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2016


Bioengineered and biohybrid bacteria-based systems for drug delivery
Bioengineered and biohybrid bacteria-based systems for drug delivery

Hosseinidoust, Z., Mostaghaci, B., Yasa, O., Park, B., Singh, A. V., Sitti, M.

Advanced Drug Delivery Reviews, 106, pages: 27-44, Elsevier, November 2016 (article)

Abstract
The use of bacterial cells as agents of medical therapy has a long history. Research that was ignited over a century ago with the accidental infection of cancer patients has matured into a platform technology that offers the promise of opening up new potential frontiers in medical treatment. Bacterial cells exhibit unique characteristics that make them well-suited as smart drug delivery agents. Our ability to genetically manipulate the molecular machinery of these cells enables the customization of their therapeutic action as well as its precise tuning and spatio-temporal control, allowing for the design of unique, complex therapeutic functions, unmatched by current drug delivery systems. Early results have been promising, but there are still many important challenges that must be addressed. We present a review of promises and challenges of employing bioengineered bacteria in drug delivery systems and introduce the biohybrid design concept as a new additional paradigm in bacteria-based drug delivery.

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DOI Project Page [BibTex]

2016


DOI Project Page [BibTex]


Creating body shapes from verbal descriptions by linking similarity spaces
Creating body shapes from verbal descriptions by linking similarity spaces

Hill, M. Q., Streuber, S., Hahn, C. A., Black, M. J., O’Toole, A. J.

Psychological Science, 27(11):1486-1497, November 2016, (article)

Abstract
Brief verbal descriptions of bodies (e.g. curvy, long-legged) can elicit vivid mental images. The ease with which we create these mental images belies the complexity of three-dimensional body shapes. We explored the relationship between body shapes and body descriptions and show that a small number of words can be used to generate categorically accurate representations of three-dimensional bodies. The dimensions of body shape variation that emerged in a language-based similarity space were related to major dimensions of variation computed directly from three-dimensional laser scans of 2094 bodies. This allowed us to generate three-dimensional models of people in the shape space using only their coordinates on analogous dimensions in the language-based description space. Human descriptions of photographed bodies and their corresponding models matched closely. The natural mapping between the spaces illustrates the role of language as a concise code for body shape, capturing perceptually salient global and local body features.

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pdf [BibTex]

pdf [BibTex]


A 5-D localization method for a magnetically manipulated untethered robot using a 2-D array of Hall-effect sensors
A 5-D localization method for a magnetically manipulated untethered robot using a 2-D array of Hall-effect sensors

Son, D., Yim, S., Sitti, M.

IEEE/ASME Transactions on Mechatronics, 21(2):708-716, IEEE, October 2016 (article)

Abstract
This paper introduces a new five-dimensional localization method for an untethered meso-scale magnetic robot, which is manipulated by a computer-controlled electromagnetic system. The developed magnetic localization setup is a two-dimensional array of mono-axial Hall-effect sensors, which measure the perpendicular magnetic fields at their given positions. We introduce two steps for localizing a magnetic robot more accurately. First, the dipole modeled magnetic field of the electromagnet is subtracted from the measured data in order to determine the robot's magnetic field. Secondly, the subtracted magnetic field is twice differentiated in the perpendicular direction of the array, so that the effect of the electromagnetic field in the localization process is minimized. Five variables regarding the position and orientation of the robot are determined by minimizing the error between the measured magnetic field and the modeled magnetic field in an optimization method. The resulting position error is 2.1±0.8 mm and angular error is 6.7±4.3° within the applicable range (5 cm) of magnetic field sensors at 200 Hz. The proposed localization method would be used for the position feedback control of untethered magnetic devices or robots for medical applications in the future.

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


High-Performance Multiresponsive Paper Actuators
High-Performance Multiresponsive Paper Actuators

Amjadi, M., Sitti, M.

ACS Nano, 10(11):10202-10210, American Chemical Society, October 2016 (article)

Abstract
There is an increasing demand for soft actuators because of their importance in soft robotics, artificial muscles, biomimetic devices, and beyond. However, the development of soft actuators capable of low-voltage operation, powerful actuation, and programmable shape-changing is still challenging. In this work, we propose programmable bilayer actuators that operate based on the large hygroscopic contraction of the copy paper and simultaneously large thermal expansion of the polypropylene film upon increasing the temperature. The electrothermally activated bending actuators can function with low voltages (≤ 8 V), low input electric power per area (P ≤ 0.14 W cm–2), and low temperature changes (≤ 35 °C). They exhibit reversible shape-changing behavior with curvature radii up to 1.07 cm–1 and bending angle of 360°, accompanied by powerful actuation. Besides the electrical activation, they can be powered by humidity or light irradiation. We finally demonstrate the use of our paper actuators as a soft gripper robot and a lightweight paper wing for aerial robotics.

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DOI Project Page Project Page [BibTex]

DOI Project Page Project Page [BibTex]


Programmable assembly of heterogeneous microparts by an untethered mobile capillary microgripper
Programmable assembly of heterogeneous microparts by an untethered mobile capillary microgripper

Giltinan, J., Diller, E., Sitti, M.

Lab on a Chip, 16(22):4445-4457, Royal Society of Chemistry, October 2016 (article)

Abstract
At the sub-millimeter scale, capillary forces enable robust and reversible adhesion between biological organisms and varied substrates. Current human-engineered mobile untethered micromanipulation systems rely on forces which scale poorly or utilize gripper-part designs that promote manipulation. Capillary forces, alternatively, are dependent upon the surface chemistry (which is scale independent) and contact perimeter, which conforms to the part surface. We report a mobile capillary microgripper that is able to pick and place parts of various materials and geometries, and is thus ideal for microassembly tasks that cannot be accomplished by large tethered manipulators. We achieve the programmable assembly of sub-millimeter parts in an enclosed three-dimensional aqueous environment by creating a capillary bridge between the targeted part and a synthetic, untethered, mobile body. The parts include both hydrophilic and hydrophobic components: hydrogel, kapton, human hair, and biological tissue. The 200 μm untethered system can be controlled with five-degrees-of-freedom and advances progress towards autonomous desktop manufacturing for tissue engineering, complex micromachines, microfluidic devices, and meta-materials.

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


Composition-dependent underwater adhesion of catechol-bearing hydrogels
Composition-dependent underwater adhesion of catechol-bearing hydrogels

Wu, H., Sariola, V., Zhao, J., Ding, H., Sitti, M., Bettinger, C. J.

Polymer International, 65(11):1355-1359, John Wiley & Sons, Ltd, September 2016 (article)

Abstract
Interfacial adhesion-mediated transfer printing processes can integrate functional electronic microstructures with polymeric substrates that are bendable and stretchable. Transfer printing has also been extended to catechol-bearing adhesive hydrogels. This study presents indentation adhesion tests between catechol-bearing hydrogel substrates with catechol concentrations varying from 0 to 10% (mol/mol) and thin-film materials commonly used in microelectronic fabrication including polymers, noble metals and oxides. The results indicate that the interfacial adhesion of catechol-bearing hydrogels is positively correlated with the concentration of catechol-bearing monomers as well as the retraction velocity during transfer printing. This study can inform transfer printing processes for microfabricated structures to compliant hydrated substrates such as hygroscopic monomers, mesoporous polymer networks and hydrogels. © 2016 Society of Chemical Industry

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DOI [BibTex]

DOI [BibTex]


Bacteria-Driven Particles: Patterned and Specific Attachment of Bacteria on Biohybrid Bacteria-Driven Microswimmers (Adv. Healthcare Mater. 18/2016)
Bacteria-Driven Particles: Patterned and Specific Attachment of Bacteria on Biohybrid Bacteria-Driven Microswimmers (Adv. Healthcare Mater. 18/2016)

Singh, A. V., Sitti, M.

Advanced Healthcare Materials, 5(18):2306-2306, September 2016 (article)

Abstract
On page 2325, Ajay Vikram Singh and Metin Sitti propose a facile surface patterning technique and a specific, strong biotin–streptavidin bonding of bacteria on patterned surfaces to fabricate Janus particles that are propelled by the attached bacteria. Such bacteria-driven Janus microswimmers could be used for future medicine in targeted drug delivery and environmental remediation.

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DOI Project Page [BibTex]


The effect of temperature and humidity on adhesion of a gecko-inspired adhesive: implications for the natural system
The effect of temperature and humidity on adhesion of a gecko-inspired adhesive: implications for the natural system

Stark, A. Y., Klittich, M. R., Sitti, M., Niewiarowski, P. H., Dhinojwala, A.

Scientific Reports, 6, pages: 30936, Nature Publishing Group, August 2016 (article)

Abstract
The adhesive system of geckos has inspired hundreds of synthetic adhesives. While this system has been used relentlessly as a source of inspiration, less work has been done in reverse, where synthetics are used to test questions and hypotheses about the natural system. Here we take such an approach. We tested shear adhesion of a mushroom-tipped synthetic gecko adhesive under conditions that produced perplexing results in the natural adhesive system. Synthetic samples were tested at two temperatures (12 °C and 32 °C) and four different humidity levels (30%, 55%, 70%, and 80% RH). Surprisingly, adhesive performance of the synthetic samples matched that of living geckos, suggesting that uncontrolled parameters in the natural system, such as surface chemistry and material changes, may not be as influential in whole-animal performance as previously thought. There was one difference, however, when comparing natural and synthetic adhesive performance. At 12 °C and 80% RH, adhesion of the synthetic structures was lower than expected based on the natural system’s performance. Our approach highlights a unique opportunity for both biologists and material scientists, where new questions and hypotheses can be fueled by joint comparisons of the natural and synthetic systems, ultimately improving knowledge of both.

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DOI [BibTex]

DOI [BibTex]


Magnetic propulsion of robotic sperms at low-Reynolds number
Magnetic propulsion of robotic sperms at low-Reynolds number

Khalil, I. S., Fatih Tabak, A., Klingner, A., Sitti, M.

Applied Physics Letters, 109(3):033701, AIP Publishing, July 2016 (article)

Abstract
We investigate the microswimming behaviour of robotic sperms in viscous fluids. These robotic sperms are fabricated from polystyrene dissolved in dimethyl formamide and iron-oxide nanoparticles. This composition allows the nanoparticles to be concentrated within the bead of the robotic sperm and provide magnetic dipole, whereas the flexibility of the ultra-thin tail enables flagellated locomotion using magnetic fields in millitesla range. We show that these robotic sperms have similar morphology and swimming behaviour to those of sperm cells. Moreover, we show experimentally that our robotic sperms swim controllably at an average speed of approximately one body length per second (around 125 μm s−1), and they are relatively faster than the microswimmers that depend on planar wave propulsion in low-Reynolds number fluids.

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DOI [BibTex]

DOI [BibTex]


{Body Talk}: Crowdshaping Realistic {3D} Avatars with Words
Body Talk: Crowdshaping Realistic 3D Avatars with Words

Streuber, S., Quiros-Ramirez, M. A., Hill, M. Q., Hahn, C. A., Zuffi, S., O’Toole, A., Black, M. J.

ACM Trans. Graph. (Proc. SIGGRAPH), 35(4):54:1-54:14, July 2016 (article)

Abstract
Realistic, metrically accurate, 3D human avatars are useful for games, shopping, virtual reality, and health applications. Such avatars are not in wide use because solutions for creating them from high-end scanners, low-cost range cameras, and tailoring measurements all have limitations. Here we propose a simple solution and show that it is surprisingly accurate. We use crowdsourcing to generate attribute ratings of 3D body shapes corresponding to standard linguistic descriptions of 3D shape. We then learn a linear function relating these ratings to 3D human shape parameters. Given an image of a new body, we again turn to the crowd for ratings of the body shape. The collection of linguistic ratings of a photograph provides remarkably strong constraints on the metric 3D shape. We call the process crowdshaping and show that our Body Talk system produces shapes that are perceptually indistinguishable from bodies created from high-resolution scans and that the metric accuracy is sufficient for many tasks. This makes body “scanning” practical without a scanner, opening up new applications including database search, visualization, and extracting avatars from books.

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pdf web tool video talk (ppt) [BibTex]

pdf web tool video talk (ppt) [BibTex]


Six-degree-of-freedom magnetic actuation for wireless microrobotics
Six-degree-of-freedom magnetic actuation for wireless microrobotics

Diller, E., Giltinan, J., Lum, G. Z., Ye, Z., Sitti, M.

The International Journal of Robotics Research, 35(1-3):114-128, SAGE Publications Sage UK: London, England, June 2016 (article)

Abstract
Existing remotely actuated magnetic microrobots exhibit a maximum of only five-degree-of-freedom (DOF) actuation, as creation of a driving torque about the microrobot magnetization axis is not achievable. This lack of full orientation control limits the effectiveness of existing microrobots for precision tasks of object manipulation and orientation for advanced medical, biological and micromanufacturing applications. This paper presents a magnetic actuation method that allows remotely powered microrobots to achieve full six-DOF actuation by considering the case of a non-uniform magnetization profile within the microrobot body. This non-uniform magnetization allows for additional rigid-body torques to be induced from magnetic forces via a moment arm. A general analytical model presents the working principle for continuous and discrete magnetization profiles, which is applied to permanent or non-permanent (soft) magnet bodies. Several discrete-magnetization designs are also presented which possess reduced coupling between magnetic forces and induced rigid-body torques. Design guidelines are introduced which can be followed to ensure that a magnetic microrobot design is capable of six-DOF actuation. A simple permanent-magnet prototype is fabricated and used to quantitatively demonstrate the accuracy of the analytical model in a constrained-DOF environment and qualitatively for free motion in a viscous liquid three-dimensional environment. Results show that desired forces and torques can be created with high precision and limited parasitic actuation, allowing for full six-DOF actuation using limited feedback control

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DOI [BibTex]

DOI [BibTex]


Capturing Hands in Action using Discriminative Salient Points and Physics Simulation
Capturing Hands in Action using Discriminative Salient Points and Physics Simulation

Tzionas, D., Ballan, L., Srikantha, A., Aponte, P., Pollefeys, M., Gall, J.

International Journal of Computer Vision (IJCV), 118(2):172-193, June 2016 (article)

Abstract
Hand motion capture is a popular research field, recently gaining more attention due to the ubiquity of RGB-D sensors. However, even most recent approaches focus on the case of a single isolated hand. In this work, we focus on hands that interact with other hands or objects and present a framework that successfully captures motion in such interaction scenarios for both rigid and articulated objects. Our framework combines a generative model with discriminatively trained salient points to achieve a low tracking error and with collision detection and physics simulation to achieve physically plausible estimates even in case of occlusions and missing visual data. Since all components are unified in a single objective function which is almost everywhere differentiable, it can be optimized with standard optimization techniques. Our approach works for monocular RGB-D sequences as well as setups with multiple synchronized RGB cameras. For a qualitative and quantitative evaluation, we captured 29 sequences with a large variety of interactions and up to 150 degrees of freedom.

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Website pdf link (url) DOI Project Page [BibTex]

Website pdf link (url) DOI Project Page [BibTex]


Gallium Adhesion: Phase Change of Gallium Enables Highly Reversible and Switchable Adhesion (Adv. Mater. 25/2016)
Gallium Adhesion: Phase Change of Gallium Enables Highly Reversible and Switchable Adhesion (Adv. Mater. 25/2016)

Ye, Z., Lum, G. Z., Song, S., Rich, S., Sitti, M.

Advanced Materials, 28(25):5087-5087, May 2016 (article)

Abstract
Gallium exhibits highly reversible and switchable adhesion when it undergoes a solid–liquid phase transition. The robustness of gallium is notable as it exhibits strong performance on a wide range of smooth and rough surfaces, under both dry and wet conditions. Gallium may therefore find numerous applications in transfer printing, robotics, electronic packaging, and biomedicine.

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DOI [BibTex]


Patterned and Specific Attachment of Bacteria on Biohybrid Bacteria-Driven Microswimmers
Patterned and Specific Attachment of Bacteria on Biohybrid Bacteria-Driven Microswimmers

Singh, A. V., Sitti, M.

Advanced Healthcare Materials, 5(18):2325-2331, May 2016 (article)

Abstract
A surface patterning technique and a specific and strong biotin–streptavidin bonding of bacteria on patterned surfaces are proposed to fabricate Janus particles that are propelled by the attached bacteria. Bacteria-driven Janus microswimmers with diameters larger than 3 μm show enhanced mean propulsion speed. Such microswimmers could be used for future applications such as targeted drug delivery and environmental remediation.

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DOI [BibTex]


Shape-programmable magnetic soft matter
Shape-programmable magnetic soft matter

Lum, G. Z., Ye, Z., Dong, X., Marvi, H., Erin, O., Hu, W., Sitti, M.

Proceedings of the National Academy of Sciences, 113(41):E6007–E6015, National Acad Sciences, May 2016 (article)

Abstract
Shape-programmable matter is a class of active materials whose geometry can be controlled to potentially achieve mechanical functionalities beyond those of traditional machines. Among these materials, magnetically actuated matter is particularly promising for achieving complex time-varying shapes at small scale (overall dimensions smaller than 1 cm). However, previous work can only program these materials for limited applications, as they rely solely on human intuition to approximate the required magnetization profile and actuating magnetic fields for their materials. Here, we propose a universal programming methodology that can automatically generate the required magnetization profile and actuating fields for soft matter to achieve new time-varying shapes. The universality of the proposed method can therefore inspire a vast number of miniature soft devices that are critical in robotics, smart engineering surfaces and materials, and biomedical devices. Our proposed method includes theoretical formulations, computational strategies, and fabrication procedures for programming magnetic soft matter. The presented theory and computational method are universal for programming 2D or 3D time-varying shapes, whereas the fabrication technique is generic only for creating planar beams. Based on the proposed programming method, we created a jellyfish-like robot, a spermatozoid-like undulating swimmer, and an artificial cilium that could mimic the complex beating patterns of its biological counterpart.

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DOI [BibTex]

DOI [BibTex]


Inflated soft actuators with reversible stable deformations
Inflated soft actuators with reversible stable deformations

Hines, L., Petersen, K., Sitti, M.

Advanced Materials, 28(19):3690-3696, March 2016 (article)

Abstract
Most soft robotic systems are currently dependent on bulky compressors or pumps. A soft actuation method is presented combining hyperelastic membranes and dielectric elastomer actuators to switch between stable deformations of sealed chambers. This method is capable of large repeatable deformations, and has a number of stable states proportional to the number of actuatable membranes in the chamber.

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DOI Project Page [BibTex]


Chemotaxis of bio-hybrid multiple bacteria-driven microswimmers
Chemotaxis of bio-hybrid multiple bacteria-driven microswimmers

Zhuang, J., Sitti, M.

Scientific reports, 6, pages: 32135, Nature Publishing Group, March 2016 (article)

Abstract
In this study, in a bio-hybrid microswimmer system driven by multiple Serratia marcescens bacteria, we quantify the chemotactic drift of a large number of microswimmers towards L-serine and elucidate the associated collective chemotaxis behavior by statistical analysis of over a thousand swimming trajectories of the microswimmers. The results show that the microswimmers have a strong heading preference for moving up the L-serine gradient, while their speed does not change considerably when moving up and down the gradient; therefore, the heading bias constitutes the major factor that produces the chemotactic drift. The heading direction of a microswimmer is found to be significantly more persistent when it moves up the L-serine gradient than when it travels down the gradient; this effect causes the apparent heading preference of the microswimmers and is the crucial reason that enables the seemingly cooperative chemotaxis of multiple bacteria on a microswimmer. In addition, we find that their chemotactic drift velocity increases superquadratically with their mean swimming speed, suggesting that chemotaxis of bio-hybrid microsystems can be enhanced by designing and building faster microswimmers. Such bio-hybrid microswimmers with chemotactic steering capability may find future applications in targeted drug delivery, bioengineering, and lab-on-a-chip devices.

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


Targeted drug delivery and imaging using mobile milli/microrobots: A promising future towards theranostic pharmaceutical design
Targeted drug delivery and imaging using mobile milli/microrobots: A promising future towards theranostic pharmaceutical design

Vikram Singh, A., Sitti, M.

Current Pharmaceutical Design, 22(11):1418-1428, Bentham Science Publishers, March 2016 (article)

Abstract
Miniature untethered medical robots have been receiving growing attention due to technological advances in microactuation, microsensors, and microfabrication and have significant potential to reduce the invasiveness and improve the accessibility of medical devices into unprecedented small spaces inside the human body. In this review, we discuss therapeutic and diagnostic applications of untethered medical microrobots. Wirelessly controlled milli/microrobots with integrated sensors are revolutionizing micromanipulation based medical interventions and are enabling doctors to perform minimally invasive procedures not possible before. 3D fabrication technologies enabling milli/microrobot fabrication at the single cell scale are empowering high-resolution visual imaging and in vivo manipulation capabilities. Swallowable millirobots and injectabale ocular microrobots allow the gastric ulcer imaging, and performance of vitreoretinal microsurgery at previously inaccessible ocular sites. Many invasive excision and incision based diagnostic biopsy, prostrate, and nephrolgical procedures can be performed minimally or almost noninvasively due to recent advancements in microrobotic technology. Advances in biohybrid microrobot systems are pushing microrobotic systems even smaller, using biological cells as on-board microactuators and microsensors using the chemical energy. Such microrobotic systems could be used for local targeted delivery of imaging contrast agents, drugs, genes, and mRNA, minimally invasive surgery, and cell micromanipulation in the near future.

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link (url) [BibTex]


Parallel microcracks-based ultrasensitive and highly stretchable strain sensors
Parallel microcracks-based ultrasensitive and highly stretchable strain sensors

Amjadi, M., Turan, M., Clementson, C. P., Sitti, M.

ACS Applied Materials \& Interfaces, 8(8):5618-5626, American Chemical Society, Febuary 2016 (article)

Abstract
There is an increasing demand for flexible, skin-attachable, and wearable strain sensors due to their various potential applications. However, achieving strain sensors with both high sensitivity and high stretchability is still a grand challenge. Here, we propose highly sensitive and stretchable strain sensors based on the reversible microcrack formation in composite thin films. Controllable parallel microcracks are generated in graphite thin films coated on elastomer films. Sensors made of graphite thin films with short microcracks possess high gauge factors (maximum value of 522.6) and stretchability (ε ≥ 50%), whereas sensors with long microcracks show ultrahigh sensitivity (maximum value of 11 344) with limited stretchability (ε ≤ 50%). We demonstrate the high performance strain sensing of our sensors in both small and large strain sensing applications such as human physiological activity recognition, human body large motion capturing, vibration detection, pressure sensing, and soft robotics.

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DOI [BibTex]

DOI [BibTex]


Stretchable, Skin-Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review
Stretchable, Skin-Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review

Amjadi, M., Kyung, K., Park, I., Sitti, M.

Advanced Functional Materials, 26, pages: 1678-1698, Febuary 2016 (article)

Abstract
There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin-mountable, and wearable strain sensors are needed for several potential applications including personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin-mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.

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DOI [BibTex]

DOI [BibTex]


Size optimization of a magnetic system for drug delivery with capsule robots
Size optimization of a magnetic system for drug delivery with capsule robots

Munoz, F., Alici, G., Li, W., Sitti, M.

IEEE Transactions on Magnetics, 52(5):1-11, IEEE, January 2016 (article)

Abstract
In this paper, we present a methodology for the size optimization of an external magnetic system made of arc-shaped permanent magnets (ASMs). This magnetic system is able to remotely actuate a drug-release module embedded in a prototype of a capsule robot. The optimization of the magnetic system is carried out by using an accurate analytical model that is valid for any arbitrary dimensions of the ASMs. By using this analytical model, we perform parametric studies and conduct a statistical analysis [analysis of variance (ANOVA)] to investigate efficient ways to distribute the volume of the ASMs so that the dimensions and volume of the magnetic system are minimized while optimal flux densities and magnetic torques are obtained to actuate the drug delivery system (DDS). The ANOVA results, at 5% significance level, indicate that changes in the angular width followed by changes in the length of the ASMs have the highest impact on the magnetic linkage. Furthermore, our experimental results, which are in agreement with the analytical results, show that the size optimization of the magnetic system is effective for the actuation of the DDS in capsule robots.

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DOI [BibTex]

DOI [BibTex]


Human Pose Estimation from Video and IMUs
Human Pose Estimation from Video and IMUs

Marcard, T. V., Pons-Moll, G., Rosenhahn, B.

Transactions on Pattern Analysis and Machine Intelligence PAMI, 38(8):1533-1547, January 2016 (article)

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data pdf dataset_documentation [BibTex]

data pdf dataset_documentation [BibTex]


Moving-horizon Nonlinear Least Squares-based Multirobot Cooperative Perception
Moving-horizon Nonlinear Least Squares-based Multirobot Cooperative Perception

Ahmad, A., Bülthoff, H.

Robotics and Autonomous Systems, 83, pages: 275-286, 2016 (article)

Abstract
In this article we present an online estimator for multirobot cooperative localization and target tracking based on nonlinear least squares minimization. Our method not only makes the rigorous optimization-based approach applicable online but also allows the estimator to be stable and convergent. We do so by employing a moving horizon technique to nonlinear least squares minimization and a novel design of the arrival cost function that ensures stability and convergence of the estimator. Through an extensive set of real robot experiments, we demonstrate the robustness of our method as well as the optimality of the arrival cost function. The experiments include comparisons of our method with i) an extended Kalman filter-based online-estimator and ii) an offline-estimator based on full-trajectory nonlinear least squares.

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


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NimbRo Explorer: Semi-Autonomous Exploration and Mobile Manipulation in Rough Terrain

Stueckler, J., Schwarz, M., Schadler, M., Topalidou-Kyniazopoulou, A., Behnke, S.

Journal of Field Robotics (JFR), 33(4):411-430, Wiley, 2016 (article)

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[BibTex]

[BibTex]


Shape estimation of subcutaneous adipose tissue using an articulated statistical shape model
Shape estimation of subcutaneous adipose tissue using an articulated statistical shape model

Yeo, S. Y., Romero, J., Loper, M., Machann, J., Black, M.

Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 0(0):1-8, 2016 (article)

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publisher website preprint pdf link (url) DOI Project Page [BibTex]

publisher website preprint pdf link (url) DOI Project Page [BibTex]


Probabilistic Duality for Parallel Gibbs Sampling without Graph Coloring
Probabilistic Duality for Parallel Gibbs Sampling without Graph Coloring

Mescheder, L., Nowozin, S., Geiger, A.

Arxiv, 2016 (article)

Abstract
We present a new notion of probabilistic duality for random variables involving mixture distributions. Using this notion, we show how to implement a highly-parallelizable Gibbs sampler for weakly coupled discrete pairwise graphical models with strictly positive factors that requires almost no preprocessing and is easy to implement. Moreover, we show how our method can be combined with blocking to improve mixing. Even though our method leads to inferior mixing times compared to a sequential Gibbs sampler, we argue that our method is still very useful for large dynamic networks, where factors are added and removed on a continuous basis, as it is hard to maintain a graph coloring in this setup. Similarly, our method is useful for parallelizing Gibbs sampling in graphical models that do not allow for graph colorings with a small number of colors such as densely connected graphs.

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pdf [BibTex]


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Multi-Layered Mapping and Navigation for Autonomous Micro Aerial Vehicles

Droeschel, D., Nieuwenhuisen, M., Beul, M., Stueckler, J., Holz, D., Behnke, S.

Journal of Field Robotics (JFR), 33(4):451-475, 2016 (article)

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[BibTex]

[BibTex]


The GRASP Taxonomy of Human Grasp Types
The GRASP Taxonomy of Human Grasp Types

Feix, T., Romero, J., Schmiedmayer, H., Dollar, A., Kragic, D.

Human-Machine Systems, IEEE Transactions on, 46(1):66-77, 2016 (article)

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publisher website pdf DOI Project Page [BibTex]

publisher website pdf DOI Project Page [BibTex]


Map-Based Probabilistic Visual Self-Localization
Map-Based Probabilistic Visual Self-Localization

Brubaker, M. A., Geiger, A., Urtasun, R.

IEEE Trans. on Pattern Analysis and Machine Intelligence (PAMI), 2016 (article)

Abstract
Accurate and efficient self-localization is a critical problem for autonomous systems. This paper describes an affordable solution to vehicle self-localization which uses odometry computed from two video cameras and road maps as the sole inputs. The core of the method is a probabilistic model for which an efficient approximate inference algorithm is derived. The inference algorithm is able to utilize distributed computation in order to meet the real-time requirements of autonomous systems in some instances. Because of the probabilistic nature of the model the method is capable of coping with various sources of uncertainty including noise in the visual odometry and inherent ambiguities in the map (e.g., in a Manhattan world). By exploiting freely available, community developed maps and visual odometry measurements, the proposed method is able to localize a vehicle to 4m on average after 52 seconds of driving on maps which contain more than 2,150km of drivable roads.

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pdf Project Page [BibTex]

pdf Project Page [BibTex]

2011


High-quality reflection separation using polarized images
High-quality reflection separation using polarized images

Kong, N., Tai, Y., Shin, S. Y.

IEEE Transactions on Image Processing, 20(12):3393-3405, IEEE Signal Processing Society, December 2011 (article)

Abstract
In this paper, we deal with a problem of separating the effect of reflection from images captured behind glass. The input consists of multiple polarized images captured from the same view point but with different polarizer angles. The output is the high quality separation of the reflection layer and the background layer from the images. We formulate this problem as a constrained optimization problem and propose a framework that allows us to fully exploit the mutually exclusive image information in our input data. We test our approach on various images and demonstrate that our approach can generate good reflection separation results.

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Publisher site [BibTex]

2011


Publisher site [BibTex]


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A human inspired gaze estimation system

Wulff, J., Sinha, P.

Journal of Vision, 11(11):507-507, ARVO, September 2011 (article)

Abstract
Estimating another person's gaze is a crucial skill in human social interactions. The social component is most apparent in dyadic gaze situations, in which the looker seems to look into the eyes of the observer, thereby signaling interest or a turn to speak. In a triadic situation, on the other hand, the looker's gaze is averted from the observer and directed towards another, specific target. This is mostly interpreted as a cue for joint attention, creating awareness of a predator or another point of interest. In keeping with the task's social significance, humans are very proficient at gaze estimation. Our accuracy ranges from less than one degree for dyadic settings to approximately 2.5 degrees for triadic ones. Our goal in this work is to draw inspiration from human gaze estimation mechanisms in order to create an artificial system that can approach the former's accuracy levels. Since human performance is severely impaired by both image-based degradations (Ando, 2004) and a change of facial configurations (Jenkins & Langton, 2003), the underlying principles are believed to be based both on simple image cues such as contrast/brightness distribution and on more complex geometric processing to reconstruct the actual shape of the head. By incorporating both kinds of cues in our system's design, we are able to surpass the accuracy of existing eye-tracking systems, which rely exclusively on either image-based or geometry-based cues (Yamazoe et al., 2008). A side-benefit of this combined approach is that it allows for gaze estimation despite moderate view-point changes. This is important for settings where subjects, say young children or certain kinds of patients, might not be fully cooperative to allow a careful calibration. Our model and implementation of gaze estimation opens up new experimental questions about human mechanisms while also providing a useful tool for general calibration-free, non-intrusive remote eye-tracking.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Detecting synchrony in degraded audio-visual streams

Dhandhania, K., Wulff, J., Sinha, P.

Journal of Vision, 11(11):800-800, ARVO, September 2011 (article)

Abstract
Even 8–10 week old infants, when presented with two dynamic faces and a speech stream, look significantly longer at the ‘correct’ talking person (Patterson & Werker, 2003). This is true even though their reduced visual acuity prevents them from utilizing high spatial frequencies. Computational analyses in the field of audio/video synchrony and automatic speaker detection (e.g. Hershey & Movellan, 2000), in contrast, usually depend on high-resolution images. Therefore, the correlation mechanisms found in these computational studies are not directly applicable to the processes through which we learn to integrate the modalities of speech and vision. In this work, we investigated the correlation between speech signals and degraded video signals. We found a high correlation persisting even with high image degradation, resembling the low visual acuity of young infants. Additionally (in a fashion similar to Graf et al., 2002) we explored which parts of the face correlate with the audio in the degraded video sequences. Perfect synchrony and small offsets in the audio were used while finding the correlation, thereby detecting visual events preceding and following audio events. In order to achieve a sufficiently high temporal resolution, high-speed video sequences (500 frames per second) of talking people were used. This is a temporal resolution unachieved in previous studies and has allowed us to capture very subtle and short visual events. We believe that the results of this study might be interesting not only to vision researchers, but, by revealing subtle effects on a very fine timescale, also to people working in computer graphics and the generation and animation of artificial faces.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


Trajectory Space: A Dual Representation for Nonrigid Structure from Motion
Trajectory Space: A Dual Representation for Nonrigid Structure from Motion

Akhter, I., Sheikh, Y., Khan, S., Kanade, T.

Pattern Analysis and Machine Intelligence, IEEE Transactions on, 33(7):1442-1456, IEEE, July 2011 (article)

Abstract
Existing approaches to nonrigid structure from motion assume that the instantaneous 3D shape of a deforming object is a linear combination of basis shapes. These basis are object dependent and therefore have to be estimated anew for each video sequence. In contrast, we propose a dual approach to describe the evolving 3D structure in trajectory space by a linear combination of basis trajectories. We describe the dual relationship between the two approaches, showing that they both have equal power for representing 3D structure. We further show that the temporal smoothness in 3D trajectories alone can be used for recovering nonrigid structure from a moving camera. The principal advantage of expressing deforming 3D structure in trajectory space is that we can define an object independent basis. This results in a significant reduction in unknowns, and corresponding stability in estimation. We propose the use of the Discrete Cosine Transform (DCT) as the object independent basis and empirically demonstrate that it approaches Principal Component Analysis (PCA) for natural motions. We report the performance of the proposed method, quantitatively using motion capture data, and qualitatively on several video sequences exhibiting nonrigid motions including piecewise rigid motion, partially nonrigid motion (such as a facial expressions), and highly nonrigid motion (such as a person walking or dancing).

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pdf project page [BibTex]

pdf project page [BibTex]


Loose-limbed People: Estimating {3D} Human Pose and Motion Using Non-parametric Belief Propagation
Loose-limbed People: Estimating 3D Human Pose and Motion Using Non-parametric Belief Propagation

Sigal, L., Isard, M., Haussecker, H., Black, M. J.

International Journal of Computer Vision, 98(1):15-48, Springer Netherlands, May 2011 (article)

Abstract
We formulate the problem of 3D human pose estimation and tracking as one of inference in a graphical model. Unlike traditional kinematic tree representations, our model of the body is a collection of loosely-connected body-parts. In particular, we model the body using an undirected graphical model in which nodes correspond to parts and edges to kinematic, penetration, and temporal constraints imposed by the joints and the world. These constraints are encoded using pair-wise statistical distributions, that are learned from motion-capture training data. Human pose and motion estimation is formulated as inference in this graphical model and is solved using Particle Message Passing (PaMPas). PaMPas is a form of non-parametric belief propagation that uses a variation of particle filtering that can be applied over a general graphical model with loops. The loose-limbed model and decentralized graph structure allow us to incorporate information from "bottom-up" visual cues, such as limb and head detectors, into the inference process. These detectors enable automatic initialization and aid recovery from transient tracking failures. We illustrate the method by automatically tracking people in multi-view imagery using a set of calibrated cameras and present quantitative evaluation using the HumanEva dataset.

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pdf publisher's site link (url) Project Page Project Page [BibTex]

pdf publisher's site link (url) Project Page Project Page [BibTex]


Point-and-Click Cursor Control With an Intracortical Neural Interface System by Humans With Tetraplegia
Point-and-Click Cursor Control With an Intracortical Neural Interface System by Humans With Tetraplegia

Kim, S., Simeral, J. D., Hochberg, L. R., Donoghue, J. P., Friehs, G. M., Black, M. J.

IEEE Transactions on Neural Systems and Rehabilitation Engineering, 19(2):193-203, April 2011 (article)

Abstract
We present a point-and-click intracortical neural interface system (NIS) that enables humans with tetraplegia to volitionally move a 2D computer cursor in any desired direction on a computer screen, hold it still and click on the area of interest. This direct brain-computer interface extracts both discrete (click) and continuous (cursor velocity) signals from a single small population of neurons in human motor cortex. A key component of this system is a multi-state probabilistic decoding algorithm that simultaneously decodes neural spiking activity and outputs either a click signal or the velocity of the cursor. The algorithm combines a linear classifier, which determines whether the user is intending to click or move the cursor, with a Kalman filter that translates the neural population activity into cursor velocity. We present a paradigm for training the multi-state decoding algorithm using neural activity observed during imagined actions. Two human participants with tetraplegia (paralysis of the four limbs) performed a closed-loop radial target acquisition task using the point-and-click NIS over multiple sessions. We quantified point-and-click performance using various human-computer interaction measurements for pointing devices. We found that participants were able to control the cursor motion accurately and click on specified targets with a small error rate (< 3% in one participant). This study suggests that signals from a small ensemble of motor cortical neurons (~40) can be used for natural point-and-click 2D cursor control of a personal computer.

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pdf publishers's site pub med link (url) Project Page [BibTex]

pdf publishers's site pub med link (url) Project Page [BibTex]


A Database and Evaluation Methodology for Optical Flow
A Database and Evaluation Methodology for Optical Flow

Baker, S., Scharstein, D., Lewis, J. P., Roth, S., Black, M. J., Szeliski, R.

International Journal of Computer Vision, 92(1):1-31, March 2011 (article)

Abstract
The quantitative evaluation of optical flow algorithms by Barron et al. (1994) led to significant advances in performance. The challenges for optical flow algorithms today go beyond the datasets and evaluation methods proposed in that paper. Instead, they center on problems associated with complex natural scenes, including nonrigid motion, real sensor noise, and motion discontinuities. We propose a new set of benchmarks and evaluation methods for the next generation of optical flow algorithms. To that end, we contribute four types of data to test different aspects of optical flow algorithms: (1) sequences with nonrigid motion where the ground-truth flow is determined by tracking hidden fluorescent texture, (2) realistic synthetic sequences, (3) high frame-rate video used to study interpolation error, and (4) modified stereo sequences of static scenes. In addition to the average angular error used by Barron et al., we compute the absolute flow endpoint error, measures for frame interpolation error, improved statistics, and results at motion discontinuities and in textureless regions. In October 2007, we published the performance of several well-known methods on a preliminary version of our data to establish the current state of the art. We also made the data freely available on the web at http://vision.middlebury.edu/flow/ . Subsequently a number of researchers have uploaded their results to our website and published papers using the data. A significant improvement in performance has already been achieved. In this paper we analyze the results obtained to date and draw a large number of conclusions from them.

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pdf pdf from publisher Middlebury Flow Evaluation Website [BibTex]

pdf pdf from publisher Middlebury Flow Evaluation Website [BibTex]


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Design and application of a wire-driven bidirectional telescopic mechanism for workspace expansion with a focus on shipbuilding tasks

Lee, D., Chang, D., Shin, Y., Son, D., Kim, T., Lee, K., Kim, J.

Advanced Robotics, 25, 2011 (article)

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[BibTex]

[BibTex]


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Waalbot II: Adhesion recovery and improved performance of a climbing robot using fibrillar adhesives

Murphy, M. P., Kute, C., Mengüç, Y., Sitti, M.

The International Journal of Robotics Research, 30(1):118-133, SAGE Publications Sage UK: London, England, 2011 (article)

pi

Project Page [BibTex]

Project Page [BibTex]


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Automated 2-D nanoparticle manipulation using atomic force microscopy

Onal, C. D., Ozcan, O., Sitti, M.

IEEE Transactions on Nanotechnology, 10(3):472-481, IEEE, 2011 (article)

pi

[BibTex]

[BibTex]


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Biaxial mechanical modeling of the small intestine

Bellini, C., Glass, P., Sitti, M., Di Martino, E. S.

Journal of the mechanical behavior of biomedical materials, 4(8):1727-1740, Elsevier, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


Neural control of cursor trajectory and click by a human with tetraplegia 1000 days after implant of an intracortical microelectrode array
Neural control of cursor trajectory and click by a human with tetraplegia 1000 days after implant of an intracortical microelectrode array

(J. Neural Engineering Highlights of 2011 Collection. JNE top 10 cited papers of 2010-2011.)

Simeral, J. D., Kim, S., Black, M. J., Donoghue, J. P., Hochberg, L. R.

J. of Neural Engineering, 8(2):025027, 2011 (article)

Abstract
The ongoing pilot clinical trial of the BrainGate neural interface system aims in part to assess the feasibility of using neural activity obtained from a small-scale, chronically implanted, intracortical microelectrode array to provide control signals for a neural prosthesis system. Critical questions include how long implanted microelectrodes will record useful neural signals, how reliably those signals can be acquired and decoded, and how effectively they can be used to control various assistive technologies such as computers and robotic assistive devices, or to enable functional electrical stimulation of paralyzed muscles. Here we examined these questions by assessing neural cursor control and BrainGate system characteristics on five consecutive days 1000 days after implant of a 4 × 4 mm array of 100 microelectrodes in the motor cortex of a human with longstanding tetraplegia subsequent to a brainstem stroke. On each of five prospectively-selected days we performed time-amplitude sorting of neuronal spiking activity, trained a population-based Kalman velocity decoding filter combined with a linear discriminant click state classifier, and then assessed closed-loop point-and-click cursor control. The participant performed both an eight-target center-out task and a random target Fitts metric task which was adapted from a human-computer interaction ISO standard used to quantify performance of computer input devices. The neural interface system was further characterized by daily measurement of electrode impedances, unit waveforms and local field potentials. Across the five days, spiking signals were obtained from 41 of 96 electrodes and were successfully decoded to provide neural cursor point-and-click control with a mean task performance of 91.3% ± 0.1% (mean ± s.d.) correct target acquisition. Results across five consecutive days demonstrate that a neural interface system based on an intracortical microelectrode array can provide repeatable, accurate point-and-click control of a computer interface to an individual with tetraplegia 1000 days after implantation of this sensor.

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pdf pdf from publisher link (url) Project Page [BibTex]


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Aqueous droplet manipulation by optically induced Marangoni circulation

Hu, W., Ohta, A. T.

Microfluidics and nanofluidics, 11(3):307-316, Springer-Verlag, 2011 (article)

pi

[BibTex]

[BibTex]


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An optically controlled 3D cell culturing system

Ishii, K. S., Hu, W., Namekar, S. A., Ohta, A. T.

Advances in optoelectronics, 2011, Hindawi, 2011 (article)

pi

[BibTex]

[BibTex]


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Assembly and disassembly of magnetic mobile micro-robots towards deterministic 2-D reconfigurable micro-systems

Diller, E., Pawashe, C., Floyd, S., Sitti, M.

The International Journal of Robotics Research, 30(14):1667-1680, SAGE Publications Sage UK: London, England, 2011 (article)

pi

[BibTex]

[BibTex]


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Modeling of stochastic motion of bacteria propelled spherical microbeads

Arabagi, V., Behkam, B., Cheung, E., Sitti, M.

Journal of Applied Physics, 109(11):114702, AIP, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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The effect of aspect ratio on adhesion and stiffness for soft elastic fibres

Aksak, B., Hui, C., Sitti, M.

Journal of The Royal Society Interface, 8(61):1166-1175, The Royal Society, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


Modelling pipeline for subject-specific arterial blood flow—A review
Modelling pipeline for subject-specific arterial blood flow—A review

Igor Sazonov, Si Yong Yeo, Rhodri Bevan, Xianghua Xie, Raoul van Loon, Perumal Nithiarasu

International Journal for Numerical Methods in Biomedical Engineering, 27(12):1868–1910, 2011 (article)

Abstract
In this paper, a robust and semi-automatic modelling pipeline for blood flow through subject-specific arterial geometries is presented. The framework developed consists of image segmentation, domain discretization (meshing) and fluid dynamics. All the three subtopics of the pipeline are explained using an example of flow through a severely stenosed human carotid artery. In the Introduction, the state-of-the-art of both image segmentation and meshing is presented in some detail, and wherever possible the advantages and disadvantages of the existing methods are analysed. Followed by this, the deformable model used for image segmentation is presented. This model is based upon a geometrical potential force (GPF), which is a function of the image. Both the GPF calculation and level set determination are explained. Following the image segmentation method, a semi-automatic meshing method used in the present study is explained in full detail. All the relevant techniques required to generate a valid domain discretization are presented. These techniques include generating a valid surface mesh, skeletonization, mesh cropping, boundary layer mesh construction and various mesh cosmetic methods that are essential for generating a high-quality domain discretization. After presenting the mesh generation procedure, how to generate flow boundary conditions for both the inlets and outlets of a geometry is explained in detail. This is followed by a brief note on the flow solver, before studying the blood flow through the carotid artery with a severe stenosis.

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[BibTex]

[BibTex]


 Geometrically Induced Force Interaction for Three-Dimensional Deformable Models
Geometrically Induced Force Interaction for Three-Dimensional Deformable Models

Si Yong Yeo, Xianghua Xie, Igor Sazonov, Perumal Nithiarasu

IEEE Transactions on Image Processing, 20(5):1373 - 1387, 2011 (article)

Abstract
In this paper, we propose a novel 3-D deformable model that is based upon a geometrically induced external force field which can be conveniently generalized to arbitrary dimensions. This external force field is based upon hypothesized interactions between the relative geometries of the deformable model and the object boundary characterized by image gradient. The evolution of the deformable model is solved using the level set method so that topological changes are handled automatically. The relative geometrical configurations between the deformable model and the object boundaries contribute to a dynamic vector force field that changes accordingly as the deformable model evolves. The geometrically induced dynamic interaction force has been shown to greatly improve the deformable model performance in acquiring complex geometries and highly concave boundaries, and it gives the deformable model a high invariancy in initialization configurations. The voxel interactions across the whole image domain provide a global view of the object boundary representation, giving the external force a long attraction range. The bidirectionality of the external force field allows the new deformable model to deal with arbitrary cross-boundary initializations, and facilitates the handling of weak edges and broken boundaries. In addition, we show that by enhancing the geometrical interaction field with a nonlocal edge-preserving algorithm, the new deformable model can effectively overcome image noise. We provide a comparative study on the segmentation of various geometries with different topologies from both synthetic and real images, and show that the proposed method achieves significant improvements against existing image gradient techniques.

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[BibTex]

[BibTex]


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Enhancing adhesion of biologically inspired polymer microfibers with a viscous oil coating

Cheung, E., Sitti, M.

The Journal of Adhesion, 87(6):547-557, Taylor & Francis Group, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Piezoelectric polymer fiber arrays for tactile sensing applications

Sümer, B., Aksak, B., Şsahin, K., Chuengsatiansup, K., Sitti, M.

Sensor Letters, 9(2):457-463, American Scientific Publishers, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]