Bioprocess engineering is concerned with translating biological science into biologically based manufacturing. To be prepared for the biological manufacturing systems of the future, it is important to identify the fields of science and technology that have reached or will soon reach early prototypes and to begin to develop engineering systems to deal with them. The lead time in development of any new technology is long. Biological science is so prolific that any present list of future developments of technology must be incomplete. It is, however, straightforward to identify subjects in which new engineering techniques must be developed now, if the technologies are to be available when they are needed in large-scale manufacturing 5–15 years from now.
6.1.1 Biopharmaceuticals and Biopesticides from Insect Cell-Baculovirus System
Insect cells from moths can be cultivated in a manner similar to (but not identical with) the manner in which mammalian cells can. Unlike mammalian cells, insect cells are naturally continuous cell lines. They can be adapted easily to growth in serum-free media. The unique biphasic life cycle of the baculovirus, which readily infects cultured insect cells, makes it an ideal vector for expression of foreign genes. The baculovirus contains a late promoter that is very strong—perhaps the strongest eukaryotic promoter known. Consequently, the insect cell-baculovirus expression can be used to produce very high levels of protein (up to 40% of total protein) in a
nontransformed host cell (i.e., noncancerous) with a vector that is non-pathogenic to vertebrate animals. Those features of high expression levels and increased safety distinguish this system from the commonly used mammalian expression systems. However, the high expression levels are not typically obtained with secreted, glycosylated proteins. Although insect cells have most of the posttranslational machinery of mammalian cells, proteins produced in the baculovirus system are not processed in precisely the same way as in mammalian hosts (Luckow, 1990; Shuler et al., 1990).
Currently, the insect cell-baculovirus system is widely used to produce research quantities of proteins in many industrial laboratories. It is a convenient system for gene expression, and most proteins are produced in the correctly folded conformation. One product, a coat protein from HIV (the virus responsible for AIDS) produced from the baculovirus system, is in Phase II clinical trials and could be produced commercially within 5 years. Other commercial developments of the baculovirus system will depend on bioprocess research to increase expression levels of secreted glycosylated proteins.
The baculovirus itself has been approved for use as a pesticide. Genetic modifications to the virus to increase its effectiveness (e.g., speed of killing) are being tested. Large-scale production of such a biopesticide with cell culture will present unprecedented challenges for large-scale, inexpensive animal-cell reactor designs.
6.1.2 Gene-Based Pharmaceuticals and Gene Therapy
New classes of products are being tested for use in humans and animals, all sharing genes as common targets. Products based on antisense technology directed toward neutralizing messenger RNA are probably being pursued most vigorously; gene therapy through permanent alteration of chromosomes might hold the greatest potential for treatment of diseases like cancer and for correction of genetic disease. The products depend either on classes of compounds that are related to nucleic acids (oligonucleotides and oligonucleotide analogues), on cells that have been genetically altered, of on viruses that bear appropriate nucleic acids. For the large-scale production of nucleotides and nucleotide analogues, new molecular techniques must be developed. There are now no procedures for making substantial quantities of these types of materials in high purity and with appropriate chirality. Basic chemical and biochemical techniques must be developed for their preparation; new techniques (probably based on high-pressure chromatography) will be required for large-scale purification, and biological methods might be required for preparation of precursors and perhaps for formation of bonds. For genetically modified cells and viruses, the usual techniques for mammalian-cell culture and molecular biology will be required, as will additional measures for safety and for economical, patient-specific production.
Vignette 6 Cell-Transplantation Therapy
Cell transplantation is being explored as a means of replacing tissue function. Individual cells are harvested from a healthy section of donor tissue, isolated, expanded in culture, and implanted in a patient at the desired site of the functioning tissue. Also, cell-based therapies are being developed that involve the return of genetically altered cells to the host with gene-insertion techniques.
Cell transplantation has several advantages over whole-organ transplantation. Because the isolated cell population can be expanded in vitro with cell culture, only a small number of donor cells are needed to prepare an implant. Consequently, the living donor need not sacrifice an entire organ. The need for a permanent synthetic implant is eliminated through the use of natural tissue constituents without the disruption and relocation of a whole piece of normal tissue. The use of isolated cells also allows removal of other cell types that might be the target of immune responses, thus diminishing the rejection process. In addition, major surgery on the recipient and donor, with its inherent risks, is avoided. Finally, the cost of the transplantation procedure can be reduced substantially.
Isolated cells cannot now be made from new tissues in complete isolation. They require specific environments that often include supporting material to act as a template for growth. Three-dimensional scaffolds will probably be used to mimic their natural counterparts, the extracellular matrices (ECMs) of the body. The scaffolds will serve as both a physical support and an adhesive substrate for isolated parenchymal cells during in vitro culture and later implantation.
Because of the multiple functions of the materials, the physical and chemical requirements are numerous. To accommodate a sufficient number of cells for functional replacement, a cell-transplantation device must have a large surface area for cell adhesion. High porosity provides adequate space for cell seeding, growth, and ECM production. A uniformly distributed and interconnected pore structure is important for easy distribution of cells throughout the device and formation of an organized network of tissue constituents. This allows for cell-cell communication through direct contact and through soluble factors. Also, nutrients and waste products must be transported to and from differentiated groups of cells, often in ways that maintain cell polarity. In the reconstruction of structural tissues, such as bone and cartilage, tissue shape is integral to function. Therefore, the scaffolds must be processable into devices of varied thickness and shape. Furthermore, because of the goal of eventual human implantation, the scaffold must be made of biocompatibte materials. As the transplanted-cell population grows and the cells function normally, they will begin to secrete their own ECM support. The need for an artificial support will gradually diminish; if the implant is biodegradable, it will be eliminated as its function is replaced.
Two major research thrusts are required to develop technology for cell transplantation. The first deals with appropriate cell-culture techniques, and the second addresses the nature of the scaffold. The two are closely related, and examination of one issue will influence the other. Both require innovative bioprocess engineering to produce differentiated and structured products at a cost that our national health-care system can afford.
The study of the adhesive interactions between cells and both synthetic and biological substrates will be pivotal in determining the effect of different physical and
chemical factors on cell and tissue growth and function. Until recently, most research in the field has focused on minimizing biological fluid and tissue interactions with biomaterials in an effort to prevent fibrous encapsulation from foreign-body reaction or clotting in blood that has contact with artificial devices. In short, much biomaterials research has focused on making the material invisible to the body. Innovations that use the inverse approach-programmed extensive interaction of the material with biological tissue-will give biomaterials research a new focus. Novel biomaterials that incorporate specific peptide sequences will be developed to improve cell adhesion and promote differentiated-cell growth by releasing growth factors, angiogenesis factors, and other bioactive molecules.
Cell-based therapies and artificial organs have the potential to have a great impact in medicine for treatment of diseases of aging, degenerative diseases, burns, blood and lymphoid disorders, orthopedic problems, and others. A multidisciplinary approach based on recent advances in biochemistry, cell biology, and materials science will be necessary to respond to emerging technology problems. Developing the needed differentiated-cell culture in three dimensions on a large enough scale to be economically feasible will remain a challenge for bioprocess engineers well into the twenty-first century.
6.1.3 New Catalysts
New types of catalysts based on biological systems are being developed. Among them are catalytic antibodies (abzymes) and catalytic nucleic acids (ribozymes). Those types of materials can, in principle, be used both in specialty-chemical production and in human therapy. Although the techniques required for preparing abzymes will be the same as those used in other kinds of monoclonal-antibody manufacture, production of ribozymes (initially for applications in human health) will require an entire new array of manufacturing, purification, and production technologies; there are no large-scale methods for preparation, isolation, and purification of high-molecular-weight nucleic acids.
6.1.4 Cells, Organs, and Biomaterials
Production of human skin is already a commercial business in the United States; clonal production of lymphocytes is in an early stage of development. With the enormous advances in the biology of differentiation and development, a clear target for the future is large-scale production of cells (initially) and intact organs (later) for use in therapy and organ replacement. Bioprocess engineering will be required to develop new types of reactors and to delineate biological mechanisms that affect growth and maintenance of the cells and differentiated state of these cells. Although lymphocytes in culture can be prepared now, economical production still requires substantial improvement of existing techniques.
The technology for production of organs will be much more complex. The rapid increase in knowledge concerning the role of growth factors, cytokines, and other molecules important in cellular communication, coupled with the realization that the three-dimensional matrix in which tissue cells grow is crucial in maintaining cell phenotype, has opened up the possibility of cultivation of viable functioning organ structures. The first applications, already well under way, are in bone marrow cultures and tissues for cosmetic reconstruction. With the increasing concern about the safety of blood products, the ability to culture specific types of blood cells might be crucial for treatment of many diseases and wounds and for surgical procedures. There are serious engineering challenges in developing a system for successful large-scale cultures. Important problems remain in understanding the role of mass transfer, protein matrix for cell attachment and growth, and medium formulation, particularly the proper combination of growth factors required to optimize production of specific cell types. Cosmetic applications include cartilage and artificial skin. Great strides in the latter field in the last decade have resulted in many applications, from burn treatment to reconstruction after surgical procedures, such as breast-cancer removal. But there is need for much improvement even here.
Longer-range opportunities include hepatic, pancreatic, and kidney cell cultures. A complex three-dimensional substrate is required to maintain cell differentiation and organ function. Again, many engineering problems must be solved. Providing new vasculature for substrate delivery and product removal is vital. Most organ cells have a polarity that is required for proper function. The overall basic biology of the complex systems required to direct and control differentiating cells is not now understood, and it is impractical to specify in any detail the types of reactors that will be required in the future, other than to say that they will be much more complex and interactive than those now used.
With an aging population, there is increasing interest in biologically compatible materials for replacement of organs, joints, and ligaments and for related applications. Collagen, biologically derived polyesters, hyaluronic acid, and other materials have all shown attractive properties in some applications. New biological materials (for example, spider silk or protein adhesives from barnacle and mussel) might be usable for such applications as sutures and bioadhesives. They are ''specialties,'' rather than true pharmaceuticals, even if they are used in human health-care applications. Thus, the economics of production are more important for them than for conventional drugs, and the process aspects of their production are critical.
6.1.5 Transgenic Animals
Transgenic animals are being developed for a wide variety of applications, and bioprocess engineering will play a role in the use of these ani-
mals in several ways. If transgenic animals are used as factories for production of biological substances (e.g., as protein in milk), bioprocess engineering will be required to develop appropriate techniques for isolation and purification of the desired products. More important in the short term is that transgenic animals might provide test beds for proving the safety of new pharmaceutical entities and for accelerating their passage through the regulatory process. Bioprocess engineering can play an important role in controlling the testing technologies, perhaps in maintaining transgenic tissues and organs, and in coupling the testing available for use in transgenic animals with the development of processes that are acceptable and robust from a regulatory viewpoint.
6.1.6 Transgenic Plants
Transgenic plants are capable of generating specialty chemicals or other bioproducts. Special bioprocessing capabilities will then also need to be developed for extracting, concentrating, and purifying such products from plant tissue. This sector of bioprocess engineering might also be important to the prospects of expanding crops or developing new varieties that are rich in fermentable carbohydrates, which are readily used as feedstocks for large-scale manufacturing of specialty and industrial chemicals.
Transgenic tobacco plants have been developed to produce monoclonal antibodies identical in function with the original mouse antibody. Other proteins produced in plants are human serum albumin and enkephalins (Hiatt et al., 1989; Hein et al., 1991). Processes to recover and purify proteins from plant-cell extracts will be needed if such systems are commercialized.
6.1.7 Nontraditional Organisms
Many unusual chemicals or enzymes with unique properties come from organisms that are difficult to culture effectively. In particular, marine microbes (especially algae) and extremophiles (primarily the archaebacteria) present important, but long-range opportunities. Bioprocess engineers have already demonstrated the ability to design devices and protocols to culture microbes from deep-sea vents and undoubtedly have the skills necessary to develop techniques for other difficult-to-culture organisms.
6.1.8 Energy and Renewable Resources
A broad range of technical opportunities might require large-scale engineering. For example, if biologically produced materials (surfactants and viscosifiers) are used in enhanced oil recovery and in transportation of heavy crudes and coal slurries, appropriate biological manufacturing facilities must be developed. Particularly for those purposes, the ability to pro-
duce materials economically on-site from local raw materials might be important and might require development of completely new technology. Although ideas for desulfurization of coal and liquid hydrocarbons seem, at present, to be improbable, the development of materials from biological processes to aid in transportation and burning of coal, for example, seems plausible.
The largest-volume process that bioprocess engineering might be called on to address would be consumption of carbon dioxide (CO2) from combustion. If it is necessary to reduce CO2 emissions from stationary sources substantially to ameliorate the greenhouse effect, a plausible approach would be to couple CO2 release with growth of a CO2-requiring organism (either photosynthetic or nonphotosynthetic). The scale of any facility that would be used in this type of application would be enormous and would require innovative engineering to minimize costs.
In addition to those large-scale processes, there are plausible uses for biological catalysts on a smaller scale in a number of fields related to energy production and bioprocessing. For example, fuel cells based on enzymatic catalysis would provide an attractive method of using ethanol and perhaps other biologically derived fuels with high thermodynamic efficiency in an environmentally acceptable way. A range of chemicals can, of course, in principle be produced from renewable resources. The process for production of acrylamide from acrylonitrile has re-emphasized the practicality of large-volume production of some types of commodity chemicals with enzymatic catalysis (Nagasawa and Yamada, 1989). If energy costs continue to go up, if petroleum feedstocks become more expensive or more erratic in supply, and if processes based on conventional nonbiological catalytic systems become unacceptable from an environmental point of view, biological processing might be able to overcome what is usually an intrinsic economic disadvantage. In that event, bioprocess engineering will be called on to provide reactors and control systems appropriate for the production of commodity products (chemicals and fuels) with tight environmental and economic constraints.
Bioprocess engineering is an essential component for addressing those challenges. Fundamental understanding of the changes that occur in pre-treated cellulose to make it more reactive and identification of inexpensive approaches to the engineering of large-scale processes are first steps in producing a reactive substrate. Improvement of both the rate and the extent of xylose fermentation to ethanol requires an understanding of microbial physiology and of the optimal control of fermentation conditions to maximize productivity and yield. The fractionation of solutes from water is a challenge common to most fermentations, where the product is present at less than 10% concentration and is less volatile than water. Identification
of sorbents, for example, that remove the solutes from the water could be an important first step in improving the process.
6.1.9 Agricultural Chemicals and Food
Bioprocess engineering in agriculture and the food industry involves the application of biocatalysts (living cells or their components) to produce useful and value-added products, and it offers opportunities to design and produce new or improved agricultural and food products and their manufacturing processes. This will likely have a great impact on the U.S. food-processing industry, which has estimated annual sales of $255 billion. In our increasingly health-conscious society, genetically engineered microorganisms and specialty enzymes will find increased use in improving the nutritional, flavoring, and storage characteristics and safety of food products. Products under development range from genetically improved strains of freeze-resistant yeast used in frozen bakery products to phage-resistant dairy (yogurt) starter cultures. Chymosin, a product of recombinant E. coli, is already used in the milk-clotting step of cheese manufacture, and a recombinant maltogenic amylase is being used as an antistaling agent. Enzyme-based immunoassays could develop into a widely used method for detecting pesticides in foods at parts-per-billion concentrations. Challenges that must be addressed include the economics of production and regulatory issues (Glaser and Dutton, 1992).
The most important applications of bioprocess-engineering research and development related to agriculture and food involve production of agricultural chemicals for control of animal and plant diseases, growth-stimulating agents for improved yield, and biological insecticides and herbicides; increasing bioprocess efficiencies for fermented foods, natural food additives, food enzymes as processing aids, and separation and purification of the products; use of plant-cell culture systems to produce secondary metabolites or chemical substances of economic importance; and efficient use of renewable biomass resources for production of liquid fuel and chemical feedstocks and efficient treatment and management of agricultural wastes and wastes from food-processing industries.
6.1.10 Plant-Cell Culture
The commercial potential of plant-cell tissue culture has not yet been fully recognized and is underexploited. Plant-cell tissue culture has two primary products: plant tissue for efficient micropropagation of plants and the use of plant-tissue culture to produce specialty chemicals.
Plant-cell, -tissue, and-organ cultures can be used in processes analo-
gous to traditional fermentation processes for producing chemicals. Although less than 5% of the world's plants have even been identified taxonomically, from among the known plants over 20,000 chemicals are produced—about 4 times as many as from all microorganisms. Very few of the chemicals in pure or semipure form have been tested for their pharmacological activity for other uses. The enzymatic systems in plants can be used to generate completely new compounds when supplied with analogues of natural substrates; thus, plants contain an underused biochemical diversity. Even the limited use of this vast biochemical potential has had important impacts on mankind; in western countries, about one-fourth of all medicines are derived from compounds extracted from plants. Other plant products are used as flavors, fragrances, or pesticides.
Plant-cell tissue culture to produce chemicals commercially has been exploited in Japan, although regulatory approval for medicinal uses has proved difficult and commercial production is restricted to food uses and pigment production. In Japan, a government-sponsored consortium of universities and corporations was recently developed to establish a foundation for plant-cell culture exploitation (i.e., a precompetitive research thrust). In the United States, plant-cell tissue is not being exploited for chemical production, although at least two companies are actively developing processes for the production of the chemotherapeutic agent taxol.
The major technical barriers to the commercial exploitation of plant-cell tissue culture are low growth rates and relatively low product yields. To mitigate those problems, research is needed in subjects as diverse as bioreactor strategies to maintain high-density cultures and enable large-scale production of chemicals through organ cultures and a mechanistic understanding of the role of elicitors in activating pathways for secondary metabolites that could lead to higher productivities of compounds with therapeutic value.
6.1.11 Plants and Seeds
Basic research in plant molecular biology has allowed the clonal production of plants through the process of somatic embryogenesis, in which somatic cells develop through the stages of embryogenesis to yield whole plants without gamete fusion. Somatic embryos have been induced from a variety of plant tissues, and this system is commercially attractive for the high-volume multiplication of genetically improved embryos in culture. The clonal embryos are synthetic "seeds" that can be delivered to commercial growers. For many applications, somatic embryos have powerful advantages over conventional clonal propagation methods and other in vitro regeneration systems for mass propagation. One advantage is the very high multiplication rates. Depending on the plant species, virtually unlimited numbers of embryos can be generated from a single explant. A second advantage is that, for many species, growth and tissue development of somatic embryos
can be carried out in a liquid medium. That fact gives somatic embryogenesis the potential to be combined with engineering technology to create large-scale culture systems. The development of such engineering technology is the limiting step in commercialization.
The use of submerged liquid culture for the efficient mass production of embryos, artificial seeds, or plant propagates is a promising industrial technique now used in Israel and other countries. For crop and forest plants, micropropagation on solid medium is too expensive. The use of bioreactors, which reduces labor costs greatly, will probably be necessary for mass production of crop and forest plants generated by genetic engineering or nontraditional breeding methods. The key engineering problem in such systems is the control of environmental conditions necessary for development of organized tissues from unorganized, minimally differentiated tissues. Fundamental studies on the interaction of concentration gradients with cellular developmental processes are required.
6.1.12 The Environment
Many environmental problems will require bioprocess engineering. Some are discussed elsewhere in this report. Here we mention that, in addition to the types of problems commonly considered (minimization of manufacturing waste, treatment of municipal waste, environmentally friendly manufacturing), new classes of problems might arise from the concept of "life-cycle environmental responsibility." That idea is being actively considered in various European countries for such products as automobiles. The manufacturer would be responsible for its product throughout its life cycle, including its ultimate disposal. If that responsibility becomes a reality in any of the major markets, it will be necessary to develop new classes of processes for final disposal of components. The need for biodegradable polymers, for example, coupled with efficient biodegradation systems for disposing of manufactured components, would become a reality. Large volume and low cost in operation would be essential. Because there are virtually no counterparts for them at present, there is no experience to guide future development; these types of engineering and process problems would be truly novel.
The removal and oxidation of organic gases from contaminated air by microorganisms fixed in beds of soil, compost, or other solid materials might gain expanded acceptance as a process by which air is cleaned through biological means. Biofiltration has already enjoyed industrial success in Europe and Japan. Nonetheless, significant bioprocess engineering challenges remain in the use of organisms to remove gas-phase organic chemicals. These include gas-solid contacting, maintaining stable microbial populations, and predicting performance for scaleup purposes.
The unique problems presented by the manned exploration and colonization of space pose major and important challenges for bioprocess engineering. Space biology—the behavior of living systems in a zero-gravity (and perhaps high-radiation) environment—is just beginning to be investigated. The long-term influence of the space environment on cellular development remains to be determined. In principle, however, a plausible (from an economic point of view) application of processing in space would be to produce new cell lines. If it is possible to carry out manipulations of genetic materials or cell types in space that cannot be conducted on earth and if the modifications of cell behavior or germ-line composition that result from the manipulations can be preserved on return to earth, very high value could, in principle, be achieved. Because cells can be propagated and relatively small volumes of starting material (genetically altered cells) can be converted into large numbers of product cells after return to earth, the very high cost of manipulations in space would have a smaller affect on the overall cost of genetic manipulation of cell lines than of products that are sold by weight. The development of reactor systems and assay systems that are appropriate for use in space thus represents an important investment in this speculative field.
Reduced gravity (Moon and Mars) and microgravity (space station) would present some unique opportunities for the study of complex biological systems. One new interest is in the possible use of a microgravity environment to produce three-dimensional differentiated tissue structures in the fluid phase without a solid support. That could lead to a new tool for tissue engineering and the study of cell differentiation and developmental biology. Limitations in the knowledge of how cell suspensions and cell-to-cell communication affect the growth of such biomaterials might be quickly overcome once experiments are carried out on a space platform in low earth orbit. The objective would be research on manufacturing technologies, rather than manufacturing itself. Specific objectives include developing and testing experimental models for testing mammalian cell and tissue properties and for providing the necessary nutrients, biomodifiers, gases, and control. Important studies in developmental biology should be possible, including the generation of high-order tissue morphology of primary cells and ultimately perhaps complete organ generation. Once developed, the necessary techniques could be brought back to earth for manufacture. Bioprocess engineering is an element of all phases of such a project, from the design and implementation of orbiting bioprocess laboratory experiments to the implementation of the results for manufacturing processes on earth.
The problem of development of life-support systems for humans and other organisms in space is separate and highly important (if specialized).
The engineering of even conventional equipment for the space environment presents a unique set of problems. If the National Aeronautics and Space Administration (NASA) continues with its long-term goal of manned exploration of space, a major component of the reduction of space biology to engineering systems appropriate for life support of astronauts on long voyages will require the development of a specialized, light-weight, gravity-insensitive set of operations for handling and maintaining the appropriate environments for biological systems in space. The number of appropriately trained bioprocess engineers required for that effort would be substantial. NASA supports relatively small programs in space biotechnology through the Microgravity Science and Applications Division (MSAD) and the Life Sciences Division. One field in which the lack of density-gradient-driven convection could be important is protein nucleation and crystallization. Several active research projects are supported by MSAD (NASA, 1991). Another potential use of microgravity is in separation of large biological molecules (such as chromosomes) or cells (such as lymphocyte subpopulations), in which again gravity-induced sedimentation and density-gradient-driven convection could destroy separation ability.
This committee feels that space manufacturing of biological products for use on earth will not be fiscally feasible in the near future. For example, improvements in earth-based crystallization and separation systems and rapid developments in three-dimensional matrices for tissue engineering will make space-manufactured biomaterials too expensive. The space environment does provide a laboratory for interesting experiments in developmental biology and physiology, which should be pursued. Integration of those experiments into the space stations or the Moon-and Mars-based modules will require substantial collaboration between bioprocess engineers and basic biological scientists. That is particularly true because changes in local mass transport and fluid mechanics can often have important biological consequences (Nollert et al., 1991) on cell growth and structure formation, which must be separated from any effects of microgravity alone.
6.2 DEFENSE AND NATIONAL SECURITY
The Department of Defense (DOD) and Department of Energy face enormous problems in cleanup of military bases as they are closed or moth-balled and in cleanup of weapons laboratories. In the former, biological methods might play an important part. Much of the contamination in military bases is in the form of hydrocarbons, explosives, and related chemicals that are intrinsically biodegradable. If it proves economically feasible to use biodegradation rather than, say, incineration or controlled detonation to
dispose of unwanted ordnance and to clean up contaminated areas, the scale of the problem will require the development of new types of processes that can accommodate very large volume and low cost. Because military bases will be under government control, the sites could provide excellent opportunities for prototyping and developing cleanup technology that would be transferable directly into the civilian sector for municipal and hazardous-waste cleanup problems.
The weapons laboratories present special problems. The central problem is the management of radioisotopes, often in very dilute form as ground or water pollutants. Even here, however, biological systems might be useful. A key element in the cleanup of weapons laboratories is the reconcentration of dilute radioisotopes into concentrated form. Some microorganisms are very effective in mobilizing and concentrating specific elements. The development of appropriate organisms that would concentrate radioisotopes is not out of the question, but the engineering of systems required for processing contaminated materials and soils and for manipulating the biological products that would be produced does not now exist.
6.2.2 Chemical and Biological Warfare
A continuing problem in DOD concerns chemical and biological warfare. The stated U.S. position is to be prepared in a defensive mode, but not to be involved in production of biological weapons. The importance of either chemical or biological agents as practical weapons systems remains to be established. They are, however, systems for which protection must be available, and the potential for the use of either chemical or biological agents in the context of terrorism remains important. The defensive requirement for the ability to produce vaccines in large quantities with high flexibility for protection of military personnel (and, in some circumstances, civilian personnel) remains important. Some materials, like abzymes, have been considered for protection against chemical threats. Although that type of vaccine and countermeasure production can be carried out with conventional technologies, the opportunity to increase the responsiveness of the manufacturing systems, to allow manufacturing to produce tailored agents rapidly to meet new threats, and to lower the cost of production, particularly in episodic high-volume use, will benefit from development of new types of biological processes and manufacturing systems.
6.2.3 Stabilization of Developing Countries
A crucial element in national security is the stabilization of developing countries. Those countries might suffer from chronic deficits in food, energy, and transportation. They could, at the same time, have adequate sources
of renewable resources and abundant and inexpensive labor. A plausible connection between needs and available resources lies in the production of foods and energy from renewable resources with local labor and local processing facilities. Although this type of research is not the kind that is best done in the United States, it represents a worthwhile investment for the United States, through such international organizations as the World Health Organization, as a way of improving the standard of living and political stability in developing countries.
To meet the challenges posed by the long-term opportunities in biological engineering and manufacturing, the field of bioprocess engineering must address education and training, technology, and manufacturing.
6.3.1 Education and Training
In advanced bioprocesses (as in the ones that are of current interest), the key issue is education and training. For the United States to take maximal advantage of opportunities in biology, it will be necessary to have engineers who are thoroughly familiar with current biology and biologists who are interested in engineering. The development of programs to couple training in engineering with training in molecular biology and other life sciences is of the highest priority.
The development of analytical systems, sensors, and methods for production of ultrapure products is crucial in all manufacturing processes (especially for therapeutic products) based on molecules. Those systems will be as important for nucleic acids, nucleic acid analogues, and carbohydrates as for proteins—or perhaps more important. The details of the systems for nucleic acids, carbohydrates, and proteins will, however, each be substantially different. Bioprocess engineering should begin to develop appropriate sensors and purification systems for the next generation of products.
A number of applications in human therapy will require the isolation and clonal amplification of specific cell types (perhaps with stimulation by specific growth factors, cytokines, or antigens). Cell sorting is a laboratory technique. The engineering development of processes capable of inexpensive, automated, large-volume cell sorting will be important for projects that rest heavily on mammalian cells (as opposed to molecules).
Bioprocess engineering went through a phase in which substantial work
was invested in sophisticated reactors to obtain protein products from various types of cells. In general, those reactors have not been used: it has proved simpler to use relatively conventional reactors for such manufacturing processes. For more complex systems, however—especially of the sort required for organ culture and culture of other differentiated structures—new types of reactors will almost certainly be required.
Manufacturing is the ultimate product of engineering. Experience in the more classical kinds of manufacturing—automobiles, machine tools, electronic devices, and consumer appliances—indicates that a key to long-term profitability and quality is the integration of design, engineering, and manufacturing. Such phrases as ''design for manufacturing,'' "design for assembly," and now "design for disassembly" are common in industries involved in mechanical and electronic systems. They are less common in biomanufacturing. The development of disciplines that use engineering to couple early-stage science and prototyping with efficient manufacturing will be important in bioprocess engineering. In addition to "design for production," there might also be a discipline of "design for regulatory clearance" -the design of processes that are intrinsically robust to process variation and that will convincingly be presentable to the Food and Drug Administration and other regulatory agencies as safe and sure to yield products with acceptably small degrees of variance.
The outstanding performance of the United States in the basic life sciences should be maintained. The discoveries emanating from the basic life sciences provide the fundamental knowledge from which new concepts for products and biologically based manufacturing systems are derived. The committee strongly recommends that federal funding of biotechnology research be extended to support efforts that provide the science and technology base for producing and manufacturing products from biology. Targeted long-term research support would speed the development of commercial products, provide the trained personnel needed to support industrial activities, protect the entry-level U.S. products, provide the basis for low-cost production of the largest-volume (and highest-revenue) products, and help to integrate processes and concepts from biological science and bioprocess engineering. The United States has made an enormous, and enormously successful, investment in basic biological science. To protect that investment, and to capitalize on it, there must be an investment in bioprocess engineering.
Glaser, V., and G. Dutton. 1992. Food processors seek to adapt bioproducts for large-scale manufacturing. GEN 12(2):6–8.
Hein, M. B., Y. Tang, D. A. McLeod, K. D. Janda, and A. Hiatt. 1991. Evaluation of immunoglobulins from plant cells Biotechnol. Prog. 7:455–461.
Hiatt, A., R. Cafferkey, and K. Bowdish. 1989. Production of antibodies in transgenic plants. Nature 342:76–78.
Luckow, V. A. 1990. Cloning and expression of heterologous genes in insect cells with baculovirus vectors. In Recombinant DNA Technology and Applications, C. Ho, A. Prokop, and R. Bajpai, eds. New York: McGraw-Hill Book Company.
Nagasawa, T., and H. Yamada. 1989. Microbial transformations of nitriles. Trends Biotechnol. 7(6):153–158.
NASA (National Aeronautics and Space Administration). 1991. Pp. 87–104 in Microgravity Science and Application Program Tasks, Technical Memorandum 4284, 1990 Revision. Washington, D.C.: National Aeronautics and Space Administration.
Nollert, M. U., S. L. Diamond, and L. V. McIntire. Hydrodynamic shear stress and mass transport modulation of endothelial cell metabolism. Biotechnol. Bioeng. 38:588–602.
Shuler, M. L., T. Cho, T. Wickham, O. Ogonah, M. Kool, D. A. Hammer, R. R. Granados, and H. A. Wood. 1990. Bioreactor development for production of viral pesticides or heterologous proteins in insect cell cultures. Ann. NY Acad. Sci. 589:399–422.