US3487739A

US3487739A - Ultramicrotome

Info

Publication number: US3487739A
Application number: US547714A
Authority: US
Inventors: Alan P Murphy; George L Mcneil
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1966-05-02
Filing date: 1966-05-02
Publication date: 1970-01-06
Anticipated expiration: 1987-01-06

Description

A. P. MURPHY ET AL mmmmsw ULTRAMIGROTOME Filed May 2, 1966 2 Sheets-$heet 1 INVENTORS Alon P. Murphy George L. McNeil Jan. 6, 1970 A. P. MURPHY ET AL fifiwfiw ULTRAMICROTOME Filed May 2, 1966 2 Sheets-Sheet 2 INVENTORS- Alan P. Murphy Fi 2 George L. McNey ATTORNEY United States Patent 3,487,739 ULTRAMICROTOME Alan P. Murphy, Colerain Township, Hamilton County,

Ohio, and George L. McNeil, deceased, late of Colerain Township, Hamilton County, Ohio, by Anna Louise McNeil, executrix, Colerain Township, Hamilton County, Ohio, assignors to The Procter & Gamble Company, Cincinnati, Ohio, a corporation of Ohio Filed May 2, 1966, Ser. No. 547,714 Int. Cl. B26d 7/06 U.S. Cl. 83-410 6 Claims ABSTRACT OF THE DISCLOSURE An ultramicrotome for consistently cutting highquality ultrathin specimen sections for examination in the electron microscope. In its preferred form, the ultramicrotome has a marble base having a negligible coefiicient of expansion at normal room temperatures. A specimen rod is attached to and extends from the base at one end, and a knife edge is mounted on the other end of the base. A suitable mechanism is provided for moving the distal end of the specimen rod in a closed path such that the specimen moves substantially in a straight line as it passes over the knife edge when cutting a sampie. Consistently good samples having a thickness averaging 250 angstrom units are made with this instrument.

This invention relates to an ultramicrotome for cutting ultrathin specimen sections for direct examination in the electron microscope. More particularly, the invention relates to an ultramicrotome that is extremely reliable and accurate in cutting ultrathin sections of various hard and soft specimens such as, for example, sections of mature human tooth enamel to a thickness of only about 250 angstrom units.

The use of an utramicrotome for cutting thin sections from biological specimens for examination in the electron microscope is a known and well established laboratory procedure. The cutting of ultrathin sections is extremely difiicult to accomplish with consistently good results, however, particularly when the sections are being cut to a thickness of only about a few hundred angstrom units. Ultramicrotomes for cutting samples to such thicknesses require maximum stability between the sample being sectioned and the knife edge. Previously known ultramicrotomes have been excessively sensitive to and substantially affected by thermal and mechanical forces that may normally be encountered under routine laboratory conditions.

The principal object of the present invention is to overcome the diificulties that have been encountered in prior ultramicrotomes when cutting ultrathin sections particu larly from hard substances such as fully maturated human tooth enamel.

Another object of the invention is the provision of an ultramicrotome that is essentially free of thermal and mechanical instability in order that a plurality of high quality ultrathin sections can be cut in succession.

Still another object of the present invention is the provision of an ultramicrotome having a positive drive throughout its cutting stroke in order to cut an ultrathin section of uniform thickness and leave a unifo;mly smooth surface for examination in the electron microscope.

A further object of the invention is the provision of an ultramicrotome which is designed for the cutting of ultrathin sections and in particular, the cutting of ultrathin sections of hard materials including but not limited to human tooth enamel, relatively soft metals and the like.

The nature and substance of the invention can be briefly summarized as comprising an ultramicrotome having a base formed from a block of material which has a coefficient of expansion of approximately zero in its horizontal plane. An elongated and flexible specimen rod projects through an enlarged bore in said base. One end of the specimen rod is secured to the base, the other end of the rod is free so that it can be readily flexed. A specimen is suitably secured to the free end of the specimen rod. A knife edge is supported by the base in close proximity to the free end of the specimen rod. The free end of the specimen rod is moved in a closed path by means of a suitable mechanism including an eccentric drive. A sample is cut from the specimen where it is moved over the knife edge during the cutting stroke portion of the path of movement of the free end of the specimen rod. The elements of the drive are so constructed and arranged that the specimen rod is essentially unfiexed just prior to the initiation of the cutting stroke. Means are provided to produce rectilinear motion of the free end of the specimen rod as the specimen is passed over the knife edge. The drive mechanism is so arranged that the amount of fiexure in the specimen rod is minimal during the cutting stroke. The use of a base material having a coefficient of expansion of approxi mately zero substantially eliminates thermal forces that can affect the quality of cut samples.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawings in which:

FIGURE 1 is an elevation partially in cross section showing the entire ultramicrotome of the present invention.

FIGURE 2 is an elevation of the drive mechanism for the specimen. rod taken on the line 2-2 of FIGURE 1 and including a schematic showing of the control for the drive mechanism.

FIGURE 3 is a fragmentary elevation in cross section taken on the line 3 3 of FIGURE 2 but extended to include the elements on the left of the section line 2 2 of FIGURE 1.

FIGURE 4 is a fragmentary view taken in elevation to illustrate the relative position of the drive bearing and the specimen rod prior to the initiation of cutting when the rod is substantially unflexed and the drive bearing momentarily breaks contact with the specimen rod.

Referring now to the drawings and in particular, FIG- URE 1 thereof, the ultramicrotome of the present invention includes a massive base 10 which is longitudinally cored out at 11 and has openings to atmosphere at 12 and 13. A conventional knife stage 14 having a knife edge 15 is mounted on one end of the base as shown. When cutting hard materials, the knife edge 15 is preferably formed from a diamond.

The mechanical and thermal stability of the device is achieved by the utilization of marble for the base 10. In particular, marble from the State of Georgia in the United States of America is preferred as it has a coetficient of thermal expansion of approximately zero at normal room temperatures. In fact, it has been found that marble from the quarry of the Georgia Marble Company of Tate, Georgia is preferred in the practice of the invention as its coeificient of expansion at room temperature (about 70-75 F.) measured in a horizontal plane (parallel to the quarry bed) approximates zero. This is most important along the axis of specimen travel. A massive block of this marble properly oriented to provide such minimal expansion is used as the one-piece base 10.

The massive nature of the microtome base as well as its unique thermal properties result in minimizing the effects of building vibration, ambient temperature changes and the like.

A specimen rod 16 passes through the cored channel 11 and is secured at one end of the base by the use of jam nuts as shown in FIGURE 1. The rod 16 is resilient and flexible and is preferably made of a high nickel steel such as Invar. The forward end of the specimen rod 16 has a conventional chuck 17 secured thereto. The chuck 17 may be of any well known type such as a jewelers chuck or any equivalent thereof. The specimen 18 is embedded in the specimen holder 19 which is held securely by the jaws of the chuck 17.

A resistance heater 20 is wound on the rod 16 to provide a means of advancing the specimen in timed sequence with each successive cutting stroke. Power supply to the heater 20 is controlled by a conventional variable low voltage supply. The amount of expansion in the rod 16 is dependent on the length of the heater 20 and the temperautre to which it is heated. A blower 21 can be used to cool the specimen rod 16 and cause it to contract to its original position after a sufficient number of samples have been cut from the specimen 18. Normally, the blower 21 is not operated when samples are being cut. Exhaust from the blower passes through the opening 13 in the base 10.

The mechanism for driving and moving the end of the specimen rod 18 in a closed path is best seen in FIG- URES 2 and 3. The drive mechanism includes a rotatable drive member 22 mounted for rotation in the

bearings

23 and 24, which, in turn, are mounted, respectively, in the bearing housing 25 and the support member 26. Support member 26 is secured to the base 10 as by the screws 27 and the bearing housing 25 is, in turn, secured to the member 26 by screws 28 (only one shown in FIGURE 3). A worm gear 29 is attached to the drive member 22 as shown. The worm gear 29 is driven by a worm 30 mounted on shaft 31 and supported in bearings 32 and 33, the latter being attached to the support member 26.

The rotating drive member 22 has an eccentrically located central bore as at 34. A drive bearing loosely fitted over the specimen rod 16 is secured in the bore 34 as shown. The bore of the drive bearing 35 is preferably of arcuate shape as illustrated in FIGURE 3. In addition, there is substantial clearance between the bore in the drive bearing 35 and the specimen rod 16 as indicated at 36 in FIGURE 2. The drive bearing 35 is preferably made from a bearing material which is smooth, tough and long wearing. Especially preferred is Rulon which is a chemically inert material suited for use as a nonlubricated bearing which is available from the Dixon Corporation of Bristol, R.I.

From the foregoing description it will be appreciated that rotation of the drive member 22 will cause the drive bearing 35 to move in a closed circular path relative to the support member 26. The bore of the drive bearing 35 bears against the specimen rod 16 and causes its free end to be flexed and moved in a closed path with the same relative motion as the drive bearing 35 when in sole contact with the bore thereof. Cutting of the specimen 18 occurs during the cutting stroke portion of the path of movement of the specimen rod 16 during which the free end of the rod 16 moves in a rectilinear path as will be more fully explained in the ensuing description.

A vertical guide or cam 37 is secured along one side of the bearing housing 25 as shown in FIGURE 2. The guide 37 has a vertical straight surface 38 which is preferably lapped and mounted substantially perpendicular to the knife edge 15. The specimen rod 16 bears against the surface 38 for that portion of its path of movement during which a sample is cut from the specimen. This causes the rod 16 to always follow the same path during th cutt ng s oke p rt on of it p t o movement The specimen rod 16 having the specimen 18 secured thereto is so mounted at the rear of the base 10 that it is substantially unfiexed when the specimen 18 is just above the knife edge 15. The position of the drive bearing 35 relative to the rod 16 at this point in its path of movement is shown in FIGURE 4. In fact, the bearing 35 is momentarily out of contact with the rod 16 which in this position makes very light contact with the surface 38 so that the rod 16 is substantially unflexed. When the drive bearing 35 is out of contact with the specimen rod 16, it also eliminates vibrations and standing wave forms which may have been induced in the rod 16 from contact with the bearing 35 during the previous cutting stroke. On further rotation, the drive bearing 35 reengages the r specimen rod 16 whereupon the latter is moved downwardly while remaining in contact with the straight edge 38 throughout the period that a sample is being cut from the specimen 18. The drive mechanism thus provides essentially rectilinear movement of the specimen 18 over the knife edge 15. The drive mechanism also provides a positive drive of the free end of the specimen rod 16 during the entire cutting stroke portion of its path of movement. This results in mechanical stability and good cutting performance.

In its preferred form the invention is practiced such that the drive member 22 is rotated at a relatively greater speed during that portion of its cycle beginning just after a sample has been cut until just before the next sample is to be cut. This can be accomplished by a drive and control as shown schematically in FIGURE 2.

The drive and control includes a motor 42 which drives the shaft 31 through a conventional two-speed magnetic clutch 43. A pair of

contiguous cams

44 and 45 are secured for rotation to the drive member 22 (see FIG- URES 2 and 3). The cams are held in place by screws 45a. The

cams

44 and 45 can be rotatively adjusted relative to one another such that the length of the low portion 46 can be adjusted relative to the length of the high portion 47. A switch 48 is actuated by the roller 49. The switch 48 indirectly actuates the magnetic clutch 43 by means of the control 50. When the roller 49 of the switch 48 contacts the low portion 46 of the cams 44-45, the magnetic clutch 43 is actuated to drive the shaft 31 at relatively slow speed. The rotation of cams 44-45 is timed such that the shaft 31 is driven at relatively slow speed during the portion of the cycle in the movement of the rod 16 during which a sample is being cut from the specimen 18. On the other hand, when the roller 49 is raised and travels on the high portion 47 of the cams 44-45 the magnetic clutch 43 is actuated by the switch 48 through the control 49 to drive the shaft 31 at a relatively high speed during the noncutting portion in the movement cycle of the specimen rod 16. This latter action is desirable to prevent excessive heating and expansion of the rod 16 between successive cuts. It is thus possible to cut successively ultrathin samples having a thickness in the range of several hundred angstrom units.

With the use of the ultramicrotome as described above, successive ultrathin sections of high quality have been cut from relatively hard materials. In particular, consistent sections for examination in the electron microscope have been cut from fully maturated human tooth enamel to an average thickness of 250 angstrom units. In addition, sections of gold, brass and aluminum have been cut to an average thickness of 250 angstrom units to permit examination in the electron microscope. While the ultramicrotome of this invention is primarily designed for cutting hard materials, its use is not so limited. The ultramicrotome can be used with equal facility to cut sections of soft biological tissue as well.

While a particular embodiment of the invention has been illustrated and described it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of he invention a d it is te ded to cover in the appended claims all such changes and modifications that are within the scope of this invention.

What is claimed as new is:

1. An ultramicrotome comprising a base, said base being formed from a block of material having a coefficient of expansion in a horizontal plane of approximately zero at normal room temperature, an elongated specimen rod, one end of said specimen rod being secured to the base at one end, the other end of said specimen rod being free for flexing movement in a closed path, a specimen secured to the free end of said specimen rod, means for moving said free end of said specimen rod in a closed path including a cutting stroke, said means including a rotatable drive member having an eccentric bore therein, a drive bearing mounted in said bore, said free end of said specimen rod passing through said drive bearing there being substantial clearance between said rod and said drive bearing, means for rotating said drive member, a knife edge supported by said base in proximity to the free end of said specimen rod, said specimen having a sample cut from its end as it is moved over said knife edge during the cutting stroke portion of the path of movement of said specimen rod, said specimen rod being substantially unfiexed just prior to the initiation of said cutting stroke, said moving means moving the free end of said specimen rod in a rectilinear path during said cutting stroke.

2. An ultramicrotome as claimed in claim 1 wherein said means for moving the free end of said specimen rod in a rectilinear path during said cutting stroke includes a vertical guide secured to said base, said vertical guide having a straight edge, said drive bearing moving said specimen rod through the cutting stroke portion of its path of movement with the free end of said specimen rod in contact with said straight edge.

3. An ultramicrotome as claimed in claim 2 including drive and control means for said drive member, said drive and control means being operative to rotate said drive member at a relatively slow speed during the cutting stroke portion of the path of movement of said free end of said specimen rod and at a relatively higher speed during the noncutting portion of the path of movement of said free end of said specimen rod.

4. An ultramicrotome as claimed in claim 1 wherein said block of material for said base is marble.

S. An ultramicrotome as claimed in claim 4 wherein said marble is from the Tate Marble Company located in Georgia in the United States of America.

6. An ultramicrotome as claimed in claim 4 wherein said marble is from the Tate Marble Company located in the Town of Tate, State of Georgia, United States of America.

References Cited UNITED STATES PATENTS 2,739,507 3/1956 Cocks et a1 83-17O 2,753,761 7/1956 Hillier 83--17O 2,843,014 7/1958 Sitte 83170 2,875,669 3/1959 Sjostrand et al. 83-170 2,948,190 8/1960 Blum 83410 ANDREW R. JUHASZ, Primary Examiner US. 01. X,R, 83-915,

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CERTIFICATE OF CORRECTION Patent No. 3'437'739 Dated January 6, d 1970 Inventor) Alan P. Murphy and George L. McNeil deceased It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 21, "temperautre" should be temperature Column 6, line 14, delete "the Tate Marble Company" and insert a quarry Column 6, line 14, after the words "located in" insert the State of SIGNED A'ND SEALED JUN 161970 (SEAL) Attest:

Edward M. Fle r. 1 wm m I E. M: Lh" m. Attesung Officer Comissioner of Patznts