Biomedical subjects

Hidemitsu Furukawa

Publications and source records attributed to Hidemitsu Furukawa.

5 recordsLinked to original sources

PubMed2006

Anisotropic nucleation growth of actin bundle: a model for determining the well-defined thickness of bundles.

Biopolymers such as DNA, F-actins, and microtubules, which are highly charged, rodlike polyelectrolytes, are assembled into architectures with defined morphology and size by electrostatic interaction with multivalent cations (or polycations) in vivo and in vitro. The physical origin to determine their morphology and size is not clearly understood yet. Our results show that the actin bundle formation consists of two stages: the thickness of actin bundles is determined nearly at the initial stage, while the length of actin bundles is determined later on. It is also found that the thickness of actin bundles decreases with the increase of polycation-mediated attraction between F-actins. From these results, we propose the anisotropic nucleation-growth mechanism, in which the thickness of actin bundles is determined by critical nucleus size, whereas the length of actin bundles is determined by the concentration of free actins relative to nucleus concentration. Observing that polycations are concentrated in some sites of actin bundles, which are thought to be nucleation sites to initiate the formation of actin bundles, supports this model. This anisotropic nucleation-growth mechanism of actin bundles can be broadly applied to the self-assembly of rodlike polyelectrolytes.

Actins↗

PubMed2005

Elastic-hydrodynamic transition of gel friction.

We report the surface sliding friction of a high strength gel against a glass substrate under a normal pressure range of 0.01-2.5 MPa. The friction of the gel swollen with different viscous solvents is investigated over a wide velocity range. A velocity-viscosity conversion relationship is established. From the velocity-viscosity conversion relationship, a master curve that is characteristic to the elastic-hydrodynamic transition is observed. The results indicate that the adsorption model proposed by our previous work is valid even under a pressure up to MPa orders, which is the order of pressure that a cartilage sustains in the articular joints.

Adsorption↗

PubMed2005

Effect of polymer entanglement on the toughening of double network hydrogels.

The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M(w). The experimental results reveal that, for toughening of the DN gels, (1) M(w) is one of the dominant parameters; (2) there is a critical value of M(w) = 10(6) for a remarkable enhancement; (3) the fracture energy of DN gels with a M(w) larger than 10(6) reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta], where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm, it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.

Journal Article↗

PubMed2004

Crystal-like pattern formation in polymerization-induced phase separation.

A unique domain structure was found in liquid-liquid phase separation induced by radical polymerization of 4-chlorostyrene monomer in the presence of random copolymer poly(dimethylsiloxane-co-diphenylsiloxane). Droplets with a narrow size distribution were generated by phase separation, and these droplets hardly coalesced by collisions. With the growth of droplet size, droplets gradually filled the space and spontaneously arranged themselves in a regular array like a crystal. The mechanism of regular array formation was discussed based on the large difference in viscoelastic properties between two segregating components.

Journal Article↗

PubMed2003

Swelling-induced modulation of static and dynamic fluctuations in polyacrylamide gels observed by scanning microscopic light scattering.

The nature of inhomogeneities in vinylpolymer gels has hardly been clarified yet. Inhomogeneities on submicron and nanometer scales in polyacrylamide gels have been investigated by using a scanning microscopic light-scattering system and applying a general formula for an ensemble-averaged correlation function. The network structure of the gels is modified by varying the preparation conditions and can be roughly divided into two types. Swelling-induced modulation of inhomogeneities depends on the type of the network structure. At low monomer concentrations in preparation, both submicron- and nanometer-scale inhomogeneities increase with swelling. At high monomer concentrations in preparation, submicron-scale inhomogeneities increase with swelling, but nanometer-scale inhomogeneities decrease anomalously. This behavior is explained by a model of inhomogeneous network structure of vinylpolymer gels, where macrogel is formed from a large number of microgel particles.

Journal Article↗