Biorheology - Volume 41, issue 5

Authors: Iacob, Gh. | Rotariu, O. | Strachan, N.J.C. | Häfeli, U.O.

Article Type: Research Article

Abstract: The in vivo targeting of tumors with magnetic microspheres is currently realized through the application of external non‐uniform magnetic fields generated by rare‐earth permanent magnets or electromagnets. Our theoretical work suggests a feasible procedure for local delivery of magnetic nano‐ and microparticles to a target area. In particular, thin magnetizable wires placed throughout or close to the target area and magnetized by a perpendicular external uniform background magnetic field are used to concentrate magnetic microspheres injected into the target organ's natural blood supply. The capture of the magnetic particles and the building of deposits thereof in the blood vessels of …the target area were modeled under circumstances similar to the in vivo situation. This technique could be applied to magnetically targeted cancer therapy or magnetic embolization therapy with magnetic particles that contain anticancer agents, such as chemotherapeutic drugs or therapeutic radioisotopes. Show more

Keywords: Magnetic targeting, ferromagnetic wires, magnetic capture, magnetic drug targeting, local radiotherapy, emboliza‐ tion, magnetic microspheres, magnetic nanospheres

Citation: Biorheology, vol. 41, no. 5, pp. 599-612, 2004

Authors: Goodman, S.A. | May, S.A. | Heinegård, D. | Smith, R.K.W.

Article Type: Research Article

Abstract: The effect of strain and transforming growth factor beta on equine tendon fibroblasts (tenocytes) was assessed in vitro. Tenocytes were isolated from flexor and extensor tendons of horses from foetal to 10 years of age. These cells were cultured until confluent on collagen‐coated silicone dishes. Cyclic biaxial strain of 9±1% was applied at 0.5 Hz for 24 hours with or without added TGFβ1 or 3 (10 ng/ml). Proliferation and synthetic responses were dependent on the tendon of origin. Neither strain nor TGFβ caused flexor tenocytes to proliferate significantly, while strain alone did proliferate extensor tenocytes. TGFβ, with or without strain, …increased the incorporation of [3 H]‐proline and the production of types I and III collagen and COMP in both cell types, although the effect on COMP production was more marked in flexor tenocytes, perhaps reflecting the higher levels found in this tendon in vivo. Immature flexor tenocytes synthesised more collagen and COMP than those from mature animals, while age had little effect in extensor tenocytes. Our results suggest that tenocytes become differentiated at an early age and present tendon‐specific responses. Show more

Citation: Biorheology, vol. 41, no. 5, pp. 613-628, 2004

Authors: Nishimura, M. | Kawata, M. | Yan, W. | Okamato, A. | Nishimura, H. | Ozaki, Y. | Hamada, T. | Kato, Y.

Article Type: Research Article

Abstract: We determined elasticity (G′) and viscosity (G″) of various aggrecan–hyaluronan solutions using a controlled‐stress rheometer with high (10 Hz) to low (0.1 Hz) frequencies. Aggrecan solution (50 mg/ml) alone showed little elasticity at any frequency, but the addition of 3300 kDa hyaluronan at 0.001–0.1 mg/ml markedly increased the elasticity, but not the viscosity, at all frequencies. Increasing hyaluronan concentration at >0.1 mg/ml did not further increase the elasticity of the aggrecan solution, and the elasticity of the aggrecan–hyaluronan complex solution reached a plateau at a 500 :1 (w/w) ratio. In studies with increasing concentrations of aggrecan and a constant concentration (0.5 …mg/ml) of 3300 kDa hyaluronan, aggrecan induced elasticity only at >20 mg/ml, indicating the presence of a critical concentration for elasticity. In the presence of 50 mg/ml aggrecan, 1000 kDa hyaluronan had far less effect on the elasticity of the aggrecan solution than did 3300 kDa hyaluronan. These findings suggest that only ∼50% reduction in aggrecan concentration (<20 mg/ml), or reduced hyaluronan size (<1000 kDa) – compared with their physiological levels in young cartilage – can abolish the elastic network of the aggrecan–hyaluronan complex. Show more

Keywords: Hyaluronan, aggrecan, viscosity, elasticity

Citation: Biorheology, vol. 41, no. 5, pp. 629-639, 2004

Authors: Jordan, A. | David, T. | Homer‐Vanniasinkam, S. | Graham, A. | Walker, P.

Article Type: Research Article

Abstract: The effects of platelet margination and enhanced platelet diffusivity, as induced by red blood cells, on the adhesion of platelets, were investigated for a range of haematocrits, under 2D axi‐symmetric flow, simulating previous in vitro experiments [Microvasc. Res. 17 (1979), 238–262]. The effect of margination was incorporated via use of an elevated platelet inlet mass fraction, Φe , in a manner similar to that of Wootton [Ann. Biomed. Eng. 29 (2001), 321–329], and a shear and haematocrit dependent platelet diffusivity, according to the model presented by Zydney and Colton [Physico Chem. Hydrodyn. 10 (1988), 77–96] was used. A combination of …the two models was required to simulate the deposition of platelets to a collagen coated surface, under the complex flow, which exhibited a recirculation zone and stagnation point. Results obtained showed qualitative agreement with in vitro results, for a range of haematocrits (11–50%), and also showed that the effects of margination were not linearly dependent on haematocrit. Agreement may be improved in future simulations by incorporating the effects of depleted cell concentrations in the vortex which have been observed previously [Phil. Trans. Roy. Soc. (Lond.) B279 (1977), 413–445]. It would also be advantageous to devise a full mathematical description for platelet margination effects as a function of shear rate and haematocrit and a description of the accompanying effect of apparent blood viscosity. Show more

Keywords: Numerical modelling, haematocrit, apparent viscosity, axi‐symmetric expansion tube, vortex

Citation: Biorheology, vol. 41, no. 5, pp. 641-653, 2004

Authors: Chen, Huai‐Qing | Tian, Wei | Chen, Yun‐Shuang | Li, Liang | Raum, Jeffrey | Sung, K.‐L. Paul

Article Type: Research Article

Abstract: We investigated neutrophil activation, specifically F‐actin content and distribution, in situations mimicking the in vivo environment using steady and oscillatory shear. Under low steady shear (<150 s−1 ) F‐actin levels were decreased for both treated (n‐formyl‐L‐methioryl‐L‐leucyl‐L‐phenylalanine (fMLP)) and untreated neutrophils. The F‐actin content increased with a change to higher steady shear levels. Neutrophils show the same behavior of decreased F‐actin content for oscillatory shear (26.7 s−1 ) as they did for steady shear. In both situations, the low shear levels caused a decrease in F‐actin content. However, as the magnitude of the shear rate increased, cells showed a reversal to …increasing F‐actin content. Shear caused a decrease in F‐actin in the cell cortex for both control and fMLP treated cells. Ctyochalasin B (CB), a common F‐actin assembly blocker, significantly decreased F‐actin content. The results indicate that neutrophils regulate their actin network based on the level and type of shear stress they encounter in the bloodstream. Show more

Keywords: Leukocyte, fluid shear stress, actin

Citation: Biorheology, vol. 41, no. 5, pp. 655-664, 2004