US3799029A

US3799029A - Precision trimmer for an encapsulated specimen

Info

Publication number: US3799029A
Application number: US00316627A
Authority: US
Inventors: W Cole; J Harrison; J Martich; B Kotula; T Tahmisian
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1972-12-19
Filing date: 1972-12-19
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26

Abstract

A specimen trimmer includes a carriage assembly which reciprocates a knife blade along a slanted table surface. The specimen is supported in a holder and precisely advanced by means of a micrometer screw towards the blade through an opening in the table surface. Periodically during the trimming operation, the specimen is precisely rotated with a goniometer to obtain a trapezoidal cross section of the trimmed portion of the specimen.

Description

United States Patent [19] Cole et al.

[ 51 Mar. 26, 1974 PRECISION TRIMMER FOR AN ENCAPSULATED SPECIMEN [75] Inventors: William R. Cole, Aurora; James W.

Harrison, Markham; Bruno S. Kotula, Chicago; Theodore N. Tahmisian, Oak Lawn; Jovo S. Martich, Hillside, all of I11.

[73] Assignee: The United States of America as represented by the United States Atomic Energy Commission, Washington, DC.

[22] Filed: Dec. 19, 1972 [2]] Appl. No.: 316,627

[52] US. Cl 90/38 R, 83/1, 83/9155 51 Int. Cl B23d 1/08 [58] Field of Search 83/1, 915.5; 90/38, 43,

[56] References Cited UNITED STATES PATENTS Wistedt et a] 90/24 R FOREIGN PATENTS OR APPLICATIONS 40,100 9/1956 Poland ..83/9l5.5 l,344.316 10/1963 France ..308/6R Primary Examiner-Andrew R. Juhasz Assistant Examiner-William R. Briggs Attorney, Agent, or Firm-John A. Horan; Arthur A. Churm; Hugh W. Glenn, Jr.

[ 5 7 ABSTRACT A specimen trimmer includes a carriage assembly which reciprocates a knife blade along a slanted table surface. The specimen is supported in a holder and precisely advanced by means of a micrometer screw towards the bladethrough an opening in the table surface. Periodically during the trimming operation, the specimen is precisely rotated with a goniometer to obtain a trapezoidal cross section of the trimmed portion of the specimen.

6 Claims, 3 Drawing Figures PATENIEBIARZB m4 3.799029 SHEET 1 OF 2 PRECISION TRIMMER FOR AN ENCAPSULATED SPECIMEN CONTRACTUAL ORIGIN OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the UNITED STATES ATOMIC ENERGY COMMISSION.

BACKGROUND OF THE INVENTION In order to provide extremely thin slices of a specimen for microscopic examination, the specimen is often encapsulated in an epoxy resin or other hard plastic material prior to sectioning. For instance, liquid.

resin with a curing agent is introduced into a gelatin capsule and the specimen floated on the surface of the resin. The specimen is normally saturated with a volatile dehydrating agent such as propylene oxide which evaporates while the specimen floats in the resin. After the dehydrating agent is replaced with, the liquid resin, the specimen sinks to the bottom of the capsule where it remains as the resin sets to form a hard plastic. The gelatin capsule is next dissolved away to reveal the specimen at one end of a solid epoxy block. The end portion of the block containing the specimen is trimmed to remove excess epoxy and to shape the specimen into a desired cross section.

It has been found that trapezoidally shaped sections can be conveniently handled even when sliced into sections of less than 0.1 micrometer in thickness. The trapezoidal sections can be made to adhere together at their parallel edges to form a straight ribbon as they are sliced on a suitable ultramicrotome. The wider of the two parallel edges precedes the narrower edge as the ribbon is floated on a water trough behind the ultramicrotome knife. The trapezoidal shape of each section facilitates proper alignment within the ribbon and thereby allows uniform displacement of each previously cut section as a new section is sliced. Consequently, distortion or corrugation of the ribbon or individual sections is minimized.

Previously, the trimming and shaping operation has been done laboriously by hand with razor blades while observing the specimen block under a microscope. This hand trimming technique is not only tedious and time consuming but also inaccurate. Often a portion of the specimen is cut away or insufficient epoxy is removed. Furthermore, it is very difficult to hand cut straight edge surfaces around the trapezoidal cross section. Consequently, the ribbon of specimen sections produced by the ultramicrotome may become curved or the individual sections may not adequately adhere together.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a precision trimming device for preparing specimens for subsequent ultramicrotome sectioning.

It is also an object to provide such a trimmer which can quickly and easily shape flat-edged trapezoidal cross sections in specimen blocks of hard epoxy resin.

In accordance with the present invention, a specimen trimmer is presented which includes a specimen holder and a reciprocable carriage assembly supported on a base. Means are provided with the specimen holder for its rotational adjustment about its axis and its linear advancement towards a knife mounted on the carriage assembly. The knife blade is provided with a sharp edge for trimming off portions of a specimen block held within the specimen holder as the carriage reciprocates. The blade edge is fixedly aligned at an oblique angle to the specimen holder axis and the direction of reciprocation of the carriage assembly. By adjusting the position and rotational alignment of the specimen, a precise trapezoidal cross section can be achieved at the trimmed end of the specimen block.

DESCRIPTION OF THE DRAWINGS The present invention is illustrated in the accompanying drawings wherein:

FIG. 1 is an elevation view in cross section of a precision specimen-block trimmer.

FIG. 2 is a cross sectional view taken along lines 22 of FIG. 1.

FIG. 3 is a diagrammatic illustration of one manner of cutting and shaping the specimen within the trimmer of FIGS. 1 and 2.

DETAILED DESCRIPTION Referring now to FIGS. 1 and 2 where a specimenblock trimmer is shown supported on a base 11. In general, the trimmer includes a metal table 13 having a slanting upper surface 15 on which a knife blade 17 with a sharp edge 16 is made to reciprocate. The blade is mounted on a carriage assembly 19 that can be moved back and forth with handle 20 in a direction perpendicular to the plane of the drawing in FIG. 1. The specimen block 21 is received through a central opening 23 to slightly protrude above the table surface 15 for engagement with the knife blade 17.

The specimen block 21 is firmly supported between the two jaws of a compression-type holder 25. The jaws are pivoted about an inserted pin 31 and are pressed into contact with the specimen block by a retention screw 27. An opening 33 through one side of table 13 allows access for loosening or tightening retention screw 27 after moving the carriage assembly aside. Another opening 35 through the opposite side portion of table 13 faces a recess 37 within the specimen holder. A lever 39 is removably pivoted on a fulcrum support 41 and can be used to engage and lift the specimen above the slanted surface 15 for convenient removal.

Specimen holder 25 is mounted on a vertical shaft 43 that extends downwardly into base 11 where it is supported on a pair of sliding wedge blocks 45a and 45b. Wedge block 45b is positioned horizontally by a micrometer screw mechanism 47 in engagement at the slanted surfaces with wedge blocks 45a. An index wheel 49 is attached to mechanism 47 to allow precise and measured horizontal movement of block 45b. Since block 45a supports vertical shaft 43, the measured horizontal movement of block 45b is translated into a proportional vertical movement of specimen 21 in respect to the slanted table surface 15. Of course, the slope of the intercommunicating surfaces between the wedge blocks determines the ratio of horizontal to vertical movement.

Shaft 43 is laterally supported within the hub of a goniometer wheel 51. The shaft 43 is fastened to rotate coaxially with wheel 51 but engages the inside hub surfaces with a slip fit to permit vertical translation. This type connection can be made with a spring loaded set screw or pin 52 which radially passes through goniometer wheel 51 into engagement with slot 42 of shaft 43. Also, shaft 43 merely rests on or is loosely pinned to wedge block 45a to allow relative rotation. The goniometer wheel 51 is provided with a graduated circular index for measuring the rotation of both the shaft 43 and specimen 23 about a common central axis. From the above description, it can be seen that the specimen 21 can be angularly orientated and upwardly advanced in measured amounts respecting knife blade 17.

Carriage assembly 19 is reciprocatively supported I from two guide rails 53a and 53b on two parallel arrays of bearings 57. The guide rails are preferably of unit or cast construction with the carriage assembly to ensure precision movement. The top portion of the carriage, however, includes a large circular or elongated opening 61 through which the cutting operation can be observed under a microscope (not shown).

Bearings 57 are retained in two parallel raceways 55a and 55b between the guide rails and the sides of table member 13. It is preferable that cylindrical or roller bearings be selected for use and that the bearings be arranged in the crossed roller configuration as shown in FIG. 2 with alternate rollers aligned perpendicular to adjacent rollers. Roller bearing and raceways arranged in this manner are commercially available, for instance from the Scully Jones Company, a subsidiary of the Bendix Corporation. Such bearing assemblies can be adjusted to precisely align and maintain the reciprocative motion of the knife blade 17 in respect to the specimen 21.

Knife blade 17 is securely fastened within a blade holder 14 to the underside of carriage assembly 19 and reciprocates in sliding engagement with the upper surface 15 of table 13 as the assembly is moved laterally across the inclined table surface. The table surface 15 acts as a linear support bearing at the underside of the blade to ensure stability and prevent deflection of the blade edge as it engages a hard encapsulating material such as an epoxy resin within the specimen block 21. As best shown in FIG. 2, the forward cutting edge 16 of blade 17 intercepts the specimen block at an oblique angle to the direction of carriage reciprocation to impart a smooth slicing action across the specimen block surface. Since blade edge 16 also slopes downwardly across the slanted table surface 15, it is also obliquely disposed to the central axis of the specimen block, thereby allowing side portions of the block to be trimmed. It has been found that a table slope of about 45 degrees to horizontal and the specimen axis along with a blade slope of about 7 degrees to the direction of reciprocation is particularly suited to this purpose.

It can be seen in the drawings that the blade edge 16 traverses over more than one-half of the specimen cross section during the reciprocation of the blade. This feature in combination with the downward slope of the blade permits the specimen to be cut in thin slices from its edge to its axis. Where a rounded specimen block 21 is employed the blade edge will first intercept the block along the side of the dome surface. As the specimen is advanced upwardly the blade edge 16 will approach the dome apex thus allowing the total cut to proceed at least halfway across the specimen from any direction.

In employing the specimen-block trimmer of the present invention, a specimen, for instance biological media, is encapsulated near one end surface of a hard block of epoxy or other stiff plastic material. The hard epoxy encasement is required to support extremely thin sections for microscopic analysis. To prevent dulling or otherwise damaging a precision microtome blade which is ordinarily employed for preparing such sections, it is desirable to remove as much excess epoxy material as possible. The specimen block is, therefore, secured within the trimmer as shown with the end containing the specimen under investigation directed towards the slanted table surface. It should be recognized that the specimen may not be located on or near the specimen block axis, thus requiring unequal trimming on opposite sides of the specimen.

The manner of trimming the specimen block is illustrated in FIG. 3 with dashed lines 63 representing each of a number of cutting strokes. The specimen 65 is located within the specimen block 21 and can be viewed through opening 61 in the carriage assembly either with the naked eye or under a microscope. Shaft 43 is rotated with goniometer wheel 51 to select one of the specimen sides on which trimming is to be performed. Micrometer 47 is adjusted to position the specimen block slightly above the table surface 15 prior to the trimming operation. Several slices illustrated by dashed lines 63 are made across the side portion of the specimen block to avoid biting in too deep on a single cut and deflecting the blade or damaging the specimen. The specimen block is slightly advanced by a measured amount towards the knife blade in between strokes.

After a sufficient amount of epoxy resin has been cut away to form a flat edge or surface 67a against or very near the specimen, the specimen block can be rotated by a measured angle and cutting resumed to form an adjacent edge or surface 67b. The operation is continued until the perimeter of hard resin material has been cut away from all sides of the specimen.

Although any number of straight sided cross sections can be conveniently produced with the trimmer described herein, it is preferable-that a trapezoidal cross section be cut into the specimen block as illustrated in FIG. 3. A trapezoidal shaped cross section facilitates subsequent section preparation on a suitable, commercially available ultramicrotome. The sliced trapezoidal sections will adhere together at the parallel edges to form a straight ribbon of separable specimen sections. Discrete sections are recognizable because adjacent edges along the ribbon are of unequal width. The parallel edges of each trapezoidal section are cut precisely parallel to produce a straight ribbon which can be easily recovered from the ultramicrotome blade. It will of course be understood that other shaped cross sections having parallel sides of unequal length can also be provided if more than four sides are formed. For instance adjacent corners of a cubic or rectangular cross section can be trimmed away. However, the preparation of such cross sections requires a more elaborate trimming operation than that required to trim trapezoidal sections.

From the foregoing it can be seen that the present invention provides a precision trimming device for removing tough encapsulating material from the perimeter of a specimen. Consequently, the slicing blade of the ultramicrotome used to section the specimen is not dulled as rapidly as if it were used to cut through both the encapsulating material and the specimen. The trimmer can also shape the specimen into a trapezoidal cross section with precisely parallel edges to allow the ultramicrotome to conveniently cut discrete trapezoidal sections.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A trimmer for shaping a specimen encapsulated in hard plastic material comprising:

a. a base;

b. a specimen holder supported by said base;

c. carriage assembly reciprocably mounted on said base proximate to said specimen holder;

d. adjustable means for positioning said specimen holder along a central axis thereof in respect to said carriage assembly and for rotatably adjusting said specimen holder about said central axis;

e. a knife blade mounted to reciprocate with said carriage assembly and having a cutting edge at one end'thereof aligned oblique to the direction of reciprocation and oblique to said central axis of said specimen holder; and

. a stationary table aligned above said base, in parallel and slidable communication with said knife blade, said table including an oblique passageway from the surface thereof aligned with said specimen holder for allowing advance of said specimen toward said knife blade.

2. The trimmer of claim 1 wherein said carriage assembly is supported between two guide rails having a plurality of cylindrical rollers arranged in linear arrays with alternate rollers axially aligned perpendicularly to adjacent rollers.

3. The trimmer of claim 2 wherein said carriage assembly is substantially open above said specimen to allow microscopic observance of the trimming operation.

4. The trimmer of claim 1 wherein said adjustable means comprises a micrometer positioning device for linearly advancing said specimen towards said knife blade and a goniometer device for rotatably adjusting said specimen about its central axis.

5. The trimmer of claim 1 wherein said knife blade is made of hardened steel and includes a rigid body portion and a tapered blade portion.

6. The trimmer of claim 1 wherein a fulcrum and pivotable lever are provided in combination with said table for raising said specimen substantially above the surface of said table to permit its removal from said passageway.

Claims

1. A trimmer for shaping a specimen encapsulated in hard plastic material comprising: a. a base; b. a specimen holder supported by said base; c. carriage assembly reciprocably mounted on said base proximate to said specimen holder; d. adjustable means for positioning said specimen holder along a central axis thereof in respect to said carriage assembly and for rotatably adjusting said specimen holder about said central axis; e. a knife blade mounted to reciprocate with said carriage assembly and having a cutting edge at one end thereof aligned oblique to the direction of reciprocation and oblique to said central axis of said specimen holder; and f. a stationary table aligned above said base, in parallel and slidable communication with said knife blade, said table including an oblique passageway from the surface thereof aligned with said specimen holder for allowing advance of said specimen toward said knife blade.