Preparing hydroxyapatite powders with controlled morphology

doi:10.1016/0142-9612(96)00019-1

Biomaterials

Volume 17, Issue 20, October 1996, Pages 1959-1964

https://doi.org/10.1016/0142-9612(96)00019-1 Get rights and content

Abstract

We developed a synthesis method for hydroxyapatite particles with different morphologies. The process involved chemical precipitation and spray drying, which produced spherical, agglomerated hydroxyapatite granules with controlled particle sizes and structures. These granules contained nanoparticles with an average crystalline size of about 10 nm. We controlled the morphologies of the granules by adjusting the spray-drying conditions, such as the volume fraction of feed slurry and the atomization pressure. The spray-dried granules were doughnut shapes, solid spheres, or hollow spheres, and their sizes were controlled by varying the atomization pressure and the concentration of the feed slurry.

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Cited by (114)

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This paper addresses the powder synthesis of nanocrystalline hydroxyapatite (HA) in a hydrothermal autoclave reactor using deionized water and the chemical reactants Ca(NO3)2 and (NH4)2HPO4 at varying pH values (7–11) and temperatures ranging from 50 to 130 °C. Analysis of the synthesized powder products included XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), SEM/EDX (scanning electron microscopy), and TG/DTG (thermogravimetry). Hexagonal and monoclinic hydroxyapatite crystallized mostly after 24-h hydrothermal processing at different initial pH values and temperatures (50–130 °C). When the temperature rose from 50 to 110 °C at a fixed pH of 10, the hexagonal phase became more prevalent while the monoclinic phase decreased proportionally. The monoclinic phase crystallite size reduced from 231.08 to 31.51 nm. Despite a constant temperature of 80 °C, pH levels ranging from 7 to 11 revealed substantial hexagonal and monoclinic hydroxyapatite with minimal monetite and brushite. FTIR spectroscopy confirmed the functional groups associated with hydroxyapatite spectra. The SEM method also revealed HA powder with spherules and anhedral agglomerates having Ca/P ratios (1.1–2.15). TG/DTG results confirmed that hydrothermal-derived HA nanosized powders are thermally stable microstructures for biomedical applications.
Spray dried hydroxyapatite-based supraparticles with uniform and controllable size and morphology
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Citation Excerpt :
However, the effect of PS agglomeration degree induced by salt on the morphology of supraparticles was unclear due to the lack of characterization of the size of PS dispersed in the suspension after adding salt. Additionally, changing the solid content of HAP [24], adding dispersant of polyvinyl alcohol [25] or introducing pore forming agent of ammonium bicarbonate [26] generated SD supraparticles of doughnut-shaped, spherical or hollow porous structure. As the supraparticle is formed by a controlled agglomeration of primary nano(micro)particles, it is clear that the resulting structure directly relates to the balance of forces acting between the particles and the kinetics of the assembly process via spray drying.
This work aims to prepare uniform spray dried hydroxyapatite-based (SD HAP-based) supraparticles with controllable morphology via micro-fluidic spray drying. Sodium polyacrylate (PAAS) and sodium chloride (NaCl) were used to prepare the precursor suspensions by regulating the inter-particle repulsive forces and electrostatic shielding effect, respectively. The particle size (D50) and zeta potential of the suspension were highly associated with the mass ratio of HAP to PAAS (m_H/m_P) and the NaCl concentration (C_NaCl), which further had significant effect on the permeability (k) of the droplet shell formed during spray drying and ultimately the supraparticle morphology. D50 ˂ 2 µm and absolute zeta potential ˃ 20 mV, obtained when m_H/m_P ˂ 100 under low C_NaCl, rendered ultralow k and consequently deformed supraparticles; Whereas D50 ˃ 2 µm and absolute zeta potential ˂ 20 mV, achieved by decreasing PAAS amount, i.e. m_H/m_P ≥ 100 or improving C_NaCl to efficiently screen surface net charge of HAP, high k and spherical supraparticles were thus preferentially formed.
Effect of the modification of spray drying parameters on the fabrication of bovine-derived hydroxyapatite microspheres for biomedical applications
2022, Materials Today Communications
Citation Excerpt :
The formation of granules begins with the migration of the solid towards the surface of the drop, generating a rigid shell [63,64]. The formation of this layer depends mainly on the additives and the concentration of the slurry [32,34,65]. The presence of the additive on the surface could restrict the mass exchange, and together with a low concentration of solids, it may produce cracks and broken particles as a consequence of a thin shell (Fig. 6, conditions C1 and C2).
In this work, the effect of the spray dryer parameters on bovine-derived hydroxyapatite (BHAp) was studied to fabricate microspheres with controlled particle size distribution and morphology. A factorial design was implemented to establish the impact of spray drying process parameters on the final BHAp powder properties. The critical process factors were solid content in the slurry, atomization pressure, and hot air flow rate, whereas the studied experimental outputs were particle size distribution and morphology, characterized by laser diffraction and scanning electron microscopy, respectively. Additionally, the Ca/P molar ratio was evaluated from X-ray diffraction data. The obtained results showed a strong influence of the atomization pressure and the solid slurry content on the particle size distribution (increasing from 2.56 ± 0.02 µm to 32.46 ± 0.78 µm) and particle morphology (with an increased circularity from 0.3502 ± 0.0172 to 0.8688 ± 0.0039), being both properties suitable for thermal spray (TS) applications. Moreover, the BHAp crystalline structure and Ca/P molar ratio did not present any changes with the spray drying process parameters employed. Finally, it was found that magnesium was preserved in the spray dried particles, the former being also present in the starting powder feedstock.
Additive manufacturing of ceramic alumina/calcium phosphate structures by DLP 3D printing
2022, Materials Chemistry and Physics
Producing micro and macroporous 3D structures that mimic the bone architecture of a specific anatomic region, namely the rounded trabeculae in trabecular bone, is a considerable challenge, to which additive manufacturing can make a fundamental contribution. The main objective of the work was to explore the Digital Light Processing (DLP) technique in obtaining customized parts, from a ceramic suspension composed of two different materials, specifically alumina and hydroxyapatite (HA), with a trabecular bone architecture, using Computer Assisted Design (CAD) modelling techniques and additive manufacturing. Hydroxyapatite (HA) was added to the alumina matrix to improve the biocompatibility and bioactivity of the composites after sintering. After optimizing all printing parameters and the suspensions rheological properties, samples in alumina and alumina-hydroxyapatite with the desired architecture were obtained. The influence of the incorporation of hydroxyapatite in the alumina formulations was also analyzed, with increasing hydroxyapatite contents: 5, 10, and 15 wt%. The rheological behaviour of the suspensions was studied in a plate-to-plate system. The physical-chemical and mechanical characterization of produced samples were carried out by X-ray diffraction, Scanning electron microscopy, and compressive tests. The suspensions prepared with two different materials showed adequate viscosity to achieve a good spread and homogeneous layers in the 3D printing process. In the produced samples, the occurrence of a hibonite phase (CaAl₁₂O₁₉), resulting from the reaction between alumina and hydroxyapatite during the sintering step, increased the compressive strength of the samples. The high temperature needed for sintering alumina led to the conversation of HA into TCP. The achieved mechanical strength results from the porosity level and the thickness of the struts of the printed architecture. DLP showed to be a precision printing technology of low cost that can be used to fabricate parts in the industry from a suspension composed of a mixture of alumina and HA powders, which is very useful in the bone repair field and not previously reported.
Tailoring hydroxyapatite microspheres by spray-drying for powder bed fusion feedstock
2022, Powder Technology
The present work deals with a study on the physical characteristics of stoichiometric hydroxyapatite microspheres produced by spray-drying process through different operating conditions. Obtained hydroxyapatite microspheres are intended to be used as powder feedstock in powder bed selective laser processing additive manufacturing technologies where the flowability and the particle size distribution of the powder feedstock are of special importance. The powders produced at different spray-drying operating parameters were evaluated by analysing the particle size, shape, moisture, and agglomerates strength. Spray air pressure (0.25–2 bars) and the solid content of the slurries (10–50% wt.) were the most influent parameters to control the final particle size distribution, whereas the higher process recovery rate (79%) was obtained at specific values of inlet temperature (250 °C), spray air pressure (2 bar), and feed rate (4.9 kg.h⁻¹). A 5 wt% of polyvinyl alcohol as an organic binder to the ceramic part was found to increase the strength of the granules. The flowability of the produced hydroxyapatite microspheres (x₅₀ = 64 μm; span = 1.77) was found to fulfil the defined feedstock requirements (e.g., Hausner ratio < 1.25), without alteration of the physico-chemical properties of the material. These promising results confirm the use of a spray dryer as an efficient method for the production of hydroxyapatite microspheres for powder bed selective laser processing.
Screening method for producing suitable spray-dried HA powder for SLS application
2021, Powder Technology
Citation Excerpt :
Particle size information is displayed in Fig. 9 and Table 3. It has been reported in the related bibliography that a higher atomization pressure decreases the particle size [35,38,40]. This observation is in accordance with our results, when comparing SD09 and SD11 (same slurry feed and SD11 with higher atomization pressure), SD11 possesses lower particle values for D10 and D50.
Screen methods are time-saving tools, assisting the establishment of a new process or technique for laboratory and industrial scale. This paper presents a step-by-step approach to use spray drying (SD) for obtaining hydroxyapatite (HA) powder, with suitable characteristics to be used as a filler in a polymer matrix, for selective laser sintering (SLS) processing. The proposed method consists of adjusting the departing HA suspension and SD processing parameters, briefly discussing relevant elements that must be considered. Suspension's rheological behavior and spray-dried powder morphological features were investigated, serving as selection criteria for the favorable set-up. Variations on slurry feed and atomization pressure of SD processing parameters have allowed obtaining different powder characteristics. A major influence of atomization pressure variation was identified, a greater pressure value resulted in smaller particle size. Desirability function was employed to determine the optimal SD processing parameters, in other words, conditions that made it possible to obtain spherical particles with the proposed mean diameter in the range of 15 to 25 μm, with narrow particle size distribution.

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Preparing hydroxyapatite powders with controlled morphology

Abstract

Arch Biochem Biophys

Mater Sci Eng C3

J Liq Chromatogr

Bio-Rad Bull 1927 US/EG REV A