School of Mechanical Engineering Seminar
Wednesday, April 15, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Active Catheter Driven by a Thermo-Hydraulic Actuation

Yonatan Horovitz

MSc Student of Dr. Gabor Kosa

Catheters and flexible endoscopes are usually steered by mechanical wires that are driven from the base of these tools. Due to friction and buckling there is a need to place the driving actuator of the catheter at the catheter's tip. Such active catheter's maneuverability is much higher than the wire-driven devices. A problem with active catheters is the difficulty to create high enough bending torques or bending forces using micro-actuators placed at the catheter's tip.

In this study, a novel actuation method is presented to overcome this problem. The bending torque is created using internal pressure in a sealed tube, and the bending direction is controlled by varying stiffness in the tube’s cross-section.

In order to create the varying stiffness, two mechanisms were investigated. The first mechanism is based on electrostatic actuation, where parallel plate actuators were used to increase the tube’s stiffness at specific regions. The second mechanism is based on thermal actuation, using resistance wires embedded in the tube’s wall to locally soften the tube.

Both methods were modeled and optimized theoretically. Actuator prototypes were designed and tested. The electrostatic actuator did not achieve significant bending results. On the other hand, with the thermal actuator we were able to show the feasibility of the actuation method. We found that a 4 mm OD actuator made of TPU can bend up to ±12° although the heating of the tube was significant, at about 100°C.

ברי הפקולטה להנדסה מברכים את תלמידיה בתואר ראשון אשר יקבלו תעודת הצטיינות מטעם רקטור האוניברסיטה על הישגיהם האקדמיים בשנה"ל תשע"ד:

• גולדנברג דמיטרי מהמגמה להנדסת תעשייה וניהול
• ורבין דור מהמגמה להנדסת חשמל ואלקטרוניקה ופיזיקה
• מונד טל מהמגמה להנדסת חשמל ואלקטרוניקה
• קורמן טל, מהמגמה להנדסה מכנית
• רוזנר עמית  מהמגמה להנדסה ביו-רפואית     

מקבלי תעודות הערכה מטעם דקאן הפקולטה:

(רשימה זו מורכבת מ-5% התלמידים המצטיינים בכל מגמת לימוד, בחלוקה לפי שנים)

הטקס יתקיים ביום ב', א' באייר תשע"ה, 20.4.15, בשעה 16:00, באולם בר-שירה

School of Mechanical Engineering Seminar
Monday, March 30, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Mechanical Interaction between Cells and their Surrounding 3D Fibrous Environments

Ayelet Lesman

Division of Chemistry and Chemical Engineering, California

 Institute of Technology, Pasadena, CA.

Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.

The forces cells apply to their surroundings control biological processes such as growth and migration. In the past 20 years, a number of experimental techniques have been developed to measure such cell tractions. These approaches have primarily measured the tractions applied by cells to synthetic two-dimensional substrates, which do not mimic physiological conditions for most cell types. Our work aimed at developing and applying an experimental technique for quantifying cellular forces in a natural, fibrous 3D gel matrix. The approach is based on confocal time-lapse imaging to observe cells and their surrounding matrix in three dimensions. We then use a digital volume correlation (DVC) approach to map the displacements of the matrix in space and time (x, y, z, and t). Tracking the movement of the matrix is a key step in this process. I describe two ways of tracking, either by embedding fluorescent particles in the gel or by directly imaging the fiber structure of the gel. The direct imaging approach allows to discern the local deformation or reorientation of the gel fibers in response to cellular forces (details we cannot achieve when using particles).

The 3D traction measurement approach is used to investigate how cells mechanically interact with the matrix in biologically relevant processes such as division, invasion and cell-cell interaction. During division, a single mother cell undergoes a drastic morphological change to split into two daughter cells. We find that tensile forces applied by dividing cells on the matrix, far from the cell body, oriented the cell division axis. Cell invasion into a 3D matrix is the first step required for cell migration in three dimensions, and is prerequisite for cancer metastasis. Using our direct approach of imaging matrix fibers to compute displacements, we find that cells generate large plastic deformation of the matrix by applying both pushing and pulling forces. Lastly, our measurements provide insight into mechanical communication between cells. We measured the propagation of displacements induced by contractile cells in fibrous gels and found that they are effective over longer distances than predicted by linear elastic models. Finite element simulations suggest that fiber buckling is a key feature of the fibrous network responsible for this effect. This helps rationalize our observations that cells separated by large distances (~100-200 microns) are coupled by aligned, dense fibers in tether-like bends. We suggest that cells may exploit the non-linear properties of the fibrous environment to communicate over long ranges by sensing the deformation induced by their neighbors.