Contributed Talks

Novel Materials from Renewable Chemical Feedstocks

Dr. Pete Iovine, University of San Diego

Biopolymers represent structurally diverse raw materials for the construction of functional polymers. Starch, in particular, is a low cost hydrophilic biopolymer that exhibits excellent biodegradability and biocompatibility. Beyond these favorable biomaterial properties, starch is an attractive raw material because its structure can easily be manipulated. Starch, therefore, is one of the most versatile polysaccharides for synthesizing new biopolymer or hybrid materials and establishing structure−function relationships. Two projects will be described in this talk. First, I will highlight the synthesis and function of a new class of amphiphilic hybrid polymer derived from starch (hydrophilic) and a sesquiterpene (hydrophobic). Second, I will describe a novel starch-derived biomaterials platform for the sustained delivery of iodine for antimicrobial applications.

Simulation of colloidal systems with active polymer crosslinkers

Elisabeth Rennert, M. Das

Rochester Institute of Technology

The Brownian Dynamics of a diffuse system of colloids crosslinked with polymers was investigated. The model was first developed with colloids only interacting via a Lennard-Jones potential and undergoing Brownian motion to test and refine the simulation. Characteristic material properties of the system were quantified. Then polymer crosslinkers that connect the colloids via an attractive spring force were added, and the resulting material properties were investigated. Order parameter and elastic moduli were calculated for various colloid densities, interaction strengths, and crosslinker rest lengths. Future outlook consists of implementing crosslinkers that are active and dynamically attach and detach thereby altering the behavior of the colloidal system.

Tailoring FGF2 interactions in heparinoid-protein conjugates to influence human mesenchymal stem cell proliferation

Greg Rieger, Verespy III, P. Gordts, K. Godula

University of California San Diego

Human mesenchymal stem cells (hMSC) offer great potential in the field of regenerative medicine for their ability to differentiate into both mesenchymal and nonmesenchymal lineages. However, this potential has not been fully met because several hurdles must still be overcome, namely, low differentiation rates and a tendency of hMSCs to differentiate into unwanted mesenchymal lineages upon transplantation. A major driver of differentiation and growth of stem cells is growth factor signaling, events which are typically regulated through sulfated extracellular matrix glycoasminoglycans (GAGs), such as heparan sulfate (HS). In order to gain information on the structural requirements associated with heparan sulfate-mediated growth factor signaling, we grew hMSCs in environments with immobilized heparin (a highly sulfated form of HS) or selectively desulfated heparinoids and measured proliferation as well as MAPK signaling, observing correlative outcomes relative to the FGF2 binding characteristics of the biomaterials.

Hierarchical Protein Assemblies as Precursors in the Native Formation of Spider Dragline Silk

David Onofrei, G. Holland

San Diego State University

Biological polymers have historically served as a template for materials science research. Spider silk is one such biopolymer with a host of potential biomimetic applications such as high-performance fibers for medical, industrial and defense applications. Our research is focused on the formation of spider dragline silk from its soluble protein precursor contained within the silk producing gland. Using 4M urea to maintain the silk proteins’ native unfolded state, we used NMR to measure the self-diffusion of silk oligomers in solution and directly imaged these precursors with cryo-TEM. Both techniques indicate the presence of a disordered silk protein micellar assembly on the 200-400 nm length scale. We found this structure to be sensitive to mechanical shear resulting in the formation of uniaxial fiber-like structures within the larger assemblies. Combining results from both methods, we propose a model for the pre-assembly of spider silk in the gland environment.

Electrostatic Control of protein partitioning into a DNA liquid droplet

Gabrielle Abraham, O. Saleh

University of California Santa Barbara

DNA Nanostars (NSs) are limited-valence macromolecules created by hybridizing single stranded DNA oligos into a set number of double stranded arms extending from a flexible center. DNA NSs form coacervates through the binding of self-complementary single-stranded sequences at the end of each arm. These liquid droplets act as a simple model for membraneless organelles; therefore, it is of interest to look into protein partitioning into the droplet phase. Since the DNA liquid is highly negatively charged, we focus on the role of electrostatics in controlling partitioning. As a model system, we use the protein neutravidin, whose pkA of 6.3 permits tuning of the protein’s net charge with near-physiological pH. As expected, we observe exclusion of the protein from the droplet at high pH, and partitioning at low pH. We further observe an unexpected aggregation regime, and distinctly slow dynamics of the partitioning process; we discuss the origin of these effects. Overall, this simple model system presents an unexpectedly rich behavior which gives insight into the behavior of macromolecular liquids.

High-molecular-weight polymers from dietary fiber drive aggregation of particulates in the murine small intestine

Asher Preska Steinberg, S. Datta, T. Naragon, J. Rolando, S. Bogatyrev, R. Ismagilov

California Institute of Technology

The lumen of the small intestine (SI) is filled with particulates: microbes, therapeutic particles, and food granules. The structure of this particulate suspension could impact uptake of drugs and nutrients and the function of microorganisms; however, little is understood about how this suspension is re-structured as it transits the gut. Here, we demonstrate that particles spontaneously aggregate in SI luminal fluid ex vivo. We find that mucins and immunoglobulins are not required for aggregation. Instead, aggregation can be controlled using polymers from dietary fiber in a manner that is qualitatively consistent with polymer-induced depletion interactions, which do not require specific chemical interactions. Furthermore, we find that aggregation is tunable; by feeding mice dietary fibers of different molecular weights, we can control aggregation in SI luminal fluid. This work suggests that the molecular weight and concentration of dietary polymers play an underappreciated role in shaping the physicochemical environment of the gut.

Single molecule and ensemble dynamics of DNA molecules crowded by cytoskeletal proteins

Kathryn Regan, D. Wulstein, H. Rassmussen, S. Ricketts, R. McGorty, R. Anderson

University of San Diego

In order to carry out key processes such as gene transcription and cell replication, DNA must diffuse through a highly crowded cellular environment. Previous studies aimed at understanding intracellular DNA transport have mainly focused on the effect of small mobile crowders. However, the cytoskeleton, composed of filamentous proteins such as semiflexible actin and rigid microtubules, has been identified as a key factor suppressing viral transfection and gene delivery. Here, we investigate the effect that cytoskeletal proteins have on the transport properties of linear and circular DNA. Specifically, we use fluorescence microscopy and custom single-molecule tracking algorithms to measure center-of-mass transport and time-varying conformational changes of single DNA molecules diffusing in in vitro composite networks of actin and microtubules. We determine the role that DNA topology (linear vs circular), as well as cytoskeletal filament rigidity (actin vs microtubules), has on DNA transport and conformational states. We specifically quantify DNA diffusion coefficients, degrees of anomalous diffusion, and conformational sizes and shapes for protein networks with varying concentrations and polymerizations states of actin and microtubules.

Stretchable Conductive Polymers for Wearable Electronics

Dr. Laure Kayser, D. Lipomi

University of California San Diego

The recent development of highly flexible and stretchable organic electronics has prompted novel applications in wearable and bio-integrated electronics where skin-like properties (stretchable up to 40%, soft) are desirable for an intimate contact with the human body. But, polymers which are conductive, mechanically compliant, biosafe and solution-processable remain difficult to obtain. To address these limitations, we have synthesized a conductive material based on poly(3,4-ethylenedioxythiophene) (PEDOT) and a poly(styrene sulfonate)-based block copolymer. The conductive elastomers can be stretched up to 40% with minimal loss in conductivity, are tougher than previously reported materials and can be healed with water after damage.

Thermodynamics of Complexes of Oppositely Charged Conjugated Polyelectrolytes

Will Hollingsworth, T. Magnanelli, C. Segura, A. Bragg, A. Ayzner

University of California Santa Cruz

Conjugated polyelectrolytes (CPEs) are an attractive class of materials for light harvesting owing to their large absorption cross sections, delocalized electronic states, and tendency toward self-assembly in water. This makes them potentially well suited to forming electronic energy transfer relays – like those found in biological systems, with CPEs acting in place of natural pigments. Our previous work has shown that oppositely charged CPEs (cationic polyfluorene and anionic polythiophene) will form complexes that undergo donor/acceptor electronic energy transfer, but only if the complexes are formed at elevated temperatures. This stands in contrast to non-conjugated polyelectrolyte complexes which readily form at room temperature. The thermodynamics appear to be controlled, in part, by the “unravelling” of the anionic polythiophene, which is natively coiled due to strong π-π interactions. This process has a convex Arrhenius behavior more commonly observed in proteins around their low temperature dynamical glass transition.

Measurement of hard-sphere like dynamics in concentrated alpha-crystallin suspensions using coherent X-rays

Nuwan Karunaratne*, Preeti Vodnala, Laurence Lurio, George Thurston, Elizabeth Gaillard, Suresh Narayanan and Alec Sandy

Orange Coast College

The dynamics of concentrated suspensions of the ocular protein, alpha crystallin have been measured using X-ray Photon Correlation Spectroscopy (XPCS). Measurements were made at wavevectors corresponding to the first peak in the hard-sphere structure factor. The dynamics were measured at volume fractions close to the critical volume fraction for the glass transition, where the intermediate scattering function, f (q, τ) could be well fit using a double exponential decay. The measured relaxation times were in reasonable agreement with published molecular dynamics simulations for the relaxation times of hard-sphere colloids. Overall our results lend support to the hard sphere colloid model as a good description of concentrated suspensions of alpha crystallin.

POSTERS

Varying binding interactions tune mechanics of co-entangled actin and microtubules

S. Ricketts, R. Anderson, M. Francis, L. Farhadi, J. Ross

University of San Diego

The cytoskeleton is a complex network of proteins, including semiflexible actin filaments, rigid microtubules, and numerous binding proteins that crosslink these filaments. The physical interactions along with various crosslinking motifs of actin and microtubules allows cells to precisely tune their strength and structure in order to support structural changes during apoptosis and meiosis. To determine the role crosslinking versus steric interactions has on cytoskeleton composites we create composites of co-entangled actin and microtubules with varying crosslinking motifs and use optical tweezers microrheology and dual-color confocal microscopy to characterize the composites. Specifically, we look at equimolar actin-microtubule composites in which no filaments are crosslinked, only actin is crosslinked, only microtubules are crosslinked, and both filaments are co-crosslinked. We optically drive a microsphere through composites and measure the resulting microscale force response. We image spectrally distinct filaments to characterize actin and microtubule integration and mobility within the composite.

Mathematically modeling the mechanobiology of the vitreous gel: Linear and nonlinear mechanical response of collagen and HA networks

P. Lwin, M. Das, S. Franklin, G. Thurston, D. Ross, and M. Das

Rochester Institute of Technology

The vitreous gel in the human eye is a viscoelastic composite network of stiff collagen fibers and softer hyaluronic acid (HA) polymers. Its material properties are critical to vitreous function, and ultimately to that of the eye, and depend on applied stresses, concentrations, and constituent filament stiffness. Although it has long been known to undergo dramatic changes with aging and disease, the key vitreous gel phase transitions and their mechanical consequences are not well understood. We mathematically model and investigate the mechanical response of the primary components of the vitreous gel: (i) a stiff network of collagen fibers, and (ii) a flexible polyelectrolyte network of HA. Our preliminary results relate the linear and nonlinear mechanical response of these networks to the structure, micromechanics, and concentrations of the constituents. Ongoing work consists of studying composite networks of collagen and HA, and may provide insights into mechanical changes associated with vitreous disorders

SPIDDM to characterize DNA dynamics in crowded cytoskeleton networks

D. Wulstein, C. Matsuda, K. Regan,R. McGorty, R. Robertson-Anderson

University of San Diego

New techniques to quantitatively characterize how the dynamics of DNA in crowded cytoskeletal environments may differ from simple diffusion and to link those anomalous dynamics to properties of the crowders are required to fully understand the complex transport. Here we demonstrate a technique that measures the ensemble and single molecule dynamics over a large range of time and length scales. We use light-sheet microscopy (LS) to observe the dynamics of fluorescently labeled DNA molecules in varying networks of actin and microtubules. We use differential dynamic microscopy (DDM) to analyze ensemble dynamics. We observe anomalous diffusion in the network environments and varying degrees of heterogeneity in the dynamics. Though we measure identical diffusive dynamics of DNA in a buffer solution using both single-particle tracking and DDM, we find significantly different dynamics using these two techniques in the crowded network environments. We are currently exploring the cause of this difference.

Dynamic Light Scattering of Native Spider Silk Spinning Dope

D. Stengel, G. Holland

San Diego State University

Spider silk is an impressive biological polymer whose material properties are being investigated for medical, industrial and defense applications. Our research involves studying the molecular characteristics of glandular silk before it is formed into fiber. Recently, we have used dynamic light scattering (DLS) to measure the size of these proteins before they are spun into silk. DLS indicates the presence of two species, 45nm and 400nm in diameter, which correspond to a monomer and supramolecular structure, respectively. In follow-up experiments, we investigated the effect of protein concentration and pH on the two species. Higher protein concentrations resulted in a reduction of monomer size. Conversely, lowering the pH increases monomer size. These results have given us considerable insight as to how glandular spider silk proteins are stored as well as how they behave during the nascent stages of fiber formation.

Main-Chain Triazoline Polymers and Their Conversion to (Poly)Aziridines

A. Saiz, P. Iovine

University of San Diego

Interfaces between chemistry and other disciplines, such as materials, require the creation of structure-function relationships where cycles of make-and-measure uncover new properties and allow researchers to optimize target physical properties. Our research has a particular focus on making polymers that respond to mechanical force to undergo chemical transformations. Triazolines are formed by the cycloaddition of an azide and a suitable dipolarophile such as maleimide or norbornene without a catalyst. Herein we present the synthesis of main-chain poly(triazoline) linear polymers using functionalized maleimide and azido building blocks. We investigate the poly(triazoline) stimuli-responsive behavior given the propensity of triazolines to ring contract into an aziridine under photochemical and thermal treatment. Utilization of the 1,3-dipolar cycloaddition, an example of “click” chemistry, has been a reliable synthetic technique. Spectroscopic and quantitative data supporting the formation of triazoline units and aziridine units in the backbone of the polymer after photochemical treatment will be presented.

Mathematically modeling the mechanobiology of the vitreous gel: Linear and nonlinear mechanical response of collagen and HA networks

Pancy Lwin, S. Franklin, G. Thurston, D. Ross, and M. Das

Rochester Institute of Technology

Optical Tweezer Measurements in Biological Systems

M.Gomez, C. Jones, W. Ahmed

California State University, Fullerton

Recently, optical tweezers have been used to study force fluctuations in equilibrium systems and to determine the physical properties of complex materials. We are currently implementing two calibration methods, the photon-momentum method and the active-passive method, to measure displacements and forces at the nanometer and piconewton scales. Here, we study the force fluctuations of chlamydomonas microswimmers as well as the rheological properties of xylem sap. By locally trapping a chalmydomonas, we are able to measure its beating frequency as well as the force generated to beat at that frequency. We calculated the stochastic force spectrum by estimating the power spectral density of the fluctuating force signal. We are applying a theoretical framework to extract the non-equilibrium microswimmer forces from the total force spectrum. Xylem sap is a fluid found in plants that is vital to the plant's ability to transport nutrients throughout the plant's system. The xylem sap was analyzed through an active microrheological experiment (AMR). We are quantifying xylem sap rheology to investigate the physics of negative pressure and cavitation phenomena in plants.

Influence of Ionic Surfactants on Conjugated Polyelectrolyte Complexes: Chain Uncoupling and Formation of Super-Complexes

C. Segura, A. Ayzner

University of California Santa Cruz

This work focuses on the role that ternary ionic surfactants have in controlling complex formation of conjugated polyelectrolyte (CPE) complexes in a donor-acceptor system composed of oppositely charged CPEs. The interaction between the CPEs and the ionic surfactants at concentrations above and below their respective critical micelle concentrations were studied in aqueous solution by UV-visible absorption, steady state fluorescence spectroscopy, DLS and SAXS. Addition of an anionic dodecyl sulfate surfactant leads to the straightening of the cationic CPE backbone and a decoupling the anionic CPE, leading to a shutdown of electronic energy transfer (EET). In contrast, the addition of a cationic dodecyl trimethylammonium surfactant leads to a distortion of the PTAK backbone but no significant changes in the EET efficiencies. Our results indicate that the ionic self-assembly and excited state dynamics of the CPEs is highly dependent on the ionic character of the surfactant head group as well as the surfactant concentration.

The Glass Transition Temperature of Linear and Cyclic Polystyrene Dependence on Film Thickness and Molecular Weight

G. Mendoza, A. Baljon

San Diego State University

The glass transition of linear and cyclic polystyrene (PS) was studied to better understand the experimentally found relationship between the glass transition temperature (Tg) and film thickness. United-atom molecular-dynamic simulations were performed on free standing films of varying thicknesses of polystyrene. It was found that the large number of end groups near the interfacial layer contribute to the Tg dependence on film thickness. Current studies are focused on the experimentally found relationship between the Tg and molecular weight in bulk. Utilizing various methods such as the density, diffusion and p2 relaxation the Tg was found for cyclic polystyrene is determined.

Active self organization of actin-microtubule composite system

L. Farhadi, J. Ross

UMass Amherst

Active matter is the field that studies non- equilibrium systems in different scales, from schools of fish to cytoskeleton of living cells. Playing an important role in cell functions, microtubules and actin are two types of filaments in the cytoskeleton that interact with their associated motor proteins, myosin and kinesin respectively. We study both filaments and their motors in an in vitro motility assay while they hydrolyze ATP for gliding. I looked at phase transition of actin filaments going from isotropic to nematic state, and isotropic to nematic and then polar state for microtubules, while the concentrations of filaments have been increased. All the other possible variables such as motors concentrations, temperature and length of the filaments are constant in this study.

Characterizing Liquid-Liquid Phase Separation

C. Riedstra, R. McGorty

University of San Diego

Recent work has shown that the intracellular environment is organized not only through membrane-bound organelles but also through fluid droplets that have phase separated from the cytosol. Intracellular liquid-liquid phase separation (LLPS) has attracted more attention recently because fluid droplets within the cell may play roles in cells’ responses to stress, gene regulation and in neurodegenerative diseases. Our understanding of intracellular liquid-liquid phase separation has advanced through multiple quantitative biophysical techniques. Here, we describe an undergraduate lab module that highlights some of these biophysical techniques. Using various optical microscopy techniques and quantitative image analysis, we characterize liquid-liquid phase separated samples in terms of their viscosity and surface tension. We use different phase imaging techniques, differential interference contrast and phase contrast, and fluorescence microscopy to observe droplets coalescing, beads diffusing in the different liquid phases and photobleaching. We compliment experimental work by computationally investigating the Flory-Huggins model to understand phase separation.

Dynamics of Microbeads Diffusing Through Cytoskeletal Protein Networks

S. Anderson, C. Matsuda, R. Robertson-Anderson

University of San Diego

The cytoskeleton of cells, which is comprised of varying concentrations of semi-flexible protein filaments known as actin and stiff rodlike proteins known as microtubules, is key to the structure and motility of cells. These proteins also act to hinder the diffusion of biological molecules through the cell. Here we study the diffusion of microbeads through networks of actin and microtubules to characterize the impact of these networks on intracellular transport. We do this by using in fluorescence microscopy to track single one micron polymer beads diffusing through actin networks, microtubule networks, and equimolar composite networks of both proteins. Using custom-written software, we track the center-of-mass of each microbead and determine the corresponding mean-squared-displacements and diffusion coefficients. We show that microbead diffusion is most restricted in actin, while microtubules have the least impact on suppressing diffusion.

Diffusion in cytoskeletal networks using light sheet microsopy

C. Matsuda, S. Anderson, R. McGorty

University of San Diego

The purpose of this project is to study diffusion in crowded cell-like environments of cytoskeletal protein networks. We create networks of actin, microtubules and composites of actin and microtubules. Measuring movements and conformations of macromolecules in such environments will further our understanding of transport phenomena within cells. We add 1 micron fluorescent beads to the various networks, recording videos of the samples using light sheet microscopy. Dynamics of the beads in the networks are analyzed using two techniques: particle tracking and differential dynamic microscopy. These techniques produce complementary data and allow for comparing transport of particles in the different networks. We find that diffusion in these networks is anomalous to varying degrees, and that there is a significant difference in the heterogeneity of bead dynamics between actin and microtubule environments. We are currently using this data of bead dynamics to interpret similar data of DNA molecules diffusing in these environments.

Building a Custom Microscope –An advanced lab to study Brownian motion

H. Seyforth, W. Ahmed

California State University, Fullerton

The process of building a microscope from scratch provides the students with a basic understanding of each individual component of the optical set-up. Subsequent digital image recording and data analysis provide an introduction to image processing and statistical analysis. Our goal is to create an advanced laboratory module for students to build an optical microscope, calibrate it, and make precise measurements of Brownian motion and diffusion using multiple approaches such as mean squared displacement analysis and differential dynamic microscopy. We constructed an optical microscope based on the design by Kemp et al. (arXiv:1606.03052). Then, using a 40x objective, we study the Brownian motion of 1 micron colloidal particles. A digital camera is used to record videos of colloidal motion, ImageJ is used to post-process the images, and matlab is used to calculate the diffusion coefficient of the particles using two independent approaches. We use both single particle tracking and image correlation techniques to analyze colloidal diffusion. To do this, we use publicly available matlab codes for particle tracking, msd analysis, and differential dynamic microscopy analysis to calculate the diffusion coefficient. Our advanced lab module is intended to be an introduction to physics research, fortify concepts from optics and statistical physics, and give students hands-on experience in building optical systems and analyzing noisy data.

Spider prey-wrapping silk is an alpha-helical coiled-coil / beta-Sheet hybrid nanofiber

B. Addison, G. Holland

San Diego State University

Solid-State NMR results on 13C-Ala/Ser and 13C-Val enriched Argiope argentata prey-wrapping silk show that native, freshly spun aciniform silk fibers are dominated by alpha-helical (~50% total) and random-coil (~35% total) secondary structures, with minor beta-sheet nanocrystalline domains (~15% total). This is the most in-depth study to date characterizing the protein structural conformation of the toughest natural biopolymer: aciniform prey-wrapping silks.

Determining how crosslinker proteins influence the mechanics of the cytoskeleton

M. Francis, S. Ricketts, R. M. Robertson-Anderson

University of San Diego

The strength, architecture and motility of cells is dependent upon the interactions between two protein filaments that comprise the cell cytoskeleton: actin and microtubules. Studies on wound healing suggest microtubule and actin filaments are interconnected with one another as actin flowing towards the wound borders transports microtubules with them. This research focuses on how varying the concentrations of crosslinkers in networks of actin and microtubules influences their viscoelastic properties, response to stress and strain, and their relaxation after release from stress. We created co-polymerized, fluorescent-labeled networks of actin and microtubules with varying concentrations of crosslinkers that crosslink only actin, only microtubules, or both filaments. We use optical tweezers to apply microscale strains to these networks by trapping embedded microspheres and oscillating them at various frequencies or dragging them various distances at different speeds. We measure the force the networks exert to resist these strains. Results indicate that increasing the concentration of crosslinkers surprisingly yields a decreased resistive force as well as lower viscoelasticity of the system.

Building the Spectator Glycocalyx with Mucin-Like Structures to Investigate the Effects of Steric Bulk on Cell Surface Interactions

D. Honigfort, M. O Altman, M. Zhang, K. Godula

University of California San Diego

The glycocalyx has complex three dimensional architecture, extending from glycolipids proximal to the cell surface to massive mucin glycoproteins, which extend hundreds of nm in length. The glycocalyx provides a physical and chemical barrier on the outer membrane of the cell, and acts as a gate-keeper that dictates interactions with many extracellular signals, including with growth factors, lectins, and pathogens. Here we seek to better understand the role of the glycocalyx as a physical barrier. We synthesize linear glycopolymers of varying sizes, and utilize a cholesterol anchor for incorporation into cellular membranes as well as fluorophore to visualize in biological contexts. Turkey Red Blood Cells (tRBCs) are utilized here as a model system for cell surface interactions due to their relatively limited native glycocalyx (~10nm), as well as their limited capacity for endocytosis. In this poster we will present new findings on the ability of bulky mucin like polymers to influence the biophysical properties of these RBCs, namely in the ability of a bulky glycocalyx to alter cell morphology and interact with soluble factors such as lectins and virus particles.

Elucidation of the Molecular Structure and Dynamics of Egg Sac Spider Silks using Solid-State NMR

S. Davidowski, J. Bennett Addison, G. Holland, J. Yarger

Arizona State University

Spider silk has been the focus of many ongoing investigations due to it being a biopolymer with remarkable mechanical properties and interesting structure-function relationships. Spiders surround their eggs with an enclosure of silk to protect them during development; this silk is known as egg sac (case) silk. In an effort to further the understanding of the structure-function relationship of the silks used to produce egg sacs, a combination of 1-dimensional(1D) and 2-dimensional (2D) solid-state nuclear magnetic resonance (ssNMR) spectroscopy techniques have been implemented to interrogate the structure of the egg case silk from several species of spider. Furthermore, mechanical testing and scanning electron microscopy (SEM) have been utilized to gain an understanding of the mechanical properties of the egg sac silks.

Targeted Cell Surface Engineering with Nucleic Acid Based Glycomaterials

S. Purcell, N. Marroquin, M. Huang, K. Godula

University of California San Diego

We report a nucleic-acid mediated cell surface engineering strategy to target the activity of synthetic nanoscale glycomaterials to specific cells. The ability to manipulate the glycocalyx and tailor glycan mediated growth factor interactions at the extracellular matrix cell specifically is poised to allow for control over cellular functions in artificial tissues and cell-based therapies. A synthetic glycopolymer scaffold serves as a functional mimetic of native proteoglycans while a nucleic acid domain targets and non-covalently anchors the materials to the surface of live cells. This strategy offers a powerful tool to elucidate the roles of HSPGs in regulating cellular differentiation and has applications in cell therapy and regenerative medicine.

Viscoelastic Properties of Aqueous DNA Solutions - Optical Microrheology Approach

K. Peddireddy, M. Lee, R. Robertson-Anderson

University of San diego

I present viscoelastic properties of a biologically inspired DNA composite – ring and linear DNA- that were obtained through optical microrheology approach. Our final aim is to combine optical tweezers microrheology, conformational tracking of single molecules, and mesoscale fluorescence image analysis to directly connect stresses induced in biopolymer blends to corresponding molecular deformations and network rearrangement with unprecedented temporal (~millisecond), spatial (~nanometer) and molecular (~basepair, monomer) resolution and control.

Synthesis of Biorenewable Starch-Farnesene Amphiphilic Conjugates via Transesterification of Terpene-Derived Diels-Alder Adducts

B. Orzolek, P. Iovine, A. Rahman

University of San Diego
Herein we describe a new class of terpene-starch esters synthesized from biorenewable building blocks. Although our work is specific to starch, we believe the synthetic methodology can be extended to a wide range of polysaccharide substrates. In our approach, an ester functionality is first introduced to the farnesene backbone via high yielding, solvent-free Diels-Alder chemistry. The farnesene esters are subsequently transesterified with starch to produce a range of starch-farnesene amphiphilic biopolymers. The key transesterification reaction between farnesene and starch employs 1,5,6-triazabicyclo[4.4.0]dec-5-ene (TBD) as a guanidine base organocatalyst and is capable of producing materials with a high degree of substitution (DS). The DS can be modulated by altering the starch:farnesene feed ratio. Low DS starch-farnesene esters show surfactant-like properties while the higher DS materials were successfully solvent-cast into standalone films. Thermal and mechanical tests reveal starch-terpene esters to be robust under both solution and thermal processing conditions. Given the versatility of the synthetic method, the bio-renewability of the components, and the biodegradability of the ester linkage joining the subunits, the newly produced polymer amphiphiles appear to be a promising class of new green materials.

Amphiphilic Starch Graft Polymers for Iodine Delivery and Tissue Engineering

J. Young, P. Iovine

University of San Diego

Using Triazabicyclodecene (TBD) to catalyze the novel, single step, transesterification of starch with polycaprolactone, we are seeking to synthesize a starch graft polymer film capable of delivering iodine in a dose-dependent manner with a sustained release for biomedical applications. Furthermore, using the novel starch-TBD reaction conditions, we explore other applications for this transesterification chemistry with starch and poly(methyl acrylate) for tissue engineering purposes.

Towards continuous, optics-free measurements of cell stiffness using elastohydrodynamics

C. Dhong, D. Lipomi

University of California San Diego

Recent work in biomechanics has identified several diseases that may be identified by abnormal cell stiffness. There are, however, few high-throughput methods to measure the stiffness of cells. Here we demonstrate a method of measuring particles that transit in an elastic channel by measuring the minute deformation on the elastic sidewalls caused by the particle in a fluid. Using ultra-sensitive metal-on-graphene strain sensors, we transduced the wall deformation into a voltage profile. This non-contact technique circumvents the need for expensive optical equipment or fluorescent probes, which improves throughput. It is some of the first demonstrations of harnessing elastohydrodynamic phenomenon as a sensing modality with widespread application.