• KSBB Journal
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• v.15 no.6
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• pp.548-555
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• 2000

A hydrogel, poly(N-isopropylacrylamide-co-N, N-dimethylaminopropylmethacrylamide), sensitive to both pH and temperature, was synthesized and characterized at $^13∼23{\circ}C$ and pH of 10.3∼12.3. The gel was more transparent and mechanically stronger at lower preparation temperature and pH. Large pores observed in scanning electron microscope seem to be responsible for the lower biomolecular separation efficiency. The lower critical solution temperature (LCST) decreased at a higher polymerization temperature. At $25^{\circ}C$, which is lower than the LCST, the gel was swollen regardless of the solution pH. At $40^{\circ}C$, however, the gel was swollen at neutral and acidic pHs even though the temperature was higher than the LCST. The gel collapse pH, defined as the point at which the gel made its largest volume decrease per unit pH increment, increased as the gel preparation temperature increased.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.5
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• pp.326-331
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• 2001

With the aim of developing of pH-sensitive controlled drug release system, a poly(Llysine) (PLL) based cationic semi-interpenetrating polymer network (semi-IPN) has been synthesized. This cationic hydrogel was designed to swell at lower pH and de-swell at higher pH and therefore be applicable for achieving regulated drug release at a specific pH range. In addition to the pH sensitivity, this hydrogel was anticipated to interact with an ionic drug, providing another means to regulate the release rate of ionic drugs. This semi-IPN hydrogel was prepared using a free-radical polymerization method and by crosslinking of the polyethylene glycol (PEG)-methacrylate polymer through the PLL network. The two polymers were penetrated with each other via interpolymer complexation to yield the semi-IPN structures. The PLL hydrogel thus prepared showed dynamic swelling/de-swelling behavior in response to pH change, and such a behavior was influenced by both the concentrations of PLL and PEG-methacrylate. Drug release from this semi-IPN hydrogel was also investigated using a model protein drug, streptokinase. Streptokinase release was found to be dependent on its ionic interaction with the PLL backbones as well as on the swelling of the semi-IPN hydrogel. These results suggest that a PLL semi-IPN hydrogel could potentially be used as a drug delivery platform to modulate drug release by pH-sensitivity and ionic interaction.

• Polymer(Korea)
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• v.37 no.6
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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.

• Journal of Microbiology and Biotechnology
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• v.29 no.2
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• pp.200-208
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• 2019

Probiotics show low cell viability after oral administration because they have difficulty surviving in the stomach due to low pH and enzymes. For the oral delivery of probiotics, developing a formula that protects the probiotic bacteria from gastric acidity while providing living cells is mandatory. In this study, we developed tablets using a new pH-sensitive phthalyl inulin (PI) to protect probiotics from gastric conditions and investigated the effects of different compression forces on cell survival. We made three different tablets under different compression forces and measured survivability, disintegration time, and kinetics in simulated gastric-intestinal fluid. During tableting, there were no significant differences in probiotic viability among the different compression forces although disintegration time was affected by the compression force. A higher compression force resulted in higher viability in simulated gastric fluid. The swelling degree of the PI tablets in simulated intestinal fluid was higher than that of the tablets in simulated gastric fluid due to the pH sensitivity of the PI. The probiotic viability formulated in the tablets was also higher in acidic gastric conditions than that for probiotics in solution. Rapid release of the probiotics from the tablet occurred in the simulated intestinal fluid due to the pH sensitivity. After 6 months of refrigeration, the viability of the PI probiotics was kept. Overall, this is the first study to show the pH-sensitive properties of PI and one that may be useful for oral delivery of the probiotics.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.223-226
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• 1995

Polymers have been developed and applied in many biomedical areas as well as engineering and industrial fields. The first essential to achieve successful development and applications is that properties of such polymer materials would be investigated. In many cases, such investigations are accomplished by observing polymeric behavior arising from the environmental changes such as pH, temperature, and ionic concentration. It has long been known that NMR is extremely sensitive to many biochemical and physical changes occurring in the polymer samples. In the present study we focus our study on NMR Microimaging, which is one of the important NMR applications, to characterize the swelling effect by observing the time dependent spatial variations of polymer specimens. For the samples three kinds of polyvinyl alcohol (PVA) specimens are prepared with different degrees of cross linking density. $^1H$ NMR microimages are acquired as a function of time to visualize the swelling behavior as well as volumetric changes occurring in the specimens. From the acquired time dependent images, the swelling process is exploited.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.762-765
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• 2003

에틸렌글리콜(ethyleneglycol)을 이용한 폴리비닐에테르(polyvinyl ether)와 같은 고분자물질을 활용하여 Co$^{30}$ 방사선원으로부터 ${\gamma}$선을 조사시켜, 고분자 물질의 성질을 변화시킴으로써 화학, 전기전자, 환경 및 기타 여러 가지 응용분야에 적용하여 이용할 수 있는 기술을 개발하였다. 이를 바탕으로 관련재료의 단량체(monomer)로부터 중합체(polymer)를 합성하여 water swelling을 시키는 과정에서 각종 (금속) 이온을 흡입-제거하는 방법의 환경복원기술, 흡입 금속이온을 표면에 밀집시켜 금속막을 형성하는 응용기술, 생체조직의 대용물질로 활용하는 의용공학 및 열감지특성(thermal sensitive property) 또는 pH 감지특성(pH sensitive property)을 이용하여 의용기술에 적용하는 polymer 응용기술 등의 폭넓은 활용을 위하여 그 일환으로 전도성 고분자 제조기술로의 활용가능성을 연구하였다.

• Macromolecular Research
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• v.17 no.12
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• pp.1025-1031
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• 2009

Several kinds of biodegradable hydrogels were prepared via in situ photopolymerization of Pluronic F127/poly($\varepsilon$-caprolactone) macromer and acrylic acid (AA) comonomer in aqueous medium. The swelling kinetics measurements showed that the resultant hydrogels exhibited both thermo- and pH-sensitive behaviors, and that this stimuli-responsiveness underwent a fast reversible process. With increasing pH of the local buffer solutions, the pH sensitivity of the hydrogels was increased, while the temperature sensitivity was decreased. In vitro hydrolytic degradation in the buffer solution (pH 7.4, $37^{\circ}C$), the degradation rate of the hydrogels was greatly improved due to the introduction of the AA comonomer. The in vitro release profiles of bovine serum albumin (BSA) in-situ embedded into the hydrogels were also investigated: the release mechanism of BSA based on the Peppas equation was followed Case II diffusion. Such biodegradable dual-sensitive hydrogel materials may have more advantages as a potentially interesting platform for smart drug delivery carriers and tissue engineering scaffolds.

• 한국생물공학회:학술대회논문집
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• 2000.04a
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• pp.562-565
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• 2000

pH- and thermo-sensitive hydrogels containing maleilated chitosan(MC) and N-isopropylacrylamide(NIPAAm) were prepared and characterized for their swelling behavior, biodegradability and drug release profiles. The hydrogels exhibited a typical pH-sensitivity due to the carboxylic acid groups of maleilated chitosan. The change of ratio of NIPAAm to MC in weight did not affect on either lower critical solution temperature(LCST) or EWC significantly. The pH sensitivity of the hydrogel, however, depended on the amounts of carboxylic acid groups of MC. MC was degradable up to 80% weight reduction in 2 hours. The in vitro drug relase profiles were established both in buffer solution pH 1.4 and pH 7.4. Only a negligible amount of indomethacin was released at pH 1.4 in 6 hours, while at pH 7.4 more than 90% of the total drug in the hydrogel was gradually released over ca. 5 hours.

• Macromolecular Research
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• v.17 no.9
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• pp.709-713
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• 2009

The aim of this study was to develop novel intestinal specific drug delivery systems with pH sensitive swelling and drug release properties. The carboxyl group of ibuprofen was converted to a vinyl ester group by reacting ibuprofen and vinyl acetate as an acylating agent in the presence of catalyst. The glucose-6-acrylate-1, 2, 3, 4-tetraacetate (GATA) monomer was prepared under mild conditions. Cubane-1, 4-dicarboxylic acid (CDA) linked to two 2-hydroxyethyl methacrylate (HEMA) group was used as the crosslinking agent (CA). Methacrylic-type polymeric prodrugs were synthesized by the free radical copolymerization of methacrylic acid, vinyl ester derivative of ibuprofen (VIP) and GATA in the presence of cubane cross linking agent. The structure of VIP was characterized and confirmed by FTIR, $^1H$ NMR and $^{13}C$ NMR spectroscopy. The composition of the cross-linked three-dimensional polymers was determined by FTIR spectroscopy. The hydrolysis of drug polymer conjugates was carried out in cel-lophane membrane dialysis bags, and the in vitro release profiles were established separately in enzyme-free simulated gastric and intestinal fluids (SGF, pH 1 and SIF, pH 7.4). The detection of a hydrolysis solution by UV spectroscopy at selected intervals showed that the drug can be released by hydrolysis of the ester bond between the drug and polymer backbone at a low rate. Drug release studies showed that increasing the MAA content in the copolymer enhances the rate of hydrolysis in SIP. These results suggest that these polymeric prodrugs can be useful for the release of ibuprofen in controlled release systems.

• Korean Membrane Journal
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• v.6 no.1
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• pp.24-29
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• 2004

Poly(vinyl alcohol)(PVA) and hyaluronic acid(HA) hydrogel membranes were prepared with varying HA contents from 10 to 50 wt% of PVA. The water contents of the resulting PVA-HA hydrogel membranes in various pH conditions were measured. And the permeation coefficient of indomethacin was determined using several PVA-HA hydrogel membranes at various pH conditions and also 37$^{\circ}C$.