947 research outputs found
A new cultivation method for microbial oil production: cell pelletization and lipid accumulation by Mucor circinelloides
The recent energy crisis has triggered significant attention on the microbial synthesis of lipids, which comprise the raw material for biodiesel production. Microbial oil accumulation with filamentous fungi has great potential because filamentous fungi can form pellets during cell growth, and these pellets are much easier to harvest from cell broth. This paper focuses on the cell pelletization process of the oleaginous Mucor circinelloides. We have studied the effect of various cultural conditions on pelletized cell growth and lipid accumulation. This study is the first to report that pH adjustment during cell growth plays a key role in pellet formation of M. circinelloides and describes a handy method by which to induce cell pelletization in submerged fungal cultivation. Our study reveals that cell growth and lipid production are not significantly affected by pelletization and that lipid accumulation is triggered at stressed conditions, such as a high carbon-to-nitrogen ratio and high temperature
Microstructure evolution under the space-time variational solidification conditions in a melt pool: A multi-scale simulation study
The properties of welded components are dominated by the microstructure
evolution in the pool, where the solidification conditions are space-time
variational. To represent the variational solidification conditions in the
pool, the multi-scale simulation is carried out in this paper, combining
microscopic Phase-Field (PF) equations with macroscopic thermal processes.
First, two different models, the GR model and TF model, are employed to
simulate the single crystal solidification at a local region of pool. Results
suggest the TF model is more suitable to reflect the variational conditions
than the GR model. Then the single-crystal solidification and poly-crystal
solidification at the whole region of pool are carried out through the TF
model. The results indicate the space-time variabilities of solidification
conditions across the pool. Meanwhile, the variational solidification
conditions influence the microstructure evolution significantly, including the
onset of initial instability at the epitaxial growth stage and the directional
evolutions of the converging grain boundaries (GBs) and diverging GBs at the
competitive growth stage. Moreover, the formation of axial grain structures is
observed, which can be regarded as the competition between the grains along the
axial direction and radial direction. This study indicates the necessity of
considering variational conditions in a pool. Meanwhile, the PF model can
simulate microstructure evolution under variational conditions accurately,
which has a great potential for investigating solidification dynamics in a melt
pool.Comment: 30pages, 14 figure
Controlled release of chitosan/heparin nanoparticle-delivered VEGF enhances regeneration of decellularized tissue-engineered scaffolds
Regeneration deficiency is one of the main obstacles limiting the effectiveness of tissue-engineered scaffolds. To develop scaffolds that are capable of accelerating regeneration, we created a heparin/chitosan nanoparticle-immobilized decellularized bovine jugular vein scaffold to increase the loading capacity and allow for controlled release of vascular endothelial growth factor (VEGF). The vascularization of the scaffold was evaluated in vitro and in vivo. The functional nanoparticles were prepared by physical self-assembly with a diameter of 67–132 nm, positive charge, and a zeta potential of ∼30 mV and then the nanoparticles were successfully immobilized to the nanofibers of scaffolds by ethylcarbodiimide hydrochloride/hydroxysulfosuccinimide modification. The scaffolds immobilized with heparin/chitosan nanoparticles exhibited highly effective localization and sustained release of VEGF for several weeks in vitro. This modified scaffold significantly stimulated endothelial cells’ proliferation in vitro. Importantly, utilization of heparin/chitosan nanoparticles to localize VEGF significantly increased fibroblast infiltration, extracellular matrix production, and accelerated vascularization in mouse subcutaneous implantation model in vivo. This study provided a novel and promising system for accelerated regeneration of tissue-engineering scaffolds
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