44 research outputs found
The formation and characterization of nanocrystalline phases by mechanical milling of biphasic calcium phosphate/poly-L-lactide biocomposite
Biphasic calcium phosphate/poly-L-lactide granules of 150-200 mu m sizes were subjected to high-energy mechanical milling in a planetary ball mill for up to 480 minutes. Characterization of the material obtained was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), environmentally scanning electronic microscopy (ESEM), transmission electron microscopy (TEM) and infrared spectroscopy (IR). These techniques confirmed that mechanical milling induced significant changes in the biocomposite structure and properties. The most significant changes are reduction of the HAp crystallites size from 99.8 to 26.7 nm and beta-TCP from 97.3 to 29.6, as well as crystallinity of PLLA phases. Homogeneous phase distribution (arrangement) is obtained by extending the duration of mechanical milling
Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.
The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition
Visual Laterality of Calf–Mother Interactions in Wild Whales
Behavioral laterality is known for a variety of vertebrate and invertebrate animals. Laterality in social interactions has been described for a wide range of species including humans. Although evidence and theoretical predictions indicate that in social species the degree of population level laterality is greater than in solitary ones, the origin of these unilateral biases is not fully understood. It is especially poorly studied in the wild animals. Little is known about the role, which laterality in social interactions plays in natural populations. A number of brain characteristics make cetaceans most suitable for investigation of lateralization in social contacts.) in the greatest breeding aggregation in the White Sea. Here we show that young calves (in 29 individually identified and in over a hundred of individually not recognized mother-calf pairs) swim and rest significantly longer on a mother's right side. Further observations along with the data from other cetaceans indicate that found laterality is a result of the calves' preference to observe their mothers with the left eye, i.e., to analyze the information on a socially significant object in the right brain hemisphere.Data from our and previous work on cetacean laterality suggest that basic brain lateralizations are expressed in the same way in cetaceans and other vertebrates. While the information on social partners and novel objects is analyzed in the right brain hemisphere, the control of feeding behavior is performed by the left brain hemisphere. Continuous unilateral visual contacts of calves to mothers with the left eye may influence social development of the young by activation of the contralateral (right) brain hemisphere, indicating a possible mechanism on how behavioral lateralization may influence species life and welfare. This hypothesis is supported by evidence from other vertebrates
Mechanical Influences on Morphogenesis of the Knee Joint Revealed through Morphological, Molecular and Computational Analysis of Immobilised Embryos
Very little is known about the regulation of morphogenesis in synovial joints. Mechanical forces generated from muscle contractions are required for normal development of several aspects of normal skeletogenesis. Here we show that biophysical stimuli generated by muscle contractions impact multiple events during chick knee joint morphogenesis influencing differential growth of the skeletal rudiment epiphyses and patterning of the emerging tissues in the joint interzone. Immobilisation of chick embryos was achieved through treatment with the neuromuscular blocking agent Decamethonium Bromide. The effects on development of the knee joint were examined using a combination of computational modelling to predict alterations in biophysical stimuli, detailed morphometric analysis of 3D digital representations, cell proliferation assays and in situ hybridisation to examine the expression of a selected panel of genes known to regulate joint development. This work revealed the precise changes to shape, particularly in the distal femur, that occur in an altered mechanical environment, corresponding to predicted changes in the spatial and dynamic patterns of mechanical stimuli and region specific changes in cell proliferation rates. In addition, we show altered patterning of the emerging tissues of the joint interzone with the loss of clearly defined and organised cell territories revealed by loss of characteristic interzone gene expression and abnormal expression of cartilage markers. This work shows that local dynamic patterns of biophysical stimuli generated from muscle contractions in the embryo act as a source of positional information guiding patterning and morphogenesis of the developing knee joint
Development of the mouse mandibles and clavicles in the absence of skeletal myogenesis
In this report we employed double-knock-out
mouse embryos and fetuses (designated as Myf5-/-:
MyoD-/- that completely lacked striated musculature to
study bone development in the absence of mechanical
stimuli from the musculature and to distinguish between
the effects that static loading and weight-bearing exhibit
on embryonic development of skeletal system. We
concentrated on development of the mandibles (=
dentary) and clavicles because their formation is
characterized by intramembranous and endochondral
ossification via formation of secondary cartilage that is
dependent on mechanical stimuli from the adjacent
musculature. We employed morphometry and
morphology at different embryonic stages and compared
bone development in double-mutant and control
embryos and fetuses. Our findings can be summarized as
follows: a) the examined mutant bones had significantly
altered shape and size that we described
morphometrically, b) the effects of muscle absence
varied depending on the bone (clavicles being more dependent than mandibles) and even within the same
bone (e.g., the mandible), and c) we further supported
the notion that, from the evolutionary point of view,
mammalian clavicles arise under different influences
from those that initiate the furcula (wishbone) in birds.
Together, our data show that the development of
secondary cartilage, and in turn the development of the
final shape and size of the bones, is strongly influenced
by mechanical cues from the skeletal musculature
Spectral sensitivity of the perch (Perca fluviatilis) from the Danube
In spectral sensitivity studies, electroretinograms (ERG) were recorded from the in situ eyecup of immobilized perch (Perca fluviatilis) electrofished in the floodplain zone of the Danube River. It is shown that the ERG b-wave is a good indicator of spectral sensitivity, although it reflects the activity of photoreceptors indirectly. With a maximum around 542 mm, the scotopic spectral sensitivity of perch obtained using fitted amplitude-log intensity functions for threshold calculation and two models developed in our laboratory for computer-assisted fitting of spectral sensitivity curves did not differ from the sensitivity determined using the microspectrophotometric and isolated pigment methods (maximum around 541 nm)
Mechanochemical synthesis of nanostructured fluorapatite/fluorhydroxyapatite and carbonated fluorapatite/fluorhydroxyapatite
Powder mixture of Ca(OH)(2)-P2O5-CaF2 were milled in planetary ball mill. A carbonated fluorhydroxyapatite, FHA Ca-10(PO4)(1-y)(CO3)(y)(PO4)(5)(OH)(2-2x1)(F)(2x1) was formed after 5 h of milling and carbonated fluoroapatite Ca-10(PO4)(1-y)(CO3)(y)(PO4)(5)(F)(2) was formed after 9 h of milling. Complete transformation of the carbonated form of FA into then single phase of FA occurred after 9 h milling and thermally treating. The various experimental techniques like X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), Infrared Spectroscopy (IR), Transmission Electron Microscopy and Scanning Electron Microscopy (SEM) were used to characterize the synthesized powders and to postulate reaction mechanisms steps- transformations of reactants involved. (C) 2004 Elsevier Inc. All rights reserved