Hydrothermally processed 1D hydroxyapatite: Mechanism of formation and biocompatibility studies

Abstract

Recent developments in bone tissue engineering have led to an increased interest in one-dimensional (1D) hydroxyapatite (HA) nano- and micro-structures such as wires, ribbons and tubes. They have been proposed for use as cell substrates, reinforcing phases in composites and carriers for biologically active substances. Here we demonstrate the synthesis of 1D HA structures using an optimized, urea-assisted, high-yield hydrothermal batch process. The one-pot process, yielding HA structures composed of bundles of ribbons and wires, was typified by the simultaneous occurrence of a multitude of intermediate reactions, failing to meet the uniformity criteria over particle morphology and size. To overcome these issues, the preparation procedure was divided to two stages: dicalcium phosphate platelets synthesized in the first step were used as a precursor for the synthesis of 1D HA in the second stage. Despite the elongated particle morphologies, both the precursor and the final product exhibited excellent biocompatibility and caused no reduction of viability when tested against osteoblastic MC3T3-E1 cells in 2D culture up to the concentration of 2.6 mg/cm2. X-ray powder diffraction combined with a range of electron microscopies and laser diffraction analyses was used to elucidate the formation mechanism and the microstructure of the final particles. The two-step synthesis involved a more direct transformation of DCP to 1D HA with the average diameter of 37 nm and the aspect ratio exceeding 100:1. The comparison of crystalline domain sizes along different crystallographic directions showed no signs of significant anisotropy, while indicating that individual nanowires are ordered in bundles in the b crystallographic direction of the P63/m space group of HA. Intermediate processes, e.g., dehydration of dicalcium phosphate, are critical for the formation of 1D HA alongside other key aspects of this phase transformation, it must be investigated in more detail in the continuous design of smart HA micro- and nano-structures with advanced therapeutic potentials.

Preparation of Micro/Nano-Structure Copper-Substituted Hydroxyapatite Scaffolds with Improved Angiogenesis Capacity for Bone Regeneration

“…Each solution was adjusted to have a pH of 2.50 ± 0.05 by dropwise addition of HNO 3 . Additionally, 1 g of urea (CH 4 N 2 O) was added to increase the super saturation and support the elongation of HA crystals [ 19 ]. The as-sintered HA scaffolds, i.e., Solutions (1), (2) and (3), were immersed in three containers.…”

Hydroxyapatite and Titanium Dioxide Nanoparticles: Radiolabelling and In Vitro Stability of Prospective Theranostic Nanocarriers for 223Ra and 99mTc

“…Its artificial analogue is used in medicine as a part of bone and tooth implants [ 11 , 12 ]. Other HAp applications, for example as an additive to sunscreens [ 13 ] or biologically active material for cell proliferation and osteogenic differentiation, are under research [ 14 ]. The content of calcium and phosphorus in HAp structure in stoichiometric ratio of 1.67 (Ca to P) leads to the most stable modification.…”

Multifunctional and hybrid systems based on calcium-phosphate and hydroxyapatite for preventive and regenerative medicine

“…Hidrotermalna metoda je jedna od do sada najčešće korišćenih metoda za dobijanje nanočestica hidroksiapatita i obično se odvija reakcijama u vodenim rastvorima na povišenoj temperaturi i pritisku [18,19]. Produkti mogu biti visokog stepena kristaliničnosti, jasno definisane i često uniformne strukture, a variranjem parametara sinteze može se uticati na svojstva dobijenih produkata.…”

“…Modifikovanom hidrotermalnom metodom izvršena je sinteza jednodimenzionalnog (1D) hidroksiapatita, i to u dva koraka. Dikalcijumfosfat sintetizovan u prvom koraku je korišćen kao prekursor za sintezu 1D HAp-a u drugom koraku [19].…”