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Silk apatite composites from electrospun fibers
Li, Chunmei,Jin, Hyoung-Joon,Botsaris, Gregory D.,Kaplan, David L. Cambridge University Press (Materials Research Soc 2005 Journal of materials research Vol.20 No.12
<P>Human bone is a three-dimensional composite structure consisting of inorganic apatite crystals and organic collagen fibers. An attractive strategy for fabricating mimics of these types of composite biomaterials is to selectively grow apatite on polymers with control of structure, mechanical properties, and function. In the present study, silk/apatite composites were prepared by growing apatite on functionalized nanodiameter silk fibroin fibers prepared by electrospinning. The functionalized fibers were spun from an aqueous solution of silk/polyethylene oxide (PEO) (78/22 wt/wt) containing poly(L-aspartate) (poly-Asp), which was introduced as an analogue of noncollageous proteins normally found in bone. Silk fibroin associated with the acidic poly-Asp and acted as template for mineralization. Apatite mineral growth occurred preferentially along the longitudinal direction of the fibers, a feature that was not present in the absence of the combination of components at appropriate concentrations. Energy dispersive spectroscopy and x-ray diffraction confirmed that the mineral deposits were apatite. The results suggest that this approach can be used to form structures with potential utility for bone-related biomaterials based on the ability to control the interface wherein nucleation and crystal growth occur on the silk fibroin. With this level of inorganic-organic control, coupled with the unique mechanical properties, slow rates of biodegradation, and polymorphic features of this type of proteins, new opportunities emerge for utility of biomaterials.</P>
Kaplan, Kyle F.,Dinerstein, Harriet L.,Oh, Heeyoung,Mace, Gregory N.,Kim, Hwihyun,Sokal, Kimberly R.,Pavel, Michael D.,Lee, Sungho,Pak, Soojong,Park, Chan,Oh, Jae Sok,Jaffe, Daniel T. American Astronomical Society 2017 The Astrophysical journal Vol.838 No.2
<P>We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R similar to 45,000) and instantaneous broad wavelength coverage (1.45-2.45 mu m), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H-2) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H2 and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T = 50-250 K, n(H) = 10(5)-10(7) cm(-3)) embedded in a warmer lower density medium (T = 250-1000 K, n(H) = 10(4)-10(5) cm(-3)). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H2 level populations well, to constrain the temperature to a range of 600-650. K and the density to n(H) = 2.5 x 10(3) -10(4) cm(-3). The best-fit model gives T = 625 K and n(H) = 5 x 10(3) cm(-3). This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.</P>
Water-Stable Silk Films with Reduced &bgr;-Sheet Content
Jin, H.-J.,Park, J.,Karageorgiou, V.,Kim, U.-J.,Valluzzi, R.,Cebe, P.,Kaplan, D. L. WILEY-VCH Verlag 2005 Advanced Functional Materials Vol.15 No.8
<P>Silk fibers have outstanding mechanical properties. These fibers are insoluble in organic solvents and water, are biocompatible, and exhibit slow biodegradation in vitro and in vivo due to the hydrophobic nature of the protein and the presence of a high content of &bgr;-sheet structure. Regenerated silk fibroin can be processed into a variety of materials normally stabilized by the induction of &bgr;-sheet formation through the use of solvents or by physical stretching. To extend the biomaterial utility of silk proteins, options to form water-stable silk-based materials with reduced &bgr;-sheet formation would be desirable. To address this need for more rapidly degradable silk biomaterials, we report the preparation of water-stable films from regenerated silk fibroin solutions, with reduced &bgr;-sheet content. The keys to this process are the preparation of concentrated (8 % by weight) aqueous solutions of fibroin and a subsequent water-based annealing procedure. These new materials degrade more rapidly due to the reduced &bgr;-sheet content, as determined in vitro via enzymatic hydrolysis, yet support human adult stem-cell expansion in vitro in a similar or improved fashion to the crystallized proteins in film form. These new silk-based materials extend the range of biomaterial properties that can be generated from this unique family of proteins.</P> <B>Graphic Abstract</B> <P>In order to extend the utility of silk-based biomaterials, water-stable films with reduced &bgr;-sheet formation have been formed via a water-annealing process, leading to improved biodegradability and elasticity. The Figure shows a) a fracture surface (scale: 100 &mgr;m), b) a layer from the film surface (scale: 20 &mgr;m), and c) individual layer thickness (scale: 100 nm). <img src='wiley_img/1616301X-2005-15-8-ADFM200400405-content.gif' alt='wiley_img/1616301X-2005-15-8-ADFM200400405-content'> </P>