AFM-based identification of the dynamic properties of globular proteins: simulation study

Nowadays a mathematical model-based computational approach is getting more attention as an effective tool for understanding the mechanical behaviors of biological systems. To find the mechanical properties of the proteins required to build such a model, this paper investigates a real-time identification method based on an AFM nanomanipulation system. First, an AFM-based bio-characterization system is introduced. Second, a second-order time-varying linear model representing the interaction between an AFM cantilever and globular proteins in a solvent is presented. Finally, we address a real-time estimation method in which the results of AFM experiments are designed to be inputs of the state estimator proposed here. Our attention is restricted to a theoretical feasibility analysis of the proposed methodology. We simply set the mechanical properties of the particular protein such as mass, stiffness, and damping coefficient in the system model prior to running the simulation. Simulation results show very good agreement with the preset properties. We anticipate that the realization of the AFM-based bio-characterization system will also provide an experimental validation of the proposed identification procedure in the future. This methodology can be used to determine a model of protein motion for the purpose of computer simulation and for a real-time modification of protein deformation. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Jungyul Park received the B.S. and M.S. degrees in mechanical design and production engineering from the Seoul National University in 1998 and 2000, respectively and received Ph.D. degree in School of Mechanical & Aerospace Engineering from the Seoul National University, Korea in 2005. He is currently an assistant professor in the mechanical engineering department, Sogang University, in Korea (since 2007). Previously he had worked at the Korea Institute of Science and Technology and at the biomedical engineering department, Johns Hopkins University. His research interests are design, fabrication and analysis of BioMEMS, manipulation, characterization and identification of cells/biomolecules using micro/nano technology, and precise control for micro/nano manipulation.     

Real-time measurement of the contractile forces of self-organized cardiomyocytes on hybrid biopolymer microcantilevers

We present a microfabricated hybrid biopolymer microcantilever, in which the contractile force of self-organized cardiomyocytes can be measured and studied, as a prototype for the development of cell-driven actuators. The microcantilever is made of a flexible, transparent, biocompatible poly(dimethylsiloxane) substrate, using a simple microfabrication technique. Seeding and culturing cardiomyocytes on the specific cantilever allows us to perform highly sensitive, quantitative, and noninvasive measurement of the contractile force of the self-organized cells in real time. The motions of the microcantilever showed good agreement with an analytical solution based on Stoney's equation and finite element modeling (FEM) of the hybrid system. Immunostaining of the cells on the hybrid system showed continuous high-order coalignment of actin filaments and parallel sarcomeric organization in the direction of the longitudinal axis of the microcantilever without structural constraints, such as microgrooves or lines, and proved our FEM and the synchronous contraction of cardiomyocytes. The presented device should facilitate measurement of the contractile force of self-organized cardiomyocytes on a specific area, which may help the understanding of heart failure and the design of optimal hybrid biopolymer actuators, as well as assist development of a microscale cell-driven motor system.     

Multimodal and Covert–Overt Convertible Structural Coloration Transformed by Mechanical Stress

Most materials and devices with structurally switchable color features responsive to external stimuli can actively and flexibly display various colors. However, realizing covert–overt transformation behavior, especially switching between transparent and colored states, is more challenging. A composite laminate of soft poly(dimethylsiloxane) (PDMS) with a rigid SiO₂-nanoparticle (NP) structure pattern is developed as a multidimensional structural color platform. Owing to the similarity in the optical properties of PDMS and SiO₂ NPs, this device is fully transparent in the normal state. However, as their mechanical strengths differ considerably, upon compressive loading, a buckling-type instability arises on the surface of the laminate, leading to the generation of 1D or 2D wrinkled patterns in the form of gratings. Finally, an application of the device in which quick response codes are displayed or hidden as covert–overt convertible colored patterns for optical encryption/decryption, showing their remarkable potential for anticounterfeiting applications, is demonstrated.     

Identification and control of a sensorized microgripper for micromanipulation

This paper presents the design and control of a sensorized microgripper using a voice coil motor and a flexure mechanism. To increase the gripping sensitivity, shape design and determination of sensor attachment position are performed using finite element analysis. Empirical models of the microgripper are acquired for the design of position control and gripping force control. By using the identified models, both the perfect tracking controller for position control and the adaptive zero-phase error tracking controller for force control are implemented. The effectiveness of the proposed model-based control methods is verified by experimental studies.     

Information technology in the 1990s: More footloose or more location-bound?

This article examines whether the growth of information technology (IT) is associated with a dispersion or concentration of economic activities. The locational Gini coefficient and Morans I are first applied to ascertain the relationship between the growth of information technology and the distribution pattern of economic activities at the metropolitan scale. Next, using the G _i ^* statistic as the dependent variable and the level of information infrastructure as the independent variable, the above relationship is analysed at an intra-metropolitan scale. The results suggest that trends at a metropolitan scale do not necessarily reflect the trends at an intra-metropolitan scale in association.Received: 13 August 2002, Accepted: 10 May 2003, JEL Classification: R1, R3Jungyul Sohn: The author is indebted to three anonymous referees for their helpful comments. The author also thanks the editor for the comprehensive editorial review.     

Design and performance evaluation of a 3-DOF mobile microrobot for micromanipulation

In this paper, a compact 3-DOF mobile microrobot with sub-micron resolution is presented. It has many outstanding features: it is as small as a coin ; its precision is of sub-micrometer resolution on the plane; it has an unlimited travel range; and it has simple and compact mechanisms and structures which can be realized at low cost. With the impact actuating mechanism, this system enable both fast coarse motion and highly precise fine motion with a pulse wave input voltage controlled. The 1-DOF impact actuating mechanism is modeled by taking into consideration the friction between the piezoelectric actuator and base. This modeling technique is extended to simulate the motion of the 3-DOF mobile robot. In addition, experiments are conducted to verify that the simulations accurately represent the real system. The modeling and simulation results will be used to design the model-based controller for the target system. The developed system can be used as a robotic positioning device in the micromanipulation system that determines the position of micro-sized components or particles in a small space, or assemble them in the mesoscale structure.     

Transfer Printing of Cell Layers with an Anisotropic Extracellular Matrix Assembly using Cell‐Interactive and Thermosensitive Hydrogels

The structure of tissue plays a critical role in its function and therefore a great deal of attention has been focused on engineering native tissue‐like constructs for tissue engineering applications. Transfer printing of cell layers is a new technology that allows controlled transfer of cell layers cultured on smart substrates with defined shape and size onto tissue‐specific defect sites. Here, the temperature‐responsive swelling‐deswelling of the hydrogels with groove patterns and their versatile and simple use as a template to harvest cell layers with anisotropic extracellular matrix assembly is reported. The hydrogels with a cell‐interactive peptide and anisotropic groove patterns are obtained via enzymatic polymerization. The results show that the cell layer with patterns can be easily transferred to new substrates by lowering the temperature. In addition, multiple cell layers are stacked on the new substrate in a hierarchical manner and the cell layer is easily transplanted onto a subcutaneous region. These results indicate that the evaluated hydrogel can be used as a novel substrate for transfer printing of artificial tissue constructs with controlled structural integrity, which may hold potential to engineer tissue that can closely mimic native tissue architecture.     

Do birds of a feather flock together?: Economic linkage and geographic proximity

Spatial association patterns of manufacturing activities are examined in this paper with the corresponding economic linkage patterns. Four specifications are used to measure the spatial association pattern: intraindustry/intracounty (locational Gini), intraindustry/intercounty (Morans I), interindustry/ intracounty (correlation coefficient) and interindustry/intercounty (spatial correlation coefficient). Two sets of spatial specification were used for the different locational context: unconstrained (full dataset) and constrained (dataset without zeros). The result on the 3,110 US counties for 361 manufacturing sectors revealed that, in the intraindustry context, there is little proof that stronger economic linkage results in and/or from a more concentrated pattern of the industry. However, interindustry economic linkage reflected and/or was reflected from the spatial distribution pattern in a significantly positive way. There was a pattern in the intraindustry model that the industry that showed clustering at a county scale had relatively weaker spatial concentration at a multi-county scale and vice versa. Results of the unconstrained and constrained specification of the data revealed important differences, implying that special care should be taken in the spatial specification to be used and how the results are to be interpreted. However, the relationship between economic linkage and spatial proximity did not substantially change between two cases except Morans I that had conflicting signs.This is the revised version of a finalist paper om tje 16th Annual Competition of the Charles M. Tiebout Prize in Regional Science, 2002. The author is indebted to Luc Anselin for his comments on an earlier draft and to Geoffrey J.D. Hewings for his comprehensive comments and suggestions.     

Information technology and urban spatial structure: A comparative analysis of the Chicago and Seoul regions

This paper examines comparatively the impact of information technology on urban spatial structure in the Chicago and Seoul metropolitan regions in an attempt to measure the potential influence of IT on urban form and structure. We analyzed the metropolitan areas to understand ways in which the information technology has influenced the distribution of urban economic activities: concentration or dispersion by examining two aspects of impacts: an attraction effect on a zone (level of activity) and a spillover effect on surrounding areas (distributional effects).