The fabrication of hydroxyapatite mineralized hydrogels for bone tissue engineering

Bone is a complex but orderly mineralized tissue with hydroxyapatite(HA)as the inorganic phase and collagen as the organic phase.Inspired by natural bone tissues,HA-mineralized hydrogels have been widely designed and used in bone tissue engineering.HA is majorly utilized for the treatment of bone defects because of its excellent osteoconduction and bone inductivity.Hydrogel is a three-dimensional hydrophilic network structure with similar properties to the extracellular matrix(ECM).The combination of HA and hydrogels produces a new hybrid material that could effectively promote osteointegration and accelerate the healing of bone defects.In this review,the structure and growth of bone and the common strategies used to prepare HA were briefly introduced.Importantly,we discussed the fabrication of HA mineralized hydrogels from simple blending to in situ mineralization.We hope this review can provide a reference for the development of bone repair hydrogels.

Dynamic recrystallization mechanism of as-cast nickel base superalloy N10276 during primary hot working

The dynamic recrystallization(DRX)mechanism of as-cast nickel base superalloy N10276 during primary hot working was investigated by compression tests at temperatures of 1000–1200℃ and strain rates between 0.01 and 10 s^(-1).Optical microscopy,scanning electron microscopy,electron backscattered diffraction technique and transmission electron microscopy were used to characterize the evolution of microstructure.At higher deformation temperature or lower strain rate,the true stress–true strain curves exhibit the characteristic of a peak stress followed by a steady state flow stress under large strains,confirming the occurrence of DRX.The degree of DRX increases with elevating deformation temperature.With the progress of DRX,low angle grain boundaries gradually decrease,while high angle grain boundaries increase continuously.Microstructure studies have shown that discontinuous dynamic recrystallization is the main recrystallization mechanism.Since there are few original grain boundaries and twin boundaries,and lack of second phase particles for particle stimulated nucleation,geometrically necessary boundaries are formed as supplementary nucleation sites through sub-grain boundary rotation and deformation twin boundaries.The annealing twins dominated by Σ3 grain boundaries are generated in large quantities during the growth of recrystallized grains.