Advantages of boice reproduction and the development of a biomimetic self-regulating double-clack valve for a prosthesis of the larynx - a feasibility study

The human larynx is a versatile organ. Main functions are phonation, protection and regulation of the air ways. Patients suffer severely from the diagnosis of a laryngeal carcinoma of the stages T3 and T4. In most cases this diagnosis will lead to a total laryngectomy, which is usually dissatisfying in the sense of postoperative rehabilitation. The postoperative consequences include the loss of the native voice, the loss of regular air ways via mouth and nose, sense of smell, and the inability to build up an abdominal pressure. In this paper we focus on the feasibility of a modular larynx prosthesis which enables the laryngectomee to talk with his native voice, to breathe via the regular air ways, and to build up abdominal pressure. In particular we will give insights for a postoperative solution - a modular prosthesis based on a biomimetic self-regulating double clack-valve and on a voice reconstruction module, a so called vocoder. The vocoder is a device to reproduce the natural human voice. Most important for the use is an additional device required to analyze, conserve and manage voice characteristics of the patient before surgery. The self-regulating double clack-valve is designed to build up an abdominal pressure e.g. to cough. Therefore, our valve-system is working in both directions - a two-way valve system. By bridging the gap of the regular air ways lost by laryngectomy, the sense of smell and taste are restored. In the following we will present details and characteristics of these two main components required for a modular prosthesis of the larynx in laryngectomees

Functional gradients in the pericarp of the green coconut inspire asymmetric fibre-composites with improved impact strength, and preserved flexural and tensile properties

Here we investigate the mechanical properties and structural design of the pericarp of the green coconut (Cocos nucifera L.). The pericarp showed excellent impact characteristics, and mechanical tests of its individual components revealed gradients in stiffness, strength and elongation at break from the outer to the inner layer of the pericarp. In order to understand more about the potential effect of such gradients on 'bulk' material properties, we designed simple, graded, cellulose fibre-reinforced polylactide (PLA) composites by stacking layers reinforced with fibres of different mechanical properties. Tensile properties of the graded composites were largely determined by the 'weakest' fibre, irrespective of the fibre distribution. However, a graded design led to pronounced asymmetric bending and impact properties. Bio-inspired, asymmetrically graded composites showed a flexural strength and modulus comparable to that of the strongest reference samples, but the elongation at maximum load was dependent on the specimen orientation. The impact strength of the graded composites showed a similar orientation-dependence, and peak values exceeded the impact strength of a non-graded reference composite containing identical fibre fractions by up to a factor of three. In combination, our results show that an asymmetric, systematic variation of fibre properties can successfully combine desirable properties of different fibre types, suggesting new routes for the development of high-performance composites, and improving our understanding of the structure-function relationship of the coconut pericarp

HF/6-31G ∗ Energy Surfaces for

ABSTRACT: The HF/6-31G ∗ level of theory was used to calculate relaxed potential energy surfaces for 12 analogs of disaccharides. The analogs were made by replacing glucose with tetrahydropyran and fructose with 2-methyltetrahydrofuran. Molecules had zero, one or two anomeric carbon atoms, and di-axial, axial-equatorial, and di-equatorial linkages. Despite the absence of hydroxyl groups, the surfaces account well for conformations that are observed in crystals of the parent disaccharides. Thus, torsional energy and the simple bulk of ring structures are major factors in determining disaccharide conformation. The contour shapes around the global minima depend on the number of anomeric carbons involved in the linkage, while the presence of alternative minima that have relative energies less than 4 kcal/mol mostly requires equatorial bonds. However, molecules with two adjacent anomeric centers gave exceptions to these rules. Flexibility values related to a partition function show that the di-axial trehalose analog is the most rigid. The di-equatorial pseudodisaccharide analog with no anomeric centers is most flexible. Reproduction of these surfaces is proposed as a simple test of force fields for modeling carbohydrates. Also, these surfaces can be used in a simple hybrid method for calculating disaccharide energy surfaces. c ○ 2000 John Wiley &amp

Systematic Assessment of the Photochemical Stability of Photoinitiator-Derived Macromolecular Chain Termini

The photostability of polymeric materials is crucial for their applicability, especially under potentially harsh environmental conditions. In the current study, the influence of methyl-substitution on the photochemical stability of photoinitiator-derived benzoyl end groups is systematically investigated by a combination of pulsed-laser polymerization and subsequent size exclusion chromatography coupled with electrospray ionization mass spectrometry (PLP-SEC-ESI-MS), chemically induced dynamic nuclear polarization-nuclear magnetic resonance spectroscopy (CIDNP-NMR), and density functional theory (DFT) calculations. Poly(methyl methacrylate)s (pMMA) were synthesized employing benzoin-type photoinitiators with systematically substituted benzoyl moieties (i.e., 2-methylbenzoin, 3-methylbenzoin, 4-methylbenzoin, 2,4-dimethylbenzoin, 2,6-dimethylbenzoin, 2,4,6-trimethylbenzoin, 2,3,5,6-tetramethylbenzoin, and 2,3,4,5,6-pentamethylbenzoin). Photoinduced cleavage of the photoinitiator-based end group (irradiation at 351 and 355 nm) occurs solely for polymeric species with benzoyl end groups carrying no or only one ortho-methyl substituent/s, whereas all of the other substitution patterns lead to stable chain termini. The theoretical calculations suggest that the different reactivity can be traced back to shifts of the n-π∗ transitions by approximately +0.25 eV. The current investigation unambiguously evidences that methylation in both ortho-positions of the benzoin-type photoinitiator critically enhances the photostability of the resulting polymer chain termini providing a clear instruction for photoinitiator design leading to polymers with stable chain termini. © 2015 American Chemical Society

Constructing and evaluating energy surfaces of crystalline disaccharides

This paper focuses on the methods used to construct Ramachandran plots for disaccharides. Our recent work based on a hybrid of molecular mechanics and quantum mechanics energies pointed to the need to take extra care when making these maps. Care is also important in the quantitative validation of these energy surfaces with linkage conformations that were determined by crystallography. To successfully predict conformations that have been observed experimentally, the calculation of the energy should include stereoelectronic effects and correctly weight the hydrogen bonding. Technical concerns include the method used to scan the range of conformations, starting geometries, and finding the zero of relative potential energy on a surface where the values were collected at regular intervals. The distributions of observed conformations on energy maps of sucrose, maltose, and laminarabiose at dielectric constants of 1.5 and 7.5 illustrate the effects of an elevated dielectric constant for the MM3 component of the hybrid energy calculations. At dielectric constants of 3.5 and 7.5, the overall average energies of observed conformations of sucrose and seven disaccharides of glucose were less than 1.0 kcal mol �1. The distribution of corresponding energies of the various crystalline conformations conformed well to a Boltzmann-lik