Bioactive Silk Proteins as
Geotextile Substrates
Masuhiro
Tsukada1, Shafiul Islam2 and Yoshio Ishiguro3
1)
National Institute of Sericultural & Agrobiological Sciences,
Tsukuba, Ibaraki 305-8634 Japan
2)
TexTek Solutions,
Ontario, Canada. textek.weebly.com textek@gmail.com
3) Center for Food Quality, Labeling &
Consumer Services, Nakadori, Yokohama 231-0003 Japan
Dedicated to Prof. Dr. Sueo Kawabata, CText FTI (1931-2001)
Abstract
There is a wave of interest in using
natural textile substrates in diverse bioengineering applications1-9
such as soil erosion and sedimentation control designs especially in
environmentally sensitive areas. This research article evaluates the tensile
properties and morphological features of silk fibers as a function of degree of
biodegradation, burring time in the soil.
Introduction
Natural biopolymers including silk proteins seem critical geotextile materials as
microorganisms decompose them gradually.
Silk fibers provide superior performance as a
bioactive surgical suture even under the most demanding medical
conditions. Silk fibers are conducive to
living cells growth that attached on the
surface of silk fibers.
We studied
the in vitro biodegradation of silk fibers and films with proteolytic enzymes
and examined the tensile properties of silk fibers with increasing incubation
time1. We used silk protein
fibers considering their potential geotextile applications, examined their
tensile properties and morphological features as biodegradable geotextile
substrates.
Experimental
Materials
Silk
fibers2 with different chemical compositions are obtained from
domestic silkworm, Bombyx mori and
wild silkworm, Antheraea pernyi. Degummed
silk fibers obtained by reeling the cocoons fibers were buried in the
horticultural gardening soil (Kompal, Bark Compost Association, Tokyo) up to 3
months. The temperature was maintained
at around 24-30 °C throughout the experiment under moist
condition by sprinkling water every 2-5 days to enhance biodegradation process.
Measurements
The tensile properties of
silk fibers were evaluated by Tensilon UTM-II (Orientec, Tokyo) under standard
conditions with 500 gf load-cell, 100 mm gauge length and 40 mm/min strain
rate. The surface morphology was examined with a
JOEL JAX-333S scanning electron microscope (SEM), after gold coating at 15 keV
acceleration voltage.
Results and discussions
Tensile properties
Table
1 compares the tensile properties of silk
fibers, which were buried in soil for predetermined periods. The tensile strength, elongation and moduli
of Bombyx mori and Antheraea pernyi silk fiber buried in
the ground decreases with increasing burring times. It is obvious that the tensile
strength of Antheraea pernyi Tussah
silk fibers deteriorates more rapidly than Bombyx
mori silk fiber, when they are buried in the soil.
Table
1: Biodegradation of silk fibers under the soil
|
||||||
Bombyx mori
silk
|
Tussah
silk
|
|||||
Tensile
Parameters
|
Embedding
Period (months)
|
|||||
0
|
1
|
2
|
0
|
1
|
2
|
|
Strength
(gf)
|
3.5
|
1.8
|
1
|
3.6
|
1
|
0.3
|
Elongation
(%)
|
15.5
|
7
|
5.2
|
40.1
|
29
|
21
|
Modulus
(kg/mm2)
|
850
|
760
|
380
|
730
|
322
|
205
|
Morphology
10 μm
|
|
|||||
Fig.
1 Biodegradation
of Bombyx mori silk fibre
|
Fig.
2
Biodegradation: Antheraea
Pernyi silk
fibre
|
Figure 1 and 2
shows the Scanning Electron Microscopy SEM images: biodegradation features of Bombyx mori and Antheraea Pernyi silk fibers, respectively, which were buried under
the soil for 2 months. Silk fibers prior
to decomposition tests were apparently smooth.
It is apparent that the microorganisms eroded the Antheraea pernyi fiber surface and created numerous voids, while less voids are distinct on the Bombyx mori silk fiber
probably due to their ordered dense microstructures.
Conclusion
The microorganisms in the soil do
not practically decompose artificial
polymers, such as polystyrene, polyethylene, polypropylene and polyester. This creates
enormous environmental concerns. The
biodegradation of protein polymers offers significant advantages from
additional recycling and decomposition. Silk’s excellent inherent tensile
properties and subsequent biodegradability
makes them unique geotextile
materials.
The potential grafting, coating and
engineering scopes to tailor specialized functional features to bioactive
natural protein polymers have created a wave of interest in demanding
applications1-9.
At the outset silk protein fibers exhibit
excellent tensile properties, their inherent properties decrease as a function
of burring periods due to their time dependent degradation by various microorganisms in the burring soil. The decay in tensile properties of tussah silk
fibers was higher than that of Bombyx
mori silk, which matched the finding - tussah silk fiber contained highly
porous microstructure, such as visual voids4
with large size and leaf-pleated sheet structure within the silk fiber. This leads to rapid degradation of tussah silk
fiber following decomposition by various microorganisms contrary to Bombyx mori silk fibers with highly
consolidated microstructure, yielded a slow rate of biodegradation than that of
tussah silk fibers.
Silk fibers are fairly expensive compared to other natural fibers, cotton and cellulose and as well as commonly used artificial man made fibers. We can however cut costs by using silk fibrous by-products. Silk fibers exhibit excellent elastic modulus and high absorbency5. Since living cells grow cohesively on the surface of silk substrates - these biophysical properties are critical for certain geotextile applications.
References
1. T Arai, G Freddi, R Innocenti, M
Tsukada, Biodegradation of Bombyx mori Silk Fibroin Fibers and
Films, J. of Appl. Poly. Sci., 91, 2383-2390, 2004
2. M Tsukada et
al., Structural Changes of Silk
Fibers Induced by Heat-Treatment, J.of Appl. Poly. Sci., 46, 1945-1953, 1992
3. S Islam, Synthetic Silk Synthesis,
Technitex Symposium, BTTG, Leeds, UK 6-7 Nov, 2002
4. T Narumi, M. Kobayashi, A Method of Morphometry for
Voids in Saturniidae Cocoon Filaments
Using Image Processing Techniques, J. Seri. Sci. of Japan, 64, 203-208, 1995
5. S Islam, et al., Methods and apparatus for spinning spider silk
protein, USP 7,057,023 Jun 6, 2006
6. M Tsukada, S Islam et al., Antibiotic
Silk Substrates for Healthcare, Text. J. 121(5) 47-49, 2004
7. C Karatzas, S Islam et
al., High-toughness Spider Silk Fibers Spun from Soluble
rc-Silk Produced in Mammalian Cells, Biopolymers, Vol. 8: Polyamides
and Complex Proteinaceous Materials II: Chapter 5, ISBN 3-527-30223-9,
Wiley-VCH: Weinheim Germany. Apr 97-117, 2003
8.
M Tsukada, S Islam et
al., Microwave
Irradiation Technique to Enhance Protein Fiber Properties, Autex Res. J. 5(1)
40-48, 2005
9.
M Tsukada, S Islam et
al., Enhancing Sorption Properties of Natural
Fibrous Protein Substrates. Part I:
Absorption of malodorous gases, Text. J., 121(6) 48-50, 2004
TTS :: NIAS R&D
Initiative
:: 20060906 ::
::::
No comments:
Post a Comment