Some properties of aqueous xanthan gels formed under the action of aluminium(III) ions

Aqueous xanthan solutions form gels when aluminium salts are added and the solutions are heated above 45 °C. The gelation process was followed by dynamic light scattering. Characterization was based on the heterodyne and nonergodic approaches. Both techniques gave the same fast relaxation times, but for the slow motion much larger values were found in the heterodyne than in the nonergodic approach. The heterodyne fraction 1-X was found to correlate closely with the plateau height of the time correlation function (TCF) at large delay times in the nonergodic experiments. Three methods of gel point determination are demonstrated: (i) onset of heterodyne/nonergodic behavior, (ii) observation of a sharp maximum for the fast relaxation time at the gel point, (iii) observation of power-law behavior of the TCF. The statistics of nonergodic fluctuations were examined and evaluated. The potential of this procedure for detailed structure evaluation of inhomogeneities in the gel is emphasized.     

(Meth)acrylate‐based photoelastomers as tailored biomaterials for artificial vascular grafts

Cardiovascular disease is one of the leading causes of morbidity and mortality in the western hemisphere. Currently available synthetic vascular conduits, like Dacron or ePTFE show excellent long‐term results for large‐caliber arterial reconstruction (aorta, iliac vessels) but when used for small diameter (<4 mm) vessel reconstruction, patency rates are extremely poor. We therefore aim at developing suitable blood vessel substitutes out of biocompatible photopolymer formulations, which can be printed by rapid prototyping. Rapid prototyping offers the possibility to create cellular structures within the grafts that favor the ingrowth of tissue. To meet the high requirements for artificial biomaterials, it is necessary to develop new resin formulations. Beside the biocompatibility, the mechanical properties—a low elastic modulus (500 kPa) at a relatively high tensile strength (1.0 MPa) and a high strain at break (130%)—play a central role. Resin systems containing cyanoethyl acrylate have shown to be highly reactive, have good mechanical properties and sufficient in vitro biocompatibility. Elastic modulus and tensile strength which should be similar to natural blood vessels were adjusted by the ratio of acrylate‐based crosslinkers and—in case of hydrogels —the percentage of water. Finally, we were able to print small diameter conduits by microstereolithography. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2664–2676, 2009     

A quantum-mechanical model for the ionization and excitation of atoms during sputtering

A quantum-mechanical model is developed for the process by which an atom is excited or ionized as it is sputtered from a metal surface. The probability of excitation is given by R = (A/ΔE)²(hv/aΔE)ⁿ, where A is the binding energy of a surface atom before sputtering, v is its average velocity after sputtering, a is the thickness of the surface, and Δ E the excitation energy. For ionization, ΔE = I?φ, with I the ionization energy of the sputtered atom, and φ the work function of tke surface. Available experimental data for ionization are fitted best with a = (1.4 ± 0.3)A?, and n = 2.5 ± 0.3. The model is expected to be applicable to bombarding energies up to about 100 keV.