Adsorption of Enamel Matrix Proteins to a Bovine Derived Bone Grafting Material and its Regulation of Cell Adhesion, Proliferation and Differentiation

The use of various combinations of enamel matrix derivative (EMD) and grafting materials has been shown to promote periodontal wound healing/regeneration. However, the downstream cellular behavior of periodontal ligament (PDL) cells and osteoblasts has not yet been studied. Furthermore, it is unknown to what extent the bleeding during regenerative surgery may influence the adsorption of exogenous proteins to the surface of bone grafting materials and the subsequent cellular behavior. In the present study, the aim is to test EMD adsorption to the surface of natural bone mineral (NBM) particles in the presence of blood and determine the effect of EMD coating to NBM particles on downstream cellular pathways, such as adhesion, proliferation, and differentiation of primary human osteoblasts and PDL cells.

Effect of external electric field on hydrogen adsorption over activated carbon separated by dielectric materials

Energy crisis and worldwide environmental problem make hydrogen a prospective energy carrier. However, storage and transportation of hydrogen in large quantities at small volume is currently not practical. Lots of materials and devices have been developed for storage hydrogen, but to today none is able to meet the DOE targets. Activated carbon has been found to be a good hydrogen adsorbent due to its high surface area. However, the weak van der Waals force between hydrogen and the adsorbent has limited the adsorption capacity. Previous studies have found that enhanced adsorption can be obtained with applied electric field. Stronger interaction between the polarized hydrogen and the charged sorbents under high voltage is considered as the reason. This study was initiated to investigate if the adsorption can be further enhanced when the activated carbon particles are separated with a dielectric coating. Dielectric TiO2 nanoparticles were first utilized. Hydrogen adsorption measurements on the TiO2-coated carbon materials, with or without an external electric field, were made. The results showed that the adsorption capacity enhancement increased with the increasing amount of TiO2 nanoparticles with an applied electric field. Since the hydrogen adsorption capacity on TiO2 particles is very low and there is no hydrogen adsorption enhancement on TiO2 particles alone when electric field is applied, the effect of dielectric coating is demonstrated. Another set of experiments investigated the behavior of hydrogen adsorption over TiO2-coated activated carbon under various electric potentials. The results revealed that the hydrogen adsorption first increased and then decreased with the increase of electric field. The improved storage was due to a stronger interaction between charged carbon surface and polarized hydrogen molecule caused by field induced polarization of TiO2 coating. When the electric field was sufficient to cause considerable ionization of hydrogen, the decrease of hydrogen adsorption occurred. The current leak detected at 3000 V was a sign of ionization of hydrogen. Experiments were also carried out to examine the hydrogen adsorption performances over activated carbon separated by other dielectric materials, MgO, ZnO and BaTiO3, respectively. For the samples partitioned with MgO and ZnO, the measurements with and without an electric field indicated negligible differences. Electric field enhanced adsorption has been observed on the activated carbon separated with BaTiO3, a material with unusually high dielectric constant. Corresponding computational calculations using Density Functional Theory have been performed on hydrogen interaction with charged TiO2 molecule as well as TiO2 molecule, coronene and TiO2-doped coronene in the presence of an electric field. The simulated results were consistent with the observations from experiments, further confirming the proposed hypotheses.

In vitro characterization of a synthetic calcium phosphate bone graft on periodontal ligament cell and osteoblast behavior and its combination with an enamel matrix derivative.

OBJECTIVES Recent studies suggest that a combination of enamel matrix derivative (EMD) with grafting material may improve periodontal wound healing/regeneration. Newly developed calcium phosphate (CaP) ceramics have been demonstrated a viable synthetic replacement option for bone grafting filler materials. AIMS This study aims to test the ability for EMD to adsorb to the surface of CaP particles and to determine the effect of EMD on downstream cellular pathways such as adhesion, proliferation, and differentiation of primary human osteoblasts and periodontal ligament (PDL) cells. MATERIALS AND METHODS EMD was adsorbed onto CaP particles and analyzed for protein adsorption patterns via scanning electron microscopy and high-resolution immunocytochemistry with an anti-EMD antibody. Cell attachment and cell proliferation were quantified using CellTiter 96 One Solution Cell Assay (MTS). Cell differentiation was analyzed using real-time PCR for genes encoding Runx2, alkaline phosphatase, osteocalcin, and collagen1α1, and mineralization was assessed using alizarin red staining. RESULTS Analysis of cell attachment revealed significantly higher number of cells attached to EMD-adsorbed CaP particles when compared to control and blood-adsorbed samples. EMD also significantly increased cell proliferation at 3 and 5 days post-seeding. Moreover, there were significantly higher mRNA levels of osteoblast differentiation markers including collagen1α1, alkaline phosphatase, and osteocalcin in osteoblasts and PDL cells cultured on EMD-adsorbed CaP particles at various time points. CONCLUSION The present study suggests that the addition of EMD to CaP grafting particles may influence periodontal regeneration by stimulating PDL cell and osteoblast attachment, proliferation, and differentiation. Future in vivo and clinical studies are required to confirm these findings. CLINICAL RELEVANCE The combination of EMD and CaP may represent an option for regenerative periodontal therapy in advanced intrabony defects.

The Adsorption of Polyatomic Molecules on Carbon Surfaces

Carbon nanotubes exhibit the structure and chemical properties that make them apt substrates for many adsorption applications. Of particular interest are carbon nanotube bundles, whose unique geometry is conducive to the formation of pseudo-one-dimensional phases of matter, and graphite, whose simple planar structure allows ordered phases to form in the absence of surface effects. Although both of these structures have been the focus of many research studies, knowledge gaps still remain. Much of the work with carbon nanotubes has used simple adsorbates1-43, and there is little kinetic data available. On the other hand, there are many studies of complex molecules adsorbing on graphite; however, there is almost no kinetic data reported for this substrate. We seek to close these knowledge gaps by performing a kinetic study of linear molecules of increasing length adsorbing on carbon nanotube bundles and on graphite. We elucidated the process of adsorption of complex admolecules on carbon nanotube bundles, while at the same time producing some of the first equilibrium results of the films formed by large adsorbates on these structures. We also extended the current knowledge of adsorption on graphite to include the kinetics of adsorption. The kinetic data that we have produced enables a more complete understanding of the process of adsorption of large admolecules on carbon nanotube bundles and graphite. We studied the adsorption of particles on carbon nanotube bundles and graphite using analytical and computational techniques. By employing these methods separately but in parallel, we were able to constantly compare and verify our results. We calculated and simulated the behavior of a given system throughout its evolution and then analyzed our results to determine which system parameters have the greatest effect on the kinetics of adsorption. Our analytical and computational results show good agreement with each other and with the experimental isotherm data provided by our collaborators. As a result of this project, we have gained a better understanding of the kinetics of adsorption. We have learned about the equilibration process of dimers on carbon nanotube bundles, identifying the “filling effect”, which increases the rate of total uptake, and explaining the cause of the transient “overshoot” in the coverage of the surface. We also measured the kinetic effect of particle-particle interactions between neighboring adsorbates on the lattice. For our simulations of monomers adsorbing on graphite, we succeeded in developing an analytical equation to predict the characteristic time as a function of chemical potential and of the adsorption and interaction energies of the system. We were able to further explore the processes of adsorption of dimers and trimers on graphite (again observing the filling effect and the overshoot). Finally, we were able to show that the kinetic behaviors of monomers, dimers, and trimers that have been reported in experimental results also arise organically from our model and simulations.

Real-time monitoring of electrochemically active biofilm developing behavior on bioanode by using EQCM and ATR/FTIR

In the current study, the relationship between current and biomass and bio-adhesion mechanism of electrogenic biofilm on electrode were investigated using EQCM and ATR-SEIRAS linking electrochemistry. The results indicated that cellular biomass of biofilm on QCM-crystal surface showed maximum value of 6.0 μg/cm2 in initial batch and 11.5 μg/cm2 in the second batch on mature biofilm, producing a similar maximum current density of 110 μA/μg. Especially, the optimum cell biomass linking high electricity production ratio (110 μA/μg) occurred before maximum biomass coming, implying that over-growth mature biofilm is not an optimum state for enhancing power output of MFCs. On the other hand, the spectra using ATR-SEIRAS technique linking electrochemistry obviously exhibited water structure adsorption change at early biofilm formation and meanwhile the water adsorption accompanied the adsorbed bacteria and the bound cells population on the electrode increased with time. Meanwhile, the direct contact of bacteria and electrode via outer-membrane protein can be confirmed via a series spectra shift at amide I and amide II modes and water movement from negative bands displacing by adsorbed bacteria. Our study provided supplementary information about the interaction between the microbes and electrode beyond traditional electrochemistry.

On the behavior of the Pt(1 0 0) and vicinal surfaces in alkaline media

We address in this paper a voltammetric study of the charge transfer processes characteristic of Pt(1 0 0) and vicinal surfaces in alkaline media. The electrochemical behavior of a series of stepped surfaces of the type Pt(S)[n(1 0 0) × (1 1 1)] has been characterized using cyclic voltammetry at different pHs, charge displacement measurements and FTIR experiments for adsorbed CO. The results from these techniques allow assigning the different peaks appearing in the voltammogram to hydrogen and/or OH adsorption on the different sites of these surfaces, namely, terrace and step sites. Additionally, the potential of zero total charge (pztc) of the electrodes was determined. The resulting pztc values shift to more negative values when the step density increases on the surface up to n = 5. FTIR spectroscopy experiments have been used to monitor the adsorption of CO on the different surfaces as well as the consequent CO oxidation, accompanying a positive potential sweep. The oxidation of adsorbed CO on (1 0 0) terraces is catalyzed by the presence of the (1 1 1) steps. The FTIR spectra revealed that CO is mostly bonded in bridge configuration at low potentials interconverting to on-top when the electrode potential is increased.

A unique behavior of sub-critical hydrocarbon permeability in activated carbon at low pressures

In our study on sub-critical hydrocarbon permeation in activated carbon, a minimum in the total permeability (B-T) at low pressure has been observed for only long-chain hydrocarbons such as n-hexane and n-heptane. Such an observation suggests that the minimum appearance depends on the properties of permeating vapors as well as the porous medium. In this paper a permeation model is presented to explain the minimum behavior with the allowance of the collision-reflection factor in the Knudsen diffusivity to be a function of surface loading. Surface diffusion was found to be very significant compared to other transport mechanisms such as Knudsen diffusion and gaseous viscous flow at low pressures. Since the gaseous viscous flow contributes negligibly to the B, at low pressures, the minimum appearance in the B, is mainly attributed to the interplay between Knudsen diffusion and surface diffusion. Also, the molecular structure of adsorbates plays an important role in the minimum appearance.

Effects of the juxtaposition of carbonaceous slit pores on the overall transport behavior of adsorbed fluids

It is a common approximation in the modeling of adsorption in microporous carbons to treat the pores as slit pores, whose walls are considered to consist of an infinite number of graphitic layers. In practice, such an approximation is appropriate as long as the number of graphitic layers in the wall is greater than three. However, it is understood that pore walls in microporous carbons commonly consist of three or fewer layers. As well as affecting the solid-fluid interaction within a pore, such narrow walls permit the interaction of fluid molecules through the wall, with consequences for the adsorption characteristics. We consider the effect that a distributed pore-wall thickness model can have on transport properties. At low density we find that the only significant deviation in the transport properties from the infinite pore-wall thickness model occurs in pores with single-layer walls. For a model of activated carbons with a distribution of pore widths and pore-wall thicknesses, the transport properties are generally insensitive to the effects of finite walls, in terms of both the solid-fluid interaction within a pore and fluid-fluid interaction through the pore walls.

Application of density functional theory to equilibrium adsorption of argon and nitrogen on amorphous silica surface

We present a new version of non-local density functional theory (NL-DFT) adapted to description of vapor adsorption isotherms on amorphous materials like non-porous silica. The novel feature of this approach is that it accounts for the roughness of adsorbent surface. The solid–fluid interaction is described in the same framework as in the case of fluid–fluid interactions, using the Weeks–Chandler–Andersen (WCA) scheme and the Carnahan–Starling (CS) equation for attractive and repulsive parts of the Helmholtz free energy, respectively. Application to nitrogen and argon adsorption isotherms on non-porous silica LiChrospher Si-1000 at their boiling points, recently published by Jaroniec and co-workers, has shown an excellent correlative ability of our approach over the complete range of pressures, which suggests that the surface roughness is mostly the reason for the observed behavior of adsorption isotherms. From the analysis of these data, we found that in the case of nitrogen adsorption short-range interactions between oxygen atoms on the silica surface and quadrupole of nitrogen molecules play an important role. The approach presented in this paper may be further used in quantitative analysis of adsorption and desorption isotherms in cylindrical pores such as MCM-41 and carbon nanotubes.

Evaluation of 1-site and 5-site models of methane on its adsorption on graphite and in graphitic slit pores

In this paper, we evaluate the performance of the 1- and 5-site models of methane on the description of adsorption on graphite surfaces and in graphitic slit pores. These models have been known to perform well in the description of the fluid-phase behavior and vapor-liquid equilibria. Their performance in adsorption is evaluated in this work for nonporous graphitized thermal carbon black, and simulation results are compared with the experimental data of Avgul and Kiselev (Chemistry and Physics of Carbon; Dekker: New York, 1970; Vol. 6, p 1). On this nonporous surface, it is found that these models perform as well on isotherms at various temperatures as they do on the experimental isosteric heat for adsorption on a graphite surface. They are then tested for their performance in predicting the adsorption isotherms in graphitic slit pores, in which we would like to explore the effect of confinement on the molecule packing. Pore widths of 10 and 20 angstrom are chosen in this investigation, and we also study the effects of temperature by choosing 90.7, 113, and 273 K. The first two are for subcritical conditions, with 90.7 K being the triple point of methane and 113 K being its boiling point. The last temperature is chosen to represent the supercritical condition so that we can investigate the performance of these models at extremely high pressures. We have found that for the case of slit pores investigated in this paper, although the two models yield comparable pore densities (provided the accessible pore width is used in the calculation of pore density), the number of particles predicted by the I-site model is always greater than that predicted by the 5-site model, regardless of whether temperature is subcritical or supercritical. This is due to the packing effect in the confined space such that a methane molecule modeled as a spherical particle in the I-site model would pack better than the fused five-sphere model in the case of the 5-site model. Because the 5-site model better describes the liquid- and solid-phase behavior, we would argue that the packing density in small pores is better described with a more detailed 5-site model, and care should be exercised when using the 1-site model to study adsorption in small pores.

Adsorption of argon from sub- to supercritical conditions on graphitized thermal carbon black and in graphitic slit pores: A grand canonical Monte Carlo simulation study

In this paper we consider the adsorption of argon on the surface of graphitized thermal carbon black and in slit pores at temperatures ranging from subcritical to supercritical conditions by the method of grand canonical Monte Carlo simulation. Attention is paid to the variation of the adsorbed density when the temperature crosses the critical point. The behavior of the adsorbed density versus pressure (bulk density) shows interesting behavior at temperatures in the vicinity of and those above the critical point and also at extremely high pressures. Isotherms at temperatures greater than the critical temperature exhibit a clear maximum, and near the critical temperature this maximum is a very sharp spike. Under the supercritical conditions and very high pressure the excess of adsorbed density decreases towards zero value for a graphite surface, while for slit pores negative excess density is possible at extremely high pressures. For imperfect pores (defined as pores that cannot accommodate an integral number of parallel layers under moderate conditions) the pressure at which the excess pore density becomes negative is less than that for perfect pores, and this is due to the packing effect in those imperfect pores. However, at extremely high pressure molecules can be packed in parallel layers once chemical potential is great enough to overcome the repulsions among adsorbed molecules. (c) 2005 American Institute of Physics.

Modeling of adsorption on nongraphitized carbon surface: GCMC simulation studies and comparison with experimental data

We model nongraphitized carbon black surfaces and investigate adsorption of argon on these surfaces by using the grand canonical Monte Carlo simulation. In this model, the nongraphitized surface is modeled as a stack of graphene layers with some carbon atoms of the top graphene layer being randomly removed. The percentage of the surface carbon atoms being removed and the effective size of the defect ( created by the removal) are the key parameters to characterize the nongraphitized surface. The patterns of adsorption isotherm and isosteric heat are particularly studied, as a function of these surface parameters as well as pressure and temperature. It is shown that the adsorption isotherm shows a steplike behavior on a perfect graphite surface and becomes smoother on nongraphitized surfaces. Regarding the isosteric heat versus loading, we observe for the case of graphitized thermal carbon black the increase of heat in the submonolayer coverage and then a sharp decline in the heat when the second layer is starting to form, beyond which it increases slightly. On the other hand, the isosteric heat versus loading for a highly nongraphitized surface shows a general decline with respect to loading, which is due to the energetic heterogeneity of the surface. It is only when the fluid-fluid interaction is greater than the surface energetic factor that we see a minimum-maximum in the isosteric heat versus loading. These simulation results of isosteric heat agree well with the experimental results of graphitization of Spheron 6 (Polley, M. H.; Schaeffer, W. D.; Smith, W. R. J. Phys. Chem. 1953, 57, 469; Beebe, R. A.; Young, D. M. J. Phys. Chem. 1954, 58, 93). Adsorption isotherms and isosteric heat in pores whose walls have defects are also studied from the simulation, and the pattern of isotherm and isosteric heat could be used to identify the fingerprint of the surface.

Features of nitrogen adsorption on nonporous carbon and silica surfaces in the framework of classical density functional theory

Equilibrium adsorption data of nitrogen on a series of nongraphitized carbon blacks and nonporous silica at 77 K were analyzed by means of classical density functional theory to determine the solid-fluid potential. The behavior of this potential profile at large distance is particularly considered. The analysis of nitrogen adsorption isotherms seems to indicate that the adsorption in the first molecular layer is localized and controlled mainly by short-range forces due to the surface roughness, crystalline defects, and functional groups. At distances larger than approximately 1.3-1.5 molecular diameters, the adsorption is nonlocalized and appears as a thickening of the adsorbed film with increasing bulk pressure in a relatively weak adsorption potential field. It has been found that the asymptotic decay of the potential obeys the power law with the exponent being -3 for carbon blacks and -4 for silica surface, which signifies that in the latter case the adsorption potential is mainly exerted by surface oxygen atoms. In all cases, the absolute value of the solid-fluid potential is much smaller than that predicted by the Lennard-Jones pair potential with commonly used solid-fluid molecular parameters. The effect of surface heterogeneity on the heat of adsorption is also discussed.

The Behavior of Hydroxyl Units of Synthetic Goethite and its Dehydroxylated Product Hematite

The behavior of the hydroxyl units of synthetic goethite and its dehydroxylated product hematite was characterized using a combination of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) during the thermal transformation over a temperature range of 180-270 degrees C. Hematite was detected at temperatures above 200 degrees C by XRD while goethite was not observed above 230 degrees C. Five intense OH vibrations at 3212-3194, 1687-1674, 1643-1640, 888-884 and 800-798 cm(-1), and a H2O vibration at 3450-3445 cm(-1) were observed for goethite. The intensity of hydroxyl stretching and bending vibrations decreased with the extent of dehydroxylation of goethite. Infrared absorption bands clearly show the phase transformation between goethite and hematite: in particular. the migration of excess hydroxyl units from goethite to hematite. Two bands at 536-533 and 454-452 cm(-1) are the low wavenumber vibrations of Fe-O in the hematite structure. Band component analysis data of FTIR spectra support the fact that the hydroxyl units mainly affect the a plane in goethite and the equivalent c plane in hematite.