Preparation and characterization of pH‐ and temperature‐responsive semi–interpenetrating polymer network hydrogels based on linear sodium alginate and crosslinked poly(N‐isopropylacrylamide)

In this study, pH‐ and temperature‐responsive hydrogels based on linear sodium alginate (SA) and crosslinked poly(N‐isopropylacrylamide) (PNIPAAm) were prepared by semi‐interpenetrating network (semi‐IPN) technique. The dually responsive hydrogels were characterized by FTIR, DSC, and SEM, and their temperature‐ and pH‐responsive behaviors were investigated by measuring equilibrium swelling ratios and pulsatile swelling experiments. The results showed that these hydrogels underwent volume phase transition at around 33°C irrespective of the pH value of the medium, but their pH sensitivity was evident only below their volume phase transition temperature. Under basic conditions, the swelling ratios of SA/PNIPAAm semi‐IPN hydrogels were greater than that of pure PNIPAAm hydrogel and increased with increasing SA content incorporated into the hydrogels, but the case was inverse under acidic conditions. The pulsatile swelling experiments indicated that the higher the SA content in SA/PNIPAAm semi‐IPN hydrogels, the faster the response rate to both pH and temperature change. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1931–1940, 2005     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006     

Synthesis and characteristics of semi‐interpenetrating polymer network hydrogels based on chitosan and poly(hydroxy ethyl methacrylate)

Semi‐interpenetrating polymer networks (semi‐IPNs), composed of chitosan and poly(hydroxy ethyl methacrylate) hydrogels, were prepared and the effects of various pH, temperatures, and an electric‐field on the swollen hydrogels were investigated. The swelling kinetics increased rapidly, reaching equilibrium within 60 min. Semi‐IPN hydrogels exhibited relatively high swelling ratios, 150～350%. The swelling ratio increased when the pH of the buffer was below pH 7 as a result of the dissociation of ionic bonds. Semi‐IPN hydrogels showed electroresponsiveness by shrinking when an electric field was applied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 86–92, 2005     

Preparation and characterization of thermosensitive poly(N‐isopropylacrylamide)/poly(ethylene oxide) semi‐interpenetrating polymer networks

Temperature‐sensitive poly(N‐isopropylacrylamide) hydrogels were successfully synthesized by using poly(ethylene oxide) as the interpenetrating agent. The newly prepared semi‐interpenetrating polymer network (semi‐IPN) hydrogels exhibited much better properties as temperature‐sensitive polymers than they did in the past. Characterizations of the IPN hydrogels were investigated using a swelling experiment, FTIR spectroscopy, and differential scanning calorimetry (DSC). Semi‐IPN hydrogels exhibited a relatively high temperature dependent swelling ratio in the range of 23–28 at room temperature. DSC was used for the determination of the lower critical solution temperature of the semi‐IPN hydrogel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3032–3036, 2003     

Synthesis and properties of the semi‐interpenetrating polymer network–like,thermosensitive poly(N‐isopropylacrylamide) hydrogel

A new strategy was used to prepare a semi‐interpenetrating polymer network (semi‐IPN)–like poly(N‐isopropylacrylamide) (PNIPAAm) polymeric hydrogel, consisting of either low (2300) or high (33,000) molecular weight linear PNIPAAm chains and the crosslinked PNIPAAm network. The properties of the resulting PNIPAAm hydrogels were characterized by DSC and SEM as well as their swelling ratios at various temperatures, the deswelling in hot water (48°C), and the oscillating shrinking–swelling properties within small temperature cycles. It was found that the deswelling rate of these semi‐IPN–like PNIPAAm hydrogels was improved if the molecular weight and/or composition of the linear PNIPAAm chains within the semi‐IPN–like PNIPAAm hydrogels were increased. This improved deswelling rate was attributed to the fast response nature of the linear PNIPAAm chains and the increased pore number in the matrix network, which provided numerous water channels for the water to diffuse out during the deswelling process at a temperature above the lower critical solution temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1935–1941, 2003     

Preparation of hydrogels composed of poly(vinyl alcohol) and polyethyleneimine and their electrical response

Semi‐ and full‐interpenetrating polymer network (IPN) hydrogels composed of poly(vinyl alcohol) and polyethyleneimine (PEI) were prepared to investigate the bending behavior under the electric response. To find out the characteristics of the hydrogel in the medium, swelling ratio, and rate and water state of the hydrogels were measured. The swelling ratio of the semi‐IPN hydrogels increased with PEI content in the matrix, whereas that of full‐IPN hydrogels dramatically decrease with increase of PEI contents in the hydrogels. In the water state of hydrogel, the bound water and free water of semi‐IPN hydrogels increased with PEI weight ratio. The full‐IPN hydrogels show the lower free water content in comparison with the semi‐IPN hydrogel. The IPN hydrogels exhibited bending angle change in response to external stimulus such as voltage, the bending angle increased with PEI concentration. In addition, the repeated bending behaviors according to the magnitude of the applied electric field revealed that the bending angle is reversible without collapse of formation of hydrogel in all samples. Thus, the hydrogels will be useful as novel modulation systems in the field of artificial organ and matrix for drug delivery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characteristics of an amphoteric semi‐IPN hydrogel composed of acrylic acid and poly(diallydimethylammonium chloride)

Semi‐interpenetrating polymer network (IPN) hydrogels, with acrylic acid (AA) and poly(diallydimethylammonium chloride) (PDMDAAC), were constructed by a sequential IPN method. The characterizations of the IPN hydrogels were investigated by FTIR, DTA, and swelling tests under various conditions. The prepared semi‐IPN hydrogels exhibited relatively high swelling capacity, in the range of 477–630 g/g at 25°C. The results show that the swelling capacity of AA/PDMDAAC semi‐IPN hydrogels was pH and temperature dependent. Swelling behaviors were also studied in the different salt solutions. Swelling kinetic parameters are given. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 345–350, 2007     

Development and characterization of thermosensitive hydrogels based on poly(N‐isopropylacrylamide) and calcium alginate

This work refers to the synthesis and characterization of thermosensitive hydrogels based on interpenetrating polymer networks (IPNs) of poly(N‐isopropylacrylamide) (PNIPAAm) and calcium alginate in the form of films. The influence of the crosslinking degree of PNIPAAm and alginate content on thermal, swelling, mechanical, and morphological properties of hydrogels is investigated in detail. Characterization of pure PNIPAAm hydrogels and IPN hydrogels was performed by FTIR, DSC, DMA, and SEM. In addition, the studies of equilibrium swelling behavior as well as swelling, deswelling, and reswelling kinetics are performed. The results obtained imply the benefits of synthesizing IPNs based on PNIPAAm and calcium alginate over pure PNIPAAm hydrogels. The presence of calcium alginate contributes to the improvement of mechanical properties, the deswelling rate of hydrogels, and the network porosity, without altering the thermosensitivity of PNIPAAm significantly. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Preparation and Swelling Properties of Temperature‐Sensitive Semi‐Interpenetrating Polymer Networks Composed of Poly[(N‐tert‐butylacrylamide)‐co‐acrylamide] and Hydroxypropyl Cellulose

Summary: Temperature‐responsive hydrogels based on linear HPC and crosslinked P(NTBA‐co‐AAm) were prepared by the semi‐IPN technique. The structure of these semi‐IPN hydrogels was investigated by FT‐IR spectroscopy. An increase in normalized band ratios (A₂₉₈₀/A₁₆₆₅) was observed with increasing HPC content in the initial mixture. The swelling kinetics and water transport mechanism of these semi‐IPN hydrogels were examined and their temperature responsive behaviors were also investigated by measuring equilibrium swelling ratios and pulsatile swelling experiments. The results showed that these semi‐IPN hydrogels underwent a volume phase transition between 18 and 22 °C irrespective of the amounts of MBAAm and HPC. However, below the volume phase transition temperature, their equilibrium swelling ratios were affected by the amount of MBAAm and HPC. The pulsatile swelling experiments indicated that the lower the MBAAm and the higher HPC contents in semi‐IPN hydrogels the faster the response rate temperature change.

Equilibrium swelling ratios of the semi‐IPN P(NTBA‐co‐AAm)/HPC hydrogels in water shown as a function of temperature.     

Swelling characterizations of chitosan and polyacrylonitrile semi‐interpenetrating polymer network hydrogels

Temperature‐ and pH‐responsive semi‐interpenetrating polymer network (semi‐IPN) hydrogels constructed with chitosan and polyacrylonitrile (PAN) were studied. The characterizations of semi‐IPN hydrogels were investigated using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). IPN hydrogels exhibited a relatively high swelling ratio, 23.31%–145.20% at room temperature. The swelling ratio of hydrogels depends on pH and temperature. DSC was used to determine the amount of free water in IPN hydrogels. The amount of free water increased with increasing chitosan content in the semi‐IPN hydrogels. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2011–2015, 2003     

Temperature sensitive semi‐IPN microspheres from sodium alginate and N‐isopropylacrylamide for controlled release of 5‐fluorouracil

Semi‐interpenetrating network (IPN) of sodium alginate (NaAlg) and N‐isopropylacrylamide (NIPAAm) microspheres were prepared by water‐in‐oil (w/o) emulsification method. The microspheres were encapsulated with 5‐fluorouracil (5‐FU) and release patterns carried in 7.4 pH at temperatures of 25 and 37°C. The semi‐IPN microspheres were characterized by Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) and scanning electron microscopic studies were done on the drug‐loaded microspheres to confirm the polymorphism of 5‐FU and surface morphology of microspheres. These results indicated the molecular level dispersion of 5‐FU in the semi‐IPN microspheres. Particle size and size distribution were studied by laser light diffraction technique. Microspheres exhibited release of 5‐FU up to 12 h. The swelling studies were carried in 1.2 and 7.4 pH buffer media at 25 and 37°C. Drug release from NaAlg‐NIPAAm semi‐IPN microspheres at 25 and 37°C confirmed the thermosensitive nature by in vitro dissolution. The micro domains have released in a controlled manner due the presence of NIPAAm in the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of hydrogels based on chitosan and copolymer of poly(dimethylsiloxane) and poly(vinyl alcohol)

Copolymers composed of poly(vinyl alcohol) (PVA) and poly(dimethylsiloxane) (PDMS) were crosslinked with chitosan to prepare semi‐interpenetrating polymer network (IPN) hydrogels by an ultraviolet (UV) irradiation method for application as potential biomedical materials. PVA/PDMS copolymer and chitosan was cast to prepare hydrogel films, followed by a subsequent crosslinking with 2,2‐dimethoxy‐2‐phenylacetophenone as a nontoxic photoinitiator by UV irradiation. Various semi‐interpenetrating polymer networks (semi‐IPNs) were prepared from different weight ratios of chitosan and the copolymer of PVA/PDMS. Photocrosslinked hydrogels exhibited an equilibrium water content (EWC) in the range of 65–95%. Swelling behaviors of these hydrogels were studied by immersion of the gels in various buffer solutions. Particularly, the PCN13 as the highest chitosan weight ratio in semi‐IPN hydrogels showed the highest EWC in time‐dependent and pH‐dependent swelling. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2591–2596, 2002     

The swelling behaviors and network parameters of cationic starch‐g‐acrylic acid/poly(dimethyldiallylammonium chloride) semi‐interpenetrating polymer networks hydrogels

Amphiphilic semi‐interpenetrating polymer networks (semi‐IPN) hydrogels were prepared by a sequential‐IPN method by acrylic acid graft copolymerization into cationic starch in mild aqueous media of poly(dimethyldiallylammonium chloride). Some main factors were investigated to evaluate the swelling of hydrogels, and the network parameters M_c were given accordingly to elaborate the interaction between polymers. The chemical structure of the resulting hydrogel was confirmed using Fourier transform infrared spectroscopy. The cationic starch‐based semi‐IPN hydrogels achieved a high swelling capacity of 1070 g/g in deionized water and 94 g/g in 0.9 wt % NaCl solution, respectively) and high compressive stress in a high water content. Besides, a different pH‐dependent behavior was found for this semi‐IPN hydrogel. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of full and semi Interpenetrating hydrogel from polyvinyl alcohol and poly (acrylic acid‐co‐hydroxyethylmethacrylate) copolymer: Study of swelling behavior,network parameters,and dye uptake properties

Semi and full interpenetrating network (IPN) hydrogels were synthesized by allowing free radical copolymerization of acrylic acid (AA) and hydroxyethyl methacrylate (HEMA) in the matrix of polyvinyl alcohol (PVOH). Accordingly, four different semi IPN hydrogels were prepared with PVOH: copolymer mass ratio of 1 : 1, 1 : 0.75, 1 : 0.5, and 1 : 0.25. These hydrogels were designated as SEMIIPN1, SEMIIPN2, SEMIIPN3, and SEMIIPN4, respectively. In all of these SEMIIPN, after polymerization PVOH was crosslinked with 2 mass % glutaraldehyde to form the semi IPN structure. In a similar way, sequential full IPN were prepared from PVOH and copolymer of AA and HEMA (designated as PAAHEMA) with same composition except in this case apart from crosslinking of PVOH by 2 mass % glutaraldehyde the PAAHEMA copolymer was further crosslinked with N,N′‐methylenebisacrylamide (NMBA) to produce four full IPN hydrogels designated as FULLIPN1, FULLIPN2, FULLIPN3, and FULLIPN4. All of these semi and full IPN type hydrogels were characterized by carboxylic %, FTIR, UV, DTA‐TGA, XRD, SEM, and mechanical properties. The network parameters, swelling and diffusion characteristics of these hydrogels were also studied. The performance of these semi and full IPNs were compared in terms of their relative abilities for removing varied concentration of rhodamine B (RB) and methyl Violet (MV) dyes from water. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical behavior of chitosan and poly(hydroxyethyl methacrylate) hydrogel in the contact system

Semi‐interpenetrating polymer networks (semi‐IPNs), as polymer hydrogels composed of chitosan and poly(hydroxyethyl methacrylate) (PHEMA), exhibiting electrical‐sensitive behavior, were prepared. The swelling behavior of the chitosan/PHEMA hydrogels was studied by immersing the gels in various concentrations of aqueous NaCl solution. The electrical responses of the semi‐IPN hydrogel, in applied electric fields, were also investigated. When the semi‐IPN hydrogels were swollen, where one electrode was placed in contact with the gel and the other fixed 30 mm apart from one, they exhibited bending behavior on the application of an electric field on a contact system. The electroresponsive behavior of the present semi‐IPN was also affected by the electrolyte concentration of the external solution. The semi‐IPN also showed various degrees of increased bending behavior depending on the electric stimulus. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 915–919, 2004     

Tuning the Mechanical Properties of BIEE‐Crosslinked Semi‐Interpenetrating,Double‐Hydrophilic Hydrogels

Double‐hydrophilic, semi‐interpenetrating (semi‐IPN) hydrogels are synthesized by encapsulating hydrophilic polyvinylpyrrolidone (PVP) linear chains in structure‐defined 1,2‐bis‐(2‐iodoethoxy)ethane (BIEE)‐crosslinked (poly(2‐(dimethylamino)ethyl methacrylate) (pDMAEMA) hydrogels. A series of semi‐IPN double‐hydrophilic hydrogels are prepared in which the pDMAEMA/BIEE content is kept the same and only the PVP content is varied, from 0 up to 33 wt%. The mechanical properties of the water‐swollen hydrogels are experimentally evaluated under unconfined compressive loading conditions, while a nonlinear hyperelastic constitutive equation is used to predict their mechanical response. No significant difference is found in the mechanical response of the semi‐IPN PVP/pDMAEMA/BIEE hydrogel containing 5 wt% PVP compared to the pDMAEMA/BIEE analog, however, for greater loading percentages (15 and 33 wt% of PVP), the semi‐IPN hydrogels exhibit less stiffness/higher ductility. Furthermore, in vitro biocompatibility studies are carried out for the pDMAEMA/BIEE and the semi‐IPN PVP/pDMAEMA/BIEE, indicating that both the formulations exhibit no toxicity in cultured cells.     

Synthesis and characteristics of interpenetrating polymer network hydrogels composed of alginate and poly(diallydimethylammonium chloride)

Temperature‐ and pH‐responsive interpenetrating polymer network (IPN) hydrogels, with sodium alginate (SA) and poly(diallydimethylammonium chloride) (PDADMAC), constructed by a sequential IPN method, were studied. The characterizations of the IPN hydrogels were investigated by FTIR, DSC, and swelling tests under various conditions. The prepared IPN hydrogels exhibited relatively high swelling ratios, in the range of 380–690%, at 25°C. The swelling ratios of SA/PDADMAC IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the freezing and nonfreezing water contents of the hydrogels. The amount of free water increased with the increasing PDADMAC content of the IPN hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3705–3709, 2004     

Rapid temperature/pH response of porous alginate-g-poly(N-isopropylacrylamide) hydrogels

To improve the swelling and deswelling rate, comb-type macroporous hydrogels were prepared. The temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) was grafted on the surface or bulk of the pH-responsive alginate. The larger surface area in pores and free chain mobility by comb-type graft copolymer reached its equilibrium swollen state within a minute. The swelling ratio of porous hydrogel in equilibrium state was over fifteen times greater than that of nonporous hydrogels. The increase of surface area by pores caused water molecules to transfer easily in and out of the matrix, resulting in a rapid deswelling. The degree of change in swelling ratio during deswelling might be affected by the phase transition behavior of PNIPAAm attached on only the surface of the pore rather than PNIPAAm grafted into mainchain of alginate. Surface-grafted alginate/PNIPAAm gels had a suitable mechanical strength without collapsing during the repeatable shrinkage and expansion due to swelling and deswelling, whereas bulk-grafted gels easily collapsed.     

Carrageenan‐g‐poly(acrylamide)/poly(vinylsulfonic acid,sodium salt) as a novel semi‐IPN hydrogel: Synthesis,characterization, and swelling behavior

A semi‐interpenetrating polymer network (semi‐IPN) hydrogel based on kappa‐carrageenan (κC) and poly (vinylsulfonic acid, sodium salt) (PVSA) was prepared by graft copolymerization of acrylamide (AAm) using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. FTIR spectroscopy was used for confirming the structure of the final product. It was found that the chemical composition of the Semi‐IPN hydrogel is equal to the initial homopolymers and monomer feed compositions. The swelling capacity of the hydrogel was shown to be affected by the MBA, APS, and AAm concentration as well as κC/PVSA weight ratio. The swelling behavior of the hydrogel was also investigated in various pHs and salt solutions. Since the highly swelling biopolymer‐based hydrogel exhibits low salt‐sensitivity, it may be referred to as an anti‐salt superabsorbent hydrogel. The swelling kinetics of the superabsorbent hydrogels was studied as well. POLYM. ENG. SCI., 47:1388–1395, 2007. © 2007 Society of Plastics Engineers