CENTER
FOR BIOMEDICAL ENGINEERING
Physiological
Systems Engineering
Molecular medicine is widely heralded as the health care technology heir of the revolutionary advances in biotechnology, with efforts increasingly being directed toward the use of molecular-, cell- and tissue-based approaches to diagnosis and treatment of a great number and broad variety of pathologies and injuries. Start-up companies and major pharmaceutical and device corporations alike are investing heavily in this envisioned next wave of health care technology, offering a variety of approaches: cytokines, monoclonal antibodies, gene transfer, anti-sense oligonucleotides, cell transplantation, tissue regeneration... Indeed, with the expected completion of the human genome mapping in the next decade followed by its subsequent sequencing, the identities of molecular components underlying physiology and pathology will be ready for therapeutic targeting.
Despite this tremendous potential, the road from laboratory discovery to effective clinical practice has been difficult for most of the "magic bullets" proposed over the past decade. Monoclonal antibody approaches have not been anywhere near as effective against tumors as originally touted, mainly because of physical transport and chemical kinetic limitations -- issues that can be addressed by incorporating engineering design at almost every stage in the process. Biomaterials implants and encapsulated cell transplants have not yet reliably resisted inflammatory and immune responses, requiring improved design of materials' chemical and mechanical properties. Cytokines such as epidermal growth factor and interferon have failed clinical trials because dosing regimens and modalities yielding desirable local cell responses but avoiding undesirable systemic complications have not been dealt with satisfactorily from a quantitative perspective.
It is becoming increasingly appreciated that many therapies will require an ability to diagnose and then correct or regenerate function of an integrated tissue structure, including appropriate cells and environmental molecules. Accomplishing this will depend on an ability to introduce the cells and molecules within carefully designed synthetic materials scaffolding which can then interact with the host in a manner that causes proper development of a functioning tissue-equivalent.
Clearly, the road for molecular medicine is not as straightfoward as identifying a crucial gene or protein or cell and then obtaining a desired physiological function by simply generating, replacing, inhibiting, or modifying that entity. Important molecules and/or cells must be identified, their structural properties characterized, and the key physicochemical properties upon which their functional effects are based must be elucidated. Target locations for the molecules and/or cells must be identified, and their delivery to that location in appropriate concentrations or with proper dynamics must be achieved -- indeed, what those concentrations and dynamics should be must first be understood. And, when delivery of the molecules and/or cells may be achieved, prediction or even assessment of their activity -- both locally and systemically -- must be accomplished in the most noninvasive ways feasible.
The following pages describe interests of participating CBE investigators in synergistic collaborative efforts aimed at making the sorts of contributions outlined above, according to the three major Thrust Areas.
Efforts in the Molecular Engineering Thrust Area are aimed at identification and characterization of structure and function of important biological macromolecules. A prominent example is DNA-based diagnostics, considered to be the next important development in preventative health care. However, progress in this field is perceived to be limited by the lack of suitable instrumentation to allow high volume, high throughput molecular analysis. Microdevices have a potential to gather and manipulate biochemical and genetic data in a fashion similar to integrated circuits, with the distinction that biochemical -- rather than electronic -- data would be managed. Nearly all of the analogous advantages of scaling to smaller size and greater parallelism apply. Much advanced microfabrication, and optoelectronics technology can be applied. Paul Matsudaira (Biology; Whitehead Institute)is undertaking studies to evaluate the design and construction of microfabricated systems for rapid automated sequencing of DNA. Typical applications require a microfluidic handler, a biomolecular separation device (operating on physical chemistry principles), a molecular identification device (doing selective biochemistry), and a sensor. Most additionally require an automated interface to sample preprocessing and to data analysis/archival storage. A collaboration with Dan Ehrlich (Lincoln Laboratory)is developing DNA hybridization arrays which employ immobilized single-strand probes in miniaturized geometry. These are read through fluorescence, chemiluminescence, radio tag, and direct measurement of dielectric properties of the array site. The approach allows massively parallel matching of DNA samples against templates. Arrays are currently several hundred elements, a size already very suitable for clinical diagnostics (to begin this year). He is also developing a microelectrophoresis chip for massive, low-cost DNA sequencing.
Marty Schmidt (Electrical Engineering & Computer Science)is creating individual components and integrated systems to sense and actuate liquid and gas flows, measure pressure and shear in these flows, and carry out chemical synthesis in microscale mixing chambers and reaction vessels. The technology employs methods of etching and bonding to form three-dimensional microstructures in single crystal silicon combined with conventional integrated circuit technology. Martha Gray (Electrical Engineering & Computer Science)is establishing technology for making optical measurements on molecular components of cells in flowing fluids, to produce an optical flow cytometer on a microchip. Paul Laibinis (Chemical Engineering)is developing nano-channeled structures with specifically-modified surface chemistry as a strategy for generating high surface area molecular biosensor elements. The resulting technology will provide signal amplification with thousand-fold signal amplification over substrates currently used in amperometric, fluorometric, and piezoelectric biosensors, offering a corresponding thousand-fold miniaturization of analytical and diagnostic systems.
Another example is characterization of DNA and protein structure/function relationships, so that the biochemical and biophysical properties crucial to molecular mechanisms in cell and tissue function can be understood and designed. Paul Matsudaira (Biology; Whitehead Institute)is studying DNA mechanical properties and their role in transcription, using an optical trap (or "laser tweezers") to generate stretch deformation so that subsequent elastic relaxation can be followed. Of special interest is the effect of condensation into chromatin, which should yield vastly different mechanical responses. Ian Hunter (Mechanical Engineering)is collaborating to develop microscopic chemical spectroscopies for probing associated structural alterations in response to imposed physical forces. Doug Lauffenburger (Chemical Engineering)and Don Ingber (Harvard Medical School)are interested in analogous effects of physical forces on protein/protein linkages such as receptor/ligand or receptor/cytoskeleton bonds or enzyme/substrate interactions. Forces imposed on magnetic microbeads can stress attached proteins, allowing measurement of associated changes in biochemical processes.
The Cell & Tissue Engineering Thrust Area focuses on effective delivery of drug, gene, and cell therapies, and fabrication of materials and devices necessary for regeneration of tissue function.
Essential to successful administration of therapeutic proteins or synthetic pharmacological agents is an ability to generate effective concentrations over necessary time periods without generating undesirable side effects. In many cases this requires local, rather than systemic, delivery modes. Bob Langer (Chemical Engineering)is pursuing a spectrum of innovative approaches toward these ends. His laboratory is developing controlled-release systems based on synthetic polymer encapsulation that can be triggered magnetically, ultrasonically, or enzymatically in order to increase release rates when desired. He is simultaneously creating new approaches for delivering drugs across complex tissue resistances in the body such as the blood-brain barrier, the lung, and the skin. In the latter case, approaches using external forces such as ultrasound or electricity are being investigated along with chemically-induced transport enhancement. Another area is production of polymeric nanoparticles that can circulate in the bloodstream for prolonged periods, for use in delivering drugs or genes or to specific cells. Bill Deen (Chemical Engineering),Alan Grodzinsky (Electrical Engineering & Computer Science), and Rakesh Jain (Harvard Medical School)are elucidating principles governing diffusive and convective transport of macromolecules through tissue, combining mathematical modeling with sophisticated microscopy techniques. Doug Lauffenburger (Chemical Engineering) is attempting to design improved peptide-based molecular conjugates to aid in delivering genes or therapeutic proteins more selectively and effectively. His approach exploits dynamic interactions of these with tissue cell receptors for endocytic uptake leading to intracellular localization or recycling back to the extracellular environment for reuse.
Elazer Edelman (Health Sciences & Technology),is applying a number of related approaches specifically to pathologies and injuries in the cardiovascular system. A major emphasis is on manipulating interactions of cytokines such as fibroblast growth factor with glycoprotein receptors and proteoglycans on blood vessel endothelial cell and smooth muscle cell surfaces, and with extracellular matrix components, for purposes of improving responses to treatments for atherosclerosis and other invasive cardiac procedures. Endovascular implants delivering therapeutic compounds, including anti-sense oligonucleotides, are being verified for angioplasty, endovascular stent placement, and bypass surgery.
In a growing number of applications cells can produce desired therapeutic molecules directly or be genetically-engineered in order to do so. This approach requires that specific cell populations be selected and delivered to appropriate tissue sites. When the cells are from foreign origin, they must be encapsulated by materials permitting passage of nutrients from, as well as therapeutic proteins out into, the surrounding environment -- but preventing factors that would stimulate an immune response against the implant. Clark Colton (Chemical Engineering) is investigating polymer membranes for implanting pancreatic cells to treat diabetes, attempting to provide immunoisolation properties along with inducing vascularization to improve molecular transport to and from the implant. He is also examining antibody-coated hollow-fiber membranes for affinity-based separations of specific cell populations for use in a variety of cell-based therapies. Shuguang Zhang (Biology)is synthesizing a novel class of self-assembling peptide biomaterials for cell encapsulation, with design criteria being developed by Roger Kamm (Mechanical Engineering)to ensure that membranes fabricated from these materials possess essential mechanical strength and molecular transport properties.
Not only can molecules and cells be delivered for therapeutic purposes, but a new generation of technologies capable of regenerating functional tissue from appropriate combinations of molecules, cells, and polymeric scaffolding is on the horizon. Yanni Yannas (Mechanical Engineering; Materials Science & Engineering)has developed tissue analogues based on collagen and proteoglycans for enhanced healing of skin wounds and nerve injuries, and in collaboration with Myron Spector (Harvard Medical School) is applying a similar approach to regeneration of damaged cartilage. Cartilage is a skeletal connective tissue which serves as a support structure between articulating joints, and as a scaffolding for bone development. It has an extensive extracellular matrix which confers the necessary mechanical properties, and contains chondrocytes -- cells which synthesize and maintain the extracellular matrix in accordance with functional demands. Degeneration of the matrix occurs in the various forms of arthritis. An understanding of the mechanism and manner by which mechanical forces modify chondrocyte behavior is crucial to regenerating cartilege via tissue engineering approachs, as well as to early, nonivasive diagnosis of degeneration. Alan Grodzinsky (Electrical Engineering & Computer Science)and Martha Gray (Health Sciences & Technology; Electrical Engineering & Computer Science) are employing a variety of methodologies to explore how cartilage properties and underlying chondrocyte functions are influenced by a combination of physical stresses and regulatory molecules.
Innovative engineering approaches to regenerating function of other tissues and organs are also being pursued energetically; prominent among these are liver, bone, blood vessels, and heart valves. Bob Langer (Chemical Engineering)is synthesizing and characterizating novel degradable polymers that encourage selective cell adhesion, migration, anding magnetic resonance imaging to monitor cartilage degeneration or regeneration as well as its transport properties for drugs and therapeutic cytokines. Fluorescence microscopy and immunohistochemistry are being employed by Elazer Edelman (Health Sciences & Technology) to follow dynamics of growth factor and receptor distributions in normal and diseased tissue, including cardiovascular applications with Bob Rosenberg (Biology, Harvard Medical School). In order to dramaticallcation process known as "3-dimensional printing" to generate devices possessing fine architectural features that allow spatial patterning of different ligands and cell types within, to aid in organization of developing tissues. Prevascularization of cell-seeded devices before implantation is an especially important outcome that this approach may enable. A close collaborator in many of these tissue regeneration projects is Joseph Vacanti (Harvard Medical School),a pioneer in the field of tissue engineering and its application to surgical reconstruction and repair of damaged organs. Quantitative, physico-chemical principles governing ligand- and architecture-controlled cell behavioral functions involved in these tissue engineering approaches are being studied by Doug Lauffenburger (Chemical Engineering)and Don Ingber (Harvard Medical School).
Physiological
Systems Engineering
A central direction in the Physiological Systems Engineering Area is quantitative measurement of cell and tissue function in vivo, for diagnostic purposes as well as assessment of therapeutic effectiveness.
One set of approaches emphasizes a spectrum of imaging modalities. Bob Rubin (Health Sciences & Technology)is applying advanced system ultrasound to study vascular biology in patients undergoing innovative therapies, and to determine whether analytical techniques can be developed to permit the measurement of visceral blood flow in real time. He is also exploring the use of positron emission tomography to monitor tissue pharmacokinetics and pharmacodynamics of important drugs, as well as ligand-receptor interactions in such tissues as the brain. This latter approach has been joined to a quantitative analysis of motor learning developed by Neville Hogan (Mechanical Engineering).Additionally, radionuclides are being used to delineate the trafficking of specific white cell populations in the body, a technique that may be useful in the study of innovative therapies for such disparate conditions as AIDS and multiple sclerosis. This methodology should be similarly valuable to cell-based immunotherapy approaches. Finally, diffusion-weighted magnetic resonance imaging is being applied to evaluate new therapies for ischemia-reperfusion injury of the brain. Martha Gray (Health Sciences & Technology, Electrical Engineering & Computer Science) is similarly using magnetic resonance imaging to monitor cartilage degeneration or regeneration as well as its transport properties for drugs and therapeutic cytokines. Fluorescence microscopy and immunohistochemistry are being employed by Elazer Edelman (Health Sciences & Technology)to follow dynamics of growth factor and receptor distributions in normal and diseased tissue, including cardiovascular applications with Bob Rosenberg (Biology, Harvard Medical School). In order to dramatically enhance capabilities for acquistion, storage, transmission, and analysis of these various types of imaging data, Forbes Dewey (Mechanical Engineering) is developing state-of-the-art computer algorithms and network technologies.
A different approach toward noninvasive diagnosis and assessment using chemical and mechanical probes employes innovative microscopic spectroscopies under creation by Ian Hunter (Mechanical Engineering).One example is laser speckle interferometry to monitor reactions of corneal tissue to contact lens biomaterials. Another is development of a next-generation confocal scanning laser microscope that combines multiple optical imaging modalities sensitive to different cell or tissue structures and biochemical components. Envisioned is a capability for discerning 3-dimensional information through optically-thick tissue sections, permitting visualization of therapeutic proteins or gene products. Yet another approach to local monitoring of tissue conditions, for instance during skin wound healing, is measurement of regulatory molecules whose transport from tissue into sensor elements is enhanced by dermally-applied low-frequency ultrasound, being pursued by Bob Langer (Chemical Engineering).
Assessment of tissue physiology, of course, requires not only measurement of relevant molecular species but also of macroscopic function. Thus, it is essential that quantitative engineering methodologies be used to determine functional consequences of molecular-, cell-, and tissue-based therapies. Examples include monitoring of neuromuscular responses by Neville Hogan (Mechanical Engineering),renal transport properties by Bill Deen (Chemical Engineering),airway smooth muscle contraction by Roger Kamm (Mechanical Engineering),convective ion flows in cartilage by Alan Grodzinsky (Electrical Engineering & Computer Science),and heat and mass transfer in tumors by Rakesh Jain (Harvard Medical School). For implanted biomaterials such as cardiovascular and orthopedic prostheses and assist devices as well as structures serving as scaffolding for encapsulation or support of cells in tissue engineering, it is crucial to determine mechanisms of failure, sub-clinical interactions, and structural correlations of successful function, as performed in the program of Fred Schoen (Harvard Medical School).The objectives of his studies are to understand the problems that limit the success of currently available devices and to develop improved designs and management strategies. Tissues affected by implantation are studied by histology, scanning and transmission electron microscopy, energy-dispersive X-ray analysis, and biochemical assays. And to permit crucial toxicological testing of therapeutic compounds and regimens, a novel tissue engineering approach is being constructed by Linda Griffith (Chemical Engineering),Joseph Vacanti (Harvard Medical School),and Bob Rubin (Health Sciences & Technology)in which human liver tissue is generated in vitro in a vascularized device that can be joined to the circulation of experimental animals. In all these cases, and numerous others, these sorts of engineering measurements are crucial to understanding how to successfully accomplish the broad spectrum of treatments arising in "molecular" medicine.
