PubMed · 5537875
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H Bünte. 1970-03-27. [Stenosing esophagitis].. https://pubmed.ncbi.nlm.nih.gov/5537875/
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Hydrogel/apatite nanocomposites are the ideal biomaterial to mimic the physio-chemical and biologic properties of the bone and to fabricate scaffolds for bone regeneration. The objective of this work was to investigate the effect of an osteonectin derived glutamic acid sequence on the viscoelastic properties of poly(lactide-ethylene oxide-fumarate) (PLEOF)/apatite composite, as a model degradable material in bone regeneration. Osteonectin is an extracellular acidic glycoprotein of the bone matrix, which is believed to be involved in linking the collagen network to hydroxyapatite (HA), the mineral phase of the bone. We synthesized a 6-glutamic acid sequence in solid phase with affinity to HA crystals via ionic interactions. One end of the synthesized peptide was functionalized with an acrylate group to covalently attach the peptide (Ac-Glu6) to the aqueous-based biodegradable and in situ crosslinkable PLEOF hydrogel matrix. To determine the effect of energetic interactions between the fillers and hydrogel matrix, HA nanoparticles were also treated with an acrylate functionalized 6-glycine amino acid peptide (Ac-Gly6) that interacts with the fillers only by van der Waals and polar interactions (without ionic interactions). Crosslinked PLEOF/apatite scaffolds were prepared using PLEOF as the degradable macromer, HA nanofillers treated with Ac-Glu6 peptide linker, and a neutral redox initiation system. The viscoelastic properties were studied by dynamic time sweep, strain sweep, and small amplitude oscillatory rheometry. Composites without surface treatment, treated with Ac-Gly6, and treated with Ac-Glu6 at different volume fractions and various particle sizes were examined. The results showed that the 6-mer glutamic acid sequence significantly affects the shear modulus of the scaffold because of ionic interactions between the peptide and HA crystals.
The cross-correlation algorithm used to compute the local strain components for elastographic imaging requires a minimum radio-frequency data segment length of around 10 wavelengths to obtain accurate and precise strain estimates with a reasonable signal-to-noise ratio. Shorter radio-frequency data segments generally introduce increased estimation errors as the information content in the data segment reduces. However, shorter data segments and increased overlaps are essential to improve the axial resolution in the strain image. In this paper, we propose a two-step cross-correlation technique that enables the use of window lengths on the order of a single wavelength to provide displacement and strain estimates with similar noise properties as those obtained with a 10 wavelength window. The first processing step utilizes a window length on the order of 10 wavelengths to obtain coarse displacement estimates between the pre- and post-compression radio frequency data frames. This coarse displacement is then interpolated and utilized as the initial guess-estimate for the second cross-correlation processing step using the smaller window. This step utilizes a single wavelength window to improve the axial resolution in strain estimation, without significantly compromising the noise properties of the image. Simulation and experimental results show that the signal-to-noise and contrast-to-noise ratio estimates improve significantly at the smaller window lengths with the two-step processing when compared with the use of a similar sized window in the currently utilized single window method.
The thermodynamic framework of Prigogine, de Groot, and Mazur is extended to study the transport of ions and water in thermoporoelastic materials assuming infinitesimal deformations. New expressions are developed for the first and second principles of nonequilibrium thermodynamics of multicomponent systems and a generalized power balance equation is derived. For porous materials, all the components cannot be treated on a symmetric basis. A Lagrangian framework associated with deformation of the solid phase is introduced and, in this framework, Curie's principle is used to set up the form of the linear constitutive equations describing the transport of ions, water, and heat through the pore network. The material properties entering these equations were recently obtained by Revil and Linde [J. Colloid Interface Science 302 (2006) 682-694] using a volume-averaging approach based in the Nernst-Planck and Stokes equations. This provides a way to relate the material properties entering the constitutive equations to two textural parameters characterizing the topology of the pore space of the material (namely the tortuosity of the pore space and the permeability). The generalized power balance equation is used to derive the linear poroelastic constitutive equations (including the osmotic pressure) to describe the reversible contribution of deformation of the medium in response to ions and water transport through the connected porosity.