Razi Vago

Hard tissue remodeling using biofabricated coralline biomaterials.

Biotechnical and biomedical approaches were combined in an attempt to identify potential uses of biofabricated marine carbonate materials in biomedical applications, particularly as biomatrices for remodeling bone and cartilage tissue. After grafting, it is desirable for bone ingrowth to proceed as quickly as possible because the strength of the implanted region depends on a good mechanical bond forming between the implant and surrounding regions in the body. Ingrowth can take place as a result of growth of tissue and cells into the implanted porous material, or it may be promoted by transplanting cells seeded onto such a material. The rate at which ingrowth occurs is dependent on many factors, including pore size and the interconnectivity of the implanted structure. In vivo graftings into osteochondral defects demonstrated that our biofabricated porous material is highly biocompatible with cartilage and bone tissue. The biofabricated matrix was well incorporated into the biphasic osteochondral area. Resorption was followed by bone and cartilage formation, and after 4 months, the biomaterial had been replaced by new tissue. Ossification was induced and enhanced without introduction of additional factors. We believe that this is the first time that such biofabricated materials have been used for biomedical purposes. In face of the obvious environmental disadvantages of harvesting from limited natural resources, we propose the use of bioengineered coralline and other materials such as those cultured by our group under field and laboratory conditions as a possible biomatrix for hard tissue remodeling.

Hyaluronan and mesenchymal stem cells: from germ layer to cartilage and bone.

A simple, linear polysaccharide with unique molecular functions, hyaluronan is a glycosaminoglycan whose biomechanical and hydrodynamic properties have been thoroughly characterized. However, the exact role the molecular mechanisms and signaling pathways of hyaluronan play in the regulation of stem cell fate, such as self-renewal and differentiation, remains to be determined. The abundance of hyaluronan in embryonic tissues indicates that it is highly important in developmental processes. Recent studies have focused on understanding the mechanisms of hydrated hyaluronan action and its interaction with neighboring substances. This review is an attempt to elucidate the complex role of hyaluronan signaling in the initialization and regulation of developmental processes, particularly in events dictating the fates of mesenchymal stem cells during the organogenetic phases of chondrogenesis and osteogenesis.

Life is three dimensional-as in vitro cancer cultures should be.

For many decades, fundamental cancer research has relied on two-dimensional in vitro cell culture models. However, these provide a poor representation of the complex three-dimensional (3D) architecture of living tissues. The more recent 3D culture systems, which range from ridged scaffolds to semiliquid gels, resemble their natural counterparts more closely. The arrangement of the cells in 3D systems allows better cell-cell interaction and facilitates extracellular matrix secretion, with concomitant effects on gene and protein expression and cellular behavior. Many studies have reported differences between 3D and 2D systems as regards responses to therapeutic agents and pivotal cellular processes such as cell differentiation, morphology, and signaling pathways, demonstrating the importance of 3D culturing for various cancer cell lines.

A computerized tank system for studying the effect of temperature on calcification of reef organisms.

Mediated by algal symbionts, calcification in reef building corals is one of the important processes, which enable corals growth. In the present study, we used a buoyant weighing technique to study calcification of two coralline species, Stylophora pistillata and the hydrocoral Millepora dichotoma. The colonies were grown in a tank system, in which light, nutrition and water motion were kept constant and temperature was elevated by means of a computerized controlled apparatus. An almost constant rate of calcification was observed in the two species at 22-28 degrees C. Elevation of the temperature above this range to 29-31 degrees C caused a slow down in calcification in both species. A grater number of S. pistillata colonies became bleached at temperatures of >or=29 degrees C, whereas M. dichotoma colonies suffered from bleaching only after three days at 31 degrees C. For both species, control groups, remained viable during the experimental period. The differences in responses to changes in temperature of the two species may be as a consequence of different adaptive mechanisms or to different susceptibilities of the corals to elevated temperatures. We have shown that elevating temperatures above annual maximal ranges have a significant effect on coral calcification. We also demonstrated that sessile calcified marine organisms having ecological and biomedical significance could be cultured and manipulated under laboratory conditions.

Colony architecture of Millepora dichotoma Forskal

Abstract In the Gulf of Elat, the hydrozoan coral, Millepora dichotoma Forskal exhibits four main morphotypes: encrusting, delicate lace-like, leaf-like bladed and robust “box-work”. The distribution of these morphotypes was found to vary with depth and between locations. The encrusting form was found in all sites and appeared to be the initial growth form adopted by M. dichotoma . The distribution of the other three growth forms suggested that further development from the encrusting form depends upon environmental conditions. The encrusting form was found at all sites but was dominant in highly energetic environments. The lace-like form develops from the encrusting form in low energy environments. In somewhat higher energy environments, repeated damage to the lace-like form moves development towards the bladed growth form and the box-work growth form. A model of this development is presented in which critical factors controlling the development of the different growth forms are sediment levels and damage to colonies. Both of these factors are linked with levels of turbulence in particular environments.

Beyond the skeleton: Cnidarian biomaterials as bioactive extracellular microenvironments for tissue engineering.

Biomaterials play a pivotal role as scaffolding materials in the study of three-dimensional (3D) cell and tissue development and in a variety of bioengineering strategies for the restoration of damaged and malfunctioning tissues. Both in vitro and in vivo (e.g. cell-based therapies) bioengineering strategies deliver cells or a mixture of cells and signaling factors to a target tissue together with an acellular scaffolding material that triggers tissue ingrowth and regeneration. Bioengineering strategies in which tissue-like constructs are produced under controlled conditions are based on 3D lattices as vehicles for the cells that regenerate into the required tissues. Fabrication of engineered tissue is a complicated task, since tissue function is controlled by complex spatially and temporally ordered cues, each of which is the product of a myriad of cell-to-cell and cell-to-extracellular matrix (ECM) interactions.

The role of aragonite matrix surface chemistry on the chondrogenic differentiation of mesenchymal stem cells.

In the present research we study the effects of surface chemistry of an aragonite crystalline biomatrix on the chondrogenesis of mesenchymal stem cells (MSCs). An aragonite matrix obtained from the coral Porites lutea and a gold-coated P. lutea matrix were seeded with MSCs, with and without the addition of growth factors (GFs). Scanning electron microscopy, histochemical staining, immunofluorescence, biochemical analyses and quantitative polymerase chain reaction showed that the chemistry of the matrix influenced the differentiation process of the MSCs. The calcium carbonate composition of the coral promoted osteogenesis, while impeding cell-material contact (by gold coating) altered the differentiation lineage of MSCs towards chondrogenic fate. Supplementation of the culture medium with GFs intensified the influence of the surface composition on the differentiation of MSCs, and the synergistic effect of the biomatrix surface composition and the GFs induced chondrogenesis and facilitated maintenance of the chondrocyte phenotype. Therefore, we suggest that scaffolding material candidates for tissue engineering should be examined for their effects on the MSCs differentiation process and their effect on signal transduction events in the cells.

Aragonite crystalline matrix as an instructive microenvironment for neural development

The ability to mimic cell–matrix interactions in a way that closely resembles the natural environment is of a great importance for both basic neuroscience and for fabrication of potent scaffolding materials for nervous tissue engineering. Such scaffolding materials should not only facilitate cell attachment but also create a microenvironment that provides essential developmental and survival cues. We previously found that porous aragonite crystalline matrices of marine origin are an adequate and active biomaterial that promotes neural cell growth and tissue development. Here we studied the mechanism underlying these neural cell–material interactions, focusing on the three‐dimensional (3D) surface architecture and matrix activity of these scaffolds. We introduced a new cloning technique of the hydrozoan Millepora dichotoma, through which calcein or 45Ca2+ were incorporated into the organisms growing skeleton and neuronal cells could then be cultured on the labelled matrices. Herein, we describe the role of matrix 3D architecture on neural cell type composition and survival in culture, and report for the first time on the capacity of neurons and astrocytes to exploit calcium ions from the supporting biomatrix. We found that hippocampal cells growing on the prelabelled aragonite lattice took up aragonite‐derived Ca2+, and even enhanced this uptake when extracellular calcium ions were chelated by EGTA. When the aragonite‐derived Ca2+ uptake was omitted by culturing the cells on coral skeletons coated with gold, cell survival was reduced but not arrested, suggesting a role for matrix architecture in neural survival. In addition, we found that the effects of scaffold architecture and chemistry on cell survival were more profound for neurons than for astrocytes. We submit that translocation of calcium from the biomaterial to the cells activates a variety of membrane‐bound signalling molecules and leads to the subsequent cell behaviour. This kind of cell–material interaction possesses great potential for fabricating advanced biomaterials for neural tissue‐engineering applications. Copyright

The structural, compositional and mechanical features of the calcite shell of the barnacle Tetraclita rufotincta.

The microstructure and chemical composition of the calcite shell of the sea barnacle Tetraclita rufotincta (Pilsbry, 1916) were investigated using microscopic and analytical methods. The barnacle shell was separated mechanically into its three substructural units: outer, interior, and inner layers. The organic matrices of these structural parts were further separated into soluble and insoluble constituents and their characteristic functional groups were studied by FTIR. Investigation of the mechanical properties of the interior mass of the shell reveals remarkable viscoelastic behavior. In general, the mechanical behavior of the shell is a function of its geometry as well as of the material, of which it is constructed. In the case of T. rufotincta, as calcite is a brittle material, the elastic behavior of the shell is apparently related to its micro- and macroarchitecture. The latter enables the shell to fulfill its primary function which is to protect the organism from a hostile environment and enables its survival. Our detailed identification of the similarities and differences between the various structural components of the shell in regard to the composition and properties of the organic component will hopefully throw light on the role of organic matrices in biomineralization processes.

Skeletal architecture and microstructure of the calcifying coral Fungia simplex

This study presents the characterization of the skeletal structure of the coral Fungia simplex, a hermatypic resident of the shallow zones of tropical reefs. In contrast to most cnidarians, this species has a unique multi-septal skeletal architecture. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed the skeletal microstructure to be made up of bundles of thin needles of prismatic crystals. X-ray diffraction (XRD) indicated that the crystals are composed of aragonite with a preferred orientation exposing the {221} planes parallel to the septal surface and tilted by 20° with respect to the growth (c-) direction.