Adhesion Mechanisms of the Mussel Foot Proteins …ceweb/gss/pdfs/gss2009_poster_abstracts.pdfAdhesion Mechanisms of the Mussel Foot Proteins Mfp ... presumably due to capability of

Adhesion Mechanisms of the Mussel Foot Proteins Mfp-1 and Mfp-3

Travers H. Anderson(a), Jing Yu(a), Hongbo Zeng(a), Dong Soo Hwang(b), J. Herbert Waite(b, c) and Jacob Israelachvili(a, c)

(a) Department of Chemical Engineering, University of California, Santa Barbara (b) Department of Molecular, Cellular and Developmental Biology, University of California, Santa

Barbara

Mussels adhere to a variety of surfaces by depositing a highly specific ensemble of 3,4-dihydroxyphenyl-L-alanine (DOPA) containing proteins. The adhesive properties of Mytilus edulis foot proteins mfp-1 and mfp-3 on mica (a common alumino-silicate clay mineral) and TiO2 surfaces were directly measured at the nano-scale by using a surface forces apparatus (SFA). The adhesion energy between mfp-3 and mica was on the order of W=3×10-4 J/m2 which corresponds to an approximate force per plaque of ~100 gm – more than enough to hold a mussel in place if no peeling occurs. In contrast, no adhesion was detected between mica surfaces bridged by mfp-1. AFM imaging and SFA experiments showed that mfp-1 can adhere well to a single mica surface, but in order for bridging to occur between two mica surfaces the protein must be sheared or allowed extended contact time with the opposing surface. On TiO2 surfaces the mfp-1 interaction is 10-fold stronger than with mica, presumably due to capability of DOPA to form coordination bonds with the TiO2 surface. The results are consistent with the apparent function of the proteins, i.e., mfp-1 is disposed as a “protective” coating and mfp-3 as the adhesive or “glue” that binds mussels to surfaces. While mussel foot protein is capable of making strong adhesive bonds with TiO2, the adhesion to mica is actually weak and likely due to weak physical interactions rather than chemical bonding. However, strong adhesion forces of mussel plaques can arise as a consequence of plaque geometry (i.e., their inability to be peeled off) even on surfaces such as mica that do not have a high intrinsic surface or adhesion energy, W.

Figure 1: Schematic drawing of a mussel byssal thread attached to a substrate.

References: Lin, Q.; Gourdon, D.; Sun, C.; Holten-Anderson, N.; Anderson, T. H.; Waite, J. H.; Israelachvili, J. N. PNAS 2007, 104, 10, 3782-3786.

Engineering Micelles as Multifunctional Nanoparticles for Targeting and Delivery

Matthew Blacka,b, Mark Kastantina, Dimitris Missirlisa,b, Matthew Tirrellb

a) Department of Chemical Engineering, University of California, Santa Barbara b) Department of Bioengineering, University of California, Berkeley

Self-assembled lipid-based micelles can be used to combine targeting, imaging, and therapeutic functions and deliver them efficiently to tumors or other tissues in vivo. The micelles are formed from monomers of functional biomolecules conjugated to lipids, often via a hydrophilic PEG spacer. We have demonstrated that these micelles are useful for in vivo disease targeting and delivery of a therapeutic or imaging payload. Despite their versatility and ease of production, little is known about micelle behavior in vitro or in vivo and what fundamental principles may link their structure and composition to their ability to perform desired therapeutic and diagnostic tasks. In this work, the effect of micelle stability and composition on the behavior of the micelles has been investigated for tumor targeting and therapy. By attaching and varying the length of a hydrophobic tail to the apoptosis inducing peptide, (KLAKLAK)2, the efficacy of the peptide can be increased by up two orders of magnitude. Increasing the length and number of hydrophobic tails was shown to significantly slow micelle break up. Incorporating (KLAKLAK) 2 into mixed micelles containing a targeting and internalizing peptide, LyP-1, has also been shown to increase its efficacy in vitro. Current work is aimed at further optimizing how micelle composition, stability, and shape affect the efficacy of therapeutic micelles. In addition to advancing a specific strategy useful for cancer treatment, the insights contained in this work will help provide a blueprint for future design of therapeutic and diagnostic micelles.

Multiscale optimization of coarse-grained models via the relative entropy

Aviel Chaimovich and M. Scott Shell

Department of Chemical Engineering, University of California Santa Barbara

Multiscale simulation methods are commonly used to study the properties of complex systems with multiple length and time scales [1]. These methods often connect detailed all-atom (AA) molecular models with simplified coarse-grained (CG) ones that enable longer and larger simulation studies. However, it has been challenging to identify optimal yet universal parameterization methodologies for the development of CG models. Recently, we introduced a rigorous theoretical framework for such a task: given an AA model, an optimal CG one can be determined by minimizing an informatic property termed the relative entropy [2]. In physical terms, the relative entropy measures deviations in the configurational ensemble probabilities as molecular features are coarse-grained away. In a previous work, it was shown that the relative entropy method naturally reproduces important inverse problems in statistical mechanics, including uniqueness theorem and variational mean field theory [2].

In this work, we present two methods for numerical optimization of CG models using relative entropy minimization. One is based on the original formulation of the relative entropy, and it involves computing property averages via simulations in both the AA and CG ensembles. Using standard free energy perturbation techniques, we present an alternative approach that requires only averages in the AA ensemble, allowing for a very fast implementation; furthermore, this reformulation of the relative entropy permits a basic expansion which yields analytical expressions for optimization in special cases. We first compare the statistical efficiency and convergence behavior of these approaches via an elementary test case, the “coarse-graining” of the nearest-neighbor lattice gas into the comparable mean-field system. We demonstrate that our mean-field solution performs in a superior manner with respect to the traditional mean-field approach. Moreover, we show that the relative entropy systematically signals the performance of the mean-field systems, thus serving as an apparent universal metric for the aptitude of CG models. Subsequently, we use the relative entropy approach to parameterize a simple (off-lattice) spherically-symmetric model of liquid water [3]. We evaluate the ability of the optimized CG water in reproducing water’s bulk thermophysical properties and the hydrophobic effect [3]. Again, we show that the relative entropy serves as an indicator of the capability of these optimized models.

References: [1] G. A. Voth, Journal of Chemical Theory and Computation 2, 463 (2006). [2] M. S. Shell, The Journal of Chemical Physics 129, 144108 (2008). [3] A. Chaimovich, and M. S. Shell, Physical Chemistry Chemical Physics 11, 1901 (2009).

Nonlinear Microrheology of Brownian Ellipsoids

Ryan J DePuit, Aditya S Khair, Todd M Squires

Department of Chemical Engineering, University of California, Santa Barbara

Microrheology uses colloidal probes to measure bulk viscoelastic properties of soft materials. 'Passive' microrheology exploits the fluctuation-dissipation theorem to quantitatively recover linear response properties. However, this theoretical foundation is limited to near-equilibrium behavior, and does hold true for the investigation of nonlinear behavior. Squires (Langmuir, 2008) discussed a variety of theoretical issues inherent to nonlinear microrheology, including Lagrangian unsteadiness, non-viscometric flows, and inhomogeneous stresses. To investigate these issues, we have developed a computational system to examine simplest model system that exhibits non-trivial rheology: a spherical colloidal probe translating through a dilute suspension of rigid ellipsoids or rods. We explicitly compute the (Lagrangian) transient, spatially-inhomogeneous microstructure in the bulk around the probe, the associated microstructural stresses upon the fluid, and the consequent retarding force upon the probe. Finally, we examine the effect that these issues have upon the quantitative comparisons between the velocity-dependent "micro-viscosity" and the macroscopically-measured rate-dependent shear viscosity of the same material.

Coalescence of Bubbles and Drops

John M. Frostad and L. Gary Leal

Chemical Engineering Department, University of California, Santa Barbara

The morphology of polymeric foams is governed in part by the rate of coalescence of the dispersed bubbles of gas during the formation process. The interaction time required for coalescence to occur can be measured by the drainage time, which is defined as the time required for the thin film of liquid between the bubbles to drain and rupture. In order to perform a fundamental study of the drainage time, the simplified system of two gas bubbles expanding at a constant volumetric growth rate in a quiescent fluid is studied. The bubbles are grown in an axisymmetric fashion from the ends of two opposing capillaries. With this system, a scaling relationship is sought for the nondimensionalized drainage time as a function of the viscosity ratio of the dispersed fluid to that of the suspending fluid, the Capillary number, and a dimensionless Hamaker constant. In a previous study, low viscosity drops in a high viscosity fluid were studied using the same experimental setup [1]. It was assumed that this liquid-liquid system having a viscosity ratio similar to that of a gas-liquid system would provide equivalent data to the gas-liquid system at the same range of Capillary numbers. This study also derived a scaling theory that should be expected to hold for both systems in the limit of small viscosity ratio, small Capillary number and small Reynolds number. In the present work however, it was found that data from the gas-liquid system are not equivalent to the liquid-liquid system. In addition, the data for the gas-liquid system do not agree with the proposed scaling theory. Furthermore, repeating the experiments done with the liquid-liquid system revealed that the scaling theory does not agree with the data for liquid-liquid system either. Possible explanations for the differences between the two systems and the disagreement with the theory are discussed. References: [1] M Borrell and LG Leal, “Viscous coalescence of expanding low-viscosity drops; the dueling drops experiment,” Journal of Colloid and Interface Science 2008, 319, no. 1, 263-269.

Engineering the Specificity of a Stable Peptide Scaffold

Jennifer A. Getz, Jeffrey J. Rice, and Patrick S. Daugherty

Department of Chemical Engineering, University of California, Santa Barbara

The ability to generate high-affinity and high-stability peptide ligands is critical in the production of robust biosensors, stable peptide therapeutics, and highly specific imaging reagents. Kalata B1 (KB1) is a cyclic cystine knot peptide that resists enzymatic, thermal, and chemical denaturation, and acyclic permutants have been shown to retain these properties. KB1 was investigated as a peptide scaffold in an effort to generate low molecular weight and enzymatically stable affinity ligands. Using bacterial cell surface display, a large library of variants was constructed by randomizing seven residues within the KB1 scaffold. The library was then sorted to identify peptides that bind specifically to human thrombin. From the selected clones, several distinct consensus groups were identified and the peptides were ranked by their dissociation rate. Thrombin-specific peptide variants were purified and characterized using HPLC and mass spectrometry. The peptide variants exhibited equilibrium dissociation constants in the high nanomolar range as measured using surface plasmon resonance. To determine if the thrombin-binding KB1 peptides retain the stability of the original scaffold, their resistance to trypsin was measured. Our results indicate that the KB1 scaffold may be useful for creating high-stability affinity ligands.

Molecular Studies of the Electric Double Layer

Brian Giera

Department of Chemical Engineering, UC Santa Barbara

In the United States, roughly 98% of electricity is immediately produced, transmitted, and then consumed without ever passing through energy storage devices. When the demand for electricity (called the load) exceeds the power supplied, a situation analogous to everyone simultaneously flushing their toilets occurs where, instead of a lower water pressure, the ac frequency drifts from its 60 Hz baseline. Overall, mistakes in power regulation are estimated to cost tens of billions of dollars worldwide due to power outages or equipment damage in severe cases. Just as water towers are used to regulate water pressure, supercapacitors enhance power regulation by instantaneously surging (or soaking up) excess power into over (under) loaded grids. A supercapacitor functions much like a conventional parallel plate capacitor that stores its electrical energy between two charged plates separated by an insulator. The electrodes of a supercapacitor are submerged in an electrolyte and, when charged, attract oppositely charged counter-ions to its surface. The electrostatic attraction is balanced by the ions’ tendency to travel down concentration gradients (away from the surface) forming a non-conductive nanometer thick region called the electric double layer (EDL). Furthermore, these electrodes are made using high surface area porous carbon. A supercapacitor, therefore, yields the same (super) capacitance as would two high surface area parallel plates separated by mere nanometers. Molecular Dynamics (MD) models were used to study the EDL formation – a critical mechanism of supercapacitor charging. Ion concentration profiles were generated as a function of time to investigate the behavior of EDL formation for liquids whose charged species have different sizes and valencies in a parallel plate geometry.

Asymmetric Effect of Reactive Compatibilizer on Immiscible Polymer Blends

Yanli Gong and L. Gary Leal

Department of Chemical Engineering, UCSB

Reactive compatibilizer is commonly used when blending immiscible polymers. Our experimental system consisted of same viscosity polybutadiene (PBd) and polydimethylsiloxane (PDMS) and the ratio of PBd and PDMS varied from 20:80 to 80:20. Compatibilizer was produced by an interfacial reaction between same molecular weight functionalized homopolymers (PBd-COOH and PDMS-NH2 both with Mw=26,000 g/mol). Experiments were conducted on blends containing 0.1 or 1 wt. % compatibilizer. All blends have a droplet matrix-structure with the major phase being the continuous phase. The rheological behavior of the blends shows that the compatibilizer increases the terminal complex viscosity, which can be interpreted in terms of a partial surface immobilization. In blends in which PBd forms the continuous phase, 1 wt. % of compatibilizer can suppress the coalescence of PDMS drops completely, while this is not found in the 0.1 wt. % compatibilized case, or when PDMS is the continuous phase. Also, in blends with PBd as the continuous phase, the terminal complex viscosity is comparable to that of a suspension of rigid spheres, which suggests, that the interface has been immobilized almost completely. We speculate that the PBd block is highly swollen by the low Mw PBd homopolymers and it is an effective barrier to coalescence when PBd is the continuous phase. Also there are two interfacial relaxation process found in the blend, manifested as shoulders in G’ and η*. The first is corresponding to deformation and relaxation of the droplets during the oscillatory experiment at high frequency. The second is attributed to flow induced gradients in compatibilizer concentration and, hence, flow induced interfacial tension gradients on the interface at low frequency. For 1 wt. % compatibilized blend both of the relaxation happened at higher frequency than 0.1 wt. % case because the Marangoni effect is larger at higher compatibilizer concentration. For 0.1 wt. % compatibilized blend, when PDMS is the drop phase, the interfacial tension relaxation is faster than PBd as the drop phase. This can also be interpreted by larger Marangoni effect. We conclude that both the steric hindrance and Marangoni effect are main mechanisms for the asymmetric effect of reactive compatibilizer in the current system.

Evaluation of the Impact of Blood Glucose Sampling Frequency on an Algorithm for Hypoglycemic Alarming

Rebecca A. Harvey, BS; Eyal Dassau, PhD; Howard Zisser, MD; Lois Jovanovič, MD; Bruce A. Buckingham, MD; Francis J. Doyle III, PhD

University of California, Santa Barbara An alarm is an important safety mechanism to alert people with type 1 diabetes mellitus (T1DM) to impending hypoglycemic events. Continuous glucose sensors currently provide glucose values in 1, 5, and 10 minute intervals. We therefore tested the effectiveness of our alarm using these various sampling frequencies. An algorithm was developed to predict impending hypoglycemia events. The algorithm calculates the rate of change of blood glucose (BG) with the ability to overcome data gaps. The time of crossing a BG threshold (70, 80, or 90 mg/dL) was predicted and an alarm was raised if two successive points were within a prediction horizon (35, 45, or 55 minutes). The algorithm was tested on data from a study on 18 people with T1DM (mean age of 20 years). Hypoglycemia was induced by increasing the basal infusion rate by an average of 180% and BG data were taken from the Abbott Freestyle Navigator® (ADC, Alameda, CA) calibrated with finger-stick measurements. To evaluate the viability of alarming using longer delays in sampling frequency calculations were made at steps of 1, 5, and 10 minutes. Using longer intervals, fewer hypoglycemia events were alarmed: 67%, 47%, and 43% of hypoglycemia events were alarmed within 60 minutes of the event for 1, 5, and 10 minute intervals, respectively. Conversely, more alarms were within the prediction horizon of the threshold for longer intervals: 78%, 88% and 95%. This algorithm effectively predicts pending hypoglycemia with a minimum of false alarms with up to 10 minute sampling times. However, the decrease in the number of events alarmed indicates that longer sampling times may not be sufficient to alarm patients to hypoglycemia events.

Block Copolymer Lithography: New Patterns and Formulations

Su-Mi Hur(a), Carlos J. García-Cervera(b), and Glenn H. Fredrickson(a,c)

(a) Department of Chemical Engineering, UCSB (b) Department of Mathematics, UCSB

(c) Department of Materials, UCSB

The nanometer scale of microdomain ordering and its facility in the modulation of size and patterns renders block copolymer thin films promising candidates for high resolution lithographic tools. However, creation of robust, defect-free feature arrays is still a challenge for block copolymer lithography. Moreover, in order to fabricate non-periodic features such as bent lines with sharp corners, T-junctions, and non-periodic arrays of dots, it is necessary to devise confinement or patterning strategies for block copolymer films that disrupt, modify, or truncate the periodic copolymer microdomains that occur naturally in the bulk. Currently, there is also substantial interest in the tetragonal (square) packing of cylinders. This structure is attractive, since it represents a canonical micro-lithographic structure that is consistent with the industry standard integrated circuit design architecture for addressability and transistor interconnection. In this study, we investigate various approaches to achieving defect-free tetragonal arrays of microdomains. One approach involves subjecting a simple AB block copolymer system to graphoepitaxial confinement in a square well and stabilizing the phase through the addition of A homopolymer. Another approach utilizes a binary blend of AB and B'C diblock copolymers in which the B and B' blocks have attractive supramolecular interactions. Self-consistent field theory (SCFT) studies of phase morphology in these systems have been performed, where a number of parameters were varied including the composition of the blend, the interaction between the segments, and the confinement conditions. We identified optimal sets of parameters that promote the formation of a defect-free tetragonal array and construct the phase diagram of the various observed and possible configurations. This phase diagram will assist the design of experimental systems. For the confined system, we also investigated microdomain ordering within square wells subject to boundary perturbations in order to confirm the robustness of tetragonal ordering to line edge roughness.

Figure 1: Phase diagram for an AB block copolymer/A homopolymer blend thin film subject to square confinement with A-wetting conditions and fixed ratio of homopolymer to diblock lengths, 2.1. x- and y-axis are A homopolymer fraction VAh and side length of square confinement L, respectively.

Shape and size control of gold nanoparticles by thermal decomposition of (CH3)2Au(acac)

Taeho Hwang a, Ryan C. Nelson a, Miyako Hisamoto a, Susannah L. Scott* a, b

a Department of Chemical Engineering, b Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-5080, U.S.A.

Gold nanoparticles (Au NPs) dispersed on reducible oxides or on activated carbon show high activities and selectivities in a variety of oxidation reactions, including the low-temperature oxidation of CO [1]. Their catalytic properties are a strong function of nanoparticle size and shape, with the highest activity generally observed for particle diameters 1 - 10 nm. A long-term goal of this project is to control the size and shape of Au NPs via the controlled thermal decomposition of supported molecular precursors, and apply this methodology to the synthesis of uniform gold catalysts. Thermal decomposition of (CH3)2Au(acac) to Au0 NPs (shown in Fig.1), which is extremely solvent dependent [2], was monitored in several different solvents and with various additives. The growth of the particles can be monitored via their surface plasmon resonance, whose energy is size-dependent according to Mie theory. Kinetic profiles suggest that the conversion of Au(III) to Au(0) is pseudo-zero-order in dehydrated solvents, but become distinctly autocatalytic when labile protons are present. An autocatalytic rate law was derived from the proposed reaction mechanism and used to extract rate constants by non-linear least-squares curve-fitting [3]. In order to explore the mechanism further, reaction intermediates were monitored using solution-state 1H NMR with and without added water and surface capping agents. DFT calculations suggest dechelation of the acetylacetonate ligand induced by water or another protic agent (which may include the hydroxyl-terminated surface of the catalyst support) [4]. We believe the result in solution state can be applied to the formation of Au NPs on supporting materials for the highly dispersed gold catalysts.

References:

[1] Haruta, M.; The Chemical Record 2003, Vol. 3, 75-87 [2] Klassen, R.B., Baum, T.H., Organometallics, 1989, 8, 2477-2482. [3] Besson, C., Finney, E.E., Finke, R.G.; J. Am. Chem. Soc 2002, 124, 5796. [4] Hisamoto, M., Nelson, R.C., Lee, M.Y., Eckert, J., Scott, S.L.; J. Phys. Chem. C 2009, 113, 8794–8805.

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Figure 1: TEM image of (a) gold nanoparticles formed by decomposition of 0.367 mM (CH3)2Au(acac) at 70 °C in 2-PrOH; and (b) close-up view of nanoparticle

Measuring the interfacial rheological properties of lung surfactant monolayers

KyuHan Kim, Siyoung Choi, Siegfried Steltenkamp Joseph A. Zasadzinski, and Todd M. Squires

Department of Chemical Engineering, University of California, Santa Barbara

Lung surfactant (LS) is essential to respiration because it reduces surface tension at the interface between water and air in the alveoli. In addition, LS stabilizes the alveoli against collapse during exhalation. LS is composed of lipids, mainly dipalmitoylphosphatidylcholine (DPPC), and proteins. We are interested in the rheological properties of a pure DPPC film as a first step towards understanding complex LS rheology. During exhalation, we hypothesize that a large surface tension gradient occurs between the alveolar sacs and the bronchioles which should cause LS to flow away from the alveoli. Because LS does not readily leave the alveoli through the trachea, there must be the drag effect with an opposing direction to the flow induced form the surface tension gradient. Previous work has shown that the surface shear viscosity of LS increases exponentially at low surface tensions, which may be sufficient to prevent the flow of surfactant out of the lungs. Additionally, a yield stress in the interfacial LS film would also help to prevent the flow. My results have shown that a yield stress exists for a pure DPPC monolayer at certain surface pressures.

Model-Based Therapeutic Target Discrimination Using Stochastic Simulation and Robustness Analysis in an Insulin Signaling Pathway

Eric Kweia, Jason Shoemakera, Kevin Sanftb, Linda Petzoldb, and Francis Doyle, IIIa

aDepartment of Chemical Engineering bDepartment of Computer Science, University of California-Santa Barbara

Insulin resistance, which precedes the onset of type 2 diabetes mellitus (T2DM), is a decreased sensitivity of response to normal insulin levels which has been linked to a number of possible changes in the insulin signal transduction network. In this work, we simulate two hypothesized resistance-inducing perturbations using a published differential equation model of insulin signaling, estimate noise in this signaling model with stochastic simulation, and predict sets of optimal multi-drug targets that are robust against the estimated signaling noise using structured singular value analysis.

A New Model for Capturing the Effect of Supersaturation on Crystal Shape

Michael A. Lovette, and Michael F. Doherty

University of California at Santa Barbara, Department of Chemical Engineering, Santa Barbara, CA 93106

Shape can impact the downstream processing efficiency and end-use efficacy of crystalline products. It is known that some crystalline materials exhibit notably different shapes when grown from solutions with only small differences in supersaturation (e.g., paracetamol, which changes its shape from a rod to a nearly equant shape [1] over a range of supersaturations from 10 – 15%). In light of these observations, we have developed a predictive model that captures the effects of supersaturation on the steady-state shape of a growing crystal. This model is mechanistic in nature and requires only the crystal structure and solubility parameter data as inputs. Previous predictive models for crystal shape have assumed that all F faces (faces with 2 or more periodic bond chains, further defined in Lovette et al. [2]) grow by a spiral mechanism limiting their application to growth at low supersaturation. Our new model captures the effects of supersaturation on growth shape by accounting for growth by both spiral and two-dimensional (2D) nucleation mechanisms; evaluating the applicability of each on a face-by-face basis over a given range of supersaturation. For each face the growth model developed by Snyder and Doherty [3] was applied over the supersaturation range where spiral growth was determined to be the dominant mechanism. At higher supersaturations, a new model for 2D nucleation, developed in agreement with the bond structure of the face, was applied. The implementation of this composite growth model is tested through a case study of naphthalene grown in ethanol, for which the model yields predictions that are in good agreement with the experimentally obtained shapes. References: [1] Ristic, R.; Finnie, S.; Sheen, D.; Sherwood, J. J. Phys. Chem. B, 2001, 105, 9057. [2] Lovette, M. A.; Browning, A. R.; Griffin, D. W.; Sizemore, J. P.; Snyder, R. C.; Doherty, M. F., I.E.C.R, 2008, 47, 9812. [3] Snyder, R. C.; Doherty, M. F. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2009, 465, 1145.

DNA Binding and Nuclear Targeting Peptide Amphiphiles

Rachel Marulloa, Raymond Tub, and Matthew Tirrellc

(a) Chemical Engineering Department, University of California, Santa Barbara (b) Chemical Engineering Department, City College of New York (c) Bioengineering Department, University of California, Berkeley

Peptide amphiphiles can be used to create multivalent, multifunctional, self-assembled nanostructures for applications such as immunotherapy, cancer treatment, and in this case gene therapy. We have conjugated di-C16 hydrophobic tails to bZip, a thirty-eight amino acid sequence derived from the transcription factor GCN4, to promote the formation of extended micelles in solution. The peptide amphiphile headgroups adopt a high degree of alpha-helical content in the micelle corona compared to the free peptide chains as shown by circular dichroism. The hydrophobic moiety facilitates the DNA binding of bZip amphiphiles in an orthogonal arrangement similar to the native protein, in contrast to the unmodified peptide which binds via electrostatic collapse onto DNA. The peptide amphiphiles bind DNA in a cooperative fashion but do not recognize the AP-1 sequence that GCN4 binds specifically, although further modification of the monomers may enhance their biofunctionality. To implement the DNA binding peptide amphiphiles in gene therapy applications, a nuclear targeting platform is being developed by appending a hydrophobic tail to a nuclear localization signaling (NLS) peptide. The tail enhances cellular uptake of the peptide and delivery to the nucleus of HeLa cells as observed by fluorescence microscopy. Incorporating NLS peptide amphiphiles into a mixed micelle displaying DNA binding peptides or other therapeutic agents may aid in targeted delivery to the nucleus.

Structural transition with thickness in films of poly-(styrene-b-2vinylpyridine) (PS-b-P2VP) diblock copolymer/homopolymer blends

Vindhya Mishraa, Su-Mi Hura, Eric Cochranc, Edward J. Kramera,b, Glenn H. Fredricksona,b

a Department of Chemical Engineering, UC Santa Barbara; b Department of Materials, UC Santa Barbara; cDepartment of Chemical Engineering, Iowa State University;

In multilayer thin films of spherical morphology block copolymers, the surface layers prefer hexagonal symmetry while the inner layers prefer BCC. Thin films with spherical morphology PS-b-P2VP blended with short homopolymer polystyrene (hPS) chains have an HCP structure up to a thickness n* at which there is a transition to a face centered orthorhombic structure. Using grazing incidence small angle X-ray scattering and transmission electron microscopy we show that n* increases from 5 to 8 with increase in hPS from 0 to 8 vol%. For thicknesses just below n* the HCP and FCO structures coexist, but on long annealing HCP prevails. Self consistent field theory simulations designed to mimic the experimental system show that the PS homopolymer segregates to the interstices of the HCP unit cell, which suggests that the homopolymer reduces the stretching of the PS block and the free energy penalty of HCP relative to BCC inner layers. This result is consistent with the hypothesis that the excessive stretching requirement in an HCP arrangement is the cause of its higher free energy as compared to the BCC lattice.

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Figure 2: Distribution of the homopolymer for films containing 8% hPS, as computed by SCFT

Guided Self Assembly of Block Copolymer Thin Films

Adetunji Onikoyi, Edward Kramer

Chemical Engineering department, University of California, Santa Barbara

The use of block copolymer (BCP) thin films to create periodic structures on a nanolength scale has proved to be very effective [1-3]. However, removing defects and improving translational order in the periodic structures remain important goals. This study exploits a form of graphoepitaxy as a means to influence translational and orientational order in a polystyrene-b-poly-2-vinylpyridine (PS-b-PVP) diblock copolymer. Here, the assembly of the sphere domains of a BCP thin film is guided by sub-micron sized wells of various shapes. Effects on order and 2D melting behavior are examined. The wells are patterned into silicon substrates using both optical and electron-beam lithography. Secondary ion mass spectroscopy, scanning force microscopy and Transmission electron microscopy are then used to characterize the self-assembly process. Results show that a near perfect hexagonal 2D lattice can be obtained in diamond shaped wells of appropriate dimensions. Perfect 6 fold symmetry is disfavored in square wells; rather, regions of meta-stable square packing or defect dense regions of hexagonal packing are observed. Further studies are being performed to understand these effects on melting behavior. References: [1] Segalman et al. Phys. Rev. Lett 2003, 91, 196101 [2] Kim et al. Nature 2003, 424, 411 [3] Guarini et al. International Electron Devices Meeting

An Induced Charge Electro-Osmosis Micropump for Microfluidic Devices

Joel S. Paustian, Andrew J. Pascall, and Todd M. Squires

Department of Chemical Engineering, University of California-Santa Barbara

Recent years have brought great advances in microfludic devices. These devices can be used to create chemical laboratories which fit in the palm of your hand. These “Labs-on-a-chip” are finding application in many areas of science and technology, especially medicine and biotechnology. If these devices could be made portable, it would allow them to be used for many new applications, such as point-of-care medical testing or implantable devices. One of the technological barriers to making microfluidic devices portable is the current lack of a miniaturizable fluid pumping technology which operates at low enough voltage for portable batteries.

One possible way to make such a “micropump” would be to use the physical phenomenon of Induced Charge Electro-Osmosis (ICEO) [1] [2]. ICEO flows are produced under certain conditions when an electric field is applied at a conductor-electrolyte interface. In microfluidic devices, ICEO can be used to move fluid at low voltages, meaning that a micropump based on ICEO could be used to help make portable microfluidic devices a reality.

One approach to making an ICEO micropump is to use doped silicon to create ICEO flows. The advantage of this design is that silicon processing technology can be used to create nanoscale features in the micropump, which can result in large pressures being generated. We will discuss various approaches to the ICEO micropump, including our investigations into silicon-based micropumps.

[1] Squires, T.; Bazant, M. J. Fluid Mech. 2004, 509, 217–252. [2] Squires, T.; Bazant, M. J. Fluid Mech. 2006, 560, 65-101.

Using confocal microscopy to better understand the interfacial behavior of lung surfactant

Ian C. Shieh and Joseph A. Zasadzinski

Department of Chemical Engineering, University of California, Santa Barbara

Lung surfactant (LS) is a mixture of lipids and proteins that lines the air-liquid interface of the alveolar walls. It modulates the surface tension in the lungs which greatly reduces the mechanical work of breathing and also prevents the collapse of the alveoli upon expiration. Blood serum leaking into the alveoli during lung trauma can lead to LS inhibition, which is one characteristic of acute respiratory distress syndrome (ARDS). One mode of LS inhibition as observed during ARDS is the competitive adsorption of albumin to the air-liquid interface of the alveoli. Albumin blocks LS from forming a functional monolayer and significantly reduces the surface tension modulation normally seen in the lungs. The addition of hydrophilic polymers to the liquid subphase has been shown to reverse albumin’s deleterious effects on LS in vitro [1, 2]. We image our system via confocal microscopy in order to simultaneously track multiple components and determine their relative lateral and axial concentrations. The air-liquid interface can be oriented either parallel to the imaging plane using a Langmuir trough or perpendicular to the imaging plane using a constrained sessile drop device. As a result of these imaging capabilities, we can better understand the mechanisms behind albumin’s inhibition of LS as well as the reversal of this inhibition by the addition of hydrophilic polymers. References: [1] Stenger, P. C.; Zasadzinski, J. A. Biophysical Journal 2007, 92, 3-9. [2] Stenger, P. C.; Palazoglu, O. A.; Zasadzinski, J. A. Biochimica Et Biophysica Acta-Biomembranes 2009, 1788,

1033-1043.

Local Electronic Environments in Shape- and Size- Controlled ZnSe Nanoparticles

Benjamin Smith(a), Sylvian Cadars(a), Nataly Belman(b), Yuval Golan(b) Bradley Chmelka(a)

(a) Department of Chemical Engineering, University of California, Santa Barbara, CA 93106 USA. (b) Department of Materials Engineering, Ben-Gurion University, Beer-Sheva 84105, Israel

Shape- and size-controlled ZnSe nanoparticles with high extents of atomic positional order are

shown to exhibit large size-dependent variations in their local electronic environments. Solid-state 77Se and 67Zn NMR spectra reveal increasingly broad distributions of 77Se and 67Zn environments with decreasing nanoparticle sizes, in contrast to high degrees of atomic positional order established by TEM and XRD. First-principles calculations of NMR parameters distinguish between atomic positional and electronic disorder that propagate from the nanoparticle surfaces into the interior. Examining both cubic zincblende and hexagonal wurtzite ZnSe structures, the organic surfactant ligands are shown to influence local electron density distributions to depths of greater than 1 nm below the nanoparticle surface. Combined solid-state 77Se NMR and first-principles calculations establish that the surface coverage and binding sites of surfactant head groups affect the electronic structure near the nanoparticle surfaces. Increasing extents of electronic disorder correlate with and are expected to influence size-dependent electronic, optical, and catalytic properties of nanoparticles.

Microfabricated deflection tensiometers for measuring surface pressure of insoluble surfactants

Zachary Zell, SiYoung Choi, L. Gary Leal, Todd M. Squires

Department of Chemical Engineering, University of California, Santa Barbara Monolayers of phospholipids and fatty acids provide simple model systems for fluid-fluid interfaces in biological systems and microemulsions. Although the Wilhelmy plate technique is the most conventional method for measuring surface pressure, limitations exist when dealing with small samples or enclosed systems. Inspired by the idea of Hu et al [1], who related the elastic deformation (deflection) of a teflon wire loop to the surface pressure, we have developed a new technique for microtensiometry. Using a simple design equation derived from elastic beam theory, we microfabricate micro-tensiometers and validate their use by comparing measured surface pressure isotherms for fatty acids and phospholipid monolayers at air-water and fluid-fluid interfaces against simultaneous Wilhelmy plate measurements, with excellent quantitative agreement. Our technique offers a high degree of design flexibility due to control of geometry, materials and surface chemistry, is relatively inexpensive and enables measurements in small or enclosed systems. Finally, minor modifications enable our tensiometers to function as Langmuir micro-troughs for insoluble surfactants. References: [1] Hu, Y.; Lee, K.Y.C.; Israelachvili, J. Langmuir, 2003, 19, 100-104.