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This paper concerns the role of apoptosis during the onset of bone histogenesis. Previous investigations by us performed on intramembranous ossification revealed the existence of two types of osteogenesis: static (SBF) and dynamic bone formation (DBF). During SBF, the first to occur, stationary osteoblasts transform into osteocytes in the same location where they differentiated, forming the primary spongiosa. DBF takes place later, when movable osteoblastic laminae differentiate along the surface of the primary trabeculae. The main distinctive feature between SBF and DBF is that the latter involves the invasion of pre-existing adjacent tissue, whereas the former does not. To ascertain whether programmed cell death during the invasive DBF process determines the fate of surrounding pre-existing mesenchyme differently from that occurring during the non-invasive SBF process, we studied apoptosis in ossification centres of tibial diaphysis in chick embryos and newborn rabbits with TUNEL and TEM. It emerged that, in both SBF and DBF, apoptosis affects mesenchymal cells located between the forming trabeculae and capillaries. However, apoptotic cells were observed more frequently during DBF than during SBF. This suggests that, during bone histogenesis, apoptosis, which is mostly associated with the invasive process of DBF, is probably dedicated to making space for advancing bone growth.
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PMID:Apoptosis during intramembranous ossification. 1468 94

The classic biomimetic apatite coating process can be accelerated by first immersing substrates into concentrated simulated body fluid, 5x SBF (SBF1), at 37 degrees C, to form an initial coating of precursor apatite spheres, and subsequently transferring to a second 5x SBF (SBF2) solution which is devoid of crystal growth inhibitors to promote phase transformation of SBF1-derived precursor apatite spheres into final crystalline apatite plates. Since SBF1 governs the formation kinetics and composition of the initial precursor spheres, we hypothesized that the pH of the SBF1 solution will also influence the final structure of the SBF2-derived crystalline apatite. To test this hypothesis, polystyrene substrates were immersed into SBF1 with different pH (5.8 or 6.5), and then immersed into the identical SBF2 (pH=6.0). The resultant apatites exhibited similar 2 theta XRD peaks; FTIR spectra in terms of hydroxyl, phosphate and carbonate groups; and Ca/P atomic ratio (1.42 for SBF1(5.8) apatite; 1.48 for SBF1(6.5) apatite). SEM, TEM and electron diffraction show that while SBF1(6.5) (pH 6.5) precursor spheres transform into larger, single crystals plates, SBF1(5.8) (pH 5.8) precursor spheres developed minute, polycrystalline plate-like structures over predominantly spherical precursor substrate.
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PMID:The effect of pH on the structural evolution of accelerated biomimetic apatite. 1511 Apr 83

Porous bioactive resorbable silica-calcium phosphate nanocomposite (SCPC) was prepared by a sintering technique. XRD analyses showed that the main crystalline phases of the SCPC are Na(3)CaPSiO(7) (clinophosinaite), beta-NaCaPO(4) (rhenanite), Na(2)CaSiO(4), and beta-quartz (SiO(2)). The clinophosinaite is a novel cyclosilicate bioactive mineral that enhanced the mechanical and bioactivity properties of the SCPC. TEM analysis showed that the grain sizes of the multiphase SCPC are in the nanometer scale. Moreover, the SCPC was engineered with nano- and microscale porosity. The SCPC had significantly higher compressive strength than porous hydroxyapatite (HA). FTIR analyses revealed the formation of biological hydroxyapatite layer on the SCPC surface after 4 days of immersion in SBF. When SCPC was loaded with rhBMP-2, it provided a superior release profile of biologically active rhBMP-2 compared to porous HA. Bone-marrow cells incubated with medium treated with the rhBMP-2 released from the SCPC-rhBMP-2 hybrid expressed significantly higher alkaline phosphatase activity than that expressed by cells incubated with media treated with rhBMP-2 released from HA-rhBMP-2. In addition, cells attached to the SCPC-rhBMP-2 hybrid produced mineralized extracellular matrix (ECM) and bone-like tissue that covered the material surface and filled pores in the entire thickness of the template after 3 weeks in culture. In contrary, cells attached to the HA-rhBMP-2 produced limited amount of unmineralized ECM after the same time period. Results of the study strongly suggest that the porous bioactive silica-calcium phosphate nanocomposite can serve as a delivery system for cells and biological molecules. The SCPC-rhBMP-2-marrow cell hybrid may serve as an alternative to autologous bone grafting.
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PMID:Cyclosilicate nanocomposite: a novel resorbable bioactive tissue engineering scaffold for BMP and bone-marrow cell delivery. 1547 Jul 21

Chitosan/nano-hydroxyapatite composites with different weight ratios were prepared through a co-precipitation method using Ca(OH)(2), H(3)PO(4) and chitosan as starting materials. The properties of these composites were characterized by means of TEM, IR, XRD, burn-out test and universal matertial test machine. Additionally, in vitro tests were also conducted to investigate the biodegradability and bioactivity of the composite. The results showed that the HA synthesized here was poorly crystalline carbonated nanometer crystals and dispersed uniformly in chitosan phase and there is no phase-separation between the two phases. Because of the interactions between chitosan and n-HA, the mechanical properties of these composites were improved, and the maximum value of the compressive strength was measured about 120 MPa corresponding to the chitosan/n-HA composite with a weight ratio of 30/70. The specimens made of 30/70 chitosan/n-HA composite exhibit high biodegradability and bioactivity when being immersed in SBF solutions. The composite is appropriate to being used as scaffold materials for bone tissue engineering. (c) Springer Science + Business Media, Inc.
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PMID:Preparation and in vitro investigation of chitosan/nano-hydroxyapatite composite used as bone substitute materials. 1574 12

Hydroxyapatite and 'duplex' hydroxyapatite + titania bond coat layers were deposited onto Ti6Al4V substrates by atmospheric plasma spraying (APS) at moderate plasma enthalpies. From as-sprayed coatings and coatings incubated in simulated body fluid (r-SBF) electron-transparent samples were generated by focused ion beam (FIB) excavation and investigated by STEM/TEM in conjunction with energy-dispersive X-ray analysis (EDX), electron diffraction (ED), and electron energy loss spectroscopy (EELS). Adjacent to the metal surface a thin layer of amorphous calcium phosphate (ACP) was deposited whose Ca/P ratio is determined by the presence or absence of the bond coat. No clear indication of a Ca-Ti oxide reaction layer was found at the interface titania bond coat/calcium phosphate. After in vitro incubation of duplex coatings for 24 weeks Ca-deficient defect apatite needles precipitated from ACP. During incubation of hydroxyapatite without a bond coat for 1 week diffusion bands were formed within the ACP of 1-2 microm width parallel to the interface metal/coating, presumably by a dissolution-precipitation sequence.
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PMID:Formation and transformation of amorphous calcium phosphates on titanium alloy surfaces during atmospheric plasma spraying and their subsequent in vitro performance. 1613 52

The apatite forming ability of biopolymer bacterial cellulose (BC) has been investigated by soaking different BC specimens in a simulated body fluid (1.5 SBF) under physiological conditions, at 37 degrees C and pH 7.4, mimicking the natural process of apatite formation. From ATR-FTIR spectra and ICP-AES analysis, the crystalline phase nucleated on the BC microfibrils surface was calcium deficient carbonated apatite through initial formation of octacalcium phosphate (OCP) or OCP like calcium phosphate phase regardless of the substrates. Morphology of the deposits from SEM, FE-SEM, and TEM observations revealed the fine structure of thin film plates uniting together to form apatite globules of various size (from <1 mum to 3 mum) with respect to the substrates. Surface modification by TEMPO (2,2,6,6-tetramethylpyperidine-1-oxyl)-mediated oxidation, which can readily form active carboxyl functional groups upon selective oxidation of primary hydroxyl groups on the surface of BC microfibrils, enhanced the rate of apatite nucleation. Ion exchanged treatment with calcium chloride solution after TEMPO-mediated oxidation was found to be remarkably different from other BC substrates with the highest deposit weight and the smallest apatite globules size. The role of BC substrates to induce mineralization rate differs according to the nature of the BC substrates, which strongly influences the growth behavior of the apatite crystals.
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PMID:Surface functional group dependent apatite formation on bacterial cellulose microfibrils network in a simulated body fluid. 1711 6

Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO(3)(-) concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (002) diffraction line at 2theta=26 degrees compared to the 100% intensity peak of the (211) plane at 2theta=32 degrees . The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO(3)(-) concentration of 5 mmol/l to 19 nm in SBF27 with a HCO(3)(-) concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO(3)(-) content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca(10-x-y)Mg(y)(HPO(4))(x-z)(CO(3))(z)(PO(4))(6-x)(OH)(2-x-w)(CO(3))(w/2). According to FTIR and Raman analyses, it can be supposed that as long as the HCO(3)(-) concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0<z<1; w=0) precipitates. At higher HCO(3)(-) concentration, it can be assumed that AB-type HCA (z=1;0<w<1) is formed.
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PMID:Biomimetic apatite coatings--carbonate substitution and preferred growth orientation. 1785 64

In this study, a high glass forming system, Ti41.5Zr2.5Hf5Cu37.5Ni7.5Si1Sn5 (TZHCNSS) bulk metallic glass (BMG), is studied in terms of microstructure, surface analysis, mechanical properties, corrosion resistance, in vitro cytotoxicity and in vivo biocompatibility. It is found that the as-prepared TZHCNSS samples are fully amorphous by XRD and TEM observations, as well as DSC curve. Comparing with pure Ti, TZHCNSS BMG shows superior mechanical properties with higher hardness and better wear resistance. Due to the oxide film formed on its surface, TZHCNSS BMG shows great corrosion resistance close to pure Ti in electrochemical measurements. The pitting corrosion potential in artificial saliva solution is much higher than that in SBF solution. The indirect and direct cytotoxicity results show that TZHCNSS extracts had obvious low cell viability on both L929 and NIH3T3 cells. However, the in vivo testing results proved that TZHCNSS BMG could integrate with bone tissue, showing excellent osseointegration.
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PMID:In vitro and in vivo studies on Ti-based bulk metallic glass as potential dental implant material. 2370 38

The objective of the present study is to investigate the influence of surface modification on systemic stability of NPs. Vitamin E TPGS (1% w/v) was used for surface modification of berberine chloride nanoparticles. Naked and surface modified NPs were incubated in different SBFs (pH 6.8 and 7.4) with or without bile salts and human plasma. NPs were observed for particle agglomeration and morphology by particle size analyzer and TEM, respectively. The haemocompatibility studies were conducted on developed NPs to evaluate their safety profile. The surface modified NPs were stable compared to naked NPs in different SBFs due to the steric stabilization property of vitamin E TPGS. Particle agglomeration was not seen when NPs were incubated in SBF (pH 6.8) with bile salts. No agglomeration was observed in NPs after their incubation in plasma but particle size of the naked NPs increased due to adhesion of plasma proteins. The TEM images confirmed the particle size results. DSC and FT-IR studies confirmed the coexistence of TPGS in surface modified NPs. The permissible haemolysis, LDH release, and platelet aggregation revealed that NPs were compatible for systemic administration. Thus, the study illustrated that the surface modification is helpful in the maintenance of stability of NPs in systemic conditions.
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PMID:Investigations on agglomeration and haemocompatibility of vitamin E TPGS surface modified berberine chloride nanoparticles. 2516 37

Lithium modified bioactive glass nanoparticles were prepared for multiple deliveries of lithium ions and drugs. The particle size, structure and thermal behavior of nanoparticles were analyzed using TEM, FTIR and DSC respectively. The porosity% and specific surface area of glass nanoparticles were about 68.6% and 224.92 (m(2)/g), respectively. The in vitro bioactivity evaluation in SBF revealed that glass nanoparticles were capable of inducing apatite layer over their surfaces. This could be considered as a good indicator for their future abilities to regenerate bone tissue in vivo. Also, lithium ions were released from glass nanoparticles via diffusion controlled process which could activate Wnt signaling pathway and enhance osteogenesis. As a final point, the possibility of utilizing the glass nanoparticles as a controlled delivery device for vancomycin or 5-FU was verified. Fitting vancomycin or 5-FU release profiles to various mathematical models pointed out that both drugs were released by a diffusion-controlled mode.
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PMID:Bioactive glass nanoparticles designed for multiple deliveries of lithium ions and drugs: Curative and restorative bone treatment. 2715 53


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