SPECIMEN COOLING AND WARMING APPARATUS AND METHOD

Abstract: A specimen cooling and warming apparatus and method comprising a chamber (12) with a lid (16) and having a temperature gradient in the chamber (12). A carriage (18) is provided and controlled by a control means (40) and a drive mechanism (10) to move through the temperature gradient at desired rates to achieve desired rates of cooling to freezing or warmming from freezing, specimens including biological specimens.

Description: TITLE SPECIMEN COOLING AND WARMING APPARATUS AND METHOD DESCRIPTION The present invention relates to a specimen cooling and warming apparatus and method particularly envisaged for use in cooling specimens to a state of freezing and warming frozen specimens to room temperature. FIELD OF THE INVENTION In general, cooling specimens to a frozen state has been effected by placing the specimens into a fully enclosed chamber and gradually reducing the temperature therein. Temperature reduction to low temperatures is conveniently achieved using liquid nitrogen. Introduction of the liquid nitrogen is performed by a pump mechanism. A complex control system is required to monitor the temperature in the chamber and regulate the pump mechanism to achieve a desired cooling rate and substan¬ tially uniform temperature throughout the chamber. Once the specimens are frozen they are transferred to a long term storage container. Such fully enclosed chambers are expensive to install, complex in operation, and have a relatively high consumption of liquid nitrogen and do not lend themsel¬ ves to transportability. A less common cooling and warming apparatus comprises a relatively large chamber supplied with liquid nitrogen and having a substantially uniform temperature through¬ out and a smaller container arranged to be located in it. The smaller container is provided with a heating means and arranged to store the specimen. A control system is provided to operate the heating means in order to allow cooling and warming of the specimen. Such apparatus are relatively inexpensive and of low complexity but are also of low accuracy and are prone to overheat or even cook the specimen (in the case of a biological specimen) . In the case of biological specimens it is particularly important to be able to accurately control the rate of cooling to a frozen state and warming from a frozen state to rates found to be most desirable for a particular biological specimen. If accurate control is not achieved reproducability of results from batches of the bilogical specimens may be degraded and erratic results may occur. SUMMARY OF THE INVENTION The present invention provides a specimen cooling and warming apparatus employing a temperature gradient for use in cooling and warming specimens. in accordance with the present invention there is provided a specimen cooling and warming apparatus characterised in that it comprises a chamber having a base and one or more walls thereabout and having a moveable carriage located in it, the carriage being arranged to carry a specimen, a cooling means to form a temperature gradient in the chamber and a control means to move the carriage through the temperature gradient. In accordance with a further aspect of the present invention there is provided a method of cooling and warming a specimen, characterised in that it comprises - 3 - the steps of placing the specimen onto a carriage of a specimen cooling and warming apparatus having a temp¬ erature gradient within its confines, moving the carriage through the temperature gradient at a rate or rates set by a raising/lowering rate means. The present invention will hereinafter be described with particular reference to the specimen being a biological specimen, such as, for example, semen, although it is to be understood that it is of general applicability. For the purposes of the present invention relatively warm temperatures are those about room temperature and relatively cold temperatures are those between -100°C to -200°C. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example, with reference to the accompanying drawings, in which:- Figure 1 is an upper perspective view of a specimen cooling and warming apparatus according to the present invention; Figure 2 is a functional block diagramme of a control means of the specimen cooling and warming apparatus; and Figure 3 is a control circuit diagramm of a control algorithm of the control means of Figure 2. DESCRIPTION OF THE INVENTION In Figure 1 there is shown a specimen cooling and warming apparatus 10 comprising a chamber 12 conven¬ iently formed from 4 walls 14 and a base bounded by the walls 14. The walls 14 and the base may be made with a stainless steel outer covering and an inner insulation layer. The insulation may conveniently be polystyrene or polyurethane. The chamber 12 also comprises a lid 16 hinged atop one of the walls 14 and disposed to close off the chamber 12 so that turbulance in air outside the chamber is less likely to produce turbulance inside the chamber 12. The chamber 12 also comprises a carriage 18 located within its confines. The carriage 18 is conveniently in the form of a tray 20 having two swing pivots 22. The swing pivots 22 each receive a first arm 24 fixed to a rotatable rod 26. Rotation of the rod 26 produces an angular displacement of the first forms 24 and a corres¬ ponding raising or lowering of the tray 20. Preferably, the tray 20 is made of material having low thermal mass. It is envisaged that the tray 20 could therefor be made substantially of plastics materials. It has been found that use of other than low thermal mass materials in the tray 20 result in the tray 20 acting as a heat source as the carriage 18 and the specimen are lowered into the chamber. In such cases the cooling of the tray may take longer than the cooling of the specimen and so may unduly effect the cooling of the specimen. The rod 26 also conveniently has fixed to it two second arms 28 disposed to rotate with the rod 26. The second arms 28 are arranged to raise the lid 16 when the carriage 18 is in a raised condition, as shown in Figure 1. The second arms 28 are not fixed to the lid 16 but are arranged to slidingly engage with the lid. When the carriage 18 is lowered the second arms 28 are angularly displaced and lower the lid 16. Once the lid 16 comes into contact with tops of the walls 14 the second arms 28 continue to rotate downwardly. The specimen cooling and warming apparatus 10 also comprises a drive mechanism 30 which is configured to rotate the rod 26 and hence the first and second arms 24 and 28. It is intended that the drive mechanism 30 comprise a stepper motor connected to receive electrical impulses to cause it to accordingly rotate an output shaft connected to a speed reduction gear box (not shown) and hence to the rod 2β. The specimen cooling and warming apparatus 10 also comprises a cooling means. In the present embodiment the cooling means is conveniently in the form of a volume of relatively cold liquid stored within the chamber 12. The store of relatively cold liquid may be a store of liquid nitrogen 32 which has a temperature of about -196°C. The store of liquid 32 produces a temperature gradient inside the chamber -12. The temperature gradient varies from about -196°C adjacent the store of liquid 32 to about room temperature adjacent the lid 16. Preferably, the chamber 12 comprises means providing greater inailation effect toward the base and lesser insulation effect toward the lid 16 so as to aid in maintaining the temperature gradient. For example, the thickness of the insulation in the walls 14 could be varied from relatively thick toward the base to relatively thin toward the lid 16. Further, the walls 14 could comprise ventilation means adjacent the lid 16 to allow escape of nitrogen vapour but whilst reducing the chance of external air flows causing turbulance within the chamber, which turbulance could otherwise disturb the temperature gradient. It is preferred to establish a linearity in the temperature gradient. When the lid 16 is closed it has been found that the temperature gradient reduces with time as the temper¬ ature adjacent the lid 16 decreases and the temperature throughout the chamber 12 becoming more uniform, hence the preferrement for a gradual insulation effect in the walls 14. The specimen cooling and warming apparatus 10 also comprises a control means 40 as shown in Figure 2. The control means 40 comprises a temperature sensor 42 arranged to be in contact with the specimen. It is intended that the temperature sensor 42 be in the form of a thermistor and be located within the specimen. It has been found preferable to use thermistors since they display reproducable resistance/temperature characteristics which can be readily characterised and display a relatively high sensitivity as compared with thermocouples. It has been found most desirable, especially with biological specimens such as semen, to place the temp¬ erature sensor 42 inside the specimen since during freezing the temperature of the specimens may not precisely match the temperature of the tray 20. The control means 40 also comprises a sample and hold circuit 44 connected to the temperature sensor 42 and configured to periodically sample a voltage appearing across the resistance of the thermistor. An analogue to digital converter (A/D) 46 is provided to convert the sampled thermister voltage measurement from an analogue value to a digital value. A measurement converter 48 is connected to the A/D converter 46 is configured with information regarding the resistance/temperature characteristics of the thermistor. The measurement converter 48 thereby converts the digitized voltage into an absolute temp¬ erature in degrees celcius for example. The absolute temperature reading may be stored by a data logger 50 for later use and experimentation in developing optimum cooling and warming rates for various specimens. The control means 40 also comprises a control algorithm means 52 as detailed in Figure 3. The control algorithm means 52 has an input C from the measurement converter 48 and an input R from a cooling/warming., rate means 54 and an output U to a position controller 56 arranged to send electrical pulses to the drive mechanism 30. The control algorithm means 52 comprises means for proportional and differential control of the angular position of the rod 26 dependent upon the measured temperature of the specimen. In Figure 3 the letters employed have the following meanings: R - input from the cooling/warming rate means 54 T - sample interval between the periodic temperature samples. C - specimen temperature at current temperature sample OLDC - specimen temperature at previous temperature sample Kp, KJJ, K and f - constants dependent on the specimen cooling and warming apparatus 10. The control algorithm means 52 comprises determination functions of the proportional and differential type and having the followingcharacterising rules: E = R - C F = E - K R (C - OLDC) T ϋ = K p F OLDC = C The cooling/warming rate means 54 comprises a keyboard 58 (Figure 1) configured to allow entry of data corres¬ ponding to desired cooling and warming rates. The data may include the rate in terms of temperature per unit time at which cooling and warming is to take place and the absolute temperature at whcih such rate is to commence or cease. The data may also include a time period for which the temperature is to be maintained constant. The control algorthm means interprets the data from the cooling/warming rate means 54 and activates the position controller 56 accordingly. It is envisaged that cooling and warming rates could be in the range from 0.1 to 20°C/minute although it is estimated that slower rates could be used. It has been found that faster cooling rates may be used once the specimen is frozen. It has also been found that at freezing a latent heat of fusion is released and may increase the temperature of the specimen by 5 to 10°C. Accordingly, the control means 40 is preferably configured to disregard such changes. It is envisaged that a further temperature sensor could be provided on the tray 20 to sense changes in the temperature gradient before they cause corresponding changes in the temperature in the specimen. it is envisaged that a different control algorithm means 52 would be required for such a further sensor. In use, the specimen cooling and warming apparatus 10 is employed to cool to freezing a specimen to be subse¬ quently stored in a long term cold storage flask or to warm from a frozen state a specimen removed from such a flask. To set up the apparatus 10 data is entered into the keyboard 58 relating to the desired or experimentally prcoven rates of cooling for the specific- type of specimen. The data is then made available to the cooling/warming rate means 54. The apparatus 10 is then supplied with a store of the liquid 32 to establish the temperature gradient. Then the temperature sensor 42 is placed in contact with the sample and both are placed on the tray. An operator of the apparatus 10, via the keyboard 58, then directs the control means 40 to automatically lower the carriage 18 with the specimen into the chamber 12. The control algorithm means 52 sets the position controller 56 to send electrical pulses to the drive mechanism 30 to rotate the rod 36 to angularly displace the first and second arms 24 and 14 and hence lower the tray 20. Simultaneously, the sample and hold circuit 44 measures the temperature of the specimen -with the thermistor and the A/D converter 46 and the measurement converter 48 convert the sample into an absolute temperature reading which is then recorded by the data logger 50. Subject to the temperature measured the control means 40 varies or maintains the rate of lowering of the tray 20. When the measured temperature reaches a certain value the rate of lowering may be altered as directed by the cooling/warming rate means 54. It is envisaged that any number of cooling and warming rates could be used, although 3 to 5 different rates are considered to be most likely. For example, the rates of cooling shown in Table 1 may be used to freeze semen: Table 1 possible cooling rates for semen . RATE BREAK TEMPERATURE . °C/minute . °C -5 0 -0.5 -10 -2 -30 -10 . -80 The break temperature is the temperature at which the rate of cooling is altered to the next rate. During such cooling a display means 60 display the temperature of the specimen. Once the fixed desired temperature is reached the control means 40 may be directed by the operator to lower the carriage 18, under manual control, into the store of liquid 32 to reduce the specimen to the temperature of the liquid 32. The the carriage 18 may be manually raised as described hereinabove and the lid 16 opened, the specimen removed and placed in a long term storage flask. The reverse procedure is used to warm to room temper¬ ature a frozen specimen. The apparatus 10 is then ready for cooling and warming of the specimens. Since the temperature gradient in the chamber 12 is substantially maintained during cooling and warming procedures the apparatus 10 is virtually immediately ready for further such procedures. Consequently, the apparatus 10 of the present invention has been found to be relatively efficient and speedy in performing multiples of such procedures. It is to be noted that prior art apparatus have gener¬ ally not considered the desirability of .controlled warming of frozen specimens. The rates of cooling and warming generally decided to be used depend inter alia on the thermal mass of the specimen. The apparatus 10 has been found to consume liquid nitrogen at rates substantially less than prior art apparatus. Further the apparatus 10 by virtue of its low complexity and a small demand on electrical power may be used whilst in transport. Such use is particularly impor- tant in collecting animal semen specimens from farms. The provision of the data logger 50 is expected to aid in experimentation in evaluating the effect of cooling and warming rates on particular specimens and to produce optimum rates. Modifications and variations such as would be .apparent to a skilled addressee are deemed within the scope of the present invention. For example, a screw thread type drive mechanism could be used to raise and lower the carriage 18. Also the cooling/warming rate means 54 could be provided with predefined series of cooling and warming rates.

Claims: CLAIMS 1. A specimen cooling and warming apparatus character¬ ised in that it comprises a chamber having a base and one or more walls thereabout and having a moveable carriage located in it, the carriage being arranged to carry a specimen, a cooling means to form a temperature gradient in the chamber and a control means to move the carriage through the temperature gradient. 2. A specimen cooling and warming apparatus according to claim 1, characterised in that the cooling means is a volume of relatively cold liquid located in the chamber. 3. A specimen cooling and warming apparatus according to claim 1 or 2 , characterised in that the control means comprises a temperature sensor arranged to be located in , contact with the specimen, a drive mechanism connected to raise and lower the carriage and a cooling/warming rate means configured to direct the rate of raising and lowering of the carriage subject to the temperature sensed by the temperature sensor. 4. A specimen cooling and warming apparatus according to any one of the preceding claims, characterised in that the chamber comprises a lid hinged to it and disposed to in one condition substantially close off the chamber and to reduce the occurance of turbulance therein and disposed in a further condition to allow access to the carriage. 5. A specimen cooling and warming apparatus according to any one of the preceding claims, characterised in that the chamber comprises insulation varying in thick- ness from relatively thin towards the lid to relatively thick towards the base in order to assist in maintaining the temperature gradient within the chamber. 6. A specimen cooling and warming apparatus according to claim 4 or 5, characterised in that the walls of the chamber comprise ventilation means adjacent the lid to assist in maintaining the temperature gradient within the chamber. 7. A specimen cooling and warming apparatus according to any one of the preceding claims, characterised in that the carriage comprises a tray made substantially of low thermal mass materials. 8. A specimen cooling and warming apparatus according to claim 7, characterised in that the tray is made substantially of plastics materials. 9. A specimen cooling and warming apparatus according to claim 3, characterised in that the cooling/warming rate means is configured or configurable to direct raise and lower of the carriae at various rates dependent upon time lapsed, temperature of the specimen and the type of specimen. 10. A method of cooling and warming a specimen, charac¬ terised in that it comprises the steps of placing the specimen onto a carriage of a specimen cooling and warming apparatus having a temperature gradient within its confines, moving the carriage through the temper¬ ature gradient at a rate or rates set by a raising/ lowering rate means. 11. A method of cooling and warming a specimen accor- ding to claim 10 characterised in that it comprises the steps of moving the carriage through the temperature gradient at a rate or rates dependent upon time lapsed, temperature of the specimen and/or the type of specimen under direction of the raising/lowering rate means. 12. A method of cooling and warming specimen according to claim 10 or 11, characterised in that cooling of the specimen comprises the step of lowering the carriage through the temperature gradient from relatively warm temperatures to relatively cold temperatures. 13. A method of cooling and warming specimens according to claim 10 or 11, characterised in that warming of a relatively cold specimen comprises the step of raising the carriage through the temperature gradient from relatively cold temperatures to relatively warm temp¬ eratures.

Inventors: ATTIKOUZEL YIANNI, BEILBY JOHN ANDREW, ATTIKOUZEL, YIANNI, BEILBY, JOHN, ANDREW
Applicants: ATTIKOUZEL YIANNI, BEILBY JOHN ANDREW, ATTIKOUZEL, YIANNI, BEILBY, JOHN, ANDREW
Application year: 1986
Main classification: F25D3
IPC codes: A01N1, B01L7, F25D3, G01N1