ISSN 0020-1685, Inorganic Materials, 2018, Vol. 54, No. 3, pp. 305–314. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © S.A. Gerk, O.A. Golovanova, V.N. Odazhiu, 2018, published in Neorganicheskie Materialy, 2018, Vol. 54, No. 3, pp. 332–341.
Structural, Morphological, and Resorption Properties of Carbonate
Hydroxyapatite Prepared in the Presence of Glycine
S. A. Gerk*, O. A. Golovanova, and V. N. Odazhiu
Dostoevsky State University, pr. Mira 55-A, Omsk, 644077 Russia
Received September 16, 2016; in final form, June 25, 2017
Abstract⎯Carbonate-containing hydroxyapatite has been synthesized from prototype human synovial fluid
in the presence of glycine. The resultant powders have been shown to contain 75 to 80 wt % the amino acid.
If the model solution contains less than 0.08 mol/L of glycine, the latter influences neither the composition
of the solid phase nor the size of the forming crystallites, but changes the degree of their crystallinity and the
specific surface area of the material. At high amino acid concentrations, we observe the formation of poorly
crystallized composites consisting of smaller nanocrystallites. The dissolution of the samples in a 0.9% NaCl
solution has been shown to be a two-step process. The highest solubility under weakly acidic conditions has
been demonstrated by the precipitates containing the largest amount of the amino acid.
Keywords: biocompatible materials, composites, carbonate hydroxyapatite, glycine, resorption, specific sur-
face area, crystallization
Human bone tissue is a biochemical system having
a multilevel structural organization and multicomponent
mineralogical and organic composition of the intercellular
matrix [1–4]. Its life activity is known to be based on
remodeling, which comprises two mutually connected
and interchangeable processes: osteogenesis (the forma-
tion of new bone tissue) and resorption (disintegration of
the bone structures formed ). A key element of remod-
eling is bone mineralization: deposition of ultradisperse
crystalline carbonate-containing hydroxyapatite (CHA),
10 – х/2 – у/2
3–х – у
, on colla-
gen protein microfibers from human body fluids
(intercellular, synovial, and other fluids) .
The mechanism underlying the interaction
between the organic and inorganic bone components
has not yet been studied in sufficient detail. The depo-
sition of CHA crystals is thought to begin in zones
between collagen fibrils when these are shifted by a
quarter of their length, and the first forming crystals
act as nucleation centers for further formation of the
inorganic component of the bone tissue [5–9]. As
shown earlier [9, 10], polypeptide collagen chains
contain crystalline segments in the form of –Gly–X–
Y– triplets consisting largely of neutral amino acids
(Gly = glycine, 33 wt %; X = proline or hydroxypro-
line, 22 wt %; Y = hydroxylysine), and amorphous
segments consisting of polar amino acids (lysine, his-
tidine, and others). However, the role played by indi-
vidual amino acids and collagen regions in binding
with the solid phase is essentially unexplored.
This problem can be partially resolved in experi-
ments aimed at investigating calcium phosphate
(brushite, hydroxyapatite (HA), octacalcium phos-
phate, etc.) biomineralization processes in artificial
systems (urine, saliva, and others), as well as by com-
puter simulation [3, 4, 10–15]. As shown earlier,
amino acids and proteins may inhibit or stimulate
crystallization of calcium phosphates through adsorp-
tion interactions with their surface and complexation
with calcium ions, thus influencing the crystallinity,
morphology, and particle size of the solid phase. How-
ever, since data available in the literature are limited
mainly to the proposed models, gaining insight into
the role of organic substances on CHA formation pro-
cesses is of great current interest.
The purpose of this work was to assess the effect of
glycine on the morphology, degree of crystallinity, and
resorption properties of CHA synthesized from model
solutions of human joint synovial fluid (synovia).
Glycine was chosen as a reference because its mol-
ecule has small dimensions without lateral radicals
and active centers with opposite (acidic and basic)
properties and enters into the composition of various
proteins, including collagen [8, 10–12].