RESUMEN
Samples of enamel and dentin from human molar teeth were heated in air from room temperature (25°C) up to 1200°C and the phase transition from hydroxyapatite (HAP) to tricalcium phosphate (ß-TCP) was recorded. The changes produced in morphology and chemical composition in the tooth during heating were analysed by light microscopy, scanning electron microscopy (SEM), characteristic x-ray energy dispersion spectroscopy (EDS), x-ray diffraction (XRD), electron diffraction, transmission electron microscopy (TEM) and high-resolution electron microscopy (HRTEM). The results indicated a high correlation relationship among Ca content, P content, O content and Na content, and the existence of the Kirkendall effect during the HAP- ß-TCP phase transition. LAY DESCRIPTION: This work is related with tooth materials. Samples of enamel and dentine from human molar teeth were heated in air from 25°C up to 1200°C and the phase transition from hydroxyapatite (HAP) to tricalcium phosphate (ß-TCP) was recorded. The ß-TCP phase is also known as whitlockite. The changes produced in morphology and chemical composition in the tooth during heating were analysed by electron microscopy and X-ray diffraction. The results indicated a high correlation relationship among Ca, P, O and Na contents, and the existence of the Kirkendall effect, the atomic diffusion producing voids, during the HAP- ß-TCP phase transition.
Asunto(s)
Materiales Biocompatibles/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Durapatita/efectos de la radiación , Microscopía Electrónica , Diente Molar/efectos de la radiación , Transición de Fase/efectos de la radiación , Esmalte Dental/efectos de la radiación , Dentina/efectos de la radiación , Calor , Humanos , Análisis EspectralRESUMEN
The real-time polymerization of light-curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2-bis[4-(2-ethoxy-3-methacryloyloxy propoxy)phenyl]propane (Bis-EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2-hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40-50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier-transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm-2 ) for either 20 or 40 s, infrared spectra were collected from the bottom of 2-mm-thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%-92.4%), while the DC of control composites was significantly lower (53.5%-68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5-min postcure polymerization: 12.9%-21.5% for the ACP composites and 2.7%-5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1-4.3 s) and at lower DC (9.9%-10.4%) than did the ACP composites (17.4-22.0 s and 43.5%-49.3%, respectively).
Asunto(s)
Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Resinas Compuestas/química , Resinas Compuestas/efectos de la radiación , Luces de Curación Dental , Polimerizacion/efectos de la radiación , Compuestos de Bario , Materiales Biocompatibles/química , Fenómenos Químicos , Materiales Dentales/química , Materiales Dentales/efectos de la radiación , Cinética , Ensayo de Materiales , Metacrilatos , Polietilenglicoles , Ácidos Polimetacrílicos , Dióxido de Silicio , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Factores de Tiempo , Circonio/químicaRESUMEN
This paper presents the experimental results of the thermoluminescence (TL) induced by gamma radiation in synthetic hydroxyapatite (HAp) obtained by the precipitation method, using Ca(NO3)2·4H2O and (NH4)2HPO4 and calcined at different temperatures. The structural and morphological characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. TL response as a function of gamma radiation dose was in a wide range, where intensity was enhanced in the sample annealed at 900°C, which tricalcium diphosphate (TCP) phase appear. Fading of the TL was also studied.
Asunto(s)
Durapatita/química , Durapatita/efectos de la radiación , Sustitutos de Huesos/química , Sustitutos de Huesos/efectos de la radiación , Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Calor , Humanos , Técnicas In Vitro , Microscopía Electrónica de Rastreo , Difracción de Polvo , Dosimetría TermoluminiscenteRESUMEN
KrF excimer laser precision machining of porous hard-brittle ceramic biomaterials was studied to find a suitable way of machining the materials into various desired shapes and sizes without distorting their intrinsic structure and porosity. Calcium phosphate glass ceramics (CPGs) and hydroxyapatite (HA) were chosen for the study. It was found that KrF excimer laser can cut both CPGs and HA with high efficiency and precision. The ablation rates of CPGs and HA are respectively 0.081 µm/(pulse J cm(-2)) and 0.048 µm/(pulse J cm(-2)), while their threshold fluences are individually 0.72 and 1.5 J cm(-2). The cutting quality (smoothness of the cut surface) is a function of laser repetition rate and cutting speed. The higher the repetition rate and lower the cutting speed, the better the cutting quality. A comparison between the cross sections of CPGs and HA cut using the excimer laser and using a conventional diamond cutting blade indicates that those cut by the excimer laser could retain their intrinsic porosity and geometry without distortion. In contrast, those cut by conventional machining had distorted geometry and most of their surface porosities were lost. Therefore, when cutting hard-brittle ceramic biomaterials to prepare scaffold and implant or when sectioning them for porosity evaluation, it is better to choose KrF excimer laser machining.
Asunto(s)
Materiales Biocompatibles/química , Fosfatos de Calcio/química , Cerámica/química , Durapatita/química , Láseres de Excímeros , Ensayo de Materiales , Materiales Biocompatibles/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Cerámica/efectos de la radiación , Fuerza Compresiva/efectos de la radiación , Durapatita/efectos de la radiación , Dureza/efectos de la radiación , Calor , Propiedades de Superficie/efectos de la radiaciónRESUMEN
Biocompatible nanoparticles possessing fluorescent properties offer attractive possibilities for multifunctional bioimaging and/or drug and gene delivery applications. Many of the limitations with current imaging systems center on the properties of the optical probes in relation to equipment technical capabilities. Here we introduce a novel high aspect ratio and highly crystalline europium-doped calcium phosphate nanowhisker produced using a simple microwave-assisted solution combustion synthesis method for use as a multifunctional bioimaging probe. X-ray diffraction confirmed the material phase as europium-doped hydroxyapatite. Fluorescence emission and excitation spectra and their corresponding peaks were identified using spectrofluorimetry and validated with fluorescence, confocal and multiphoton microscopy. The nanowhiskers were found to exhibit red and far red wavelength fluorescence under ultraviolet excitation with an optimal peak emission of 696 nm achieved with a 350 nm excitation. Relatively narrow emission bands were observed, which may permit their use in multicolor imaging applications. Confocal and multiphoton microscopy confirmed that the nanoparticles provide sufficient intensity to be utilized in imaging applications.
Asunto(s)
Fosfatos de Calcio/síntesis química , Cristalización/métodos , Europio/química , Microscopía de Fluorescencia por Excitación Multifotónica/métodos , Nanopartículas/química , Fosfatos de Calcio/efectos de la radiación , Medios de Contraste/síntesis química , Medios de Contraste/efectos de la radiación , Europio/efectos de la radiación , Calor , Ensayo de Materiales , Microondas , Nanopartículas/ultraestructura , Tamaño de la Partícula , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Calcium phosphate nanoplates and nanorods with controllable pores and enhanced protein loading and tuneable release characteristics are first synthesized without the use of any toxic surfactants by an energy efficient microwave assisted chemical process, hence demonstrating their viability as a tool for controllable drug delivery in biomaterial systems.
Asunto(s)
Fosfatos de Calcio/química , Cristalización/métodos , Nanocápsulas/química , Nanocápsulas/ultraestructura , Albúmina Sérica Bovina/química , Fosfatos de Calcio/efectos de la radiación , Difusión , Ensayo de Materiales , Microondas , Nanocápsulas/efectos de la radiación , Porosidad , Albúmina Sérica Bovina/administración & dosificaciónRESUMEN
Dy(3+)-doped NaCaPO(4) phosphor was synthesised at an initiating combustion temperature of 600°C, using urea as the fuel. The crystallinity of the phosphor was investigated by using X-ray diffraction. The photoluminescence and thermoluminescence (TL) behaviours of NaCaPO(4):Dy(3+) phosphor was also studied. It has a simple TL glow curve structure, which does not change when exposed to gamma-rays. A TL glow peak is observed at 230°C and TL intensity is around 1.15 times more compared with commercial CaSO(4):Dy TLD phosphor. The TL characteristics of the phosphor prepared show that it has good sensitivity, linear response with gamma-rays exposure, emission in the blue-yellow regions of the spectrum, negligible fading and excellent reusability. These results make Dy(3+)-doped NaCaPO(4) phosphor attractive for TLD applications.
Asunto(s)
Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Mediciones Luminiscentes/métodos , Fosfatos/química , Fosfatos/efectos de la radiación , Dosimetría Termoluminiscente/métodos , Relación Dosis-Respuesta en la Radiación , Dosis de RadiaciónRESUMEN
The influence of several subthreshold laser procedures on chorioretinal complex (CRC) tissues was experimentally studied in rabbits using histological and histochemical methods. Subthreshold micropulse laser radiation and transpupillar thermotherapy were found to have the most attenuated and advantageous effect on CRC structure. The feature of subthreshold laser exposure is partly reversible selective changes in CRC, that have temporary stimulating effect on cellular metabolism and local regenerative processes providing an opportunity for still viable tissues to function adequately.
Asunto(s)
Fosfatos de Calcio/efectos de la radiación , Coroides/efectos de la radiación , Histocitoquímica/métodos , Hipertermia Inducida , Rayos Láser , Traumatismos Experimentales por Radiación , Epitelio Pigmentado de la Retina/efectos de la radiación , Animales , Biometría , Fosfatos de Calcio/metabolismo , Coroides/metabolismo , Coroides/patología , Relación Dosis-Respuesta en la Radiación , Hipertermia Inducida/efectos adversos , Hipertermia Inducida/métodos , Hipertermia Inducida/normas , Rayos Láser/efectos adversos , Rayos Láser/normas , Conejos , Traumatismos Experimentales por Radiación/metabolismo , Traumatismos Experimentales por Radiación/patología , Epitelio Pigmentado de la Retina/metabolismo , Epitelio Pigmentado de la Retina/patologíaRESUMEN
The degradation and/or apatite layer precipitation ability of porous ß-tricalcium phosphate(ß-TCP) samples treated and untreated with microwave radiation during synthesis is investigated. Microwave heating was used to accelerate the formation of CDHA with the Ca/P ratio 1.5 in a shorter processing time which later forms ß-TCP at around 650 â¦C. Soaking in simulated body fluid (SBF) for several periods (4, 8, 12, 24, 36, 48, 60 and 72 h) is performed in a cumulative manner. The deposition of an apatite layer is followed through diffuse reflected FT-IR, SEM and EDS. A microwave-treated sample having a smaller particle size than its parent induces the formation of a homogeneous carbonated apatite layer on its surface.On the other hand, the parent ß-TCP sample exhibited less ability to induce CaP formation after being soaked in SBF. The formation of an apatite layer is attributed to the increase in surface area consequent to reduced particle and grain sizes besides the presence of a minor amount of hydroxyapatite phase in the microwave-treated ß-TCP sample. The results prove that it is possible to control the biodegradation and apatite layer formation on sintered ß-TCP porous disks through controlling the particle size.
Asunto(s)
Implantes Absorbibles , Líquidos Corporales/química , Sustitutos de Huesos/síntesis química , Fosfatos de Calcio/química , Durapatita/síntesis química , Nanopartículas/química , Sustitutos de Huesos/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Durapatita/efectos de la radiación , Ensayo de Materiales , Microondas , Nanopartículas/efectos de la radiación , Nanopartículas/ultraestructura , Tamaño de la PartículaRESUMEN
In the present paper, we report the indigenous development of a neutron-sensitive thermoluminescent dosemeter (TLD) based on CaSO4:Dy Teflon TL disc. The study includes indigenous development of a neutron dosemeter and its response in terms of operational quantity to different energies of neutrons under various irradiation conditions. It was found that the thermal neutron sensitivity of the CaSO4:Dy Teflon neutron disc is about one-third of TLD-600. However, the thermal neutron sensitivity with respect to CaSO4:Dy Teflon gamma disc is about 42 times for in-air irradiation and about 84 times for on-phantom irradiation condition. This newly developed neutron dosemeter can be used as a routine TLD with a slight change in the design of the TLD badge system in the mixed fields of gamma and neutrons of energy up to 500 keV for radiation workers engaged in nuclear fuel cycle operation and other applications.
Asunto(s)
Fosfatos de Calcio/química , Dosimetría Termoluminiscente/instrumentación , Fosfatos de Calcio/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Diseño de Equipo , Análisis de Falla de Equipo , Neutrones , Dosis de Radiación , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
In the present paper, we demonstrate the feasibility of depositing a tailored calcium phosphate (Ca-P) coating on a Ti-6Al-4V substrate by using a pulsed Nd:YAG laser system. Different textures were obtained by varying the laser spot overlap with change in laser traverse speed. Surface roughness measurements using laser confocal microscopy indicated a decrease in roughness with increasing laser scan speed. X-ray diffraction studies revealed the formation of alpha-TCP, TiO2, Ti and Al as the major phases. An instrumented nanoindenation technique used to study the mechanical properties of the coatings, revealed a very high hardness and Young's modulus of the coating surface as compared to the substrate. This further proved the retainment of the ceramic phase on the surface. Wear studies in a simulated biofluid (SBF) environment demonstrated an increased wear resistance of the coated samples as compared to the bare Ti-6Al-4V. Formation of an apatite-like layer after immersion in SBF for different time periods further demonstrated the bioactivity of the coated samples.
Asunto(s)
Líquidos Corporales/química , Sustitutos de Huesos/química , Fosfatos de Calcio/química , Materiales Biocompatibles Revestidos/química , Cristalización/métodos , Láseres de Estado Sólido , Titanio/química , Aleaciones , Sustitutos de Huesos/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Materiales Biocompatibles Revestidos/efectos de la radiación , Ensayo de Materiales , Propiedades de Superficie , Titanio/efectos de la radiaciónRESUMEN
Nano-sized calcium deficient hydroxyapatite (CDHA) powders with an average particle size less than 100 nm were prepared by a co-precipitation method at low temperature. The initial Ca/P molar ratio was chosen to be less than the stoichiometric ratio of beta-TCP (1.5). Additionally, lowering the temperature and pH values accelerated HPO(4)(2-) incorporation in the CDHA structure. HPO(4)(2-) is considered as an essential source for beta-TCP formation. Sulfate ion doping during the maturation period is proved to be an effective step to eliminate the pyrophosphate P(2)O(7)(2-) phase that results during the calcination of CDHA with Ca/P < 1.5. Furthermore, the heating effect of microwave irradiation resulted in an increase in Ca ion concentration and lowered the CDHA deficiency which affected beta-TCP purity despite its ability to reduce the particle size. A purity of 99.32% beta-TCP with respect to the P(2)O(7)(2-) phase was achieved by increasing the sulfate ion concentration from 2% to 3% and the calcination temperatures from 900 degrees C to 1100 degrees C.
Asunto(s)
Sustitutos de Huesos/química , Fosfatos de Calcio/química , Nanoestructuras/química , Nanoestructuras/ultraestructura , Sulfatos/química , Implantes Absorbibles , Absorción , Líquidos Corporales/química , Sustitutos de Huesos/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Elasticidad/efectos de la radiación , Dureza/efectos de la radiación , Iones , Ensayo de Materiales , Microondas , Nanoestructuras/efectos de la radiación , Tamaño de la Partícula , Dosis de Radiación , Sulfatos/efectos de la radiaciónRESUMEN
The gradient of structural alteration and molecular exchange across CO(2) laser-irradiated areas in dental enamel was analyzed by Raman and attenuated total reflectance infrared microspectroscopy. The type and the degree of structural changes in morphologically distinguishable zones within the laser spot vary depending on the laser-irradiation parameters--power (1 and 3 W), treatment time (5 and 10 s), and operational mode (super pulse and continuous wave). Using higher power, irrespective of the operation mode, the enamel tissue ablates and a crater is formed. The prevalent phase at the bottom of the crater is dehydrated O(2) (2-)-bearing apatite, that is, the fundamental framework topology is preserved. Additional nonapatite calcium phosphate phases are located mainly at the slope of the laser crater. No structural transformation of mineral component was detected aside the crater rim, only a CO(3)-CO(2) exchange, which decays with the radial distance. A lower-power laser irradiation slightly roughens the enamel surface and the structural modification of enamel apatite is considerably weaker for continuous wave than for super pulse mode. Prolonged low-power laser treatment results in recrystallization, and thus structural recovering of apatite might be of clinical relevance for enamel surface treatments.
Asunto(s)
Esmalte Dental/química , Esmalte Dental/efectos de la radiación , Terapia por Láser , Apatitas/química , Apatitas/efectos de la radiación , Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Dióxido de Carbono , Calor , Humanos , Técnicas In Vitro , Ensayo de Materiales , Espectrofotometría Infrarroja , Espectrometría Raman , Difracción de Rayos XRESUMEN
The surface properties of biomedical implant materials control the dynamic interactions at tissue-implant interfaces. At such interfaces, if the nanoscale features influence protein interactions, those of the microscale and mesoscale aid cell orientation and provide tissue integration, respectively. It seems imperative that the synthetic materials expected to replace natural hard tissues are engineered to mimic the complexity of their hierarchical assembly. However, the current surface engineering approaches are single scaled. It is demonstrated that using laser surface engineering a controlled multiscale surface can be synthesized for bioactive functions. A systematic organization of bioactive calcium phosphate coating with multiphase composition on Ti-alloy substrate ranging from nano- to mesoscale has been achieved by effectively controlling the thermo physical interactions during laser processing. The morphology of the coating consisted of a periodic arrangement of Ti-rich and Ca-P-deficient star-like phases uniformly distributed inside a Ca-P-rich self-assembled cellular structure with the presence of CaO, alpha-tricalcium phosphate, CaTiO(3), TiO(2) and Ti phase in the coating matrix. The cellular structures ranged in diameter from 2.5 microm to 10 microm as an assembly of cuboid shaped particles of dimensions of approximately 200 nm x 1 microm. The multiscale texture also included nanoscale particles that are the precursors for many of these phases. The rapid cooling associated with the laser processing resulted in formation, organization and controlling dimensions of the Ca-P-rich glassy phase into a micron scale cellular morphology and submicron scale clusters of CaTiO(3) phase inside the cellular structures. The self-assembly of the coating into multiscale structure was influenced by chemical and physical interactions among the multiphases that evolved during laser processing.
Asunto(s)
Materiales Biocompatibles/química , Fosfatos de Calcio/química , Rayos Láser , Materiales Biocompatibles/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Ensayo de Materiales , Tamaño de la Partícula , Propiedades de Superficie/efectos de la radiaciónRESUMEN
Calcium phosphate (CaP) coatings are used for obtaining a desired biological response. Usually, CaP coatings on metallic substrates are crystallized by annealing at temperatures of at least 400-600 degrees C. For polymeric substrates, this annealing is not possible due to the low melting temperatures. In this work, we present a more suitable method for obtaining crystalline coatings on polymeric substrates, namely laser crystallization. We were successful in obtaining hydroxyapatite coatings on polyethylene. Because of the UV transmission characteristics of the CaP coatings, the use of a low wavelength (157 nm) F(2) laser was necessary for this. As a result of the laser treatment, the CaP coating broke up into islands. The cracks between the islands became larger and the surface became porous with increasing laser energy. The mechanism behind the formation of this morphology did not become clear. However, the fact that crystalline CaP coatings can be obtained on polymeric substrates in an easy way, possibly allows for the development of new products.
Asunto(s)
Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Materiales Biocompatibles Revestidos/química , Materiales Biocompatibles Revestidos/efectos de la radiación , Cristalización/métodos , Rayos Láser , Polietileno/química , Polietileno/efectos de la radiación , Ensayo de Materiales , Propiedades de Superficie , TemperaturaRESUMEN
Octacalcium phosphate (OCP) and Mn(2+)-doped carbonate hydroxyapatite (Mn-CHA) thin films were deposited on pure, highly polished and chemically etched Ti substrates with pulsed laser deposition. The coatings exhibit different composition, crystallinity and morphology that might affect their osteoconductivity. Human osteoblasts were cultured on the surfaces of OCP and Mn-CHA thin films, and the cell attachment, proliferation and differentiation were evaluated up to 21 days. The cells showed a normal morphology and a very good rate of proliferation and viability in every experimental time. Alkaline phosphatase activity was always higher than the control and Ti groups. From days 7 to 21 collagen type I production was higher in comparison with control and Ti groups. The level of transforming growth factor beta 1 (TGF-beta1) was lower at 3 and 7 days, but reached the highest values during following experimental times (14 and 21 days). Our data demonstrate that both calcium phosphate coatings favour osteoblasts proliferation, activation of their metabolism and differentiation.
Asunto(s)
Fosfatos de Calcio/química , Rayos Láser , Osteoblastos/citología , Osteoblastos/fisiología , Titanio/química , Fosfatos de Calcio/efectos de la radiación , Tamaño de la Célula , Supervivencia Celular/fisiología , Células Cultivadas , Materiales Biocompatibles Revestidos/química , Materiales Biocompatibles Revestidos/efectos de la radiación , Calor , Humanos , Ensayo de Materiales , Propiedades de Superficie , Titanio/efectos de la radiaciónRESUMEN
The acid resistance of Nd:YAG laser-ablated enamel surfaces was studied by evaluating crystal structure, mineral distribution, and fluorescence radiance and image in the present study. For comparison, 37% phosphoric acid etching was performed. The formation of beta-tricalcium phosphate (beta-TCP) was confirmed in the laser-ablated surface. The Ca/P ratio increased after ablation due to mineral re-distribution. In contrast, the Ca/P ratio decreased after acid etching due to mineral loss. The laser-ablated enamels showed a smaller increase of fluorescence radiances and less clear laser confocal scanning microscope images than those observed in the acid-etched enamels. The former suggests a minimized mineral loss. The Nd:YAG laser irradiation will enhance the acid resistance and retard the carious progression in enamel.
Asunto(s)
Solubilidad del Esmalte Dental/efectos de la radiación , Esmalte Dental/efectos de la radiación , Rayos Láser , Ácidos , Silicatos de Aluminio , Calcio/análisis , Fosfatos de Calcio/efectos de la radiación , Cristalografía , Esmalte Dental/efectos de los fármacos , Solubilidad del Esmalte Dental/efectos de los fármacos , Microanálisis por Sonda Electrónica , Fluorescencia , Humanos , Microscopía Confocal , Minerales/análisis , Neodimio , Ácidos Fosfóricos/farmacología , Fósforo/análisis , Espectrometría Raman , Desmineralización Dental/metabolismo , Difracción de Rayos X , ItrioRESUMEN
In this study, radiofrequency sputtered calcium phosphate (CaP) coatings were evaluated after 1h post-deposition heat treatment at either 350 degrees C, 400 degrees C, 450 degrees C, 500 degrees C or 600 degrees C in the presence or absence of water vapor. X-ray diffraction analyses indicated the as-sputtered coatings to be amorphous. With different post-deposition heat treatments used, in this study, crystallinity of CaP coatings was observed to be in the range of 0-68%. The 400 degrees C and 450 degrees C heat-treated CaP coatings in the absence of water vapor were poorly crystalline, exhibiting a crystallinity of 2+/-1%. In comparison to heat treatments at 450 degrees C in the absence of water vapor, the presence of water vapor at 450 degrees C heat treatment resulted in a significant increase in coating crystallinity. However, this effect was not observed at higher temperatures. A coating crystallinity of 60-68% was observed for coatings heat treated at 450 degrees C in the presence of water vapor, and at 500 degrees C and 600 degrees C in the presence or absence of water vapor. In addition, increases in the degree of coating crystallinity were observed to be consistent with the increasing number of PO(4) peaks observed as a result of different post-deposition heat treatments. It was concluded that the presence of water vapor at 450 degrees C post-deposition heat treatment significantly affect the crystallinity of CaP coatings, whereas an increase to temperature higher than 450 degrees C and in the presence of water vapor has no significant effect on crystallinity.
Asunto(s)
Fosfatos de Calcio/química , Fosfatos de Calcio/efectos de la radiación , Materiales Biocompatibles Revestidos/química , Materiales Biocompatibles Revestidos/efectos de la radiación , Cristalización/métodos , Calor , Ensayo de Materiales/métodos , Agua/química , Gases/química , Microscopía Electrónica de Rastreo , Conformación Molecular , Espectroscopía Infrarroja por Transformada de Fourier , Difracción de Rayos XRESUMEN
A strategy is described for exploiting temperature driven self-assembly of collagen and thermally triggered liposome mineralization to form a mineralized collagen composite from an injectable precursor fluid. Optical density and rheological experiments demonstrated the formation of a collagen gel when acid-soluble type I collagen solutions (1-7 mg/ml) were heated to 24-30 degrees C. Scanning calorimetry experiments demonstrated that mixtures of calcium- and phosphate-loaded liposomes composed of dipalmitoylphosphatidylcholine (90 mol%) and dimyristoylphosphatidylcholine (10 mol%) were stable at room temperature but formed calcium phosphate mineral when heated above 35 degrees C, a consequence of the release of entrapped salts at the lipid chain melting transition. The formation of calcium phosphate mineral induced by triggered release of calcium and phosphate was detected as an endothermic transition (deltaH=6.2+/-1.1 kcal/mol lipid) near the lipid chain melting transition (Tm=37 degrees C). Combining an acid-soluble collagen solution with calcium- and phosphate-loaded liposomes resulted in a liposome/collagen precursor fluid, which when heated from room temperature to 37 degrees C formed a mineralized collagen gel. The dynamic storage modulus of the collagen scaffold increased upon mineralization, and direct nucleation of mineral from the collagen scaffold was detected by electron microscopy.
Asunto(s)
Materiales Biomiméticos/síntesis química , Calcificación Fisiológica/fisiología , Fosfatos de Calcio/química , Colágeno/química , Calor , Liposomas/química , Liposomas/efectos de la radiación , Materiales Biomiméticos/efectos de la radiación , Biomimética/instrumentación , Biomimética/métodos , Calcificación Fisiológica/efectos de la radiación , Fosfatos de Calcio/efectos de la radiación , Colágeno/efectos de la radiación , Materiales Manufacturados , Ensayo de Materiales , Minerales/químicaRESUMEN
Thermokinetics method was used to study the self-setting kinetics of a new kind of calcium phosphate cement (CPC) in the present study. A calcium-deficient hydroxyapatite CPC was developed by using alpha-TCP and other calcium phosphate bioceramics. The mixing liquids used were deionized water and 0.25 M NaH2PO4/Na2HPO4, respectively. The calorimetric curves, heat evolution curves and total heat evolution in the setting and hardening process of CPC were determined. It has been found that mixing liquids, reaction temperature had influences on the calorimetric curves and heat evolution, and mixing liquids exhibited the greatest influence on the kinetics of CPC during the self-setting and hardening process. Based on the calorimetric curves obtained, the kinetic model equation was simulated, and the reaction control step was determined.