In this study, Computational Fluid Dynamics(CFD) is used to investigate and compare the impact of bioreactor parameters(such as its geometry, medium flow-rate, scaffold configuration) on the local transport phenomena ...In this study, Computational Fluid Dynamics(CFD) is used to investigate and compare the impact of bioreactor parameters(such as its geometry, medium flow-rate, scaffold configuration) on the local transport phenomena and, hence, their impact on human mesenchymal stem cell(hM SC) expansion. The geometric characteristics of the TissueFlex174;(Zyoxel Limited, Oxford, UK) microbioreactor were considered to set up a virtual bioreactor containing alginate(in both slab and bead configuration) scaffolds. The bioreactor and scaffolds were seeded with cells that were modelled as glucose consuming entities. The widely used glucose medium, Dulbecco's Modified Eagle Medium(DMEM), supplied at two inlet flow rates of 25 and 100 μl·h^(-1), was modelled as the fluid phase inside the bioreactors. The investigation, based on applying dimensional analysis to this problem, as well as on detailed three-dimensional transient CFD results, revealed that the default bioreactor design and boundary conditions led to internal and external glucose transport, as well as shear stresses, that are conducive to h MSC growth and expansion. Furthermore, results indicated that the ‘top-inout' design(as opposed to its symmetric counterpart) led to higher shear stress for the same media inlet rate(25 μl·h^(-1)), a feature that can be easily exploited to induce shear-dependent differentiation. These findings further confirm the suitability of CFD as a robust design tool.展开更多
Topological pumping refers to transfer of a physical quantity governed by the system topology,resulting in quantized amounts of the transferred quantities.It is a ubiquitous wave phenomenon typically considered subjec...Topological pumping refers to transfer of a physical quantity governed by the system topology,resulting in quantized amounts of the transferred quantities.It is a ubiquitous wave phenomenon typically considered subject to exactly periodic adiabatic variation of the system parameters.Recently,proposals for generalizing quasi-periodic topological pumping and identifying possible physical settings for its implementation have emerged.In a strict sense,pumping with incommensurate frequencies can only manifest over infinite evolution distances,raising a fundamental question about its observability in real-world finite-dimensional systems.Here we demonstrate that bi-chromatic topological pumping with two frequencies,whose ratio is an irrational number,can be viewed as the convergence limit of pumping with two commensurate frequencies representing the best rational approximations of that irrational number.In our experiment,this phenomenon is observed as the displacement of a light beam center in photorefractive crystals induced by two optical lattices.The longitudinal periods of the lattices,that in the paraxial approximation emulate two pumping frequencies,are related as Fibonacci numbers,successively approaching the golden ratio.We observed that a one-cycle displacement of the beam center at each successive approximation is determined by the relation between successive Fibonacci numbers,while the average direction of propagation(emulating average pumping velocity)of the beam is determined by the golden ratio.展开更多
基金Department of Engineering Science, University of Oxford, Scholarship
文摘In this study, Computational Fluid Dynamics(CFD) is used to investigate and compare the impact of bioreactor parameters(such as its geometry, medium flow-rate, scaffold configuration) on the local transport phenomena and, hence, their impact on human mesenchymal stem cell(hM SC) expansion. The geometric characteristics of the TissueFlex174;(Zyoxel Limited, Oxford, UK) microbioreactor were considered to set up a virtual bioreactor containing alginate(in both slab and bead configuration) scaffolds. The bioreactor and scaffolds were seeded with cells that were modelled as glucose consuming entities. The widely used glucose medium, Dulbecco's Modified Eagle Medium(DMEM), supplied at two inlet flow rates of 25 and 100 μl·h^(-1), was modelled as the fluid phase inside the bioreactors. The investigation, based on applying dimensional analysis to this problem, as well as on detailed three-dimensional transient CFD results, revealed that the default bioreactor design and boundary conditions led to internal and external glucose transport, as well as shear stresses, that are conducive to h MSC growth and expansion. Furthermore, results indicated that the ‘top-inout' design(as opposed to its symmetric counterpart) led to higher shear stress for the same media inlet rate(25 μl·h^(-1)), a feature that can be easily exploited to induce shear-dependent differentiation. These findings further confirm the suitability of CFD as a robust design tool.
基金supported by the Fundacao para a Ciência e Tecnologia under the project 2023.13176.PEX(DOI https://doi.org/10.54499/2023.13176.PEX)by national funds,under the Unit CFTC-Centro de Física Teórica e Computacional,reference UID/00618/2025,financing period 2025–2029+4 种基金funding from the project FFUU-2024-0003 of the Institute of Spectroscopy of the Russian Academy of Sciencesfunding from the Shanghai Outstanding Academic Leaders Plan(No.20XD1402000)Shanghai Leading Talent Program 1 of Eastern Talent Plan(The 16th Shanghai Leading Talent Program)the support of the National Natural Science Foundation of China(No.12404385,No.12304366)China Postdoctoral Science Foundation(No.BX20230217,No.BX20230218,No.2023M742295,No.2024M751950).
文摘Topological pumping refers to transfer of a physical quantity governed by the system topology,resulting in quantized amounts of the transferred quantities.It is a ubiquitous wave phenomenon typically considered subject to exactly periodic adiabatic variation of the system parameters.Recently,proposals for generalizing quasi-periodic topological pumping and identifying possible physical settings for its implementation have emerged.In a strict sense,pumping with incommensurate frequencies can only manifest over infinite evolution distances,raising a fundamental question about its observability in real-world finite-dimensional systems.Here we demonstrate that bi-chromatic topological pumping with two frequencies,whose ratio is an irrational number,can be viewed as the convergence limit of pumping with two commensurate frequencies representing the best rational approximations of that irrational number.In our experiment,this phenomenon is observed as the displacement of a light beam center in photorefractive crystals induced by two optical lattices.The longitudinal periods of the lattices,that in the paraxial approximation emulate two pumping frequencies,are related as Fibonacci numbers,successively approaching the golden ratio.We observed that a one-cycle displacement of the beam center at each successive approximation is determined by the relation between successive Fibonacci numbers,while the average direction of propagation(emulating average pumping velocity)of the beam is determined by the golden ratio.
