US3220290A

US3220290A - Microtome knife clamp with knife cooling means

Info

Publication number: US3220290A
Application number: US312957A
Authority: US
Inventors: Shandon Ernest Robert
Original assignee: C Reichert Optische Werke AG
Current assignee: C Reichert Optische Werke AG
Priority date: 1962-10-15
Filing date: 1963-10-01
Publication date: 1965-11-30
Anticipated expiration: 1982-11-30
Also published as: DE1216567B; GB975795A

Description

; NOV. 30, 1965 s oN MICROTOME KNIFE CLAMP WITH KNIFE COOLING MEANS 3 Sheets-Shet 1 Filed Oct. 1, 1963 /N (ISA/Tot Nov. 30, 1965 E. R. SHANDON 3,220,290

MICROTOME KNIFE CLAMP WITH KNIFE COOLING MEANS Filed Oct. 1, 1963 3 Sheets-Sheet 2 560 57 521227 Saw/v00 Nov. 30, 1965 E. R. SHANDON 3,220,290

MIGROTOME KNIFE CLAMP WITH KNIFE COOLING MEANS Filed Oct. 1, 1963 3 Sheets-Sheet. 3

United States Patent 3,220,290 MICROTOME KNIFE CLAMP WITH KNIFE COOLING MEANS Ernest Robert Shandon, London, England, assignor, by mesne assignments, to C. Reichert Optische Werke A.G., Vienna, Austria, an Austrian company Filed Oct. 1, 1963, Ser. No. 312,957 Claims priority, application Great Britain, Oct. 15, 1962, 38,957/ 62 5 Claims. (Cl. 83-171) This invention relates to microtomes and, more specif ically, to a microtome suitable for cutting sections from a frozen specimen.

The microtome is a precision instrument for enabling Wafer-thin sections of accurately controlled thickness, which may be of the order of a few microns, to be taken from specimens mounted thereon and comprises essentially a massive stand having a clamp holder for clamping in position an object clamp in which the specimen can be held, and a knife clamp in which a replaceable microtome knife may be gripped. To take a section from the block the two clamps are moved relative to one another so that the cutting edge of the knife slices across the face of the block or specimen at a correct inclination and tilt to produce a section of the desired thickness.

The texture of some specimens is so soft that if attempts are made to section them directly using the microtome the sections produced are so severely distorted or damaged as to be useless. To handle such specimens, the microtome is commonly provided with a freezing stage which can be substituted for the object clamp and is equipped with means for freezing the specimen. Once the specimen is frozen it adheres firmly to the freezing stage and its texture is made more suitable for withstanding sectioning. Freezing is conveniently effected by passing over the specimen a stream of carbon dioxide.

To take sections, the microtome knife must also be reduced to the temperature of the specimen as otherwise the relative warmth of the knife would melt the section whilst being cut so that it collapses into a wet slime on the knife. One method of suitably cooling the knife is to play on its surface, prior to the out being made, a jet of cooling carbon dioxide obtained from the same source as is used to freeze the specimen.

A second method which has been proposed is to clamp a thermo-electric cooling device, such as a Peltier cooling junction, directly onto the surface of the microtome knife and then to cool the knife by connecting the device to a suitable electrical circuit. By passing a unidirectional electric current through the circuit in the correct direction, heat will be extracted from the microtome knife by the cooling device and liberated at the heat sink which can be located remote from the knife. However, as microtome knives require frequent replacement they must either be individually provided with cooling devices which would be both expensive and cumbersome, or the cooling device must be so arranged that it can be transferred from knife to knife between the fitting of successive knives to the microtome. Such a process would be laborious to carry out. Furthermore, it is not practicable to use this method of electrical cooling on microtome knives less than centimetres in length as there is inadequate space on the knife to mount the cooling device.

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An object of this invention is the provision of improved means for cooling a microtome knife.

Another object of the invention is to enable a standard, unmodified microtome knife to be cooled for slicing frozen sections without having intermittently to play a stream of cooling fluid on its cutting edge.

A further object of the invention is to provide a microtome with the advantage obtained by using electrical cooling equipment for cooling a microtome knife and the advantage obtained by being able to use a standard, unmodified microtome knife with the microtome.

An additional object of the invention is the provision of an electrically cooled microtome knife clamp having means for ensuring that the knife temperature remains below a selected temperature.

Yet another object of the invention is the provision of a microtome with dual purpose clamping means serving both to grip the knife and to provide part of a thermally conductive path extending from the knife to a heat sink inside the knife clamp.

In accordance with the present invention, a microtome knife clamp is provided with jaws for gripping a knife, a mechanism for opening and closing the jaws to release and to hold the knife respectively, a heat sink provided with a cooling unit built into the clamp, and a heat-transmitting element terminating in a pad for contacting the knife and extending to the heat sink.

A microtome knife is kept cold when gripped by a knife clamp constructed in accordance with the invention, by

the conduction of heat from the knife by way of the padand heat transmitting element to the heat sink which is maintained cool by operation of the cooling unit. The

knife clamp of the invention is able to receive standard,

unmodified microtome knives and thus sectioning of frozen specimens can be effected quickly and easily without having to attach to individual microtome knives spe-- cial cooling apparatus and without having to provide special cooling apparatus for cooling the knife by discharging a stream of cooling fiuid onto it.

The cooling unit on the knife clamp may comprise a reservoir through which cooling carbon dioxide or other coolant fluid can be passed. Alternatively, the reservoir may be adapted to receive a charge of liquid air or other cooling fluid which extracts heat from the knife during vaporisation of the fluid. Suitably, the heat conducting element comprises a plate of material having good heat conducting properties such as silver, aluminum or copper and having one side forming one wall of the reservoir or heat sink and the other side shaped to form a pad having a surface contour complementary to that of the surface of the microtome knife which is to be engaged by the pad.

Means may also be provided on the knife clamp for maintaining the knife below a desired maximum temperature and/or for measuring its temperature. Such means may comprise a thermistor arranged to control an electrical circuit which regulates the operation of the cooling unit. Alternatively, or additionally, the thermistor may be arranged to control a suit-able circuit connected to temperature indicating means which provide an indication of the knife temperature.

The preferred form of cooling unit, however, comprises a thermo-electric cooling device or devices connectable in an electric circuit energisable to cause the cooling device to extract heat from its immediate vicinity. One

suitable form of thermo-electric cooling device is a Peltier' junction which is cooled when a unidirectional electrical current is passed through it in a suitable direction. A Peltier heating junction is connected in series with the cooling junction and arranged at some distance from the knife at one side of a cooling chamber through which a cooling fluid is passed. The electrical current flowing through both Peltier junctions causes the cooling junction to extract heat which is liberated at the other junction and is removed from the vicinity of the clamp by the cooling fluid.

The knife clamp of the invention may be used separately from a microtome or may be fixed permanently to it as is usually the case with precision-built microtomes. Thus the clamp of the invention is suitably combined with a microtome having a massive stand, a holder for a freezing stage, and means for effective relative movement between the clamp and the holder so that a section can be sliced from a frozen specimen on the freezing stage.

Suitably the microtome is also provided with an object clamp which may be mounted in the holder in place of the freezing stage when it is desired to take sections from an object block or a specimen not requiring freezing. The invention will now be described in more detail, by way of examples, with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic perspective view of the principal parts of a microtome;

' FIGURE 2 is a plan view of a two-part knife clamp used on the microtome;

FIGURE 3 is a section through part of the knife clamp shown in FIGURE 2 and taken on the line indicated by the arrows IIIIII in that figure;

FIGURE 4 shows in plan a part of a knife clamp of similar form to that shown in FIGURE 2, but modified in accordance with the second embodiment of the invention; and

FIGURE 5 is a section through FIGURE 4 taken on the line indicated by the arrows V-V in that figure.

FIGURE 1 shows a microtome comprising a massive stand 1 adapted to be clamped to an edge of a table (not shown) and provided with an upright limb 2 Serving to hold in place a vertical spindle 3 which extends alongside the limb 2 and is pivoted at its ends thereto. A horizontal carrier arm 4 is fixed at one end to the upper end of the spindle 3 and carries at its free end a knob 5 which is gripped by the hand during arcuate movements of the arm 4 about the spindle axis.

A box-like knife clamp 6 is rotatably mounted on the carrier arm 4 and comprises a hinged, split two-part casting, the two parts of which are adapted to be drawn together by two screws 11 and respectively comprise upper and

lower jaws

7 and 8 for gripping the marginal portions of the upper and lower surfaces of a knife 12 well away from the central portion of its cutting edge 13. Each jaw is provided at each end with a projection 14 extending laterally away from the carrier arm 4 and for engaging a surface of the knife at one end thereof.

Referring to FIGURES 2 and 3 each projection 14 is provided adjacent the position of the gripped knife 12 with a heat sink which includes a cooling unit built into the clamp. The heat sink includes a metal plate 23 which is shaped on one side to form a pad of complementary shape to the surface of the knife 12 and to contact such surface when the knife is gripped, as shown, between the

jaws

7 and 8. The plate 23 is made of a metal having good heat-conducting properties, such as silver, copper or aluminum, so as to provide a good heat-conducting path betwen the knife 12 and a set of Peltier cooling junctions 15 bonded to the other side of the plate 23.

The Peltiervcooling junctions 15 are connected by a number of semiconductor elements 20 to a set of Peltier heating junctions 17. The heating junctions 17 are bonded to one face of a plate 123 which is also made of a good heat-conducting metal and has its other face located at one side of a chamber 18 formed inside the projection 14. The chamber 18 is provided at opposite ends with an inlet 21 and an outlet 22 for passing cooling water through the chamber and the two chambers 18 at each end of the knife 12 are interconnected by a piece of flexible tubing 28 for serial flow of water between them. The tubing 28 allows the jaws to be opened and closed without interference when the microtome knife requires replacing with a sharper knife.

Each jaw of the knife clamp is additionally provided with a temperature sensing device comprising a thermistor 24 mounted alongside one of the Peltier cooling junctions 15. Electrical terminals 27 on each jaw enable external electrical circuiting to be connected to the two sets of

junctions

15 and 17 and to the thermistor 24, so that the electrical current flowing through the junctions can be controlled in accordance with the temperature as sensed by the thermistor 24. The thermistor 24 may be connected to a control circuit which regulates the current through the

junctions

15 and 17 automatically, and/or it may be connected to an indicator from which the knife temperature may be read directly by the microtome user. Each thermistor 24 may be provided with adjusting means (not shown) alterable to change the setting of the thermistor and thus enable the temperature of the knife to be closely regulated and/ or measured.

All the surfaces of the jaws, apart from the metal plates 23 which are in contact with the gripped knife may be provided with a layer of thermal insulation 30 to reduce the transfer of heat therebetween. The layer of insulation may comprise a plastic material. As will be noted from FIGURE 2, the screws 11 for drawing the two jaws together are so positioned that they do not come in contact with the microtome knife when it is gripped between the jaws so that heat conduction to the knife from the screws is prevented.

The knife clamp is provided with two rearwardly extending clamping screws 31 which enable it to be fixed in a desired angular position on the carrier arm 4. By slackening these screws the angle of attack of the knife to the specimen to be sectioned can be altered.

Referring again to FIGURE 1, the path of movement of the knife is determined by an arcuate track 42 coaxially arranged around the axis of the spindle 3 along the top of a curved web 43. The end portion of the carrier arm 4 adjacent the knob 5 is provided with a pad (not shown) which is guided by the track 42 during cutting movement of the knife across the top of the specimen. The engagement of the pad and the track ensures that any vertical forces applied to the knob 5 do not influence the thickness of the section cut from the specimen. A spring return (not shown) normally biases the carrier arm to some intermediate position on the track.

The specimen 36 to be sectioned is mounted on a freezing stage 32 which is removably mounted in an object clamp holder 34 and held therein by a locking device 35. The freezing stage 32 may be removed and replaced by an object clamp (not shown) when desired, when it is required to section an object block which does not have to be frozen.

The freezing stage 32 shown in FIGURE 1 comprises a drum having an annularly grooved upper surface to which water can be applied which, on freezing, freezes the specimen 36 to the freezing stage 32. Cooling of the freezing stage to freeze the specimen and water, may be effected in known manner by means of a stream of cold carbon dioxide, or in a novel manner by means of a number of Peltier cooling junctions built into the freezing stage 32 and connected to a source of unidirectional current of appropriate polarity and to .a heat sink having a number of heating junctions for dissipating the heat extracted from the freezing stage 32 by the Peltier cooling junctions. The arrangement used for cooling the freezing stage 32 by cooling junctions may be similar to that already described with reference to FIGURES 2 and 3 and will not, therefore, be again described. A thermistor device may also be built into the freezing stage for sensing its temperature and for controlling the current through the cooling junctions and/or providing an indication of the freezing stage temperature accordingly.

The object clamp holder 34 is mounted on a verticaladjusting mechanism 40 which is actuated by a crank handle 41 extending from the underside of the microtome stand to raise or lower the object clamp holder 34. A micrometer screw (not shown) accurately controls the movement of the specimen towards and away from a cutting plane along which the cutting edge of the knife 12 moves, so that the thickness of the sections taken is always known. To use the microtome the operator slackens the screws 11 and fits a microtome knife between the clamping

jaws

7 and 8. The screws 11 are then tightened so that the metal plates 23 associated with the cooling junctions 15 are pressed into close contact with the adjacent surfaces of the knife 12. Cooling water is then circulated between the inlet 21 and the outlet 22 of each of the cooling chambers 18 and a suitable source of unidirectional current is connected to the two terminals 27 with the correct polarity to ensure that the cooling junctions 15 extract heat and the heating junctions 17 dissipate heat. The temperature of the knife may be determined by the thermistors 24 or alternatively the approach of the temperature of the knife to the value desired may be determined from experience of the length of time required to cool the knife from room temperature. The knife is cooled "by the extraction of heat via the plates 23, which are cooled by the cooling junctions 15. The heat extracted by the cooling junctions 15 is liberated by the associated heating junctions 17 and is conducted via the plates 123 to the cooling fluid flowing through the associated chambers 18. While the knife is being cooled, the clamp screws 31 can be slackened and the knife set at the desired angle of attack by rotating the knife clamp 6 around the carrier arm 4. Also, the specimen to be sectioned can be frozen to the freezing stage during this period.

To take sections, the operator grips the knob 5 at the end of the carrier .arm 4 and swings the arm in a horizontal are around the axis of the spindle 3. Return movement of the carrier arm after a cut has taken place is effected by the spring return and is also arranged to drive the vertical adjusting mechanism 40 to raise the specimen by a thickness equal to the section which has previously been cut. The thickness of the section can be varied :by means of a feed setting. Thus, after each section is taken, the height of the specimen is automatically adjusted. The microtome may be set for manual adjustment of the specimen height instead of the above described automatic adjustment should successive sections of different thickness be desired.

FIGURES 4 and 5 show a knife clamp modified by the replacement of the electrical cooling units with reservoir cooling units. For the sake of simplicity only the pro ection 14 at the left-hand end of the upper jaw 7 has been shown in FIGURE 4 and it will be understood that the right-hand projection 14 is similarly constructed. Proection 14 is formed internally with a reservoir 50 which is insulated from the section 14 by a double layer of thermal insulation 51. The reservoir 50 is provided at one end with an inlet port 52 which is normally closed by a closure cap (not shown), and with an outlet port 53 disposed at the other end of the reservoir. The floor of the reservoir is formed by a metal plate having its undersurface constituting a pad 54 of complementary shape to the top surface of the adjacent portion of a knife when gripped between the

jaws

7 and 8.

Referring to FIGURE 5 the bottom jaw 8 of the clamp 6 has the knife-engaging surfaces of the two projections 14 covered by a layer of thermal insulation 55. In this construction of clamp, there is no electrical control of the knife temperature and thus no thermistors are provided. All the surfaces of both of the jaws in contact with the knife apart from the metal pads 54, are covered by a layer of thermal insulation to reduce the transfer of heat between the clamp and the knife.

To cool a knife, held in the clamp, a cooling fluid, either liquid or gaseous, is circulated through the reservoir 50 between the inlet port 52 and the outlet port 53. This coolant fluid may flow around a closed circuit and by extracting heat continuously from the metal pad 54 the knife temperature is held below a desired maximum value.

The knife clamp shown in FIGURES 4 and 5 may be modified to obtain exceedingly low temperatures of the knife, by plugging up the outlet port 53 and admitting liquid air into the reservoir 50 by means of the inlet port 52. Liquid air having a very low temperature rapidly cools the knife to a very low temperature. The inlet port should not be closed in order to allow the vaporised liquid air to leave the reservoir 50.

Various modifications of the above described knife clamps are possible. For example, silver pads, which are preferable, may be replaced by copper pads or aluminium pads to provide a cheaper microtome with very little loss of performance.

Although the clamp of the invention has been described with reference to a microtome in which the knife is moved in relation to the specimen to be sectioned, it will be appreciated that the invention is usable in microtomes where the section is moved and the knife is held stationary, and indeed in microtomes where the specimen is mounted between a couple of guide surfaces, and a knife mounted in a knife clamp adapted to be held by the hand is moved down the surfaces to section the specimen.

From the above description it will be understood that the invention provides an improved microtome knife clamp able to grip a conventional microtome knife and capable of holding the knife at a sufiiciently low temperature to prevent any tendency for a frozen section to thaw on the knife and collapse into a shapeless wet lump before it can be examined.

I claim:

1. A microtome comprising, in combination:

(a) a massive stand including a freezing stage holder;

(b) a knife;

(c) means for effecting relative movement between the knife and the holder;

(d) a knife clamp having a pair of jaws for gripping the knife, and a mechanism operatively connected to the jaws to open and close them to release and to hold the knife, respectively;

(e) a heat sink in the jaws, the knife extending into the heat sink when held by the jaws;

(f) a thermoelectric cooling unit in the heat sink, said cooling unit having heating and cooling junctions utilizing the Peltier effect;

(g) heat-conductive pads adjacent the cooling junctions and having surfaces in conforming contact with the knife;

(h) heat transmitting elements adjacent the heating junctions and in contact with the heat sink; and

(i) electrical circuit means extending through the jaws to the heating and cooling junctions.

2. The microtome of claim 1, wherein said junctions are bonded respectively to said pad and to said heat transmittin g element.

3. The microtome of claim 1, wherein said jaws define cooling chambers adjacent the heat transmitting elements, the jaws having inlet and outlet ports communicating with the chambers to circulate a collant fluid therethrough.

4. The microtome of claim 1, further comprising a thermistor bonded to the thermoelectric cooling unit adjacent the knife cutting edge, the electrical circuit means being connected also to the thermistor.

5. The microtome of claim 1, further comprising a layer of heat insulating material between all surfaces of the jaws and the knife at locations where the knife is not in contact with the heat-conductive pads.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Rusterholz 83700 Mac Donald 83699 Ott 83-699 Turner 83915.5 Jacoby 83 915.5 Herbain 83-915.5

Sparer 83-915.5 Tuck 136-4.2 Baude 323-69 Hirschhorn 62--3 Meyers 83171 ANDREW R. JUHASZ, Primary Examiner.

WILLIAM W. DYER, JR., Examiner.

Claims

1. A MICROTOME COMPRISING, IN COMBINATION: (A) A MASSIVE STAND INCLUDING A FREEZING STAGE HOLDER; (B) A KNIFE; (C) MEANS FOR EFFECTING RELATIVE MOVEMENT BETWEEN THE KNIFE AND THE HOLDER; (D) A KNIFE CLAMP HAVING A PAIR OF JAWS FOR GRIPPING THE KNIFE, AND A MECHANISM OPERATIVELY CONNECTED TO THE JAWS TO OPEN AND CLSE THEM TO RELEASE AND TO HOLD THE KNIFE, RESPECTIVELY; (E) A HEAT SINK IN THE JAWS, THE KNIFE EXTENDING INTO THE HEAT SINK WHEN HELD Y THE JAWS; (F) A THERMOELECTRIC COOLING UNIT IN THE HEAT SINK, SAID COOLING UNIT HAVING HEATING AND COOLING JUNCTIONS UTILIZING THE PELTIER EFFECT; (G) HEAT-CONDUCTIVE PADS ADJACENT THE COOLING JUNCTIONS AND HAVING SURFACES IN CONFORMING CONTACT WITH THE KNIFE; (H) HEAT TRANSMITTING ELEMENTS ADJACENT THE HEATING JUNCTIONS AND IN CONTACT WITH THE HEAT SINK; AND (I) ELECTRICAL CIRCUIT MEANS EXTENDING THROUGH THE JAWS TO THE HEATING AND COOLING JUNCTIONS.