Engineering, 2012, 5, 189-191
doi:10.4236/eng.2012.410B049 Published Online October 2012 (
Copyright © 2012 SciRes. ENG
Development of Hormone-Active Fiber in the Form of
Artifici al Insulin Depot
A. Medovic Baralic, P. Skundric, Lj. Sretkovic, I. Pajic Lijakovic, M. Kostic
Dept. of Textil e Engin eer in g , Faculty of T echo l ogy and Metall urgy, U niv ersity of Belgrade, Belgrade, Republ ic of Se r bi a
Received 2012
This study examines the phenomena of the hormone-active fibers obtaining process, in the form of artificial insulin depot. As a fibr-
ous carrier of insulin cation-exchange polyacrylonitrile (PAN) fibers and biodegradable polysaccharide alginate fibers were used.
The process of obtaining fibrous artificial insulin depot was based on the chemisorption of insulin from insulin aqueous solutions by
these fiber s. The par ameters of in sulin ch emisorption reaction were determined and their influence on quantities of bonded insulin in
the artificial depot was studied. The impact of fiber polymer nature on the intensity of insulin chemisorption was studied and deter-
mined. Also, the location and deposition of insulin in and onto the fiber, fiber topography were studied. The maximum amounts of
bounded insulin for the cation-exchange PAN fibers were 395.0 mg porcine insulin chromatographic / g of fiber, and for the alginate
fibers were about 300 mg of porcine insulin chromatographic / g of fiber.
Keywords: Cation-exchange Fibers; Alginate Fiber s; Insulin; Chemisorption; Artificial Depot
1. Introduction
Insulin release from implantable biologically-active complexes
polymer-insulin are the subject of a numerous researchers stu-
dies, around the world. Although these systems could be classi-
fied into the group of "smart" bio-materials, they are not yet
included in cli ni cal practice.
Implantable insulin-polymer systems are designed so that
prolonged insulin release directly into the bloodstream thus
excluding daily insulin injection into a vein. Previous research
in this field yielded promising results in terms of development
of highly sensitive polymer - insulin complexes in which insu-
lin release is initiated by a change of the surrounding environ-
ment parameters. [1-3]
Fibrous insulin-releasing implants belonging to the new di-
rections of research related to the improvement of diabetes and
insulin therapy, and it was subject of this study.
The cation -exchange acr ylic (P AN) fibers and alginate fibers
are suitable for the chemisorption of insulin in relation with
their molecular structure. With their structural characteristics,
geometrical form, developed surface, and possibility of chemi-
cal modification, these fibers have real potentials to be carriers
of large molecules as insulin. For such needs an action-ex-
change polyacrilonytrile fiber saponified with sodium met sili-
cate has been developed [4-6]. This fiber, besides carboxyl
groups also contains smaller number of polar amino and hy-
droxyl groups, as well as non specified CN- groups. It is cha-
racterized by a high ζ (zeta) potential and it enables establishing
of a polyfuncional interaction of sorbet and insulin. Consider-
ing the specific properties of nitride groups, ion-exchange P AN
fibers, in fact, always has amphoteric properties, so the division
of the cati on, anion and amph oteric fiber has a con ditional ch a-
Within this work, research has been directed towards obtain-
ing of hormone-active polysaccharide fibers as an artificial
insulin depot, possessing the possibility of resorption in organ-
ism. As fibrous carriers of insulin, alginate fibers have been
used. Alginate is highly hydrophilic, biocompatible and biode-
gradable polysaccharide material. Alginates are linear un-
branched polysaccharide polymers containing β - (1,4)-linked
D-mannuronic acid (M) and α-(1,4)-linked L-guluronic acid (G)
residues. It is obtained by extraction of brown and red seaweed.
Alginates are not random co-polymers but, according to the
sour ce algae, co ns ist o f blocks o f similar an d st rictly alternating
residues (i.e. MMMMMM, GGGGGG, GMGMGM), each of
which have different conformational preferences and behavior.
Very broad application of alginate is based on its three main
characteristics: good solubility in water and the clotting ability,
gelation in the presence of calcium ions (gel forming does not
depend on temperature) and the ability to shape the film
(Na-alginate an d Ca - al ginate films) and fibers . Alginate fibers
are typical chemical composition of calcium salts. Given the
highly developed surface, the chemical and physical properties
and the presence of COO-groups, alginate fibers are very at-
tractive for obtaining controlled release drug depot.
Alginat e and PAN fibers ch aracteri zed by a series o f positive
structural properties. Requirements concerning of biocompati-
bility, non-toxity and hydrophility, of both fibers are excellent,
so that pra ctically no limit can be used for medical purposes.
The procedure of obtaining artificial insulin depot is based
on chemisorption of insulin from water solutions by PAN and
alginate fibers.
The chemisorption process comprises the following four
diffusion of insulin (from the bath) in the direction of the
fibrous material,
adsorption of insulin by the fiber external surface,
Copyright © 2012 SciRes. ENG
• diffusion of insulin inside the fibrous material and chem-
ical bonding of insulin and fibrous material.
Chemisorption progresses slowly. In practice, one hour or
even more is required for the absorption of the insulin from the
bath by fibrous. The process beginning by the adsorption of the
insulin on the external surface of the fiber and equilibrium is
achieved practically in several seconds. The fixation of the
insulin on the fiber, by bonding of insulin molecules with ma-
cromolecules of the fibrous material, in present case is a mo-
mentary process. The chemisorption rate is determined by the
speed of insulin diffusion in the pores, both from the solution
and from the external surface of the fiber. The speed of insulin
diffusion inside the fiber depends on the size of the insulin
particles and on the state of the fiber.
The chemisorption process of insulin of ion-exchanged fiber s,
depends directly on the type and forms of fibrous, static
ion-exchange capacity, concentration of insulin solution, pH
value, temperature and duration of the contact between insulin
and fiber, bath modulus, etc that have been shown in ours pre-
vious experimental r es earch. [6-9]
2. Materials and Methods
2.1. Catio n -exchanged PAN fibers
For this study, cation-exchange polyacrilonitrile fiber, capacity
of 1.4 mmol/g to 1.77 mmol/g, fineness of 6.4 dtex obtained at
the Laboratory of Fiber of Faculty of Technology and Metal-
lurgy in Bel grade, were used.
2.2. Alginate Fibers
In the present work the bio-degradable polysaccharide alginate
fiber s, of Russian origin, fineness of 2.5 dtex and the strength
of 17-22 cN/dtex, were used.
2.3. Insulin
To obtain an artificial depot insulin, porcine insulin, chromato-
graphic insulin, „Novo Nordisk ", Denmark, was used.
2.4. UV Spectrophotometry
Insulin chemisorption by cation-exchange PAN and alginate
fibers was monitored by UV spectrophotometer. UV spectra
were recorded on a spectrophotometer Shimadzu UV-Visible
Recording spectrophotometer, UV-260; in the wavelength
range 200-400 nm, i.e. in the near UV area.
The sorbed quantity of biologically active preparation was
determined by taking UV specters of the solution from which
chemisorption has been performed, in previewed intervals of
time. In that way the kinetics of chemisorption reaction was
also studied. The intensity of the characteristic absorption
maximum for insulin decreased in time, this fact pointing out to
a decrease of preparation concentration in solution. By reading
the absorbency and by using a calibration diagram formed on
the bases of spectra belonging to different, in advance defined
concentration of insulin, the quantities of preparation bonded to
fiber were calculated.
2.5. Scanning Electron M icroscopy (SEM)
Morphological characteristics of the obtained fiber depot insu-
lin were studied by scanning electron microscopy (JEOL JSM
T-20 and JEOL JSM-35). Fiber samples were sputtered by gold
under hig h v a c uum.
3. Result and Discussion
Kinetics and intensity of insulin chemisorption by ion-change
fibers (PAN and alginate) were studied depending on the con-
centration of insulin solution from which sorption was per-
Alginate fibers were used in its H-form, cation-exchange
PAN fiber in the Na-form. Insulin was sorbed of the buffer
solution, concentration of 0.5 and 1.0 g/dm3. Based on prelimi-
nary studies determined the optimal chemisorption condition:
pH 2.7 +0.1 (for alginate fibers), pH 4.0+0.1 (for PAN fibers)
and chemisorption temperature 20 + 2°C. Chemisorption of
insulin was carried out of the liquor ratio 1: 500 (for PAN fi-
bers) 1:100 (for alginate fibers).
Results of fibrous artificial insulin depot obtaining are shown
in Table 1 and Table 2.
Experimental results showed that chemisorption flowing
freely in both concentrations of insulin solutions, with very
high insulin exhaustion from solution. Insulin sorption by ca-
tion-exchanged PAN from insulin concentration of 0.5 g/dm3
was about 80 % and bounded quantity of insulin was 198.9
mg/g of fiber. Bounded insulin quantity from insulin concentra-
tion of 1.0 g/dm3 was 396.0 mg/g of fiber. The maximum
amount of insulin bounded by alginate fibers, from the concen-
tration of 0.5 g/dm3 is 49.9 mg /g of fiber and from concentra-
tion of 1.0 g/dm3 is 95.3 mg/g of fiber. It was obvious that the
time required to achieve the exhaustion of the insulin solution
significantly reduced in chemisorption by alginate fibers. This
shown that the multiple insulin sorption by alginate fibers,
could get an artificial depots of insulin with a much higher
quantity of bounded insulin. Results of the multiple insulin
sorption by alginate fibers from concentration of 0.5g/dm3 were
shown in Table 2.
Table 1. Chemisor ption of insulin by ion-e xchanged pan fibers and
polysaccharide alginate fibers.
Type of
fi bers
Conc. of
quantity of
insulin, Q
PAN fibers
0.5 120 198. 9 83.6
1.0 1200 395. 0 80,0
Alginate fibers 0.5 60 49,9 96.9
1.0 420 95.5 95.3
Table 2. Multiple chemisorption of insulin by polysaccharide algi-
nate fibers.
Num ber of im m ersion i n a
fresh solution of insulin Time,
[min] Bonded quantity of
insulin, Q [mg/g]
Copyright © 2012 SciRes. E NG
By multiple sorption reactions quantity of bonded insulin to
300 mg/g o f alginate fiber was achieved.
With information on the molecular weight o f algin ate an d th e
time required for its bio-degradation in the body, it was possi-
ble to calculate in advance the required amount of insulin
sorbed in the artificial depot.
Explanations for the different amounts of sorbed insulin by
PAN and alginate fibers, lying in the different fibrous nature
and their interaction with insulin. These fibers were characte-
rized by a layered structure. Layered structure was especially
characteri stic of the oriented polymers ob tained from any rege-
neratio n of natural polymers, in the case of algin ate fibers. The
presence of small po res and micro vacuoles in the fibers, had a
posi tive impact on in creasing the accessibility of active centers
and ionic groups for chemisorption process of insulin, as a large
protein macromolecules.
Relatively smooth surface and poorly marked structural ele-
ments, probably as a result of intense swelling of the fibers
during production, characterized topography of alginate fibers.
During the insulin chemisorption, most of insulin macromole-
cules, through the pore system, penetrated the alginate fiber.
Topography of gained artificial insulin depots, on base of algi-
nate an d PAN fibers, was p r es ent ed on Figure 1 .
Based on electron microscopic images was evident that the
topography of the obtained artificial depot was very different.
Cation-exchanged fibers, deposited a quantity of insulin on the
surface of th e fiber, while the al ginate fibers on the surface had
an insignificant fraction of insulin. The main mass of insulin in
both fibers was deposited on the inside, ie by weight of fibers.
Figure 1. SEM images-The topography of gained artificial insulin
depots obtained by chemisorption reaction of insulin by: (a) bio-
degr adable pol ys acch aride a l ginat e fibers an d (b) PAN fibers.
Given the large amount of sorbed insulin by cation- ex-
changed PAN fiber, a part of insulin is deposited on the surface
of the fiber, as is evident in Figure 1 (b). Structural details on
the PAN fiber surface could come form an insulin agglomerates
or clusters. The explanation for the difference in topography of
obtained artificial depots of insulin could be linked to the dif-
ferent porous structure of fibrous substrate.
4. Conclusion
The possibility of obtaining a hormone-active
non-biodegradable and biodegradable fibers by insulin chemi-
sorption of PAN and alginate fibers, has been shown. The
maximum amounts of bounded insulin of the cation-exchange
PAN fibers are 396.0 mg insulin per g of fiber, and for the al-
ginate fibers are about 300 mg of insulin g of fiber. The expe-
rimental researches showed that the intensity of chemisorption
depends in great extent on more parameters: concentration of
the insulin, pH value, temperature, liquor ratio, type of fibrous
adsor bent, etc.
Depending on the nature of fibrous matrices, molecular
weight and speed of degradation of alginate and sorbed
amounts of insulin can be designed artificial depots with the
desired amount of insulin and desired service life in the body.
Hormone-active PAN fibers are not biodegradable and resorp-
tive, so that on depletion of insulin must be removed from the
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