Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session U21: Biomedical Physics |
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Sponsoring Units: DBP Chair: Herbert Levine, University of California, San Diego Room: LACC 409A |
Thursday, March 24, 2005 8:00AM - 8:12AM |
U21.00001: Optimizing coherence domain imaging system for biomedical imaging Ping Yu, David Nolte Holographic optical coherence imaging (OCI) system has shown promise in record full-frame depth-resolved images in tumor tissues, allowing real-time video display. Normally a holographic OCI system consists of a low coherence interferometry, a dynamic coherent filter and a CCD camera for image record and display. The key component in the system is photorefractive multiple quantum wells (PRQW) devices that act as the coherence filter passing full-frame image bearing light while rejecting the scattered background. Holographic OCI system is optimized by considering adaptive capabilities, speckle suppression and higher diffraction efficiency of the devices. Both AlGaAs/GaAs and InGaAs/GaAs devices have been examined at different working wavelengths based on degenerate four-wave mixing and non-degenerate four-wave mixing. [Preview Abstract] |
Thursday, March 24, 2005 8:12AM - 8:24AM |
U21.00002: Medical Image Provessing using Transient Fourier Holography in Bacteriorhodopsin Films Sri-Rajasekhar Kothapalli, Pengfei Wu, Chandra Yelleswarapu, Rao Devulapalli A real-time optical Fourier image processing system is demonstrated for early detection of microcalcifications in screen film as well as digital mammograms. The principle is based on recording and reconstructing the transient photoisomerizative grating formed in the bR film. At first Fourier hologram is recorded by spatially overlapping the Fourier transformed object beam with the reference beam in the bR film. Then the object beam is blocked and the reference beam performs the reconstruction of the recorded Fourier hologram. The optimum of diffraction efficiency occurs when object beam intensity is matched to the reference beam intensity. We exploit this technique to process mammograms in real-time for identification of microcalcifications buried in the soft tissue for early detection of breast cancer. A novel feature of the technique is the ability to transient display of selected spatial frequencies in the reconstructing process which enables the radiologists to study the features of interest in time scale. [Preview Abstract] |
Thursday, March 24, 2005 8:24AM - 8:36AM |
U21.00003: Ultra-High Speed Observations of the Mechanism of Sonoporation Paul Campbell, Paul Prentice Cells that are exposed to varying amounts of ultrasound energy may undergo either permanent cell membrane damage (lethal sonoporation) or a transient enhancement of membrane permeability (reversable or non lethal sonoporation). The merits of each mode are clear: lethal sonoporation constitutes a significant tumour therapy weapon, whilst its less intrusive counterpart, reversible sonoporation, makes for an effective non-invasive and targeted drug delivery approach. Until now, the mechanism of these interactions has remained unknown. We will demonstrate, for the first time, how an innovative hybridization of hologram based optical trapping technology, together with the application of millisecond pulsed ultrasound energy and parallel observation at MHz frame-rates using microscope objectives, has been used to elucidate the fundamental microscopic mechanism behind sonoporation. We will demonstrate the dependence of the permeabilisation mechanism on both the ultrasound field characteristics and the controlled displacement between individual microbubbles and single cells. High speed movies will be used to illustrate each category, whilst parallel fluorescence microscopy allows bioeffect to be quantified. Strategies for sonoporation optimisation are also illustrated. [Preview Abstract] |
Thursday, March 24, 2005 8:36AM - 8:48AM |
U21.00004: GOLD AND IRON-GOLD NANOPARTICLES FOR INTRACELLULAR TRACKING AND IN VIVO MEDICAL APPLICATONS Wei Fu, Gurinder Saini, Dinesh Shenoy, Dattatri Nagesha, Mansoor Amiji, Srinivas Sridhar We have fabricated Au and Fe-Au nanoparticles for potential use in ex vivo experiments such as intracellular tracking, as well as a variety of in vivo medical applications. In order to improve their targeting potential, circulation time and flexibility, gold NPs were surface modified using a hetero-bifunctional poly(ethylene glycol) (PEG, MW 1,500) spacers. A coumarin-PEG-gold NP complex was formed and cell viability studies and optical fluorescence experiments were carried out demonstrating the use of these surface-modified gold NPs for drug delivery, gene therapy and cell trafficking experiments. Fe-Au nanoparticles were also fabricated and show significant contrast enhancement in MRI studies through a substantial reduction of the T2 relaxation time. [Preview Abstract] |
Thursday, March 24, 2005 8:48AM - 9:00AM |
U21.00005: Viscoelastic and ultrasonic measurements of canine tissue Miklos Kiss, Tomy Varghese Mechanical properties, of biological tissues, such as the complex modulus, are of interest for assessing the performance of elastographic methods that evaluate the stiffness characteristics of tissue. Determination of the mechanical properties of biological tissues is often limited by proper geometry of the sample, as well as homogeneity of the stress-strain relationship. Viscoelastic measurements were performed on in vitro canine liver tissue specimens, using a dynamic testing system, from 0.1 -- 100 Hz, and ultrasonic attenuation measurements were performed from 6 -- 9 MHz . Both normal tissues as well as thermal lesions prepared by immersion heating at several temperatures were tested. Experiments were conducted by uniaxially compressing tissue samples and measuring the load response. The resulting moduli spectra were then fit to both the Kelvin-Voigt model, as well as the Kelvin-Voigt fractional derivative model. The data agree well with the models and in comparing the results from the normal tissue with that of the thermal lesions, the concept of a complex modulus contrast is introduced and its applications to elastography are discussed. [Preview Abstract] |
Thursday, March 24, 2005 9:00AM - 9:12AM |
U21.00006: Loading of Cervical Spine when Head is Rotated Saami J. Shaibani The neck is more susceptible to injury during an insult in the forward direction if the head is not initially facing straight ahead. (A typical example of this is when a vehicle occupant is checking traffic to the right or left at an intersection before proceeding.) However, the ability to characterize this behavior has not progressed much beyond the qualitative because practical constraints limit testing with conventional physical surrogates. This shortfall is tackled in this study by employing a model validated elsewhere to represent a range of real-world events with the power of great specificity for parameters of importance. Of primary concern is the variation in head angle, which can now be investigated across a wide spectrum of values that was not possible with previous approaches. The quantitative results computed here provide an extraordinarily high level of detail and they show how the potential for injury can change from low to significant within a matter of degrees. This explains why a seemingly harmless impact can cause trauma in some cases when none would otherwise be expected. [Preview Abstract] |
Thursday, March 24, 2005 9:12AM - 9:24AM |
U21.00007: In-Situ Atomic Force Microscopy of Bone Fracture Surfaces Reveals Collagen Fibrils Individually Coated with Mineral Particles of Varying Shape and Size Johannes H. Kindt, Georg E. Fantner, Philipp Thurner, Georg Schitter, Paul K. Hansma High resolution AFM images of bovine trabecular bone fracture surfaces reveal individual fibrils coated with extrafibrillar mineral particles. Treating bone with EDTA removes the mineral particles on these fibrils, and reveals the underlying collagen structure. The mineral particles show distinctly different size and morphology in different regions. Significantly, we rarely observed bare collagen fibrils in fracture surfaces before EDTA treatment. This implies that fractures propagate between the mineral particles on one fibril, and the mineral particles on another fibril. Thus, to understand the mechanics of fracture on the molecular scale, it will be crucial to understand the molecular nature of the adhesion between the mineral particles that coat adjacent collagen fibrils, because this is the weak interface that fails during fracture. [Preview Abstract] |
Thursday, March 24, 2005 9:24AM - 9:36AM |
U21.00008: High-Speed Photography during Compression Testing Human Trabecular Bone Philipp Thurner, John Langan, Jeff Scott, Maria Zhao, Blake Erickson, Zachary Schriock, Georg Fantner, Paul Hansma The mechanical properties of healthy and diseased bone are extensively studied. Most of this research is motivated by the immense costs in health care due to osteoporosis. To address the problem of assessing bone microarchitecture and concomitant microcracking behavior, we recently combined mechanical compression testing of trabecular bone with high-speed photography. In an exemplary study, we investigated healthy, osteoarthritic, and osteoporotic human vertebral trabecular bone. Bone samples were loaded along their principal load-bearing axis at high strain rates simulating boundary conditions as experienced in individuals during falls. Even at small global strains huge local deformations could be seen in the recorded high-speed photography frames. Moreover, strained trabeculae were seen to whiten with increasing strain, which could be associated with areas of high deformation using a motion energy filter. Presumably the effect seen is due to microcrack formation in these areas, similar to stress whitening in synthetic polymers. This hypothesis is currently tested applying en bloc microcrack staining and histology. [Preview Abstract] |
Thursday, March 24, 2005 9:36AM - 9:48AM |
U21.00009: Investigations on the Feedback Loop that controls Bone Remodeling Markus A. Hartmann, Richard Weinkamer, Peter Fratzl, Yves Brechet Bone is a living tissue that can adapt its shape and inner architecture to withstand mechanical loading experienced in daily life. The bone tissue is continuously renewed in a process called bone remodeling involving specialized cells: osteoblasts deposit bone, osteoclasts remove bone. The process is regulated by a feedback loop, where the probability for bone deposition (resorption) is related to a local mechanical stimulus. Our interest is the effect of different relations (i.e., different remodel laws) on the resulting bone mass and geometry. We developed a computer model [1], where the spongy architecture of trabecular bone is mapped onto a lattice and the local mechanical loading is calculated using a simple algorithm. Depending on the remodel law, the simulations show remarkable differences in the heterogeneity of the bone architecture and the reaction to perturbations (e.g., changes in the osteoclastic activity). Comparison of these results to data obtained from real bone gives further insight in the underlying feedback loop. \\ $[1]$ Weinkamer et al., PRL {\bf 93}, 228102 (2004) [Preview Abstract] |
Thursday, March 24, 2005 9:48AM - 10:00AM |
U21.00010: Effect of Polymer Matrix on the Electrophoretic Mobility of Linear and Branched DNA in Polymer Solutions Sourav Saha, Daniel Heuer, Lynden Archer The electrophoretic mobility of linear T2 and 3-arm star branched DNA is studied in low polydispersity index linear polyacrylamide (LPA) solution of varying molecular weights in tris-acetate buffer. In semidilute solution (above the overlap concentration) we have found that the linear and the star-branched DNA of similar size have similar mobility below a certain threshold concentration. This threshold concentration is observed to increase with LPA molecular weight and correspond to about 10 blobs (hydrodynamic screening length) per polymer chain N/g. At concentrations below this threshold, the biased repation with fluctuations model and constraint release could not explain the observed electrophoretic mobility dependence on LPA concentration and molecular weight, and the DNA mobility is found to be independent of the DNA conformation, sensitive to the ionic concentration and the electric field, and determined by the local non-Newtonian viscosity due to shear thinning of LPA in the electric double layer (EDL).Whereas above this threshold concentration, star branched DNA is found to have mobility lower than that of linear DNA and both the star branched and the linear DNA mobility are found to depend on the entanglements among polymer chains characterized by N/g. [Preview Abstract] |
Thursday, March 24, 2005 10:00AM - 10:12AM |
U21.00011: Interactions between the HIV TAT domain and cell membranes Abhijit Mishra, Hongjun Liang, Gerard Wong Biologically active molecules such as proteins and oligonucleotides can be transduced into cells with high efficiency when covalently linked to a Protein Transduction Domain (PTD), such as the TAT domain in the HIV virus. All PTDs have a high content of basic amino acids resulting in a net positive charge. Electrostatic interactions between cationic PTDs and the negatively charged phospholipids that constitute the plasma membrane seem to be responsible for peptide uptake, but no detailed structural studies exist. We present recent results on the structures of self-assembled complexes of the cationic TAT domain and anionic lipid bilayers using synchrotron x-ray scattering and electron microscopy, and examine possible mechanisms of the anomalous transduction. [Preview Abstract] |
Thursday, March 24, 2005 10:12AM - 10:24AM |
U21.00012: Transfection efficiency and structural studies on nonviral gene carriers containing cholesterol and other sterols Heather Evans, Alexandra Zidovska, Kai Ewert, C. R. Safinya Lipid based nonviral gene delivery currently focuses on cationic liposomes, which typically consist of a mixture of cationic and neutral (helper) lipids. Motivated by the plasma membrane composition of mammalian cells, which contain large amounts of cholesterol, this molecule is often used as a helper lipid. The presented work investigates the effect of cholesterol and structurally related molecules on the transfection efficiency (TE) of cationic lipid-DNA (CL-DNA) complexes in mammalian cells. Previous studies have identified the membrane charge density as a universal parameter, predicting TE for CL-DNA complexes in the lamellar L$\alpha ^{C} $ phase [1,2]. Addition of cholesterol to low transfecting CL-DNA complexes results in dramatic improvements in TE that significantly deviate from the TE model for lamellar complexes. A model system using negatively charged giant vesicles has been developed to mimic the cell membrane and understand the behavior pattern of CL-DNA complexes containing cholesterol. Funding provided by NIH GM-59288. [1] Lin AJ, Slack NL, Ahmad A, George CX, Samuel CE, Safinya CR, \textit{Biophys. J.}, 2003, V84:3307 [2] Ahmad A, Evans HM, Ewert K, and Safinya CR, \textit{J. Gene Med., }accepted [Preview Abstract] |
Thursday, March 24, 2005 10:24AM - 10:36AM |
U21.00013: Energy Partitioning in FEL Tissue Ablation Shane Hutson, Gilma Adunas-Rivas, Yaowu Xiao The wavelength-dependence of FEL tissue ablation has been attributed to partitioning of absorbed energy between protein and saline. We have taken two approaches to test the hypothesis that such energy-partitioning allows wavelengths targeting the protein component to diminish the structural integrity of tissue before water vaporization commences. First, models of this process predict that energy-partitioning should play little role in near-threshold ablation, but become much more important as the fluence is increased. Thus, we have measured the ablation efficiency on cornea across large swaths of the fluence versus wavelength parameter space. We find that the effects of energy-partitioning do grow as the fluence is increased. Second, we have analyzed the protein components of the ablation plume for signatures of protein structural change. FTIR and NMR spectra of plume components reveal that the secondary and tertiary structure of the protein (collagen) fibers has been lost. These spectra also reveal new functional groups in the ablated material, most likely nitriles or alkynes that could have arisen via oxidative degradation of the protein. However, there is no evidence for widespread scission of protein backbones. [Preview Abstract] |
Thursday, March 24, 2005 10:36AM - 10:48AM |
U21.00014: Charged binary fluid confined to cylindrical monolayer: Pattern formation Yury Velichko, Monica Olvera de la Cruz Stoichiometric mixtures of acidic and basic peptide--amphiphile molecules (PA) composed of a hydrophobic block and a peptide block that favors $\beta$-sheet formation with a charged end--group co-assemble in the water solution at physiological pH--conditions into long cylindrical nanofibers. These fibers form a network that resembles extracellular matrix found in living tissue. PA--molecules self--aggregate because of competition between hydrophobic--hydrophilic interactions and stabilize aggregate structures by forming hydrogen bonds between peptide blocks and surface charges. On the other hand, small chemical distinction between cationic and anionic components may cause local segregation and formation of patterns. We investigate the phase behavior of stoichiometric charged two-component fluid confined to cylindrical monolayer to describe pattern formation on the surface of self--assembled cylindrical aggregates, such as peptide amphiphiles. The net incompatibility among different components results in appearance of segregated domains which growth is inhibited by electrostatics. We find that the transition from isotropic to striped phase begins from the formation of small domains and proceeds through an intermediate state governed by defects. Detailed results of study of heat capacity, static structure factor, susceptibility and cluster asphericity parameter independence on the radius of the cylinder and degree of incompatibility we will present during the talk. [Preview Abstract] |
Thursday, March 24, 2005 10:48AM - 11:00AM |
U21.00015: Today's ``safe" radiofrequency (RF) exposure limits DON'T protect human health near transmitters! Marjorie Lundquist Maxwell's theory implies that electromagnetic (EM) radiation carries both energy and momentum. ``The momentum may have both linear and angular contributions; angular momentum [AM] has a spin part associated with polarization and an orbital part associated with spatial distribution. Any interaction between radiation and matter is inevitably accompanied by an exchange of momentum. This often has mechanical consequences ..."$^2$ Voluntary consensus standards [ANSI C95; NCRP; INCIRP] protect human health from most {\it thermal} [energy transfer] effects, but no standards yet exist to protect health against {\it athermal} [momentum transfer] effects, though laboratory transfer of spin AM was reported by 1935$^3$ and of orbital AM by 1992$^2$ for an optical vortex [tip of Poynting vector (PV) traces a helix about the beam axis]. In the {\it far field} of a dipole RF transmitter, radiation is linearly polarized ({\it minimal} spin AM) and locally approximated by a plane wave ({\it zero} orbital AM), but in the {\it near field} the orbital AM is {\it non-zero} [tip of PV traces an ellipse$^4$ in air] implying an {\it athermal hazard} [{\it e.g.}, brain tumors in cellular phone users] against which {\it no standard now in use anywhere in the world} protects! \hfil \break $^2$ L. Allen {\it et al}. Phys. Rev. {\bf A 45}:8185-9(1992). $^3$ R.A. Beth, Phys. Rev. {\bf 48}:471(1935); {\bf 50}:115-25 (1936). $^4$ F. Landstorfer, Archiv f\"ur Elektronik und \"Ubertragungstechnik {\bf 26}:189-96(1972) [in German]. [Preview Abstract] |
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U21.00016: Mechanical Asphyxiation in Proximity with Ceramic Surface Saami J. Shaibani A lack of air reaching the lungs may involve several components, including obstruction of some part of the breathing path. When such an obstruction is effected by external constriction of the trachea, some level of pressure must be applied over some period of time to cause death by asphyxia. The nature of these physical quantities depends on the anatomy of the person concerned and on the geometry of the circumstances. Special emphasis is placed in this research on the interaction between anatomy and geometry in order to calculate the forces associated with the reported rest position of a deceased female against a bathroom commode. The first step in the analysis is to derive the distribution of body weight for this particular individual by employing extensive anthropometric measurements. This methodology produces an optimum representation with a large number of body segments, whose finite number of arrangements are examined to find the forces at certain points of interest. The values obtained are reviewed to see if the apparent rest position is consistent with elementary laws of physics. [Preview Abstract] |
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U21.00017: Monitoring stiffness contrast in elastography Miklos Kiss, Shyam Bharat, Tomy Varghese, Udomchai Techavipoo, Wu Liu Elastography is an imaging modality used to image tissue strains resulting from external quasi-static compression of tissue. Therefore, elastograms can be used to study variations in the stiffness of thermally coagulated regions of tissue. In this study, the variations in stiffness contrast of lesions formed by radio frequency (RF) ablation of canine liver tissue have been investigated. RF ablation was performed on in vitro canine liver tissue over a range of temperatures from 70 - 100 degrees C, and over a range of ablation times from 1 -- 8 minutes. Elastography was then performed on these samples and on normal tissue. It was expected that stiffness contrast would increase with increasing lesion temperature and ablation duration, on the basis that higher temperature and greater ablation durations lead to increased protein denaturation. This increase was seen with ablation duration, but is not obvious with ablation temperature. These and other results will be discussed. [Preview Abstract] |
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