Reversible Swelling Behavior Research Articles

Synthesis of Starch-g-poly (acrylic Acid-co-2-hydroxy Ethyl Methacrylate) as Potential pH-sensitive Hydrogel-based Drug Delivery System

The present work focused on the design of drug delivery system (DDS) based on a pH-sensitive hydrogel. The hydrogels were prepared via graft copolymerization of mixtures of acrylic acid (AA) and 2-hydroxy ethyl methacrylate (HEMA) onto starch backbones by a free radical polymerization technique. Sodium bicarbonate (NaHCO3) was added to function as a foaming agent under acidic conditions, rendering the hydrogels to be porous. Porous structure of hydrogel was essential in this system to yield a large surface area so that 5-fluorouracil (5-FU) release could be facilitated. The hydrogel thus prepared possessed a porous structure as determined by scanning electron microscopy. Due to the reversible swelling behavior of the hydrogels, the synthesized networks can sense the environmental pH change and achieve an oscillatory release pattern. Using drug 5-FU as a model molecule, the in vitro controlled drugrelease behaviors of these hydrogels were investigated. The results indicate that the main parameter affecting the drug-release behavior of hydrogels is the pH of the solution. The release rate of 5-FU from hydrogel at pH 7.4 was faster than that at pH 1.2 due to the shrinkage of the hydrogel at pH 1.2.These results suggest that a porous hydrogel could potentially be a useful local delivery system to release drugs primarily at a specific site of body.

Synthesis of starch-g-poly (acrylic acid-co-2-hydroxy ethyl methacrylate) as potential pH-sensitive hydrogelbased drug delivery system

The present work focused on the design of drug delivery system (DDS) based on a pH-sensitive hydrogel. The hydrogels were prepared via graft copolymerization of mixtures of acrylic acid (AA) and 2-hydroxy ethyl methacrylate (HEMA) onto starch backbones by a free radical polymerization technique. Sodium bicarbonate (NaHCO3) was added to function as a foaming agent under acidic conditions, rendering the hydrogels to be porous. Porous structure of hydrogel was essential in this system to yield a large surface area so that 5-fluorouracil (5-FU) release could be facilitated. The hydrogel thus prepared possessed a porous structure as determined by scanning electron microscopy. Due to the reversible swelling behavior of the hydrogels, the synthesized networks can sense the environmental pH change and achieve an oscillatory release pattern. Using drug 5-FU as a model molecule, the in vitro controlled drugrelease behaviors of these hydrogels were investigated. The results indicate that the main parameter affecting the drug-release behavior of hydrogels is the pH of the solution. The release rate of 5-FU from hydrogel at pH 7.4 was faster than that at pH 1.2 due to the shrinkage of the hydrogel at pH 1.2.These results suggest that a porous hydrogel could potentially be a useful local delivery system to release drugs primarily at a specific site of body.

A novel reversible thermo-swelling hydrogel

A novel reversible thermo-swelling gel was prepared from poly(vinyl alcohol)-trimellitate (PVA-T) by crosslinking with ethylene glycol diglycidyl ether (EGDGE). Only in the presence of sulfate anion, this polymer gel showed a significant and reversible swelling behavior with increasing the temperature from 5 to 40°C, and vice versa, prob- ably due to the scission and formation of the inter- and/or intramolecular hydrogen-bondings (HBs) between the carboxyls on the side groups. The involvement of inter- and/or intramolecular HBs for the thermo-swelling behavior was also sug- gested by a significant dependence on HCl concentration of the swelling degree. In addition, the swelling reversibility and reproducibility were confirmed via the temperature jump between 5 and 40°C, well satisfying for a candidate as a thermo- sensitive material.

Preparation and characterization of poly(acrylic acid)/pillared clay superabsorbent composite

Pillared clay-based superabsorbents (PILC-SA) were synthesized by using Al pillared-montmorillonite K10 and KSF via graft copolymerization reaction of acrylic acid (AA). Swelling behavior of pillared clay-based superabsorbent films in distilled water and at different pH values were investigated at room temperature. It was also obtained that Al-KSF and Al-K10 based superabsorbents were pH dependent and showed a reversible swelling behavior. Water absorbency of Al-KSF based superabsorbent was higher than that of Al-K10 based one. SEM, FTIR, and XRD analysis were conducted for further characterization of the PILC-SA. FTIR analyses lead to ester formation between PILC and SA. XRD revealed the basal spacing of the pillared clays before and after in situ incorporation indicating that the morphology of the superabsorbent was exfoliated and the layers of clay dispersed on the composite.

Fabrication and characterization of hyaluronic-acid-based antigen sensitive degradable hydrogel

Biomolecule sensitive hydrogel, as an important part of intelligent materials, has extensive applications in the biochemical and biomedical fields. In this paper, an antigen sensitive degradable hydrogel based on hyaluronic acid (HA) has been prepared. Antigen and antibody were covalently attached to the hydrogel simultaneous, while HA was cross-linked used adipic dihydrazide (ADH) as cross-linking agent primarily. We describe the synthesis, characteristics, and the antigen sensitive behavior of the hydrogel. The hydrogel can exhibit a reversible swelling behavior while the native antigen is present or not. This property of the antigen sensitive hydrogel may be applied as novel drug delivery system, which can release drug by the presence of native antigen.

Preparation and swelling behavior of physically crosslinked hydrogels composed of poly(vinyl alcohol) and chitosan

The physically crosslinked poly(vinyl alcohol)/chitosan (CS) composite hydrogels were prepared by cyclic freezing/thawing techniques, and the microstructure and swelling behavior of the hydrogels in the simulated gastric (pH 1.0) and intestinal (pH 7.4) media were investigated. The experimental results of infrared spectra (IR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC) demonstrated that poly(vinyl alcohol) and chitosan had good miscibility in the composite hydrogels, and the addition of chitosan perturbed the formation of poly(vinyl alcohol) crystallites. The swelling kinetics results indicated that the composite hydrogels had good pH sensitive properties to the acidic environments, and with the increase of chitosan content in the blend, the maximum swelling degreed and the swelling rate both increased, but it led to more dissolution at pH 1.0. And the composite hydrogels also exhibited good reversible swelling behavior with pH value of the swelling medium altering between 1.0 and 7.4. In addition, the higher freezing/thawing cycle times resulted in the lower swelling rate. Therefore, the swelling behavior of the composite hydrogels could be adjusted by changing the chitosan contents and the freezing/thawing cycle times.

Synthesis of pH dependent chitosan‐EPI hydrogel films and their application for in vitro release of promethazine hydrochloride

AbstractChitosan‐epichlorohydrin hydrogel films (ChitEPI) were synthesized by using chitosan in the presence of epichlorohydrin (EPI) as a crosslinking agent at various amounts. SEM, FTIR, TGA, and DSC analysis were conducted for the characterization of the hydrogels. The DSC measurements indicate that ChitEPI hydrogels did not exhibit better thermal stability when compared to chitosan. Swelling behavior of Chitosan‐EPI hydrogel film is pH dependent and showed a reversible swelling behavior with a fast response. The hydrogels were used for in vitro release of promethazine hydrochloride (PHCl) in pH = 1.2 and pH = 7.4 phosphate buffer solutions (PBS). The release of PHCl synthesized from hydrogels at pH = 7.4 is quite low while at pH = 1.2, the highest value was observed as 49% for ChitEPI600. It has been also found that PHCl release from ChitEPI thin films is mainly controlled by diffusion control mechanism. ChitEPI hydrogels may be used for the delivery of drug in stomach and gastrointestinal tract. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and Characterization of a pH‐ and Ionic Strength‐Responsive Hydrogel

Novel polyelectrolyte hydrogels based on methacrylic acid (MAA) and acrylonitrile (AN) monomers were prepared in the presence of a cross‐linker, N,N‐methylenebisacrylamide. The effect of pH and ionic strength of buffer solutions on swelling behavior of the hydrogels was examined. In particular, a reversible swelling behavior at pH 1.4 and 7.4 solutions was investigated. The structure and morphologies of the sensitive hydrogels were characterized by a Fourier transformation infrared spectroscopy (FTIR) and a scanning electron microscope (SEM). A differential scanning calorimeter (DSC) was used to analyze the state of water and to quantitively determine the amount of free water, non‐freezing bound water, and so on. The results indicated that the hydrogels were strikingly sensitive to pH value and ionic strength of buffer solutions. The swelling ratios of gels increased with the increase in pH values, but decreased with ionic strength increased. The gels presented reversible phase transition characteristics with the change in environmental pH. It is concerned with the formation and dissociation of the carboxyl groups and is expected to be adopted as an excellent material in oral drug controlled release.

Preparation and characterization of poly(acrylic acid)‐iron rich smectite superabsorbent composites

AbstractA novel poly(acrylic acid)‐iron rich smectite (IRS) superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) in the presence of N,N‐methylenebisacrylamide (MBA) as a crosslinker. IRS was used to strengthen the hydrogel products in the polymerization process. Water absorbencies for these superabsorbent composites in water and saline solutions were investigated. IRS caused a reduced equilibrium swelling as low as 8–26%. However, grafted IRS particles resulted in improved gel strength as high as 66% compared to the IRS‐free sample. IRS modified superabsorbent hydrogel composites exhibited higher thermal stability compared to the IRS‐free sample. The pH dependent reversible swelling behavior of hydrogels was also investigated. It is found that the swelling process is pH dependent and reversible for synthesized superabsorbent. Superabsorbent hydrogel composites were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR spectroscopy was confirmed grafting of acrylic chains onto the surface of IRS particles. From the standpoint of these results, these strengthened and thermostabilized hydrogels may be considered as good candidates for a controlled release study and agricultural applications. Copyright © 2007 John Wiley & Sons, Ltd.

Preparation and Properties of Novel Biodegradable Hydrogel based on Cationic Polyaspartamide Derivative

Novel copolymers consisting of poly(2-hydroxyethyl aspartamide-co-N,N'-dimethyl-1,3-propane aspartamide) (PHEA-DPA) were prepared from polysuccinimide (PSI), which is the thermal polycondensation product of aspartic acid, via a ring-opening reaction with N,N'-dimethyl-1,3-propane diamine (DPA) and ethanolamine. The prepared water-soluble copolymer was then crosslinked by reacting it with hexamethylene diisocyanate to provide the corresponding gel. The swelling behavior and morphology of the crosslinked hydrogels were investigated. The degree of swelling decreased with increasing crosslinking reagent due to the higher crosslinking density. It was also confirmed that the swelling property is affected by pH. At low pH (< pH 4), swelling is increased due to the ionization of DPA with a tertiary amine moiety. In addition, a reversible swelling and de-swelling behavior was demonstrated by adjusting the pH of the solution. The prepared hydrogels showed a well-interconnected microporous structure with regular 5-20 <TEX>$\mu$</TEX>m sized pores.

Swelling Behavior of Hyaluronic Acid/Polyallylamine Hydrochloride Multilayer Films

The reversible swelling behavior of multilayer films containing hyaluronic acid and polyallylamine hydrochloride was investigated using in situ ellipsometry, since many of the natural functions and applied uses of hyaluronic acid are related to the extraordinary ability of this biopolymer to swell, and to respond conformationally to the local solution environment. This swelling was observed to be substantial, and depended strongly on the film thickness, the pH conditions used to prepare the films, and the swelling solution pH and ionic strength. The swelling results were also rationalized in terms of the dissociation behavior of the polyelectrolytes in the multilayer assemblies, measured by the zeta potential, on colloidal particles. The films were found to swell by as much as 8 times their dry thickness, and the extent of film hydration was observed to depend on the thickness of the films in a nonlinear fashion. This was related to the internal structure of the films, which is dictated by the assembly pH conditions. In addition, the swelling solution pH and ionic strength influence the electrostatic environment in the films and, in turn, have a substantial effect on the overall swelling behavior.

Thermodynamic considerations of microgel swelling behavior.

A simple but novel thermodynamic model is presented, based upon van't Hoff analysis, for the reversible swelling behavior of colloidal microgels. The swelling, as a function of temperature, of poly(N-isopropylacrylamide/N,N'-methylenebisacrylamide) as well as poly(N-isopropylacrylamide/vinylpyridine/N,N'-methylenebisacrylamide) and poly(N-isopropylacrylamide/acrylic acid/N,N'-methylenebisacrylamide) microgel dispersions in H2O and D2O has been studied by photon correlation spectroscopy (PCS). PCS data was used to obtain the hydrodynamic diameter and hence the volume of the microgels (before and after reconstitution following freeze-drying) as a function of temperature. The choice of standard reference states, for analyzing the data attained, is discussed, and the one selected is that of the volume of the microgels at 333 K in H2O. For all microgels examined the volume, at this temperature, is shown to be independent of solvent (H2O, D2O). The derived data has allowed the exploration of a novel thermodynamic approach to the study of the swelling behavior of the microgels. The constant volume, at 333 K, for each of the polymer systems constituting the microgels is suggested to be an intrinsic property of the polymers themselves.

Design of a novel hydrogel-based intelligent system for controlled drug release

The present work focused on the design of an assembled drug delivery system (DDS) to provide multifunctions, such as drug protection, self-regulated oscillatory release, and targeted uni-directional delivery by a bilayered self-folding gate and simple surface mucoadhesion. In this device, a pH-sensitive hydrogel together with a poly(hydroxyethyl methacrylate) (HEMA) barrier was used as a gate to control drug release. In addition, poly(HEMA) coated with poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO–PPO–PEO) surfactant was utilized to enhance mucoadhesion on the device surface. The release profiles of two model drugs, acid orange 8 (AO8) and bovine serum albumin (BSA) were studied in this assembled system, which compared with the conventional drug-entrapped carriers and enteric-coating systems. Furthermore, targeted uni-directional release was demonstrated in a side-by-side diffusion cell. In conclusion, for such an assembled device, the poly(HEMA) layer not only affects the folding direction but also serves as a barrier to protect the model drugs. The release time can be controlled by the thickness of the bilayered gate and the drug reservoir. Due to the reversible swelling behavior of poly(methyacrylic acid-g-ethylene glycol) (p(MAA-g-EG)) gels, the bilayered gate can sense the environmental pH change and achieve an oscillatory release pattern. Moreover, the local targeting and uni-directional release have been successfully demonstrated in vitro.

Surface Potential Driven Swelling of Polyelectrolyte Multilayers

The adsorption of polyelectrolytes to charged surfaces can be applied to build up multilayers of polyelectrolytes of alternating charge by layer-by-layer assembly. The hydration of such multilayers adsorbed to colloidal particles in dilute aqueous dispersions is investigated by NMR, namely, water 1H spin relaxation rates R2. For the system of alternating layers of poly(diallyl dimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfate) (PSS) adsorbed to silica particles (PDADMAC/PSS), a linear increase of multilayer thickness and R2 with the number of layers is found, reflecting an increasing amount of hydration water. For the system (PAH)/PSS, involving the weak polyelectrolyte poly(allylamine hydrochloride) (PAH), it is found that while adsorption of a positive layer leads to an increase of R2, a decrease of R2 is observed after the adsorption of a negative layer. This reveals an increase of the net water mobility involving dehydration. Evidence is given that the reversible swelling behavior ...

Formation, Structure, and Temperature Behavior of Polyelectrolyte Complexes between Ionically Modified Thermosensitive Polymers

Thermosensitive polymers such as poly(N-isopropylacrylamide) (PNIPAM) have a lower critical solution temperature in water in a temperature range between 32 and 35 °C. Micro- and macrogels of such polymers show a temperature-controlled reversible swelling behavior. Therefore, they are of great interest for a variety of applications (e.g., the controlled drug delivery and accessibility of enzymes). Up to now such gels were prepared by covalent cross-linking. A new and promising route for the preparation of microgels down to the nanometer scale consists of the formation of polyelectrolyte complex particles between ionically modified thermosensitive polymers. The formation, structure, and temperature behavior of complexes between PNIPAM with differing contents of anionic and cationic groups was studied by viscometry and static and dynamic light scattering. The level of aggregation of such complexes increases with increasing mixing ratio, while the polymer concentration has only a marginal effect. The complexe...