US3727506A

US3727506A - Microtome blade holder

Info

Publication number: US3727506A
Application number: US00140678A
Authority: US
Inventors: D Taylor; D Pease
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-05-06
Filing date: 1971-05-06
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17

Abstract

A holder for rigidly mounting a conventional razor blade on a microtome, the blade being adhesively secured to the holder on a precisely ground mounting face defined downwardly by an upwardly directed shoulder and an undercut groove. Assembly of a blade on the holder is accomplished by first coating one face of the blade and the mounting face of the holder with a flowable adhesive such as cyano acrylate polymerizing cement, then pressing the coated face of the blade against the upper edge of the holder, then pivoting the blade about that line into full contact with the mounting face, thus squeezing excess adhesive downwardly into the undercut groove, and finally sliding the blade downwardly so that its base bottoms against the shoulder. The shoulder must be sufficiently shallow to insure that no portion of the shoulder is exposed when the blade is mounted thereon, so that no obstruction impedes the downward sliding movement of a tissue section. Removal of a used blade is accomplished by inserting a pointed tool into the groove and prying the blade away from the holder.

Description

United States Patent 91 Taylor et a1.

[451 Apr. 17, 1973 MICROTOME BLADE HOLDER [76] Inventors: Dermot B. Taylor, 3914 Sierks Way, Malibu, Calif. 90265; Daniel C. Pease, 13011 Sunset Boulevard, Los Angeles, Calif. 90049 [22] Filed: May 6,1971

21 App]. No.: 140,678

Primary Examiner-Andrew R. Juhasz Assistant ExamirierW. D. Bray AttorneyMiketta, Glenny, Poms & Smith ABS'I RACT A holder for rigidly mounting a conventional razor blade on a microtome, the blade being adhesively secured to the holder on a precisely ground mounting face defined downwardly by an upwardly directed shoulder and an undercut groove. Assembly of a blade on the holder is accomplished by first coating one face of the blade and the mounting face of the holder with a flowable adhesive such as cyano acrylate polymerizing cement, then pressing the coated face of the blade against the upper edge of the holder, then pivoting the blade about that line into full contact with the mounting face, thus squeezing excess adhesive downwardly into the undercut groove, and finally sliding the blade downwardly so that its base bottoms against the shoulder. The shoulder must be sufficiently shallow to insure that no portion of the shoulder is exposed when the blade is mounted thereon, so that no obstruction impedes the downward sliding movement of a tissue section. Removal of a used blade is accomplished by inserting a pointed tool into the groove and prying the blade away from the holder.

3 Clailm, 6 Drawing Figures MICROTOME BLADE HOLDER BACKGROUND AND SUMMARY OF THE INVENTION:

This invention relates generally to razor or similar disposable blade holders, and more particularly to such a holder especially adapted for mounting razor blades in a microtome or similar precision cutting instrument.

Microtomes are machine tools extensively used for cutting thin sections of animal or vegetable tissue for microscopic examination in clinical pathology, in medical research, and other medial areas. The sections, typically only a few microns in thickness, are usually sliced from a block of tissue which has been frozen or plasticized for rigidity. The problems presented in the design and use of knives in these machines are different from and generally much more severe than those which occur in other fields, such as surgical knives and the like.

In a microtome, a block of biological tissue, usually either frozen or embedded in wax or plastic, is moved past an accurately positioned cutting edge, and a very thin section of the tissue is sliced from the block. This section of tissue, typically less than microns in thickness, must slide smoothly across the front surface of the knife in order to prevent its being deformed or torn. After the cut is completed and before the next stroke, the block of tissue is advanced mechanically by a precise distance, equal to the thickness of the section to be cut. The block of tissue is then again moved past the cutting edge and another section is cut therefrom. The thickness of the section and the cleanness and uniformity of the slicing action quite clearly depend upon the accurate positioning and sharpness of the knife used.

The conventional microtome knife is a rigid slab of special steel, approximately 4 to 10 inches long and of a wed ge-shaped cross section, the apex of the wedge constituting the cutting edge and being directed generally upwardly. The knife is held in the microtome in an inclined position so that its center line is about 30 to the plane of movement of the tissue. The frozen or plasticized tissue, cut by the knife, has many of the characteristics of a solid block of ice, and the force exerted on cutting edge of the microtome knife by the tissue block is considerable. Therefore the knife must have sufficient rigidity to resist this force. Not only must the cutting edge of the knife resist this force but it must not deflect while so resisting. If the knife edge is deflected by the cutting force, the section may not have a uniform thickness and hence may be unusable.

Clearly then the knife for a microtome must be extraordinarily rigid and maintain its shape and position within very close tolerances despite being subjected to considerable force on its cutting edge. Moreover, with such a fine cut, the cutting edge of the microtome knife must be uniform, straight and as sharp as it is possible to achieve. These specific requirements are unique to knives for use in microtomes, and hence knives suitable for other applications are not suitable for use in microtomes.

The major problem presented by a conventional microtome knife is sharpness. Conventional microtome knives are made as sharp as possible, but this sharpness heretofore has not approached the sharpness attained by a conventional razor blade. The reasons for this lack of sharpness are primarily economic, i.e. there is not enough demand for microtome knives to justify spending the money required for research and production of a resharpenable microtome knife which would be as sharp as a modern razor blade.

Not only are microtome knives not as sharp as razor blades, but after a few cutting strokes in a microtome, the sharpness of a microtome knife is reduced. Eventually the cutting edge of the microtome knife becomes so dull or nicked that the knife is unusable and then the blade must be resharpened. Current medical practice is to purchase a specially made microtome knife together with a complex and expensive machine to sharpen the microtome knives. Even with such equipment the cutting edge achieved does not approach in sharpness the edge on a modern razor blade available through conventional sales outlets.

Another advantage of the razor blade is that it typically has a coating of plastic which facilitates movement of a tissue section past the cutting edge.

Therefore it is desirable to use a commercially made razor blade as the cutting edge in a microtome knife and thereby utilize the sharpness of the razor blade to cleanly cut thin tissue sections. However, there are many problems presented by such an improvement before it would be practical. One problem is presented by the flexibility of a razor blade. Another problem associated with the use of a razor blade in a microtome is the accurate positioning of the razor blade relative to the plane of movement of the tissue block.

The principal object of this invention is to provide a novel holder for mounting a razor blade in a microtome or the like.

Other and additional objects of this invention are to provide such a blade holder which will rigidly support the razor blade subjected to the forces required to cut a frozen or plasticized block of tissue; to provide a blade holder which will locate the razor blade with the required accuracy to cut a thin slice of tissue from a frozen or plasticized block; to provide a blade holder which supports the blade along its surface to prevent the blade from buckling and breaking away; to provide a blade holder with a blade thereon, which provides a smooth upper surface over which the thin sections of frozen or plasticized tissue may move after being cut; to provide a blade holder which will accurately align the cutting edge of the razor blade thereon with respect to the frozen block; to provide a blade holder which will accurately align more than one razor blade thereon; to provide such a blade holder from which the razor blades can be easily removed when they become dull, and to which replacement blades can be mounted; and to provide such a blade holder which is inexpensive to manufacture, adapted for use in existing microtomes, and which is easy and convenient for a technician to use.

The present blade holder is generally V-shaped in section with its apex directed generally upwardly. Its front surface is inclined forwardly from the plane of tissue movement by approximately 30, and its rear surface is inclined to that plane by about 10 or less. Thus the apex angle of the holder may be 20 or thereabouts.

The front surface of the holder includes a precisely ground mounting face extending downwardly from the upper edge or apex, and defined downwardly by an undercut groove and an upwardly directed shoulder, both the groove and shoulder being parallel to the apex.

Thus the mounting face is recessed rearwardly from the front surface of the holder by the depth of the shoulder. That depth is desirably equal to or slightly less than the thickness of the razor blade to be mounted thereon. In any event, no portion of the shoulder may be permitted to be exposed when the razor blade is in its operative position. As will be understood, the exposed portion of the shoulder would then constitute a partial obstruction to the smooth downward sliding movement of a tissue section, and might deform or tear the section.

In assembling a blade on the holder, the operator first coats one face of the clean blade and the mounting face of the holder with a flowable adhesive such as cyano acrylate polymerizing cement and then presses the coated face of the blade against the upper edge of the holder, with the blade cutting edge projecting slightly above the holder apex. The operator then pivots the blade about the apex into full contact with the mounting face, thus squeezing any excess adhesive downwardly into the undercut groove. Finally the operator slides the blade downwardly so that its lower edge of base bottoms against the shoulder. For maximum rigidity of the blade cutting edge, it is essential that the distance between the apex and shoulder be virtually equal to the distance between the base edge of the blade and the beginning of the bevel of the blade cutting edge.

After a blade has become too dull for further use, the

operator can easily remove it from the holder by inserting a pointed tool in the undercut groove of the holder and then prying the blade loose from its adhesive attachment to the holder mounting face. Any adhesive remaining on the holder should of course then be removed by a suitable solvent such as nitromethane, dimethylsulfoxide or dimethylformamide, before a new blade is mounted thereon. The invention will be better understood from a reading of the following description of a preferred embodiment of the invention, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a simple microtome having mounted thereon a holder in accordance with the present invention; in dotted outline there is shown an illustrative path of movement of a tissue section after being cut, together with the hands of an operator.

FIG. 2 is an elevational view on an enlarged scale of the holder having mounted thereon a razor blade in accordance with the present invention and, fragmentarily shown, two adjacent blades mounted on the holder.

FIG. 3 is a sectional view on a greatly enlarged scale taken on arrows III-III of FIG. 2.

FIG. 4 is a sectional view similar to FIG. 3, but showing the relationship of a razor blade and the holder during assembly.

FIG. 5 is a view of a conventional double edged razor blade, showing cuts which may be made in order to adapt one-half of the complete blade for use in accordance with the present invention.

FIG. 6 is a fragmentary view, similar to FIG. 2, showing a used blade being removed from the holder.

DETAILED DESCRIPTION Referring now to the drawing, in FIG. 1 there is indicated generally a simple microtome operated by hand having mounted thereon a holder in accordance with the present invention. As will be understood, the particular design of the microtome is immaterial to the present invention, which is applicable to virtually all microtomes presently used. The holder in accordance with the present invention is indicated generally at 12 and is desirably made of strong rigid material such as steel. The holder may be of any suitable length, illustratively about 6 inches. Holder 12 has mounted thereon a razor blade indicated generally at 14, and a typcial path of movement of a tissue section after being cut is shown in dotted outline at 16.

In FIG. 2 there is shown, on an enlarged scale, a portion of holder 12 having mounted thereon blade 14 as well as, fragmentarily shown,

adjacent blades

18 and 19.

As will be understood by reference to FIG. 3, holder 12 is generally wedge-shaped as seen in section, having a rear wall 20 and a front wall 21. In the upper portion of the holder there is formed a-precision mounting face 22, recessed from the plane of wall 21 and desirably parallel thereto. Mounting face 22 and rear wall 20 join upwardly at upper edge or apex 25. Angle A of apex 25 is desirably about 20. The plane of movement or travel of the tissue block being cut is indicated at 26, and rear wall 20 of the holder is inclined forwardly from that plane by an angle B, which may be approximately 10.

Precision mounting face 22 is defined downwardly by an undercut groove indicated generally at 30, here shown as semicircular in profile, although the groove may assume any other convenient shape. Groove 30 terminates downwardly in a shoulder 32 which is perpendicular to the plane of mounting face 22. Blade 14 is mounted on holder 12, having its cutting edge 34 directed generally upwardly, and its lower wall or base 36 bottomed against shoulder 32. The blade is retained in position by a coating of adhesive 38. When the adhesive used in retaining the blade and holder in assembled relation is flowable, as is presently preferred, it is important to minimize, and preferably to eliminate, the possibility that some of the excess adhesive will flow upwardly as seen in FIG. 3 beyond apex 25 of the holder. If such adhesive does flow in that direction, it would harm the tissue block during its downward movement while a section is being cut. In FIG. 4 there is shown a step in assembly of the blade and holder in order to minimize leakage of the adhesive upwardly around apex 25. Thus, a coating of adhesive 38 is applied to the precision mounting face 22 of the holder. A small amount of adhesive may also be applied to the rear face of blade 14, but such application of adhesive to the blade itself should be primarily in the lower portion of the blade as seen in FIG. 4. The blade is then pressed against the apex, and the blade is then pivoted about the apex as a fulcrum, maintaining a tight line of contact between the blade and the apex, and thereby preventing adhesive from flowing upwardly beyond the apex. Thus the entire face of the blade is swung into contact with adhesive 38 on the mounting face 22, and in FIG. 4, in dotted outline, there is shown the lower portion of the blade after being so swung. The blade is then moved downwardly so that its base 36 bottoms against the shoulder 32, as seen in the completely assembled view FIG. 3. It is to be noted that, during the swinging movement just referred to, as well as the downward sliding movement into the position of FIG. 3, a certain amount of excess adhesive will be forced downwardly along face 22, and will be received in the undercut groove 30. The groove thus serves in effect as a sump, and prevents the possibility that adhesive may flow onto shoulder 32 where it would form a sticky deposit difficult to clean off.

Ideally shoulder 32 is made to be precisely prependicular to the plane of the precision mounting face 22. It is important that the included angle forming shoulder 32 be not an obtuse angle. If any tolerance is permitted in the manufacture, it must be in the direction to make the included angle acute, for example 88 or 89. As will be understood, if the included angle of shoulder 32 were greater than 90, there would be an inaccurate bottoming of blade 14 on the holder.

With particular reference to the upper portion of FIG. 3, in the region of apex 25, it will be seen that, as is conventional, the upper end portion of blade 14 is beveled at 40 to the cutting edge 34. For maximum strength and rigidity of the assembly, apex should be as close as possible to the base of bevel 40.

The razor blade to be used in accordance with the present invention may be of the single edge injector type; or, preferably, one-half of a conventional double edged blade. Such a double edged blade is shown in FIG. 5, including an upper portion indicated generally at 14, the blade previously referred to in the above description. Similarly, the blade includes an identical lower portion indicated generally at 45, the two blade portions being symmetrically disposed about the longitudinal center line of the complete blade. End portions 46 and 47 of the blade may be cut or broken off, in order to convert the double edged blade into a pair of blades usable in accordance with the present invention.

Removal of a used blade is easily accomplished in accordance with the present invention. As shown in FIG. 6, the undercut groove of holder 12 is sized to receive the end of a small tool, indicated generally at 50, the end portion 51 desirably constituting a hook and thus serving to pull the blade loose from its adhesive mounting on holder 12. The blade thus removed is of course discarded. After removal of a used blade, the holder, and particularly the precision mounting face 22, is cleaned of any remaining adhesive by suitable solvent means.

A typical adhesive usable in the present invention is cyano acrylatc polymerizing cement, and a solvent for removal of excess or remaining adhesive after removal ofa used blade may be, for example, nitromethane.

Groove 30 not only serves as a sump as discussed above, but is additionally advantageous during manufacture of the holder in insuring that the blade will be positioned as exactly as possible in its proper position on the holder. As previously pointed out, apex 25 must be as nearly as possible exactly aligned with the base of bevel on the blade for maximum rigidity of the assembly. If no groove were used, and if the precision mounting face 22 and indexing shoulder 32 were formed by a single grinding operation, several problems arise which would seriously militate against the desideratum of accurate alignment of apex 25 with the base of bevel 40.

Two of the major problems, discussed in detail below, are summarized as follows:

1. Maintaining true planarity of indexing shoulder 32 intersecting the plane of mounting face 22 at a sharp right angle.

2. Accurately controlling the distance from indexing shoulder 32 to apex 25.

With reference to maintaining true planarity of shoulder 32, it will be understood that the use of a grinding wheel or similar movable abrasive member to form precision mounting face 22 would inevitably fail to form a sharp interior right angle at the intersection of face 22 and shoulder 32. Wear on the grinding wheel edge would produce a curved contour of that intersection, preventing accurate bottoming of the base of the razor blade on the shoulder.

With reference to the accurate control of the distance from indexing shoulder 32 to apex 25, it will be evident that the process of grinding or otherwise forming the precision mounting face 22 produces a shift downwardly of apex 25 by a distance several times greater than the depth by which the mounting face'22 is recessed from the plane of front wall 21 of the holder. Specifically, the downward shift of apex 25 will be equal to the cotangent of angle A multiplied by such recessed depth. If angle A assumes the preferred value of 20, cot A 2.75, and the downward shift of the apex will thus be almost 3 times the recessed depth. By the same token, and more important for present purposes, variations in the apex downward shift from nominal will similarly be almost 3 times the variations from nominal of the recess depth. Thus the tolerance of the recessed depth would have to be about one-third of what would otherwise be permissible in order to maintain the distance from apex 25 to shoulder 32 within acceptable limits of accuracy.

Modifications and changes from the illustrative forms and dimensions hereinabove described and illustrated are within the contemplation of the invention, and are intended to be embraced within the scope of the appended claims.

We claim:

1. A holder for rigidly mounting a razor balde in a microtome or the like, said blade having a cutting edge and a base edge parallel to the cutting edge, comprisa block of strong rigid material, wedge shapedin section, having an upper apex edge, the front surface downwardly from the edge constituting a planar mounting face defined downwardly by an undercut groove terminating in an upwardly directed shoulder projecting forwardly from the plane of the mounting face by a distance no greater than the thickness of a razor blade to be mounted thereon, the groove and shoulder being parallel to the apex edge.

2. The invention as defined in claim 1 wherein the shoulder lies in a plane perpendicular to the mounting face.

3. The invention as defined in claim 2 wherein thedistance from the plane of said shoulder to the apex edge is slightly less than the depth of a blade to be mounted thereon, whereby the blade cutting edge projects only slightly above the apex edge when the razor base is in abutting contact with the shoulder.

Claims

1. A holder for rigidly mounting a razor blade in a microtome or the like, said blade having a cutting edge and a base edge parallel to the cutting edge, comprising: a block of strong rigid material, wedge shaped in section, having an upper apex edge, the front surface downwardly from the edge constituting a planar mounting face defined downwardly by an undercut groove terminating in an upwardly directed shoulder projecting forwardly from the plane of the mounting face by a distance no greater than the thickness of a razor blade to be mounted thereon, the groove and shoulder being parallel to the apex edge.

3. The invention as defined in claim 2 wherein the distance from the plane of said shoulder to the apex edge is slightly less than the depth of a blade to be mounted thereon, whereby the blade cutting edge projects only slightly above the apex edge when the razor base is in abutting contact with the shoulder.