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The unifying theme of our research is the science of miniaturization and the interface between engineered and living systems
Prof. Gracias delivering a Frontiers of Science Lecture on Self-Assembly
NSF's Science Nation: New 3D structures assemble with remarkable precisionSelf-folding polyhedra, sheets and micogrippers on youtube
We develop new methods to fabricate very small devices and integrated structures, and characterize these systems using microscopy and spectroscopy. A major thrust of our research is focused on constructing miniaturized 3D devices which are especially challenging to fabricate at small size scales. We are also particularly interested in understanding, synthesizing and characterizing self-assembling, intelligent and hybrid biotic-abiotic systems. We utilize a range of experimental techniques including photo-, e-beam and nano-imprint lithography; thin film deposition, molding, etching, culture of prokaryotic (E coli) and eukaryotic (e.g. fibroblasts, islets, myoblasts) cells, biological assays (e.g. fluorescent stains, ELISA, cytology), non-linear optical spectroscopy, electron microscopy (TEM & SEM with fixation), RF measurements such as GHz spectrum analysis, electrochemical methods such as potentiometry and chronoamperometry and four point electrical testing with femto-amp resolution. We also utilize analytical methods as well finite element methods (HFSS, Surface Evolver, COMSOL) to model data. Our lab is multidisciplinary and students in our lab have had backgrounds in Chemical and Biomolecular Engineering, Electrical Engineering, Physics, Chemistry, Materials Science, Biomedical Engineering and Medicine.
Research Themes We acknowledge research support from the National Institutes of Health (NIH), National Science Foundation (NSF), Defense Threat Reduction Agency (DTRA), Defense Intelligence Agency (DIA), Army Research Office (ARO), Semiconductor Research Corporation (SRC), DuPont, Northrop Grumman, Goldman Philanthropic Foundation, Arnold and Mabel Beckman Foundation, Camille & Henry Dreyfus Foundation, Iacocca Family Foundation and Alexander Von Humboldt Foundation 1. Self-folding across length scales 1. Nanoscale Origami: First demonstration of the self-folding of 100 nm sized curved and polyhedral metallic and dielectric structures with 10 nm resolved patterns in all three dimensions. Representative Publications: Self-assembly of lithographically patterned nanoparticles, Nano Letters (2009); Three dimensional nanofabrication using surface forces, Langmuir (2010); Curving nanostructures using extrinsic stress, Advanced Materials (2010); Nanoscale Origami for 3D Optics, Small (2011). 2. Origami inspired self-assembly of polyhedral containers / capsules / particles: Invention of a high-throughput methodology to create well sealed and precisely patterned hollow polyhedra with metals, semiconductors and polymers. Representative Publications: Fabrication of micrometer-scale, patterned polyhedra by self-assembly, Advanced Materials (2002); Self-assembled three dimensional radio frequency (RF) shielded containers for cell encapsulation, Biomedical Microdevices (2005); Surface tension driven self-folding polyhedra, Langmuir (2007); Thin film stress driven self-folding of microstructured containers, Small (2008), Self-folding micropatterned polymeric containers, Biomedical Microdevices (2011), Origami inspired self-assembly of patterned and reconfigurable particles, JOVE(2013), U.S. Patent 8,236,259 B2, U.S. Patent 8,246,917 B2 3. Self-folding sheets: First demonstration of geometrically programmable self-folding sheets composed of lithographically patterned metals and polymers. Sheets feature hundreds to thousands of folds, and fold up without any human intervention, wires or circuits. Representative Publications: Patterning thin film mechanical properties to drive assembly of complex 3D structures, Advanced Materials (2008); Microassembly based on Hands Free Origami with Bidirectional Curvature, Applied Physics Letters (2009). 4. Curved, folded and flexible microfluidics / Tissue scaffolds: First demonstration of self-folding microfluidic networks and cell-laden hydrogels reminiscent of vascularized leaves and tissues. Representative Publications: Directed Growth of Fibroblasts into Three Dimensional Micropatterned Geometries via Self-Assembling Scaffolds, Biomaterials (2010); Differentially photo-crosslinked polymers enable self-assembling microfluidics, Nature Communications (2011); Bio-origami hydrogel scaffolds composed of photocrosslinked PEG bilayers, Advanced Healthcare Materials (2013). Representative Publications: Photolithographically Patterned Smart Hydrogel Based Bilayer Actuators, Polymer (2010); Reversible actuation of microstructures by surface chemical modification of thin film bilayers, Advanced Materials (2010); Laser triggered sequential folding of microstructures, Applied Physics Letters (2012); Stimuli responsive self-folding using thin polymer films, Current Opinion in Chemical Enginering (2013). 6. Self-folding of interesting shapes: Like the classic saddle shape of a potato chip, self-folding of curved 2D shapes display a rich phase behavior. Representative Publication: Plastic deformation drives wrinkling, saddling and wedging of annular bilayer nanostructures, Nano Letters (2010).
2. Micro and Nanomedicine 1. Surgery with untethered tools: First sub-mm scale completely wire-free surgical microgripper; first enzymatically responsive microgripper. The first ever in vivo biopsy with sub-mm scale surgical tools. Representative Publications:Tetherless thermobiochemically actuated microgrippers, PNAS (2009); Toward a miniaturized mechanical surgeon, Materials Today (2009); Enzymatically Triggered Actuation of Miniaturized Tools, JACS (2010), Biopsy with thermally-responsive untethered microtools, Advanced Materials (2013), Biologic tissue sampling with untethered microgrippers, Gastroenterology (2013). 2. 3D nanoporous immunoisolating devices for encapsulated cell therapy: Synthetic and precisely structured 3D nanoporous cell encapsulants for Type 1 diabetes therapy. Representative Publications: Self-loading lithographically structured microcontainers: 3D patterned, mobile microwells, Lab Chip (2008); Three-dimensional microwell arrays for cell culture, Lab Chip (2010); Self-folding immunoprotective cell encapsulation devices, Nanomedicine (2011). 3. Nanoscale neurochemical recording: In vitro dopamine recording with very long nanowires of different diameters Representative Publications: Patternable nanowire sensors for electrochemical recording of dopamine, Analytical Chemistry (2009).
1. Cellular Self-Organization: First demonstration of the self-organization of bacteria into a well-defined 3D space curve; a helix. Representative Publications: Three Dimensional Chemical Patterns for Cellular Self-Organization, Angewandte Chemie (2011); Assembling backpacking bacteria for diagnostics and therapeutics MicroTAS (2011). 4. Uncovering the rules of self-assembly 1. Patterns in aggregative 3D assembly: We have solved the surface patterning rules for 3D self-assembly of polyhedra. 2. Rules for self-folding polyhedra: Convincingly demonstrated that compact nets with high vertex connections result in high yielding self-assembly processes. Representative Publications: Compactness determines the success of cube and octahedron self-assembly, PLoS One (2009); Algorithmic design of self-folding polyhedra, PNAS (2011). 1. Microchemomechanical Systems: First reversible chemically actuated microgripper; Ferromagnetic microgripper closes and opens on exposure to chemicals and is strong enough to hold and transport cargo without the need for any wires, tethers or batteries. Representative Publications: Pick-and-place using chemically actuated microgrippers
2. Bacterial Backpacking: Propelling individual nanoscale cargo with a single bacterium. Representative Publications: Enabling Cargo-Carrying Bacteria via Surface Attachment and Triggered Release, Small (2011). Representative Publications: Self-Propelled Nanotools, ACS Nano (2012), Rolled-up magnetic microdrillers: Towards remotely controlled minimally invasive surgery, Nansocale (2013).
Chemistry with controlled release particles: Controlling reactions by engineering the release of chemicals in space and time. Representative Publications: Spatially controlled chemistry using remotely guided nanoliter scale container, JACS (2006); Remote radio frequency controlled nanoliter chemistry and chemical delivery on substrates, Angew Chemie (2007); Reconfigurable microfluidics with metallic containers, JMEMS (2008), Chemistry with spatial control using particles and streams, RSC Advances (2012).
7. Self-assembling electronics and nanoscale soldering
1. Directed assembly of nanowire circuits: High throughput directed assembly of nanowires on substrates using magnetic and dielectrophoretic forces. Representative Publications: Integrating nanowires with substrates using directed assembly and nanoscale soldering, IEEE Transactions on Nanotechnology (2006); Dielectrophoretic assembly of reversible and irreversible metal nanowire networks and vertically aligned arrays, Applied Phyics Letters (2006), Quantitative analysis of parallel nanowire array assembly by dielectrophoresis, Nanoscale (2011). 2. Soldering and bonding nanowires: First demonstration of robust solder connections between nanowires; robust bonding of nanowires using polymerizable liquids. Representative Publications: Surface tension driven self-assembly of bundles and networks of 200 nm diameter rods using a polymerizable adhesive, Langmuir (2004); Reflow and electrical characteristics of nanoscale solder, Small (2006); Three dimensional electrically interconnected nanowire networks formed by diffusion bonding, Langmuir (2007). 3. 3-axis sensors and 3D electronics: Self-assembly of 3D eletronic devices, sensors and networks. Representative Publications: Forming electrical networks in three dimensions by self-assembly, Science (2000); Fabrication of a cylindrical display by patterned assembly, Science (2002); Self-assembly of orthogonal 3-axis sensors, Applied Physics Letters (2008); A three dimensional self-folding package (SFP) for electronics MRS proceedings (2010). 1. Polyhedral metamaterials: Creation of truly three dimensional optically active metamaterials Representative Publications: Three-dimensional surface current loops in terahertz responsive microarrays, Applied Physics Letters (2010); Nanoscale Origami for 3D Optics, Small (2011). 2. Non-Linear (IR+Visible) Sum Frequency Spectroscopy: Representative Publications: Probing Organic Field Effect Transistors In-Situ During Operation Using SFG, JACS (2006); Correlations between electrical properties and SFG spectra of organic field effect transistors, JPC (2007).
1. Nanowire sensors for threat detection (Collaboration with Johns Hopkins Applied Physics Laboratory): Representative Publication: Nanowire-based surface-enhanced Raman spectroscopy (SERS) for chemical warfare simulants, Proc. SPIE (2012). 2. Active microstructures with communicable modules (Collaboration with the US Army Research Laboratory): Representative Publications: Tetherless Microgrippers with Transponder Tags, JMEMS (2011), Initiation of nanoporous energetic silicon by optically triggered, residual stress powered microactuators, Proc. IEEE MEMS (2012). Representative Publication: Solvent driven motion of lithographically fabricated gels, Langmuir (2008). 2. Spontaneous pattern formation in thin films of Au/Cr/Si: Simply on heating, rings appear in these multilayer thin film stacks!! Representative Publication: Concentric ring pattern formation in heated chromium-gold thin films on silicon, Applied Physics Letters (2008).
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