POLYSSACHARIDE-BASED MAGNETIC HYDROGELS AS

POTENTICAL VECTORS FOR EXTERNAL-CONTROLLED

SOLUTE RELEASE

Alexandre T. Paulino

1,2

, Laurence A. Belfiore

, Matt J. Kipper

and Elias B. Tambourgi

School of Chemical Engineering, Department of Chemical System Engineering, Separation Process Laboratory

State University of Campinas, Av. Albert Einstein, 500, Bloco A, Cidade Universitária, Campinas, SP 13083-852, Brazil

Department of Chemical & Biological Engineering, Polymer Physics & Engineering Laboratory

Colorado State University, Fort Collins, CO 80523, U.S.A.

Keywords: Magnetic hydrogel, Polysaccharide, External-controlled solute release.

Abstract: This work describes the synthesis of polysaccharide-based magnetic hydrogels with the introduction of

magnetite nanoparticles in the polymer network. The magnetic hydrogels were characterized by Fourier-

transform infrared spectroscopy (FTIR) and magnetization curves. FTIR analysis confirmed the efficiency

of the polysaccharide-modifying process. The amounts of diffused water into or out-of a hydrogel network

were measured. The degree of swelling of the polysaccharide-based magnetic hydrogels was less than that

found for the regular polysaccharide-based hydrogels and there was no variation in the water diffusion

mechanism. The absence of hysteresis loops and coercivity observed through magnetization curves

indicated that magnetic hydrogels can be applied in external-controlled solute release.

1 INTRODUCTION

In recent years, there has been substantial interest in

the potential applications of functionalized

hydrogels. These types of hydrogels have many

important properties and offer advantages over non-

functionalized hydrogels (Chaterji et al., 2007);

(Bajpai et al., 2008). The advantages of such

hydrogels have been observed through some studies

on controlled drug release systems, cell

proliferation, water treatment, soil conditioning and

so forth. (Oh et al., 2008); (Arizaga et al., 2010);

(Deligkaris et al., 2010).

Functionalized hydrogels based on

polysaccharides, proteins and amino acids have been

extensively studied for medical, pharmaceutical and

biological application due to their properties of

biocompatibility with living organisms,

biodegradability, accessibility and renewability

(Morelli and Chiellini, 2010). In this contribution,

external magnetic field-sensitive functionalized

hydrogels based on gum arabic, chitosan and

maltodextrin were synthesized with the introduction

of magnetite nanoparticles in the polymer network.

The potentiality of these hydrogels as magnetic

vectors for external-controlled solute release was

investigated by FTIR, magnetization curves and

water absorption kinetic.

2 EXPERIMENTAL

PROCEDURES

2.1 Materials

Chitosan (Aldrich), acetic acid (Merck), acrylic acid

(Merck), glycidyl methacrylate (Across Organics),

methylenebisacrylamide (Merck), hydrochloric acid

(Merck), ammonium persulfate (Aldrich), gum

arabic (Sudan), sodium hydroxide (Nuclear),

acrylamide (Aldrich), potassium acrylate (Aldrich),

maltodextrin (Aldrich), ethanol (TEDIA), magnetite

nanoparticles (Fe

) purchased from Fisher

Scientific and characterized elsewhere (Paulino et

al., 2009). All experiments were performed using

Milli-Q

water.

2.2 Hydrogel Synthesis

1% chitosan solution was prepared by diluting the

263

T. Paulino A., A. Belﬁore L., J. Kipper M. and B. Tambourgi E..

POLYSSACHARIDE-BASED MAGNETIC HYDROGELS AS POTENTICAL VECTORS FOR EXTERNAL-CONTROLLED SOLUTE RELEASE.

DOI: 10.5220/0003870802630268

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2012), pages 263-268

ISBN: 978-989-8425-91-1

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

appropriate amounts of the polysaccharide with

acetic acid in a 50-mL beaker. Gaseous nitrogen

was purged into the system for 30 min in order to

remove the dissolved oxygen. Known amounts of

ammonium persulfate were then introduced to

initiate chitosan for the generation of radicals. The

complete polymerization reaction took place at 70

ºC for three hours after adding 15 mL of Milli-Q

water, acrylic acid, methylene-bis-acrylamide and

magnetite nanoparticles. The hydrogel was purified

and dried in an oven at 50 ºC for 12 to 24 hours.

Prior to synthesizing the hydrogels based on

either gum arabic or maltodextrin, the specific

polysaccharide was modified through

functionalization using glycidyl methacrylate

(Dorkoosh et al., 2002

, 2002

). Each synthesis was

carried out through the solubilization of the specific

modified polysaccharide in an aqueous solution

containing acrylamide, potassium acrylate,

ammonium persulfate and magnetite nanoparticles.

The solution was heated to 65 °C for some minutes

under constant stirring. The hydrogel obtained was

purified and dried in an oven at 50 ºC for 12 to 24

hours.

2.3 Water Uptake Mechanism

Pieces of previously dried hydrogel with masses

ranging from 50 to 100 mg were placed in contact

with 100 mL of water for different contact times,

with pH controlled at around 6.5. The degree of

swelling (DS) was calculated using Eq. 1:

DS=



−m



(1)

in which m

and m

are the masses of swollen and

dried hydrogel, respectively.

The absorption mechanism of water in a three-

dimensional hydrogel structure has been described

based on the diffusion phenomena and

macromolecular relaxation of the three-dimensional

structure. This approach is related to Fickian

diffusion processes, in which the coefficient (n) is a

parameter that describes the adsorption mechanism

(Hallinan et al., 2010), the values (1/min) of which

are determined from the fraction curves of diffused

water (M

) in function of time, as presented

mathematically in Eq. 2:





=kt



(2)

in which M

and M

are the masses (g) of water

absorbed by a hydrogel at a specific time and in

equilibrium, respectively, and k (dimensionless) is

the proportionality constant of the polymer network

of a particular hydrogel.

The Fickian diffusion model sets the absorption

of water in a three-dimensional structure until 70 %

of initial absorption. Above 70 %, there is no

linearity in the graph curve ln(M

) versus time

(t). The linear regression of Eq. 2 is seen in Eq. 3:

log 









=log+ log





(3)

The n values for different released solutes have been

commonly characterized by Fickian diffusion, non-

Fickian diffusion (anomalous) and Super Case II

models. For n values equal to 0.45, the solute

transport is characterized by the Fickian diffusion

model. In this case, it is considered that water

molecules may simply diffuse through the polymer

network by diffusion processes. For n values

between 0.45 and 0.89, the solute diffusion is

characterized by the non-Fickian diffusion model. In

this case, the diffusion mechanism is characterized

by two processes occurring simultaneously –

diffusion through the pores and macromolecular

structure relaxation. When the phenomenon of

macromolecular relaxation is involved, there is a

direct relationship with the flexibility of the polymer

network. Finally, when the n value is higher than

0.89, the diffusion mechanism of solutes in three-

dimensional polymer structures is governed

exclusively by macromolecular structure relaxation,

i.e., Super Case II model (Halligan et al., 2010;

Paulino et al., 2011).

2.4 FTIR Analysis

The samples of the polysaccharide-based hydrogels

were characterized in potassium bromide pellets

using FTIR spectra (FT-GO

max

Bomem Easy

MB−100, Nickelson). To achieve the best resolution

(4.0 cm

−1

), 21 scans min

−1

were run for each

spectrum.

2.5 Magnetization Analysis

Magnetization curves for the polysaccharide-based

magnetic hydrogel were measured using a vibrating-

sample magnetometer (physical properties

measurement system (PPMS)−9, Quantum Design,

SQID magnetometer), with a maximal magnetic

field of 7 T and sensibility of 10

-6

emu at a

temperature of 573 K.

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

264

3 RESULTS AND DISCUSSIONS

3.1 Degree of Swelling

The degree of swelling decreased from 8.78 to 6.48

g of water per gram of chitosan-based dried

hydrogel concurrently with the increase in magnetite

concentration from 0.0 to 5.5 wt.-%, respectively.

The degree of swelling of the chitosan-based

magnetic hydrogels was less than that found for the

chitosan-based hydrogel without magnetic behavior

(0 wt.-% of magnetite). The same behavior was

observed with hydrogels based on modified

maltodextrin and modified gum arabic, as a lesser

degree of swelling occurred in magnetic hydrogels.

An electrostatic repulsion generated between the

ionized groups of both the magnetic hydrogels and

the hydrogels without magnetic properties may

expand the polymer network (Jiang et al., 2010).

This phenomenon helps destabilize the structures of

the material, thereby allowing the diffusion of water

and solutes in and out-of the polymer matrix

(Paulino et al., 2009; 2010). Thus, a greater amount

of magnetite used in the hydrogel synthesis leads to

a greater degree of crosslinking due to the formation

of covalent bonds between the iron and hydroxyl or

amine groups. With this logic, a greater density of

crosslinking decreases the swelling rate.

3.2 Water Diffusion Mechanism

Table 1: Water diffusion exponent values (n) at 25

C into

hydrogels based on chitosan, modified maltodextrin and

modified gum arabic (pure hydrogel) and with known

amounts of magnetite (magnetic hydrogel).

Chitosan-based hydrogel (Pure hydrogel) and magnetic

hydrogels

(n) (R

)

Pure hydrogel

1.9 wt.-% magnetite

0.5478

0.5474

0.9918

0.9907

2.9 wt.-% magnetite 0.5910 0.9841

5.5 wt.-% magnetite 0.6046 0.9885

Modified-maltodextrin-based hydrogel (Pure hydrogel)

and magnetic hydrogels

(n) (R

)

Pure hydrogel 0.5430 0.9950

1.9 wt.-% magnetite 0.5545 0.9993

2.9 wt.-% magnetite 0.5479 0.9973

5.5 wt.-% magnetite 0.5492 0.9982

Modified-gum-arabic-based hydrogel (Pure hydrogel) and

magnetic hydrogels

(n) (R

)

Pure hydrogel 0.6201 0.9982

1.9 wt.-% magnetite 0.6307 0.9927

2.9 wt.-% magnetite 0.6385 0.9857

5.5 wt.-% magnetite 0.6496 0.9921

Table 1 displays the water diffusion exponent (n) for

hydrogels based on chitosan, modified maltodextrin

and modified gum arabic, containing magnetite

concentrations ranging from 0.0 to 5.5 wt.-%. The n

values ranged from 0.5430 to 0.6496, indicating the

non-Fickian diffusion model, with a tendency

toward macromolecular structure relaxation.

Moreover, these results indicate that there is no

variation in the water diffusion mechanism between

regular and magnetic hydrogels, confirming

previous studies (Paulino et al., 2009; 2010; 2011).

3.3 FTIR Analysis

Fig. 1 displays the FTIR spectra of the chitosan-

based hydrogel and chitosan-based magnetic

hydrogel. All hydrogels exhibited a broad absorption

band between 1715 and 1724 cm

-1

, corresponding to

the carbonyl group stretch in protonated carbonyl

acid, which means that these hydrogels are

polycations. This carbonyl comes from the

acetylated chitosan with a 10% degree of

acetylation. In the chitosan-based magnetic hydrogel

spectrum, the peak shifted to lower values due to

hydrogen bonds and interactions with magnetite

nanoparticles. The band appearing at 1574 cm

-1

corresponds to the amine group vibrations (amide II)

in the chitosan molecule, which interacted with

magnetite nanoparticles, appearing at 1552 cm

-1

the magnetic hydrogel spectrum. The band at 1451

-1

may be attributed to the methyl groups. The

peak at 1401 cm

-1

may be associated to CH

scissoring of the six carbons of the glucosamine

residues. The sharp bands around 1322 cm

-1

reveal

the presence of carboxylic groups and appeared at

1249 cm

-1

in the magnetic hydrogel spectrum due

the interaction with the magnetite nanoparticles. The

remaining broad absorption bands between 1110 and

1155 cm

-1

may be associated to vibration modes of

the saccharide rings and C-N stretching. The C-O-C

stretching vibration is also expected to take place

around 1000 cm

-1

and appears as a small shoulder on

the broad absorption band. There were important

differences between the chitosan-based hydrogel and

chitosan-based magnetic hydrogel spectra, which

were used to characterize the modification achieved

with the embedding of magnetite nanoparticles. The

main differences were related to the shifting to lower

values of the absorption bands at 1724, 1574 and

1322 cm

-1

due the formation of covalent bonds with

magnetite molecules.

Fig. 2 displays the FTIR spectra of the purified

maltodextrin, glycidyl methacrylate, modified

maltodextrin and modified maltodextrin-based

POLYSSACHARIDE-BASED MAGNETIC HYDROGELS AS POTENTICAL VECTORS FOR

EXTERNAL-CONTROLLED SOLUTE RELEASE

265

magnetic hydrogels. The band appearing at 1649 cm

in the purified maltodextrin spectrum corresponds

to the C-OH group stretching of polysaccharides.

The absorption band at 1452 cm

-1

was attributed to

the methyl groups and the band at 1420 cm

-1

was

attributed to CH

scissoring. The peak at 1371 cm

-1

may be attributed to -OH in plane bending vibration.

These peaks were also noted in the modified

maltodextrin spectrum. Moreover, purified

maltodextrin, modified maltodextrin and modified

maltodextrin-based magnetic hydrogels exhibited

similar peaks between 1025 and 1245 cm

-1

. The C-O

group stretching may appear at ~1245 cm

-1

Figure 1: Transmission FTIR spectra for chitosan-based

hydrogel and chitosan-based magnetic hydrogel.

Figure 2: Transmission FTIR spectra for modification of

purified maltodextrin with glycidyl methacrylate and

modified maltodextrin-based magnetic hydrogels.

Absorption bands between 1000 and 1152 cm

-1

may be attributed to ether bonds. These bands were

also observed in the modified maltodextrin-based

magnetic hydrogel. After the modification of

purified maltodextrin using glycidyl methacrylate, a

new absorption band appeared at 1704 cm

-1

, which

was attributed to carbonyl stretching of the

conjugated ester groups derived from a glycidyl

methacrylate molecule. The appearance of this band

was associated to the efficiency of the

polysaccharide-modifying process (Chatterjee et al.,

2003). The absorption bands at 1704 and 1649 cm

-1

shifted to lower values (1675 and 1619 cm

-1

respectively) after the modified maltodextrin-based

magnetic hydrogel synthesis. This was associated to

interactions between these specific groups and the

magnetite molecules, as previously described in the

FTIR spectra for chitosan-based magnetic hydrogels.

Fig. 3 displays the FTIR spectra of the purified

gum arabic, glycidyl methacrylate, modified gum

arabic and modified gum arabic-based magnetic

hydrogels.

Figure 3: Transmission FTIR spectra for the modification

of gum arabic with glycidyl methacrylate and modified

gum arabic-based magnetic hydrogels.

Considering the purified gum arabic spectrum,

an absorption band at 1616 cm

-1

was observed,

corresponding to the C-OH groups from purified

polysaccharides. The absorption bands at 1450 and

1424 cm

-1

correspond to the methyl groups and CH

scissoring, respectively. The bands at 1024 and 1076

-1

correspond to the ether bond vibrations. The

new absorption band at 1704 cm

-1

appearing in the

modified gum arabic spectrum was attributed to the

carbonyl stretching frequency of the conjugated

ester groups derived from a glycidyl methacrylate

molecule. As observed for the modified

maltodextrin-based magnetic hydrogel, the

absorption bands at 1704 and 1616 cm

-1

shifted to

lower values (1679 and 1616 cm

-1

, respectively) due

the presence of hydrogen bonds and covalent bonds

between hydrogel groups and magnetite molecules.

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

266

3.4 Magnetization Curves

Fig. 4 displays the magnetization loops

[magnetization versus applied magnetic field (B−H)]

of the chitosan-, modified maltodextrin- and

modified gum arabic-based magnetic hydrogels,

containing 1.9 wt.-% magnetite nanoparticles.

Figure 4: Magnetization vs. applied magnetic field for

magnetic hydrogels based on chitosan, modified

maltodextrin and modified gum arabic; magnetic

hydrogels containing 1.9 wt.-% magnetite.

The saturation magnetization values ranged from

150 to 160 emu g

-1

. Neither remanence nor

coercivity was observed for the magnetic hydrogels

due to the absence of hysteresis loops. This is a

characteristic of nanoparticulate materials embedded

in hydrogels (Chatterjee et al., 2003); (Mahkam,

2010). Therefore, it may be assumed that the

polysaccharide-based magnetic hydrogels support

nanoparticulate structures. It may also be stated that

the magnetite nanoparticles embedded in the

magnetic hydrogels through covalent bonding are

magnetic/superparamagnetic (Chatterjee et al.,

2003); (Mahkam, 2010). The superparamagnetic

properties supported by the magnetic hydrogels may

be directly related to the smaller size of magnetite

nanoparticles and their satisfactory dispersion

throughout the hydrogel network (Paulino et al.,

2010). Otherwise, a lack of either magnetization or

superparamagnetic properties would be observed. A

ferromagnetic material with either low or no

coercivity is said to be soft and may be used in some

kind of electronic devices. In many applications,

small hysteresis loops are driven around points in

the B-H plane. Loops near the origin have greater

magnetic permeability (Chatterjee et al., 2003);

(Mahkam, 2010).

4 CONCLUSIONS

A hydrogel with and without magnetic properties

may be synthesized by conventional methods and

characterized through methods such as FTIR,

magnetometry and water absorption kinetic studies.

Detained FTIR results were particularly useful in

demonstrating that the magnetic hydrogels were

formed by a cross-linking reaction of the natural

polymers in the presence of magnetite nanoparticles.

The superparamagnetic properties obtained through

magnetization may be directly related to the smaller

size of magnetite nanoparticles and their satisfactory

dispersion throughout the hydrogel network;

otherwise, a lack of either magnetization or

superparamagnetic properties would have been

observed. A ferromagnetic material with either low

or no coercivity is said to be soft and may be used in

many kinds of electronic devices. The water uptake

analysis revealed that a greater amount of magnetite

in the magnetic hydrogel network led to lesser water

uptake. On the other hand, a greater amount of

magnetite made the hydrogel more sensitive to a

externally applied magnetic field. If the main goal of

these materials is the application in remote-

controlled drug release, it could be supposed that

after applying an external magnetic field to a loaded

magnetic hydrogel with a specific drug encapsulated

in its structure, magnetic spins of magnetite would

be aligned in the same direction as the applied

magnetic field and, consequently, an enhanced

attractive force between north and south poles would

narrow the hydrogel network and deliver both water

and drug toward-out from the polymer network.

Accordingly, remote-controlled drug release can be

monitored and controlled by an external applied

magnetic field through a non-invasive procedure.

Furthermore, the magnetic hydrogels synthesized

here could effectively be applied as a magnetic

biosorbent, a magnetic biosensor, a soil conditioner

or even in cancer cell treatment.

ACKNOWLEDGEMENTS

A. T. Paulino and E. B. Tambourgi thank the State

of São Paulo Research Foundation (FAPESP,

Brazil) for the post-doctorate fellowship (Process N

2008/00285-7). A. T. Paulino, L. A. Belfiore and M.

J. Kipper thank the Coordination of Improvement of

Higher Education Personnel (CAPES, Brazil) for the

post-doctorate fellowship abroad (Process N

5267/09-9).

POLYSSACHARIDE-BASED MAGNETIC HYDROGELS AS POTENTICAL VECTORS FOR

EXTERNAL-CONTROLLED SOLUTE RELEASE

267

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