Growth Of Calcium Phosphate Research Articles

Topography and Surface Energy Dependent Calcium Phosphate Formation on Sol−Gel Derived TiO2 Coatings

Heterogeneous nucleation and growth of calcium phosphate (CaP) on sol-gel derived TiO(2) coatings was investigated in terms of surface topography and surface energy. The topography of the coatings was derived from AFM measurements, while the surface energy was determined with contact angle measurements. The degree of precipitation was examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The precipitation of CaP was found to be dependent on both topography and surface energy. A high roughness value when combining the RMS roughness parameter S(q) with the number of local maxima per unit area parameter S(ds) enhances CaP formation. The hydrophilicity of the coating was also found to be of importance for CaP formation. We suggest that the water contact angle, which is a direct measure of the hydrophilicity of the surface, may be used to evaluate the surface energy dependent precipitation kinetics rather than using the often applied Lewis base parameter.

A novel approach of homogenous inorganic/organic composites through in situ precipitation in poly-acrylic acid gel

A new in situ precipitation technique was developed to promote high-affinity nucleation and growth of calcium phosphate in the polymer hydrogel. Poly-acrylic acid/ hydroxyapatite (HAP) composites have been prepared using template-driven reaction. Nano-sized hydroxyapatite particles were distributed within organic template homogenously, furthermore, inorganic particles were fine and uniform. A kind of specific product with the characteristic of fractal was also obtained. During the composite process, 3D network of organic matrices played an important role in the superfine interaction of HAP and hydrogel through the compartment-effect of interior of hydrogel. This method provides an efficient approach toward inorganic/organic nanocomposites with high-uniformity decentralization for biomimetic replant applications. This paper discussed the mechanism of compartment-effect, and the concept of in situ precipitation in gel was brought forward. SEM and TEM were employed in the analysis of the morphological characteristic of uniform inorganic/organic composites and inorganic minerals separated from organic template. SEM-associated EDS area analysis and TEM-associated EDS analysis were employed in the analysis of component characteristic of inorganic/organic composite and inorganic particles. X-ray diffraction was employed in the analysis of precipitation phase crystal structure of inorganic component.

Biomineralization of calcium disilicide in porous polycaprolactone scaffolds

The incorporation of CaSi(2) grains within a polycaprolactone (PCL) framework results in bioactive and biodegradable scaffolds which may be used in bone tissue regeneration. Porous PCL scaffolds were prepared via a combination of salt-leaching and microemulsion methods. To provide markedly different structural environments for the inorganic phase, calcium disilicide powder was either added to a mixed-composition porogen during a given scaffold preparation, or alternatively added to pre-formed scaffolds. Selective fluorescent labeling, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis were employed to assess scaffold calcification in vitro. The process of CaSi(2)/PCL scaffold calcification under zero bias, during which calcium phosphate growth is significantly dependent on the structural degradation of CaSi(2) grains, has a similar mechanism as the calcium phosphate growth on bioactive glasses/ceramics. The biomineralization of these scaffolds is initiated solely by the silicide phase and can be accelerated by the degradation of the polymer matrix.

In Vitro Mineralization and Cell Adhesion on Surface Modified Poly (2 - hydroxy ethyl methacrylate-co-methyl methacrylate

Poly(2-hydroxyethyl methacrylate-co- methyl methacrylate) HM, was synthesized by free radical copolymerization, cross-linked with ethylene glycol dimethacrylate and phosphorylated. The phosphate coupling was ensured by ATR spectroscopy. The in vitro mineralization ability of the phosphorylated HM (designated as PHM) was investigated by studying the nucleation and growth of calcium phosphate on its surface by immersing in simulated body fluid (SBF) solution. The coating morphology was studied by SEM and the Ca/P ratio of the coating by EDX analysis. The cell adhesion behaviour of PHM was studied by seeding Human osteosarcoma (HOS) cells for one week followed by SEM analysis along with HM as control. It was observed that HOS cells exhibited biomineralization of calcium phosphate on the surface of HM as well as on PHM with a significantly higher amount on the surface of PHM as observed by von kossa staining method. The results show that PHM is capable of in vitro mineralization under simulated physiological condition, promotes cell adhesion by providing an excellent cell friendly surface and it exhibits biomineralization of calcium phosphate in presence of HOS cells.

P-recovery by secondary nucleation and growth of calcium phosphates on magnetite mineral

Precipitation of calcium phosphates from supersaturated solutions seeded with magnetite powder (magnetite mineral, Fe 3O 4) has been studied in lab scale in the pH range 6.9–7.7. While the initial concentration of phosphorus was 1.29 mmol/l, the initial molar ratio of Ca/P was taken one to three times of the stoichiometric calcium to phosphorus ratio of hydroxyapatite. To bring out the secondary nucleation, the precipitation system was allowed to relax and pH of the solution was maintained at the initially preset value. The period before base was added for the first time during relaxation was defined as lagtime and sodium hydroxide added during the relaxation was evaluated as the degree of growth. The lagtime was found to be dependent on the solution pH, therefore on the initial amount of precipitation. Coverage of seed surface by heterogeneous nucleation is essential. Since all precipitation by secondary nucleation took place on the seed material, precipitation during relaxation was due to growth of the solid phase on the seed surfaces. It was found that there was a pH range in which growth rate was directly proportional to pH. However, at lower residual concentrations of phosphorus, despite relatively higher pH, the growth rate was decreased.

01aD07 Role of phosvitin on nucleation and growth of calcium phosphates under physiological conditions(NCCG-36)

01aD07 Role of phosvitin on nucleation and growth of calcium phosphates under physiological conditions(NCCG-36)

NOVEL SYNTHESIS OF CALCIUM PHOSPAHTE CERAMICS AND COMPOSITE-FROM BIOACTIVE TO BIO-FUNCTIONAL INTEGRATION-

New syntheses of calcium phosphate ceramics and its composite materials are studied. The properties of the developed materials are from bioactive properties for medical applications to bio-functional integration for advanced applications. The newly developed syntheses; mechanochemical synthesis, coatings with interlayer forming, hydrothermal synthesis with organic molecules, phosphorylation and partially hydrolysis, and mesopores coatings into hyper structure formation, templating of macromolecules into ordered structure, are based on low energy and with conscious biological structure formation. Here the development from bioactive to biofunctional integration are descried as follow as high strength calcium phosphate ceramics prepared using mechanochemical synthesized fine powders, calcium phosphate coating on high strength materials, estimation of biocompatibility of bioceramics by tissue culture method, research on water polluted water, morphology control of HAp, stimulation of calcium phosphate growth on polymeric substrate and highly oriented collagen fibers and apatite composite materials through biomimetic route, and biointegaration for multifunctional materials..

Nucleation and growth of calcium phosphate on amine-, carboxyl- and hydroxyl-silane self-assembled monolayers

Upon implantation, calcium phosphate (Ca–P) surfaces form on materials that are bone bioactive. In this study, the evolving surface characteristics associated with calcium phosphate precipitation are modeled using self-assembled monolayers (SAMs), in a one-step nucleation process. SAMs were used to create amine (–NH 2), carboxyl (–COOH) and hydroxyl (–OH) functionalized surfaces by grafting 3-aminopropyltriethoxysilane, 3-triethoxysilylpropyl succinic anhydride and glycidoxypropyl tri-methoxysilane, respectively, onto oxidized silicon wafers. The SAM surfaces were characterized using ellipsometry to establish the presence of grafted molecules. On the surfaces incubated in simulated physiological fluids for 7 days, the thickness of Ca–P layer grew slowly over the first few hours, increasing strongly between 1 and 5 days and then slowed down again. FTIR showed the dependence of calcium phosphate morphology on the type of surface groups, with stronger P–O bands seen on the OH-terminated surface. SEM analysis showed dispersed Ca–P precipitates on the –COOH and –OH terminated surfaces after 1 day immersion. After 7 days, all SAM surfaces were covered with uniformly dispersed and denser Ca–P precipitates. The underlying Ca–P layer showed cracks on the –NH 2-terminated surface. Rutherford backscattering spectrometry (RBS) data analysis confirmed that Ca/P ratio is in excellent agreement with the theoretical value of 1.67 for hydroxyapatite. X-ray diffraction (XRD) analysis also showed evidence of apatite formation on all the surfaces, with stronger evidence on the –OH-terminated surface. Highly porous Ca–P precipitates were observed on the SAM surfaces portrayed by the AFM scans with nanoscale RMS roughness. Thus, using highly controlled surface chemistry, under physiological conditions, in vitro, this study demonstrates that a hydroxylated surface enhances Ca–P nucleation and growth relative to other surfaces, thereby supporting the concept of its beneficial effect on bone tissue formation and growth.

Effect of Phosvitin on the Nucleation and Growth of Calcium Phosphates in Physiological Solutions

The promoting effect of phosvitin on the nucleation of hydroxyapatite (HAP) and the inhibitory effect of phosvitin on the transformation from amorphous calcium phosphate (ACP) to HAP were investigated. Atomic force microscopy observations showed that the nucleation of HAP on collagen substrate was greatly enhanced when the phosvitin was bound on the collagen surface. Nucleated crystals were uniformly distributed with a high nucleation rate on the collagen surface in the presence of phosvitin, while, in the absence of phosvitin, crystals nucleated slowly and were observed only at some particular area. Time-resolved static light scattering measurements revealed that the transformation from ACP to HAP was inhibited when free phosvitin was present in the calcium phosphate solutions. The transformation kinetics in the absence of phosvitin, which is a direct reconstruction of the inner ACP structure to HAP, was changed to heterogeneous growth of HAP on ACP with time.

In vitro bioactivity of MOEP grafted ePTFE membranes for craniofacial applications

The bioactivity of three methacryloyloxyethyl phosphate (MOEP) grafted expanded polytetrafluoroethylene (ePTFE) membranes with varying surface coverage as well as unmodified ePTFE was investigated through a series of in vitro tests: calcium phosphate (CaP) growth in simulated body fluid (SBF), serum protein adsorption, and a morphology and attachment study of human osteoblast-like SaOS-2 cells. The graft copolymers were prepared by means of gamma irradiation induced grafting and displayed various surface morphologies and wettabilities depending on the grafting conditions used. Unmodified ePTFE did not induce nucleation of CaP minerals, whereas all the grafted membranes revealed the growth of CaP minerals after 7 days immersion in SBF. The sample with lowest surface grafting yield (24% coverage), a smooth graft morphology and relatively high hydrophobicity ( θ adv = 120 ° , θ rec = 80 ° ) showed carbonated hydroxyapatite growth covering the surface. On the other hand, the samples with high surface grafting yield (76% and 100%), a globular graft morphology and hydrophilic surfaces ( θ adv = 60 ° and 80°, θ rec = 25 ° and 15°, respectively) exhibited irregular growth of non-apatitic CaP minerals. Irreversibly adsorbed protein measured after a 1 h immersion in serum solution was quantified by the amount of nitrogen on the surface using XPS, as well as by weight increase. All grafted membranes adsorbed 3–6 times more protein than the unmodified membrane. The sample with the highest surface coverage adsorbed the most protein. Osteoblast-like SaOS-2 cells cultured for 3 h revealed significantly higher levels of cell attachment on all grafted membranes compared to unmodified ePTFE. Although the morphology of the cells was heterogeneous, in general, the higher grafted surfaces showed a much better cell morphology than both the low surface-grafted and the control unmodified sample. The suite of in vitro tests confirms that a judicious choice of grafted monomer such as the phosphate-containing methacrylate monomer (MOEP) significantly improves the bioactivity of ePTFE in vitro.

The Effects of Prestrain and Collagen Fibril Alignment on In Vitro Mineralization of Self-Assembled Collagen Fibers

Collagen fibers are under tension in most extracellular matrices both prior to and during normal loading. This tension not only provides mechanical advantages, but also appears to establish a loading basis for the stimulation of mechanochemical transduction processes. The presence of tensile loads applied to collagen fibers also results in physical alignment of the collagen fibrils along the tensile axis. This alignment may influence biological processes such as mineralization.In this study we report a comparison between elastic and viscous stress-strain curves and mineral contents of self-assembled collagen fibers that were strained to 30% of their original lengths and then mineralized, and self-assembled collagen fibers that were not strained before being mineralized. We concluded that the application of strain changes the organization of the collagenous matrix and alters the calcium phosphate nucleation and/or growth in the matrix. In addition, when the mechanical behavior of collagen fibers is compared with mechanical data from mineralized turkey tendon, the results indicate that collagen fibril-to-fibril interactions present in turkey tendon appear to be more organized compared with self-assembled aligned collagen fibers. We concluded that organized collagen-collagen interactions appear to be an important characteristic required for elastic energy storage in tendon.

A Study on Biomineralization Behavior of N‐Methylene Phosphochitosan Scaffolds

Biomimetic growth of calcium phosphate over natural polymer may be an effective approach to constituting an organic/inorganic composite scaffold for bone tissue engineering. In this work, N-methylene phosphochitosan (NMPCS) was prepared via formaldehyde addition and condensation with phosphoric acid in a step that allowed homogeneous modification without obvious deterioration in chitosan (CS) properties. The NMPCS obtained was characterized by using FT-IR and elemental analysis. The macroporous scaffolds were fabricated through a freeze-drying technique. A comparative study on NMPCS and CS scaffold biomimetic mineralization was carried out in different media, i.e, a simulated body fluid (SBF) or alternative CaCl(2) and Na(2)HPO(4) solutions respectively. Apatite formation within NMPCS and CS scaffolds was identified with FT-IR, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffractometery (XRD). The results revealed alternate soaking of the scaffolds in CaCl(2) and Na(2)HPO(4) solutions was better than soaking in SBF solution alone in relation to apatite deposition on the scaffold pore walls. Biomineralization provides an approach to improve nature derived materials, e.g., chitosan derivative NMPCS properties e.g., compressive modulus, etc. SEM image of a NMPCS/apatite composite scaffold.

Use of sol-gel-derived titania coating for direct soft tissue attachment.

A firm bond between an implant and the surrounding soft tissue is important for the performance of many medical devices (e.g., stents, canyls, and dental implants). In this study, the performance of nonresorbable and reactive sol-gel-derived nano-porous titania (TiO(2)) coatings in a soft tissue environment was investigated. A direct attachment between the soft tissue and the sol-gel-derived titania coatings was found in vivo after 2 days of implantation, whereas the titanium control implants showed no evidence of soft tissue attachment. The coated implants were in immediate contact with the connective tissue, whereas the titanium controls formed a gap and a fibrous capsule on the implant-tissue interface. The good soft tissue attachment of titania coatings may result from their ability to initiate calcium phosphate nucleation and growth on their surfaces (although the formation of poorly crystalline bonelike apatite does not occur). Thus, the formation of a bonelike CaP layer is not crucial for their integration in soft tissue. The formation of bonelike apatite was hindered by the adsorption of proteins onto the initially formed amorphous calcium phosphate growth centers, thus preventing the dissolution/reprecipitation processes required for the formation of poorly crystalline bonelike apatite. These findings might open novel application areas for sol-gel-derived titania-based coatings.

Nano-scale study of the nucleation and growth of calcium phosphate coating on titanium implants

The nucleation and growth of a calcium phosphate (Ca-P) coating deposited on titanium implants from simulated body fluid was investigated by using atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). Forty titanium alloy plates were assigned into two groups. One group with a smooth surface having a maximum roughness R max<0.10 μm (s-Ti6Al4V) and a group with a rough surface with an R max<0.25 μm (r-Ti6Al4V) were used. Titanium samples were immersed in SBF concentrated by five (SBF×5) from 10 min to 5 h and examined by AFM and ESEM. Scattered Ca-P deposits of approximately 15 nm in diameter appeared after only 10 min of immersion in SBF×5. These Ca-P deposits grew up to 60–100 nm after 4 h on both s- and r-Ti6Al4V substrates. With increasing immersion time, the packing of Ca-P deposits with size of tens of nanometers in diameter formed larger globules and then a continuous Ca-P film on titanium substrates. A direct contact between the Ca-P coating and the Ti6Al4V surface was observed. The Ca-P coating was composed of nanosized deposits and of an interfacial glassy matrix. This interfacial glassy matrix might ensure the adhesion between the Ca-P coating and the Ti6Al4V substrate. In the case of s-Ti6Al4V substrate, failures within this interfacial glassy matrix were observed overtime. Part of the glassy matrix remained on s-Ti6Al4V while part detached with the Ca-P film. The Ca-P coating detached from the smooth substrate, whereas the Ca-P film extended onto the whole rough titanium surface over time. In the case of r-Ti6Al4V, the Ca-P coating covered evenly the substrate after immersion in SBF×5 for 5 h. The present study suggested that the heterogeneous nucleation of Ca-P on titanium was immediate and did not depend on the Ti6Al4V surface topography. The further growth and mechanical attachment of the final Ca-P coating strongly depended on the surface, for which a rough topography was beneficial.

Formation and growth of calcium phosphate on the surface of oxidized Ti–29Nb–13Ta–4.6Zr alloy

The bioconductivity of a new biomedical titanium alloy Ti–29Nb–13Ta–4.6Zr achieved by a combination of surface oxidation and alkali treatment is reported in this paper. Oxidation treatment at 400°C for 24 h was found to result in the formation of a hard layer on the surface of the alloy. Immersion in a protein-free simulated body fluid and fast calcification solution led to the growth of calcium phosphate (Ca–P) phase on the oxidized and alkali-treated alloy, and the new bioconductive surface was still harder than the substrate. The surface processes during various treatment and immersion processes were investigated in detail, and the morphology of the calcium phosphate crystals was shown to be determined by the concentrations of Ca and P in the solution.

Nucleation and Growth of Calcium Phosphate from Physiological Solutions onto Self-Assembled Templates by a Solution-Formed Nucleus Mechanism

The nucleation and growth mechanisms of calcium phosphate were investigated using supersaturated solutions similar to physiological conditions and model self-assembled monolayer substrates tailored to have functional groups that mimicked chemistries found in bone organic matrices. Deposition kinetics were studied using an in situ microbalance and showed a long induction period followed by a second region of extensive growth, both of which depended on the solution supersaturation. Solution studies revealed that the growth of calcium phosphate onto the surfaces after the induction period corresponded to nucleation and growth in solution. Nuclei formed in solution, started to grow, adsorbed onto the substrates, and then grew further to form apatite films composed of coalesced, oriented crystallites. The solution-formed critical nucleus mechanism is in contrast to heterogeneous nucleation and reveals an important mechanism for calcium phosphate growth onto surfaces.

Biomimetic Growth of Calcium Phosphate over ATP Coupled PMMA Films

Biomimetic Growth of Calcium Phosphate over ATP Coupled PMMA Films

A new approach to mineralization of biocompatible hydrogel scaffolds: an efficient process toward 3-dimensional bonelike composites.

As a first step toward the design and fabrication of biomimetic bonelike composite materials, we have developed a template-driven nucleation and mineral growth process for the high-affinity integration of hydroxyapatite with a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel scaffold. A mineralization technique was developed that exposes carboxylate groups on the surface of cross-linked pHEMA, promoting high-affinity nucleation and growth of calcium phosphate on the surface, along with extensive calcification of the hydrogel interior. Robust surface mineral layers a few microns thick were obtained. The same mineralization technique, when applied to a hydrogel that is less prone to surface hydrolysis, led to distinctly different mineralization patterns, in terms of both the extent of mineralization and the crystallinity of the apatite grown on the hydrogel surface. This template-driven mineralization technique provides an efficient approach toward bonelike composites with high mineral-hydrogel interfacial adhesion strength.

Preparation of pHEMA–CP composites with high interfacial adhesion via template-driven mineralization

We report a template-driven nucleation and mineral growth process for the high-affinity integration of calcium phosphate (CP) with a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel scaffold. A mineralization technique was developed that exposes carboxylate groups on the surface of crosslinked pHEMA, promoting high-affinity nucleation and growth of calcium phosphate on the surface along with extensive calcification of the hydrogel interior. External factors such as the heating rate, the agitation of the mineral stock solution and the duration of the process that affect the outcome of the mineralization were investigated. This template-driven mineralization technique provides an efficient approach toward bonelike composites with high mineral-hydrogel interfacial adhesion strength.

Growth of calcium phosphate onto chemically-functionalized cottons

The growth of calcium phosphate onto both cotton fibers and chemically-modified cotton fibers with three different degrees of carbonyl groups contents, immersed in saturated calciumphosphate solutions at 60°C and 7.4 pH for 6, 9 and 12 days, has been investigated by scanning electron microscopy, energy dispersed spectrometry and transmission electron microscopy as a function of the type and amount of functionalized groups. The functionalized cotton fibers were obtained through the reaction of alkali cellulose with sodium chloroacetate and the immersion solution was changed every three days. Without modification no crystallization in the cotton sample was observed, whereas in the functionalized samples, with higher substitution we obtained calcium phosphate crystallization onto the fibers as long vesicles with sizes ranging from 1 μm to 24 μm wide; these vesicles are formed by long platelets with certain orientation and ordered arrangement. In the presence of the most functionalized cotton fibers we observed the highest calcium phosphate crystallization onto the fibers; the Ca/P molar ratio obtained by EDS was 1.58. One of the calcium phosphate identified by transmission microscopy was octacalcium phosphate (Ca8H2(PO4) · 6.5H2O, OCP). The chemical functionalization of the cotton via carbonyl group determined the growth and the amount of calcium phosphate onto the fiber.