WO1997014454A1

WO1997014454A1 - Multi-textured cannula and method for making same

Info

Publication number: WO1997014454A1
Application number: PCT/US1996/015405
Authority: WO
Inventors: Nabil Hilal
Original assignee: Applied Medical Resources Corporation
Priority date: 1995-10-20
Filing date: 1996-09-25
Publication date: 1997-04-24

Abstract

A medical device providing access across body tissue and into a body cavity includes a cannula (14) having an axis and a wall extending between a proximal end and a distal end. An outer surface (23) of the wall contacts the body tissue when the cannula (14) is moved through the body tissue and operatively disposed across the body tissue. First portions (41) of the wall provide the outer surface (23) with a finish having a first roughness while second portions (43) of the wall provide the outer surface with a finish having a second roughness different than the first roughness. Multiple embodiments each providing a multi-textured cannula (19), minimize insertion forces, glare and axial migration. Associated methods of manufacture include bombarding the different sections with grits (61, 63) having different parameters or alternatively molding the different sections to provide the multi-textured outer surface.

Description

Multi-Textured Cannula and Method for Making Same

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to medical access devices and more specifically to the textures associated with the outer surface of a trocar cannula.

Discussion of the Prior Art

A trocar is a surgical device having an elongate tubular configuration which is typically positioned across the abdominal wall to provide access to the abdominal cavity. The tubular portion of the trocar, commonly referred to as the cannula, defines a working channel through which various instruments can be deployed and operated in order to perform surgical tasks within the abdominal cavity. The first instrument typically inserted is an obturator which has a sharp distal tip. This obturator is used to initially puncture the abdominal wall permitting the cannula to extend through the puncture into the abdominal cavity. Then the obturator is removed from the working channel so that other instruments can be inserted to accomplish their respective surgical tasks.

The texture on the outer surface of the cannula is of interest during several different steps associated with the operative procedure. Initially the texture on the outer surface of the cannula is of interest when the obturator and cannula are inserted through the abdominal wall. It is desirable during this initial step of insertion that the surface finish, at least in the distal regions of the cannula, provide a relatively low coefficient of friction with the tissue of the abdominal wall in order to minimize insertion forces.

The surface finish of the cannula is also of interest once the cannula is operatively disposed, typically in its fully inserted position. Once the cannula is operatively positioned, it is desirable that the surface finish provide a relative high coefficient of friction with the tissue in order to inhibit axial movement of the cannula during the surgical procedure.

At all times it is of interest that the surface finish of the cannula inhibit glare which might be caused, for example, by light from an endoscope or other fiberoptic instrument.

These considerations are of interest whether the cannula is manufactured of metal or plastic. However, glare may be less of a problem with plastic particularly if it is black and opaque. With a plastic cannula it has also been economically feasible to provide facia threads which substantially inhibit axial movement of the cannula during the operative procedure. These facia threads, which dramatically increase the trauma to the patient, do not constitute a surface finish but nevertheless have generally inhibited axial movement of the cannula.

In spite of these attempts of the prior art, there has been no solution which addresses all of the problems relating to entry force, holding force and glare for these cannulae and access devices of the prior art. SUMMARY OF THE INVENTION

In accordance with the present invention, the outer surface of the cannula is addressed in at least two different regions, a first region located near a distal tip of the cannula and a second region disposed proximally of the first region. In these regions, the texture or roughness of the outer surface is of interes . This roughness is a parameter commonly expressed as the average distance between peaks and typically measured in units of microinches. In the first region, the outer surface is provided with a texture having a roughness such as about 32 microinches which provides a relatively low coefficient of friction between the cannula and the body tissue. This results in reduced insertion forces for the cannula.

Throughout the length of the cannula, a surface finish can be provided which holds glare to a minimum. This generally requires a surface roughness greater than 16 microinches. This area of reduced glare may be created between the first region and the second region, for example. Alternatively the first and second regions may be formed adjacent to each other.

In one aspect of the invention, a medical device is adapted to provide access across body tissue and into a body cavity. The device includes a cannula having an axis extending between a proximal end and a distal end, the cannula being adapted for insertion across the body tissue and into the body cavity. A wall of the cannula has an outer surface adapted to contact the body tissue when the cannula is moved through the body tissue and operatively disposed across the body tissue. First portions of the wall of the cannula provide the outer surface with a finish having a first roughness. Second portions of the wall of the cannula provide the outer surface with a surface finish having a second roughness. The first roughness is less than the second roughness, and the first portions of the wall are disposed distally of the second portions of the wall. An associated method for preparing the surface of an access device includes the step of providing the device with a cannula having an axis extending between a proximal end and a distal end. A first section of the outer surface of the cannula is bombarded with a first grit having first parameters including a first material, a first particle size, a first distance, and a first pressure. A second section of the outer surface of the cannula is bombarded with a second grit having second parameters including a second material, a second particle size, a second distance, and a second pressure. During the second bombarding step, one of the first parameters associated with the first grit is changed so that the second parameters are different than the first parameters. As a result, the first section of the outer surface of the cannula has a first surface finish, while the second section has a second surface finish different than the first surface finish.

These and other features and advantages of the invention will be more apparent with the description of preferred embodiments and reference to the associated drawings.

DESCRIPTION OF THE DRAWING

Fig. 1 is a side elevation view of a trocar including a valve housing, cannula and obturator, the obturator and cannula being inserted through an abdominal wall to provide access to an abdominal cavity; Fig 2. is a side elevation view of the valve housing and cannula operatively disposed across the body wall and providing access for a fiberoptic endoscope;

Fig. 3 is a side elevation view of an additional embodiment of the cannula associated with the present invention;

Fig. 4 is a side elevation view of a further embodiment of the cannula associated with the present invention; Fig. 5 is a side view of the cannula with separate regions of the outer surface of the cannula being bombarded to produce different surface finishes in the respective regions; and

Fig. 6 is a perspective view of a process for molding a disposable catheter having surface regions with different surface finishes.

DESCRIPTION OF PREFERRED EMBODIMENTS AND BEST MODE OF THE INVENTION

A trocar is illustrated in Figure 1 and designated generally by the reference numeral 10. Included in the trocar 10 are a valve housing 12 that defines with a cannula 14 a working channel 16 which extends between a proximal end 18 and distal end 21 of the trocar 10. The cannula 14, which may be formed from metal or plastic, has an outer surface 23. An obturator 25 includes a handle 27 and a shaft 30 which extends to a sharp tip 32. When the obturator 25 is operatively positioned, the sharp tip 32 extends beyond the distal end 21 of the cannula 14. With this orientation, the trocar 10 and obturator 24 can be inserted through body tissue, such as that forming an abdominal wall 34 which defines an abdominal cavity 36. Of particular interest to the present invention are two regions of the cannula 14 which are axially disposed relative to each other. These regions include a first region 41 which is disposed at the distal end 21 of the cannula 14 and a second regions 43 which is disposed proximally of the first region 41. In accordance with the present invention, these regions 41 and 43 are provided with different surface finishes for reasons discussed in greater detail below. One of the reasons takes into consideration the entry force which must be applied to the obturator 24 as the trocar 10 is inserted through the body wall 34. This entry force is illustrated by an arrow 38 in Figure 1. It is desirable to maintain this entry force at a minimum in order to facilitate placement of the trocar 10. In accordance with the present invention, one method for reducing the entry force along the arrow 38 is to reduce the coefficient of friction between the cannula 14 and the tissue of the wall 34. This can be accomplished by reducing the roughness of the outer surface 23 in the first region 41.

In order to facilitate insertion of the trocar 10 and obturator 25, it is desirable to provide the first region 41 with a surface finish which minimizes the coefficient of friction between the cannula 14 and the body wall 34. It has been found that insertion forces such as 9 pounds associated with the prior art devices, can be reduced to 7 pounds, for example, by providing the first region 41 with a surface finish having a reduced coefficient of friction.

Referring now to Figure 2, it will be noted that the cannula 14 is operative disposed so that the working channel 16 extends across the body wall 34 and into the body cavity 36. With the cannula operatively disposed, the obturator 24 has been removed from the working channel and replaced with the fiberoptic instrument, such as an endoscope 50 having a light 52 at its distal tip. When the cannula 14 is operative positioned, the second region 43 of the cannula 14 is disposed in contact with the tissue of the body wall 34.

It will also be noted that in this operative position, the first region 41 of the cannula 14, and perhaps portions of the second region 43, are exposed to the light 52 associated with the endoscope 50. Any attempt to view the abdominal cavity 36 through the endoscope 50, or through other instruments inserted through other trocars, would be hindered by reflection of the light 52 on the outer surface 23 of the cannula 14.

Surface finishes, particularly onmetal instruments, are commonly designated by the distance between peaks in the geometry of the roughened surface. When the peaks are closely spaced, the surface is smoother and more glossy. When the peaks are spaced, the surface is more dull and has an increased roughness with a corresponding increase in coefficient of friction. The distance between peaks, which is used as a measure of roughness, is commonly described in units of microinches.

In a preferred embodiment of the invention, the outer surface 23 in the first region 43 of the cannula 14 is provided with a surface finish having a roughness ranging between 20 and 50 microinches. This roughness in the best mode of the invention is about 32 microinches which generally equates to an entry force of 7 pounds for a cannula 14 having a 12 millimeter diameter. In order to avoid the problem associated with glare, the outer surface 23 can be provided with a roughness in a range between 16 and 50 microinches. The characteristics at the lower end of this range provide for more glare than those at the higher end of the range. As noted, the best mode of the invention provides the surface 23 in the first region 41 with a roughness of about 32 microinches.

When the cannula 14 is fully inserted, as illustrated in Figure 2, the second region 43 is in contact with the abdominal wall 34. In order to retain the cannula 14 in this operative position while various instruments are being inserted and removed from the working channel 16, it is desirable for the outer surface 23 in the second region 43 to be provided with a surface finish which has a relatively high degree of roughness. This equates to a high coefficient of friction, both static and dynamic, which facilitates retention of the cannula 14 in its operative position.

In general, it has been found that a surface finish providing roughness in a range between 200 to 1000 microinches is preferred for this purpose. In the best mode of the invention, the outer surface 23 in the region 43 has a roughness of about 250 microinches. This of course greatly exceeds the roughness necessary to prevent glare so this solution addresses both problems relating to axial stability and glare.

Although the first and second regions 41 and 43 respectively are disposed in juxtaposition in the foregoing embodiments, it may be desirable to separate these regions as illustrated in Figure 3. In such an embodiment a third region, designated by the reference numeral 50, can be disposed between the first region 41 and second region 43. Since this third region 50 does not contribute greatly to either of the problems associated with insertion forces or axial stability, the primary objective of the third region 50 is merely to reduce glare. For this reason, the texture of the outer surface 23 in the third region 50 may be provided with a roughness as low as 16 microinches. On the other hand, manufacturability may be increased if the roughness factor of the third region 50 is maintained at the same level as that of the region 41. Thus in a preferred embodiment, the regions 41, 50 and 43 have roughness factors of 32, 32 and 225, respectively. Alternatively, the third region 50 may provide a gradual change in the roughness from that associated with the region 41 to that associated with the region 43.

The length of the respective first, second and third regions 41, 43 and 50 may vary widely within the concept of the present invention. In general, the first and second regions 41 and 43 respectively may have axial lengths ranging between 0.75 and 1.25 inches. In an embodiment such as that illustrated in Figure 3, each of the regions 41, 43 and 50 has an axial length of about one inch. In an embodiment such as that illustrated in Figures 1 and 2, the axial length of the first region 41 may range between 0.75 and 1.25 inches while the axial length of the second region 43 may range between 2.50 and 3.00 inches. In a preferred embodiment of the invention, the first region 41 is one inch in length, and the second region 43 is 2.75 inches in length.

In a further embodiment, the roughness of the outer surface 23 ' is graduated along the entire length of the cannula 14 as illustrated in Figure 4. Thus, the cannula 14 can be provided with a relatively low roughness factor such as 16 at its distal end 21, and a relatively high roughness factor such as 225 at its proximal end 18. Between the distal and proximal ends, the roughness factor would increase with progressive proximal positions (illustrated by an arrow 52) along the cannula 14.

Various methods can be used to provide the degree of surface finish desired for the regions 41, 43, and 50. By way of example, surface roughness can be achieved by milling, electron beam cutting, laser cutting, electrochemistry, barrel finishing, electrolytic grinding, roller burnishing, grinding, honing, polishing, lapping, extruding or die casting.

In a preferred method illustrated in Figure 5, the regions 41 and 43 are bombarded by grits 61 and 63 which are projected from nozzles 65 and 67, respectively. The degree of roughness achieved by this method is dependent upon several parameters, such as the types of material included in the grits 61, 63, the size of the grit particles, the pressures exerted by the grits 61, 63 on the surface 23, as well as the distances of the nozzles 65, 67 from the surface 23. A further factor which affects the surface roughness in both of the regions 41 and 43 is the nature of the material forming the cannula 14. For purposes of explanation, the parameters associated with the nozzle 65 include a pressure which is designated P_: and a distance designated d_x . With respect to the nozzle 67, the pressure is designated P₂ while the distance is designated d₂. In a process wherein the cannula 14 is formed from stainless steel, a surface finish providing a roughness of 32 is achieved in the distal section 41 with a grit comprising glass beads having a diameter of about .008 inches, a pressure P_l of 80 psi, and a distance d of about 5 inches. In the proximal region 43, a surface finish in the range of 225 microinches can be achieved with a grit 63 formed from aluminum oxide and beads having a diameter of about .005 inches. In this case, the pressure P₂ is about 50-60 psi and the distance d₂ is about 4 to 5 inches. Although the surface treatments associated with the regions 41 and 43 can be accomplished using two nozzles 65, 67, it may also be possible to use a single nozzle and a single grit where only pressure and distance are varied to provide different surface finishes. Another method for manufacturing the multi- textured cannula 14 is by way of a molding process as illustrated in Figure 6. In this case, separate dies 70, 72 are provided with cavities which mold the desired surface finish as the cannula 14 is formed. In this molding process, formation of the rougher surface finish associated with the second region 43 is easily accomplished by providing substantially the same surface finish on the cavity of the molds 70, 72. This molding process is of particular interest to embodiments of the cannula 14 which are formed from plastic. In such an embodiment wherein glare is of a lesser concern, the finish on the surface 23 associated with the first region 41 may be about 32 microinches, while the finish associated with the region 43 may be about 250 microinches.

There are many variations on the foregoing concept of a multi-textured cannula. Different embodiments as well as methods of manufacture will now be apparent in order to achieve a single solution to the problems of entry force, glare, and axial movement. Multiple regions of the cannula 14 can be provided with surface finishes which are either constant or graduated. Certainly there will be many variations within the ranges disclosed for particular embodiments and procedures. In a grit blasting process such as that disclosed with reference to Figure 5, many variations in the bombardment parameters will be possible.

Given the wide range of these variations, which are all within the scope of this concept, one is cautioned not to restrict the invention to the embodiments which have been specifically disclosed and illustrated, but rather encouraged to determine the scope of the invention only with reference to the following claims.

Claims

Multi-textured Cannula and Method for Making SameCLAIMS

1. A medical device adapted to provide access across body tissue and into a body cavity, comprising: a cannula having an axis and being adapted for insertion across the body tissue and into the body cavity; a wall of the cannula extending between a proximal end and a distal end of the cannula, the wall having an outer surface adapted to contact the body tissue when the cannula is moved through the body tissue and operatively disposed across the body tissue; first portions of the wall of the cannula providing the outer surface with a surface finish having a first roughness,- second portions of the wall of the cannula providing the outer surface with a surface finish having a second roughness when the cannula is operatively disposed across the body tissue; the first portions of the wall of the cannula being disposed distally of the second portions of the wall of the cannula; and the first roughness being less than the second roughness.

2. The medical device recited in Claim 1 further comprising: third portions of the wall disposed between the first portions of the wall and the second portions of the wall and providing the outer surface with a surface finish having a roughness which increases with increasing proximal positions along the wall of the cannula.

3. The medical device recited in Claim 1 wherein the first roughness associated with the first portions of the wall of the cannula is in a range between 16 and 50 microinches.

4. The medical device recited in Claim 3 wherein the second roughness associated with the second portions of the wall of the cannula is in a range between 200 and 1000 microinches.

5. The medical device recited in Claim 1 wherein the first portions of the wall of the cannula have an axial length in a range between 0.75 and 1.25 inches.

6. The medical device recited in Claim 5 wherein the second portions of the wall of the cannula have an axial length in a range of 2.50 and 3.0 inches.

7. The medical device recited in Claim 1 wherein the cannula forms part of an access device.

8. The medical device recited in Claim 7 wherein the access device is a trocar.

9. A method for preparing the surface of an access device adapted to extend across body tissue and into a body cavity, the method comprising the steps of: 14 providing the access device with a cannula having an axis and an outer surface extending between a distal end and a proximal end; bombarding a first section of the outer surface of the cannula with a first grit having first parameters including a first material, a first particle size, a first distance and a first pressure; bombarding a second section of the outer surface of the cannula with a second grit having second parameters including a second material, a second particle size, a second distance and a second pressure; and during the second bombarding step changing one of the first parameters so that the second parameters associated with the second grit are different than the first parameters associated with the first grit; whereby the first section of the outer surface of the cannula has a first surface finish resulting from the first bombarding step, the second section of the outer surface of the tube has a second surface finish resulting from the second bombarding step, and the first surface finish is different than the second surface finish.

10. The method recited in Claim 9 wherein: the first bombarding step includes the step of bombarding the first section at the distal end of the cannula; and the second bombarding step includes the step of bombarding the second section proximally of the first section of the outer surface of the cannula.

11. The method recited in Claim 10 wherein the second bombarding step includes the step of bombarding the second section of the outer surface of the cannula to provide the second surface finish with a higher degree of roughness than the first surface finish.