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© 2008 Wiley Periodicals, Inc.
BIOCOMPATIBILITY STUDY OF
HYDROXYAPATITE-CHITOSAN
COMPOSITE FOR MEDICAL
APPLICATIONS AT MICROWAVE
FREQUENCIES
Robin Augustine, Ullas G. Kalappura, and K. T. Mathew
Microwave Tomography and Materials Research Laboratory,
Department of Electronics, Cochin University of Science and
Technology, Cochin 682022, India; Corresponding author:
ktm@cusat.ac.in
Received 12 March 2008
ABSTRACT: Hydroxyapatite (HAp, Ca10(PO
4
)
6
(OH)
2
) bioceramic and
chitosan (poly [(-1-4) D-glucosamine]) biopolymer show good biocom-
patibility in vivo. They have biological origin and show excellent inter-
actions with microwave. Microwave study of HAp made using different
drying techniques and their composites with chitosan in the ISM band is
presented. Pastes are made using HAp and chitosan with different ratios
of mixing. The dielectric properties of this composites match with that of
human fat, collagen tissues. Some of the compositions exhibit dielec-
tric property close to that of natural bone. This makes them more
biocompatible and better substitutes for natural bone. Thus compos-
ite bioceramics can be considered as phantom model constituents for
imaging purposes. Their dielectric properties prove that they are
biocompatible. © 2008 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 50: 2931–2934, 2008; Published online in Wiley Inter-
Science (www.interscience.wiley.com). DOI 10.1002/mop.23806
Key words: bioceramics; hydroxyapatite (HAp); chitosan; dielectric
properties; osteoconductivity
1. INTRODUCTION
Biomaterials such as hydroxyapatite (HAp) and chitosan are being
used in bone replacement procedures, e.g., alveolar ridge recon-
struction, periodontal bone filling, treatment of osteomytitis, max-
illofacial and orthognathic implantation. HAp is produced by hy-
drothermal precipitation and successive drying, whereas chitosan
is obtained from chitin after deacetylation procedure. Pastes are
made using HAp and chitosan with different ratios of mixing.
These pastes are used as fillers in bone fissures. It is found that
their dielectric properties are more close to natural bone when
compared to other bioceramic compounds. This makes them more
biocompatible and better substitutes for natural bone.
Chitosan (poly [-1-4]) D-glucosamine) biopolymer has proved
to be effective in diverse fields such as clarification, purification,
chromatography, paper and textiles photography, food, nutrition,
agriculture, pharmaceutical and medical implants [1]. Chitosan
mixed with HAps (Ca
10
(PO
4
)
6
(OH)
2
) and other bioceramic mate-
rials facilitates better collagen growth in implants [2].
2. THEORY
For the development of any material for a particular application,
proper knowledge about the dielectric and mechanical properties
of a material is essential.
Biological materials are very much influenced by microwaves.
Therefore all biomaterials used for or deposited in living system
will interact with microwaves in the same way as that of biological
system.
The cavity perturbation technique [3] is employed for the study
of dielectric properties of chitosan. A closed section of waveguide
constitutes the waveguide cavity resonator. The cavity resonator
can be of transmission or reflection type. Electromagnetic energy
is coupled through the cavity using coupling irises at the ends of
the cavity. A nonradiating slot is provided at the broad wall of the
cavity for the introduction of the sample. The cavity resonates at
different frequencies, depending on its dimensions. The basic
principle involved in the technique is that the field within the
cavity resonator is perturbed by the introduction of the dielectric
sample through the nonradiating slot. The resonant frequency and
the quality factor of the cavity are shifted due to perturbation. The
determination of the complex permittivity and conductivity is
based on the theory of perturbation. When a dielectric material is
introduced in a cavity resonator at the position of maximum
electric field, the contribution of magnetic field for the perturbation
is minimum. The field perturbation due to the introduction of
dielectric sample at the position of maximum electric field is
related as [3]
'
r
- 1 =
f
c
- f
s
2f
s
V
c
V
s
, (1)
r
=
V
c
4V
s
Q
c
- Q
s
Q
c
Q
s
. (2)
The real part, '
r
, of the complex permittivity is usually known as
dielectric constant. The imaginary part,
r
, of the complex permit-
tivity is associated with dielectric loss of the material. The effec-
tive conductivity,
e
, is given as
e
= = 2f
0
r
, (3)
where tan is the loss tangent, given as tan =
r
/'
r
.
The relation of skin depth [3] with resonant frequency and
conductivity is given by
s
=
2
, (4)
where is radian frequency, = 4 10
-7
H/m the perme-
ability and the conductivity. Practically all applications of poly-
mers in electrical and electronic engineering require materials with
a low tan. However, one application that takes advantage of a
high value of loss tangent is high-frequency dielectric heating. In
this application, the efficiency of heating is usually compared [3]
by means of microwave heating coefficient (J), which is defined as
J =
1
r
tan
. (5)
Higher the J value, poorer will be the polymer for dielectric
heating purposes. Of course, the heat generated in the polymeric
material comes from the loss tangent, but the loss does not come
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 11, November 2008 2931