Chengeng Qu

Characterization of mechanical behavior of an epithelial monolayer in response to epidermal growth factor stimulation

Cell signaling often causes changes in cellular mechanical properties. Knowledge of such changes can ultimately lead to insight into the complex network of cell signaling. In the current study, we employed a combination of atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) to characterize the mechanical behavior of A431 cells in response to epidermal growth factor receptor (EGFR) signaling. From AFM, which probes the upper portion of an individual cell in a monolayer of cells, we observed increases in energy dissipation, Youngs modulus, and hysteresivity. Increases in hysteresivity imply a shift toward a more fluid-like mechanical ordering state in the bodies of the cells. From QCM-D, which probes the basal area of the monolayer of cells collectively, we observed decreases in energy dissipation factor. This result suggests a shift toward a more solid-like state in the basal areas of the cells. The comparative analysis of these results indicates a regionally specific mechanical behavior of the cell in response to EGFR signaling and suggests a correlation between the time-dependent mechanical responses and the dynamic process of EGFR signaling. This study also demonstrates that a combination of AFM and QCM-D is able to provide a more complete and refined mechanical profile of the cells during cell signaling.

Cellular biophysical dynamics and ion channel activities detected by AFM-based nanorobotic manipulator in insulinoma β-cells

UNLABELLED Distinct biochemical, electrochemical and electromechanical coupling processes of pancreatic β-cells may well underlie different response patterns of insulin release from glucose and capsaicin stimulation. Intracellular Ca(2+) levels increased rapidly and dose-dependently upon glucose stimulation, accompanied with about threefold rapid increases in cellular stiffness. Subsequently, cellular stiffness diminished rapidly and settled at a value about twofold of the baseline. Capsaicin caused a similar transient increase in intracellular Ca(2+) changes. However, cellular stiffness increased gradually to about twofold until leveling off. The current study characterizes for the first time the biophysical properties underlying glucose-induced biphasic responses of insulin secretion, distinctive from the slow and single-phased stiffness response to capsaicin despite similar changes in intracellular Ca(2+) levels. The integrated AFM nanorobotics and optical investigation enables the fine dissection of mechano-property from ion channel activities in response to specific and non-specific agonist stimulation, providing novel biomechanical markers for the insulin secretion process. FROM THE CLINICAL EDITOR This study characterizes the biophysical properties underlying glucose-induced biphasic responses of insulin secretion. Integrated AFM nanorobotics and optical investigations provided novel biomechanical markers for the insulin secretion process.

Video rate Atomic Force Microscopy (AFM) imaging using compressive sensing

Atomic Force Microscopy (AFM) is a powerful tool for nano-size imaging. The advantage of AFM is that it can get extraordinary high resolution image at atom level. However, AFM obtains the sample topography image through scanning on the top of sample line by line, therefore it takes couples minutes to get an image and this negative point makes it difficult to continuously observe surface change during manipulation. In this paper, a novel approach for compressive sensing based video rate AFM imaging system is proposed. In this method, compressive sensing is used for sampling topography information of sample surface efficiently. Compressive sensing could use fewer measurements for data sensing to recovery the image through image reconstruction algorithm. This technique decreases the scanning time for AFM scanner because of fewer measurements needed. The video rate for this new approach could reach as high as 1.75 seconds per frame.

Video Rate Atomic Force Microscopy: Use of compressive scanning for nanoscale video imaging

Atomic Force Microscopy (AFM) is a powerful instrument for studying and exploring the nanoworld [1]. AFM can obtain ultrahigh-resolution images at the subnanoscale level. However, AFM has a very significant drawback of slow imaging speed, which is due to its working principle. A conventional AFM conducts a raster scan of an entire area to generate a topography image. Therefore, the frame rate is low, making it impossible for observation of biological and physical processes that are dynamic in nature with a lifespan of a few minutes or even seconds, such as the structural change of cells, carbon nanotube shape change, and so forth [2]?[5]. In addition, for AFM-based nanomanipulations and nanomeasurement, the low frame rate makes it difficult to achieve a real-time visual guide manipulation [6], [7]. Operators usually have to wait for finishing imaging to visualize the manipulating results. Therefore, there is an increasing demand on a fast-imaging AFM system that can capture a continuous phenomenon occurring in seconds.

Cellular-Level Surgery Using Nano Robots

The atomic force microscope (AFM) is a popular instrument for studying the nano world. AFM is naturally suitable for imaging living samples and measuring mechanical properties. In this article, we propose a new concept of an AFM-based nano robot that can be applied for cellular-level surgery on living samples. The nano robot has multiple functions of imaging, manipulation, characterizing mechanical properties, and tracking. In addition, the technique of tip functionalization allows the nano robot the ability for precisely delivering a drug locally. Therefore, the nano robot can be used for conducting complicated nano surgery on living samples, such as cells and bacteria. Moreover, to provide a user-friendly interface, the software in this nano robot provides a “videolized” visual feedback for monitoring the dynamic changes on the sample surface. Both the operation of nano surgery and observation of the surgery results can be simultaneously achieved. This nano robot can be easily integrated with extra modules that have the potential applications of characterizing other properties of samples such as local conductance and capacitance.

Compressive feedback based non-vector space control

A non-vector space control method based on compressive feedback is presented in this paper. The non-vector space means the control is not performed in traditional vector space but in the space of sets. Consider an initial set and a goal set, a stabilizing controller is designed to make the set dynamics converge to the goal set. The compressive feedback means the controller works even when only partial elements of the feedback set are available; that is, the same controller can still stabilize the set dynamics around the goal set with the compressive feedback. The controller is applied to visual servoing by considering images as sets. In this way, image processing for feature extraction is not required, which is an essential process in conventional servo methods. Moreover, the compressive feedback can reduce the size of feedback image. It is important when the sampling is time consuming such as imaging using atomic force microscopy (AFM). The visual servoing formulation of the controller is further applied to the motion control in nanomanipulations. Simulation results suggest good performance of the controller. The framework proposed in this paper can be extended to other systems where the signals can be represented as sets.

Non-vector space control for nanomanipulations based on compressive feedbacks

AFM based nanomanipulations have been successfully applied in various areas such as physics, biology and so forth in nano scale. Traditional nanomanipulations always have to approach the problems such as hysteresis, nonlinearity and thermal drift of the scanner, and the noise brought by the position sensor. In this research, a compressive feedbacks based non-vector space control approach is proposed for improving the accuracy of AFM based nanomanipulations. Instead of sensors, the local image was used as the feedback to a non-vector space controller to generate a closed-loop control for manipulation. In this paper, there are four research topics: First, local scan strategy was used to get a local image. Second, since the feedback is an image, a non-vector space controller was designed to deal with the difficulty in vector space such as calibration and coordinate transformation. Third, in order to further decrease the time spent on local scan, compressive sensing was introduced to this system. Finally, to overcome the disadvantage that compressive sensing costs time on reconstructing the original signal, we directly use the compressive data as the feedback. Both theoretical analysis and experimental results have shown that the system has a good performance on AFM tip motion control. Therefore, the non-vector space control method can make visual servoing easier, and the compressive feedback could make a high speed real-time control of nanomanipulation possible. In addition, this new method can be applied to nano-assembly, nano-imaging and nanomanipulation.

On-line sensing and visual feedback for atomic force microscopy (AFM) based nano-manipulations

Atomic Force Microscopy (AFM) is a powerful and popular technique of single-molecule imaging both in air and liquid. Recent research and hardware development provide AFM with the function of manipulation nano-particle and modify sample surface in nano-scale. However, due to AFM usually takes several minutes to get an image and the surface change is hard to observe in real-time manipulation. In this paper, a novel approach for on-line sensing and display method is proposed and used for updating the surface change during the manipulation of cell. In this approach a cutting force detection model is used for cutting depth judgment. In addition, an adaptive local-scan strategy is involved here to get the topography of the local surface. Finally a display model is used to update the change of the surface during the manipulation. With this novel scheme the process of cell cutting become real-time visualized. So, AFM tip could work as an efficient nanolithography or cutting tool.

Bio-inspired scanning for video-imaging using an atomic force microscope

Atomic Force Microscopy (AFM) is a powerful tool that can perform nano-scale imaging. Normally AFM tip is controlled to scan on sample surface line by line to get the topographic image and this process takes several minutes. Higher sample rate is demanded so that when doing continuous imaging, the time interval between each image can be significantly shorted thus video-imaging can be achieved. In this paper, a compressive sensing based AFM video-imaging system is built, and random walk based scanning path is proposed. Compressive sensing requires random sampling. Bio-inspired random walk based scan path is able to provide a random tip moving path, which enables compressive sensing to be implemented into AFM scanning system. Experiments based on this system are set up in order to test the performance. It first raster scan the entire area and then generate a biased random tip moving path focusing on some specific areas. Compressive scan is then used to continuously scan the sample surface. Finally, video-imaging is achieved and dynamic changes in nano-scale are observed.

Comparative studies of Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance with Dissipation (QCM-D) for real-time identification of signaling pathway

Cell signaling is one of the fundamental processes that control the cell fate. It modulates the cell shape and mechanics. To identify the dynamic signaling pathway in situ, we need tools that are capable of monitor the real-time elasticity and viscosity changes as well as structural rearrangements. Atomic Force Microscopy (AFM) has been demonstrated to be an effective instrument to visualize membrane and cytoskeleton structures on live cells. It can also provide the mechanical stiffness information by recording force displacement curves. Meanwhile, the viscoelasticity change by signaling pathways can be measured as the change of dissipation of a monolayer of cells by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). In the current study, we use the human epidermoid carcinoma A431 cell line as a model system which will be stimulated by epidermal growth factor (EGF). AFM was first used to image the structure of live A431 cells before and after stimulation; force measurement was also performed to analyze the dynamic elasticity change. The change of viscoelasticity of the A431 cell induced by EGF was monitored in real time on a QCM-D in terms of dissipation change and frequency shift. The mechanical property measurements from AFM and QCM-D experiment was analyzed and compared. Quantitative analysis can be performed to obtain the dynamic modulus of the material through theoretical modeling. This novel combination can be complementary to each other. A unified profile can therefore be generated as an effective indicator of signaling pathways such as cell proliferation and apoptosis.