorillonite layers was changed after modification. Due to the introduction of interlayer organic chains, the interlayer spacing of the layers increased, and the surface organic chain benefited from the aggregation of montmorillonite layers. The higher the surface organic chain content, the larger the lamellar structure and the more stable the structure.