DSpace collection: 期刊論文

Morphology and organization of tissue cells in 3D microenvironment of monodisperse foam scaffolds

title: Morphology and organization of tissue cells in 3D microenvironment of monodisperse foam scaffolds abstract: Here we demonstrate an efficient method to fabricate large-domain monodisperse foam scaffolds made of gelatin for 3D cell culture. We tested three distinct tissue cell types cultured in foam scaffolds composed of uniform spherical pores. The cells displayed appropriate morphological and physiological characteristics: epithelial cells formed cyst-like structures and were polarized inside pores, myoblasts adopted a tubular structure and fused into myotubes, and fibroblasts exhibited a wide variety of morphologies. Scaffolds with uniform pores can thus provide a platform for systematic study of 3D cell-matrix interactions.

Context-Dependent Stridulatory Responses of Leptogenys kitteli (Hymenoptera: Formicidae) to Social, Prey, and Disturbance Stimuli

title: Context-Dependent Stridulatory Responses of Leptogenys kitteli (Hymenoptera: Formicidae) to Social, Prey, and Disturbance Stimuli abstract: Individual Leptogenys kitteli (Hymenoptera: Formicidae) workers produce stridulatory pulses at faster rates after exposure to prey larvae placed nearby the nest and after air-puff disturbances at the nest entrance than during unstimulated social interactions within the nest. Workers produce chirps (trains of stridulatory pulses) at faster rates after exposure to prey larvae than during unstimulated social interactions, including groups of chirps (bursts) where the intervals between chirps decrease below 60 ms. Such bursts do not occur in unstimulated social interactions. Chirp bursts with intervals <10 ms (disturbance bursts) occur immediately after air puffs at the nest entrance. Disturbance bursts are not observed after exposure to prey larvae or during unstimulated social interactions. The rates of disturbance bursts decline rapidly within 10 s after an air puff, whereas episodes of chirp bursts extend over periods of 30 s or longer when groups of ants are moving prey larvae into the nest. The differences in the rates of stridulatory pulses and chirps and in the durations of stridulatory activity observed in the context of different types, intensities, and durations of stimulation contribute to evidence that stridulation has a significant communicatory role in colony activities of many ant species, even in genera, such as Leptogenys, in which a stridulatory organ has not been retained in every species. A better understanding of how ants produce and interpret vibrations may lead to new methods that to improve attractiveness of baits, or repel ants from electrical equipment housings where opportunistic colonies frequently nest.

Free energy and critical force for adhesion clusters

title: Free energy and critical force for adhesion clusters abstract: Cooperative clusters of N parallel bonds confined to an anchoring surface by springs of stiffness k(s) are considered. The free energy of a cluster can be obtained from its force-displacement relation. The dissociation kinetics of the cluster can be modeled as the dissociation of an effective single bond. There is a critical force F(c) beyond which the barrier for the cluster dissociation vanishes. F(c) scales such as k(s)(1/2) and F(c)/N is small compared to the critical force of a single bond. The theoretical predictions of free energy landscape and cluster lifetime are supported by numerical simulations for large number of bonds. Our study suggests that experiments measuring force-displacement relations could be useful in exploring the dynamics of adhesion clusters.

Bursting of Neurons Induced by Inhibitory Mechanism

title: Bursting of Neurons Induced by Inhibitory Mechanism abstract: We present a model of bursting neurons that combines a Fitz-Hugh Nagumo (FHN) model with an additional dynamic variable, which is slower than those in the FHN model and plays an inhibitory role. The effects of noise from the network connections is incorporated in a single parameter. This inhibitory variable enables the neuron firing to be inhibited and generates inter-spike intervals (ISI) with long time scales resulting in bursting. This phenomenon is also observed in cortical neuronal cultures. where the bursting frequency is found to be much slower than the characteristic time scale of a neuron. It is observed that bursting occurs when the mean coordination number of a neuron with the inhibitory element exceeds a threshold value. Furthermore, in the presence of noise, the ISI distribution displays complex and nontrivial patterns which reveal the interesting property of missing spike events in bursting trains. In particular the missing spikes show a power-law decay suggesting that correlations are induced in the system. The coefficient of variation can well characterize the nature of the bursting transitions, and the associated phase diagram is also computed.