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Cryobiology as viewed by the engineer
CRYonroL.oGY Vol 1, No. 1, 1964
CRYOBIOLOGY
AS VIEWED
BY THE ENGINEER*
C. W. COWLEY Union
Carbide
Corporation, Linde Division,
If one looks over the list of disciplines represented by those of us on this panel one cannot fail to be impressed with the wide range of training and experience which is listed under the title “Interdisciplinary Approach to Cryobiology.” I, myself, could not help but be reminded of those questionnaires which are calculated to evaluate the intelligence of high school students, job applicants, etc. The question usually presents a number of words and requests a check mark against one of the words which does not belong in the context of the others. I am sure that if such a question listed the disciplines of t,hose of us on this panel and presented it to groups of people unfamiliar with cryobiology, a check mark would be placed alongside the word “engineer” by almost 100%~ of those taking the test. This, of course, is not particularly surprising and serves only to emphasize that there exists even in today’s complex technology a fundamental lack of understanding of the interdisciplinary approach which has become necessary. Cryobiology is, in my own opinion, a classical example of a science in which meaningful progress depends very heavily upon the cooperation and collaboration between many t,echnological disciplines. As an engineer I have had the privilege, over the past several years, of being a part of the team represented on this panel and to have played some small part in the tremendous advances which have been accomplished in the low temperature preservation of biological materials. As a result of this experience, and because I am the one most likely to receive the check mark, I feel that I can make a few comments and suggestions which might be of interest and of value in furthering the progress of cryobiology. Before I talk specifically about an engineer’s view of cryobiology, I would like to make some comments of a more general nature. In any scientific effort requiring inputs from many
Tonawanda, New York
different sources of technology, there is one vitally import.ant problem which requires careful and sustained attention. This is the problem of communication between all of the disciplines involved. I realize that many thousands of words have been written and spoken on this subject of interdisciplinary communication by men with far more skill and experience than I can claim. This does not mean that no more needs to be said. Communication means a lot more than just talking or writing. It means a basic understanding of the objectives which must be met and a basic agreement on the methods and philosophies which must be used to get to these objectives. There are several roadblocks which must be surmounted before good communication can be established. Common units of measurement and terminology are, perhaps, the first requirement. I am sure most of you have had some experiences in this particular area. In my own case, I recall a walk-in cold room which was ordered with the specification that it maintain -10”. The biologist ordering the unit meant -lO”C, but the engineer in picking the unit interpreted it as -10°F. The net result was a walk-in cold room designed to operate at -23°C. This was obviously not a catastrophic misunderstanding, but does serve to illustrate the point. The solution to this particular problem, of course, is simple. Those of us still using such archaic units as “F and inches must become used to the c.g.s. unit.s used universally in the scientific field. In talking about difficulties with terminology, I am reminded of a discussion on boiling heat transfer between Dr. Luyet and myself. Considerable confusion existed until we realized that the term “nucleation site” meant different things to each of us. While I was referring to sites on t,he heat transfer surface at which bubbles are formed, Dr. Luyet was thinking in terms of nucleation sites for ice crystal formation. The problems which can result from such differences in terminology should not be under-estimated. In face-to-face conversat.ions, confusion can usually be quickly overcome. In corre-
* Presented at the First Annual Meeting, Society for Cryobiology, August 24-26, 1964, Washington, D. C. 40
CRYOBIOLOGY
1zS VIEWED
spondence, however, months may elapse before a common ground is reached. Of necessity, a concentrated effort is continually required to assure that we understand the specific terms we use in our technical conversations. A few moments ago, I mentioned the need for a basic understanding of objectives and a basic agreement on methods and philosophies among the various disciplines which are necessary for meaningful progress in a science such as cryobiology. How to accomplish this is, I think, one of the most important problems which must be faced. Our new Society for Cryobiology has been formed to promote such agreements and understanding. As an engineer, perhaps I can be forgiven for taking the ult,rapractical viewpoint. Cryobiology is a science devoted to the study of the phenomena and events which occur when a biological material is cooled to the freezing point, has the heat of fusion removed, and is then cooled to temperatures below which biological and chemical phenomena cannot occur (or can occur only very slowly). As an engineer, I am most concerned with the part that I can play in using the knowledge gained in such a study in a practical manner. My biological and medical associates show great enthusiasm for a procedure which will permit the indefinite storage of bioIog:ical samples without change. They amplify thleir enthusiasm with descriptions of the problems and difficulties which they faced before such freezing and storage techniques became available. Although I am not sure that I understand more than a small percentage of the terms that are used, I too have become enthusiastic. But the gap between enthusiasm and participation is a fairly large one. An engineer usually takes well formulated and reasonably well understood information and uses it to build a practical system. At the most, he may find it necessary to check the validity of theoretical formulas or find the value of a constant or an exponent under a given set of condit’ions. My initial exposure to cryobiology quickly convinced me tha.t there were very few textbooks which woulld assist me in making a contribution to this field. It was apparent that before widespread practical applications of cryobiology could be established, a greater understanding was needed of the fundamental events
BY ENGINEER
41
which occur when a material is cooled to very low temperatures. Even at this stage, however, t,he engineer can make some contributions. All of you know that the viability of a biological material after storage at very low temperatures is critically dependent upon the rate at which the material is cooled to, and removed from, bhe storage temperature. This is not simply a rout,ine heat transfer problem which can be quickly solved by the application of textbook formulas. Since temperature is a function of time as well as position, we are dealing with an unsteady heat transfer process. In addition, the occurrence of a phase change in the middle of the cooling and warming range presents an added complication to an already complex phenomenon. There have been few analytical solutions worked out for this class of problems, and those that have have been based on many simplifying assumptions. For example, it is usually assumed that the material undergoing a temperature change is homogeneous and has constant thermal properties, such as specific heat and thermal conductivity. Most biological materials are not homogeneous and thermal conductivity values vary by a very significant amount over the temperature range of interest to the cryobiologist. Simple analytical calculations to predict accurately the cooling curve for specific locations in a sample after it is immersed in a low temperature environment are thus almost impossible to make. This, of course, is very frustrating to the engineer who would feel much more secure if he could use a set of well established formulas as a stepping off point. Nevertheless, optimum cooling and warming procedures can be determined only by relating the temperature history to which the biological sample has been subjected to the degree of viability present after thawing. It has been necessary, therefore, for the engineer to use his knowledge of heat transfer, thermodynamics, electronics, and instrumentation to assist in devising and developing experimental procedures for measuring accurately the temperature history at various points in a sample as it is cooled or warmed. This, of course, is only half the battle. Learning how to measure temperature transient.s is of little value in cryobiology without techniques for varying and controlling the cooling rate
42
C. W. COWLEY
over as wide a range as possible. The range varies all the way from a fraction of a degree per minute to hundreds of degrees per second. Fundamentally, a possible approach to this problem is to vary the cooling rate by varying the temperature driving force to which the sample is exposed by using cooling environments at different temperature levels. All of you, I am sure, are aware of the limitations to such an approach. Among other things, one is confronted wit,11 the fact that a bath of isopentane at -120°C results in faster cooling of an immersed specimen that does liquid nitrogen at -196°C. A basic knowledge of heat transfer becomes important to understand the reasons behind such phenomena and to utilize them to the best advantage. An understanding of the heat transfer characteristics of a boiling fluid such as liquid nitrogen has led to techniques for varying and controlling the cooling rates of specimens immersed in it by the application of a thin layer of a thermally insulating material to the sample container. Although it must be admitted that the effect of such insulating coatings on heat transfer to a boiling fluid was discovered by accident rather than design, a rapid realization of the potential for this technique came from an engineering background in boiling heat transfer. At the other end of the cooling rate range, the engineer has been able to contribute his know-how and experience to develop systems for precisely controlling the temperature drop of the specimen in the liquid phase and the solid phase at rates from a fraction of a degree to a few degrees per minute. Of equal importance, he has been able to provide the investigators with the means for controlling and varying the time spent by the sample in the heat of fusion. In short, the engineer has found, and continues to find, a need for his own particular brand of knowledge and experience to help the investigator broaden his basic understanding of the events which occur as biological materials are frozen and thawed. This is a satisfying experience for any engineer worthy of the name. His role is of a secondary nature-he works within the framework set by the investigator. It must be emphasized, however, that, although the engineer considers the work of the basic investigator vitally important, he thinks of it in terms of a broad base upon which to
build functional and commercially feasible systems for the Iow temperature preservation of bioIogica1 materials. Systems” is a word which has a magical ring to the engineer’s ears. It means the assembly of components and procedures in an organized and logical manner such that the whole performs in a smooth and reliable way. In such a setting, the engineer no longer considers himself to be playing a secondary role. The basic information painstakingly obtained by the investigator is used to design the components and the procedures around the objectives of the system. It seems to me that the relationship between the engineer and the biologist or medical profession takes on a new aspect here. A more equal partnership is necessary with special emphasis upon mutual request for one another’s knowledge and experience. Specifications must be agreed upon, which the engineer then attempts to fulfill. Sometimes they are impossible or impractical to meet and compromise is required. Obviously, compromise is sometimes impossible. If sterility of the sample is required, for instance, then the engineer must make sure that his system design assures it. There is no room for modifications which would not assure it. Complete and frank communication between the engineer and biological or medical disciplines in its broadest sense is the very essence of success if we are to utilize the information gained by basic investigation to its fullest extent. I feel that this brings me to the case of my own views of cryobiology. The primary reason for carrying out a study of any phenomenon is a hope and belief that the knowledge gained can be used in some way for the betterment of humanity. Only the most cynical of us will deny the truth of such a statement. At any rate, I believe it is particularly true of cryobiology. But knowledge and underst,anding of phenomena is only the first step. Using such knowledge for practical purposes is the most important consideration. It is in this effort that the engineer can play his role to the fullest extent, but-and this is a very big “but’‘-only if he has a deep understanding of the objectives and philosophies of the work he is undertaking. This I feel, very strongly, can only come by direct participation in the search for the fundamental knowledge upon which the ultimate practical system is built. Interdisciplinary team-
CRYOBIOLOGY AS VIEWED BY ENGINEER work is, by its very nature, difficult to establish. It can best be accomplished at the ground level of the study. In summary, I am making a plea for a broader interpretation of the word “cryobiology.” The engineer can, and will, make a con-
43
tribution at all levels of investigation of this science. What is most important is that his contribution can be significantly increased if he can begin his association at the more basic levels, and continue it through to attainment of the ultimate objectives.
CRYOBIOLOGY
AS VIEWED
BY THE ENGINEER*
C. W. COWLEY Union
Carbide
Corporation, Linde Division,
If one looks over the list of disciplines represented by those of us on this panel one cannot fail to be impressed with the wide range of training and experience which is listed under the title “Interdisciplinary Approach to Cryobiology.” I, myself, could not help but be reminded of those questionnaires which are calculated to evaluate the intelligence of high school students, job applicants, etc. The question usually presents a number of words and requests a check mark against one of the words which does not belong in the context of the others. I am sure that if such a question listed the disciplines of t,hose of us on this panel and presented it to groups of people unfamiliar with cryobiology, a check mark would be placed alongside the word “engineer” by almost 100%~ of those taking the test. This, of course, is not particularly surprising and serves only to emphasize that there exists even in today’s complex technology a fundamental lack of understanding of the interdisciplinary approach which has become necessary. Cryobiology is, in my own opinion, a classical example of a science in which meaningful progress depends very heavily upon the cooperation and collaboration between many t,echnological disciplines. As an engineer I have had the privilege, over the past several years, of being a part of the team represented on this panel and to have played some small part in the tremendous advances which have been accomplished in the low temperature preservation of biological materials. As a result of this experience, and because I am the one most likely to receive the check mark, I feel that I can make a few comments and suggestions which might be of interest and of value in furthering the progress of cryobiology. Before I talk specifically about an engineer’s view of cryobiology, I would like to make some comments of a more general nature. In any scientific effort requiring inputs from many
Tonawanda, New York
different sources of technology, there is one vitally import.ant problem which requires careful and sustained attention. This is the problem of communication between all of the disciplines involved. I realize that many thousands of words have been written and spoken on this subject of interdisciplinary communication by men with far more skill and experience than I can claim. This does not mean that no more needs to be said. Communication means a lot more than just talking or writing. It means a basic understanding of the objectives which must be met and a basic agreement on the methods and philosophies which must be used to get to these objectives. There are several roadblocks which must be surmounted before good communication can be established. Common units of measurement and terminology are, perhaps, the first requirement. I am sure most of you have had some experiences in this particular area. In my own case, I recall a walk-in cold room which was ordered with the specification that it maintain -10”. The biologist ordering the unit meant -lO”C, but the engineer in picking the unit interpreted it as -10°F. The net result was a walk-in cold room designed to operate at -23°C. This was obviously not a catastrophic misunderstanding, but does serve to illustrate the point. The solution to this particular problem, of course, is simple. Those of us still using such archaic units as “F and inches must become used to the c.g.s. unit.s used universally in the scientific field. In talking about difficulties with terminology, I am reminded of a discussion on boiling heat transfer between Dr. Luyet and myself. Considerable confusion existed until we realized that the term “nucleation site” meant different things to each of us. While I was referring to sites on t,he heat transfer surface at which bubbles are formed, Dr. Luyet was thinking in terms of nucleation sites for ice crystal formation. The problems which can result from such differences in terminology should not be under-estimated. In face-to-face conversat.ions, confusion can usually be quickly overcome. In corre-
* Presented at the First Annual Meeting, Society for Cryobiology, August 24-26, 1964, Washington, D. C. 40
CRYOBIOLOGY
1zS VIEWED
spondence, however, months may elapse before a common ground is reached. Of necessity, a concentrated effort is continually required to assure that we understand the specific terms we use in our technical conversations. A few moments ago, I mentioned the need for a basic understanding of objectives and a basic agreement on methods and philosophies among the various disciplines which are necessary for meaningful progress in a science such as cryobiology. How to accomplish this is, I think, one of the most important problems which must be faced. Our new Society for Cryobiology has been formed to promote such agreements and understanding. As an engineer, perhaps I can be forgiven for taking the ult,rapractical viewpoint. Cryobiology is a science devoted to the study of the phenomena and events which occur when a biological material is cooled to the freezing point, has the heat of fusion removed, and is then cooled to temperatures below which biological and chemical phenomena cannot occur (or can occur only very slowly). As an engineer, I am most concerned with the part that I can play in using the knowledge gained in such a study in a practical manner. My biological and medical associates show great enthusiasm for a procedure which will permit the indefinite storage of bioIog:ical samples without change. They amplify thleir enthusiasm with descriptions of the problems and difficulties which they faced before such freezing and storage techniques became available. Although I am not sure that I understand more than a small percentage of the terms that are used, I too have become enthusiastic. But the gap between enthusiasm and participation is a fairly large one. An engineer usually takes well formulated and reasonably well understood information and uses it to build a practical system. At the most, he may find it necessary to check the validity of theoretical formulas or find the value of a constant or an exponent under a given set of condit’ions. My initial exposure to cryobiology quickly convinced me tha.t there were very few textbooks which woulld assist me in making a contribution to this field. It was apparent that before widespread practical applications of cryobiology could be established, a greater understanding was needed of the fundamental events
BY ENGINEER
41
which occur when a material is cooled to very low temperatures. Even at this stage, however, t,he engineer can make some contributions. All of you know that the viability of a biological material after storage at very low temperatures is critically dependent upon the rate at which the material is cooled to, and removed from, bhe storage temperature. This is not simply a rout,ine heat transfer problem which can be quickly solved by the application of textbook formulas. Since temperature is a function of time as well as position, we are dealing with an unsteady heat transfer process. In addition, the occurrence of a phase change in the middle of the cooling and warming range presents an added complication to an already complex phenomenon. There have been few analytical solutions worked out for this class of problems, and those that have have been based on many simplifying assumptions. For example, it is usually assumed that the material undergoing a temperature change is homogeneous and has constant thermal properties, such as specific heat and thermal conductivity. Most biological materials are not homogeneous and thermal conductivity values vary by a very significant amount over the temperature range of interest to the cryobiologist. Simple analytical calculations to predict accurately the cooling curve for specific locations in a sample after it is immersed in a low temperature environment are thus almost impossible to make. This, of course, is very frustrating to the engineer who would feel much more secure if he could use a set of well established formulas as a stepping off point. Nevertheless, optimum cooling and warming procedures can be determined only by relating the temperature history to which the biological sample has been subjected to the degree of viability present after thawing. It has been necessary, therefore, for the engineer to use his knowledge of heat transfer, thermodynamics, electronics, and instrumentation to assist in devising and developing experimental procedures for measuring accurately the temperature history at various points in a sample as it is cooled or warmed. This, of course, is only half the battle. Learning how to measure temperature transient.s is of little value in cryobiology without techniques for varying and controlling the cooling rate
42
C. W. COWLEY
over as wide a range as possible. The range varies all the way from a fraction of a degree per minute to hundreds of degrees per second. Fundamentally, a possible approach to this problem is to vary the cooling rate by varying the temperature driving force to which the sample is exposed by using cooling environments at different temperature levels. All of you, I am sure, are aware of the limitations to such an approach. Among other things, one is confronted wit,11 the fact that a bath of isopentane at -120°C results in faster cooling of an immersed specimen that does liquid nitrogen at -196°C. A basic knowledge of heat transfer becomes important to understand the reasons behind such phenomena and to utilize them to the best advantage. An understanding of the heat transfer characteristics of a boiling fluid such as liquid nitrogen has led to techniques for varying and controlling the cooling rates of specimens immersed in it by the application of a thin layer of a thermally insulating material to the sample container. Although it must be admitted that the effect of such insulating coatings on heat transfer to a boiling fluid was discovered by accident rather than design, a rapid realization of the potential for this technique came from an engineering background in boiling heat transfer. At the other end of the cooling rate range, the engineer has been able to contribute his know-how and experience to develop systems for precisely controlling the temperature drop of the specimen in the liquid phase and the solid phase at rates from a fraction of a degree to a few degrees per minute. Of equal importance, he has been able to provide the investigators with the means for controlling and varying the time spent by the sample in the heat of fusion. In short, the engineer has found, and continues to find, a need for his own particular brand of knowledge and experience to help the investigator broaden his basic understanding of the events which occur as biological materials are frozen and thawed. This is a satisfying experience for any engineer worthy of the name. His role is of a secondary nature-he works within the framework set by the investigator. It must be emphasized, however, that, although the engineer considers the work of the basic investigator vitally important, he thinks of it in terms of a broad base upon which to
build functional and commercially feasible systems for the Iow temperature preservation of bioIogica1 materials. Systems” is a word which has a magical ring to the engineer’s ears. It means the assembly of components and procedures in an organized and logical manner such that the whole performs in a smooth and reliable way. In such a setting, the engineer no longer considers himself to be playing a secondary role. The basic information painstakingly obtained by the investigator is used to design the components and the procedures around the objectives of the system. It seems to me that the relationship between the engineer and the biologist or medical profession takes on a new aspect here. A more equal partnership is necessary with special emphasis upon mutual request for one another’s knowledge and experience. Specifications must be agreed upon, which the engineer then attempts to fulfill. Sometimes they are impossible or impractical to meet and compromise is required. Obviously, compromise is sometimes impossible. If sterility of the sample is required, for instance, then the engineer must make sure that his system design assures it. There is no room for modifications which would not assure it. Complete and frank communication between the engineer and biological or medical disciplines in its broadest sense is the very essence of success if we are to utilize the information gained by basic investigation to its fullest extent. I feel that this brings me to the case of my own views of cryobiology. The primary reason for carrying out a study of any phenomenon is a hope and belief that the knowledge gained can be used in some way for the betterment of humanity. Only the most cynical of us will deny the truth of such a statement. At any rate, I believe it is particularly true of cryobiology. But knowledge and underst,anding of phenomena is only the first step. Using such knowledge for practical purposes is the most important consideration. It is in this effort that the engineer can play his role to the fullest extent, but-and this is a very big “but’‘-only if he has a deep understanding of the objectives and philosophies of the work he is undertaking. This I feel, very strongly, can only come by direct participation in the search for the fundamental knowledge upon which the ultimate practical system is built. Interdisciplinary team-
CRYOBIOLOGY AS VIEWED BY ENGINEER work is, by its very nature, difficult to establish. It can best be accomplished at the ground level of the study. In summary, I am making a plea for a broader interpretation of the word “cryobiology.” The engineer can, and will, make a con-
43
tribution at all levels of investigation of this science. What is most important is that his contribution can be significantly increased if he can begin his association at the more basic levels, and continue it through to attainment of the ultimate objectives.