Scaled Bilateral Teleoperation and Characterization of Biological Specimens—From Tissues to Cells
J. P. Desai, N. Chopra, C. Keefer, R. Roy, D. Foran, W. Chen, L. Goodell
This project is funded in part by NSF.
Teleoperation, Atomic Force Microscopy, characterization of breast tissue, haptic feedback
The pathological state of biological samples can be identified through imaging techniques, but there is a need to quantify the state of the biological sample to identify and predict malignancy in tissue specimens. A highly versatile tool for this purpose is the Atomic Force Microscope (AFM) that has the ability to “poke” at various parts of tissue and evaluate a stiffness of these samples based on a finite indentation depth. The objective of this study would be to model the behavior of malignant and benign regions in the breast tissue specimen during force-indentation studies. However, this system suffers from lack of high-throughput, as each point has to be sampled individually. Therefore, there is a need to automate the process of quantifying the tissue environment. Thus, a concurrent focus of this project is to develop a scaled bilateral Teleoperation framework at the nanoscale. This would enable a user to use a haptic interface to move the AFM to a location of interest and evaluate the stiffness of the region. Additionally, this investigation would include study of the nonlinear interaction forces between the samples to investigate stability of the closed loop system. The study of these interactions is important as it can have important ramifications for preserving the structural integrity of the associated sample under investigation.
The other goal of this project is to extend the teleoperation capabilities to mechanically phenotype individual mouse embryonic stem cells (mESC). Pluripotent embryonic stem cells (ESC) have a strong potential for therapeutic use in treatment of disease (e.g., heart disease, Parkinson’s, and spinal cord injuries). However, inducing targeted differentiation in a controlled manner has proved to be problematic. Due to variations in ESC culture conditions, semi-controlled differentiation can occur thereby transforming the population partially into the desired cell phenotype. Moreover, there are only limited number of endpoints, including changes in mRNA and protein expression, that are available for monitoring changes in cell status as they occur. Therefore, we are interested in the use of haptics-enabled AFM monitoring to develop improved methods for targeting ESC differentiation for diagnostic and therapeutic purposes and monitoring cellular responses to environmental stimuli. Using this approach, we envision being able to distinguish different types of cells: differentiated vs. undifferentiated, live vs. fixed, and cardiac vs. neuronal differentiated cells. Just as cell markers at the end points (through fluoroscopy) can serve as a unique signature for a particular cell type, we envision adding to this a “haptics” marker, which can be used to monitor the cell “during” the process of lineage differentiation and predict where the undifferentiated cell would end up in the lineage.
The objectives of this study are:
• Development of a robust model that accounts for changes in mechanical properties of pathogenic breast tissue
• Develop the ability to model changes in the mechanical properties of ESCs during lineage differentiation
• Development of bilateral scaled teleoperative setup to improve throughput of breast tissue as well as ESC characterization.
• Investigation of the effect of time delay and scalability of force and position on the stability of the closed loop teleoperative system during characterization of biological specimens in liquid.
Overview of Approach
Characterization of Mechanical properties of breast tissue specimens: To provide a definitive understanding of mechanical properties at the nanoscale, there is a need to model the behavior of the tissue during force-indentation tests. We have studied breast tissue samples and applied the widely used “Hertz model” to quantify the elastic modulus of the sample. However, certain assumptions of the Hertz model like infinitesimal indentation and material linearity are not valid in typical tissue architecture. Furthermore, biological tissues are by nature heterogeneous and a single mechanical marker like Elastic modulus may not capture the state of a pathological specimen well enough to predict the eventual state of the specimen. Hence, there is a need to provide a robust model that accounts for factors not considered in the Hertz model.
Characterization of the mechanical properties of mESC: Atomic force microscopy (AFM) has emerged as a promising tool to characterize the mechanical property of biological materials and cells. In our studies, undifferentiated and early differentiating mouse embryonic stem cells (ESCs) were assessed 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, cells were significantly less supple as compared to undifferentiated ESCs irrespective of the ESC line (R1 or D3) or differentiation method used. We thus hypothesize that mechanical phenotyping should prove to be a valuable tool in the development of improved methods of targeted cellular differentiation of embryonic, induced pluripotent stem cells (iPS) and adult stem cells for therapeutic and diagnostic purposes.
Scaled Bilateral Teleoperation of the Atomic Force Microscope for characterization of biological specimens: The goal of this aspect of the project is to teleoperate the piezo stage of the AFM when commanded by a human operator and simultaneously reflect the nonlinear interaction forces between the cantilever and the sample to the user. The motion commands transmitted from the operator to the AFM and the force commands transmitted back to the user will have to be scaled due to the disparity in the scales between the motion of the human operator and the motion of the AFM. The presence of the sample in a liquid medium further complicates the motion control problem. One of the primary goals of this work is to automate the biological specimen characterization process by directing the AFM probe to the identified location on the specimen. This would require the study of the effect of time delay and force and position scaling on the overall stability of the teleoperated system.
Prof. Jaydev P. Desai
Director—Robotics, Automation, and Medical Systems Laboratory
Department of Mechanical Engineering
0160 Glenn L. Martin Hall
University of Maryland College Park, MD-20742
Email: jaydev (at) umd.edu