23.3.1.3 Multiple-Ion Substitution in HA

The simultaneous incorporation of more than two vivid ions within the HA lattice

has not been extensively examined, due to the intricacy of the hydroxyapatite

structure (Sprio et al. 2008). Efforts are on to synthesize multi-substituted HA to

imitate chemical composition of biological apatite for enhancing chemical, physical,

structural, and biological properties of HA. HA with simultaneous incorporation of

CO3

2
, F
, Cl
, Na+, Mg2+, and K+ was synthesized by wet precipitation method

(Kannan et al. 2011) to enhance CO3

2
incorporation within HA lattice. The Mg-,

Zn-, and Co-substituted HA presented a better cell viability, superior bioactivity, and

antibacterial activity in comparison to pure HA (Rajendran et al. 2018). In vitro and

antimicrobial activity of Mg- and Ni-substituted silicate hydroxyapatite displayed a

quicker dissolution rate in SBF (Alshemary et al. 2015). Gopi et al. (2012)

synthesized Sr/Mg/Zn HA and observed that simultaneous substitution of Sr, Mg,

and Zn in HA not only provided growth of apatite but also hastened growth onto

itself.

HA with simultaneous substitution of Mg, Zn, and SiO4

4
ions was found to

improve the growth proliferation and adhesion. In vitro studies showed the collagen

synthesis of human osteoblasts (Corina et al. 2020; O’Neill et al. 2018).

23.4

Synthesis of Novel Hydroxyapatites

In the present work, various novel hydroxyapatites have been developed. These HA

products have particle sizes in the nanodimensional range in which single, dual, or

multiple ions have been substituted in HA according to the requirement for a specific

biomedical application. The sol-gel technique used for their synthesis is a facile

method, which can be easily scaled up for commercial production to yield physically

as well as chemically uniform product.

The protocol for the synthesis of novel nanodimensional hydroxyapatites by

sol-gel technique is illustrated in Fig. 23.1. The respective moles of precursors for

various ionic substituted HAs are given in Table 23.1.

23.4.1 Stoichiometric Nanodimensional Hydroxyapatite

Stoichiometric nanodimensional hydroxyapatite (HA) was synthesized utilizing

sol-gel method. The precursors for calcium and phosphorus were used as calcium

nitrate tetrahydrate (CNT, Ca(NO3)2.4H2O, Merck, AR grade) and potassium

dihydrogen phosphate (KDP, KH2PO4, Merck, AR grade), respectively. Solution

A containing 1.0 M CNT and Solution B containing 0.6 M KDP were made in

double-distilled water (DDW), and molar ratio Ca/P was kept at 1.67. Solution A

was added dropwise to Solution B at a stirring rate of 1000 rpm for 1 h at 25  2 ^C.

The pH was adjusted to 10  0.1 throughout by adding 25% ammonium hydroxide

solution (NH4OH, Merck, AR grade). Aging of the gel was done at 25  2 ^C for

24 h. Gelatinous precipitates formed were centrifuged, and thorough washing of

23

Unleashing Potential of Bone Mimicking Nanodimensional Hydroxyapatites and. . .

425