The Role of Cellulose in the Formulation of
Interconnected Macro and Micoporous Biocompatible
Hydroxyapatite Scaffolds
J Anita Lett, M Sundareswari, Amirdha Sher Gill, K Ravichandran, J Joyce
Prabhkar
To cite this version:
J Anita Lett, M Sundareswari, Amirdha Sher Gill, K Ravichandran, J Joyce Prabhkar. The
Role of Cellulose in the Formulation of Interconnected Macro and Micoporous Biocompatible
Hydroxyapatite Scaffolds . Mechanics, Materials Science & Engineering Journal, Magnolithe,
2017, 9 (1), <10.2412/mmse.62.43.650>. <hal-01499401>
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
The Role of Cellulose in the Formulation of Interconnected Macro and
Micoporous Biocompatible Hydroxyapatite Scaffolds 35
J. Anita Lett1, M. Sundareswari1, K. Ravichandran2, Amirdha Sher Gill1, J. Joyce Prabhkar3
1 – Department of Physics, Sathyabama University, Chennai, India
2 – Department of Analytical Chemistry, University of Madras, Chennai, India
3 – Department of General Surgery, Madras Medical College, Chennai, India
DOI 10.2412/mmse.62.43.650 provided by Seo4U.link
Keywords: bone tissue engineering, pure hydroxyapatite scaffolds, cellulose, porosity.
ABSTRACT. In bone tissue engineering, ceramics are widely used as implant material to enhance bone growth formation
or as drug release vehicle. In the existing work porous Hydroxyapatite scaffolds were prepared by polymeric replication
method using Cellulose as a binding agent. The influence of binder on various sintering temperature were evaluated. The
Hydroxyapatite scaffold sintered at 1150°C was characterized for phase purity, structural analysis and porosity
measurements. Hence, it is possible to produce Hydroxyapatite scaffolds with highly inter connecting macro and micro
pores with an apparent density of 0.944g/cm3 corresponding to 75% porosity.
Introduction. Tissue engineering is a field where cells, bone/ scaffolds and signals/factors are
mutually joined with the endeavour to re-establish, preserve and improve tissue and organ utility.
Various scaffold resources have been investigated worldwide with both positive and negative
outcomes. Factors for the failure of scaffolds include undesired scaffold degradation commodities
affecting cellular functions, unaffected responses elicited by the scaffold materials themselves, lack
of cell adhesion appropriate to non-suitable surface properties, controversies in the degradation rate
of the scaffold and the growth rate of the fresh tissue, or mechanical mismatches connecting scaffolds
and the tissue at the implantation location. Calcium phosphates are amongst the most widely used
resources for bone tissue regeneration. They can be man-made as gels, pastes and solid blocks or even
as porous matrices, with orthopaedics and dentistry being their main areas of relevance.
Hydroxyapatite (HAP) are the most frequently used calcium phosphates, owed to their Stoichiometric
ratio (Ca/P) ratios close to that of natural bone and also for their stability when in contact with
physiological environment. HAP is a major constituent of bone resource and is resorbed after a long
time in the body, due to its biocompatibility [1-4]. The porous network or interconnected pores in
HAP structure permit the tissue to penetrate, which further enhances the implant tissue attachment
(Itoh et al). Several methods have been investigated to achieve the required porous scaffolds for
instance, Sopyan et al has studied with pore-creating volatile particles, ceramic foaming methods and
polymeric sponge process [5]. The polymeric sponge technique, which offers great flexibility, is
particularly of interest due to its greater advantages such as opportunity to control the pore size, for
several required complex shapes and straightforward process (Tian and Tian 2001).The polymeric
sponge technique involves covering of open-cell polymeric foam with ceramic slurry followed by
flaming out of polymeric foam in the course of sintering process which yields a duplication of the
original polymer foam in the ceramic foam structure. However, the properties of the Hydroxyapatite
scaffold prepared through the polymeric sponge technique are highly depend on the slurry properties
together with homogeneity, rheology and dispersion (Zhang et al 2006). Monmaturapoj has reported
35
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
the dispersant on the rheological behaviour of concentrated hydroxyapatite suspensions [6]. In this
study, porous hydroxyapatite scaffolds were obtained using the polymer replication method, using
cellulose as a binding agent and the morphology and its physio-chemical properties were studied.
These scaffolds can be used as matrices for bone tissue engineering or as specific release vehicles [7].
Also, they may be functionalized with molecules such as collagen, chitosan, etc, in order to enhance
their biological responses [8].
Material and Methodology.
Sample Preparation. The Hydroxyapatite powder with an average crystallite size of approximately
40 nm, was prepared according to our previous work by sol-gel [9].The template used to prepare
scaffolds were polyurethane sponges with an average pore size of 400 microns. The Cellulose, used
as a binder was made into a homogenous mixture by mixing for 2 hr with water at 50 ºC. To fabricate
scaffolds, a ceramic slurry containing 6 g of Hydroxyapatite powder, binder, tensioactive agent (A40
V Dispex provided from BASF) and water [6] were blended again for 2 hours to disperse thoroughly.
The polyurethane sponges were dipped in the slurries and the excess slurry was removed and dried at
room temperature for 2 days, followed by drying in the hot air furnace at 110 ºC until its completely
dried. The polyurethane sponge used as template was removed by heating in a muffle furnace at
600oC for 2 hrs, followed by the densification of scaffold by sintering at 1150 oC for 4 hours. Now,
these prepared scaffolds were cut into cubes for further characterization.
Physio-Chemical Characterization. The microstructure of the hydroxyapatite scaffolds was
characterized using scanning electron microscopy (FESEM: Supra VP35 Carl Zeiss, Germany) and
the macro porous structure using optical stereo zoom microscope. The phase purity of the
Hydroxyapatite scaffolds were determined by X-ray diffraction using a X’pertPro, Philips, The
Netherlands with CuKα radiation over the 2θ range of 10°–80° with a step size of 0.05°. The
functional group analysis of HAP scaffolds was carried out in the spectral range from 4000 to 650
cm−1 using a single beam Fourier transform infrared spectrometer (Agilent, Cary 630). The porosity
and density measurements of the scaffolds were calculated by simple displacement techniques [8-9].
A scaffold of weight ‘W’ was immersed in a graduated cylinder containing a known volume (V1) of
water until no air bubble emerged from the scaffold. The total volume of the water and scaffold was
then recorded as V2. The volume difference (V2 – V1) was the volume of the skeleton of the scaffold.
The scaffold was removed and the residual water was measured as V3.
The apparent density of the scaffold (ρ), was evaluated using,

W
V2  V3
(1)
The porosity of the open pores in the scaffold (ε), was evaluated using,

V1  V3
V2  V3
(2)
Results and Discussions. The nano-HAP powder used for fabricating scaffolds processed an
elongated cylindrical shape with the crystallite size of 40 nm. The scaffolds were approximately 10
mm x 10 mm x 10 mm in size. The morphology of the fabricated Hydroxyapatite is shown in Fig.1,
2. It is found that the scaffolds replicated the pores in the sponges with a pore size of approximately
500 microns. Thus, highly porous Hydroxyapatite scaffolds were produced using the polymer
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
replication method as seen in Fig. 2.With SEM observations (Fig. 2), pore diameters ranging from
400 to 500 μm were observed. On the other hand, micropores (Fig. 3) of size lesser than micron were
also visualised in the pore walls and wall struts. The microstructures of the scaffolds (Fig. 2) could
be observed that the scaffold had a compact structure and that the pores were evenly distributed. The
open as well as interconnected pore network was an essential factor for the scaffold to permit cell
growth and the transportation of nutrients and metabolic waste. Gotz et al.[13] has reported that pore
sizes around 300 µm were suggested for implants due to improved new bone and capillary formation.
Hollister et al[14] conducted in vivo studies on HAP scaffolds with pore diameters ranging between
400 µm and 1200 µm and inferred no significant difference in bone growth for scaffolds of all pore
sizes.
Fig. 1. Macro pores of Scaffold.
2µm
Fig. 2 Micro pores of Scaffold.
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
Fig. 3. XRD pattern of Sintered Scaffold.
40
20
3500
3000
2500
2000
1500
1000
635.08
603.13
569.83
479.08
464.80
448.99
440.38
1093.41
1041.49
1639.41
2078.54
2003.14
1934.21
3448.35
-20
-0
Transmittance [%]
60
80
100
The XRD patterns of the scaffolds prepared is shown in Fig. 3. All of the peaks matched with the
JCPDS pattern 09-0432 for HAP, which suggested that no other phases were present, as shown in
Fig. 3. All of the peaks were attributed to the HAP phase and no additional peaks were observed. The
results indicated that the HAP did not decompose after sintering. The characteristic peaks at two theta
31.7° corresponding to 211 diffraction became narrower and sharper for sintering temperature
1150°C. These data confirms that the major phase as Hydroxyapatite and absence of impurity such
as calcium phosphates and calcium oxide are clearly identified [22] .
500
Wavenumber cm-1
Fig. 4. FTIR pattern of Sintered Scaffold.
The FT-IR spectra of the synthesized HAP scaffold prepared using cellulose as a binding agent is
shown in Fig.4. In the FTIR spectra, the bands at 3570 and 630 cm-1[15] were recognized to the
hydroxyl stretching bands and bending bands of HAP, respectively. The broad absorption band from
3600 to 3300 cm-1[15] indicated the existence of the bending mode of absorbed water[16]. The bands
at 1093 and 1041 cm-1 were assigned antisymmetric ʋ3 [PO43− ] P-O stretching mode and the ʋ1 P-O
symmetric stretching mode was detected at 962 cm-1 [15, 17-18]. The bands at 603 and 569 cm-1 were
attributed to components of the triply degenerate ʋ4 O-P-O bending modes.
The Scaffold prepared using cellulose showed high porosity of 75% with apparent density of 0.944
g/cm3. The mechanical properties are strongly subjective by apparent density [18]. In trabecular bone,
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
the apparent density ranges from 0.14g/cm3 to 1.10g/cm3 [18]. Porosity is based on the presence of
open pores. It was found that mechanical properties varied with binders used. Moreover, a few studies
[19, 20] have reported that the decomposition of HAP would reduce its mechanical properties. Hence,
a symmetry is to be maintained between the porosity and apparent density for precise purposes, since
higher mechanical strength corresponds to higher density, while a high porosity provides a
surrounding favourable for living organism[21].
Summary. In this work, porous scaffolds were prepared using a polymeric sponge template method
using cellulose as a binding agent. A well defined elongated cylindrical HAP crystals with negligible
agglomeration was used to fabricate these scaffolds. The FESEM results exposed that the porous
Hydroxyapatite scaffolds acquired macro pores and micro pores that emerges to be interconnected
with a homogenous porous network (Fig. 3).The scaffolds comprises pure crystalline Hydroxyapatite
phase and no additional phase were produced through the spongy technique as confirmed by XRD
and FTIR. The scaffold prepared with cellulose in spite of high porosity (75%) appeared to report an
apparent density of 0.944 g/cm3 comparable with trabecular bone (0.14 g/cm3 to 1.10 g/cm3).
Thus, it is possible to produce porous scaffolds with varied porosity and density. Such scaffolds can
find its application for tissue engineering in non load bearing applications or even as a vehicle for the
delivery of biological molecules. Currently, studies are being performed in order to incorporate
collagen type I in these porous constructs, to improve their potential applications.
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Cite the paper
J. Anita Lett, M. Sundareswari, K. Ravichandran, Amirdha Sher Gill, J. Joyce Prabhkar (2017). The Role of
Cellulose in the Formulation of Interconnected Macro and Micoporous Biocompatible Hydroxyapatite
Scaffolds. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.62.43.650
MMSE Journal. Open Access www.mmse.xyz