https://orcid.org/0000-0001-5256-2919
![Sample our Bioscience journals, sign in here to start your access, Latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5925/TOC-Subject-Sample-2021-Bioscience.jpg"})
Abstract
Background:
Zinc-doped hydroxyapatite has been proposed as a graft biomaterial for bone regeneration. However, the effect of zinc on osteoconductivity is still controversial, since the release and resorption of calcium, phosphorus, and zinc in graft-implanted defects have rarely been studied.
Methods:
Microspheres containing alginate and either non-doped carbonated hydroxyapatite (cHA) or nanocrystalline 3.2 wt% zinc-doped cHA (Zn-cHA) were implanted in critical-sized calvarial defects in Wistar rats for 1, 3, and 6 months. Histological and histomorphometric analyses were performed to evaluate the volume density of newly formed bone, residual biomaterial, and connective tissue formation. Biomaterial degradation was characterized by transmission electron microscopy (TEM) and synchrotron radiation-based X-ray microfluorescence (SR-µXRF), which enabled the elemental mapping of calcium, phosphorus, and zinc on the microsphere-implanted defects at 6 months post-implantation.
Results:
The bone repair was limited to regions close to the preexistent bone, whereas connective tissue occupied the major part of the defect. Moreover, no significant difference in the amount of new bone formed was found between the two microsphere groups. TEM analysis revealed the degradation of the outer microsphere surface with detachment of the nanoparticle aggregates. According to SR-µXRF, both types of microspheres released high amounts of calcium, phosphorus, and zinc, distributed throughout the defective region. The cHA microsphere surface strongly adsorbed the zinc from organic constituents of the biological fluid, and phosphorus was resorbed more quickly than calcium. In the Zn-cHA group, zinc and calcium had similar release profiles, indicating a stoichiometric dissolution of these elements and non-preferential zinc resorption.
Conclusions:
The nanometric size of cHA and Zn-cHA was a decisive factor in accelerating the in vivo availability of calcium and zinc. The high calcium and zinc accumulation in the defect, which was not cleared by the biological medium, played a critical role in inhibiting osteoconduction and thus impairing bone repair.
Acknowledgments
This work was supported by the Brazilian financial agencies CNPq (Grant no 457541/2013-0 and 467513/2014-7), FAPERJ (Grant no E-26/102.993/2012; E-26/203.012/2016), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (Finance Code 001), National Centre of Science and Technology on Regenerative Medicine - INCT Regenera (http://www.inctregenera.org.br/). The authors wish to thank LABNANO/CBPF, the staff of the IMX and XRF beamlines of the Brazilian Synchrotron Light Laboratory (LNLS), and Carlos Perez (XRF Beamline, LNLS) and Professor Marcos Farina (Federal University of Rio de Janeiro, UFRJ) for their invaluable contributions to this work.
Disclosure
The authors report no conflicts of interest in this work.
Supplementary materials
Figure S1 SEM micrographs of cHA and Zn-cHA. (A) cHA and (B) Zn-cHA microspheres at 300X magnification; (C) cHA and (D) Zn-cHA microspheres at 3000X magnification.
Notes: 300X magnification, scale bar: 300 μm; 3000X magnification, scale bar: 40 μm.
Abbreviations: SEM, Scanning electron microscopy; cHA, Carbonated hydroxyapatite; Zn-cHA, Zn-doped carbonated hydroxyapatite.
Figure S2 SR-µXRF spectra of cHA and Zn-cHA microspheres (region 1).
Abbreviations: SR-µXRF, Synchrotron radiation-based X-ray microfluorescence; cHA, Carbonated hydroxyapatite; Zn-cHA, Zn-doped carbonated hydroxyapatite.
