Surface Of HA Research Articles

The Role of Methods for Applying Cucurbit[6]uril to Hydroxyapatite for the Morphological Tuning of Its Surface in the Process of Obtaining Composite Materials

In this work, composite materials were obtained for the first time using various methods and the dependences of the resulting surface morphologies were investigated. This involves modifying the surface with cucurbit[n]urils, which are highly promising macrocyclic compounds. The process includes applying cucurbit[6]uril to the hydroxyapatite surface in water using different modification techniques. The first method involved precipitating a dispersion of CB[6] in undissolved form in water. The second method involved using fully dissolved CB[6] in deionized water, after which the composite materials were dried to constant weight. The third method involved several steps: first, CB[6] was dissolved in deionized water, then, upon heating, a dispersion of CB[6] was formed on the surface of HA. The fourth method involved using ultrasonic treatment. All four methods yielded materials with different surface morphologies, which were studied and characterized using techniques such as infrared (IR) spectroscopy and scanning electron microscopy (SEM). Based on these results, it is possible to vary the properties and surface morphology of the obtained materials. Depending on the method of applying CB[6] to the surface and inside the HA scaffold, it is possible to adjust the composition and structure of the target composite materials. The methods for applying CB[6] to the hydroxyapatite surface enhance its versatility and compatibility with the body’s environment, which is crucial for developing new functional composite materials. This includes leveraging supramolecular systems based on the CB[n] family. The obtained results can be used to model the processes of obtaining biocomposite materials, as well as to predict the properties of future materials with biological activity.

PREPARATION AND CHARACTERIZATION OF HYDROXYAPATITE BY CHEMICAL TREATMENT

Hydroxyapatite powder (HA) was prepared using the chemical precipitation method using diammonium hydrogen phosphate and calcium nitrate tetrahydrate as the starting materials. The solution was kept stirring for 24hrs at room temperature, white precipitates were dried and calcined at 1000ºC and 1200ºC for 4hrs. The powder sample was characterized by scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), Elemental dispersive X-ray (EDX). The results showed that obtained HA powders were greatly influenced by synthetic conditions. SEM shows the morphology of crystals structure, large pores sizes were observed at 50µm and 100µm. The FTIR shows the presence of CO32- at 1390 cm-1 and 1384 cm-1 which may be due to the adsorption of atmospheric CO2 on the surface of HA. PO42- was observed at 1046 cm-1 and 1092 cm-1. The EDX shows the presence of C, O, Na, Mg, Al, P, Ca. The histogram of EDX revealed oxygen carbon, phosphorus, and calcium as the major elements, sodium, magnesium, and aluminum were also present.

Hybrid Aerogel Triboelectric Nanogenerator Based on the Synergistic Effect of Solid-Solid/Gas-Solid Triboelectricity and Piezoelectric Polarization.

Aerogels, due to their unique interconnected 3D networks, and large number of air-filled pores, extend the structural characteristics and physicochemical properties of the nanoscale to the macro level. However, aerogels made from a single component can hardly meet the needs of multifunctional energy harvesting/supply situations. Here, a BaTiO3-based hybrid aerogel (BTO HA) with 3D network structure was prepared. When the BTO HA is used as the electrode of triboelectric nanogenerator (BTO HA-TENG), high electrical output performances were obtained, which is due to the synergistic effect of solid-solid contact electrifications between the two electrification layers, the gas-solid contact electrifications between the inner surface of BTO HA and the air filled in the aerogel pores, and the piezoelectricity of the doped BaTiO3 nanoparticles. The BTO HA-TENG exhibited excellent fatigue resistance and structural stability after 12,000 cycles of alternatively contact/separation tests, and it can not only provide stable power supply for commercial capacitors, drive small mobile electronic devices but also can be used as a self-powered sensor to monitor human motion signals. Compared with traditional TENGs depending on surface charge transfer, the BTO HA-TENG exhibited its unique advantage that it can generate and transfer triboelectric charges by 3D volume, which boost TENGs' electrical output performances.

Study the Interaction Mechanism and Mechanical Properties of PVA/HA by a Molecular Dynamics Simulation

To investigate the interaction mechanism of PVA on the surface of HA, the molecular dynamics simulation was applied to simulate and calculate the binding energy between PVA of different monomers and HA crystallographic planes (001), (100) and (110), and then the mechanical properties and radial distribution function of the PVA/HA(110) system were calculated and analyzed. The results show that HA (110) has the higher binding energy with PVA than that of HA (001) and (100). The binding energy and the Young’s modulus of HA(110)/PVA system increase with the rising of PVA monomer number at the same crystallographic plane in a certain range, however, the descending trend takes place while monomers number reaching a certain value. This change trend is relating to the effective contact between two single components. By calculating the pair correlation function of HA(110)/PVA, there is a strong interaction between HA crystallographic plane (110) and PVA, it is mainly derived from the hydrogen bonds between O atoms of PVA and H atoms in HA crystal, besides, the ionic bonds interactions existing between OaandCa.

Synergistic effect of HA and BMP-2 mimicking peptide on the bioactivity of HA/PMMA bone cement

HA and bone morphogenetic protein-2 (BMP-2) possess superior osteoinductive and osteoconductive activities in the repair of bone defects. In this study, a BMP-2 mimicking oligopeptide (serine–serine–valine–proline–threonine, SSVPT) was introduced to the surface of nano-sized HA as the reinforcement phase of a poly(methyl methacrylate) (PMMA) cement, and the synergistic action of HA and oligopeptide on the bioactivity of HA/PMMA bone cement was investigated. Incorporated with 3-trimethoxysilyl propyl methacrylate (MPS)-modified HA, the compressive strength, flexural strength, and flexural modulus of HA/PMMA complied with the international standardization organization 5833 standard. Adherence measurement demonstrated that the introduction of HA and SSVPT could promote the adhesion and proliferation of human fetal osteoblast (hFOB) on the surface of HA/PMMA cement. The increased alkaline phosphatase (ALP) activity indicated that HA/PMMA could promote osteogenic differentiation of hFOB. All of the results illuminated that the HA/PMMA cement could be used as a bioactive material for regeneration and reconstruction of load-bearing bone.

N-linked glycans on influenza A H3N2 hemagglutinin constrain binding of host antibodies, but shielding is limited.

The extent of the role of N-linked glycans (N-glycans) in shielding influenza A hemagglutinin (HA) against host antibodies has proved controversial, with different authors making widely different assumptions. One common assumption is that N-glycans physically shield surface residues that are near to glycosylation sites, thereby preventing antibodies from binding to them. However, it is unclear, from existing experimental evidence, whether antibodies that bind close to N-glycans are a rare or commonplace feature of human herd immune responses to influenza AHA. The aim of this paper is to present a computational analysis of mutations in the vicinity of N-glycans that will facilitate a better understanding of their protective role. We identify, from an analysis of over 6000 influenza A H3N2 sequences, a set of residues adjacent to N-glycosylation sites that are highly likely to be involved in antigenic escape from host antibodies. Fifteen of these residues occur within 10 Å of an N-glycosylation site. Hence, we conclude that it is relatively common for antibodies to bind in close proximity to N-glycans on the surface ofHA, with any shielding effect largely attributable to the inability of host antibodies to bind across an N-glycan attachment site, rather than to the physical masking of neighboring residues.

GRAFTING POLYMERIZATION OF L-LACTIDE ON HYDROXYAPATITE NANOPARTICLES

Poly(lactid-glycolide acid)/hydroxyapatite (PLGA/HA) materials, as a class of composites,which have good bioactivity, absorbability and biodegradability, show promising applications in biomedical and tissue engineering fields. To improve the compatibility of HA and PLGA, the ring-opening polymerizations of L-lactic acid on three types of HA surfaces with different surface hydroxyl functionality : unmodified HA, HA modified with L-lactic acid, and HA modified with hexamethylene diisocyanate tethered ethylene glycol were carried out to produce poly(L-lactide acid) grafted hydroxyapatite (PLLA-g-HA). The results of FTIR, XPS, TEM and TGA show that PLLA was successfully grafted onto surface of HA by the above three methods. And the grafting rate of PLLA was dependent on the nature and steric environment of the hydroxyl groups on the HA surfaces, among which HA modified with (HMDI + EG) presented the best grafting percentage of 25%. The proportional change between inorganic and organic phase brought about little influence on PLLA grafting rate. The PLLA-g-HA can stably disperse in chloroform over 2 days without deposition. To investigate practicability of the composites used as bone guided regeneration membranes, tensile test after co-electrospinning shows that PLLA-g-HA/ PLAG nanofibrous membrane has better mechanical performance compared to HA/PLGA membrane, and its tensile force reaches maximum at 5% filling content.

Thick Hydroxyapatite Coating on Ti-6Al-4V through Sol-Gel Method

Hydroxyapatite (HA, Ca10(PO4)6(OH)2) powder along with other additives such as P2O5, Na2Co3 and KH2PO4are used for biocompatible coating of Ti-6Al-4V through sol-gel method. An in-house dip coating machine was developed to control dipping and withdrawal rates of the substrate. After passivating of the samples in nitric acid, coating of HA gel was performed followed by sintering in a vacuum furnace. Characterization of the coating layer was evaluated by the XRD and SEM. Imagej software was used for analysis of the data. It was found that increasing the sintering temperature decreases the pore size, resulting in a denser structure of hydroxyapatite and decrease in surface roughness of the coating. High sintering temperatures produced cracked surface of HA due to the α to β transition temperature of Ti and its alloys. HA with coating thickness of about 100 µm free cracks was obtained for sintering temperatures lower than 800 °C.

Light-curable composite of siloxane/hydroxyapatite prepared by the sol-gel process for bone defect treatment

The light-curable composite of siloxane/hydroxyapatite (HA) had been successfully achieved by photopolymerization of a kind of gel combined tetraethoxyorthosilicate (TEOS) and 3-methacryloxypropyltrimethoxysilane (MAPS) with siloxane-modified nano-HA (HA-g-Si). HA-g-Si was prepared by grafting reaction of 3-isocyanatopropyltrimethoxysilane (IPS) onto the surface of HA. Then, TEOS and MAPS were mixed as precursor, and photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) and as-prepared HA-g-Si were added into the precursor to form a homogenous and sticky gel. The movable gel that could be cured with UV light resulted in various sharp immovable composites of siloxane/HA in different mold. The HA, HA-g-Si nanoparticles, and composites were analyzed by Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, mechanical testing, and water contact angles. It could be a promising bone repairing material for orthopedic application. POLYM. COMPOS., © 2011 Society of Plastics Engineers.

The osteogenic differentiation of rat bone marrow stromal cells cultured with dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles

There is an increasing interest in developing novel macromolecular vehicles for the intracellular and controlled delivery of bioactive molecules, since they can allow modulation of the cellular functions in a more effective manner ex vivo, and maintain the cellular phenotype in vivo upon re-implantation. The present study was designed to investigate the effect of combining novel dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer (Dex-loaded CMCht/PAMAM) nanoparticles and, both HA and SPCL scaffolds (3D system) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells (RBMSCs) in vitro. A luminescent cell viability assay using RBMSCs was performed for screening cytotoxicity of the developed HA and SPCL scaffolds. Results corroborated previous ones which have demonstrated in vitro, the superior performance of the HA and SPCL scaffolds on supporting cells adhesion and proliferation. Furthermore, this work showed that RBMSCs seeded onto the surface of both HA and SPCL scaffolds differentiate into osteoblasts when cultured in the presence of 0.01 mg ml −1 Dex-loaded CMCht/PAMAM dendrimer nanoparticles. In addition, results demonstrated that Dex-loaded CMCht/PAMAM dendrimer nanoparticles combined with the HA enhance osteogenesis by increasing ALP activity and mineralization of the extra-cellular matrix. The pre-incubation of stem cells with these kinds of nanoparticles allows the delivery of Dex inside the cells and directly influences their cellular fate, being a promising new tool to be used in cells and tissue engineering strategies.

Osteoblast adhesion to clodronate-hydroxyapatite composite

The present study combined clodronate, one of bisphosphonates, to the surface of HA scaffold by chelation. The cell culture test and gene expression test were performed and evaluated the effect of clodronate modifying the HA on co-culturing osteoblast with HA scaffold in vitro. Characteristic peaks in XPS and FT-IR spectra indicated clodronate being immobilized on the surface of HA. The cell culture test indicated that the cells actively proliferated on the scaffolds. The results of RT-PCR showed there was no significant difference between two groups in expression of RANKL gene, while the expression of OPG gene showed higher expression in Clodronate-HA group. Clodronate had no obvious effect on the cytocompatibility of HA, and Clodronate-HA might be used as bone scaffold with potential ability to improve osteogenesis.

Tribological properties of polyvinyl alcohol hydrogel reinforced with nanometer hydroxy apatite

As a potential artificial cartilage material, the friction and wear properties of nano-hydroxy apatite (HA) particles filled poly (vinyl alcohol) hydrogel (PVA-H) composites sliding against stainless steel disk under water lubrication condition were studied by using a four ball tester. The worn surfaces were investigated by using a scanning electron microscope (SEM) to determine the wear mechanisms. Experimental results show that filling HA to PVA-H will slightly increase the friction coefficient of composites with the increasing of HA content under water lubrication condition. Meanwhile, HA particles can greatly reduce the wear mass loss of the PVA-H composites and enhance the load carrying capacity, the wear loss of the 1 wt% HA reinforced PVA-H composites can be decreased by 30 percent under 2.0 MPa to 50 percent under 0.5 MPa contact pressure. We also found that 2 wt% HA content of composites increase the wear mass loss under the same condition. SEM examination shows that the worn surface of low HA containing (1 wt%) composites are much smoother than that of pure PVA-H or high HA containing (2 wt%) composites under 1.5 MPa contact pressure. It is also found that there are big hole and big reunited HA particles in the surface of 2 wt% HA containing composites, which leads to deterioration of the surface of samples under higher loads in water lubrication. These results may be useful in the tribological design of artificial articular cartilage material.

Periodic B3LYP study of hydroxyapatite (001) surface modelled by thin layer slabs

The (001) surface of the hexagonal hydroxyapatite HA [Ca 10 (PO 4 ) 6 (OH) 2 , layer group P 3] is simulated with the slab approach by fully optimizing (cell size and internal coordinates) two models, respectively 6 A and 14 A thick, in a fully ab initio periodic approach. The B3LYP hybrid functional and a Gaussian basis set of polarized double zeta quality and pseudo potentials for Ca ions only have been adopted, as encoded in the CRYSTAL03 computer program. Both slab models are cut out of the optimized structure of the hexagonal HA bulk phase ( P 6 3 space group). Because the (001) surface derived from the hexagonal HA shows ferroelectricity due to the orientation of the OH groups, the convergence of the E surf with the slab thickness (until a thickness of about 60 A) has been studied at B3LYP level on slabs whose geometry has been optimized using the GULP program with a recently developed shell-ion model potential. Structural and electronic features are addressed and a comparison between results for the considered slabs is carried out with respect to the: i) surface energy, E surf ; ii) geometrical relaxation; iii) band gap, field across the slab and Mulliken analysis; iv) electrostatic features in close proximity of the surface; v) harmonic/anharmonic OH vibrational features. The same procedure has been adopted for non-ferroelectric slabs derived from the HA monoclinic phase (bulk belonging to the P 2 1 / b space group). E surf for hexagonal HA increases slightly, as a function of the slab thickness, from 1.080 J/m 2 (doublelayer) to 1.107 J/m 2 (nonalayer), showing that the OH ferroelectricity imparts an instability of ≈0.003 J/m 2 for each added layer (7 A thick). For the non-ferroelectric HA monoclinic phase, E surf converges to 1.337 J/m 2 within 1.0 −4 J/m 2 already for the doublelayer. It is shown that the OH ferroelectricity does not prevent the formation of a (001) slab of thickness of at least 10 nm, a fact relevant for technological applications. The HA doublelayer slab is suggested as a proper model of the HA (001) face to study adsorption processes relevant to understand the role of hydroxyapatite surface in biological processes.

Surface Structure, Hydration and Cationic Sites of Nanohydroxyapatite

In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

Evaluation of Hydroxyl Groups on Hydroxyapatite and Calcium Metaphosphate by Grafting TEOS and APTES

OH groups on hydroxyapatite (HA) and calcium metaphosphate (CMP) were evaluated by grafting tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethyloxysilane (3-APTES) which can bond covalently with OH group of ceramic biomaterials. The prepared HA and CMP disks were soaked in pH 2 and 5 of acidic water and ethanol solution respectively, where pH change of each solution was measured during soaking of samples. After grafting TEOS and 3-APTES on HA and CMP disks, samples were ultrasonically cleaned in distilled water and soaked in pH 5 of ethanol solution, and pH measurement was carried out in the same manner. The pH value of HA and CMP in aqueous solution at pH 2 increased with time continuously, resulting from dissolution of HA and CMP by acidic condition on surface. At pH 5 in aqueous solution, it was the same though the pH increase was smaller. In case of ethanol at pH 5 with HA, though pH value went up slightly, the curve became saturated with time, while there was no change in pH with CMP. After grafting TEOS and 3-APTES, pH values were stabilized with few changes, indicating that there was no direct chemical reaction between the acidic media and the surface of samples due to covalently grafted TEOS and 3-APTES layer. In conclusion, it was confirmed that OH group on the surface of HA was crystallographic and chemical one rather than physically adsorbed one by grafting TEOS or 3-APTES and it will serve an effective binding site for calcium and phosphate ions, or minerals.

Surface modification of hydroxyapatite by stearic acid: characterization and in vitro behaviors

Hydroxyapatite was modified by stearic acid (Sa) in the organic mediated solution using a reflux setup. Activation ratio was introduced to characterize the effect of organic solvents, reaction times and adding amounts of Sa. HA before and after surface modification were investigated by XRD, FTIR, particle size distribution, TEM and ICP. The optimal adding amount of Sa is about 3 wt%, and there are Sa molecules on the surface of HA with a chemical reaction between HA and Sa. Sa did not change the phases and particle size of HA. HA after modified has good bioactivity in vitro. Sa has great potential as surface modifier to improve the properties of inorganic fillers in the organic matrix.

Development of Hydroxyapatite Thin Film on Titanium Substrate by Electrophoretic Deposition

Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO2-CaO-P2O5-B2O3 bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO3 for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10~20 V for 1~20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 µm (0.5 %, 20 V, 10 min) to 4~5 µm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a co-deposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.

The properties of chitosan–gelatin membranes and scaffolds modified with hyaluronic acid by different methods

The objective of the present study was to investigate the properties of chitosan–gelatin membranes or scaffolds, which were modified by incorporation of hyaluronic acid in the surface or bulk phase through co-crosslinking with N, N-(3-dimethylamino-propyl)- N′-ethyl carbodiimide (EDC) and N-hydroxysuccinimide (NHS) in 2-morpholinoethane sulfonic acid (MES) buffer. The comparative study on properties of surface modification (HA(S)) and polyblend membranes (HA(C)) revealed that gelatin was enriched on the surface of HA(C), while hyaluronic acid was enriched on the surface of the HA(S). The HA(S) membranes made by surface modification method had a characteristic surface morphology. The corresponding scaffolds were prepared through freeze-drying. The incorporation of hyaluronic acid improved flexibility and fibroblasts adhesion, while slowing down the rate of biodegradation of chitosan–gelatin scaffold. Human fibroblasts adhered and proliferated well on the membranes or scaffolds in vitro.

Covalent bonding of PMMA, PBMA, and poly(HEMA)to hydroxyapatite particles.

In our earlier study, we showed that the surface hydroxyl groups of hydroxyapatite have the ability to react with organic isocyanate groups. In this study, the feasibility of grafting poly(methyl methacrylate) (PMMA), poly(n-butyl methacrylate) (PBMA), and Poly(hydroxyethyl methacrylate) [poly(HEMA)] by using the reaction of isocyanate groups with the hydroxyl groups on the surface of HA was investigated. Double bonds were introduced to the surface of HA via the coupling reaction of isocyanateoethyl methacrylate (ICEM) with HA, or through hexamethylene diisocyanate (HMDI) with hydroxyethyl methacrylate (HEMA) and HA, followed by radical polymerization in MMA, BMA, or HEMA. Infrared spectra indicated the existence of polymers on the surfaces of HA. Thermogravimetric analysis also confirmed the presence of grafted polymers on the surface of HA powder particles (20-26 wt%). The polymers gave typical PMMA, PBMA, or poly(HEMA) infrared spectra, with the exception of amide bands, a result of the coupling reaction of ICEM or HMDI with hydroxy groups of HA or HEMA. Therefore it is concluded that the polymers were chemically bonded to the surface of HA through the isocyanate groups of ICEM or HMDI.

The triangular halophilic archaebacteriumHaloarcula japonica strain TR-1

We have isolated a predominantly triangular disc-shaped halophilic archaebacterium, strain TR-1, from a Japanese saltern soil. The taxonomical characteristics of this strain led us to propose a new speciesHaloarcula japonica. The cell division ofHa. japonica strain TR-1 was analyzed by time lapse microscopic cinematography. Cell plates were laid down asymmetrically, generating triangular or rhombic daughter cells which then separated. We have demonstrated the occurrence of a glycoprotein with an apparent molecular mass of 170 kDa on the cell surface ofHa. japonica. The release of this cell surface glycoprotein (CSG), accompanied by a morphological change (triangular to spherical), was observed after lowering the magnesium concentration in the medium. Thus, it is likely that the CSG plays an important role in maintaining the characteristic shape ofHa. japonica.