Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F32: Responsive Polymers, Soft Materials, and Hybrids IIFocus
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Sponsoring Units: DPOLY DSOFT DBIO Chair: Jinhye Bae, University of California, San Diego Room: 504 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F32.00001: BREAK
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Tuesday, March 3, 2020 8:36AM - 8:48AM |
F32.00002: Detection of Polypeptide Conformational Transitions in Solution via Sound Velocity and Optical Rotation Alyssa Blake, Graham Parkinson, Paul Russo Of the many different core-shell particles being designed for drug delivery, protein sequestration, and other applications, polypeptide-coated silica is among the most promising. The combination of a configurable, chiral surface and a wide spectrum of surface moieties is difficult to match using conventional polymers. A model system for such polypeptide-silica composite particles (PCPs) has been constructed by covalent attachment of poly (ε-carbobenzyloxy-L-lysine) (PCBL) to silica microbeads. PCBL exhibits a reversible coil-helix transition when dissolved as a pure polymer in m-cresol, but the use of conventional optical methods (e.g., circular dichroism) to confirm such a transition for particles tethered to silica beads is confounded by solvent opacity and strong scattering. Sound velocity measurements provided comparable results to the conventional methods, such as optical rotation, but allows for optically active solvents and strongly scattering samples to be more easily measured. The combination of these two methods provides a new way to understand polypeptide transitions in complex environments and real-world formulations. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F32.00003: Giant hyaluronan polymer brushes display polyelectrolyte brush polymer physics behavior Jessica Faubel, Rhiddi P Patel, Jennifer Curtis, Blair K Brettmann We report on the polyelectrolyte brush behavior of extra-large hyaluronan polymer brushes (~15 microns) recently developed using an enzyme-mediated growth process. The giant height of the brushes enables direct characterization of 3D structure and time-dependent behavior. In this study, we explored the stimulus response of the brush to ionic strength and solvent changes. The brush displays classic osmotic brush and salted brush regime behaviors. In poor solvent (ethanol), the brush collapse by 96%. The collapse is rapid when changing from a good to a poor solvent, but re-expansion is extremely slow when changing back to a good solvent. The observed brush behavior is similar to that seen for smaller polyelectrolyte brushes, indicating that these ultra-thick brushes will serve well as model systems to study more complex phenomena, including dynamics, through confocal microscopy |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F32.00004: Detecting Bacteria with Plasmonic Microcapsules Remi Dreyfus, Céline Burel, Christopher B Murray, Bertrand Donnio Assembling nanoparticles into dispersible colloidal pH-sensitive sensors remains a challenge. Here, we show how to combine optically active plasmonic gold nanoparticles and pH-responsive thin shells into “plasmocapsules”. Upon pH change, plasmocapsules swell or shrink. Concomitantly, the distance between the gold nanoparticles embedded in the polymeric matrix varies, resulting in an unambiguous color change. Billions of micron-size sensors can thus be easily fabricated. They are non-intrusive, reusable, and sense local pH changes. Each plasmocapsule is an independent reversible microsensor over a large pH range. Finally, we demonstrate their potential use for the detection of bacterial growth, thus proving that plasmocapsules are a new class of sensing materials |
Tuesday, March 3, 2020 9:12AM - 9:48AM |
F32.00005: Enzyme-Responsive Materials for Regenerative Medicine Invited Speaker: Sarah Heilshorn In living materials, the tissue-level structure is constantly being remodeled through the molecular action of cell-secreted enzymes. Bioactive materials have been designed previously to respond to these enzymes through cleavage of individual molecular bonds. However, the resulting changes in the tissue-level material architecture has been underappreciated as a potential material design parameter that can impact cell function. Combining our experimental measurements of chemical reaction rates with a simple model of percolation network theory, we were able to accurately predict how tissue-level network structure evolves in an engineered biomaterial over time. We then demonstrated that encapsulated human endothelial cells respond to these tissue-level structural changes by forming vascular-like networks. In another example of molecular-level design enabling control of tissue-level structure and cell biology, we engineered a material for proliferating neural stem cells. Upon encapsulation, neural stem cells only maintained their stem-like behavior if they could sufficiently remodel the material through the action of a cell-produced enzyme. We further demonstrated that neural stem cell differentiation into more mature cell types is also dependent on tissue-level structure. Thus, this body of work has introduced material remodeling and tissue-level structural dynamics as key design criteria for the field of biomaterials. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F32.00006: Shape Control of Charge-patterned Nanocontainers Nicholas Brunk, Vikram Jadhao Stimuli-responsive control of the shape of nanoparticle (NP) containers enables their application as adaptive drug-delivery carriers. NP shape adaptation also provides dynamic building blocks in the design of reconfigurable, biomimetic materials. Molecular dynamics (MD) simulations are used to explore the role of surface charge patterning in controlling electrostatically-driven shape deformation of hollow, elastic NPs. Charge patterns investigated include those commonly synthesized in inverse patchy colloids: Janus particles with (N = 2) patches, striped charge patterns (N > 2), and polyhedral patterns. For Janus patterns, transitions to convex bowl, flattened hemisphere, and concave spinning-top-like conformations occur depending on the salt concentration screening the electrostatic drive to deform. As the number of stripes increases (N > 2), NPs with charged terminating ends adopt disc and rod conformations. However, (N > 2) striped particles with neutral terminating ends form concavities reminiscent of lock-and-key colloids. We also explore the shapes of polyhedrally-patterned nanocontainers and discuss the intersection between pattern-driven and buckling-driven shape control. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F32.00007: A simple mechanical model for synthetic catch bonds Kerim Dansuk, Sinan Keten Catch bonds are protein-ligand bonds which become more difficult to break as the applied force increases, a counterintuitive phenomenon that has not yet been reproduced in synthetic systems. Here, we have demonstrated that a simple mechanical design based on a tweezer-like mechanism can exhibit catch bond characteristics under thermal excitations. The tweezer has a force-sensitive switch which controls the transition of the system to a high-ligand-affinity state with additional ligand-tweezer interactions. Applying kinetic theory to a two-mass-two-spring idealized model of the tweezer, we show that by tuning the shape of the switch and the ligand-tweezer interaction energy landscapes, we can achieve greater lifetimes at larger force levels. We validate our theory with molecular dynamics simulations and produce a characteristic lifetime curve reminiscent of catch bonds. Our analysis reveals minimal design guidelines for reproducing the catch bond phenomenon in synthetic systems such as molecular switches/foldamers, DNA linkers, and nanoparticle networks. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F32.00008: Towards Tumor pH Detection Using Plain Radiography: An Injectable pH-Responsive Polyacrylic Acid Based Hydrogel Biosensor Sachindra Kiridena, Uthpala Wijayaratna, Md. Arifuzzaman, Jeffrey N. Anker A pH responsive polyacrylic acid hydrogel based injectable biosensor was developed to measure local tumor pH using plain radiography in order to study cancer pathophysiology, track tumor progression, and determine effectiveness of drugs in vivo. Although plain radiography is unable to detect local chemical concentrations directly, a chemically responsive hydrogel was synthesized to move a tantalum bead and thus report the local concentration. The hydrogel was synthesized by free radical co-polymerization of acrylic acid and n-octyl acrylate and a 13 mm disk of the gel with embedded radiopaque wire had a range of pH 4–8 with a precision of 0.065 pH units. A preliminary study was carried out to miniature this hydrogel sensor and fit it into an injectable porous metal sleeve, all fitting within a breast cancer biopsy marker needle. The 10 mm sensor showed repeatable response to pH cycling in the range of pH 4–8. We are optimizing the sensor for sensing in the pH 6.5 to 7.5 range most relevant to tumor acidosis in order to track tumor physiology and assess response to chemo/radiotherapy. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F32.00009: Modulation of hydrogel biophysical properties using photoadaptable chemistry improves formation of intestinal organoids Max Yavitt, Tobin Brown, Ella Hushka, Peter Dempsey, Kristi Anseth There is increasing interest to develop well-defined platforms for organoid growth and expansion. It is known that organoid formation from single intestinal stem cells (ISCs) in synthetic hydrogels is influenced by matrix stiffness and can be initiated by hydrogel degradation. Understanding these forces is key to improving efficiency of organoid growth. We use the adaptable allyl sulfide (AS) photochemistry to tune hydrogel biophysical properties through on demand network reorganization. We show that reorganization is dependent on the protonation state of a soluble, monofunctional thiol species. The rate of degradation can therefore be tailored by controlling the thiol pKa or the solution pH. This understanding then guides the selection of conditions that allow for more rapid degradation. Formed using a biorthogonal conjugation reaction, the AS hydrogels support organoid growth from ISCs, which show maintenance of stem cell markers. Intermittent light exposure will be applied in situ to tune the modulus of cell laden hydrogels and the resulting influence on growth, morphology, and presentation of mechanosensitive biochemical markers will be assessed. This understanding can be leveraged to optimize growth of colonies for development of intestinal organoids. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F32.00010: Biosensor physics: DNA folding in a crowded environment Mark Taylor, Wolfgang Paul At the molecular level, biological systems operate in very crowded environments. It has long been recognized that crowding can affect the stability and phase transitions of the biopolymers comprising such systems. Similar issues arise in developing biotechnology applications based of dense arrays of surface-tethered polymers. In our recent work we directly measure the entropy reduction resulting from crowding/confinement using Wang-Landau computer simulation techniques [1]. Here we discuss the folding transition of a specific stem-loop forming, single-stranded DNA oligomer that has been studied extensively by the Plaxco group [2]. We develop a coarse-grained model for ssDNA (based on a flexible hard-sphere chain with square-well patch interactions that accounts for both H-bonding and base-pair stacking) and use it to examine the entropic effects associated with surface crowding. For the tethered ssDNA oligomer crowded by other tethered oligomers, we find, in agreement with experiment, that both stabilization and destabilization of the folded state are possible depending on the conformational state of the crowders. [1] Taylor, Macromolecules 50, 6967 (2017); J. Chem. Phys. 147, 166101 (2017); [2] Watkins et al, JACS 134, 2120 (2012); JACS 136, 8923 (2014). |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F32.00011: Effect of Nanoparticle Surface Functionality on Magnetic and Interfacial Properties of Iron Oxide–Poly(ethylene oxide) Nanocomposites Donovan Weiblen, Grace L Gionta, Deniz Rende, Pinar Akcora, Rahmi Ozisik Magnetically susceptible nanoparticles (NPs) have shown promise in diverse application areas such as shape memory polymers, membranes, and drug delivery. In the current work, the impact of surface coating of iron oxide (Fe3O4) NPs on interfacial heat transfer, bulk magnetization properties, and structure of poly(ethylene oxide), PEO, nanocomposites was explored. Bare, poly(ethylene glycol) (PEG), and amine coated 10–nm–diameter Fe3O4 NPs were dispersed at concentrations less than 1% by weight in PEO. When exposed to an alternating magnetic field (AMF), temperature increases for all PEO/Fe3O4 nanocomposites. Amine and PEG coated NPs showed an improved heat generation efficiency. Analysis of magnetization curves revealed an unusual result. Amine coated NPs had the strongest magnetization, however, bare NPs showed a stronger magnetization than the PEG coated NPs. Disagreement between magnetization and magnetic heating results implies that interfacial heat transfer is impacted by NP surface modification. Simulations and experiments were carried out to identify the interfacial structure. Specific attention was paid to how the interface changes with applied AMF and how it affects the mechanism of heat transfer. |
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