Mechanical Characterization and Shape Optimization of Fascicle-Like 3D Skeletal Muscle Tissues Contracted with Electrical and Optical Stimuli

Here we present a quantitative approach to constructing effective 3D muscle tissues through shape optimization and load impedance matching with electrical and optical stimulation. We have constructed long, thin, fascicle-like skeletal muscle tissue and optimized their form factor through mechanical characterization. A new apparatus was designed and built which allowed us to measure force-displacement characteristics with diverse load stiffnesses. We have found that a) there is an optimal form factor that maximizes the muscle stress, b) the energy transmitted to the load can be maximized with matched load stiffness, and c) optical stimulation using channelrhodopsin2 in the muscle tissue can generate twitch force as large as its electrical counterpart for well developed muscle tissue. Using our tissue construct method we found an optimal initial diameter of 500 microns outperformed tissues using 250 microns by more than 60% and tissues using 760 microns by 105%. Using an optimal load stiffness, our tissues have generated 12 pJ of energy at a peak generated stress of 1.28 kPa. Additionally, the difference in optically stimulated twitch performance vs. electrically stimulated is a function of how well the overall tissue performs, with average or better performing strips having less than 10% difference. The unique mechanical characterization method used is generalizable to diverse load conditions and will be used to match load impedance to muscle tissue impedance for a wide variety of applications.National Science Foundation (U.S.) (Grant No. CBET-0939511)Singapore-MIT Alliance for Research and Technology (BioSyM IRG)National Science Foundation (U.S.). Emergent Behaviors of Integrated Cellular System

Stochastic Modeling and Control of Biological Systems: The Lactose Regulation System of Escherichia Coli

In this paper, we present a comprehensive framework for stochastic modeling, model abstraction, and controller design for a biological system. The first half of the paper concerns modeling and model abstraction of the system. Most models in systems biology are deterministic models with ordinary differential equations in the concentration variables. We present a stochastic hybrid model of the lactose regulation system of E. coli bacteria that capture important phenomena which cannot be described by continuous deterministic models.We then show that the resulting stochastic hybrid model can be abstracted into a much simpler model, a two-state continuous-time Markov chain. The second half of the paper discusses controller design for a specific architecture. The architecture consists of measurement of a global quantity in a colony of bacteria as an output feedback and manipulation of global environmental variables as control actuation. We show that controller design can be performed on the abstracted (Markov chain) model and implementation on the real model yields the desired result

Harnessing bacterial power in microscale actuation

This paper presents a systematic analysis of the motion of microscale structures actuated by flagellated bacteria. We perform the study both experimentally and theoretically. We use a blotting procedure to attach flagellated bacteria to a buoyancy-neutral plate called a microbarge. The motion of the plate depends on the distribution of the cells on the plate and the stimuli from the environment. We construct a stochastic mathematical model for the system, based on the assumption that the behavior of each bacterium is random and independent of that of its neighbors. The main finding of the paper is that the motion of the barge plus bacteria system is a function of a very small set of parameters. This reduced-dimensional model can be easily estimated using experimental data. We show that the simulation results obtained from the model show an excellent match with the experimentally-observed motion of the barge

Formation and optogenetic control of engineered 3D skeletal muscle bioactuators

Densely arrayed skeletal myotubes are activated individually and as a group using precise optical stimulation with high spatiotemporal resolution. Skeletal muscle myoblasts are genetically encoded to express a light-activated cation channel, Channelrhodopsin-2, which allows for spatiotemporal coordination of a multitude of skeletal myotubes that contract in response to pulsed blue light. Furthermore, ensembles of mature, functional 3D muscle microtissues have been formed from the optogenetically encoded myoblasts using a high-throughput device. The device, called “skeletal muscle on a chip”, not only provides the myoblasts with controlled stress and constraints necessary for muscle alignment, fusion and maturation, but also facilitates the measurement of forces and characterization of the muscle tissue. We measured the specific static and dynamic stresses generated by the microtissues and characterized the morphology and alignment of the myotubes within the constructs. The device allows testing of the effect of a wide range of parameters (cell source, matrix composition, microtissue geometry, auxotonic load, growth factors and exercise) on the maturation, structure and function of the engineered muscle tissues in a combinatorial manner. Our studies integrate tools from optogenetics and microelectromechanical systems (MEMS) technology with skeletal muscle tissue engineering to open up opportunities to generate soft robots actuated by a multitude of spatiotemporally coordinated 3D skeletal muscle microtissues.National Science Foundation (U.S.) (Science and Technology Center—Emergent Behaviors of Integrated Cellular Systems (EBICS) grant No. CBET-0939511)National Institutes of Health (U.S.) (EB00262)National Science Foundation (U.S.) (GM74048)National Science Foundation (U.S.) (HL90747)National Institute for Biomedical Imaging and Bioengineering (U.S.) (RESBIO, Integrapted Technologies for Polymeric Biomaterial)University of Pennsylvania. Center for Engineering Cells and RegenerationSingapore-MIT Alliance for Research and Technolog

Distributed Live Muscle Actuators Controlled by Optical Stimuli

A multi degree of freedom skeletal muscle system stimulated via optical control is presented. These millimeter-scale, optically excitable 3D skeletal muscle bio-actuators are created by culturing genetically modified precursory muscle cells that are activated with light: optogenetics. These muscle bio-actuators are networked together to create a distributed muscle system. Muscle systems can manipulate loads having no fixed joint. These types of loads include shoulders, the mouth, and the jaw. Topics: Actuators , Muscl

Bioengineered Fascicle-Like Skeletal Muscle Tissue Constructs

Tissue engineered skeletal muscle constructs have and will continue to be valuable in treating, and testing various muscle injuries and diseases. However a significant drawback to numerous methods of producing 3D skeletal muscle constructs grown in vitro is that muscle cell density as a fraction of total volume or mass, is often significantly lower than muscle found in vivo. Therefore a method to increase muscle cell density within a construct is needed. Topics: Biological tissues, MuscleNational Science Foundation (U.S.). Center on Emergent Behaviors of Integrated Cellular Systems (Grant CBET-0939511

Hybrid model predictive control of induction of escherichia coli

The lactose regulation system of Escherichia coli is known to exhibit a bistable behavior. The stable states correspond to the phenotypical states of the system, induced and uninduced. Stochastic modeling of the system enables us to reproduce an experimentally observed phenomenon of spontaneous transitions between the induced and uninduced states. The average behavior of a colony of a large number of cells can be accurately described by an abstract model of the system, which is a two state Markov chain. In this paper, we consider a control problem that involves regulating the fraction of induction of a colony of Escherichia coli. We use the abstract model to design a feedback controller based on model predictive control strategy. Upon simulation, we show that the model predictive control is superior to other control strategies that we have designed before, in terms of less fluctuation in the control input and less tracking error

Automated biomanipulation of single cells

Transport of individual cells or chemical payloads on a subcellular scale is an enabling tool for the study of cellular communication, cell migration, and other localized phenomena. We present a magnetically actuated robotic system for the fully automated manipulation of cells and microbeads. Our strategy uses autofluorescent robotic transporters and fluorescently labeled microbeads to aid tracking and control in optically obstructed environments. We demonstrate automated delivery of microbeads infused with chemicals to specified positions on neurons