Alain Couté

Multi-Scale Structure and Growth of Nacre: A New Model for Bioceramics

Nacre is the internal lustrous ‘mother of pearl’ layer of many molluscan shells. The structure is a brick and mortar arrangement: the bricks are fla t po ygonal crystals of aragonite and the mortar consists of organic compounds.The biological mineralization of composites such as the molluscan shell has generally been thought to be directed by preformed ganic arrays of proteins or others biopolymers.The possibility that the organic matrix behaves as a template for crystal formation by heteroepitaxial growth, is examined. The structure and g rowth of nacre of Pinctada margaritifera and Pinctada maxima are studied at different scales.We propose a new model in nacre growth and maturation. Understanding the molecular mechanisms that reg ulate biomineralization may thus provide practical routes to the synthesis of new high-performance composite m aterials. Nacreous shell growth was studied by electron microscopy after fi xation of immature nacre. It shows that the first step in crystal formation takes place in a biofilm, as evidenced by Laser Raman Spectroscopy.This biofilm is composed of organic matrix and cal cium carbonate in the aragonite crystal form. Crystalin nuclei grow in the biofilm as an aligned sequence, starting with a row of intitial nucleation centres, gradually increasing concentric ally in size and fusing together to form polygons in the next highest nacreous level. In Pinctada biomineralization takes place in a biopolymer that has the ability to initiate nucleation and to control orientation in the aragonite crystal form and growth. Al so is stressed the existence of several levels or steps of mineralization, simultaneously, as a ke y mechanism for the thickening of the shell. This natural bioceramic is studied with the aim of using it as a biomater ial in bone repair. Introduction The active role of proteins in biomineralization is fundamental [1-3]. It represents a source of inspiration for future nanotechnology with a bottom-up approach. The brick and mor tar ordering of nacre has already inspired the toughening of ceramic materials by co-processing rigid ceramic as silicon carbide and supple interlayers as boron nitride [4]. The interdigitating brickwork array of tablets, specific, in bivalve s (“sheet nacre”) is not the only interesting aspect of nacre structure. The bio-crystal itse f is a composite. It has not only the mineral structure of aragonite but possesses intracristalline or ganic material [5]. Among others Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 1009-1012 doi:10.4028/www.scientific.net/KEM.254-256.1009

Cyanophyceae (Cyanobacteria) aérophiles de Nouvelle-Calédonie

Abstract This paper deals with the aerophytic Cyanophyceae from New Caledonia sampled by Prof. Dr A. Guillaumin from Paris, Dr M.G. Baumann-Bodenheim from Zurich, Dr H. Hurlimann from Winterthur and Prof. Baas Becking from Noumea. A total of 124 samples were studied, most of them collected on soil, stones, rocks and barks. The characteristics of these samples are given. Among species, varieties and forms, a total of 85 taxa were recorded. Among them three are new for science, Gloeothece neocaledoniense nov. sp., Hydrocoryne neocaledonica nov. sp. and Scytonematopsis neocaledoniense nov. sp. One new combination is proposed, Petalonema involvens var. elongata (Bourr.) nov. comb.

Direct and indirect toxic effects of cotton-derived cellulose nanofibres on filamentous green algae

Recently, cellulose nanofibers (CNFs) have attracted considerable attention as natural, abundant polymers with excellent mechanical properties and biodegradability. CNFs provide a new materials platform for the sustainable production of high-performance nano-enable products for various applications. Given the increasing rates of CNF production, the potential for their release to the environment and the subsequent impact on ecosystem is becoming an increasing concern that needs to be addressed. Here, we used the Klebsormidium flaccidum as a bioindicator organism of terrestrial and freshwater habitats pollution using a battery of biomarkers. Our results show that cotton CNFs inhibit the proliferation of algae and induce morphological changes in them. The two main toxicity mechanisms induced by cotton CNFs are: (i) a direct contact of CNFs with the cell wall and cellular membrane and (ii) an indirect effect through the generation of reactive oxygen species (ROS).

The genus Kirchneriella Schm. (Chlorophyceae) in Argentina: Taxonomy and geographic distribution

Abstract This note deals with the taxonomic study and geographic distribution of the genus Kirchneriella Schm. in Argentina, where species and infraspecific taxa have received little attention. The classification of taxa is based on morphological and morphometric characters. Thirteen species and three varieties are recorded, among them K. contorta var. elegans (Playf.) Kom., K. danubiana Hind., K. irregularis var. spiralis Korš. and K. obtusa (Korš.) Kom. are new records for Argentina.

Pearsoniella variabilis Fritsch et Rich (Chlorophyta) en France: description et données autoécologiques

Abstract Pearsoniella variabilis Fritsch et Rich (Chlorophyta) in France: description and autoecology data. The genus Pearsoniella (Ulvophyceae, Ulotrichales, Ulotrichaceae) described by Fritsch & Rich (1924) from South Africa includes one known species: P. variabilis. It is herein recorded for the first time in France, in a part of Durance river. The ring-shaped morphology of chloroplasts is a characteristic feature of the genus and justifies its distinction from other genera of the Ulotrichaceae such as Ulothrix.