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.

Advantages of voice 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.