Sol-gel derived fluor-hydroxyapatite biocoatings on zirconia substrate

Fluor-hydroxyapatite (FHA) film was coated on a zirconia (ZrO(2)) substrate by a sol-gel method. An appropriate amount of F ions was incorporated into the hydroxyapatite (HA) during the preparation of the sols. The apatite phase began to crystallize after heat treatment at 400 degrees C, and increased in intensity above 500 degrees C. No decomposition was detected by X-ray diffraction analyses up to 800 degrees C, which illustrates the high thermal stability of the FHA films. The films showed a uniform and dense morphology with a thickness of approximately 1 microm after a precisely controlled heat treatment process. These FHA films adhered firmly to the zirconia substrate, representing notable adhesion strengths of approximately 70 MPa after heat treatment above 500 degrees C. The dissolution rate of the FHA coating layer varied according to the heat treatment temperature, which was closely related to the film crystallinity. The dissolution rate of the FHA film was lower than that of the HA film, suggesting the possibility of a functional gradient coating of HA and FHA. The MG63 cells seeded onto the FHA films proliferated in a similar manner to those seeded onto pure HA ceramic and a plastic control.     

Effect of substrate temperature on mechanical properties of calcium phosphate coatings

The effect of substrate temperature and processing parameters on mechanical properties of nanoscale calcium phosphate coatings are being studied in order to refine the processing technique for Functionally Graded Hydroxyapatite (FGHA) coatings. Coatings were deposited on titanium substrates with a set substrate temperature of 450, 550, 650, or 750 degrees C in an Ion Beam Assisted Deposition (IBAD) system using a sintered hydroxyapatite (HA) target. Mechanical properties of the coatings deposited with a set substrate temperature such as, bonding/adhesion strength to the substrate, nanohardness, and Young's Modulus as well as coating thickness were evaluated and compared with commercial plasma spray HA coatings. It is concluded that depositing FGHA coatings would better be started at 550-650 degrees C to maintain superior properties of the film at the interface. It can also be concluded that the residual stresses caused by different Coefficient of Thermal Expansions (CTEs) between the substrate and coatings are not the only factor controlling the bonding strength and mechanical properties of these samples. Other parameters such as the nature of the interface layers and their bonding to each other as well as the density and grain structure of the coatings must be taken into consideration for an appropriate evaluation of mechanical properties of calcium phosphate coatings deposited on heated substrate.     

Hydroxyapatite and titania sol-gel composite coatings on titanium for hard tissue implants; mechanical and in vitro biological performance

Hydroxyapatite (HA) composites with titania (TiO2) up to 30 mol % were coated on a titanium (Ti) substrate by a sol-gel route, and the mechanical and biological properties of the coating systems were evaluated. Using polymeric precursors, highly stable HA and TiO2 sols were prepared prior to making composite sols and coatings. Coatings were produced under a controlled spinning and heat treatment process. Pure phases of HA and TiO2 were well developed on the composites after heat treatment above 450 degrees C. The HA-TiO2 composite coating layers were homogeneous and highly dense with a thickness of about 800-900 nm. The adhesion strength of the coating layers with respect to Ti substrate increased with increasing the TiO2 addition. The highest strength obtained was as high as 56 MPa, with an improvement of about 50% when compared to pure HA (37 MPa). The osteoblast-like cells grew and spread actively on all the composite coatings. The proliferation and alkaline phosphatase (ALP) activity of the cells grown on the composite coatings were much higher than those on bare Ti, and even comparable to those on pure HA coating. Notably, the HA-20% TiO2 composite coating showed a significantly higher proliferation and ALP expression compared to bare Ti (p < 0.05). These findings suggest that the sol-gel-derived HA-TiO2 composite coatings possess excellent properties for hard tissue applications from the mechanical and biological perspective.     

Calcium phosphates and glass composite coatings on zirconia for enhanced biocompatibility

Calcium phosphates (CaP) and phosphate-based glass (P-glass, xCaO-(0.55-x) Na(2)O-0.45P(2)O(5) composition) composite coatings were obtained on a strong ZrO(2) to improve biocompatibility, the mechanical strength and biological activity. Hydroxyapatite (HA) and P-glass mixed powder slurries were coated on the ZrO(2) substrate, and subsequently heat-treated to obtain CaP- and P-glass composite coatings. The effects of glass composition (x=0.3, 0.4, 0.5 mol), mixing ratio of glass to HA (30%, 40%, 50% wt/wt), and heat treatment temperature (800 degrees C, 900 degrees C, 1000 degrees C) on the coating properties were investigated. After heat treatment, additional calcium phosphates, i.e., dicalcium phosphate (DCP) and tricalcium phosphate (TCP), were crystallized, resulting in the formation of triphasic calcium phosphates (HA-TCP-DCP) surrounded by a glass phase. The relative amounts of the crystalline phases varied with coating variables. The higher heat treatment temperature and glass amount, and the lower CaO content in the glass composition rendered the composite coatings to retain the higher amounts of TCP and DCP while the initial HA decreased. These appearance of additional crystalline phases and reduction of HA amount were attributed to the combined effects, i.e., the melting-crystallization of P-glass and the reaction between glass liquid phase and HA powder during thermal treatment. As a result of the glass phase in the composite coatings, their microstructures became much denser when compared to the pure HA coating. In particular, a completely dense structure was obtained at coating conditions with large amount of glass addition (50 wt%) at the glass composition of lower CaO content (0.3 mol CaO), and the following heat treatment above 800 degrees C for 2h. As a result, the adhesion strengths of the composite coating layers were significantly improved when compared to the pure HA coating. The highest strength of the composite coating was approximately 40 MPa, an improvement of approximately 80% with respect to the pure HA coating. The composite coatings showed much higher dissolution rates than the pure HA coating due to the newly formed crystallines (TCP and DCP) and the remaining glass phase. The osteoblast-like cells grew and spread actively on the composite coating samples. The proliferation numbers and alkaline phosphate (ALP) activities of the cells on the composite coatings were improved by approximately 30-40% when compared to Thermanox control and ZrO(2) substrate, and were comparable to the pure HA coating. These findings suggested that the CaP and P-glass composites are potentially useful for hard tissue coating system, due to their morphological and mechanical integrity, enhanced bioactivity, and favorable responses to the osteoblast-like cells.     

Fluor-hydroxyapatite sol-gel coating on titanium substrate for hard tissue implants

Hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) films were deposited on a titanium substrate using a sol-gel technique. Different concentrations of F- were incorporated into the apatite structure during the sol preparation. Typical apatite structures were obtained for all coatings after dipping and subsequent heat treatment at 500 degrees C. The films obtained were uniform and dense, with a thickness of approximately 5 microm. The dissolution rate of the coating layer decreased with increasing F- incorporation within the apatite structure, which demonstrates the possibility of tailoring the solubility by a functional gradient coating of HA and FHA. The cell proliferation rate on the coating layer decreased slightly with increasing F- incorporation. The alkaline phosphatase (ALP) activity of the cells on all the HA and FHA coated samples showed much higher expression levels compared to pure Ti. This confirmed the improved activity of cell functions on the substrates with the sol-gel coating treatment.     

Hydroxyapatite coating on titanium substrate with titania buffer layer processed by sol-gel method

Hydroxyapatite (HA) was coated onto a titanium (Ti) substrate with the insertion of a titania (TiO2) buffer layer by the sol-gel method. The HA layer was employed to enhance the bioactivity and osteoconductivity of the Ti substrate, and the TiO2 buffer layer was inserted to improve the bonding strength between the HA layer and Ti substrate, as well as to prevent the corrosion of the Ti substrate. The HA layer coated over the TiO2 showed a typical apatite phase at 400 degrees C and the phase intensity increased above 450 degrees C. The sol-gel derived HA and TiO2 films, with thicknesses of approximately 800 and 200 nm, respectively, adhered tightly to each other and to the Ti substrate. The bonding strength of the HA/TiO2 double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The highest strength of the double layer coating was 55 MPa after heat treatment at 500 degrees C. The improvement in bonding strength with the insertion of TiO2 was attributed to the resulting enhanced chemical affinity of TiO2 toward the HA layer, as well as toward the Ti substrate. Human osteoblast-like cells, cultured on the HA/TiO2 coating surface, proliferated in a similar manner to those on the TiO2 single coating and on the pure Ti surfaces. However, the alkaline phosphatase activity of the cells on the HA/TiO2 double layer was expressed to a higher degree than that on the TiO2 single coating and pure Ti surfaces. The corrosion resistance of Ti was improved by the presence of the TiO2 coating, as confirmed by a potentiodynamic polarization test.     

Synthesis of biomimetic Ca-hydroxyapatite powders at 37 degrees C in synthetic body fluids

An important inorganic phase for synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a nano-sized (approximately 50 nm), homogeneous and high-purity ceramic powder from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in modified synthetic body fluid (SBF) solutions at 37 degrees C and pH of 7.4 using a novel chemical precipitation technique. The synthesized precursors were found to easily reach a phase purity >99% after 6 h of calcination in air atmosphere at 90 degrees C, following oven drying at 80 degrees C. There was observed, surprisingly, no decomposition of HA into the undesired beta-TCP phase even after heating at 1,600 degrees C in air for 6 h. This observation showed the superior high-temperature stability of such 'biomimetic' HA powders as compared to those reported in previous studies. The former powders were also found to contain trace amounts of Na and Mg ions, originating from the use of SBF solutions instead of pure water during their synthesis. Characterization and chemical analysis of the synthesized powders were performed by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infra-red spectroscopy, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy.     

不同分散介质研磨所得纳米珍珠粉的比较

文题释义：纳米材料：物质结构在三维空间中至少有一维处于纳米尺度，或由纳米结构单元构成的且具有特殊性质的材料。在最新的一项纳米碳酸钙标准中，要求颗粒平均粒径≤100 nm。 纳米珍珠粉：以无水乙醇或水作为分散介质球磨细化珍珠粉，研磨介质为0.1 mm氧化锆球，通过扫描电镜、透射电镜、X射线衍射仪检测分析珍珠粉粒径，珍珠粉平均晶粒、平均粒径<100 nm，属于纳米材料。 背景：为了保留更多的有机质及材料生物学活性，需通过物理方法研磨细化珍珠粉。球磨法可以最大限度地保留珍珠粉中的有机质及其活性，而不同分散介质球磨制备的纳米材料效果不同。 目的：对以蒸馏水和无水乙醇两种分散介质研磨所得的纳米珍珠粉进行对比。 方法：分别以无水乙醇与水作为分散介质研磨制备纳米珍珠粉，采用扫描电镜、透射电镜、X射线衍射仪、凯氏定氮法及食品中氨基酸测定等方法比较分析研磨前后的珍珠粉。 结果与结论：①以无水乙醇为分散介质制备的纳米珍珠粉主要为类圆形颗粒，大小不等，主要分布在30-50 nm，平均晶粒20 nm，方解石碳酸钙相对百分比增至7%，蛋白质和氨基酸含量未发生明显变化；②以蒸馏水为分散介质制备的纳米珍珠粉主要为类圆形颗粒，存在较大的条状或块状不规则颗粒，大小不均，平均晶粒30 nm，方解石碳酸钙相对百分比增至10%，蛋白质和氨基酸含量有所减少；③结果表明两种分散介质研磨后珍珠粉粒度有明显差异，以无水乙醇为分散介质研磨的珍珠粉粒度更细更均匀。 ORCID: 0000-0002-9436-3464(毛秋华) 中国组织工程研究杂志出版内容重点：生物材料；骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性；组织工程     

Effect of spark plasma sintering on the microstructure and in vitro behavior of plasma sprayed HA coatings

The crystalline phases and degree of crystallinity in plasma sprayed calcium phosphate coatings on Ti substrates are crucial factors that influence the biological interactions of the materials in vivo. In this study, plasma sprayed hydroxyapatite (HA) coatings underwent post-spray treatment by the spark plasma sintering (SPS) technique at 500 degrees C, 600 degrees C, and 700 degrees C for duration of 5 and 30 min. The activity of the HA coatings before and after SPS are evaluated in vitro in a simulated body fluid. The surface microstructure, crystallinity, and phase composition of each coating is characterized by scanning electron microscopy and X-ray diffractometry before, and after in vitro incubation. Results show that the plasma sprayed coatings treated for 5 min in SPS demonstrated increased proportion of beta-TCP phase with a preferred-orientation in the (214) plane, and the content of beta-TCP phase corresponded to SPS temperature, up to 700 degrees C. SPS treatment at 700 degrees C for 30 min enhanced the HA content in the plasma spray coating as well. The HA coatings treated in SPS for 5 min revealed rapid surface morphological changes during in vitro incubation (up to 12 days), indicating that the surface activity is enhanced by the SPS treatment. The thickest apatite layer was found in the coating treated by SPS at 700 degrees C for 5 min.     

Crystal chemistry of hydroxyapatite deposited on titanium by sputtering technique

Crystalline hydroxyapatite (HA) powder was coated on titanium substrate by radio frequency (RF) magnetron sputtering. The coating was homogeneous thin film and the thickness was 1microm. Crystallinity of the HA coating was low and Ca/P ratio was high as 3.0. Particle sizes were 40 to approximately 100 nm, and the crystallite size was calculated by 30 to approximately 50 nm using an X-ray diffractometry (XRD) and a transmission electron microscopy (TEM). When the coating was heated at 800 degrees C for 1 h, the low crystalline HA grew up crystalline HA, and a diffraction pattern of CaO appeared. When the coating was immersed in pH 7.4 of bovine serum for 1 week, c-axis of HA increased.     

Novel sol-gel bioactive fibers

Bioactive fibers were produced using a sol-gel method. The rheological properties of two different sol compositions prepared from a mixture of TEOS, phosphorous alkoxide and calcium nitrate, or calcium chloride in a water-ethanol solution, are reported. The sols were extruded through a spinneret to produce continuous 10 microm-diameter fibers. Discontinuous fibers and fibrous mats were prepared by air-spraying the multicomponent sols. The sol-gel fibers were converted to the bioactive fibers by three different thermal treatments at either 600 degrees, 700 degrees, or 900 degrees C for 3 h. SEM, BET, EDX, and FTIR were used to characterize the morphology and structure of the fibers. The BET measured surface area of the fibers sintered at 900 degrees C was 0 m(2)/gm compared to a value of 200 m(2)/gm for a typical sol-gel-derived particle of similar composition. Both the continuous and discontinuous fibers exhibited in vitro bioactivity in a simulated body fluid.     

High temperature in-situ XRD of plasma sprayed HA coatings.

The control of phase transformations in plasma sprayed hydroxyapatite (HA) coatings are critical to the clinical performance of the material. This paper reports the use of high temperature X-ray diffraction (HT-XRD) to study, in-situ, the phase transformations occurring in plasma sprayed HA coatings. The coatings were prepared using different spray power levels (net plasma power of 12 and 15 kW) and different starting powder size ranges (20-45; 45-75 microm). The temperature range employed was room temperature (approximately 26 degrees C) to 900 degrees C in normal atmosphere and pressure. High temperature differential scanning calorimetry (DSC) was also employed to investigate and determine the precise onset temperature of phase transformations during the recrystallization process. Results showed that actual onset of thermal degradation in the coating into other metastable phases like TTCP, beta-TCP and CaO occurred at 638 degrees C. The aforementioned phase transitions were independent of the selected spraying parameters. The degree of melting and thermal dissociation of HA actually determines the amount of calcium phosphate phases that are formed. A high power level of 15 kW produced a greater degree of melting, resulting in more CaO, TTCP and beta-TCP being formed as a result.     

Hydroxyapatite coating on titanium by thermal substrate method in aqueous solution.

A new hydrocoating method (the thermal substrate method) is proposed for coating calcium phosphates such as hydroxyapatite (HA), on titanium substrates in an aqueous solution. Several factors (e.g., the type of ion source, the heating time and temperature, and the surface roughness of the substrate) affected the characteristics of the precipitate formed by this method. The solution used included 3 mmol dm(-3) Ca(H(2)PO(4))(2) and 7 mmol dm(-3) CaCl(2), and its pH was adjusted to 6.5. The experimental studies were conducted under the following conditions: temperature 45-160 degrees C, heating time 10-20 min, and surface roughness of substrate #120-#2000 grid ground using energy paper. A high quality of precipitate, whose predominant component was HA, was obtained on titanium substrates by the thermal substrate method in an aqueous solution. No significant difference in the precipitates was found with the type of ion source. The amount of HA precipitate increased with increasing temperature and with increasing heating time. The features of the precipitate were different, depending on the surface roughtness of the substrate: HA regularly nucleated along the grooves of the rough surface (#120 and #400 grid), and in the case of the fine surface (#1200-#2000 grid), a uniform precipitation occurred.     

TEM and STEM analysis on heat-treated and in vitro plasma-sprayed hydroxyapatite/Ti-6Al-4V composite coatings

A cogent understanding of the microstructure, and indeed nano-structure, of hydroxyapatite (HA) and the interface between Ti-6Al-4V and HA is crucial to its appropriateness as a biomaterials. This paper reports the analysis of plasma-sprayed HA/Ti-6Al-4V composites by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to elucidate the intricate nature of the materials following plasma spray processing and in vitro evaluation. The novel Ti-6Al-4V/HA composite coating, with approximately 48 wt% HA, had demonstrated attractive tensile adhesion strength (approximately 28 MPa) and improved Young's modulus (approximately 55 GPa). Experimental results demonstrated that amorphous calcium phosphate and fine HA grains were formed during rapid splat solidification in the as-sprayed composite coatings. Small Ti-6Al-4V grains were observed adjacent to the amorphous calcium phosphate. The coatings were further heat treated at 600 degrees C for 6 h, and significant crystallisation of the amorphous calcium phosphate phase took place. However, complete crystallisation was not achieved at this temperature, as the coatings invariably contained a small amount of amorphous calcium phosphate phase in some local regions. After immersion in simulated body fluid for 2 weeks and 10 weeks, TEM and STEM confirmed that the interfaces inside the coating maintained good microstructural integrity.     

Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.     

溶胶-凝胶法制备纳米羟基磷灰石超薄薄膜及其表征

分别使用有机溶胶-凝胶以及无机溶胶作为羟基磷灰石（HA）前驱体，利用浸渍涂层（Dip-coating）技术在钛表面制备纳米超薄薄膜。利用扫描电镜（SEM）和X射线衍射（XRD）表征薄膜形态、微晶尺寸分布（D）和微观应变（ε）。结果表明：在大于400℃热处理后，薄膜开始呈现磷灰石结构；在400℃～600℃范围内，热处理温度对两种磷灰石薄膜D和ε的影响显著；SEM结果证明HA前驱体种类严重影响两种纳米HA薄膜的颗粒团聚尺寸；有机溶胶-凝胶和无机凝胶在钛表面制备的HA薄膜颗粒团聚尺寸分别为25nm和100nm，薄膜厚度分别为2．5μm和5．0μm。浸渍涂层技术制备的HA薄膜表面／界面形态完整，薄膜表面无明显微裂纹。     

医用镍钛形状记忆合金羟基磷灰石涂层的制备及其生物活性

背景：目前多采用等离子喷涂技术在钛及其合金表面涂覆羟基磷灰石涂层,制备成复合材料。但由于羟基磷灰石与钛合金基体的热膨胀系数相差较大,涂层在冷却过程中易产生脱落。 目的：在医用镍钛形状记忆合金表面制备致密、均匀的羟基磷灰石生物陶瓷涂层,利用动物实验考查镍钛/羟基磷灰石涂层材料的生物相容性。 方法：利用阴极旋转法在低温条件下从含钙、磷离子的电解水溶液中在镍钛形状记忆合金表面沉积了磷酸钙涂层,经碱处理获得羟基磷灰石涂层。分析工艺参数对涂层结构的影响。利用动物植入实验对该复合材料的生物活性进行研究,并与镍钛/羟基磷灰石与Ca₃(PO₃)₂•2H2O混合涂层复合材料、医用镍钛形状记忆合金、医用钛合金进行对比。 结果与结论：电化学沉积-碱处理方法适合在镍钛形状记忆合金表面制备羟基磷灰石生物活性陶瓷涂层,沉积电压、温度对涂层结构有强烈影响。4种不同材料植入动物体内后周围均出现不同程度的组织增生,在骨膜组织切片中都可见软骨细胞且有骨小梁形成,涂覆有羟基磷灰石涂层的植入材料组织反应较轻,相应的组织切片中所显示出的软骨细胞、骨小梁数量最多,分布均匀,表明羟基磷灰石涂层提高了医用镍钛形状记忆合金的生物活性。         

Plasma-sprayed hydroxyapatite+titania composite bond coat for hydroxyapatite coating on titanium substrate

A two-layer hydroxyapatite (HA)/HA+TiO(2) bond coat composite coating (HTH coating) on titanium was fabricated by plasma spraying. The HA+TiO(2) bond coat (HTBC) consists of 50 vol% HA and 50 vol% TiO(2) (HT). The microstructural characterization of the HTH coatings before and after heat treatment was conducted by using scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffractometer (XRD) and transmission electron microscopy (TEM), in comparison with that of HT coating and pure HA coating. The results revealed that HA and TiO(2) phases layered in an alternating pattern within the HTBC, and the HTBC bonded well to HA top coating (HAT coating) and Ti substrate. The as-sprayed HT coating consists mainly of crystalline HA, rutile TiO(2) and amorphous Ca-P phase. The post-spray heat treatment at 650 degrees C for 120 min effectively restores the structural integrity of HA by transforming non-HA phases into HA. It was found that there exists interdiffusion of the elements within the HTBC, but no chemical product between HA and TiO(2), such as CaTiO(3) was formed. The cross-sectional morphologies confirmed that there is a shift towards a relatively tighter bonding from the HAT coating/HTBC interface in the as-sprayed HTH coating to the HTBC/Ti substrate interface in the heat-treated HTH coating. On quenching the coatings into water, the surface cracking indicates more apparently the positive effect of the HTBC on the decrease of residual stress in HAT coating. The in situ surface cracking also suggests that the stress on the surface of the HTH coating is stable under subjection to a repetitious heat treatment. The toughening and strengthening of HTBC is thought to be mainly due to TiO(2) as obstacles embarrassing cracking, the reduction of the near-tip stresses resulting from stress-induced microcracking and the decrease of CTE mismatch. In the HTH composite coating, the HAT coating is toughened by the decreased CTE mismatch with Ti through the addition of HTBC, which bonds well to the Ti substrate via its TiO(2) hobnobbing with the Ti oxides formed on Ti substrate.     

Raman spectroscopic study on water in aqueous gelatin gels and sols

A Raman spectroscopic study on property changes of water in aqueous gelatin media was carried out. The state of water in gelatin gels and sols at various temperatures and concentrations was studied in connection with the conformation of polymer chains. When gelatin with a low molecular weight was used, there was no gel-sol transition, and the structure of water observed by Raman spectroscopy was not significantly affected by the presence of gelatin. When gelatin with a high molecular weight was used, on the other hand, the structure of water strongly depended on the concentration of gelatin both in the gel and the sol state. A contribution of small spaces surrounded by entangled gelatin chains (which exist both in high concentration gels and sols) to the perturbation of the structure of incorporated water was suggested. It was also found that, at 60°C, gelatin chains in the low concentration region induced an enhancement of structured water. This is the first finding that water soluble polymers at high temperature induce the network structure of water.     

Characterisation of the rheological properties and zeta potential of a range of hydroxyapatite powders

The effect of precipitation temperature, i.e. particle morphology on the rheological properties of a hydroxyapatite (HA) slip was investigated and compared to a commercial HA (batch P120 supplied by Plasma Biotal, Tideswell, Derbyshire, UK). The commercial HA was highly crystalline and had a particle size much larger than the HA precipitated at 60 and 80 degrees C. With no deflocculant addition, the commercial HA had a viscosity much higher compared to the precipitated HA as expected. The commercial HA and the HA precipitated at 60 degrees C showed similar pseudoplastic behaviour, but the HA precipitated at 80 degrees C showed Newtonian behaviour. This was explained by the HA precipitated at 80 degrees C having mean particle size of 82.24 nm, but a much wider particle size distribution. This is confirmed by the electrophoretic mobility measurements which show that the HA precipitated at 80 degrees C has a much lower zeta potential at a 0 wt% addition of deflocculant. Because of the wider particle size distribution, the need to add deflocculant is much reduced.