Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A49: Biomaterials 1: Structure, Function, DesignFocus
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Sponsoring Units: DBIO DCP Chair: Pupa Gilbert, Univ of Wisconsin, Madison Room: LACC 511A |
Monday, March 5, 2018 8:00AM - 8:36AM |
A49.00001: Structure-property relations in biomaterials Invited Speaker: Debora Frigi Rodrigues This abstract not available. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A49.00002: Measuring fracture toughness of bone at the microscale Ottman Tertuliano, Bryce Edwards, Julia Greer Techniques to probe strength of materials at small scales have been established for over a decade but fracture toughness experiments are exclusively standardized for the macroscale. Notched microcantilever based methods have recently been proposed for performing fracture experiments at the microscale. Asymmetric loading conditions around the crack tip limit their viability, particularly for heterogeneous materials such as bone, a composite primarily comprised of collagen fibrils and bioaptite at the nanoscale. We developed a methodology that enables conducting 3-point bending beam fracture experiments on micron-sized samples on a variety of materials fabricated using an in situ SEM/nanoindenter. We extracted beams of ~50x10x5 µm from single crystalline silicon using a focused ion beam and measure a K1c of 0.98 MPa m1/2, in agreement with the accepted 1 MPa m1/2 . We perform site-specific fracture experiments on similarly-sized dry bone beams, fabricated with collagen fibrils oriented orthogonally to the initial crack. We report a J integral toughness of 45 J/m^2 over 2.5 µm of stable crack growth. We discuss these results in the context of the rising R curve of bone and compare observed toughening mechanisms to those reported in similar macroscale experiments in literature. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A49.00003: Computational study of remodeling of fibrin networks under compression Samuel Britton, Oleg Kim, Rustem Litvinov, John Weisel, Mark Alber Fibrin network is one of the major structural components of both physiological blood clots and pathological thrombi. Mechanical and structural properties of fibrin network contribute to clot mechanical stability and determine its deformation under pressure from blood flow. Computational study of dynamical deformations of fibrin networks under compression demonstrate that dramatic remodeling of a clot observed in experiments is based on bending and reorientation of individual fibers as well as fiber-fiber non-covalent linkage. Structures of the network used in model simulations are generated from data gleaned from confocal microscopy images of in vitro fibrin clots. Upon network compression, non-covalent interactions between fibers result in dynamic variation of network architecture. These interactions significantly affect mechanical response of the network at high compression degrees, ultimately resulting in clot stiffening. Simulation results match experimental data in both fiber linking rates and network densification under different compression rates. Finally, the model is used to predict how stress propagates through the network and how rearrangement and linking of fibrin fibers affects clot stiffening. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A49.00004: Investigating the Effects of Biofilm Viscoelasticity on Immune Cell Phagocytosis Layla Bakhtiari, Megan Davis-Fields, Kristin Kovach, Vernita Gordon Biofilm infections affect 17 million Americans, cause half a million deaths, and cost the US healthcare system billions of dollars annually. Biofilms are communities of micro-organisms embedded in a polymer and protein matrix. Biofilms are inherently more resistant to antibiotics and immune cell clearance. The matrix gives the biofilm a mechanical response to shear that is characteristic of a viscoelastic solid. Our goal is to understand how distinct mechanical properties, including elastic modulus (G’) and yield strain, impact biofilm resistance to the immune system. We focus on neutrophils, the phagocytic first-responders to infection that are involved in the body’s attempts to clear biofilm infections. The best extant estimate for the stress exerted by neutrophils during phagocytosis is ~1 kPa. This is comparable to the ~1 kPa value we measure for G’ for some biofilms, but we find that biofilms can increase or decrease G’ by adjusting production of matrix polymers. We are developing two approaches to create “model biofilms” of known and tunable mechanics: gel macrobeads and photo-crosslinked micro-structures. We will challenge “model biofilms” with neutrophils and determine threshold mechanical values below which neutrophils can break off and engulf pieces of the “biofilm”. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A49.00005: Highly tough and fast recoverable double network hydrogels Yongqiang Li, Kunlun Yang, Lin Lin, Junming Liu Hydrogels consist of a three-dimensional network structure and represent a class of wet and soft materials. It is well known that double network hydrogels exhibit excellent mechanical properties, offering potential applications not only in articular cartilage. Articular cartilage is a dense connective tissue of collagen fibers constituting a semi-circular frame combined with the bone. Here, we demonstrate a simple strategy to synthesize the CS-g-PAA/PEI-0.10 double network hydrogels, with varying contents of ethylene imine polymer (PEI) in the chitosan /acrylic acid (CS/AA) solution. The environmental SEM imaging reveals that the CS-g-PAA/PEI-0.10 double network hydrogels have the homogeneous porous network and the excellent mechanical properties under compression. The underlying mechanism is that the second network acts as the sacrificial network to make the first network rapidly recoverable, allowing the compressive stress to fast release in seconds. These favorable mechanical properties enable the high application potentials in articular cartilage. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A49.00006: Targeting the Mechanical Properties of Biofilms for New Approaches to Treating Infections Kristin Kovach, Megan Davis-Fields, Layla Bakhtiari, Vernita Gordon Biofilms are communities of bacteria embedded in a matrix of polymer and protein. Being in a biofilm greatly helps bacteria resist antibiotics and the immune system; as a result, chronic biofilm infections can last decades. Biofilm-forming bacteria can produce more than one type of matrix polymer, and matrix polymers and proteins interact to have different impacts on biofilms’ viscoelastic response to mechanical stress. In light of the increasing need for new anti-biofilm therapies, we aim to find approaches to disrupting biofilm mechanics by interfering with specific interactions between matrix components. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A49.00007: Free-floating Carbon Nanotubes Can Promote “Nucleation” of Pathogenic Bacterial Aggregates Vernita Gordon, Kristin Kovach, Indu Venu, Parth Patel, Navid Saleh, Mary Jo Kirisits Carbon nanotubes (CNTs) are increasingly used in functional materials. As an unintended consequence, this is likely to increase CNTs in aqueous environments and in water treatment and delivery systems as a result of by-products of manufacture or by material degredation once in use. Aqueous systems are reservoirs for bacteria, including human pathogens that form biofilms. Although CNTs at sufficiently-high concentrations in designer materials are known to be anti-microbial, almost nothing is known about the interactions of bacteria with CNTs suspended in fluid at sub-lethal concentrations. Here, we investigate the impact of low concentrations of CNTs on the biofilm-forming human pathogen Pseudomonas aeruginosa. Using phase contrast and confocal microscopy and flow cytometry, we find that sublethal concentrations of CNTs promote the formation of aggregates of P. aeruginosa. Previous work by others has shown that P. aeruginosa aggregates have many of the harmful characteristics associated with biofilms, including increased virulence, antibiotic resistance, and resistance to the immune system. Thus, the presence of low levels of CNTs in open water and water supplies constitutes a potential threat to public health. We suggest possible countermeasures. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A49.00008: Abstract Withdrawn
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Monday, March 5, 2018 10:00AM - 10:12AM |
A49.00009: Photodeactivation of pathogenic bacteria using graphene quantum dots synthesized by nanosecond laser pulses Ali Er, Khomidkhodzha Kholikov, Saidjafarzoda Ilhom, Zachary Thomas, Skyler Smith In this work, a graphene-based biomaterial which is a promising alternative to a standard photosensitizers was produced and its efficiency of bacteria inactivation was studied. Graphene quantum dots (GQDs) were synthesized by irradiating benzene and nickel oxide mixture using nanosecond laser pulses. High-resolution transmission electron microscopy (HR-TEM) results show GQDs whose size less than 5 nm with very good water dispersibility were successfully obtained. UV-Vis spectra of GQDs have an absorption peak around 300 nm and photoluminescence spectra shows that GQDs have maximum emission at 430 nm with the excitation wavelength of 310 nm. Also, Fourier transform infrared (FTIR) spectra further confirms the presence of GQDs. Deactivation of Escherichia coli (E. coli) a gram-negative bacterium with a photosensitizer and carbon nanoparticles was studied by irradiating with different wavelengths. The results show a significant decrease in the number of colony forming units of E. coli. Our results show that GQDs can potentially be used to develop therapies for the eradication of pathogens in open wounds, burns, or skin cancers. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A49.00010: Genetically and Morphologically Manipulated Bacteriophage as Templates for Inorganic Janus-Like Particles and Their Photocatalytic Application Joshua Plank, Michelle Lai, Tam-Triet Ngo-Duc, Elaine Haberer Recently, viruses have been investigated as versatile, hierarchical templates with site-specific affinity. Peptides displayed via genetic or chemical modification can facilitate the selective synthesis of one or more inorganic materials on viral surface proteins, while viral structure can control the long-range assembly of these materials. The M13 phage was studied here for its ability to bind multiple materials and undergo a drastic morphological change, making it a powerful scaffold for metal-semiconductor Janus particle assembly. Unlike core-shell structures which isolate one material from the surrounding environment, two-faced particles preserve the chemical activity of both materials, promoting efficient photocatalytic activity. This work characterized the M13 shape transformation then employed the phage as a template for a ZnS/Au Janus-like particle. The novel nanoparticle was used in the photo-degradation of methylene blue, and the photo-generated electron pathway was studied. This work represents one of the first examples of application of the genetically and morphologically modified M13. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A49.00011: Gold templated on spheroidal M13 bacteriophage as a photothermal bactericide Tam-Triet Ngo-Duc, Joseph Cheeney, Joshua Plank, Stephen Hsieh, Elaine Haberer Antibiotic resistant bacteria have increasingly become a health issue. Photothermal lysis using plasmonic metal nanostructures is effective against bacteria, regardless of drug resistance. Viruses provide an approach to the synthesis of bacteria-targeting metal nanoshells. A virus can be genetically programmed to both serve as a scaffold for metal nanostructure assembly and have an affinity for a specific bacterial host. In this work, we used an Au-binding M13 virus to create a photothermal bactericide for e coli. The virus geometry was converted from filament to spheroid via chloroform treatment. Au nanoshells were formed by (1) binding Au NPs to the spheroid for visible light absorption and (2) synthesizing an Au shell on the spheroid for NIR absorption. TEM and spectrophotometry were used to assess morphology and optical absorption, respectively. Nanoshell photothermal activity was quantified under either green or NIR illumination. Antibacterial activity was measured via titer count. Au/M13 nanoshells acted as photothermal bactericide. This potentially powerful approach can be generalized to target a variety of bacteria through the use of different affinity peptides. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A49.00012: Theory and Design of Photonic Crystals in Broadband Biological Reflectors Ariel Amir, Caleb Cook, Nitin Upadhyaya, Kevin Zhou In both engineering applications as well as use by living organisms, structural coloration - manipulating light using interference phenomena rather than pigments - is a common motif. Here, we will focus on the manipulation of the reflection spectra of waves using multilayered structures with two alternating indices of refraction. I will show how "chirped" structures (where the layer thickness is gradually changed throughout the structure) may lead to any reflection spectrum of choice, and how, surprisingly, disorder may be utilized to achieve certain well-defined reflection spectra, including narrow pass bands. I will compare the efficiency of chirped and disordered broadband reflectors, revealing some general principles underlying their designs. |
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