A brief list of my most important collaborations in the general area of Functional Tissue Engineering
Bob's Home Page Muscle Mechanics Lab (U of M) Biomechatronics Group @ MIT
Hugh Herr, Ph.D., MIT Artificial Intelligence Laboratory and Harvard-MIT Health Sciences and Technology
Hugh and I share a vision. We also share a laboratory at MIT to realize our vision. We have recently been funded by DARPA to develop muscle-based actuators (An Actin Myosin Machine, Hugh Herr, PI). We are aggressively developing the technology to interface muscle tissue with synthetic devices for use in both robotic and prosthetic applications. Our calculations indicate that muscle is perhaps the finest actuator available. When compared with any synthetic actuator technology, by the standard metrics muscle compares favorably, or in some cases is superior, in terms of transduction efficiency, power output per kilogram mass of actuator, force generation and mechanical bandwidth. In addition, muscle has many advantages that place it in a class of its own; muscle operates silently (you have hundreds of muscle actuators operating at this very moment, can you hear any of them?), it has built-in mechanosensors for force, displacement, and velocity, it is self-regulating, scalable (from dust mites to blue whales), can adapt to the demands placed upon it (hypertrophy, fiber type transformations, fiber architecture), can heal when injured, can utilize more than one energy source (glucose or lipids, or straight ATP), has been known to operate in organisms for more than 100 years without requiring replacement or maintenance, among actuators it has unsurpassed architectural plasticity (it occurs in nature in the form of thick and thin sheets, fans, discs, rods, cones, fibers, tubes and hollow spheres), it is entirely biodegradable, and does not produce toxic byproducts when operated, and it has compliant mechanical properties that are advantageous for smooth, natural, gentle actuation.
There are many serious technical challenges to the application of skeletal muscle as a practical actuator, but ultimately the advantages are worth the effort and expense. In addition to the robotic and prosthetic applications, there is the potential for engineering functional tissue systems for surgical correction of traumatic injury and congenital defects. Hugh and I envision the day when prosthetic devices will be engineered hybrid biomechatronic systems, with seamless integration of synthetic and living components. We envision the evolution of these hybrid devices to include increasingly greater percentages of living components, until eventually the entire device would be biologic. The advantages of this approach are that the evolving hybrid prosthetic devices could be engineered from the cells of the prosthetic user, so that eventually the technology would permit direct tissue interfaces with the user, with no biocompatibility or tissue rejection problems. By integrating tissues with synthetic components, we can make use of the advantages of each class of material, while providing a platform for the parallel technological development required for the eventual creation of totally biological prosthetic devices and organ replacement systems.
Scott and I are currently formulating a collaborative project to engineer and model functional musculoskeletal subunits in vitro. We will integrate bone, tendon, cartilage and perhaps nerve tissue in an attempt to engineer a functional joint complex in culture. The focus is on tissue interfaces, and the mechanical properties of the regions where tissues come together to form complex structures. Examples of these transitional zones include the muscle-tendon junction, and the tendon-bone interface. Based upon my research in engineered skeletal muscle tissue, I have found that the engineered tissue is weakest at the the mechanical interface. This has also been noted by Herman Vandenburgh and his colleagues at Cell Based delivery, Inc. Our objective is to build a multidisciplinary research team to study musculoskeletal tissue interfaces, and to develop approaches to engineer mechanically robust multi-tissue systems.
Paul, Herman, and I are working on the development of automated tissue culture systems to monitor the contractility and excitability of engineered skeletal muscle constructs in culture. Our objective is to provide a scalable robotic platform to automate the setup, culture, and contractile function of cultured muscle for use in drug testing and discovery. This research is closely linked to Paul and Herman's work on the engineering of skeletal muscle for use in gene therapy and the cell based delivery of bioactive compounds.
Dave and I are collaborating on the development of scaffold-based muscle tissue systems, and muscle tissue interfaces. Dave, Dan Goldman, and I have an NIDCR RO-1 (Dave Mooney, PI) to study the use of biodegradable hydrogels for use as scaffolds in engineered skeletal muscle. dave and I are also collaborating on several projects to employ polymer photochemistry and scaffold manufacturing technology to produce controlled stiffness gradient matrices, with the objective of building tissue interfaces with gradual stiffness transitions to reduce stress concentrations in engineered tissue systems. This research is directly associated with the project currently being formulated by Scott Hollister and myself, and will form an important core technology for the robotic and actuator technology that Hugh Herr and I are developing.
Rich, Hugh and I are working to identify promising candidate muscles from throughout the animal kingdom for use as muscle actuators in our DARPA funded project, An Actin Myosin Machine. Rich is a highly skilled biologist and muscle mechanist with expertise in mammalian, amphibian, and crustacean muscle physiology. We are collaborating closely to develop a muscle organ culture system for maintaining muscle in vitro for long periods of time, to determine the optimal stimulation parameters, chemical, and mechanical environment for ex vivo muscle maintenance.
Nadia, High Herr, and I are working together on a DARPA funded project (An Actin Myosin Machine) to create genetically modified mammalian muscle that will have increased robustness for use as tissue based actuators, both as explanted native (whole) muscles, as well as self-organizing muscles, cultured in vitro. Nadia has a transgenic IGF-1 mouse that demonstrates significant muscle hypertrophy and improved tissue durability for prolonged culture periods.
John and I have many ongoing collaborations in muscle mechanics (at all levels of structural organization) as well as in tissue engineering. We also collaborate in the study of tissue engineered muscle from cells of aged mammals. This work is relevant to identifying the potential for the use of muscle satellite cells from mature adults for re-engineering tissue for clinical use.
Sue, Dennis and I are currently collaborating on several projects related to the mechanics of single muscle fibers. My role is to provide guidance and technical expertise in the design and development of new instrumentation to use laser diffraction to simultaneously measure the internal and surface mechanical strain in single muscle fibers. The research is directed toward understanding the effects of genetic mutations on the cytoskeleton of individual muscle fibers, and how this manifests in changes in lateral force transmission through the cell membrane, as well as the effects on sarcomere stability and heterogeneity of sarcomere lengths, which may lead to contraction-induced injury. This research will probe the underlying mechanisms of injury in genetically modified muscle, and for diseases such as muscular dystrophy.
Bill Kuzon had a very significant involvement in my skeletal muscle tissue engineering research from the very beginning. We have extended our collaboration to include acellularized nerve conduits for surgical implantation. Currently, Bill, Paul and I are working on engineering an acellularized nerve conduit, which is subsequently recellularized with Schwann cells to provide an effective neural conduit to surgically correct nerve gaps larger then 2 cm. We have developed a successful protocol for totally acellularizing a section of cadaveric nerve, which when implanted as an allograft, results in a lower overall immune response than a cellular autograft. The acellularized conduits also support repopulation by Schwann cells harvested from the recipient animal. We are currently developing methods to isolate and amplify Schwann cells, and promote extensive repopulation within the conduit. This collaborative research has relevance both to clinical surgical applications, as well as potential use in engineered tissue systems.
Dan and Pete use my implantable muscle stimulation system to control the gene expression in denervated skeletal muscles in rats. The Idea is to control the relative expression of different subunits (g and e) of the nicotinic acetylcholine receptor (nAChR) expressed by the muscle, to allow re-innervation of the skeletal muscle after long periods of denervation. Prolonged denervation of skeletal muscle is typified by a reversion to a state where the muscle expresses subunits that are not receptive to synaptogenesis. We have demonstrated that we can control and reverse this expression, and are currently executing experiments to demonstrate an increased potential for reinnervation of the long-term denervated skeletal muscles. Marlene is also working on a doctoral project which uses my implantable stimulators to maintain muscle mass and contractility during long-term denervation.
Dan, Marlene and I are also collaborating to use this same technology to control the expression of nAChR subunits in engineered muscle in vitro, which is normally refractory to reinnervation. By applying the correct type and phasing of electrical stimulation, we hope to promote synaptogenesis in vitro in a nerve-muscle co-culture system. This has enormous impact on the potential for tissue engineering functional neuromotor systems in vitro.
Tom and I have developed a system for applying controlled electromagnetic fields to tissues in 2-dimensional and 3-dimensional culture systems. As Tom finishes his Ph.D. we are preparing two manuscripts for publication. We have collected gene array data, being confirmed by Northern analysis, to prove that rapidly changing low level magnetic fields have a significant influence on the metabolism, morphology, and gene expression in cultured nerve cells.
Dave, Jamie and I are working on a design for a sieve electrode to interpose between nerve and muscle tissue in co-culture. The sieve electrode will be designed so as to allow nerve axons to project through as they sprout toward the muscle construct. We will then monitor the nerve axon depolarization during development, as well as have the ability to depolarize individual motor axons. The objective is to allow motor unit level control of engineered neuromuscular tissues in vitro. The technology will allow the in vitro study of synaptogenesis and muscle phenotype plasticity as exerted through controlled neuronal activity.
Dave Kohn and I are developing test fixturing to apply controlled mechanical loads to bone tissue in vivo. The apparatus will allow Dave to run experiments on the chemomechanical transduction and crack propagation in living bone. The collaborative work forms a core project for one of Dave's graduate students.
Gordon and I are developing experiments to study the growth and development of engineered skeletal muscle tissue under various conditions in vitro. This research will be an important contribution in establishing the validity of an in vitro skeletal muscle model for basic research in muscle metabolism.
Bob's Home Page Muscle Mechanics Lab (U of M) Biomechatronics Group @ MIT