Nondestructive testing of defects in adhesive joints

Biomimetic synthesis of nanohybrids based on calcium hydroxyapatite and
carboxymethyl cellulose
Annamalai Pratheep Kumar a* , Kamal Khaja Mohaideen a, b and Raj Pal Singh a#
a Division of Polymer Science and Engineering,
b Physical and Materials Chemistry Division
National Chemical Laboratory, Dr. Homi Bhaba Road, Pune - 411 008, India.
E-mail # : rp.singh@ncl.res.in
Abstract
In the present paper we report biomimetic synthesis of nanohybrids based on
carboxymethyl cellulose (CMC) and hydroxyapatite (HA) nanoparticles by a coprecipitation
method. The physico-chemical characterizations were done before and after
calcination using Fourier transform infrared spectroscopy, solid state 31 P nuclear magnetic
resonance (NMR) spectroscopy and thermogravimetric analysis (TGA). The formation of
nanohybrid was observed by wide angle X-ray diffraction (WAXD), scanning electron
microscopy (SEM) with energy dispersive X-ray analysis (EDX) and transmission electron
microscopy (TEM). The nanohybrid was formed as aggregates of nanoparticles adsorbed
on CMC. With increasing content of CMC, the crystallite size of hydroxyapatite particles
decreased (with 2 wt. % 18±3 nm). The morphological aspects of calcined samples have
shown the sintering ability of HA nanoparticles. The possible mechanism for interaction
between CMC and HA, nucleation and growth of nanocrystals of HA is discussed. It is
summarized that nanohybrids of hydroxyapatite nanoparticles can be prepared for
mimicking the process of nucleation and growth in nature using biodegradable and
biocompatible macromolecules like CMC.
1. Introduction
Over the past decade, the main goal of bone tissue engineering has been to develop
biodegradable materials as bone graft substitutes for filling large bone defects. Bone and
teeth consist of a small amount of organic matrix, which manipulates the formation of
apatite into distinct microstructures suitable for the mechanical forces which they
encounter in-vivo [1, 2]. There has been widespread use of calcium phosphate bioceramics,
such as hydroxyapatite (HA) and tricalcium phosphate (TCP), for bone regeneration
applications. Their biocompatibilities are thought to be due to their chemical and structural
similarity to the mineral phase of native bone [3]. Biomineralized tissues are often found to
contain polymorphs and individual minerals whose crystal morphology, size, and
orientation are often controlled by local conditions and, in particular, by organic
macromolecules such as proteins and polysaccharides [1, 4]. Owing to their small size and
high surface area, HA nanoparticles, which are similar to that in bone tissue, can
effectively interact with living cells [8, 9]. The drawbacks of HA nanoparticles are their
instability, associated with migration of nanoparticles to surrounding tissues under the
action of blood flow, and their low solubility [10]. To overcome these, a new development
in this field is the biomimetic synthesis of nanosized calcium phosphates (mainly HA) in
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