Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments.

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because PDMS does not exhibit long-range fluidity at melting. We introduce an improved method to produce filaments of PDMS by a stepped temperature profile of the polymer as it cross-links from a fluid to an elastomer.

Gravity-Drawn Silicone Filaments: Production, Characterization, and Wormlike Chain Dynamics.

We introduce a method to produce continuous polydimethylsiloxane (PDMS) silicone filaments on the order of 0.5 m long and 100 μm in diameter. The approach overcomes traditional limitations in silicone drawing by partially precuring the polymer and drawing through a tube furnace.

An Assemblable, Multi-Angle Fluorescence and Ellipsometric Microscope.

We introduce a multi-functional microscope for research laboratories that have significant cost and space limitations. The microscope pivots around the sample, operating in upright, inverted, side-on and oblique geometries. At these geometries it is able to perform bright-field, fluorescence and qualitative ellipsometric imaging.

Configurable lipid membrane gradients quantify diffusion, phase separations and binding densities.

Single-experiment analysis of phospholipid compositional gradients reveals diffusion coefficients, phase separation parameters, and binding densities as a function of localized lipid mixture. Compositional gradients are formed by directed self assembly where rapid-prototyping techniques (i.e.

Structure-determining step in the hierarchical assembly of peptoid nanosheets.

Organic two-dimensional nanomaterials are of growing importance, yet few general synthetic methods exist to produce them in high yields and to precisely functionalize them. We previously developed an efficient hierarchical supramolecular assembly route to peptoid bilayer nanosheets, where the organization of biomimetic polymer sequences is catalyzed by an air-water interface. Here we determine at which stages of assembly the nanoscale and atomic-scale order appear.

Engineering bright sub-10-nm upconverting nanocrystals for single-molecule imaging.

Imaging at the single-molecule level reveals heterogeneities that are lost in ensemble imaging experiments, but an ongoing challenge is the development of luminescent probes with the photostability, brightness and continuous emission necessary for single-molecule microscopy. Lanthanide-doped upconverting nanoparticles overcome problems of photostability and continuous emission and their upconverted emission can be excited with near-infrared light at powers orders of magnitude lower than those required for conventional multiphoton probes. However, the brightness of upconverting nanoparticles has been limited by open questions about energy transfer and relaxation within individual nanocrystals and unavoidable tradeoffs between brightness and size.

Antibody-mimetic peptoid nanosheets for molecular recognition.

The ability of antibodies to bind a wide variety of analytes with high specificity and high affinity make them ideal candidates as molecular recognition elements for chemical and biological sensors. However, their widespread use in sensing devices has been hampered by their poor stability and high production cost. Here we report the design and synthesis of a new class of antibody-mimetic materials based on functionalized peptoid nanosheets.

Synthesis and characterization of designed BMHP1-derived self-assembling peptides for tissue engineering applications.

The importance of self-assembling peptides (SAPs) in regenerative medicine is becoming increasingly recognized. The propensity of SAPs to form nanostructured fibers is governed by multiple forces including hydrogen bonds, hydrophobic interactions and π-π aromatic interactions among side chains of the amino acids. Single residue modifications in SAP sequences can significantly affect these forces.

Direct observation of kinetic traps associated with structural transformations leading to multiple pathways of S-layer assembly.

The concept of a folding funnel with kinetic traps describes folding of individual proteins. Using in situ Atomic Force Microscopy to investigate S-layer assembly on mica, we show this concept is equally valid during self-assembly of proteins into extended matrices. We find the S-layer-on-mica system possesses a kinetic trap associated with conformational differences between a long-lived transient state and the final stable state.

Folding of a single-chain, information-rich polypeptoid sequence into a highly ordered nanosheet.

The design and synthesis of protein-like polymers is a fundamental challenge in materials science. A means to achieve this goal is to create synthetic polymers of defined sequence where all relevant folding information is incorporated into a single polymer strand. We present here the aqueous self-assembly of peptoid polymers (N-substituted glycines) into ultrathin, two-dimensional highly ordered nanosheets, where all folding information is encoded into a single chain.

Shaken, not stirred: collapsing a peptoid monolayer to produce free-floating, stable nanosheets.

Two-dimensional nanomaterials play a critical role in biology (e.g., lipid bilayers) and electronics (e.

High sensitivity deflection detection of nanowires.

A critical limitation of nanoelectromechanical systems (NEMS) is the lack of a high-sensitivity position detection mechanism. We introduce a noninterferometric optical approach to determine the position of nanowires with a high sensitivity and bandwidth. Its physical origins and limitations are determined by Mie scattering analysis.

3-nitro-tyrosine as an internal quencher of autofluorescence enhances the compatibility of fluorescence based screening of OBOC combinatorial libraries.

In the one-bead-one-compound (OBOC) combinatorial method, compounds are constructed on bead resin via split-mix library synthesis such that multiple copies of the same compound are displayed on each bead. These libraries are rapidly screened with enzyme-linked colorimetric, fluorescent, radiometric, or whole-cell binding assays. While fluorescence-based probes are powerful tools in OBOC screening, their utility is greatly limited by the intrinsic fluorescence of many commonly used solid supports, (e.

Frustrated phase transformations in supported, interdigitating lipid bilayers.

In free bilayers, the fluid to gel main phase transition of a monofluorinated phospholipid (F-DPPC) transforms a disordered fluid bilayer into a fully interdigitated monolayer consisting of ordered acyl tails. This transformation results in an increase in molecular area and decrease in bilayer thickness. We show that when confined in patches near a solid surface this reorganization proceeds under constraints of planar topography and total surface area.

Cell attachment behavior on solid and fluid substrates exhibiting spatial patterns of physical properties.

The ability to direct proliferation and growth of living cells using chemically and topologically textured surfaces is finding many niche applications, both in fundamental biophysical investigations of cell-surface attachment and in developing design principles for many tissue engineering applications. Here we address cellular adhesion behavior on solid patterns of differing wettability (a static substrate) and fluid patterns of membrane topology (a dynamic substrate). We find striking differences in the cellular adhesion characteristics of lipid mono- and bilayers, despite their essentially identical surface chemical and structural character.

Protecting, patterning, and scaffolding supported lipid membranes using carbohydrate glasses.

Disaccharides are known to protect sensitive biomolecules against stresses caused by dehydration, both in vivo and in vitro. Here we demonstrate how interfacial accumulation of trehalose can be used to (1) produce rugged supported lipid bilayers capable of near total dehydration; (2) enable spatial patterning of membrane micro-arrays; and (3) form stable bilayers on otherwise lipophobic substrates (e.g.

Bending membranes on demand: fluid phospholipid bilayers on topographically deformable substrates.

We combine hierarchical surface wrinkling of elastomers with lipid membrane deposition techniques to dynamically template complex three-dimensional topographies onto supported lipid bilayers. The real-time introduction of corresponding nano- to micrometer scale curvatures triggers spatially periodic, elastic bending of the bilayer, accompanied by molecular-level reorganizations. This ability to dynamically impose curvatures on supported bilayers and the ensuing re-equilibration promises fundamental material and biophysical investigations of curvature-dependent, static heterogeneities and dynamic reorganizations pervasive in biological membranes.

Patterning fluid and elastomeric surfaces using short-wavelength UV radiation and photogenerated reactive oxygen species.

Patterning physical, chemical, and biological functions at solid surfaces combines technological development with scientific discoveries in many disparate fields. A variety of top-down and bottom-up approaches has proved successful for applications in the solid state, affording large-area patterning at ever-shrinking length scales. Here we review a collection of recent efforts that highlight the versatility of short-wavelength ultraviolet light and photogenerated reactive oxygen species as a simple and cost-effective means to pattern a variety of challenging materials and thin-film configurations.

Surface-energy dependent spreading of lipid monolayers and bilayers.

Spontaneous spreading of phospholipids following hydration by water is directly compared on hydrophilic and hydrophobic surfaces using planar, composite substrates exhibiting binary patterns of surface energies. The use of patterned substrates-in conjunction with real-time, quantitative applications of imaging ellipsometry and epifluorescence microscopy-affords a side-by-side comparison of spreading kinetics and equilibrium morphologies following the hydration of a single parent-lipid source. We find that for fluid phospholipids ( > ), substantially contiguous bimolecular and mono-molecular lipid layers spread away from a source on hydrophilic and hydrophobic surfaces, respectively.

Characterization of physical properties of supported phospholipid membranes using imaging ellipsometry at optical wavelengths.

Subnanometer-scale vertical z-resolution coupled with large lateral area imaging, label-free, noncontact, and in situ advantages make the technique of optical imaging ellipsometry (IE) highly suitable for quantitative characterization of lipid bilayers supported on oxide substrates and submerged in aqueous phases. This article demonstrates the versatility of IE in quantitative characterization of structural and functional properties of supported phospholipid membranes using previously well-characterized examples. These include 1), a single-step determination of bilayer thickness to 0.

A class of supported membranes: formation of fluid phospholipid bilayers on photonic band gap colloidal crystals.

We report the formation of a new class of supported membranes consisting of a fluid phospholipid bilayer coupled directly to a broadly tunable colloidal crystal with a well-defined photonic band gap. For nanoscale colloidal crystals exhibiting a band gap at the optical frequencies, substrate-induced vesicle fusion gives rise to a surface bilayer riding onto the crystal surface. The bilayer is two-dimensionally continuous, spanning multiple beads with lateral mobilities which reflect the coupling between the bilayer topography and the curvature of the supporting colloidal surface.