US20060101832A1

US20060101832A1 - Apparatus for cryosubstitution or low-temperature substitution

Info

Publication number: US20060101832A1
Application number: US11/255,031
Authority: US
Inventors: Paul Wurzinger; Reinhard Lihl; Anton Lang
Original assignee: Leica Mikrosysteme GmbH
Current assignee: Leica Mikrosysteme GmbH
Priority date: 2004-11-16
Filing date: 2005-10-19
Publication date: 2006-05-18
Also published as: DE102004055148B4; DE102004055148A1

Abstract

An apparatus for cryosubstitution or low-temperature substitution is disclosed. The apparatus encompasses a Dewar vessel (1) that is embodied with a neck. A chamber (5) for reception of at least one specimen is inserted in the neck (5 ₃). The chamber (5) is embodied with a heavy base (5 ₁) that is connected to a first thermal conduction rod (7). A platform (8) is provided at the end of the first thermal conduction rod (7) facing away from the base (5 ₁). An insulator (12) is provided above the platform (8) of the first thermal conduction rod (7).

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of the German patent application 10 2004 055 148.0, filed on Nov. 16, 2004 which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention concerns an apparatus for cryosubstitution or low-temperature substitution. The invention concerns in particular an apparatus for cryosubstitution or low-temperature substitution in which the apparatus encompasses a Dewar vessel. The Dewar vessel is embodied with a neck, and is filled with a liquid coolant. A chamber for reception of a specimen is inserted in the neck, this chamber being embodied with a heavy base.

BACKGROUND OF THE INVENTION

Patent application WO 94/05995 discloses an apparatus for dewatering and/or embedding of preferably frozen specimens. The apparatus encompasses a Dewar vessel filled with liquid nitrogen and a metallic element, anchored to the base of the Dewar vessel, which is made of highly thermally conductive material. The metallic element possesses at its upper end, in the attachment region of the Dewar neck, a cover having a metallic cooling surface. The cooling surface is connected to the complementarily embodied lower contact surfaces of the thermostatically heated substitution (PLT) containers and of the lower part of a freeze-drying chamber, in such a way that good thermal conduction between the corresponding surfaces is ensured. The metallic element is embodied in the form of a thermally conductive tube. The highly thermally conductive tube requires a large wall thickness for the necessary high thermal conduction. It therefore possesses a large mass, and is anchored to a base element for support. A cryosubstitution unit is operated, depending on the process, in a very wide temperature range from −140° C. to +70° C. As described in WO 94/05995, a highly thermally conductive coupling to the cooling surface at low temperatures is necessary. For the high temperatures, however, it brings about a large heat flow from the chamber into the Dewar vessel, and therefore high nitrogen consumption. Different coupling tubes are therefore used for different temperature ranges. This method thus has the disadvantage, however, that the coupling tubes must be exchanged by the user in accordance with the process temperature that is set. On the one hand this can result in operator errors, and on the other hand the automatic control system must be assisted by manual interventions for optimum functionality, which is disadvantageous for an automatic control system.
A Dewar vessel according to the existing art is depicted in the JEOL brochure. The cooling apparatus substantially comprises a chamber or holding apparatus for the specimens, which is lowered into the cold nitrogen gas in a Dewar vessel filled with liquid nitrogen. The holding apparatus hangs from a mounting element that can be adjusted for the desired lowering depth using a locking element. Cooling is accomplished in this case by direct heat exchange with the gas or with the liquid nitrogen. In the case of the existing art depicted in FIG. 1, only relatively high temperatures can be attained as long as the specimen is sitting at a depth in the Dewar vessel that is accessible for manipulation (e.g. replacement of the substitution medium). The process temperature can be reduced by further lowering into the Dewar vessel, but the specimens must always be lifted up for manipulations. As a result, contamination with moisture from the ambient air can more easily occur.
The brochure for the Leica EM AFS discloses a unit according to the existing art. A Dewar vessel is filled with liquid nitrogen, the Dewar neck having a chamber that can be brought to a specific temperature. The temperature range extends from −140° C. to +65° C. The desired temperature is set via a control circuit and built-in heating elements. Level sensors for the liquid nitrogen are additionally mounted in the Dewar vessel, and indicate to the user the fill level of liquid nitrogen in the Dewar vessel.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to create an apparatus for cryosubstitution or low-temperature substitution that can establish all temperatures in the temperature range from −140° C. to +70° C. without intervention by a user, and with no need for the user to modify elements of the Dewar vessel.
The aforesaid object is achieved by an apparatus for cryosubstitution or low-temperature substitution that comprises: a Dewar vessel that is embodied with a neck and is filled with a liquid coolant, a chamber for reception of at least one specimen wherein the chamber is inserted in the neck, a heavy base is provided to the chamber wherein the heavy base of the chamber is connected to a first thermal conduction rod that is connected, at the end facing away from the base to a platform; and the thermal conduction rod is equipped, above the platform, with an insulator.
The apparatus for cryosubstitution or low-temperature substitution has the advantage that it encompasses a Dewar vessel that is embodied with a neck. The Dewar vessel is filled with a liquid coolant that preferably is liquid nitrogen. A chamber for the reception of at least one specimen is inserted in the neck of the Dewar vessel. The chamber is pot-shaped and possesses a heavy base. The base of the chamber is connected to a thermal conduction rod that is connected, at the end facing away from the base, to a platform. The thermal conduction rod is equipped, above the platform, with an insulator. It is particularly advantageous if the thermal conduction rod and the platform are embodied integrally. In addition, the first thermal conduction rod can be connected to a second thermal conduction rod, the second thermal conduction rod possessing a platform at one end. The second thermal conduction rod is connected, with its end located opposite to the platform, to the first thermal conduction rod. The platform of the second thermal conduction rod is directed toward a receptacle embodied at the base of the Dewar vessel.
In a preferred embodiment, the platform of the second thermal conduction rod is in contact with the receptacle. It has proven particularly advantageous, for the stability of the arrangement of the first and the second thermal conduction rod in the Dewar vessel, if the platform of the second thermal conduction rod is pot-shaped and fits around the receptacle. The second cooling rod is likewise equipped, above the platform, with an insulator.
At least one heating element and at least one temperature sensor are recessed into the base of the chamber, the heating element and temperature sensor being connected to an electronic control system.
The base of the chamber can likewise be connected to an annular plate, the at least one heating element being recessed into this plate, and the at least one temperature sensor being recessed into the base of the chamber or into the annular plate. The temperature sensor is embodied as a thermocouple or as a resistance temperature sensor. The temperature signal of the temperature sensor serves as a controlled variable for the electronic control system in order to control the chamber temperature.
It is also advantageous if a further heating element, which preferably is electronically operated, is immersed in the liquid nitrogen. Liquid nitrogen is additionally vaporized during operation by way of this further heating element, so that the cold gas cools the platform of the first cooling rod.
At least one sensor is provided in order to ascertain the liquid level of the liquid nitrogen in the Dewar vessel. At least one sensor is a temperature sensor that is connected to the electronic control system in order to measure the fill level. It is particularly advantageous if several temperature sensors are arranged along the first and the second thermal conduction rod in order thereby to ascertain the fill level of the liquid nitrogen in the Dewar vessel.
It is additionally advantageous if at least one of the insulators of the first or the second thermal conduction rod is embodied as a tube. This tube is immovably, adhesively bonded to the corresponding platform, so that the thermal conduction rod is insulated with respect to the liquid nitrogen. A pump is provided which pumps the liquid nitrogen into at least one of the tubes that surround the first and/or the second thermal conduction rod. The pump can be embodied as a membrane pump having a ball valve.
Further advantages and advantageous embodiments of the invention may be inferred from the dependent claims, and are the subject matter of the Figures below and the descriptions thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the individual drawings:
FIG. 1 is a cross section through a Dewar vessel according to the existing art;
FIG. 2 is a cross section through a Dewar vessel according to a first embodiment of the invention;
FIG. 3 is a cross section through a Dewar vessel according to a second embodiment of the invention;
FIG. 4 is a cross section through a Dewar vessel according to a third embodiment of the invention; and
FIG. 5 is a cross section through a Dewar vessel according to a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross section through a Dewar vessel according to the existing art. Dewar vessel 1 comprises substantially an outer container 1 ₁and an inner container 1 ₂. Inner container 1 ₂is insulated with respect to outer container 1 ₁. Inner container 1 ₂holds liquid nitrogen for cooling. A neck 1 ₃of Dewar vessel 1 extends from inner container 1 ₂to outer container 1 ₁. A chamber 5 can be introduced into inner container 1 ₂. Specimens 2 can be inserted into chamber 5 so that they are exposed to cryosubstitution and low-temperature substitution. Chamber 5 is connected to a mounting element 5 ₁that projects out of neck 1 ₃of Dewar vessel 1. The level of chamber 5 above liquid nitrogen 3 can be adjusted. A locking element 60 is provided in order to immobilize the position of chamber 5 above the level of liquid nitrogen 3. A desired temperature can thus be set by lowering or raising chamber 5. Cooling is accomplished in this case by direct heat exchange with the gas or with liquid nitrogen 3.
FIG. 2 is a cross section through a Dewar vessel 1 according to a first embodiment of the invention. In the description that follows, identical reference characters are used for identical elements. The cooling apparatus shown in FIG. 2 serves for cryosubstitution or low-temperature substitution of biological and/or other water-containing specimens. As already mentioned in the description referring to the existing art, the Dewar vessel encompasses an inner container 1 ₂and an outer container 1 ₁. The inner container is filled with a liquid coolant that preferably is liquid nitrogen 3. A chamber 5 is inserted into neck 1 ₃of Dewar vessel 1. Chamber 5 is pot-shaped and possesses a heavy base 5 ₁. Chamber 5 is open toward the top and can be closed off with a cover 6 for insulation with respect to ambient temperature. Chamber 5 serves to receive multiple specimen containers 2 in which specimens 30 for cryosubstitution/low-temperature substitution are located. A first thermal conduction rod 7 is joined to base 5 ₁of chamber 5. A platform 8 is provided at the end of first thermal conduction rod 7 facing away from base 5 ₁of chamber 5. Platform 8 can be detachably joined to first thermal conduction rod 7. It is furthermore conceivable for first thermal conduction rod 7 and platform 8 to be embodied integrally. Above platform 8, first thermal conduction rod 7 is surrounded by an insulator 12. Insulator 12 serves to insulate first thermal conduction rod 7 against liquid nitrogen 3 or cold nitrogen gas 3 ₁. As a result of insulator 12, the heat flux for cooling chamber 5 and base 5 ₁is directed principally through platform 8. The cooling capacity can therefore advantageously be determined by modifying the geometrical dimensions or by selecting a suitable material for first thermal conduction rod 7. The temperature in chamber 5 can be regulated by the operation of at least one heating element 14. Also provided is at least one temperature sensor 15 that is used for temperature measurement. Temperature sensor 15 can be embodied as a thermocouple or resistance temperature sensor. The temperature signal is used as feedback for an electronic control system 16 that controls the temperature of chamber 5 by adapting the heating output of heating element 14. The length of first thermal conduction rod 7 is advantageously selected so that platform 8 is immersed in liquid nitrogen 3 only above a certain fill level. With a high fill level, platform 8 is immersed in liquid nitrogen 3, and chamber 5 is coupled via first thermal conduction rod 7 directly to liquid nitrogen 3. With a low fill level, platform 8 interacts with cold nitrogen gas 3 ₁. Cold nitrogen gas 3 ₁is heated by the heat flux from chamber 5 into inner container 1 ₂of Dewar vessel 1. By convection and by interaction with the walls of inner container 1 ₂, this heat is fed back into liquid nitrogen 3 and results in an increase in the evaporation rate. A temperature equilibrium that is largely independent of the present fill level of liquid nitrogen 3 in inner container 1 ₂thus develops between platform 8 and chamber 5. It is self-evident that the thermal coupling between chamber 5 and liquid nitrogen 3 is much greater at a high fill level than at a low fill level. Lower temperatures can therefore be achieved in chamber 5 with a high fill level. On the other hand, the liquid nitrogen consumption is lower with a low fill level.
This arrangement is advantageous in that in standard substitution processes, the lowest process temperatures (−90° C. and lower) are required at the beginning of the processes. The temperature is raised in the course of the substitution processes. Because liquid nitrogen 3 is also consumed during the process, the cooling output achievable by way of first thermal conduction rod 7 and platform 8 reflects the temperature profile of the substitution process. At the same time, insulator 12 limits the coupling to liquid nitrogen 3 even with a high fill level. Even in this situation, therefore, high temperatures can be established without going beyond reasonable limits for liquid nitrogen consumption and for the necessary heating output of heating element 14.
FIG. 3 is a cross section through a Dewar vessel 1 according to a second embodiment of the invention. Here a second thermal conduction rod 9 is attached to first thermal conduction rod 7. Second thermal conduction rod 9 once again possesses a platform 10 at one end. Second thermal conduction rod 9 is in contact, at the end opposite platform 10 of second thermal conduction rod 9, with platform 8 of first thermal conduction rod 7. First thermal conduction rod 7 and second thermal conduction rod 9 are detachably joined to one another. Inner container 1 ₂of Dewar vessel 1 possesses a receptacle 11 with which platform 10 of second thermal conduction rod 9 is in contact. Advantageously, platform 10 of second thermal conduction rod 9 is pot-shaped and is dimensioned so that it fits around receptacle 11. This arrangement ensures secure support in Dewar vessel 1 of the system made up of first thermal conduction rod 7 and second thermal conduction rod 9. Like first thermal conduction rod 7, second thermal conduction rod 9 is also surrounded by an insulator 13 above platform 10. Insulator 13 thus insulates second thermal conduction rod 9 against liquid nitrogen 3. Insulators 12 and 13 around first thermal conduction rod 7 and second thermal conduction rod 9 are made from a suitable foam. It is also conceivable for insulators 12 and 13 to be constituted by tubes that are adhesively bonded to platforms 8 and 10, so that the respective thermal conduction rod 7 and 9 is insulated against liquid nitrogen 3. With the combination of first thermal conduction rod 7 and second thermal conduction rod 9, platform 8 of the first thermal conduction rod is positioned so that it is immersed in liquid nitrogen 3 when the latter's fill level is high. The cooling behavior in this case is identical to the cooling behavior as described in the embodiment according to FIG. 2. Platform 10 of second cooling rod 9 is in contact with receptacle 11 and is thus positioned close to the bottom of inner container 1 ₂of Dewar vessel 1. With a fill level below platform 8 of first thermal conduction rod 7, second thermal conduction rod 9 thus represents a permanent coupling between platform 8 of first thermal conduction rod 7 and liquid nitrogen 3. This coupling to liquid nitrogen 3 acts in addition to the coupling via cold nitrogen gas 3 ₁. The intensity of the coupling can therefore easily be adapted to the particular desired cooling parameters by way of the geometrical dimensions or the thermal conductivity of second thermal conduction rod 9.
The configuration of platform 10 of second thermal conduction rod 9 is also advantageous. Because this platform 10 is pot-shaped, a lateral support of first and second thermal conduction rods 7 and 9 against receptacle 11 is therefore achieved. This thus represents an immobilization against lateral loads, especially during transport of the device. Because thermal conduction rods 7 and 9 possess a relatively small mass, they need not be fixedly joined to receptacle 11 in order to perform this supporting function. The entire structure is therefore insensitive to tolerances in the installation surface of the Dewar vessel. The relatively small mass of thermal conduction rods 7 and 9 also offers the advantage that much less liquid nitrogen is consumed for cooling the apparatus when it is first filled.
FIG. 4 is a cross section through a Dewar vessel 1 according to a third embodiment of the invention, depicting a further capability for cooling chamber 5. In addition to heating elements 14 provided in base 5 ₁of chamber 5, an additional, preferably electrically operated, heating element 17 is immersed in liquid nitrogen 3. The heating of heating element 17 thus evaporates additional liquid nitrogen 3, and the resulting cold nitrogen gas 3 ₁cools platform 8 of first thermal conduction rod 7 and therefore also chamber 5. This cooling method is very easy to control externally, and can therefore be used for more intense short-term cooling. Electronic control system 16 provides the corresponding open- and closed-loop control of the chamber temperature. A further advantageous embodiment of the present invention is also depicted in FIG. 4. At least one sensor 18 is provided for measuring the fill level of liquid nitrogen 3 in inner container 12. The at least one sensor 18 is configured in such a way that it detects wetting by liquid nitrogen 18. Preferably, several sensors 18 are arranged along first thermal conduction rod 7 and second thermal conduction rod 9. The present fill level is therefore ascertained by way of these sensors 18, and on the one hand can be used as a basis for the control system and on the other hand can be made available as information to the user. The measurement is once again advantageously made by an electronic system that is integrated into electronic control system 16.
FIG. 5 is a cross section through the Dewar vessel according to a fourth embodiment of the invention, some elements of the apparatus having been omitted for reasons of clarity. Insulators 12 and 13 around first thermal conduction rod 7 and second thermal conduction rod 9, respectively, are embodied here as tubes 20. Tube 20 around first thermal conduction rod 7 is immovably adhesively bonded to platform 8, so that the liquid nitrogen is kept away from first thermal conduction rod 7 with the exception of platform 8. Second thermal conduction rod 9 is likewise surrounded by a tube 20 that is immovably adhesively bonded to platform 10 of second thermal conduction rod 9. Liquid nitrogen 3 is likewise kept away from second thermal conduction rod 9 with the exception of platform 10. The embodiment described in FIG. 5 creates the capability of filling tube 20 around first thermal conduction rod 7 or second thermal conduction rod 9 with liquid nitrogen 3, thus making possible a strong coupling between liquid nitrogen 3 and chamber 5 regardless of the fill level of liquid nitrogen 3 in Dewar vessel 1. With this arrangement, a very low temperature for chamber 5 or a very high cooling rate can be achieved. In the depiction of FIG. 5, the tube around second cooling rod 9 is filled. It is self-evident, however, that the tube around first cooling rod 7 can also be filled. It is likewise conceivable for an insulator that is not provided for filling with liquid nitrogen to be embodied, in the form of an insulating foam, around first thermal conduction rod 7 or second thermal conduction rod 9. Filling of tube 20 around first cooling rod 7 or second cooling rod 9 is accomplished with a pump 21 that is embodied as a membrane pump. It is likewise advantageous if pump 21 is divided, so that the pressure fluctuations generated by membranes positioned outside Dewar vessel 1 are transferred by way of a hose or tube to the valve head positioned in the liquid nitrogen. As a result of the directional effect of the valve head, the pressure fluctuations are converted into a pumping motion. The embodiment depicted in FIG. 5 also shows a further possibility for arranging the at least one heating element 14 and the at least one temperature sensor 15. For this purpose, base 5 ₁of chamber 5 is connectable to an annular plate 25. The at least one heating element 14 is recessed into this annular plate 25. The at least one temperature sensor 15 can be recessed into base 5 ₁of the chamber or into annular plate 25.

Claims

1. An apparatus for cryosubstitution or low-temperature substitution comprises: a Dewar vessel that is embodied with a neck and is filled with a liquid coolant, a chamber for reception of at least one specimen wherein the chamber is inserted in the neck, a heavy base is provided to the chamber wherein the heavy base of the chamber is connected to a first thermal conduction rod that is connected, at the end facing away from the base to a platform; and the thermal conduction rod is equipped, above the platform, with an insulator.

2. The apparatus according to claim 1, wherein the liquid coolant is liquid nitrogen.

3. The apparatus according to claim 1, wherein the first thermal conduction rod and the platform are embodied integrally.

4. The apparatus according to claim 1, wherein a second thermal conduction rod is connected to the first thermal conduction rod.

5. The apparatus according to claim 4 wherein the second thermal conduction rod is connected at one end to a platform; the end of the second thermal conduction rod located opposite to the platform is connected to the platform of the first thermal conduction rod; and the platform is directed toward a receptacle embodied at the base of the Dewar vessel.

6. The apparatus according to claim 5, wherein the platform of the second thermal conduction rod is in contact with the receptacle.

7. The apparatus according to claim 5, wherein the platform of the second thermal conduction rod is pot-shaped and fits around the receptacle.

8. The apparatus according to claim 4, wherein the second thermal conduction rod is surrounded, above the platform, by an insulator.

9. The apparatus according to claim 1, wherein at least one heating element and at least one temperature sensor are recessed into the base of the chamber; and the heating element and temperature sensor are connected to an electronic control system.

10. The apparatus according to claim 9, wherein the base of the chamber is connectable to an annular plate; the at least one heating element is recessed into this plate, the at least one temperature sensor being recessed into the base of the chamber or into the annular plate.

11. The apparatus according to claim 9, wherein the temperature sensor is embodied as a thermocouple or as a resistance temperature sensor; and its temperature signal serves as a controlled variable for the electronic control system in order to control the chamber temperature.

12. The apparatus according to claim 1, wherein a further heating element, which preferably is electrically operated, is immersed in the liquid nitrogen in order to vaporize additional liquid nitrogen so that the cold gas cools the platform of the first cooling rod.

13. The apparatus according to claim 1, wherein at least one sensor is provided which ascertains the fill level of the liquid nitrogen in the Dewar vessel.

14. The apparatus according to claim 13, wherein the at least one sensor is a temperature sensor that is connected to the electronic control system in order to measure the fill level.

15. The apparatus according to claim 14, wherein several temperature sensors are provided which are arranged along the first and the second thermal conduction rod.

16. The apparatus according to claim 5, wherein the liquid coolant is liquid nitrogen and at least one of the insulators of the first or the second thermal conduction rod is embodied as a tube that is immovably adhesively bonded to the corresponding platform so that the thermal conduction rod is insulated with respect to the liquid nitrogen.

17. The apparatus according to claim 16, wherein a pump is provided which pumps the liquid nitrogen into at least one of the tubes that surround the first and/or the second thermal conduction rod.

18. The apparatus according to claim 17, wherein the pump is embodied as a membrane pump having a membrane and ball valves.

19. The apparatus according to claim 18, wherein the pump is divided, so that the membrane is arranged outside the Dewar vessel and the ball valves provided in a valve head are arranged inside the Dewar vessel.

20. The apparatus according to claim 1, wherein the insulator that is not embodied as a tube is an insulating foam.