Microstructural Development in a TRIP-780 Steel Joined by Friction Stir Welding (FSW): Quantitative Evaluations and Comparisons with EBSD Predictions

The present work describes the effect of FSW on the result microstructure in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) of a TRIP-780 steel. X-ray diffraction (XRD), optical microscopy (OM) and EBSD were used for determinations retained austenite (RA) in the SZ, It was found that the amount of RA developed in SZ was relatively large, (approximately 11% to 15%). In addition, recrystallization and the formation of a grain texture were resolved using EBSD. During FSW, the SZ experienced severe plastic deformation which lead to an increase in the temperature and consequently grain recrystallization. Moreover, it was found that the recrystallized grain structure and relatively high martensite levels developed in the SZ lead to a significant drop in the mechanical properties of the steel. In addition, microhardness profiles of the welded regions indicated that the hardness in both the SZ and TMAZ were relatively elevated confirming the development of martensite in these regions. In particular, to evaluate the mechanical strength of the weld, lap shear tensile test was conducted; exhibited the fracture zone in the SZ with shear fracture with uniformly distributed elongation shear dimples

An engineered periosteum for efficient delivery of rhBMP-2 and mesenchymal progenitor cells during bone regeneration

During bone regeneration, the periosteum acts as a carrier for key regenerative cues, delivering osteochondroprogenitor cells and crucial growth factors to the injured bone. We developed a biocompatible, 3D polycaprolactone (PCL) melt electro-written membrane to act as a mimetic periosteum. Poly (ethyl acrylate) coating of the PCL membrane allowed functionalization, mediated by fibronectin and low dose recombinant human BMP-2 (rhBMP-2) (10-25 mu g/ml), resulting in efficient, sustained osteoinduction in vitro. In vivo, rhBMP-2 functionalized mimetic periosteum demonstrated regenerative potential in the treatment of rat critical-size femoral defects with highly efficient healing and functional recovery (80%-93%). Mimetic periosteum has also proven to be efficient for cell delivery, as observed through the migration of transplanted periosteum-derived mesenchymal cells to the bone defect and their survival. Ultimately, mimetic periosteum demonstrated its ability to deliver key stem cells and morphogens to an injured site, exposing a therapeutic and translational potential in vivo when combined with unprecedentedly low rhBMP-2 doses