Hiroshi Yoshimoto

The objective of this study was to assess bone formation from mesenchymal stem cells (MSCs) on a novel nanofibrous scaffold in a rat model. A highly porous, degradable poly(epsilon-caprolactone) (PCL) scaffold with an extracellular matrix-like topography was produced by electrostatic fiber spinning. MSCs derived from the bone marrow of neonatal rats were cultured, expanded, and seeded on the scaffolds. The cell-polymer constructs were cultured with osteogenic supplements in a rotating bioreactor for 4 weeks, and subsequently implanted in the omenta of rats for 4 weeks. The constructs were explanted and characterized by histology, immunohistochemistry, and scanning electron microscopy. The constructs maintained the size and shape of the original scaffolds. Morphologically, the constructs were rigid and had a bone-like appearance. Cells and extracellular matrix (ECM) formation were observed throughout the constructs. In addition, mineralization and type I collagen were also detected. This study establishes the ability to develop bone grafts on electrospun nanofibrous scaffolds in a well-vascularized site using MSCs.

It is shown by direct numerical simulation that the preferential concentration of small heavy particles in homogeneous isotropic developed turbulence has a self-similar multi-scale nature when the particle relaxation time is within the inertial time scales of the turbulence. This is shown by the pair correlation function of the particle distribution extending over the entire inertial range, and the probability density function of the volumes of particle voids taking a power-law form. This self-similar multi-scale nature of particle clustering cannot be explained only by the centrifugal effect of the smallest-scale (i.e. the Kolmogorov scale) eddies, but also by the effect of co-existing self-similar multi-scale coherent eddies in the turbulence at high Reynolds numbers. This explanation implies that the preferential concentration of particles takes place even when the relaxation time of particles is much larger than the Kolmogorov time, provided it is smaller than the longest time scale of the turbulence, since even the largest-scale eddies bring about particle clustering.