Orienting actin filaments for directional motility of processive myosin motors.

To utilize molecular motors in manmade systems, it is necessary to control the motors' motion. We describe a technique to orient actin filaments so that their barbed ends point in the same direction, enabling same-type motors to travel unidirectionally. Myosin-V and myosin-VI were observed to travel, respectively, toward and away from the filaments' barbed ends. When both motors were present, they occasionally passed each other while "walking" in opposite directions along single actin filaments.

Mechanical phenotyping of mouse embryonic stem cells: increase in stiffness with differentiation.

Atomic force microscopy (AFM) has emerged as a promising tool to characterize the mechanical properties of biological materials and cells. In our studies, undifferentiated and early differentiating mouse embryonic stem cells (mESCs) were assessed individually using an AFM system to determine if we could detect changes in their mechanical properties by surface probing. Probes with pyramidal and spherical tips were assessed, as were different analytical models for evaluating the data. The combination of AFM probing with a spherical tip and analysis using the Hertz model provided the best fit to the experimental data obtained and thus provided the best approximation of the elastic modulus. Our results showed that after only 6 days of differentiation, individual cell stiffness increased significantly with early differentiating mESCs having an elastic modulus two- to threefold higher than undifferentiated mESCs, regardless of cell line (R1 or D3 mESCs) or treatment. Single-touch (indentation) probing of individual cells is minimally invasive compared to other techniques. Therefore, this method of mechanical phenotyping should prove to be a valuable tool in the development of improved methods of identification and targeted cellular differentiation of embryonic, adult, and induced-pluripotent stem cells for therapeutic and diagnostic purposes.

Mechanical characterization of mouse embryonic stem cells.

Current cell detection techniques are antibody staining of specific protein markers, morphometric parameters and transgenic markers. These assays are often qualitative and do not quantitatively define the outcome of a cell progression during differentiation. Consequently, we propose to characterize the mechanical behavior of embryonic stem cell, which will predict its stage of differentiation during lineage differentiation. Using the atomic force microscope, we have performed several experiments on mouse embryonic stem cells (mESC) roughly 7-17 microm in diameter and height at the interphase stage of the cell cycle process. Specifically, we conducted single indentation studies on undifferentiated and early differentiating (6 days under differentiation conditions) mESC with a cell indentation range of 2-2.5 microm. The data was used to analyze various contact models that can accurately model the geometry of the AFM tip and mESC interaction. With the choice of appropriate contact model, we can determine the accurate modulus of the cell membrane. The experimental results confirmed our research hypothesis that the mechanical property of undifferentiated mESC is different from differentiating (6th day) mESC.

Engineering approaches to biomanipulation.

This article presents a review on the existing techniques for manipulating biological cells. Because biomanipulation involves a wide range of disciplines, from biology to engineering, we concentrate on some of the key methodologies that would result in an efficient biomanipulation system. Some of the key methodologies discussed in this article for cell manipulation relate to the use of magnetics, microelectromechanical systems (MEMS)-based approaches, optics, electric field, and mechanical techniques. Recent advances in engineering have allowed researchers worldwide to address the problems arising from conventional manipulation techniques. This paper assimilates significance and limitations of biomanipulation techniques described in the literature.