CA2220883A1 - Microfabricated therapeutic actuator mechanisms - Google Patents

Abstract

Electromechanical microstructures (70) (microgrippers), either integrated circuit (IC) silicon-based or precision machined, to extend and improve the application of catheter-based interventional therapies for the repair of aneurysms in the brain or other interventional clinical therapies. These micromechanisms can be specifically applied to release platinum coils or other materials into bulging portions of the blood vessels also known as aneurysms. The "micro" size of the release mechanism is necessary since the brain vessels are the smallest in the body. Through a catheter more than one meter long, the micromechanism located at one end of the catheter can be manipulated from the other end thereof. The microgripper (micromechanism) of the invention will also find applications in non-medical areas where a remotely actuated microgripper or similar actuator would be useful or where micro-assembling is needed.

Description

wo96138092 Pcr/Isg6/00593 MICROFABRICATED THERAPEUTIC ACTUATOR MECHANISMS
The United States Go~ Pnt has rights in this invention pursuant to Contract No. W-7405-ENG 48 between the United States D~,ent of Energy and the University of C~~liforni~ for the operation of Lawrence Livermore ~:~h~ l Laboratory.
BACKGRMJND OF THE rNVENTION
The ~fesel-l invention relates to microstructures, particlll~rly to electromech~nir~l micrcmerh~ni~m.~, and more partic~ rly to microg.-~ers for use in catheter-based i.~lelv.o.~l;on~
thPr~pi~PS or remote micr~csemkly applir~tionc.
Micro~ctu~tors for remote and precise manipulation of small objects is of great ~lller~sl in a wide variety of applir~tionc The design and development effort of such microg-;~pel devices would be useful in the art as such will apply to general microfabrication terhniques and establish the infrastructure for microPnginPPring efforts inrl~lin~ robotics, microterhnology, prevision PnginPPring~ defense, energy, and biom~p~lir~l research, as well as use in me~lir~l applir~tion~, such as for catheter-based int~ P~tion~l therapies and remote assembly - or use of microm~rh~nir~l system.
When a portion of a blood vessel weakens, it bulges and forms a ane~m, which is one of the main reasons for strokes as the vessel finally collapses and opens. These aneuly~ms have tr~lition~lly been treated by surge. ~, where the surgeol- will have to open up the area of repair before aUe-,l~Lng to surgically repair the aneurysm by clipping it. How~ver, many aneu~ - -s are at critical locations such as in the brain and are either .lifficlllt and risky to operate on or it is simply impossible. Por the last 20 years, pioneering doctors have used illlelvPr~lior~l neuroradiology techniques to aid the treatment of brain aneu.y~ Ls~ Long (1-2 meters) and narrow (i.e. 250,um to 500~m) catheters are pushed through the arteries in the groin up to the brain to reach the aneurysm. Existing catheter-based interventional instruments W096~8092 P~~ f''~ 3 rely on simplistic and usually singular means of actuation. These techniques, in~ ling balloon angioplasty, are well-established for large vessel treatments such as in the heart. It is crucial that in order to extend this medical practice into the sm~ r vessels such as those in the brain, the catheter-based tools must be mini~tllri7ed. In the most recent method, pl~timlm coils were selected to fill up the aneurysms due to its ability to fill up irregular shapes and its resistance to electrolysis in the vessels when it is charged. The coils are either pushed through the cat~eter to the aneurysm by a guide wire or rele~e~ by the electrolytic ~iicsollltic~n of a solder joint between the guide wire of the catheter and the therapeutic device, which for neurological treatments are dyyro~ t~ly 25011m or less in diameter. Although the charging of the coil causes elec~oll~rombosis around the coil, the time required to release the coil is long (4 mins to 1 hr) and many coils are usually n~e~le-l to fill tlp a regular size aneurysm. The extent to which the dissolved m~pri~l affects the body is unknown and electrolysis sokl~ring requires long terms of current in the brain and so~netimes is simply unreliable.
These ~iiffir~tlti~s ~resent potential life-threatening problems to the patient for the sur~eol~ and ~ niri~n Thus, there is a need for a micromerh~nicm which can fit into a 25011m ~i~met~r area and which would enable the physician to release and retrieve the coils or other therapy once it is r.ole~se-l at the wrong time or location. The present invention satisfies this need by providing a micrometh~nir~l release mechanism by which this - procedure becomes a safer and more reliable alternative to surgery, and which can fit into blood vessels of the brain, a 250~1m diameter area. The electrome-h~ni~ ~l microstructures, including microgriyy~.s, can be fabricated using known IC silicon-based techniques or precision microm~hining, or a combin~tic-n of these techniques. While the invention has application in various areas requiring a remotely actuated microgripper, it has particular application in catheter-based intervention~l therapies.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electro-me- h~nir~l micro~,lipyel.

W096138092 P~-l/Lb~'~C~-~3 A further object of the invention is to provide a micro~A~er with a large ~";pp;ng force, a relatively rigid structural body, and flexibility in fl-nction design.
A f-urther object of the invention is to provide an electromPrh~nir~l micromerh~nicm mounted at one end of a catheter and which can be manipulated from the other end, thereby PY~en~ling and illlyrovillg the applir~tic-n of catheter-based interventional therapies.
Another object of the invention is to provide a mi~ rogr;p~r capable of operating in an area as small as a 25011m mpt~pr~ such as in the blood vessels of the brain.
Another object of the invention is to provide a microgripper which can be used to integrate hP~tPrs and strain sensors for remote active h~P~ting and feedback control.
Another object of the invention is to provide a mi~:lo~ er which can be used as a biopsy tissue sampler, or for use as a tip ~lpci~nerl for h~n~ilin~ micn~parls.
Another object of the ii~v~ntion is to provide a mi~ogl;~per which has the ~olenlial to apply alten~aliv~ act~l~tion mPrh~nicmc, either hydlaulic or simply thprm~l bimorphic.
Another object of the invention is to provide a microgripper with a large gripping force (40mN), wherein actllati--n thereof is generated by shape-memory alloy thin films and the stress in~rerl can deflect each side of a mi~o~ er up to about 55~m for a total ~,i;p~;ng motion of about 11011m.
Other objects and advantages of the present invention will become a~aient from the following description and ~ccompanying drawings. Basically, the invention involves an electromerh~nir~l micr~ merh~nicm which can be l~tili7e~l in me-lirAl as well as non-me~ic~l applications, and is particularly applicable for catheter-based inl~ enlional therapies for the repair of aneuly~ll,s in the brain, or other small blood vessels. The microgA~el of this invention has: 1) a large ~A~ing force, 2) a relatively Agid structural body, 3) can be ~ltili7e-1 in a 250~Lm rli~meter area, 4) allows for flexibility in shaping the gA~ing jaws, 5) can be used for biopsy sampling or for handling mi~oya. l~, 6) has fast release and retrieve capabilities, 7) can be integrated with heaters and strain sensor for remote active heating and feedback control, 8) may W096t38092 PCT~B96/00593 be used with hydraulic or simple thPrmAl bimorphic actuation, and 9) may be co~ cted using ~ ve,~lio~Al integrated circuit silicon-based techniques or precision micromAt hin~, or both BRIEF DES~ ON OF THE DRAW~GS
The ac~;v~ >al-r~lg drawings, which are in~;o~o~led into and form a p_rt of the disclosure, illllctrAte e~ l~o~li...Pntc of the invention and, together with the desc~;~Lon, serve to explain the principles of the invention.
Figures lA and lB are cross-sertinnAl views of an embo~lim~Pnt of the mi~;lv~ ~r using balloon activation, and shown in the dosed and open pos;tionc~
Figure 2 is an exploded view of the Figures lA-lB
embo~1iment, with the b~llssm o~ le~1-Figures 3A and 3B illustrate another embofliment of themicr~;l~r us~g a ~n f~ tweezer-iiKe a.Lvaion Figures 4A and 4B are cross-sectiorl~l views which illustrate another embo~limPnt of the micro~ el using a shape-memory alloy (SMA) wire dicker.
Figure 5 is an exploded view of the Figures 4A~B
embo lim~Pnt with the SMA wire c~ tl~
Figure 6 is an emhoflimprlt of the invention using SMA
double coils.
Figure 7 is a ~reÇ~red embo liment of a silicon microgripper made in accordance with the ~resent invention.
- Figure 8 is a cross~ertio~l view illustrating the ellt~ctic bonding ~rocess.
Figures 9, 9A and 9B illustrate resistive heaters and Plectrir~l feed~lrough for Figure 7 a micro~
Figures 10,10A and 10B illustrate an embo liment of the heater of Figure 8A, with cross-sections as shown in Figure 10A and 10B
- greatly enlarged. -Figures 11, 11A and 11B illustrate another emborlimpnt of the heater of Figure 9, with the cross-sectionc of Figures 11A and 11B
greatly enlarged.
Figure 12 illusllales a force fee~lk~ control system for the microgripper of Figure 7.

~,ll~ltU SHEET

W0 96/38092 PCT/II~g '~ ~ -~3 Figure 13 is a view of an SMA film activated microactuator made in accordance with the invention for providing hydraulic ~res~ 2/fluid delivery from a microballoon.
DETAILED I~ESCRIPIION OF THE PREFERRED EMBODIMENTS
The invention is an elechronlerh~nical grip/release microm~rh~nicm referred to thereinafter as a microgripper or microrl~m~r. The micro~,ri~el has a large gli~ing force, a relatively rigid shuchural body, and flexibility in flmcti~r ~l design such that it can be used, for example, as a biopsy tissue s~mpler, a tip designed for h~nrllin~ mi.~ s, or as a release/retrieval m~rh~ni~m for items such as pl~ffnum coils or other materials in bulging portions of the blood vessels, known as aneulysms. The micro~ er of this invention is particularly useful to extend and improve the applir~tion of r~thPter-based inle..~P.~ n~l therapies, and is capable of use in a 250~1m diameter area, such as a small blood vessel of the brain. The micro~ ~r may be consllucted with outer 5llrhre5 which can be used to integrate heaters or strain s~co~ s for remote active heating and feedback control. One embo-liment of the microgripper, for ~ lP, is of a silicon structure and incc,l~orales shape-member alloy (SMA) thin films, and the stress inrll~ l can deflect the sides thereof to enable a g~ ing motion of about 110~1m. The micro~;r;~L can be fabAcated by precision microm~rhining or by terhniques lltili7e-1 in the fabri' ~tion of silicon-based integrated .;ii~uils.
The ~lltimllm obje-;live of the grip/release merh~nicm or microg~ er is to achieve the following: 1) the cross-section should fit into a diameter as small as a 250~1m area (open and dosed); 2) the release of materials into the blood vessels should be less than 10 seconds; 3) the le.,.~ralure range should be between 0-C and 37~C; 4) current should be less that 10 mA, for example, if electrical energy is used; 5)100%
reliability.
Using collve~l;or~l silicon bulk micromachining terhni-lues a m~rh~nic~l damper or microgripper as illustrated in Figures lA, lB, and 2 can be fabricated to include a cantilever structure therein which, for example, is about 800~m in length and the total height of the structure is 250,um. Then a silicon microballoon may be tlttli7e-l to merh,~nic:3lly deflect the cantilever arms to clamp onto foreign objects at the front end thereof, as seen in Figure lA and lB. The ~ =

.

W096/38092 P~ 5J,'00593 microballoons are well characterized and can withstand pressures of up to 10 atm. Such microballoons have also been tested for use in human blood vessels. As seen in Figures lA-lB and Figure 2, the balloon activated microg~ ,el generally indicated at 10 comprises a pair of jaws, grip arms, or gripping members 11 and 12, each having a plurality of slotted cantilevers 13 and 14, a pusher pad 15 and 16, and ~ e ~ 17 and 18. For some app~ hon~ the pusher pads may be omitte~ The jaws or g members 11 and 12 are bonded or oLllel -. ise secured together as intli~ l at 19. An eYr~nti~hle device, such as a balloon 20, is positioned between ~i~ing rrlemherc 11 and 12 and cor necte~l to a delivery tube or cath~tor 21 which ~xt~rlds along the b~lloon path 22 (See Figure 2) through which an activating fluid or gas is supplied to activate (expand) the ball~ orl 20. Pusher pads 15 and 16 serve as balloon force points 23 (See Figure V~ and when fully expanded an end of the balloon may exte~ l;~e~re~l~ the~sher pads 1~l6 as shown m Pigure lA.
With the balloon 20 in inactivated (unexpanded) position as shown in Figure lA, the grippers 15 and 16. Upon activation enlargement of the b~lloon 20, the outer ends of ~ yi~lg members 11 and 12 bend or flex outwardly at the location of slotted cantilevers 13 and 14 ~~A~-~in~ the ~;Li~l~l'~ 17 and 18 to separate, allowing the m~teri~l 24 retained therebetween to be removed therefrom, as shown in Figure lB.
The g~ members 11 and 12 may be constructed of ~ilicon~ Al~ .." nickel or other compatible metals, teflon or other cc.~ le polymers, and cerarnics with a length of 0.8mm to 1.5mm, and a width and combined height preferably not greater than about 25011m. The balloon 20 may be a silicone microballoon capable of wilhs~ ing pressures of up to 10 atmospheres, supplied through the tube 21, which may be constructed of teflon or other inert plastics having a ~ meter of 80~1m to 400~1m The balloon 20 may be replaced with other e~cp~n-l~hle devices. The bond 19 may be formed, for example, by selective eutectic boncling The pusher pads 15 and 16 have, for example, a thi~kn~s of 20~un to 4011rn, and E;r;~p~r~ 17 and 18 may have a thit~kness of 9011m to 150~1m and length of 50~1m to 15011m. The slotted cantilevers 13 and 14 may be composed of 3 to 10 slots having a width of 511m to lOOIlm and length of 50,um to 50011m. The slots of the cantilevers may be straight or tapered along the length thereof. The .

wo 96/38092 PcrlIs96loo593 m~t~?ri:ll that the gripper members 11 and 12 is constructed from must be inert to the fluid or ch~mic~ involved.
The embodiment of Figures 3A and 3B utilizes a pair of initial SMA thirr film hinges to open and close the grip arms or gripping members acco~ding to the temperature the SMA thin film is exposed to.
The SMA thin films of Figures 3A and 3B can also be replaced by a heater sandwiched by polyimide layer expands and ~lPfl~ctc the cantilever clampers or g~ e~S.
As shown in Figures 3A and 3B, the microg~ er, generally in~ tefl at 30 is composed of a pair of grip arms or ~ g members 31 and 32 forme~l~ for example, from silicon wafers, and each inrl~ l a reduced thirkn~ss of cross-section area 33 and 34 and a pair of inwardly directed spaced ~;~ D 35 and 36 only one gripper of each pair being shown, which retain a mAteriAl or part 37, such as a stem of a platinum cell (See Figure 3A). Thin films 38 and 39 are secured to gr;~;ng me~e,;j 31 and 32 ~-ljacent the re~ e~l areas 33 and 34, with films 38 and 39 being cons~ cted of SMA or polyimide layers as described above.
The g~;y~ing members 31 and 32 are also provided with pusher pads 40 and 41. Upon heating of the thin films 38 and 39 by a heater, not shown, the films ey~An~l I Allcin~ outward flexing or bending of the outer ends of ~l;yying members 31 and 32 at areas 33 and 34 causing the g~ el:~ 35 and 36 to s~arale (See Fig. 3B) whereby material 37 is removed therefrom.
By way of ~y~mple, the grip arms or gripping members 31 and 32 may be constructed of silicon, or compatible metals, polymers, or ceramics with an overall combined height and width thereof preferably not to exceed 250~m, with the thickness of members 31 and 32 being 20 to 100~m, with re-i~lce~l areas 33 and 34 having a thickness of 5 to 15~1m, and grippers 35 and 36 extending inwardly from members 31 and 32 a t~nce of 20 to 50~m. The pusher pads 40 and 41 may for example, having a thickness of 20 to 40~1m and depth (height) of 30 to 100~1m. The thin films 38 and 39, if constructed of SMA, may be composed of Ni-Ti, Ni-Ti~u, or other low temperature SMA, having a thickness of 2 to 511m, and if composed of polyimide, for example, having two layers of a thickness of 3 to 1011m and length of 30011m to 50011m, which sandwich therebetween a heater constructed of Ti-Au. Heating of the SMA films 38 and 39 is accornplished, for example, by integrating polysilicon heaters wo 96/38092 Pcr/li~s~ c ~ - ~3 or direct resistive heaters of SMA, as described hereinafter with respect to Figures 9 and 10, or by laser heating through optical fibers. Shape-memory alloys are well known, as evidenced by U.S. Patent No. 5,061,914 issued October 29, 1991 to J. D. Busch et al.
The embodiment of Figures lA-lB and 3A-3B can also be lltili7e~ to retrieve material or parts, such as platinum coils used to repair aneurysms. These embodiment have advantages over prior known mi-:rogri~ers that are Plectric~lly conductive (see C. J. Kim et al, "Silicon-Processed Ov~rh~nging Microgripper", Journal of MicroelectromerhAnicAi Systems, Vol. 1, No. 1, pp. 31-36, March 1992) and can be used to manipulate biological cells or micro parts for a~s-omhly.
The embodiment of Figures 4A-4B and Figure 5 is a microgripper that is a normAlly open release mechanism (Figure 4B), where an SMA wire is used as a latch to close the microgripper (Figure 4A), and when activated to click open the merh~ni~m. As shown, this embo~limer t, generally in~licate~ at 50, comprises a pair of grip arms or g.~ ng members 51 and 52, generally similar in construction to the g m~mh.orS 11 and 12 of the Figures lA-lB embo~limf~nt, and are provided with hook connectors 53 and 54, pusher pads 55 and 56, and pairs of ~L;~pefs 57 and 58, only one each shown. A compressive thin film 59 and 60 is secured in openings 61 and 62 of gripping members 51 and 52. Hook connectors 53 and 54 have opening 63 and 64 (see Figure 5) through which an SMA wire 65 e~t~ncls (see Figure 4A) to "close" the g members 51 and 52 and COlil~f~:SS the com~ressi~e thin films 59 and 60. Upon activation of the SMA wire 65, the wire is withdrawn from openings 63 and 64 of hook connector s 53 and 54, as indicated by the arrows 66 (see Figure 4B), whereupon the compressive thin fflms 59 and 60 expand causing the ends of gripping members 51 and 52 to flex or bend outwardly. In the closed position (see Figure 4A) the pairs of grippers 57 and 58 retain a material or part 67 therebetween, and upon activation or rlirking open of the latch (hook connectors 53 and 54 and SMA wire 65), the grippers 57 and 58 move outwardly allowing the mAt~riAl or part 67 to be removed from therebetween. As in the embo~iment of Figures lA-lB, the gripping members 51 and 52 are bonded together as indicated at 68.

W096~8092 PCTA~5~ !0 - A3 By way of example, the gripping members 51 and 52, pusher pads 55 and 56, and grippers 57 and 58 may be constructed and configured as described above in the Figures lA-lB embo-liment The hook cormPct~ 53 and-54 are composed of silicon, metals, polymers or ceramics and secured, as by micromachining, and having a height of 80 to 200~1m, width of 200 to 500~un and the openings 63 and 64 therein have a cross-section of 80 to 380,um, width of 180 to 480~1m, and may be configured other than square. The SMA wire 65 may be composed of Ni-Ti-Cu, Ni-Ti, or Ni-Ti-Hf, having a cross-section and configuration which COl. ~onds with the openings 63 and 64 of hook members 53 and 54.
The co~ ressive thin film 59 and 60 may be constructed of silicon ~lioxi~le, doped polysilicon, or polymers having a thickness of 3 to 811m, and cross-section of 250 x 250 or 250 x 400~
Figure 6 illustrates a microgripper using two SMA micro-coils, one to grip on to the stem of a plAtimlm coil, for example, and the other one to push the pl~timlnl coil outwards to assure the release, the micro-coils being se~:ured at one end to the tip of a guide wire, such as used in ~ elel~-based inLe~ ;oI~1 therapies. As shown in Figure 6, two SMA coils 70 and 71 are secured at one end to a guide wire 72. Coil 70, of substantially greater cross-section and of greater ~ m~ter than coil 71, extends (wraps around coil 71 and around an end of a stem 73 of a platinum cell, for example, and retains or grips the stem 73. The coil 71 ~ n~ between the tip 79 of guide wire 72 and end 75 of stem 73. Under nc-rmAl con~litior~ the coil 70 retains the stem 73 from moving, and upon activation the coil 71 expands pushing the stem 73 out of the coil 70.
By way of example, the larger coil 70 may be cons~-lcted of SMA wire having a diameter of 50 to 7511m, a number of turns or wraps ranging from 10 to 15, and constructed of Ni-Ti, Ni-Ti~u, or Ni-Ti-Hf.
The sm~ller coil 71 may be constructed of SMA wire composed of Ni-Ti, Ni-Ti~u, and Ni-Ti-Hf, having a ~ met~r of 30 to 50,um, with the turns or wraps ranging from 5 to 10. The micro-coils 70 and 71 may be secured to guide wire 72 by b--n~ling, sol~l.oring, etc.
The ~rerei~ed embodiment of Figure 7 uses a combination of silicon structure and SMA thin film, and is provided with a wiring jacket for signal input. This embodiment provides a microgripper that can be locally actuated at low temperatures (<100~C), with a large W096/38092 PCTnB96/00593 ing force (10 to 40mN), a relatively rigid structural body, and flexibility in functional design. Also, this microgripper has the capability to lock the target gripping object. The actuation of the microgripper is gPnPratP-l, for example, by NiTiCu shape-memory alloy thin films and the stress in~ c~l can deflect each side of the microgripper up to 5511m for a total g.i~ing motion of 110~1m. This opening motion co.les~onds to a 20mN opening force on the tip of the gripper. In a~ition the mi~o~ yel can work in a liquid environment. The opening jaws, the pusher pads, and the hollow t~ nnPl are shaped by a combination of precision sawing and bulk machinin~ of silicon. Two preprocessed silicon wafers are prevision ~ nP-l and selectively bonded, using an Au-Si el-tectic ~focess which involves ~ligning a mask on a wafer and eva~oldling through the mask onto the gripper bonding portion, as described in greater detail hereinafter with respect to Figure 8. The mi~ er of Figure 7 is lmm x 20011m x 38011m in rlimpn~ic)n~ having a pair of silicon cantilevers 12.511m thick, with 511m thick NiTiCu SMA
thin films deposite~l on the outer sides of the cantilevers or gripper arms to provide ~ctll~tion of the microgripper. The SMA thin film can generate act-~tinn stresses up to 500 MPa at transformation temperatures between 30-C to 70-C, which is a lower temperature than all known thermal bimorphic micro~,rippers. For experimPnt~l verific~tion~ the micro~ er was ac~l~t~l by PYtprn~l hP~tin~ and a video tape was ~r~ared to ~iPmonctrate the opening and closing motions.
Referring now to a specific embo-limPnt as shown in Figure 7, the microgripper generally in~ ate~l at 70 in~ es a pair of silicon cantilevers, gripper arms or gripping members 71 and 72, each member 71 and 72 having a 3011m wide pusher pad inrlil ~t~-l at 73 and 74, respeclively, and a pair of 60 x 110 x 10011m3 gripping jaws or grippers 75 and 76. The ~,liy~ing members 71 and 72 are Au-Si eutectic bonded together at an interface 77, and are each provided with an SMA thin film 78 and 79 on the outer surfaces or sides thereof. The cantilevers or ping members 71 and 72 are constructed to define a 11011m wide hollow channel 80 in the area of the bonded interface 77, which is in commlmicati-~n with one end of a catheter, for example, on which the micro~ er is mounted. The microgripper 70 is secured to a wiring jacket, generally indicated at 81, for signal inputs.

W096/38092 PCT/lb~'~~-~3 The composition of the ~ ing members 71 and 72, the SMA thin films 78 and 79, the eulectic bond 77, and the ~limen~ions of the micro~ er 70 have been set forth above. By way of example, the pusher pads 73 and 74 may have a thi~knP~ of 20 to 4011m and height of 80 to 100~m; with the gripper 75 and 76 having a height of 80 to 10011m, and end cross-section of 70 x 150,um; and with the hollow channel 80 having a width of 100 to 25011m and height of 50 to 180~1m.
The fabrication of the micro~ per emborlimPntc of Figures lA-lB, 3A-3B, 4A-4B, and 7, particularly Figure 7, allows the riPsignpr some flexibility in shaping the gli~ g jaws as the targeting spel imPnc dictate, and can either be used as a biopsy tissue sampler or a c~thPtPr tip ~1PC;~Pr1 for ~n~llin~ microparts. The outer surfaces of the mi,.o~ er, particularly Figure 7, can be used to integrate hP~tPrs or strain s~l~col;, for remote active hP~ting and possible feedback control as riPCI rihe~l hereinafter with respect to Figures 9-12. The hollow channel of the Figure 7 embo~limPrlt has the potential for either wire connection or njection of liquids and therapeutic me~ e. Another important advantage is the poscihility to apply alternative actuation merh~nicm~
on the mk.o~ er structure, either hydraulic or simply thPrm~l bimorphic. Many creative ~Psignc of practical microgrippers for various applic~ti~ can be conceived using this basic approach. Fabril ~tion process steps can be highly automated and batch fabrication of the microgl;~ers will reduce the m~nl1f~cturing cost.
App!ic~ti- rl~ of the Figure 7 microgripper indude - assembling small parts for m~nllf~cturing~ minimally-invasive in vivo biopsy tissue s~mpling~ catheter-based endovascular therapeutic ~rocedures, and remote h~n-llin~ of small particles in extreme ellvir~,l....ent~ (high/low pressures, hazardous fluids, etc.).
The microfabric~tion process for the Figure 7 embodiment can be categorized into bulk micromachining, fine alignment, etching, and Ni-Ti-Cu SMA thin film deposition. As set forth above, a specific embo~imPnt of the Figure 7 type microgripper is 1000 x 200 x 380~Lm3 in dimension. Each silicon cantilever (72 and 73) is 125~1m thick and 5~1m Ni-Ti-Cu SMA thin films (78 and 79) are deposited on the outer surfaces of the cantilevers for actuation thereof. The pusher pads (73-74) are 30~1m wide while the ~ illg jaws (75-76) are 60 x 110 x 100~1m3. The hollow ~ h~nnPl 80 is 110,um wide and 175~m in height. The gripping WO 96138092 P~ b5~'1;1;~553 ~ 12-jaws, pusher pads, and hollow channel are shaped by a combination of precision sawing and bulk machining of silicon, and thus can be batch fabri<~te~l The connection of the microgripper to external leads and milli-end effectors (as exemplified in Figure 9) requires assembly and therefore does not allow for batch fabrication. However, there is an ongoing effort to develop assembly techniques for packaging.
The cantilevers or gripper arms (71-72) of the microgripper are fabricated on two silicon wafers. This ~rocess starts with two 10011m thick (110) p-type silicon wafers, which are ground and polished from a width of 200,um to an overall width of 38011m. The cQmmon masking film for p~t~ g and etch silicon was lo00A of silicon nitri~o A test ~all~ ll is essenti~l to identify the exact (111) plane as opposed to the wafer flat, which is typically offset 2~-3~. ~lignm~ont targets are imprintefl on each of the silicon wafers using this crystal plane identifying pattern to ensure the subsequent ~ligning to the exact crystal planes. Two types of ~li~m~nt targets must be ~l~finell, one to carry out front-to-back ~lignment and another etched through the wafers to provide holes for precise pin mPrh~nic~ lignment~ for eutectic bon~ling Dicing line (211m deep) are then p~tt~rn~rl on the backside of each wafer. On the front side of each wafer, saw cut t h~nn~l guide lines are p~ rn~rl for the precision saw to form the silicon cantilevers (71-72) and the pusher pads (73-74). These patterns are imprinted by etching the silicon down lllm. After reapplying the masking silicon nitride, lathography is carried out for the ~,ip~ing jaws (75-76) and the hollow l h~nnel (80). The silicon wafers are then etched in 44% KOH, creating vertical walls 85~1m deep. The silicon nitride mask is then stripped and ready for the precision saw, such as a model 780 by Kulicke & Soffa, with positionin~ accuracies as high as 2.511m. Precision sawing was chosen to avoid the anisotropic etching limitations of silicon that does not allow vertical wall etch channels 90~ apart without careful corner compPn~tic-n and s~rrifice of fini~he-i sllrf~ces Since the width of the two cut channels are 20011m and 40011m, respectively, the blade selected was 20011m thick. The wider cut ~ h~nn~l (400~1m) was formed by making two adjacent saw cuts. The saw was indexed to leave a pusher pad (73-74) width of 3011m. For careful control of the cut depths, it is I-ecess~ry to index the depth from the bottom of the wafer. Furthermore, it is ideal to dress the blades on rougher surfaces to achieve the vertical edges. The CA 02220883 l997-ll-l2 W096138092 PCT~95i'~~593 pair of silicon cantilevers or gripper arms (71-72) formed from the silicon wafers are now reading for bonding.
Bonrlin~ of the cantilever or gripper arms of Figure 7, for example, is carried out using Au-Si eutectic bon~ling~ whereby selective areas of bonding at a low temperature (<400~C) is achieved. The silicon microstructures, such as the gripper arms of Figure 7 can be bulk micromachined on two silicon wafers, as described above, and then ellt~chr bonded, which enables (1Psigner to ~l~signer minimal gap microstructures that can also be applied as c~r~t~it~nre sensors/~c~ tc-rs and microfl~ lirc systems with tight seals.
Using Au-Si eutectic bonding a microstructure, composed of the two silicon m~chin~-l wafers, such as illustrated in Figure 7 may be f:~hrit :~te~1 as illustrated in Figure 8. On each cantilever 82 framed from a silicon wafer, Ti/Au pads, generally in~ic~te~l at 83, 500 x 500~1m in area for example, are deposited by electron beam (E-Beam) evaporation in~ te-l at 84, by arrows and patterne~ through shadow masks 85 and 86, such as illustrated in Figure 8. The Ti layer 87 is an adhesive layer and also serves as a diffusion barrier for Au layer 88. The thirkn~ss of the pads 83 are, for ~Y~mple, 500A for Ti (layer 87) and 1,um for Au (layer 88). The Annea1ing temperature is 370~C to 390~C which is above the 363~C eutectic point to assure the interface to liquidify. Soaking at this temperahlre for 5 miml~s is necessaL~. The shadow masks 85-86 are e~ elllly fabricated by etching windows out of (100) silicon wafers. By ~ligning the shadow masks to the wafer only areas coated with Ti/Au - will be bonded together. The m~ting silicon wafers should have a fully ne~l silicon surface where the bonding is to occur. The wafers are then ~ressul,zed together and held in low vacuum (nomin~lly 10-4 Torr) and so~ke-l, for example, at 380~C for three (3) minutes. An acoustic image of an array of Ti/Au eutectic bonding pads 83 seen through a pair of 2 inch silicon wafers showed that a highly uniform and solid bond has been formed. The Au-Si bond strength was measured in an instron pull test, where 9 eutectic bond pads were pulled and failed at pull stress of 5.5 GPa. The eutectic bond areas were intact, as fracturing of the silicon surrol-n~ling the bond areas occurred in the process.
During the bonding process, rnech~nical alignrnent using precise diameter pins were applied to ensure controlled processing and ~,~vent shattering of the fragile thin cantilevers. The bonded pair of wo 96/38092 Pcr/~ - c ~~93 cantilevers (71-72) are now ready for deposition of the SMA thin films (78-79).
The SMA thin films are composed of Ni-Ti-Cu deposited using a mixed dc magnetron sputtered deposition, the details of the mixed splltt~rinE process are set forth in copending application Serial No. 08/(IL-9463), filed May 1995, entitled, "Multiple Source Deposition Of Shape-M~mc)ry Alloy Thin Films" and ~Csignerl to the ~signPe of this appli- Atis~n In that sputtering process, three (3) separate targets are used to s~,tlel the alloy such that the power can be individually controlled to actively determin~ the alloy composition- The thin film was deposited at 505~C, for ~Y~mple, so that it is in sihl aI ne~le~l to relieve the residual stress. The SMA fflm was initially deposited seqll~nti~lly on the outer sides or surface of the cantilever arms (71-72) of Figure 7, for example, so that one side is ~nne~le~l twice at 505~C, but preferably deposition of the SMA film prior to bonding of the cantilever arms would reduce th~rm~l stress in the film. The following sets forth a concise process sequence for fAhri- ,~hng a micro-actuator, such as illustrated in Figure 7, the sequence includes:
a) pattern crystal plane test marks, align targets and nm~nt holes.
b) pattern saw cut ~h~nnel guide lines.
c) p~ttern silicon etch channels following the (111) plane direction.
d) anisotropic etching of the silicon etch channels by KOH.
e) shadow mask ~lignment to wafer, and deposition of Ti/Au film.
f) merh~nirAl pin alignmerlt and eutectic bonding at 380~C
(3 min.) and 10-4 Torr.
g) m~gn~tron sputter deposition of Ni-Ti-Cu films on both sides with in situ ~nne~ling at 505~C.
h) dice up individual microgrippers.
The microgripper of Figure 7, is actuated using the dc magnetron s~Llered nickel-titanium-copper-shape memory fil~n.
Shape memory acttl~tion is based on a crystalline phase transform~tion in which the low temperature phase (martensite) is easily and reversibly ~leform~ble via twins, while the high temperature phase (austenite) has one rigid configuration. The Ni42TisoCug alloy transforms just above wo96/38092 PcrlIsg6/oosg3 body temperature (37~C), making it useful for implantable medical devices, and has a narrower hysteresis than binary nickel-titanium which increases ~ffiri~ncy and improves response time. Purthermore, the ~ liti~n of copper makes the trar ~form~tic)n temperature less sensitive to film composition.
In the microgripper application, actuation occurs by the recovery of tensile residual stress in the memory film, the data thereof being obtained by measuring substance curvature as a function of temperature. The film, which is deposited at 500~C, develops a tensile thermal stress as it is cooled after deposition. When cooled below the temperature at which the martensitic l-dnsro~ ation starts, the th~rm~l stress in the film can relax by twin-related deformation. This tensile therm~l stress can be recovered by heating the film. Thus, the silicon og~ r cantilevers act as bias springs which are opened by the contracting shape-memory film (78-79) when heated, then ~l~flect~l back to a reutr~l position and stretch the shape-memory film when cooled.
Films with up to 500 MPa recoverable stress have been deposited, but the film on the cantilevers of Figure 7, for example, have a recoverable stress of 375 MPa. Testing of the stress in~ cerl by the Ni-Ti-Cu film was measured by a Tencor FLX-2320 laser system, which measures the curvature in-lllce~l by the film on an Si sul~slldle, which is translated into stress.
In order to evaluate the gripping force induced by the Ni-Ti-Cu SMA filrn, an equivalent model with an opening force at the tip was - assumed. By applying bimetallic stress equations, the relation between the Ni-Ti~u film stress and the ~lpflection of the gr;~per tip was ~'~l~ll?,te.l Por a film thi~kness of 5~m, the ~ieflechorl is calclll~te~l to be53~n. Experiment~l results showed the gl;pper opening to 55,um when fully actll~terl Using the equivalent model, it was found that it requires 20mN to deflect the microgripper to 5511m. Therefore, a gripping force of 40mN (20mN on each cantilever) is applied for a fully open microgripper.
The heating of the microgripper of Figure 7 was applied by an integrated circuit (IC) fabricated thin film resistor heater pad, as ~l~s~ribe-1 in greater detail with respe* to Figures 10 and 11. The heater pad is placed on the microgripper cantilevers and current is applied, the heat is transferred from the heater to the Si gripper cantilevers for phase CA 02220883 l997-ll-l2 W096/38092 PCTA~~.'C-~.3 transform~tion in the Ni-Ti-Cu film to take place. Thus, remote active h~ting of the SMA film can be accomplished.
Also, the microgripper of E~igure 7 is being integrated with strain sensor for feedback control as described hereinafter with respect to Figure 12.
Figures 9, 9A and 9B illustrate packaging of the microgripper of Figure 7 on a c~th~t~r. Components similar to those of Figure 7 are given corresponding reference numerals. The microgripper 70 is ~lectric~lly connected to a wiring jacket 81' via a SMA film resistive heater, generally indicated at 90 on cantilever 71 and having contract pads 91 and 92, which are connecte~l via leads 93 and 94 to contact pads 95 and 96 on cor~ rhve films 97 and 98 such as copper, bonded to a polymide member 99, of an electrirAl feedthrough ribbon generally in~ terl at 100. As in~ic~te-l by leads 93' and 94', an i~l~ntir~l resistive heater and ~lectric<ql connection arrangement is provided between cantilever 72 of microgripper 70 and the cor~ lctive film on polymide member 99' of wiring jacket 81. The polymide members 99 and 99' and ~csori~t~-l copper films are connected to insulated feedthrough wires 101/102 and 101'/102' of ribbon 100, and are located within a cat~et.or tube 103 (see Figure 9A). The polymide members 99 and 99~
protruding end sections 104 and 104' which, as indicated by the arrows 105, extend into the hollow channel 80 of microgripper 70. The wiring jacket 81' is secured to microgripper 70 by a heat shrink tube 106 (see Figure 9B).
The resistive heaters 90~ of Figure 9 located on cantilevers 71 and 72 of the microgripper 70 may be of the type illustrated in Flgures 10, 10A and 10B or of the type illustrated in Figures 11, 11A and 11B, each having piezoresistive feedback capabilities.
In the Figure 10 embo~liment, the resistive heater 90 inrlll~e~ contact pads 91 and 92, as in Figure 9, with resistive wires 107 being in electrical contact with pad 91 and resistive wires 108 being in contact with pad 92. Figure 10A is a greatly enlarged section of Figure 10 and composed of a silicon beam (cantilever 71), SMA resistive wires 107, 108, 107, of resistive heater 90, between which are layers 109 and 110 of an oxide, on top of which are layers 111 and 112 of polysilicon (poly-Si), and on top of which are sections of the SMA thin film 78, covered by an CA 02220883 l997-ll-l2 W096~8092 PCT/L~ g3 oxide or protective layer 113. Figure 10B is an enlarged cross-sectional side view of the Figure 10 embodiment.
The resistive heater 90 of Pigures 11, 11A and 11B is generally similar-to the Figure 10 embo~linl.ont, and similar reference numbers will be lltili7e~l In Figure 11, the resistive heater 90 includes contact pads 91 and 92, with resistive wires 107 conn~cte~ to pad 91 and resistive wires 108 connected to pad 92, as in the Figure 10 embolliment Figure 11A is a greatly enlarged view of a section of Pigure 11 and composed of a silicon beam (cantilever) 71, an oxide layer 114, a pair of polycilit~or e (poly-Si) layers 115 and 116 on which is deposited oxide (I.TO) layers 117 and 118, the SMA thin film 78 and an oxide or ~rolective layer 113. Figure 11B is an enlarged cross-sectional side view of the Figure 11 embo~ Pnt-Figure 12 5rhpm~tir~lly illustrates a force fee~ih~c k control ofthe micro~ ~r 70 of the Figure 7 embodiment, and similar components are given cor~ onding reference numerals. A s~n~in~
film 120 is deposited on a cantilever 71 and is connected via a strain-to-stress cor.v_.;iion, indicated at 121, as discussed above, to a specified force in~lir~t~r 122, the output of which is directed through signal processor (amplifier) 123 to an ~rtl~atic-n film (SMA film 78). While not shown, the lower cantilever 72 is provided with a similar arrangement.
The Figure 7 embo~im~nt can be modified to provide a hydraulic pressure/fluid delivery system, as illustrated in Figure 13.
Here, cantilevers 125 and 126 of a microactuator 70' are provided with - SMA thin films 127 and 128, respectively, with cantilevers 125 and 126 being ronn~rte~l by a section 129 having an opening, not shown, therein.
A microballoon 130 is position intermediate one end 131 and 132 of cantilevers 125 and 126, while the other end 133 and 134 thereof is provided with grippers or jaws 135 and 136. Upon actuation, ends 131/132 of the cantilever move inwardly, as indicated by the arrows, while the ends 133 and 134 move outwardly, as indicated by the arrows, whereby fluid within the microballoon 130 is forced therefrom as n~ terl by the arrows 137, thereby delivering the fluid 137 to a point of use.
It has thus been shown that the present invention provides an electromechanical micromechanism (either IC silicon-based or precision micromechanical) which will, for example, extend and CA 02220883 l997-ll-l2 W096/38092 PCT~B96'~'g3 improve the application of catheter-based interv.ontit-n~l therapies for the repair of arterio-aneurysms in the brain or other interventional clinical therapies. The microgripper of this invention, in addition to rr~e~lir~l applir~tic~nç, has non-medical uses, such as micro assembling and for remote and precise manipulation of small objects, and has the capability to operate in small areas having 250,um diameters, such as small blood vessels.
While particular embo~iim~ntç~ m~teri~lç, parameters, etc., having been set forth to exemplify the invention, such are not int~n~
to be limi*ng Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.

Claims (31)

1. A microgripper, comprising:
a pair of members, at least one of said members being adapted to grip an associated object, means for retaining said member in gripping contact with an associated object, and for releasing said member from gripping contact with an associated object.

2. The microgripper of Claim 1, wherein said pair of members comprises a pair of coils.

3. The microgripper of Claim 2, wherein one coil of said pair of coils is larger than another coil of said pair of coils.

4. The microgripper of Claim 1, wherein said members comprises a pair of gripping arms, said gripping arms having gripper members at one end and are secured together at an opposite end.

5. The microgripper of Claim 4, wherein said means includes a expandable device.

6. The microgripper of Claim 4, wherein said means includes shaped-memory alloy films.

7. The microgripper of Claim 4, wherein said means includes a compressive thin film.

8. The microgripper of Claim 7, wherein said means additionally includes a shape-memory alloy wire.

9. The microgripper of Claim 4, wherein each of said gripping arms is provided with means which allows an outer portion thereof to flex with respect to each other.

10. The microgripper of Claim 4, wherein said gripping arms define a hollow channel therebetween.

11. The microgripper of Claim 4, wherein each of said gripping arms include a pusher pad located in spaced relation to said gripper members.

12. The microgripper of Claim 4, wherein said pair of gripping arms are constructed of silicon.

13. The microgripper of Claim 1, wherein said pair of members are constructed to have a cross-section capable of operating in an area having a diameter as small as 250µm.

14. A micromechanism adapted to be attached to a forward end of a catheter for use as a biopsy sampler or for use in interventional therapies, comprising:
a pair of members connected at one end thereof and adapted to move at the other end thereof, each of said pair of members including at least one gripper located at said other end thereof, and means for causing movement of said other end thereof.

15. The micromechanism of Claim 14, wherein each of said pair of members additionally includes a pusher pad located in spaced relationship to said gripper.

16. The micromechanism of Claim 14, wherein each of said pair of members include a cantilever section.

17. The micromechanism of Claim 16, wherein said means for causing movement of said other end of said pair of members comprises an expandable device.

18. The micromechanism of Claim 14, wherein said means for causing movement of said other end of said pair of members includes a quantity of a shape-memory alloy.

19. The micromechanism of Claim 18, wherein said quantity of a shape-memory alloy is in the form of a wire, and wherein said pair of members include means into which said wire is removably inserted.

20. The micromechanism of Claim 18, wherein said quantity of a shape-memory alloy is in the form of a film.

21. The micromechanism of Claim 20, wherein said film extends along a surface of each of said pair of members.

22. The micromechanism of Claim 21, wherein said film is located on an outer surface of each of said pair of members.

23. The micromechanism of Claim 22, wherein said pair of members are constructed to form a hollow channel through said connected ends.

24. The micromechanism of Claim 21, wherein said film is located on an inner surface of each of said pair of members.

25. The micromechanism of Claim 24, wherein each of said pair of members includes a reduced cross-section portion located adjacent said film.

26. The micromechanism of Claim 19, wherein each of said pair of members include a section containing a compressive film.

27. The microgripper of Claim 1, additionally including means, contained a fluid located between said pair of members, whereby movement of said pair of members forces fluid from said means.

28. The microgripper of Claim 1, additionally inlcuding heating means for causing movement of said pair of members.

29. The microgripper of Claim 28, additionally including shape-memory film on each of said pair of members, said heating means causing movement of said shape-memory film thereby causing movement of said pair of members.

30. The microgripper of Claim 1, wherein said pair of members are bonded together by Au-Si eutectic bonding.

31. The microgripper of Claim 30, wherein the eutectic bonding of said pair of members is carried out by depositing an adhesive layer on at least one of the Si members, depositing an Au layer of the adhesive layer, AnneAIing to the eutectic point of the Au layer, and pressurizing the Si members together for a time period, whereby a highly uniform and solid bond is formed.