• Advances in materials Research
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• 제1권4호
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• pp.269-284
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• 2012

Thermoresponsive hydrogels based on N-Isopropylacrylamide (NIPAM) and 2-Hydroxyethylacrylate (HEA) were prepared by free radical polymerization. The hydrogels were characterized by elemental (CHN) analysis, differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA). DSC thermogram showed two endothermic transitions which are due to hydration of water present in different environments. One near $0^{\circ}C$ called melting transition of ice and was used to calculate the quantitative determination of the amounts of freezing and non freezing water. The other transition above the ambient temperature was due to the combination of hydrophobic hydration and hydrophilic hydration which changes with the copolymer compositions. Swelling and deswelling studies of the hydrogels were carried out using the aqueous media, salt and urea solutions. The experimental results from swelling studies revealed that copolymers have lower rates of swelling and deswelling than the homopolymer.

• 폴리머
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• 제31권4호
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• pp.349-355
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• 2007

열 응답성을 갖는 poly(N-isopropylacrylamide) (PNIPAAm) 수화젤의 팽윤 및 수축 특성을 변화시키기 위하여, 물을 용매로 하여 AN 함량이 10 mol% 이내인 P(NIPAAm-co-AN) 공중합체 및 이들의 수화젤을 합성하였고, AN 함량이 공중합체 수화젤의 임계젤전이온도(CGTT) 및 팽윤 거동에 미치는 영향을 분석하였다. 공중합체 수화젤들은 $30{\sim}32\;^{\circ}C$에서 CGTT를 나타내었으며, AN 함량이 증가함에 따라 CGTT는 저온 쪽으로 이동하였다. 이들 공중합체 수화젤을 CGTT 이하 온도의 물에서 팽윤시키면 AN 함량이 많아짐에 따라 팽윤속도가 느려지고 평형 팽윤비 값이 작아지지만, CGTT 이상에서 수축시키면 AN 함량이 많은 수화젤이 더 빠르고 더 많이 수축하였다.

• 폴리머
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• 제25권5호
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• pp.736-743
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• 2001

N,N-Methylenebisacrylamide (MBAA)로 가교 결합된 electro-active 고분자(EAP) (poly(2-acrylamido-2-methylpropane sulfonic acid), PAMPS) 겔을 수용액 상에서 potassium persulfate를 개시제로 하여 라디칼 중합시켜 제조하였다. PAMPS 겔의 구동성을 부여하기 위하여 계면활성제로 팽윤하며 치환하였다. 계면활성제가 치환된 PAMPS 겔은 용액내의 인가된 전압하에서, 그 전기장 변화에 의해 큰 변위를 나타내는 구동특성을 보였다. PAMPS 겔은 빠른 응답속도와 가역적인 bending을 나타내었다. 겔의 구동원리는 양극과 PAMPS 겔 음이온간의 정전기 인력, 겔의 swelling-deswelling 효과 그리고 계면활성제의 소수성 반응의 협동적 과정으로 나타난다. PAMPS 겔의 응답속도는 인가된 전압 및 가교도가 증가할수록 증가하였으며, 구동이 반복적으로 진행됨에 따라 응답속도는 증가하였다. 겔의 두께가 증가하면 응답속도는 감소하였다.

• 한국염색가공학회지
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• 제34권3호
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• pp.207-216
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• 2022

Hydrogels have gained considerable attention in various fields due to their easily transformative ability by different stimulation. In addition, metal-based conductive additives can enable the hydrogels to be conductive with dimension change. Although the development of the additives offered enhanced electrical properties to the hydrogels, correspondingly enhanced mechanical properties may limit the volume and electrical properties switching after stimulation. Here we prepared poly(N-isopropylacrylamide) (PNIPAM) thermo-responsive hydrogel that has a 32℃ of low critical solution temperature and added liquid metal particles (LMPs) as conductive additives, possessing soft and stretchable benefits. The LMPs enabled PNIPAM (PNIPAM/LMPs) hydrogels to be constricted over 32℃ with a high volume switching ratio of 15.2 when deswelled. Once the LMPs are spontaneously oxidized in hydrogel culture, the LMPs can release gallium ions into the hydrogel nature. The released gallium ions and oxidized LMPs enhanced the modulus of the PNIPAM/LMPs hydrogel, triggering high mechanical stability during repeated swelling/deswelling behavior. Lastly, highly constricted PNIPAM/LMPs hydrogel provided a 5x10⁶ of electrical switching after deswelling, and the switching ratio was closely maintained after repeated swelling/deswelling transformation. This study opens up opportunities for hydrogel use requiring thermo-responsive and high electrical switching fields.

• Macromolecular Research
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• 제11권3호
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• pp.189-193
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• 2003

pH- and temperature-sensitive bifunctional hydrogels composed of N-isopropylacrylamide (NiPAAm) and a sulfadimethoxine monomer (SDM) derived from sulfadimethoxine were prepared. These hydrogels exhibit simultaneous pH- and temperature-induced volume-phase transitions. The pH-induced volume-phase transition behavior is produced by the ionization/deionization of SDM and is very sharp. In the high pH region, the ionization of SDM induces swelling of the hydrogels. In the low pH region, the deionization of SDM induces deswelling of the hydrogels. The temperature-induced volume-phase transition behavior of the bifunctional hydrogels exhibits negative thermosensitivity because of the NiPAAm component. The hydrogels swell even at low pH as the temperature decreases. The hydrogels swell at low temperature and high pH, and deswell at high temperature and low pH. The volume of the hydrogels dependl on the balance of the swelling and deswelling produced by the two competing stimuli, pH and temperature.

• 폴리머
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• 제37권6호
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• pp.794-801
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• 2013

Novel microgels of N-isopropylacrylamide (NIPAM)-co-methacrylic acid (MAA) (NIPAM-co-MAA) with different contents of N,N-methylene bis acrylamide (MBA) were prepared by emulsion polymerization technique and were studied by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and zeta potential measurement. Effect of pH, temperature and different salts concentration on the microgel particles was investigated. DLS results have shown that the hydrodynamic radius of the microgel increased upon increasing pH and decreased upon increasing temperature. The swelling/deswelling behaviors as determined by DLS showed the ionic repulsions of the carboxyl group of the methacrylic acid and hydrophobic interaction of NIPAM. The effect of various salts on volume phase transition temperature (VPTT) was also investigated. Upon increasing salt concentration, VPTT became broad and shifted to a lower temperature. Electrophoretic mobility measurements showed an increase with increasing pH and temperature at a constant ionic strength.

• Archives of Pharmacal Research
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• 제28권8호
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• pp.983-987
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• 2005

Hydrogels composed of glycidyl methacrylate dextran (GMD) and poly(acrylic acid, PM) were prepared by UV irradiation method for colon-specific drug delivery. GMD was synthesized by coupling of glycidyl methacrylate to dextran in the presence of 4-(N,N-dimethylamino)pyridine. GMD was photo-polymerized by ammonium peroxydisulfate as initiating system in phosphate­buffered solution (0.1 M, pH 7.4). And then, acrylic acid monomer was added and subsequently heat-polymerized by 2,2'-azobisisobutyronitrile as an initiator. The hydrogels exhibited high swelling ratio (about 20) at $37^{\circ}C$, and showed a pH-dependent swelling behavior. In addition, the swelling ratio of the hydrogel was remarkably enhanced to about 45 times in the presence of dextranase at pH 7.4. The swelling-deswelling behavior proceeded reversibly for the GMD/PM hydrogels between pH 2 and pH 7.4. Release of 5-aminosalicylic acid from the GMD/PAA hydrogels was evaluated in simulated gastrointestinal pH fluids in the absence or presence of dextranase. We concluded that the hydrogels prepared could be used as a dual-sensitive drug carrier for sequential release in gastrointestinal tract.

• Archives of Pharmacal Research
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• 제19권1호
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• pp.18-22
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• 1996

Acrylate-terminated poly (ethylene glycol) (PEG) macromer was prepared by the reaction of PEG with acryloyl chloride. Photopolymerization of PEG macromer resulted in the formation of cross-linked PEG network. Interpenetrating polymer networks (IPNs) based on PEG and poly(acrylic acid) (PAA) was obtained via template polymerization of AA to the PEG network by UV curing. The swelling degree of the IPNs hydrogel increased with an increase of pH value due to the association-dissociation between carboxylic acid of PAA and either of PEG through hydrogen bounding. The swelling-deswelling behavior proceeded reversibly for the IPNs upon changing pH. Release of indomethacin from the IPNs demonstrated "on-off" regulation with pH fluctuation.

• Macromolecular Research
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• 제15권4호
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• pp.363-369
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• 2007

Novel biodegradable elastic hydrogels, based on hydrophilic and hydrophobic polymer blocks, were synthesized via the radical crosslinking reaction of diacrylates of poly(ethylene glycol) (PEG) and poly(${\varepsilon}-caprolactone$) (PCL). PEG and PCL diols were diacrylated with acryloyl chloride in the presence of triethylamine, with the reaction confirmed by FT-IR and $^1H-NMR$ measurements. The diacrylate polymers were used as building-blocks for the syntheses of a series of hydro gels, with different block compositions, by simply varying the feed ratios and molecular weights of the block components. The swelling ratio of the hydrogels was controlled by the balance between the hydrophilic and hydrophobic polymer blocks. Usually, the swelling ratio increases with increasing PEG content and decreasing block length within the network structure. The hydrogels exhibited negative thermo-sensitive swelling behavior due to the coexistence of hydrophilic and hydrophobic polymer components in their network structure, and such thermo-responsive swelling/deswelling behavior could be repeated using a temperature cycle, without any significant change in the swelling ratio. In vitro degradation tests showed that degradation occurred over a 3 to 8 month period. Due to their biodegradability, biocompatibility, elasticity and functionality, these hydrogels could be utilized in various biomedical applications, such as tissue engineering and drug delivery systems.

• Biomaterials and Biomechanics in Bioengineering
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• 제1권2호
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• pp.105-116
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• 2014

Synthesis of interpenetrating polymer network (IPN) of chitosan-gelatin (Cs-Ge) (as a primary network) and N-isopropylacrylamide (NIPAAm) monomer (as the secondary network) was carried out with different ratio. Its structure was characterized by FT-IR, which indicated that the IPN was formed. The memberanes were studied by swelling, weight loss with time. The interior morphology of the IPN hydrogels was revealed by scanning electron microscopy (SEM); the IPN hydrogels showed a interpenetrated network of NIPAAm/chitosan has layers with more minute stoma and canals compared to interpenetrated network of NIPAAm/gelatin. Lower critical solution temperature (LCST), equilibrium swelling ratio (ESR) and deswelling kinetics were measured. The DSC results noticed that LCST of IPN hydrogels with different ratio of Cs/Ge/PNIPAAm are around $33{\pm}2^{\circ}C$. The ESR obtained results showed that with a ratio of Cs/Ge/NIPAAm: 1/1/6, the swelling ratio increased drastically from room temperature to $36^{\circ}C$ but with a ratio of Cs/Ge/PNIPAAm: 1/3/6, decrease significantly at the same condition. Therefore the hydrogels have been changed from a hydrophilic structure to a hydrophobic structure. Furthermore with an increase in temperature from room to the LCST, the ESR of IPN with higher concentration of (PNIPAAm) and (Ge) decreases but de-swelling kinetics of them are faster. Due to the suitable and different kinetics of de-swelling and the equilibrium swelling ratio (ESR) in various proportions, and because of the morphology inside the mass which confirms other tests, these hydrogels are very appropriate as a smart thermosensitive hydrogels with rapid response.