Highly biocompatible, nanocrystalline hydroxyapatite synthesized in a solvothermal process driven by high energy density microwave radiation

Abstract

Abstract:A microwave, solvothermal synthesis of highly biocompatible hydroxyapatite (HAp) nanopowder was developed. The process was conducted in a microwave radiation field having a high energy density of 5 W/mL and over a time less than 2 minutes. The sample measurements included: powder X-ray diffraction, density, specific surface area, and chemical composition. The morphology and structure were investigated by scanning electron microscopy as well as transmission electron microscopy (TEM). The thermal behavior analysis was conducted using a simultaneous thermal analysis technique coupled with quadruple mass spectrometry. Additionally, Fourier transform infrared spectroscopy tests of heated samples were performed. A degradation test and a biocompatibility study in vitro using human osteoblast cells were also conducted. The developed method enables the synthesis of pure, fully crystalline hexagonal HAp nanopowder with a specific surface area close to 240 m 2 /g and a Ca/P molar ratio equal to 1.57. TEM measurements showed that this method results in particles with an average grain size below 6 nm. A 28-day degradation test conducted according to the ISO standard indicated a 22% loss of initial weight and a calcium ion concentration at 200 µmol/dm 3 in the tris(hydroxymethyl)aminomethane hydrochloride test solution. The cytocompatibility of the obtained material was confirmed in a culture of human bone derived cells, both in an indirect test using the material extract, and in direct contact. A quantitative analysis was based on the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide. Viability assay as well as on DNA content measurements in the PicoGreen test.Indirect observations were performed at one point in time according to the ISO standard for in vitro cytotoxicity (ie, after 24 hours of cell exposure to the extracts). The direct contact tests were completed at three time points: after 24 hours, on day 7, and on day 14 of a culture in an osteogenic medium. All of the tests revealed good tolerance of cells toward the material; this was also shown by means of live/dead fluorescent staining. Both quantitative results and morphological observations revealed much better cell tolerance toward the obtained HAp compared to commercially available HAp NanoXIM, which was used as a reference material.

Influence of hydrothermal synthesis parameters on the properties of hydroxyapatite nanoparticles

“…This was dried in a lyophilizing cabinet and ≈14 g (95% efficiency) was obtained from a single synthesis. In previous work [26–27] the precursor was prepared from 75 mL of the suspension (where HAp was not obtained at room temperature). 350 mL of the suspension (≈11 g of HAp) was fed to the MSS2 reactor (maximum permitted feedstock volume in MSS2 reactor’s reaction chamber), in comparison with previous work [26–27], where a different microwave reactor was used (Ertec Magnum-II) and only 70 mL of the suspension (≈2 g of HAp) could be synthesized at one time.…”

“…A range of various methods have been developed in order to produce HAp powder, among others, combustion preparation [22], and numerous wet chemistry techniques, such as direct precipitation from aqueous solutions, electrochemical deposition [23], sol–gel processes [24] and hydrothermal synthesis [25–27] (Table 1). …”

“…In a previous study [26–27], we reported microwave-driven hydrothermal synthesis of nano-HAp, with average particle size ranging from 6 to 30 nm, which varied with synthesis time. Further, it was found that the Ca/P ratio of the NPs was synthesis-time dependent.…”

Crystallinity study of electrospun poly (vinyl alcohol) nanofibers: effect of electrospinning, filler incorporation, and heat treatment

“…Nano-hydroxyapatite (nHAp) was synthesized according to a solvothermal process driven by high energy density microwave radiation reported by Smoleń et al [35]. In brief, the starting materials used for the nHAp synthesis were Ca[OH] 2 and H 3 PO 4 .…”

Introductory Chapter: The Testament of Hydroxyapatite: New Prospects in Regenerative Medicinal Treatments

“…zone of an electric furnace [32,33] a. Solvothermal process b. Spray pyrolysis Table 1. Shows the key methods for the synthesis of hydroxyapatite (HAp).…”