Papers by Keyword: Nacre

Abstract: The surface wettability of biomaterials influences on osteoblast behavior and bone formation. In this research, the variation of wettability of nacre by heat treatments was examined. Plates of the nacre were fabricated from shells of the Akoya pearl oyster. The specimens were heated at 100, 200, 300, 400, 500, and 600 °C. Characterizations of the specimens during and after heat treatments were carried out using scanning electron microscopy, X-ray diffractometry, and thermogravimetry-differential thermal analysis. The water contact angle (WCA) of the specimen was measured to evaluate wettability. The color of nacre changed from iridescent color to brownish weak-iridescence by the heating at and over 300 °C. The nacre heated at and over 300 °C became brittle because organic substances in nacre, which acts as the glue between the aragonite platelets were evaporated by the heating. The WCA of the specimen was decreased with increasing heating temperature, which should be related to the decrease in the number of organic substances in nacre by the heating.

Abstract: This paper investigates the behaviour of a bio-inspired finite element composite model (that mimics the structure of nacre, the inner layer of molluscan shells) under blast loading. Nacre, which has attracted the attention of researchers over the past few decades, comprises 95% aragonite, brittle voronoi-like polygonal tablets that are joined by an organic matrix and arranged in a brick and mortar type structure. In this work, the finite element model developed herein was constructed using voronoi diagrams and geometric algorithms capable of automatically generating staggered layers of voronoi-like aluminium tablets bonded together by a vinylester adhesive layer. Many studies have led to the belief that the magnificent toughness of nacre is mainly attributed to the inter-platelet adhesive bonds. Results obtained from the finite element analysis show that this is indeed true, and it is imperative that the adhesive bond exhibits adequate toughness in order to be able to spread damage across the entire composite, thereby delaying localised failure.

Abstract: Mollusc shells are organic-inorganic composites that are often preserved in the fossil record. However, the way the organic fraction, also called shell matrix, gets fossilized remains an unsolved question, in spite of several old and more recent studies. In the present paper, we have tried to mimic a diagenetic process by constantly heating for ten days at 100°C fresh nacre powder samples of the Polynesian pearl oyster Pinctada margaritifera. Each day, aliquots of nacre powder were sampled and the matrix was subsequently extracted. It was further analysed by direct weigh quantification, by immunological techniques and by proteomics. Our preliminary data suggest that nacre proteins, when heated at 100°C in dry condition, degrade rather slowly. We evidenced a differential degradation pattern of the soluble and insoluble fractions, and showed that some nacre proteins of the insoluble fraction are stable after ten days of heating. Factors that influence the diagenetic stability of some shell proteins are discussed.

Abstract: A literature less traveled – peaking between 1900-1920 – draws on pre-classical concepts of crystal growth and a trove of field biology, to understand ectopic shell production, the natural source of pearls. By 1907, grafts from the calcifying mantle epithelium on gonads induced nacre mineralization consistently in Pinctada margaritifera, suggesting that anomalously displaced, readily specialized cells are at least a sufficient cause of natural pearl formation. Otherwise, the epithelial sacks wrapping natural nacreous pearls must specialize for nacre production independently from the shell producing mantle – an idea supported by experiments with shell regeneration, but not amenable to a method of inducing pearl formation. At the time, chasing epithelial cell migration was technically unfeasible, signalling was news, stemness was fiction. Boldly, Jameson & Rubbel [1902-1912] marshalled natural pearl nuclei and shell repairs as mineral records of cells specializing de novo into the shell’s secretory regimes. Much of this paper reenacts the historic debate on the origin of pearls: thence bold ideas connect smoothly with new work both on bone or shell. I replicate Jameson’s choice of samples and revisit his proposal to search for an “agency [other than the] shell-secreting mechanism“ acting on ”replacement cells” as the origin of pearls. Much has changed: specialized epithelial cells reportedly migrate; non-differentiated cells remain available throughout and near the calcifying mantle epithelium – both, open possibilities for natural pearl nucleation. Interest in understanding the latter now connects with results sketching the signalling cascade in cell specialization toward bone morphogenesis. Replicating Jameson’s choice of samples, I describe the more spectacular structural changes in the mineralization of pearls associated with two instances of cell specialization: toward producing one shell material – in the event of natural pearl nucleation, or switching between two in later pearl growth. Clusters of cells producing distinctly novel mineralization – nacre over fibrous-prismatic aragonite – could be singled out next to natural pearls by Jameson. The possibility has not been probed in roughly a hundred years. Natural pearl nucleation as a cellular event has never been explored.

Abstract: Nacre composing the inner layer of mollusk shell is a typical product of biomineralization. While main components of the organics in nacre are proteins, which mediate its distinctive lamellate structure. Although kinds of nacre proteins have been reported, the whole process of nacre formation is still unclear—especially on molecular level. In this paper, homology, structure, classification and mineralization characters of nacre proteins are elaborated and summarized.

Abstract: Nacreous coatings on orthopedic implants can be advantageous because of its robust mechanical properties, high biocompatibility, and ability to promote bone growth. The biofabrication of nacreous coatings on conventional orthopedic implant materials via biomineralization process from abalone shells was examined. The objective was to investigate the effect of different materials on nacreous coating growth. The coatings were characterized by SEM/EDS and XRD. It was found that different materials resulted in different surface morphologies and coating thicknesses, although the main mineral formed was aragonite. Calcium carbonate coating was formed on the entire surface of the poly (methyl methacrylate) and high density polyethylene implants and resulted in a thick coating, while the titanium implants showed thinner coating at the same growing period.

Abstract: The formation of organic-inorganic hybrid composite with ceramic platelets and polymeric compound can have the higher strength and higher elasticity than metal, which is a nanocomposite with high strength and light weight. Ceramic platelet such as Al₂O₃ has been used to form organic-inorganic composite material using PMMA as an organic polymer. Bending strength and density of the composites prepared by infiltration and post-warm pressing were measured. FE-SEM and TG analysis were carried out to determine the microstructure of the organic-inorganic composite materials. Bending strengths and densities of the composites prepared by Al₂O₃ ceramic plate and PMMA after post-warm pressing were ~70MPa and ranged from 2.4 to 2.6, respectively.

Abstract: Formation of hydroxyapatite (HAp) in simulated body fluid (SBF) on heated nacre has been examined. Nacre is known as composite layer of aragonite platelets and organic materials. Nacre was obtained from the shell of Akoya pearl oyster after removing its prismatic layer. The nacre was heated up to 300°C in air and then soaked in SBF. Nacre heated at 300°C lost iridescent color and became brittle, implying that organic materials which plays a role as glue between aragonite platelets mostly disappeared by heating at 300°C. Formation of HAp particles on nacre in SBF was easier than that on pure Ti. Maximum formation rate of HAp particles was obtained on the nacre heated at 200°C. The amount of HAp particles formed on the nacre heated at 300°C is the smallest. The organic materials in nacre play a critical role for HAp formation on nacre in SBF.

Abstract: Nacre of molluscan shells is famous for its “brick and mortar” microstructure and possesses excellent mechanical properties. Three-point bending strengths of nacre parallel and vertical to the surfaces of platelets are tested and the different fracture surfaces were characterized. The result shows that the values of three-point bending strength in the two directions are approximately the same. Base on the microstructure of and toughening mechanism of nacre, the inspiration for architecture was put forward as follows: to redesign the building materials, toughen the architecture in several ways, and enhance the properties of architecture in all directions. The aim of the paper is to call out learning from nacre to create novel architecture and building materials.

Abstract: Nacre is one of the most attractive biological materials for its superior mechanical property which is mainly due to the “brick-mortar” microstructure. Nacre samples are heated in N₂ atmosphere at 200°C, 400°C and 600°C, separately. The microstructures of the fresh and heated samples are characterized by SEM and XRD, and the three-point bending strengths of these samples are tested by universal mechanical testing machine. TG-DSC curves are performed on the fresh nacre and the demineralized one. The results show that biopolymer plays important roles in maintaining the microstructure, toughening mechanism and the phase transformation of aragonite.