Synthesis and characterization of κ-carrageenan/poly(N,N-diethylacrylamide) semi-interpenetrating polymer network hydrogels with rapid response to temperature

POLYMERS FOR ADVANCED TECHNOLOGIES

Polym. Adv. Technol. 2008; 19: 1656–1663

nce.wiley.com) DOI: 10.1002/pat.1184
Published online 27 May 2008 in Wiley InterScience (www.interscie
Synthesis and characterization of k-carrageenan/

poly(N,N-diethylacrylamide) semi-interpenetrating

polymer network hydrogels with rapid response to

temperature

Jun Chen1, Mingzhu Liu1*, Shuping Jin1,2 and Hongliang Liu1

1Department of Chemistry and State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P.R. China2Department of Chemistry, Hexi University, Zhangye 734000, P.R. China

Received 21 December 2007; Revised 10 April 2008; Accepted 15 April 2008

*CorrespoKey Laboversity, LE-mail: mContract/Ministry20030730

In this study, a novel classical thermo- and salt-sensitive semi-interpenetrating polymer network

(semi-IPN) hydrogel composed of poly(N,N-diethylacrylamide) (PDEAm) and k-carrageenan (KC)

was synthesized by free radical polymerization. The structure of the hydrogels was studied by

Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR and

SEM revealed that the semi-IPN hydrogels possessed the structure of H-bonds and larger number of

pores in the network. Compared to the PDEAmhydrogel, the prepared semi-IPNhydrogels exhibited

a much faster response rate to temperature changes and had larger equilibrium swelling ratios at

temperatures below the lower critical solution temperature (LCST). The salt-sensitive behavior of the

semi-IPN hydrogels was dependent on the content of KC. In addition, during the reswelling process,

semi-IPN hydrogels showed a non-sigmoidal swelling pattern. Copyright # 2008 John Wiley &

Sons, Ltd.

KEYWORDS: poly(N,N-diethylacrylamide); k-carrageenan; semi-interpenetrating polymer network; thermo-sensitive; fast response

INTRODUCTION

Hydrogels are crosslinked, three-dimensional and hydro-

philic polymer networks capable of imbibing large amounts

of water or biological fluids. Considerable research attention

has focused on stimuli-responsive hydrogels, which exhibit

volume or phase transition in response to slight environ-

mental changes, such as temperature,1 solvent composition,2

pH,3 light,4 and electric field.5 Among all of the stimu-

li-responsive hydrogels, thermo-sensitive polymers are the

most favorable members and have been widely investigated.

Their chain hydrate to form expanded structures in water

when the temperature is below the lower critical solution

temperature (LCST) but become a compact structure by

dehydration above the LCST, which could be used in many

fields like controlled drug delivery,6–8 protein absorption,9

immobilization of enzymes,10 molecular separation,11 and

artificial organs.12 Among the family of thermo-sensitive

polymers, poly(N,N-diethylacrylamide) (PDEAm), as shown

in Figure 1, may be widely used because of its LCST in the

range of 25–308C, close to the body temperature.7 Moreover,

ndence to: M. Liu, Department of Chemistry and Stateratory of Applied Organic Chemistry, Lanzhou Uni-anzhou 730000, P.R. [email protected] sponsor: Special Doctoral Program Funds of theof Education of China; contract/grant number:

013.

PDEAm may be more suited for certain applications in life

science due to the molecule lacking H-atom in the side

chain.

However, the response rate of conventional PDEAm

hydrogel is known to be very slow which may restrict its

applications. There have been considerable efforts in

enhancing the response rate of the hydrogel, such as

preparing phase-separated hydrogels at temperatures above

the LCST,13,14 synthesizing hydrogels with dangling

chains,15,16 and modifying the microstructure of hydrogels

by the pore-forming agent.17,18 Unfortunately, some modi-

fications also cause unfavorable effects, such as loss in

mechanical strength. So a particular challenge in this field is

to obtain an increased response rate yet maintain higher

mechanical strength. The other methods are to incorporate

hydrophilic polymers such as poly(vinyl alcohol),19 corn

starch,20 and sodium alginate,21 which can form water-

releasing channels within the hydrogel network, by inter-

penetrating polymer network (IPN) technology. IPNs are

made up of two more incompatible crosslinked polymers in

which crosslinking can be achieved due to inter-mixing of the

network.22 If only one polymer of the IPN is crosslinked

leaving the other in linear form, the system is termed as a

semi-IPN. Compared with the former three methods, IPN

and semi-IPN have some advantages. For example, IPN

hydrogels with extremely faster response rate without the

loss of the mechanical strength can be prepared easily, and

the combination of temperature-sensitivity with other

Copyright # 2008 John Wiley & Sons, Ltd.

Figure 1. Scheme of k-carrageenan/poly(N,N-diethylacrylamide) semi-interpenetrating polymer net-

work ((KC/PDEAm semi-IPN) hydrogel

Thermo- and salt-sensitive semi-interpenetrating polymer network 1657

properties such as salt-sensitivity and biocompatibility can

also be obtained by adjusting the network structure.

k-carrageenan (KC) is an anionic and hydrophilic poly-

saccharide, and one of the most abundant and natural

occurring polysaccharide that exists as matrix material in

numerous species of seaweed. Chemically, it is a linear,

sulfated polysaccharide, composed of repeating D-galactose

and 3,6-anhydro-D-galactose units (see Fig. 1). KC is mainly

used in the food and cosmetic industry as gelling, thickening,

and stabilizing agent due to biocompatibility, biodegrad-

ability, high hydrophilicity, and mechanical strength.23

Moreover, KC has the variety of biological activities.24

Therefore, uses of KC as support materials for immobiliz-

ation of protein and controlled drug delivery system have

received the most considerable attention.25–27 Recently, KC is

used to enhance the properties of synthetic hydrogels by

incorporating into the water-solution polymer systems, such

as poly(N-vinylpyrolidone),28 poly(diallyldimethylammo-

nium chloride),29 and poly(N-isopropylacrylamide).30 How-


ever, there have been no reports on the semi-IPN hydrogel

based on KC and crosslinked PDEAm.

Based on these ideas, a kind of thermo- and salt-sensitive

semi-IPN hydrogels was synthesized in which KC had been

incorporated into PDEAm hydrogels. The novel hydrogel is

expected to be a good material for controlled drug delivery

systems which are both thermo-responsive and biodegrad-

able. The thermo- and salt-sensitivities, response rate, and

reswelling rate were investigated by measuring the equi-

librium swelling ratios in this work. It was expected that the

incorporation ofKCwould overcome the slow response rate of

PDEAm hydrogels on the one hand, and also extend the

biomedical applications of PDEAm hydrogels on the other.

EXPERIMENTAL

Materialsk-carrageenan (KC) was purchased from the golden phoenix

of Kappa-carrageenan Co. Ltd. (Tengzhou, China) and used


DOI: 10.1002/pat

1658 J. Chen et al.

without further purification. N,N-diethylacrylamide

(DEAm) was synthesized according to the literature.31

Ammonium persurfate (APS) and N,N,N’,N’-tetramethy-

lethylenediamide (TEMED) were of analytical grade and

used as received. N,N’-methylenebisacrylamide (NNMBA)

(C.P. grade) was recrystallized from ethanol. The other

reagents were of analytical grade and used without further

purification.

Preparation of the KC/PDEAm semi-IPNhydrogelsA certain amount of KC was dissolved in distilled water at

708C for 1 hr and then the monomer (DEAm) and crosslinker

(NNMBA) were added to the hot solution, and the reaction

mixture was stirred for 30min. When themixed solution was

cooled down to 268C, the solution was degassed with

nitrogen for 20min, and then a given amount of APS (1wt%)

and TEMED used as a pair of redox initiators were dropped

into the solution to initiate the polymerization reaction, and

the polymerization and crosslinking reactions were main-

tained at 268C for 24 hr. After the polymerization, the

produced opalescent hydrogels were cut into discs (12mm

diameter and about 3mm thickness), and then the disc

samples were immersed in distilled water at room tempera-

ture for 5 days and the water was refreshed every 4 hr in

order to remove the unreacted monomers. The hydrogel

samples were dried at room temperature for 2 days, and

were further dried under vacuum to constant weight at 258C.The feed compositions for the semi-IPN hydrogels and their

sample IDs are summarized in Table 1.

Characterization of gel by FTIRThe IR spectra of the samples were obtained with a Nicolet

670 FTIR spectrometer. Firstly, products were dried over-

night under a vacuum condition until constant weight. The

dried gels were pressed into powder, mixed with 10 times as

much potassium bromide powder and then compressed into

a pellet for FTIR characterization.

Interior morphology of the hydrogelsThe hydrogel samples were first equilibrated in distilled

water at room temperature, then quickly frozen in liquid

nitrogen and further freeze-dried under vacuum for 15 hr

with Labconco Freeze Dry system. After that, the freeze-

dried hydrogel samples were fractured carefully and

mounted onto aluminum stubs and coated with gold. The

Table 1. Feed compositions for the hydrogels

Compositions

Sample ID

PDEAmsemi-IPN1

semi-IPN3

semi-IPN4

semi-IPN6

KC (mg) 0.0 5.3 15.4 20.1 30.2DEAm (ml) 0.5 0.5 0.5 0.5 0.5NNMBA (mg) 9.9 10.1 9.9 10.3 10.15wt%APS (ml) 0.5 0.5 0.5 0.5 0.5TEMED (ml) 10.0 10.0 10.0 10.0 10.0H2O (ml) 5.0 5.0 5.0 5.0 5.0


interior morphology was investigated using a scanning

electron microscope (JSM-5600LV SEM, Japan).

Temperature dependence of the equilibriumswelling ratio of the hydrogelsA classical gravimetric method was used to measure the

equilibrium swelling ratio (ESR) of the hydrogel. Swelling

studies were performed in distilled water with different

temperatures (from 14 to 508C), which covered the expected

range of the LCST of the hydrogel. The samples were

immersed in distilled water to swell for at least 24 hr to reach

the equilibrium state at each predetermined temperature,

then the samples were taken out, the excess water on the

surface was blotted by wetted filter paper, and the samples

were weighed. The hydrogel samples were re-equilibrated in

distilled water at another predetermined temperature and

then weighed by the same method as above. The dry weight

of the samples was finally measured after drying in vacuum

at 258C for 48 hr to reach a constant weight. Taking the

average value of three measurements for each sample, the

ESR is defined as follows:

ESR ¼ Ws � Wdð ÞWd

(1)

whereWs is the weight of the hydrogel sample in the swollen

equilibrium and Wd is the initial weight of the dried

hydrogel.

Study on deswelling kinetics of the hydrogelsThe deswelling kinetics of the hydrogels was studied by

immersing the swollen hydrogels at 178C into distilled water

at 608C. At predetermined time intervals, the hydrogels were

taken out from the hot water and weighed after wiping off

the surface with wetted filter papers. The average value of

three measurements was taken for each sample, and the

deviation between the measurements was less than 10%.

The water retention (WR) is defined as follows:

WR ¼ Wt �Wdð ÞWs � Wdð Þ � 100 (2)

whereWt is the weight of the wet hydrogel at regular time

intervals, Wd the same as above, and Ws the weight of

hydrogel in the swollen equilibrium at 178C.

Study on reswelling kinetics of the hydrogelsThe reswelling kinetics of the dried hydrogels was measured

gravimetrically. Before the measurement, the swollen

hydrogel samples were shrunk in hot water (608C) for

6 hr, and then the shrunk hydrogels were dried in a vacuum

oven at 258C till a constant weight. The dried samples were

placed in distilled water at 208C to swell and then taken out

from water at regular time intervals. The same method as

above was utilized to record the weights of samples. The

water uptake (WU) at time t is defined as follows:

WU ¼ Wt � Wdð ÞWs � Wdð Þ � 100 (3)

whereWt is the weight of the wet hydrogel at time t at 208Cand other symbols (Wd, Ws) are the same as above.


DOI: 10.1002/pat


Study on salt-sensitivity of the hydrogelsThe ESR of hydrogels were evaluated in 0.9wt% sodium

chloride (NaCl) aqueous solution according to the above

method described for swelling measurement in distilled

water at 208C. Taking the average value of three measure-

ments for each sample, the equilibrium swelling ratio in

NaCl aqueous solution, ESRNaCl, is defined as follows:

ESRNaCl ¼ WNaCl � Wdð ÞWd

(4)

where WNaCl is the equilibrium swelling weight (ESR) of

the hydrogels in NaCl solution.

To achieve a comparative measure of salt-sensitivity of the

hydrogels, a dimensionless salt-sensitivity factor (F) is

defined as follows:

F ¼ ESR � ESRNaCl (5)

where ESR and ESRNaCl are the same as above.

RESULTS AND DISCUSSION

FTIR analysisFTIR has been widely used to detect the molecular

interactions in polymer blend systems.20,32 FTIR spectra of

KC, PDEAm, and semi-IPN hydrogels are shown in Figure 2.

It can be found that each spectrum of semi-IPN shows a

broad band at about 3441 cm�1, which belongs to –OH

stretching vibration. With the KC content increasing, these

bands become broader and lower. The peaks of these bands

appearing at lower wavenumber are a sign of the formation

of H-bonding between KC and DEAm, which is believed to

be the driving force that slows down the reswelling rate of

semi-IPN hydrogels. Moreover, the typical band at about

1636 cm�1 consisting of C––O stretch of PDEAm, and two

typical bands of C–H vibration at 1455 and 1380 cm�1 which

belong to the bands of –CH2 and –CH3 groups, respectively.

It can also be found that the typical bands of KC at 844, 949,

and 1276 cm�1, are attributed to D-galactose-4-sulfate,

Figure 2. FTIR spectra of PDEAm


3,6-anhydro-D-galactose, and ester sulfate stretching,

respectively.

Surface morphology of the hydrogelsThe interior morphology of these hydrogels is shown in

Figure 3. The results clearly illustrated that the PDEAm

hydrogel has a relatively dense structure, while the semi-IPN

hydrogels show a porous network structure. The pore size

becomes larger as the content of KC increases. For example,

semi-IPN6 has the largest pore size. Therefore, it can be

concluded from the results that a highly expanded network

can be generated by electrostatic repulsions among sulfated

anions of KC during the polymerization process. With the

increment of KC content, the expansion of the gel matrixes is

enhanced, which results in an increase in the pore size.

Based on the SEM morphology observed, these hydrogels

would be expected to have different ESR and deswelling rate

from the PDEAm hydrogel.

Temperature dependence of the swelling ratioESR is one of the most important parameters for evaluating

hydrogels. Figure 4 exhibits the ESR of the hydrogels in the

temperature range from 14 to 508C. The experimental data

also demonstrate that the LCST behavior of all semi-IPN

hydrogels is similar to that of PDEAm hydrogel: both exhibit

a LCST at about 288C. The ESR of the hydrogels increases

with the increase of KC content in the corresponding

hydrogel at temperatures below the LCST. For example,

the ESR of PDEAm is around 7.05 at 208C, while the ESR of

IPN1, IPN3, IPN4, and IPN6 are around 10.98, 13.52, 15.69,

and 18.62, respectively. Upon heating, all the hydrogels

exhibit a temperature-stimulated decrease in swelling ratio,

but with different magnitudes of the thermo-induced

decrease in swelling ratio.

Because semi-IPN has a with physically interlocked

structure of two polymer networks, there is no chemical

bond between networking. Thus each polymer network can

retain its individual properties like its homopolymer.33 It is

, KC and semi-IPN hydrogel


DOI: 10.1002/pat

Figure 3. Scanning electron microscope micrographs of PDEAm and semi-IPN hydrogels:

(a) PDEAm; (b) semi-IPN1; (c) semi-IPN4; (d) semi-IPN6

1660 J. Chen et al.

known that there are hydrophilic groups (–CONR2) and

hydrophobic groups (–CH2CH3) in the monomer DEAm,

corresponding to hydrophilic and hydrophobic regions in

the PDEAm hydrogel, respectively. When the temperature is

Figure 4. Equilibrium swelling ratio of PDEAm and semi-IPN

hydrogels in distilled water over the temperature range from

14–608C


lower than the LCST, the H-bond interactions between water

and the polymer chains are dominant, which leads to high

swelling ratios. Moreover, if a hydrophilic moiety was

incorporated into the hydrogel, the hydrophilicity of the

resulting hydrogel will be expected to increase.22,34 That is,

from PDEAm to semi-IPN6, the hydrophilicity becomes

stronger gradually, resulting in increased ESR of the

corresponding hydrogels. The surface morphological data

(Fig. 3) described previously also support this relationship

observed in Figure 4.

In the PDEAm network system, there is a hydrophilic/

hydrophobic balance resulting from H-bonds and hydro-

phobic interactions. The thermosensitivity of PDEAm

hydrogel is attributed to its alteration in hydrophilicity

and hydrophobicity of the network. At a temperature above

LCST, some of the H-bonds will be destroyed, and the

hydrophobic interactions among the hydrophobic groups in

PDEAm become dominant and consequently PDEAm

hydrogels become much less hydrophilic.31 As a result,

those entrapped water molecules are released from the

network, causing the hydrogel to collapse, and decreasing

the ESR of hydrogels dramatically. When the temperature is


DOI: 10.1002/pat

Figure 6. Reswelling kinetics of PDEAm and semi-IPN

hydrogels (water uptake versus time) at 208CFigure 5. Deswelling kinetics of PDEAm and semi-IPN

hydrogels in distilled water at 608C


much higher than the LCST (above 408C), the ESR of

semi-IPN hydrogels are almost the same as that of PDEAm

hydrogel because the hydrophobic interaction becomes fully

dominant in the hydrogels at the high temperature. The

thermosensitive property of the hydrogels has sparked

particular interest in the field of drug delivery system. The

drug is loaded into the hydrogels at below the LCST. The

release ratio is dependent on the temperature which is

determined by the swelling status of the hydrogels.7,8,35 The

benefit of using hydrogels for drug delivery may be largely

pharmacokinetic, which helps the drug to be released slowly,

maintaining a certain concentration of drug in the surround-

ing tissues over an extended period. Our samples also have a

thermosensitive property, maybe it can be used in the field of

drug delivery system.

Deswelling kinetics at 60-CThe response rate to external temperature change is a critical

factor due to its potential application. The deswelling

kinetics of the hydrogels after a temperature jump from

the equilibrium-swollen state at 178C (below the LCST) to

distilled water at 608C (above the LCST) is shown in Figure 5,

from which it can be observed that the semi-IPN hydrogels

have much faster response rates than the PDEAm hydrogel

and can shrink to the equilibrium state in a very short time.

For instance, semi-IPN1 lost at least 85% water within 2min

and over 90% water within 4min, and semi-IPN6 lost about

60% water within 2min and over 80% water within 4min,

while PDEAm lost only about 20% water within 30min.

Moreover, during the shrinking process, it can also be found

that a few bubbles appeared on the surface of PDEAm

hydrogel, while there are no bubbles formed on the surface of

semi-IPN hydrogels. Therefore, semi-IPN hydrogels have

improved surface property.

As discussed above, when the PDEAm hydrogel is

transferred into hot water (above the LCST), the hydrophobic

interactions among the hydrophobic groups in the surface

region become strong and a dense skin layer is formed on

the surface, in which the free inner water molecules are

prevented from diffusing out, and bubbles appear on the

surface of the hydrogel.36 As observed by SEM, the porous

structure is generated for semi-IPN hydrogels owing to


the presence of ionized KC, and water can be easily excluded

through the pore-tracts. Moreover, the hydrophilic chains of

KC can act as water releasing channels when the hydrogel

collapse occurs and enhances the shrinking rate.19,20 There-

fore, during the shrinking process of semi-IPN hydrogel, the

excluded water in hydrogels can diffuse out quickly and on

time, and a rapid deswelling rate can be achieved.

However, the deswelling rate of semi-IPN hydrogels does

not exhibit evident KC dependence, and it is not the same as

expected that the deswelling ratio increases with an increase

in the KC content. From Figure 5, it can be found at the

beginning that the deswelling rate of a semi-IPN6 hydrogel

is slower than that of other semi-IPN hydrogels. When

the contents of KC increase in the hydrogel system, much

more H-bonds are formed between the water molecules and

the hydrophilic groups of KC.20 When the temperature

increases, this system needs more energy to destroy these

H-bonding interactions and release the entrapped water

molecules. As a result, the shrinking rate of semi-IPN6 is

slower that of the other three semi-IPN hydrogels.

Reswelling kinetics at 20-CFigure 6 shows the reswelling process of the hydrogel

samples. It can be seen that the reswelling rate of the

hydrogels slows down with the increasing content of KC.

The reswelling rate of the dried hydrogels, which shrink in

hot water, is measured and then dried in a vacuum oven. As

a result, more H-bonds of dried hydrogel are formed

between KC and the hydrophilic groups of PDEAm, and

H-bonds with increasing KC content become stronger, which

can be demonstrated by FTIR in Figure 2. The H-bonding

interactions prevent the polymeric chains from expanding

further, and the reswelling rate is limited. Therefore, the

reswelling rate decreases with an increase in the KC content.

As we know, the reswelling process is complicated and the

swelling rates depend on the mode of diffusion of water

molecules into the hydrogel matrix and the subsequent

relaxation of its macromolecular chains.37 It is further shown

in Figure 7 (water uptake versus the square root of time),

based on the data of Figure 6 that water can diffuse into

the polymer matrix slowly. From Figure 7, it can be seen that

the amount of water uptake is directly proportional to the


DOI: 10.1002/pat

Table 2. Equilibrium swelling ratio in distilled water and NaCl

aqueous solution (0.9wt%), and salt-sensitivity factor (F) for

the hydrogels at 208C

Sample ESR (g/g) ESRNaCl (g/g) F

PDEAm 7.05 6.95 0.10semi-IPN1 10.98 10.27 0.71semi-IPN3 13.52 12.62 0.90semi-IPN4 15.69 14.30 1.39semi-IPN6 18.62 17.00 1.62

Figure 7. Reswelling kinetics of PDEAm and semi-IPN

hydrogels (water uptake versus square root of time) at 208C

1662 J. Chen et al.

square root the time. It is supposed that the strong H-bonds

interactions between PDEAm and KC still exist throughout

the whole experiment period, and the rate of diffusion is

lower than that of macromolecular relaxation.

Salt-sensitivity at 20-CMost applications of thermo-responsive hydrogels will occur

not in pure water, but in a more complex environment. Salt

solution and especially physiological saline solution in this

environment may influence the swelling behavior. The ESR

in 0.9wt%NaCl aqueous solution for the hydrogels is shown

in Figure 8. It can be found that swelling ratios of all

hydrogels are appreciably reduced in salt solutions com-

pared to the values measured in distilled water (see Fig. 4),

and the decreased value of the swelling ratio strongly

depends on the KC content. As shown in Table 2, the F value

of the samples increased from the PDEAm to the semi-IPN6

hydrogel, and the F value of the PDEAm is the smallest. The

high values of F show clearly that the hydrogel has high salt

sensitivity.

Owing to the presence of the salting-out effect, the ESR of

the nonionic PDEAm hydrogel shows a change in the salt

solution. It is well known that the salt-out effect increases

with increase in the salt content in the solutions. Therefore, in

0.9wt% NaCl aqueous solution, the F value of PDEAm

hydrogel is small. However, for ionic semi-IPN hydrogel, the

Figure 8. Equilibrium swelling ratio of PDEAm and semi-IPN

hydrogels in NaCl aqueous solution (0.9wt%) at 208C


charge repulsion among the KC segment can also be

effectively screened by the addition of electrolytes to yield

a dense molecular conformation. The charge screening effect

of the cation shields the charge of sulfate groups and

prevents an efficient electrostatic repulsion, which leads to a

decreased ionic pressure difference between the polymer

network and the external solution. Therefore, the driving

force for swelling, between the internal and the external

solutions of the network, is decreased.38 With the increasing

amount of KC, the charge screening effect is increased. As a

result, salt-sensitivity of semi-IPN hydrogels increases with

an increase in the KC content at 208C.

CONCLUSIONS

In this work, a series of temperature-sensitive semi-IPN

hydrogels composed of biocompatible KC and crosslinked

PDEAm were prepared from various compositions of KC

and DEAm by solution polymerization. The surface

morphological change and molecular interaction were

characterized by SEM and FTIR. The FTIR results showed

the presence of H-bonds (between PDEAm and KC) in the

system. The deswelling/reswelling behavior of the semi-IPN

hydrogels were investigated in detail. Experimental results

showed that the swelling ratios of the semi-IPN hydrogels

increased with the increase in the amount of KC at the same

temperature range (below the LCST), and decreased with the

increase in temperature. Most importantly, the semi-IPN

hydrogels exhibited a fast deswelling rate. In addition, the

swelling ratios reduced in the salt solution when compared

to distilled water as a swelling medium. Furthermore, the

salt-sensitivity of the semi-IPN hydrogels increases with an

increase in KC content, which suggests that the samples

would have potential applications in biomedicine.

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DOI: 10.1002/pat

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Synthesis and characterization of κ-carrageenan/poly(N,N-diethylacrylamide) semi-interpenetrating polymer network hydrogels with rapid response to temperature