Rate of Solution of Solid Particles in Agitated Liquids

Hixson and Baum have proposed generalized dimensionless equations for the rate of solution of solid particles in agitated liquids. The authors developed an improved equation and conducted additional experiments on the rates of solution of zinc and magnesium metals in dilute hydrochloric acid containing potassium nitrate. Experiments were also made on the rate of solution of benzoic acid in NaOH solutions and of sugar in water. The newly developed equation is as follows: (KD/Df)=α′(D²nρₗ/µ)ᵖ(µ/ρₗFf)q(δ³g/ν²)r(ρₛ-ρₗ/ρₗ)ᵗ The constant α′ and exponents p, q and s are presented in this paper. The authors arrived at the following conclusions: (1) At a definite critical Reynolds number, Rf (or agitator speed, Nf), solid particles are fluidized in an agitated liquid. (2) At this critical Reynolds number (or agitator speed), the rate of increase in solution velocity is abruptly decreased with further increase in agitator speed. (3) In the fluidized state where N>Nf, an increase in density difference between the solid and liquid phases combined with the effect of agitation velocity greatly reduces the diffusional resistance. (4) In the range of Reynolds numbers less than Rf, or agitator speed less than Nf, the apparent rate of solution of solid particles increases with the 1.0 to 1.4 power of Rₑ depending upon the conditions of agitation. This experimental effect may reach a value of even 2.9 for small particles. (5) From these experiments it is expected that the effect of agitation in liquid-liquid systems is mainly to increase the reaction surface area, and that the effect of agitation in diminishing diffusion resistance is rather small. The effect of agitation in solid-liquid systems in the range of fluidization is mainly to diminish diffusional resistance

Evaluation of extensional and torsional stiffness of single actin filaments by molecular dynamics analysis.

It is essential to investigate the mechanical behaviour of cytoskeletal actin filaments in order to understand their critical role as mechanical components in various cellular functional activities. These actin filaments consisting of monomeric molecules function in the thermal fluctuations. Hence, it is important to understand their mechanical behaviour on the microscopic scale by comparing the stiffness based on thermal fluctuations with the one experimentally measured on the macroscopic scale. In this study, we perform a large-scale molecular dynamics (MD) simulation for a half-turn structure of an actin filament. We analyse its longitudinal and twisting Brownian motions in equilibrium and evaluated its apparent extensional and torsional stiffness on the nanosecond scale. Upon increasing the sampling-window durations for analysis, the apparent stiffness gradually decreases and exhibits a trend to converge to a value that is close to the experimental value. This suggests that by extrapolating the data obtained in the MD analysis, we can estimate the experimentally determined stiffness on the microsecond to millisecond scales. For shorter temporal scales, the apparent stiffness is larger than experimental values, indicating that fast, local motions of the molecular structure are dominant. To quantify the local structural changes within the filament on the nanosecond scale and investigate the molecular mechanisms, such as the binding of the actin-regulatory proteins to the filaments, it is preferable to analyse the mechanical behaviour on the nanometre and nanosecond scales using MD simulation

Magnetic Targeted Delivery of Induced Pluripotent Stem Cells Promotes Articular Cartilage Repair

Cartilage regeneration treatments using stem cells are associated with problems due to the cell source and the difficulty of delivering the cells to the cartilage defect. We consider labeled induced pluripotent stem (iPS) cells to be an ideal source of cells for tissue regeneration, and if iPS cells could be delivered only into cartilage defects, it would be possible to repair articular cartilage. Consequently, we investigated the effect of magnetically labeled iPS (m-iPS) cells delivered into an osteochondral defect by magnetic field on the repair of articular cartilage. iPS cells were labeled magnetically and assessed for maintenance of pluripotency by their ability to form embryoid bodies in vitro and to form teratomas when injected subcutaneously into nude rats. These cells were delivered specifically into cartilage defects in nude rats using a magnetic field. The samples were graded according to the histologic grading score for cartilage regeneration. m-iPS cells differentiated into three embryonic germ layers and formed teratomas in the subcutaneous tissue. The histologic grading score was significantly better in the treatment group compared to the control group. m-iPS cells maintained pluripotency, and the magnetic delivery system proved useful and safe for cartilage repair using iPS cells

Surgical Treatment of dialysis-associated spondylosis

【Objective】The purposes of this study were to classify the lesions of dialysis-associated spondylosis and evaluate the results of surgical treatment. 【Subjects and methods】The subjects were 87 patients (43 men and 44 women) who underwent surgery. These patients were studied in terms of lesion classification, surgical method, duration of dialysis, duration of surgery, intraoperative blood loss, and postoperative complications. 【Results】Among patients with cervical spine involvement, 13 had destructive spondyloarthropathy (DSA), 29 had amyloid deposition, and 8 had a dens axis lesion. Among patients with lumbar spine involvement, 20 had DSA, and 17 had amyloid deposition. With regard to 6 patients with a dens axis lesion involving atlantoaxial subluxation, each had posterior fusion (PF) of the occiput to the upper cervical spine. With regard to the patients with lumbar DSA, 10 patients had posterolateral fusion (PLF), 8 patients had posterior lumbar interbody fusion (PLIF) and 2 patients had laminectomy. The duration of dialysis in cases of a dens axis lesion varied between 25 and 35 years, with the mean duration being 28.9 years. 【Conclusions】All patients who underwent surgery for dens axis lesions were long-term dialysis patients who had been on dialysis for 25 years. Lumbar spine DSA was treated with PLIF in patients with lateral slipping and marked instability, with laminectomy in patients with a narrowed intervertebral disk space and no instability

(-)-Epigallocatechin Gallate Reduces Platelet-Derived Growth Factor-BB-Stimulated Interleukin-6 Synthesis in Osteoblasts: Suppression of SAPK/JNK

We previously showed that the mitogen-activated protein (MAP) kinase superfamily, p44/p42 MAP kinase, p38 MAP kinase, and stress-activated protein kinase (SAPK)/c-Jun N-terminal (JNK), positively plays a part in the platelet-derived growth factor-BB- (PDGF-BB-) stimulated synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells while Akt and p70 S6 kinase negatively regulates the synthesis. In the present study, we investigated whether (-)-epigallocatechin gallate (EGCG), one of the major green tea flavonoids, affects the synthesis of IL-6 in these cells and the mechanism. EGCG significantly reduced the IL-6 synthesis and IL-6 mRNA expression stimulated by PDGF-BB, EGCG reduced the PDGF-BB-stimulated IL-6 synthesis also in primary-cultured osteoblasts. EGCG had no effect on the levels of osteocalcin and osteoprotegerin in MC3T3-E1 cells. The PDGF-BB-induced autophosphorylation of PDGF receptor β was not suppressed by EGCG. The PDGF-BB-induced phosphorylation of p44/p42 MAP kinase and p38 MAP kinase was not affected by EGCG. On the other hand, EGCG markedly suppressed the PDGF-BB-induced phosphorylation of SAPK/JNK. Finally, the PDGF-BB-induced phosphorylation of Akt and p70 S6 kinase was not affected by EGCG. These results strongly suggest that EGCG inhibits the PDGF-BB-stimulated synthesis of IL-6 via suppression of SAPK/JNK pathway in osteoblasts