WO2009099805A2

WO2009099805A2 - Phaco-emulsification handpiece

Info

Publication number: WO2009099805A2
Application number: PCT/US2009/032137
Authority: WO
Inventors: David E. Booth; Maureen L. Mulvihill; Brian M. Park; Roger B. Bagwell
Original assignee: Piezo Resonance Innovations, Inc.
Priority date: 2008-02-01
Filing date: 2009-01-27
Publication date: 2009-08-13
Also published as: WO2009099805A3

Abstract

A handpiece for ultrasonic surgical applications includes a member for cutting, fragmenting, emulsifying, or grasping and at least one flextensional transducer for driving the member. The flextensional transducer includes a piezoelectric material and a flexible structure coupled to the piezoelectric material that amplifies the generated piezoelectric displacement of the piezoelectric material.

Description

PHACO-EMULSMCATION HANDPIECE

SPECMCATION

CROSS-REFERENCE TO RELATED APPLICATIONS

This PCT application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Serial No. 61/063,338 filed on February 1, 2008 entitled PHACO- EMULSMCATION HANDPIECE and whose entire disclosure is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. FIELD OF INVENTION The present invention relates to ultrasonic handpieces, and more particularly to phacoemulsification handpieces driven by flextensional transducers.

2. DESCRIPTION OF RELATED ART

A cataract is an eye disorder that affects the vision of up to 50% of adults between 65-74 years of age, and up to 70% of adults over the age of 75. The most common causes of cataracts are related to the natural aging process. Other causes are medications (i.e. steroids), traumas, UV-radiation, toxic substances and systemic diseases (i.e. diabetes mellitus).

Prior to 1967, cataract surgery involved the removal of the whole lens intact (an extracapsular extraction). This procedure required a large incision and 6 to 7 stitches causing patient discomfort, an increased chance of infection and optical astigmatisms. It also required the need for post-operative care for two or three months.

Phaco-emulsification is a procedure in cataract surgery where the natural crystalline lens is shattered with acoustical cavitation, micro-streaming and mechanical motion, then aspirated in small pieces out of the sulcus of the eye. Because piezoelectric ceramics deform when exposed to an electrical input, a phenomenon known as the converse piezoelectric effect, current technologies utilize stacks of piezoelectric material such as lead-zirconate-titanate (PZT) to produce the mechanical motion.

A conventional reusable phaco-emulsification handpiece is provided with electrical leads for powering the PZT stacks. The handpiece includes a conventional titanium phaco tip covered by an infusion sleeve. The phaco tip is inserted through incisions typically 2.8mm wide into the anterior chamber of the eye following a capsulorrhexis of the sulcus. An irrigation supply line delivers balanced saline solution to the infusion sleeve, which then enters the anterior chamber of the eye through two ports in the side of the infusion sleeve. A net irrigation/aspiration fluid efflux of zero and a constant inner ocular pressure are maintained in the anterior chamber to keep the endothelial cells on the underside of the cornea from contacting the surgical tools.

Using current Langevin bolted transducer technology, such as that disclosed in U.S. Patent Publication 2007/0063618 Al, which is incorporated by reference herein, the phaco tip is vibrated axially. This vibration results in axial displacement of the phaco tip. Tip velocities are typically around 13 m/s and produce 10 to 30 watts of output power. The phaco tip shatters the lens and the small pieces of the lens are drawn up through the central lumen of the phaco tip and out to a surgical console. The Langevin transducer technology has also been advanced to include axially and/ or side-to-side simultaneous motion.

However, Langevin transducer technology includes fundamental limitations. For example, high actuation voltages are required for the Langevin transducer which can cause the PZT stacks to fail due to arching when there is a presence of moisture, such as produced during sterilization. Because non-functioning handpieces must be sent back to the factory for repair, these unpredictable failures require additional handpieces to be available in a user's inventory. Even with proper maintenance, the usable life of a handpiece averages about 500 procedures. The replacement of handpieces is also costly due to the high initial cost of a reusable handpiece.

If too much power is applied during the procedure, the phaco tip may cause damage to the irreplaceable endothelial cells. Damage has been shown to be proportional to the duration and power of ultrasonic exposure. Further, the use of too much power or too tight of an incision may cause heating between the infusion sleeve and phaco tip. The heating may result in a corneal burn, which most often will require a corneal transplant to repair. Accordingly, improvements in piezoelectric-actuated phaco handpieces are needed to overcome the above mentioned deficiencies of current technologies and provides for a smaller driver format, low cost construction and right-sized power requirements.

All references cited herein are incorporated herein by reference in their entireties.

BRIEF SUMMARY OF THE INVENTION Transducer technologies that rely on conventional, single or stacked piezoelectric ceramic assemblies for actuation are hindered by the maximum strain limit of the piezoelectric materials themselves. Because the maximum strain limit of conventional piezoelectric ceramics is about 0.1% for polycrystalline piezoelectric materials such as ceramic lead zirconate titanate (PZT) and 0.5% for single crystal piezoelectric materials, it would require a large stack of cells to approach useful displacement or actuation of for example, a handheld device usable for processes such as cutting, grasping, fragmenting and the like. However, using a large stack of cells to actuate components of a handpiece would also require that the tool size to increase beyond usable biometric design for handheld instruments.

Flextensional transducer assembly designs have been developed which provide amplification in piezoelectric material stack strain displacement. The flextensional designs comprise a piezoelectric material transducer driving cell disposed within a frame, platten, end-caps or housing. The geometry of the frame, frame, end- caps or housing provides amplification of the transverse, axial, radial or longitudinal motions of the driver cell to obtain a larger displacement of the flextensional assembly in the axial direction. Therefore, the flextensional transducer assembly more efficiently converts strain in one direction into movement (or force) in a second direction. The present invention comprises a handheld device including a cutting, fragmenting, emulsifying, grasping member which is actuated by a flextensional transducer assembly. For example, the flextensional transducer assembly may utilize flextensional cymbal transducer technology or amplified piezoelectric actuator (APA) transducer technology. The flextensional transducer assembly provides for improved amplification and improved performance which are above that of conventional handheld device. For example, the amplification may be improved by up to about 50-fold. Additionally, the flextensional transducer assembly enables handpiece configurations to have a more simplified design and a smaller format.

These and other features of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of this invention.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: Fig. 1 is a cross-sectional view of a phacoemulsification handpiece according to an embodiment of the present invention;

Fig. 2 is a side view of flextensional cymbal transducer according to an embodiment of the present invention; Fig. 3 is a cross-sectional view of a phacoemulsification handpiece according to an embodiment of the present invention;

Fig. 4 is a side view of an amplified piezoelectric actuator (APA) transducer according to an embodiment of the present invention;

Fig. 5 is a perspective view of a frame and horn extension according to an embodiment of the present invention; and

Fig. 6 is a perspective view of an integrated frame and horn extension according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a phacoemulsification handpiece according to an embodiment of the present invention. The phacoemulsification handpiece comprises a phaco tip 2 with a collar 4 coupled to a flextensional cymbal transducer 10.

As shown in Fig. 2, a cymbal transducer 10 is a flextensional transducer assembly including a piezoelectric material 12 disposed within metal endeaps 14. The metal end-caps 14 enhance the mechanical response to an electrical input, or conversely, the electrical output generated by a mechanical load. Details of the flextensional cymbal transducer technology is described by Meyer Jr., R.J., et al., "Displacement amplification of electroactive materials using the cymbal flextensional transducer", Sensors and Actuators A 87 (2001), 157-162. By way of example, a Class V flextensional cymbal transducer has a thickness of less than about 2 mm, weighs less than about 3 grams and resonates between about 1 and 100 kHz depending on geometry. With the low profile of the cymbal design, high frequency radial motions of the piezoelectric material are transformed into low frequency (about 20-50 kHz) displacement motions through the cap-covered cavity. Cymbal transducers take advantage of the combined expansion in the piezoelectric charge coefficient d₃₃ (induced strain in direction 3 per unit field applied in direction 3) and contraction in the d31 (induced strain in direction 1 per unit field applied in direction 3) of a piezoelectric material 12, along with the flextensional displacement of the end-caps 14, which is illustrated in Fig. 2.

The design of the end-caps 14 allows both the longitudinal and transverse responses to contribute to the strain in the desired direction, creating an effective piezoelectric charge constant (d_eff) according to the formula, d_eff = d₃₃ + (-A*d₃i). Since d₃i is negative, and the amplification factor (A) can be as high as 100 as the end-cap 14 bends, the increase in displacement generated by the cymbal compared to the piezoelectric material alone is significant. The end-caps 14 can be made of a variety of materials, such as brass, steel, or Kovar™, optimized for performance and application conditions. The end-caps 14 also provide additional mechanical stability, ensuring long lifetimes for the parts.

The piezoelectric material 12 may be comprised of at least one of lead zirconate titanate (PZT), multilayer PZT, polyvinylidene difluoride (PVDF), multilayer PVDF, lead magnesium niobate-led titanate (PMNPT), multilayer PMN, electrostrictive PMN-PT, ferroelectric polymers, single crystal PMN-PT (lead zinc-titanate), and single crystal PZN-PT.

An example of a cymbal transducer is described in U.S. Patent No. 5,729,077 and is incorporated by reference herein. While the end-caps shown in the figures are round, they are not intended to be limited to only one shape or design. For example, a rectangular cymbal end-cap design is disclosed in Smith N.B., et al., "Rectangular cymbal arrays for improved ultrasonic transdermal insulin delivery", J. Acoust. Soc. Am. Vol. 122, issue 4, October 2007.

The cymbal transducer 10 drives the phaco tip 2 and collar 4 mass. The cymbal transducer 10 vibrates in an axial direction moving the phaco tip 2 at the transducer's resonance frequency. Multiple cymbal transducers 10 can be stacked to increase the magnitude of the distal end of the phaco tip 2. For example, the cymbal transducer 10 may generate up to about IkN (225 lb-f) of force and about 80 to 100 microns of displacement, which is comparable to the performance of a reusable phaco handpiece.

An infusion sleeve (not shown) may be provided that covers the phaco tip 2. An irrigation supply line (not shown) may be provided to deliver balanced saline solution to the infusion sleeve and then into the anterior chamber of the eye. An aspiration cannula (not shown) may also be provided to remove the fluids from the anterior chamber of the eye, which are drawn up through the central lumen of the phaco tip 2 and out through the handpiece to a surgical console. The cymbal transducer 10 comprises an arrangement for passing the aspirated fluids through the center of the cymbal transducer, such as a center- punch, hole or cut. The cymbal transducer is isolated from moisture, for example, by o-rings, mechanical seals, conformal coating, epoxy, or a combination of thereof. Fig. 3 shows a phacoemulsification handpiece according to another embodiment of the present invention. The phacoemulsification handpiece includes all of the elements and functionalities of the embodiment of Fig. 1, except that instead of utilizing the cymbal type transducer 10 as above, the transducer assembly is an amplified piezoelectric actuator (APA) transducer 20 comprising the piezoelectric material. As shown in Fig. 4, the APA transducer 20 is a flextensional transducer assembly including a single flextensional transducer cell 22 housed within a flexible frame 24. The flextensional transducer cell 22 expands and contracts in a transverse direction to cause inverse movement in the frame 24 in the axial direction. The frame 24 may include either an elbow at the intersection of walls or corrugated pattern along the top and bottom walls of the assembly frame. In operation, the transducer 22 expands during the positive cycle of an AC voltage, which causes the sidewalls of the frame 24 to move inward. Conversely, the transducer cell 22 moves inward during the negative AC cycle, resulting in an outward displacement of the top/bottom walls of the frame 24. The transducer cell 22 may include a spacing member 30 separating at least two stacks of piezoelectric material 29. The spacing member 30 may have a passage, such as a center-punch, hole or cut, for passing the aspirated fluids through the center of the APA transducer 20.

Two examples of applicable APA transducers are the non-hinged type, and the grooved or hinged type. Details of the mechanics, operation and design of an example hinged or grooved APA transducer are described in U.S. Patent No. 6,465,936, which is incorporated by reference herein in its entirety. An example of a non-hinged APA transducer is the Cedrat APA50XS, sold by Cedrat Technologies, and described in the Cedrat Piezo Products Catalogue "Piezo Actuators & Electronics" (Copyright © Cedrat Technologies June 2005).

The APA transducer 20 further comprises a horn extension 26 for the frame 24. Depending on the horn's 26 design, varying amounts of displacement amplification can be achieved in addition to the amplification of the APA frame 24. The frame 24 may be of the grooved or hinged type. Alternatively, the frame 24 may comprise a design which is not grooved or hinged.

The horn 26 may be made of a metal, for example such as titanium, metallic glass, stainless steel, or brass but is not necessarily limited to these materials. The APA frame 24 may also comprise the same material or materials as the horn 26. The design of the APA frame 24 is not limited to any particular design so long as when acted upon by the piezoelectric material 22, the frame 24 amplifies the motion in a direction beyond the maximum strain of piezoelectric material 22.

In one embodiment of the APA transducer assembly as shown in Fig. 5, the horn extension 26 and APA transducer frame 24 are made as separate and independent units, coupled together by a fastening means 28. In another embodiment of the APA transducer assembly as shown in Fig. 6, the horn extension 26 and APA transducer frame 24 are integrated as a single unit, which does not require the above mentioned fastening means 28. While the above described embodiments of the present invention are made with respect to a handheld device utilizing a cymbal type or APA type transducer assembly for actuation, the present invention is not limited to utilizing the cymbal type or APA type transducer assemblies. Generally, any type of motor comprising a transducer assembly, further comprising a mass coupled to a piezoelectric material, the transducer assembly having a geometry which upon actuation amplifies the motion in a direction beyond the maximum strain of the piezoelectric material, would also fall within the spirit and scope of the invention.

Now that exemplary embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be construed broadly and limited only by the appended claims, and not by the foregoing specification.

Claims

WHAT IS CLAIMED IS: 1. A handpiece for ultrasonic surgical applications comprising: a member for at least one of cutting, fragmenting, emulsifying, and grasping; at least one flextensional transducer for driving said member comprising: a piezoelectric material; and a flexible structure coupled to said piezoelectric material that amplifies said generated piezoelectric displacement of said piezoelectric material.

2. The handpiece of Claim 1, wherein said flexible structure is a pair of cymbal shaped end-caps in between which said piezoelectric material is interposed, and wherein said end-caps transform a small extensional motion of said piezoelectric material into large flexural motion.

3. The handpiece of Claim 1, wherein said flexible structure is a frame with a top wall and a bottom wall, and a first side wall and a second side wall, said piezoelectric material being disposed in said frame transverse to an axial direction of said handpiece, and wherein said piezoelectric material expands and contracts in a transverse direction to cause inverse movement in said frame in said axial direction.

4. The handpiece of Claim 1, wherein said flextensional transducer has a passage allowing for continuous fluid transmission from said member through said piezoelectric material.

5. The handpiece of Claim 4, wherein said piezoelectric material includes a spacing member separating at least two portions of piezoelectric material, said spacing member having a passage allowing for continuous fluid transmission from said member through said piezoelectric material.

6. The handpiece of Claim 1, wherein said piezoelectric material is comprised of at least one of lead zirconate titanate (PZT), multilayer PZT, polyvinylidene difluoride (PVDF), multilayer PVDF, lead magnesium niobate-led titanate (PMNPT), multilayer PMN, electrostrictive PMN-PT, ferroelectric polymers, single crystal PMN-PT (lead zinctitanate), and single crystal PZN-PT.

7. The handpiece of Claim 1, wherein said piezoelectric material expands or retracts in response to electrical signals, thereby axially translating said member.

8. The handpiece of Claim 1, wherein said handpiece is a phacoemulsification handpiece.