Patent Application
20130154292
The present invention relates generally to mechanical grippers, and more particularly, to mechanical grippers for manipulation of single micro-particles.
The ability to precisely target and position single particles has numerous applications including particle-by-particle assembly of larger microstructures as well as probing and manipulation of tissues, groups of cells and single cells. There is a growing need for simple, cost-effective and robust systems that can manipulate single micro-particles in many scientific fields ranging from micro/nanotechnology to biology. Most existing particle manipulation or gripping systems found in literature require relatively expensive and complicated fabrication and instrumentation steps that significantly reduce the robustness and reproducibility in operation. Hence, many of these systems have not enjoyed wide acceptance.
Researchers have developed gripping systems that are based on piezoelectric effect to produce elastic deformation of a structure upon the application of sufficient voltage. See e.g., Basrour, S., Robert, L., 1997, “Mechanical characterization of micro-grippers realized by LIGA technique,” 1997 International Conference on Solid-state Sensors and Actuators, Vol. 1, pp. 599-602; Tan, K. K., Ng, S. C., 2001, “Computer controlled piezo micromanipulation system for biomedical applications,” Engineering and science journal, Vol. 10, pp. 249-256; Eisinberg, A., Houston, K., Caparrelli, P., Amavasai, B., Boissenin, M., 2006, “Marking techniques for vision recognition of microgrippers for micromanipulation,” Proceedings of the 2006 IEEE International Conference on Robotics and Automation, pp. 1030-1035; Ferreira, A., Agnus, J., Chaillet, N., Breguet, J., 2004, “A Smart Microrobot on Chip: Design, Identification, and Control,” IEEE/ASME Transactions on Mechatronics, Vol. 9, No. 3; Agnus, J., Nectoux, P., Chaillet, N., 2005, “Overview of Micro-grippers and Design of a Micromanipulation Station Based on a MMOC Micro-gripper,” Proceedings 2005 IEEE International Symposium on Computational Intelligence in Robotics and Automation, pp. 117-123; Grossard, M., Rotinat-Libersa, C., Chaillet, N., 2007, “Redesign of the MMOC microgripper piezoactuator using a new topological optimization method,” 2007 IEEE/ASME International conference on advanced intelligent mechatronics, pp. 1-6; and Bliderana, M. M., Fleischera, M., Grauvogelb, F., Löfflerb, K., Langerb, M. G., Kerna, D. P., 2008, “Real-time gripping detection for a mechanically actuated microgripper,” Microelectronic Engineering In Press 2008.
For example, Jericho et al. developed a piezoelectric MEMS micro-tweezers for the manipulation of micro-objects. See, Jericho, S. K., Jericho, M. H., 2004, “Micro-electra-mechanical systems micro-tweezers for the manipulation of bacteria and small particles,” Review of Scientific Instruments, Vol. 75, No. 5. As shown in
Henein et al. present a high precision flexible micro-tweezers designed for micro-objects, as depicted in
Carrozzay et al. disclose a lithography fabricated micro-tweezers, as shown in
Park et al. developed a gripping device with the three chop stick design shown in
Most commonly used piezoelectric actuators usually need high activation voltages of around 60-70V. Since they can only produce a few microns of displacement, multilayers of actuators or multiple actuators are needed. This significantly increases the complexity of the microfabrication process, which results in devices that are expensive and hard to reproduce (both in terms of fabrication and operation).
Researchers have also explored the use of thermal actuation within gripping devices. See Honnatti, M., Hughes, G., “Directed Cellular Manipulation Using Polymer Microgrippers,” Zyvex Instruments; Bordatchev, E. V., Nikumb, S. K., 2005, “Electro-thermally driven microgrippers for microelectro-mechanical systems applications,” Journal of Microlithography, Microfabrication, Microsystems. Vol. 4; Suzuki, Y., 1994, “Fabrication and evaluation of flexible microgripper,” Japan Journal of Applied Physics. Vol. 33, pp. 2107-2112; Molhave, K., Hansen, O., 2005, “Electro-thermally actuated microgrippers with integrated force-feedback.” Journal of Micromechanics and Microengineering. Vol. 15, pp. 1265-1270; Du, H., Su, C., Lim, M. K, Jin, W. L., 1999, “A micromachined thermally-driven gripper: a numerical and experimental study,” Smart Materials and Structures. Vol. 8, pp. 616-622; Volland, B. E., Ivanova, K., Ivanov, T., Sarov, Y., Guliyev, E., Persaud, A., Zöllner, J. P., Klett, S., Kostic, I., Rangelow, I. W., 2007, “Duo-action electro thermal micro gripper,” Proceedings of the 32nd International Conference on Micro- and Nano-Engineering. Vol. 84, pp. 1329-1332; Andersen, K. N., Carlson, K., Petersen, D. H., Mølhave, K., Eichhorn, V., Fatikow, S., Bøggild, P., 2008, “Electrothermal microgrippers for pick-and-place operations,” Microelectronic Engineering In Press 2008; Fraser, J., Hubbard, T., Kujath, M., 2006, “Theoretical and experimental analysis of an off-chip microgripper,” Canadian Journal of Electrical and Computer Engineering, Vol. 31, No. 2. These devices rely on localized changes in temperature for actuation. A few of these studies are summarized below.
Wang et al. describe the architecture of a three-probe MEMS nanomanipulator with nano-scale end effectors. See, Wang, X, Vincent, L., Yu, M., Huang, Y., Liu, c., 2003, “Architecture of a Three-Probe MEMS Nanomanipulator with Nanoscale End-Effectors,” Proceedings of the 2003 IEEE/ASME International Conference on Advanced Intelligent Mechatronics. Micromachining and nanofabrication techniques are employed in the fabrication of this device. Unlike the micro-tweezers discussed before which can manipulate objects in the micron range, this device shown in
Another thermally actuated device was developed by Nguyen et al. See, Nguyen, N., Ro, S., Low, Lee-Ngo, C., 2004, “A polymeric microgripper with integrated thermal actuators,” Journal of Micromechanics and Microengineering, Vol. 14, pp. 969-974. This micro-tweezers was fabricated using a polymeric surface micromachining process, which utilized 100 μm thick SU-8 deposited and patterned over silicon. A stencil wafer was fabricated using deep reactive ion etching to define heating pads. Another thermally actuated micro gripper was developed by Ivanova et al. that was fabricated from single crystal bulk silicon. See, Ivanova, K., Ivanov, T., Badar, A., Volland, B. E., 2006, “Thermally driven microgripper as a tool for micro assembly,” Microelectronic Engineering, Vol. 83, pp. 1393-1395. The gripper employs thermally grown oxide as an insulating layer on a single crystal silicon substrate with a layer of (Cr/Au) deposited on top of the oxide. Current passes through hot arms of the device to cause Joule heating. A cold arm is shorter and wider than the hot arm hence so that the short arm does not heat up at the same rate. This difference in heating causes a torque at the tips which closes the device. Chronis et al. developed another SU-8-based, thermally actuated micro-tweezers that uses a similar hot and cold arm arrangement. See, Chronis, N, Lee, L. P., 2005, “Electrothermally Activated SU-8 Microgripper for Single Cell Manipulation in Solution,” Journal of Microelectromechanical systems, Vol. 14, No. 4, pp. 857-863.
Researchers have also developed micro-grippers based on electrostatic actuation. See e.g., Millet, O., Bemardoni, P., Régnier, S., Bidaud, P., 2004, “Electrostatic actuated micro gripper using an amplification mechanism,” Sensors and Actuators, Vol. 114, pp. 371-378; Kim, Chang-Jin, Pisano, A. P., Muller, R. S., 1992, “Silicon-Processed Overhanging Microgripper,” Journal of Microelectromechanical Systems, Vol. I, No. I; Neild, A., Oberti, S., Beyeler, F., Dual, J., Nelson, B. J., 2006, “A micro-particle positioning technique combining an ultrasonic manipulator and a microgripper,” Journal of Micromechanics and Microengineering, Vol. 16, pp. 1562-1570; Almeida, V. A. L. de., 2004, “Microgrippers Driven by Electrostatic Comb Drive Actuators,” ABCM Symposium series in Mechatronics, Vol. 1, pp. 682-687; and Volland, B. E., 2002, “Electrostatically driven microgripper,” Microelectronic Engineering, Vol. 61, pp. 1015-1023. Volland et al. fabricated an electrostatically actuated micro-gripper using silicon-on-insulator wafers. See, Volland, B. E., Heerlein, H., Rangelow, L W., 2002, “Electrostatically driven microgripper,” Microelectronic Engineering, Vol. 61, pp. 1015-1023. The gripper, depicted in
Electro-static actuators are less frequently employed in micro-gripper devices than piezoelectric or electro-thermal actuators. One reason is their inherent limitation of operation in liquid. Comb drives which are the driving forces for most electrostatic actuators require an intricate and complex fabrication process. These drives are susceptible to dust contamination and comb misalignment and failure. Like piezoelectric and thermally-actuated devices, they also cannot act as standalone devices due to their external power requirement.
Another actuation method studied to a lesser extent in micro-gripping systems is pneumatic actuation. Pneumatically actuated devices make use of fluid pressure for mechanical actuation of gripper structures. See e.g., Butefisch, S., 2002, “Novel Micro-pneumatic actuator for MEMS,” Sensors and Actuators, Vol. 97, pp. 638-645. In devices of this type, pressure applied through the capillary tubes to spring elements moves pistons, which actuate the gripper tips via intricately fabricated hinges Pneumatically actuated grippers suffer from some drawbacks, the biggest being the need for external equipment to provide the fluid pressure to actuate the mechanism. This poses an additional complexity in the fabrication which increases the cost of the device and reduces its reproducibility. In addition, the device can be incapacitated with a slight defect in the sealing. In such an event, the small geometry of this device can significantly hinder the troubleshooting.
Most of the prior micromanipulation device or micro-tweezers involve a large number of complex fabrication steps that not only add to the cost of the device but quite often render it too impractical to fabricate and/or use. Unlike fabrication of most macro-scale objects, a flaw in microfabrication can rarely be fixed without starting over. Furthermore, the actuation mechanisms of all existing systems require external power consumption which not only adds to operation costs but also requires additional instrumentation, such as power supplies and amplifiers. The overall complexity of these devices (both in fabrication, instrumentation and operation) has hampered the development and use of these devices so that they are not widely used in any industry.
There is a need for a micromanipulation device for grasping and manipulating micro-sized objects that can be easily manufactured on a micro-scale and that can be operated without the need for additional instrumentation.
A micromanipulation assembly is provided for grasping and manipulating micro-sized objects, such as cells. The assembly includes a micromanipulation device in the form of a hollow frame structure having a pair of opposing resiliently deflectable arms and a saddle connected to the arms to deflect the arms toward each other upon application of a force to the saddle. The assembly further includes a force generating device, which in one embodiment is a micrometer that can generate a micro-controllable force simply by manual operation of the micrometer. A fixture is provided that supports the micromanipulation device and force generating device and that allows both devices to be easily removed and replaced. The fixture supports the two devices so that a force member of the micrometer (such as the spindle) can apply a force to the saddle.
In one feature, one arm of the micromanipulation device defines a notch for at least partially receiving a micro-sized object. The opposite arm includes a piercing element projecting toward the other arm and in alignment with the notch. The piercing element can thus pierce an object, such as a cell, captured within the notch. The piercing element may also be configured to deliver materials into the object being pierced. A suction tube may intersect the notch to apply a vacuum to help draw the object into the notch and retain the micro-sized object within the notch as it is being pierced.
The above-mentioned and other advantages of the present invention, and the manner of obtaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
a shows a 5 μm diameter bead between the ends of a MEMS fabricated piezoelectric tweezers of the prior art;
b shows a micro-gripper according to the prior art that employs a piezo-resistive force feedback sensor;
c shows lithography fabricated micro-gripper of the prior art in which external beams are pushed forward while internal beams are constrained, thus producing a rotation/translation at the tips which causes them to close;
d shows a three chopstick micro-gripper of the prior art in which a piezobender operates two outer fingers while the middle finger is displaced in the opposite direction by the piezo-stack actuator;
e shows the gripping action of a three probe tweezers with nano end-effectors of the prior art;
f and 1g show an electrostatic micro-gripper of the prior art with a detail view of the flexible hinge structure of the device;
a, 4b are graphs of displacement and stress in the arms of the device shown in
a-c are enlarged views showing deflection of the micromanipulation device.
The embodiments of the present disclosure are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
In these teachings the design, fabrication and basic application of a device which is simple to operate, robust, cost effective, completely mechanical and manually actuated (no electrical power required) is described. The device can manipulate micro-objects of varying sizes. The device has a simple fabrication procedure and is made up of few parts for easy assembly. The following sections explain in detail the design, fabrication and application of a purely mechanical MEMS-based manipulator for micro-sized objects. In one embodiment a micromanipulation apparatus includes a compliant tweezers structure that is manually actuated via a micrometer. The apparatus described herein accommodates a two-arm system that can grab objects upon actuation, that allows full closure of the arm upon application of a force, and that utilizes elastic deformation of the arm so that the arm return to an un-deformed geometry when the actuation force is removed.
The apparatus includes a micromanipulation device that grasps and manipulations a micro-sized object and a force generating device that applies the force to the micromanipulation device. Looking first at the micromanipulation device, one embodiment is illustrated in
As shown in
At least the arms 16, and preferably the entire frame structure 11, is formed of a resiliently flexible material. In one embodiment the device 10 is formed of a single crystal silicon so that the device is not only flexible but also readily fabricated using conventional microfabrication techniques such as photolithography and deep reactive ion etching (as described in more detail herein).
It can be appreciated that the hollow frame structure 11 of the device 10 provides an avenue for flexure of the arms 16 upon the application of the force F. In the embodiment of
In order to further facilitate the ease of closing the tips of the fingers, the fingers are rounded, as illustrated in
However, unlike the prior frame 11, the arms 35 of the frame 31 are curved from the ends 38 of the base 34 to the tips 36. In one embodiment, the arms 35 are curved at a substantially constant radius R. The radius is determined by the length of the base 34 between the ends 38 and the overall height of the device 30 from the base to the tips 36. In one embodiment, the base length and height are approximately equal and the radius R is approximately twice the base length.
Another difference between the frame 11 and the frame 31 of
The device 30 provides several design parameters that can be adjusted to control the amount of closure of the gap g and the amount of force F applied to the saddle 37 to achieve that closure. As explained above, the amount of closure of the gap is a function of the dimension X. In addition, the length of the base between the ends 38 (or more specifically the length between the intersections of the arms 35 with the base 34) affects the gap closure. In particular, increasing the base length increases the displacement of the tips 36. Similarly, increasing the length of the prongs 38 increases the displacement of the tips 36.
One feature of the devices 10 and 30 is that the frame structures are very suitable for microfabrication and the determination of the dimensions of the devices can be made in parallel with determining the fabrication process. In general, consideration of fabrication process flow during the general design of a MEMS structure is a necessity. Among typical micro-fabrication processes the simplest ones are those that require only one photolithography step. Deep reactive ion etching forms high aspect ratio structures by exposing a silicon wafer to a sequence of sulfur hexafluoride (SF6 for etching) and Teflon (C4F8 for side wall passivation) gases.
Since, the hollow frame structures of the present devices 10, 30 can be obtained by a through-etch of a typical single crystal silicon wafer, a preferred material is single crystal silicon. The mechanical properties of single crystal silicon (SCS) are: density—2330 kg/m3; Poisson's ratio—0.17; Young's modulus—150 GPa; and yield strength—7×106 kg/mm2. These properties were used to analyze the device 30 in terms of its response to an external force F applied at the saddle. In this analysis, the base 34 was anchored while a force was applied perpendicular to the saddle 37 directed towards the base. Additional constraints in this analysis are that the arms 35 intersect the base perpendicularly and the thickness of the wall 32 was 0.1 mm or 100 μm. The thickness was chosen because it is simple to achieve using photolithography (about 2 orders of magnitude larger than the smallest feature that photolithography can produce).
In this analysis, first the relationship of the force and the horizontal displacement of the tips (gap closure) was verified. Then the effect of the base length was studied on the tip displacement and an acceptable base length for the device was obtained. A basic stress analysis to decide an appropriate device width w was performed, while making sure that this choice and its combination with other geometric parameters result in stresses that do not exceed the yield stress of the SCS material. Finally the effects of the saddle-base spacing X and the prong length on the gap closure was studied. The design parameters were evaluated in three different force magnitudes—100 mN, 100 μN, and 100 nN—to determine the approximate force that is needed to operate the device 30.
A micromanipulation device was configured as the device 30 with the dimensions given in Table 1 below was subject to forces of 100 nN, 100 μN and 100 mN applied perpendicular to the saddle. The resulting horizontal displacements of the tips are presented in Table 2. As these results demonstrate, the horizontal displacement of the tips change in direct proportion to the applied force.
The effects of changing the base length on the overall functionality of the device was investigated. The dimensions of the devices used for this analysis are shown in Tables 3 and 4. In particular, the first device had a base length of 5 mm while the second device had a smaller base length of 1 mm. As the results of the analysis of both devices summarized in Table 5 shows, increasing the base length increases the displacement of the tips 36 of the device arms 35.
In this analysis, the reduction in base length from 5 mm to 1 mm led to a reduction in gap closure of about 90%. For a 2 mm initial undeformed gap g of 0.2 mm this 90% reduction can be problematic. Consequently, for one specific embodiment a base length of 5 mm was selected.
Relationship Between Stress and Width of the Device (“w”)
Pro-Mechanica software was used to observe points of maximum stress in the device. Increase in the width of the device provides increased surface and cross sectional areas and is thus expected to lead to reduced stresses. While variations in other dimensions can also affect the stresses it is believed that detrimental effects due to the other dimensions can be compensated by changing the wall width w. Two devices were considered: one with a width of 0.2 mm and another with a width of 0.1 mm. The common dimensions of the two devices are summarized in Table 6. Stresses produced in both the devices are presented in Table 7.
The stress value at 100 mN force for a device width of 0.1 mm is 1.36×106 kg/mms2 which is very close to the maximum yield stress of single crystal silicon (7×106kg/mms2). On the other hand, the stress value for the device width of 0.2 mm at 100 mN force is 7.6×105 kg/mms2, which is about 10 times less than the maximum yield stress of silicon. As expected, stress magnitudes decrease as the width of the device (w) increases. Stress can be decreased even further by increasing the thickness t of the device from 0.1 mm in the analysis to 0.5 mm. However, increasing the wall thickness of the frame structure reduces the displacement of the arms 35 for a given applied. In order to achieve equivalent horizontal displacement of the tips, or closure of the gap g, more force is needed if the wall thickness is increased. For the device 30, a 100 mN force provides good arm displacements for the device. While it seemed counter-intuitive to use such a large force on a device with dimensions of a few millimeters, the stress analysis demonstrates that application of such a force for the actuation of the device will not exceed the strength capabilities of the device material due to the specific geometry of the device.
With the base length at 5 mm and the width w of the device set to 0.5 mm optimization of the prong length (PL) and dimension X followed. In this analysis, the dimension X was varied from 1 to 5 mm, and at each value for X the prong length was varied from 1 to 5 mm. The analysis was performed at the same three force magnitudes applied in the prior analyses —100 nN, 100 μN, and 100 mN. For simplicity, only the results that correspond to 100 mN force is provided since this force provides maximum displacements at the tips. The results of the analysis are shown in the chart of maximum horizontal displacement in
For one device 30, the rest or undeformed gap g is 0.2 mm. Hence, each arm 35 is required to move a horizontal distance of 0.1 mm to achieve full closure of the tips. This deflection value is encircled in
As reflected in
In order to choose a value for dimension X a stress analysis was performed. The results are summarized in chart of
In view of the analyses described above, it was determined that one optimum design for a micromanipulation device for micro-sized objects has a base length of 5 mm long, a width w of 0.5 mm, and the wall thickness t of 0.1 mm, prong lengths of 2 mm and a dimension X of 3 mm. This structure is capable of being actuated comfortably by a 100 mN force.
It is noted that the size of the gap g in the device 30 can be sized to accommodate the particular micro-sized object being manipulated. In addition, the tips and prongs can be functionalized—i.e., treated with a biological entity, such as a virus, protein or DNA strain, or treated with a chemical suitable for cellular treatment in pharmacological studies. The functionalized tips and prongs can be brought in contact with cells under study to make surface contact with the cell membrane or to pierce the cell membrane to implant the biological entity within the cells (as described in more detail herein). For such applications the tips and prongs will require a rest-opening dimension or gap g appropriate for cellular manipulations.
The device 30 can be modified to permit piercing of a captured micro-sized object, such as a cell. In one embodiment, a device 50 includes the continuous wall 51 defining the opposing arms 52 and prongs 54. In order to capture an object, such as a cell, one of the prongs is modified to define a retention notch 55 adjacent the tips 53. The notch has a depth sufficient to at least temporarily retain the object. In order to help restrain or hold the object within the notch 55 the notch may be provided with a suction opening 56 associated with a suction tube 57 extending through one arm 52. The suction tube 57 is connected to a vacuum generator (such as a manual syringe) or to an external vacuum source. When the micromanipulation device 50 is used to grasp an object such as a cell, vacuum may be applied at the opening 56 to help draw the cell into the notch 55 and hold the cell in that position.
In a further feature of the device 50, the opposite arm may include a piercing element 58 aligned with the notch 55. The piercing element is configured to pierce the object, such as to pierce a cell membrane or wall. The piercing element 58 may be hollow and connected to a tube 59 extending through the opposite arm 52, as shown in
As shown in
As explained above, the micromanipulation assembly includes the device 30 and a force generating device that applies a force to the saddle 37 of the device. In one aspect of the present invention, the force generating device can be a manual actuator. In one specific embodiment, the manual actuator is a micrometer. In order to easily interface the micromanipulation device 30 with the force generating device, certain modifications to the device design may be desirable. In certain embodiments these modifications include increasing the length of the saddle for easier alignment and connection to an actuator mechanism, opening the base to simplify access for the actuator mechanism, rounding sharp corners to reduce stress riser, and increasing the gap g between the tips to accommodate larger objects. With respect to the latter modification, it can be appreciated that the gap dimension can be adjusted depending upon the micro-sized objects being manipulated. In certain embodiments, the gap g can be 0.2 mm (200 μm) or 0.3 mm (300 μm).
With respect to the saddle and base modification, a modified micromanipulation device 50 is shown in
In a further modification from the device 30, the device 50 incorporates a feature to facilitate handling of micromanipulation devices. Thus in one embodiment, a tab 63 is attached to each portion of the base 54, as shown in
The micromanipulation assembly disclosed herein further includes a force generating device that is operable to apply a force to the saddle 17, 37, 57 of the devices 10, 30, 50 described above. In one embodiment the force generating device is manually operated, which greatly simplifies the use and usability of the micromanipulation assemblies disclosed herein. A suitable device 70 constitutes a standard depth micrometer, as illustrated in
As thus far described, a micromanipulation assembly includes a micromanipulation device, such as the devices 10, 30 and 50 described above, and a force generating device, such as the micrometer 70. In certain embodiments, the micromanipulation devices 10 or 30 can be directly mounted on the micrometer 70, if appropriately dimensioned. In these embodiments, the base 15 or 34 can be supported on the hub 74 of micrometer, while the spindle 72 passes through an opening in the base. The spindle 72 can be attached to the saddle 22, 37 in a suitable manner to allow the spindle to apply a downward force F (
Consequently, in a further aspect of the disclosure, an interface or fixture is provided that easily connects the micromanipulation devices 10, 30, 50 to the force generating device 70. The interface is preferably compact so as not to interfere with the operation of the devices. Moreover, the interface preferably facilitates placement and alignment of the micromanipulation device to the interface without the need for a microscope.
A first concept for the interface is shown in
The ends 85 of the arms 84 define a mounting surface on which the micromanipulation device 50 is removably mounted. The ends may incorporate a mounting feature 86 configured to engage the tabs 63 of the device 50 (
As shown in
A detail view of the interface between the adapter 87 and the saddle 57 of the device 50 is shown in
In order to address these potential shortcomings another fixture 90 is provided, as illustrated in
In the illustrated embodiment, the fixture 90 is compact measuring only 20 mm in length (from the base to the end of the arms) and only 15 mm in width. The fixture can thus be easily manipulated by hand to mount the micromanipulation device 50 and micrometer 70. In addition, the block construction of the fixture allows the fixture to be clamped to a working surface.
One limitation of the fixture 90 and micromanipulation device 50 is that it can be difficult to hold the device and place it within the fixture. Another limitation of the device 50 is that the end face 89 of the adaptor 87 must be affixed to the underside of the saddle. In order to address these limitations a modified mounting structure is provided for the device 50 in lieu of the tabs 63. Thus, a mounting structure 110 is affixed to the hollow frame structure 51 of the device 50 shown in
In a further feature, the mounting structure 110 includes enlarged tabs 114 at the lateral ends of the bridge element 112. In order to facilitate manually grasping, the tabs are generally circular with a diameter large enough to be grasped. In one specific embodiment the tabs 114 have a 10 mm diameter.
In another aspect, the fixture 90 is modified to accommodate the bridge element 112 and circular tabs 114 of the mounting structure 110. In particular, a fixture 120 shown in
It can be appreciated that the bridge element 112 of the mounting structure 110 prevents access to the saddle 57 of the device 50 directly in the plane of the device 50 or directly along the axis of the micrometer spindle 73 when the micrometer. Consequently, in a further modification from the fixture 90, the fixture 120 offsets the annular base 121 from the plane of the device 50, as seen in
In the illustrated embodiment, the hub 131 is shown as incorporating a conical portion from which the beam 134 projects. In an alternative embodiment, the hub 131 may be extended to the location of the post 135, as depicted in the phantom lines 136. With this modification, the beam is reduced to the beam 137 depicted by the phantom lines 137. In either embodiment, the extension from the hub 131 includes a bore (not shown) for receiving the spindle 173 of the micrometer. The bore may be sized for press-fit engagement with the spindle or may be glued to the spindle. Alternatively, the bore 132 of the hub 131 may be press-fit or glued onto the spindle. The engagement between the adaptor 130 and spindle 73 must be sufficient to transmit force to the saddle of the micromanipulation device without becoming dislodged. In particular, as the micrometer spindle is retracted the post 135 contacts and exerts a force F against the saddle to thereby close the arms 55 of the device 55. Conversely, as the spindle is advanced (i.e., extended toward the device 50), the force on the saddle is relieved, and the natural elastic resilience of the device 50 causes the arms to move outward, thereby opening the tips 56 to the neutral gap g. This also demonstrates that the choice of a non-rotating spindle micrometer for the application was necessary.
The assembly of the complete micromanipulation assembly can be easily achieved by first mounting the fixture 120 on the working end of the force generating device or micrometer 70. The hub 74 of the micrometer is engaged within the annular base 121 with the spindle projecting through the bore 122 (
The micromanipulation devices 10, 30, 50 described herein are readily suited to fabrication using standard clean-room microfabrication processes. The fixtures 80, 90, 120 can be machined from sterilizable or autoclavable materials using standard machine shop techniques.
A first step in the microfabrication of the devices 10, 30, 50 can be standard photolithography to prepare a single crystal silicon wafers for a deep reactive ion etching process. In an illustrated embodiment, the silicon wafer 140 has a thickness of 0.5 mm (500 μm)-thick, and a diameter of 100 mm (4 in.), as shown in
Once the devices 50 are patterned using lithography, as shown in
The mask shown in
The following steps were followed in one specific microfabrication process to produce the wafers 50. It is of course understood that other microfabrication processes may be implemented to produce the wafers and devices disclosed herein. For the photolithography, the following steps were implemented:
The deep reactive ion etching (device formation and release) occurs using the following steps in the specific example:
The fixture 80, 90, 120 can be fabricated in a machine shop. The selected material is preferably light weight for handling and balancing during use, susceptible to micro-machining, and sufficiently strong for fabrication and utilization. Thus, in one embodiment, the fixture, including the clamps 97, 127, is formed of puca-graphite. It can be appreciated that other materials and manufacturing techniques may be utilized to produce the fixtures 80, 90, 120. For instance, the fixtures may be cast or molded from a high-density plastic.
The micromanipulator assembly 200 disclosed herein (
In one embodiment, the assembly 200 was created by first removing a micromanipulator device 50 from the wafer 140 (
Manually turning the thimble 71 of the micrometer 70 in the clockwise direction results in backward motion of the micrometer spindle (i.e., away from the tips 56 of the device arms) which thereby moves the post 135 backward. Continued clockwise rotation of the thimble moves the post back until it is in contact with the saddle of the device, as shown in
The micro-sized objects being retrieved or manipulated by the device 50 may be located on various surfaces. In the embodiment shown in
To demonstrate the basic application of the device, a micromanipulation device constructed according to the device 50 shown in
This demonstration shows that the micro-manipulation device 50 can successfully grip, translate and release individual micro-particles without mechanical failure. The deformation of the device is completely elastic since releasing of the actuation force returns it to its original un-deformed state. The actuation can be achieved entirely manually without the need for connection to any electrical or pneumatic power supplies. The device is completely re-usable since all of its components can be easily assembled and dismantled. If desired, the device 50 can be removed from the fixture and stored for future use. The entire apparatus 200 is completely portable and can be easily transported to a specific laboratory and mounted on a stationary surface, a translation stage or an electromechanical actuator.
In a further embodiment, the apparatus 200 can be integrated into a system for storing and/or treating micro-sized objects, particles or cells extracted by the micromanipulation device 50. Thus, as shown in
When used in conjunction with a motion stage, such as the Thorlabs PT1 apparatus described above, the individual micro-sized objects or particles can be individually treated and then collectively combined. For instance, multiple objects can be stacked to create 3-D geometries. As each new object or particle is added to the stack it can be treated with a substance to improve the adherence of the particle to the stack, to thereby improve he structural integrity of the 3-D geometry.
In another example of use of the apparatus 200 in conjunction with a motion stage, an individual microparticle may be grasped by the micromanipulation device, and then the entire apparatus moved by the motion stage to another device, such as a cantilever mass sensor. It is known that a cantilever mass sensor requires the particle(s) being weighed to be at the tip of the sensor for maximum sensitivity. The motion stage can accurately position the tip of the micromanipulation device at the tip of the mass sensor and then the micromanipulation device can be actuated to drop the particle onto the sensor. Multiple microparticles can be deposited on the mass sensor in the same manner to determine a combined weight.
In yet another embodiment, the apparatus 200 may be modified to incorporate a force-feedback system, or more specifically a system that can provide information about the forces experiences at the tips 56 of the micromanipulation device 50. For example, a micro-sized strain gage may be attached to the outer surface of the arms 55 to measure the strain as the arms are deflected. Appropriate circuitry can generate stress and force data from the measured strain and provide an output to the user. The force data can be used to ensure that the gripping force generated by the device does not exceed a force that could rupture the particle being manipulated or the yield strength of the arms of the device itself.
Understanding of how cells respond to stimuli is extremely important in biology and medicine. Currently these studies are performed on a large number of cells, because the tools to stimulate and manipulate single cells are limited. The ability of stimulating individual cells and observing their response is of paramount importance for understanding of diseases like cancer. In this complex disease, individual cells not only undergo detrimental modifications but also recruit healthy cells into the malignant state. The apparatus and device described herein can be used to bring a healthy cell in contact with a malignant cell to study the interactions between the two cells (with further imaging techniques such as fluorescence microscopy).
It is also known that cell biology can be altered by external forces. In fact, this phenomenon is a formal research topic among medical researchers who are actively trying to understand numerous diseases including malaria. Again, the present device can be used to apply a force to or squeeze individual cells and interrogate their response to external forces. In this instance, a force-feedback component may be desirable.
Infection of Single Cells with Viruses
This device can also be used to study infection of cells. Viral infections of cells is a profound research topic and is still not completely understood. The arms of the device can easily be loaded with viruses (such as by wetting it with a virus suspension) and then can be used to squeeze an individual cells to deliver the virus particles to its surface. The results of the infection can later on be investigated with imaging techniques.
Functionalization of microareas individually and discretely without contaminating neighboring areas can be achieved using the apparatus 200 described herein, particularly in conjunction with a motion stage. Discrete functionalization can eliminate wasting chemicals and can accurately locate and functionalize appropriate particles. For instance, a “micro-stamp” may be applied to discrete particles. In one example, polydimethylsiloxane (PDMS) is used as a stamp material to transfer “ink” to a target surface. The “ink” in the specific example is a fluorescein-isothiocyanate-labeled bovine serum albumin. The PDMS stamp is grasped by the apparatus 200 and brought into contact with specific beads in a multi-bead array. Using the motion stage, the apparatus can be moved so that the micromanipulation device holding the stamp applies slight pressure to the particle to affix the “ink”.
The ability to discriminate and move individual or groups of live cells within or outside of aqueous media can lead to arrangement of cells in specific patterns, placement of cells on sensors or isolation of individual cell spheres from a culture. The apparatus 200 can easily perform these functions. For instance, stem cells grow as multiple spheres in soft agar. Before the stem cells can be interrogated, multiple aspiration and incubation steps are used to separate all of the spheres from the viscous media, which is time-consuming and problematic since reagents typically cannot isolate a single sphere. Consequently, in traditional procedures many stem cell spheres are wasted that could otherwise remain in the media until needed. In one example, the apparatus 200 was able to isolate a single mouse prostate cell directly from the viscous media in which the cell was suspended. The gripping force provided by the micromanipulation device of the apparatus was strong enough to complete with the surface tension of the viscous gel but not so strong as to damage the cell.
While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This application claims priority to co-pending provisional application No. 61/562,803, filed on Nov. 22, 2011, the entire disclosure, including appendices, of which is incorporated herein by reference.
This invention was made in part with support from the National Institute of Health (NIH) with grant number PN2EY018230. The Government may have certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61562803 | Nov 2011 | US |
