Cellular Engineering 533 As described earlier,there are many factors which influence our ability to grow cells,however,to a large degree these are at best only partially understood.The re- sult is that,although "the cultural revolution has begun"as advertised a few years ago by Invitron,a St.Louis-based company,cell culture technology remains more an art than a science.Still,the technology used in culturing mammalian cells has become a cornerstone for the development of cell and molecular biology as a scientific dis- cipline and in the commercial applications arising out of this basic research. BASIC RESEARCH IN CELL BIOLOGY As noted in the previous section,the advent of cell culture technology has helped to dramatically accelerate advances in cell biology.This is true of the entire spectrum of research on cellular and sub-cellular phenomena.The engineer,through the vari- ety of ways in which the principles and methods of engineering can be applied,has been a participant in this area.Another key factor which links engineering to cell bi- ology is its relationship to the biophysics of a cell,i.e.,the role of physical mecha- nisms and the influence of physical factors on cellular behavior. Because most biomedical researchers,e.g.,MDs and life scientists,have a train- ing which,in general,is biochemistry based,and which does not emphasize physics, these researchers have tended to focus more on the biochemistry of a cell and not on the biophysics of a cell.However,physical factors have been demonstrated to be im- portant,and one example of this is in the influence of mechanical stresses and the re- sulting mechanics of deformation.Engineers involved in such studies of biomechanics have contributed and continue to contribute to our understanding of organ physiol- ogy and tissue behavior.They are now applying their knowledge to the investigation of the mechanical nature of much of cellular phenomena and the application of the principles of mechanics in order to understand the structure and function of cells(38). This type of cellular biomechanical phenomena can be illustrated by the process of cell division.In examining this process for an eukaryotic cell,one must consider the entire reproductive cycle of the cell(2).This cell cycle includes a number of sep- arate phases.The actual process of cell division is called M phase (M=mitosis),and the next cycle starts with the G phase(G gap)which is the period of time between the end of M phase and the beginning of DNA synthesis.The period of DNA syn- thesis is called S phase(S synthesis),and it ends when the DNA content of the nu- cleus has doubled and the chromosomes have replicated.The cell then enters the G2 phase,which may be viewed as preparatory for the actual process of cell division.The G2 phase is followed by M phase which in itself is composed of two specific events, mitosis and cytokinesis.Mitosis involves the splitting of the content of the nucleus, which causes a variety of intracellular movements,of mechanical nature,to take place during the different mitotic phases.Also,during cytokinesis,when the cell divides its cytoplasm,there is a very distinct mechanical event when the contractile ring,which has formed from cytoskeletal components,cleaves the cell into two daughter cells. These,of course,are not purely mechanical events.They are more accurately called mechano-chemical phenomena,and there is in fact an increasing recognition of the importance of such phenomena,and the strong coupling between structure and func- tion in an eukaryotic cell. The study of the influence of hemodynamics on vascular biology/pathobiology, and as a factor in the localization of atherosclerosis (45),is one area of biomedicalCellular Engineering 533 As described earlier, there are many factors which influence our ability to grow cells, however, to a large degree these are at best only partially understood. The re￾sult is that, although "the cultural revolution has begun" as advertised a few years ago by Invitron, a St. Louis-based company, cell culture technology remains more an art than a science. Still, the technology used in culturing mammalian cells has become a cornerstone for the development of cell and molecular biology as a scientific dis￾cipline and in the commercial applications arising out of this basic research. BASIC RESEARCH IN CELL BIOLOGY As noted in the previous section, the advent of cell culture technology has helped to dramatically accelerate advances in cell biology. This is true of the entire spectrum of research on cellular and sub-cellular phenomena. The engineer, through the vari￾ety of ways in which the principles and methods of engineering can be applied, has been a participant in this area. Another key factor which links engineering to cell bi￾ology is its relationship to the biophysics of a cell, i.e., the role of physical mecha￾nisms and the influence of physical factors on cellular behavior. Because most biomedical researchers, e.g., MDs and life scientists, have a train￾ing which, in general, is biochemistry based, and which does not emphasize physics, these researchers have tended to focus more on the biochemistry of a cell and not on the biophysics of a cell. However, physical factors have been demonstrated to be im￾portant, and one example of this is in the influence of mechanical stresses and the re￾sulting mechanics of deformation. Engineers involved in such studies of biomechanics have contributed and continue to contribute to our understanding of organ physiol￾ogy and tissue behavior. They are now applying their knowledge to the investigation of the mechanical nature of much of cellular phenomena and the application of the principles of mechanics in order to understand the structure and function of cells (38). This type of cellular biomechanical phenomena can be illustrated by the process of cell division. In examining this process for an eukaryotic cell, one must consider the entire reproductive cycle of the cell (2). This cell cycle includes a number of sep￾arate phases. The actual process of cell division is called M phase (M = mitosis), and the next cycle starts with the G1 phase (G = gap) which is the period of time between the end of M phase and the beginning of DNA synthesis. The period of DNA syn￾thesis is called S phase (S = synthesis), and it ends when the DNA content of the nu￾cleus has doubled and the chromosomes have replicated. The cell then enters the G 2 phase, which may be viewed as preparatory for the actual process of cell division. The G2 phase is followed by M phase which in itself is composed of two specific events, mitosis and cytokinesis. Mitosis involves the splitting of the content of the nucleus, which causes a variety of intracellular movements, of mechanical nature, to take place during the different mitotic phases. Also, during cytokinesis, when the cell divides its cytoplasm, there is a very distinct mechanical event when the contractile ring, which has formed from cytoskeletal components, cleaves the cell into two daughter cells. These, of course, are not purely mechanical events. They are more accurately called mechano-chemical phenomena, and there is in fact an increasing recognition of the importance of such phenomena, and the strong coupling between structure and func￾tion in an eukaryotic cell. The study of the influence of hemodynamics on vascular biology/pathobiology, and as a factor in the localization of atherosclerosis (45), is one area of biomedical