It was assumed for a long time that organisms produce minerals directly from a saturated solution. A few exceptions were known, including the well documented mineralized teeth of the chiton. In 1997 it was demonstrated that sea urchin larva form their calcitic spicules by first depositing a highly unstable mineral phase called amorphous calcium carbonate. This strategy has since been shown to be used by animals from other phyla and for both aragonite and calcite. Recent evidence shows that vertebrate bone mineral may also be formed via a precursor phase of amorphous calcium carbonate. This strategy thus appears to be widespread. The challenge now is to understand the mechanisms by which these unstable phases are initially formed, how they are temporarily stabilized and how they are destabilized and transform into a crystalline mature product.
Biomineralization processes result in organic/inorganic hybrid materials with complex shapes, hierarchical structures, and superior material properties. Recent developments in biomineralization and biomaterials have demonstrated that calcium phosphate particles play an important role in the formation of hard tissues in nature. In this paper, current concepts in biomineralization, such as nano assembly, biomimetic shell structure, and their applications are introduced. It is confirmed experimentally that enamel- or bone-liked apatite can be achieved by oriented aggregations using nano calcium phosphates as starting materials. The assembly of calcium phosphate can be either promoted or inhibited by different biomolecules so that the kinetics can be regulated biologically. In this paper, the role of nano calcium phosphate in tissue repair is highlighted. Furthermore, a new, interesting result on biomimetic mineralization is introduced, which can offer an artificial shell for living cells via a biomimetic method.
Implant medical research and tissue engineering both target the design of novel biomaterials for the improvement of human health and clinical applications. In order to develop improved surface coatings for hard tissue (bone) replacement materials and implant devices, we are developing micropatterned coatings consisting of polymer brushes. These are used as organic templates for the mineralization of calcium phosphate in order to improve adhesion of bone cells. First, we give a short account of the current state-of-the-art in this particular field of biomaterial development, while in the second part the preliminary results of cell culture experiments are presented, in which the biocompatibility of polymer brushes are tested on human mesenchymal stem cells.
Tissue engineering is a multidisciplinary research area that aims to develop new techniques and/or biomaterials for medical applications. The objective of the present study was to evaluate the osteogenic potential of a composite of hydroxyapatite and alginate in bone defects with critical sizes, surgically made in the calvaria region of rats. The rats (48 adult males),
Biomimetic techniques are used to produce biomimetic coatings that were made on medical devices with layers of calcium phosphate. This procedure was done under more physiological or “biomimetic” conditions of temperature and pH primarily to improve their biocompatibility and biodegradability. The mineral layers generated by biomimetic methods are comparable to biological mineral, which can be used for tissue engineering and can be degraded within a biological milieu.
The biomimetic coating technique involves the nucleation and growth of bone-like crystals upon a pretreated substrate by immersing this in a supersaturated solution of calcium phosphate under physiological conditions of temperature (37°C) and pH (7.4). The method, originally developed by Kokubo in 1990 has since undergone improvement and refinement by several groups of investigators.
Biomimetic coatings are valuable in that they can serve as a vehicle for the slow and sustained release of osteogenic agents at the site of implantation. This attribute is rendered possible by the near-physiological conditions under which these coatings are prepared, which permits an incorporation of bioactive agents into the inorganic crystal latticework rather than merely their superficial adsorption onto preformed layers. In addition, the biomimetic coating technique can be applied to implants of an organic as well as of an inorganic nature and to those with irregular surface geometries, which is a not possible using conventional methodologies.
The majority of the mineral phase of the
Carbon nanotubes (CNT) have a unique structure and feature. In the present study, cell proliferation was performed on the scaffolds of single-walled CNTs (SWCNT), multiwalled CNTs (MWCNT), and on graphite, one of the representative isomorphs of pure carbon, for the sake of comparison. Scanning electron microscopy observation of the growth of osteoblast-like cells (Saos2) cultured on CNTs showed the morphology fully developed for the whole direction, which is different from that extended to one direction on the usual scaffold. Numerous filopodia were grown from cell edge, extended far long and combined with the CNT meshwork. CNTs showed the affinity for collagen and proteins. Proliferated cell numbers are largest on SWCNTs, followed by MWCNTs, and are very low on graphite. This is in good agreement with the sequence in the results of the adsorbed amount of proteins and expression of alkaline phosphatase activity for these scaffolds. The adsorption of proteins would be one of the most influential factors to make a contrast difference in cell attachment and proliferation between graphite and CNTs, both of which are isomorphs of carbon and composed of similar graphene sheet crystal structure. In addition, the nanosize meshwork structure with large porosity is another property responsible for the excellent cell adhesion and growth on CNTs. CNTs could be the favorable materials for biomedical applications.
The morphological features of tooth enamel and enameloid in actinopterygian fish are reviewed to provide basic data concerning the biomineralization of teeth in lower vertebrates. Enameloid, which covers the tooth surface, is a unique well-mineralized tissue and usually has the same functions as mammalian tooth enamel. However, the development of enameloid is different from that of the enamel produced by dental epithelial cells. Enameloid is made by a combination of odontoblasts and dental epithelial cells. An organic matrix that contains collagen is provided by odontoblasts, and then dental epithelial cells dissolve the degenerate matrix and supply inorganic ions during advanced crystal growth in enameloid. It is likely that enameloid is a good model for studying the growth of well-mineralized hard tissues in vertebrates. Some actinopterygian fish possess a collar enamel layer that is situated at the surface of the tooth shaft, indicating that the origin of tooth enamel is found in fish. Collar enamel is thought to be a precursor of mammalian enamel, although it is thin and not well mineralized in comparison with enameloid. In
CAP-1 is a cuticle peptide isolated from the acid-insoluble fraction of the exoskeleton of the crayfish
As the carrier of biomineral aragonite, fish otoliths memorize various messages of environment throughout the fish’s life. In the past three decades, quite a few achievements have been made in the studies of fish otoliths, but no advances in research using medical instruments have been reported. The authors tentatively applied X-ray computed tomography (CT) to the studies of the internal structure of wild carp otoliths, with the CT value determined by variations in the sample density and element composition. The wild carps were collected, respectively, from the Baiyangdian Shallow Lake in Hebei Province and Miyun Reservoir in the Beijing metropolis, whose water environments are quite different. The former has suffered serious pollution and eutrophication, whereas the latter has nearly experienced no pollution. The primary result indicates that differences exists in CT values of otoliths for the carps from the above-mentioned waters. With in-depth studies, it is possible that X-ray computed tomography could serve as a useful tool in the study of fish otoliths, and the CT values can be taken as typomorphic parameters to distinguish the waters with different degrees of pollution.
Polypyrrole/multiwalled carbon nanotube (MWNT) composite films were electrochemically deposited in the presence of an ionic surfactant, sodium dodecyl sulfate (SDS), acting as both supporting electrolyte and dispersant. The effects of the surfactant and the MWNT concentrations on the structure of the resulting composite films were investigated. The electrochemical behavior of the resulting polypyrrole/MWNT composite film was investigated as well by cyclic voltammogram. The effect of the additional alternating electric field applied during the constant direct potential electrochemical deposition on the morphology and electrochemical behavior of the resulting composite film was also investigated in this study.
The Tersoff-potential based MD (molecular dynamics) method was used to simulate the radial compression of one (10,0) BN nanotube, and its compressive properties was compared with those of one (10,0) carbon nanotube. The semi-empirical PM3 QC (Quantum chemistry) method was adopted to calculate the electronic structures of the compressed BN-tube, and the effect of the radial compression on the electronic structures of the BN-tube was discussed. It is shown that (i) BN-tube has comparable radial compressive stiffness to carbon-tube, but lower energy-absorbing, load-support and deformation-support capabilities, and (ii) with the increase of compressive strain, the HOMO energy of the BN-tube increases, the LUMO energy and the LUMO-HOMO energy-gap decrease, and its chemical activity and conductance increase.
The simplified one-dimensional dislocation equation for mixed dislocations is derived briefly from the two-dimensional modified Peierls-Nabarro equation taking into account the discreteness effect of crystals. The collinear dissociated core structure of <111>{110} superdislocations in the novel B2 structure YAg and YCu are investigated with the simplified equation. Both the core width and the dissociated width are increasing with the increases in the dislocation angle of superdislocations. The dissociated width determined by continuum elastic theory is inaccurate for the high antiphase boundary energy but is recovered for the low antiphase boundary energy. The Peierls stress of the dissociated dislocation is replaced by that of superpartials. The results show that both the unstable stacking fault energy and the core width are crucial for the Peierls stress in the case of a narrow core structure. However, the core width becomes the main factor in controlling the Peierls stress in the case of a wide core.
In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera, and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welding arc, which would increase the depth of penetration as the incensement of the arc force. Several principal parameters including the distance of twin wires intersecting point to base metal, the included angle, and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased, the arc turned brighter while unobvious change of penetration occurred as the arc voltage increased, and the deepest penetration was obtained when the welding speed was 10.5 mm/s.
The fracture behavior of the diamond single crystals with metallic inclusions was investigated in the present paper. Single diamond crystals with metallic inclusions were formed by a special process with high pressure and high temperature (HPHT). The inclusions trapped in the diamond were characterized mainly to be metallic carbide of (Fe,Ni)23C6 or Fe3C and solid solution of γ-(Fe,Ni) by transmission electronic microscopy (TEM). The grain size of the inclusions is about micrometers. The fracture characteristics of the diamond single crystals, after compression and heating, were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The fracture sections of the compressed and heated diamonds were found to be parallel to the (111) plane. The interface of the inclusions and diamond is deduced to be the key factor and the original region of the fracture formation. Mechanisms of the fracture behavior of the HPHT synthesized diamonds are discussed.