Hydrogel Volume Research Articles

Water-soluble drug partitioning and adsorption in HEMA/MAA hydrogels

Two-photon confocal microscopy and back extraction with UV/Vis-absorption spectrophotometry quantify equilibrium partition coefficients, k, for six prototypical drugs in five soft-contact-lens-material hydrogels over a range of water contents from 40 to 92%. Partition coefficients were obtained for acetazolamide, caffeine, hydrocortisone, Oregon Green 488, sodium fluorescein, and theophylline in 2-hydroxyethyl methacrylate/methacrylic acid (HEMA/MAA, pKa≈5.2) copolymer hydrogels as functions of composition, aqueous pH (2 and 7.4), and salinity. At pH 2, the hydrogels are nonionic, whereas at pH 7.4, hydrogels are anionic due to MAA ionization. Solute adsorption on and nonspecific electrostatic interaction with the polymer matrix are pronounced. To express deviation from ideal partitioning, we define an enhancement or exclusion factor, E ≡ k/ϕ1, where ϕ1 is hydrogel water volume fraction. All solutes exhibit E > 1 in 100 wt % HEMA hydrogels owing to strong specific adsorption to HEMA strands. For all solutes, E significantly decreases upon incorporation of anionic MAA into the hydrogel due to lack of adsorption onto charged MAA moieties. For dianionic sodium fluorescein and Oregon Green 488, and partially ionized monoanionic acetazolamide at pH 7.4, however, the decrease in E is more severe than that for similar-sized nonionic solutes. Conversely, at pH 2, E generally increases with addition of the nonionic MAA copolymer due to strong preferential adsorption to the uncharged carboxylic-acid group of MAA. For all cases, we quantitatively predict enhancement factors for the six drugs using only independently obtained parameters. In dilute solution for solute i, Ei is conveniently expressed as a product of individual enhancement factors for size exclusion (Eiex), electrostatic interaction (Eiel), and specific adsorption (Eiad):Ei≡EiexEielEiad. To obtain the individual enhancement factors, we employ an extended Ogston mesh-size distribution for Eiex; Donnan equilibrium for Eiel; and Henry's law characterizing specific adsorption to the polymer chains for Eiad. Predicted enhancement factors are in excellent agreement with experiment.

How the reduction of O2 on enzymes and/or redox mediators affects the calibration curve of “wired” glucose oxidase and glucose dehydrogenase biosensors

In our first report we showed that dissolved O2 could be reduced on osmium-based redox polymers with formal potential E°′≤+0.07V vs. Ag/AgCl. Here, we study the effect of O2 on the calibration curves of the whole biosensors, i.e. comprising the redox polymer and the enzyme. A combination of electrodes were made with glucose oxidase (GOx) or quinoprotein-glucose dehydrogenase (PQQ-GDH), each with a redox polymer either sensitive or insensitive to O2. These electrodes were studied under aerobic and anaerobic conditions. By combining amperometric and hydrodynamic experiments with loading studies, we found that for GOx-based electrode the effect of O2 was maximal at a low glucose concentration where O2 can be reduced by GOx and the osmium complex in the whole hydrogel volume, while O2 is severely depleted in the outer layers at high glucose concentration. Further, no significant O2 depletion was observed for electrodes modified with PQQ-GDH and O2 sensitive polymer. In this case, the higher impact of O2 at low glucose concentration could be explained by the longer average distance the electrons need to cover across the O2-rich hydrogel to reach the electrode.

Treatment planning after hydrogel injection during radiotherapy of prostate cancer

Imaging for treatment planning shortly after hydrogel injection is optimal for practical purposes, reducing the number of appointments. The aim was to evaluate the actual difference between early and late imaging. Treatment planning computed tomography (CT) was performed shortly after injection of 10ml hydrogel (CT1) and 1-2weeks later (CT2) for 3patients. The hydrogel was injected via the transperineal approach after dissecting the space between the prostate and rectum with a saline/lidocaine solution of at least 20-ml. Hydrogel volume and distances between the prostate and rectal wall were compared. Intensity-modulated radiotherapy (IMRT) plans up to a dose of 78Gy were generated (rectum V70 < 20 %, rectum V50 < 50 %; with the rectum including hydrogel volume for planning). A mean planning treatment volume of 104cm(3) resulted for a prostate volume of 37cm(3). Hydrogel volumes of 30 and 10cm(3) were determined in CT1 and CT2, respectively. Distances between the prostate and rectal wall at the levels of the base, middle, and apex were 1.7cm, 1.6cm, 1.5cm in CT1 and 1.3cm, 1.2cm, 0.8cm in CT2, respectively, corresponding to a mean decrease of 24, 25, and 47 %. A small overlap between the PTV and the rectum was found only in 1patient in CT2 (0.2cm(3)). The resulting mean rectum (without hydrogel) V75, V70, V60, V50 increased from 0 %, 0 %, 0.6 %, 10 % in CT1 to 0.1 %, 1.2 %, 6 %, 20 % in CT2, respectively. Treatment planning based on imaging shortly after hydrogel injection overestimates the actual hydrogel volume during the treatment as a result of not-yet-absorbed saline solution and air bubbles.

Regulation of Stem Cell Fate in a Three‐Dimensional Micropatterned Dual‐Crosslinked Hydrogel System

Micropatterning technology is a powerful tool for controlling the cellular microenvironment and investigating the effects of physical parameters on cell behaviors, such as migration, proliferation, apoptosis, and differentiation. Although there have been significant developments in regulating the spatial and temporal distribution of physical properties in various materials, little is known about the role of the size of micropatterned regions of hydrogels with different crosslinking densities on the response of encapsulated cells. In this study, novel alginate hydrogel system is engineered that can be micropatterned three-dimensionally to create regions that are crosslinked by a single mechanism or dual mechanisms. By manipulating micropattern size while keeping the overall ratio of single- to dual-crosslinked hydrogel volume constant, the physical properties of the micropatterned alginate hydrogels are spatially tunable. When human adipose-derived stem cells (hASCs) are photoencapsulated within micropatterned hydrogels, their proliferation rate is a function of micropattern size. Additionally, micropattern size dictates the extent of osteogenic and chondrogenic differentiation of photoencapsulated hASC. The size of 3D micropatterned physical properties in this new hydrogel system introduces a new design parameter for regulating various cellular behaviors, and this dual-crosslinked hydrogel system provides a new platform for studying proliferation and differentiation of stem cells in a spatially controlled manner for tissue engineering and regenerative medicine applications.

A Closed-Loop Hydrogel-Based Chemical Sensor

State-of-the-art hydrogel-based chemical sensors directly convert the volume change of a hydrogel, induced by an external environmental chemical trigger such as pH, into an electrical or optical output signal. Because hydrogels show relaxation behavior and the network expansion is governed by slow cooperative diffusion, their long-term properties are poor and the sensor parameters, such as response time, are limited. To overcome these drawbacks, we present a closed-loop hydrogel-based pH sensor, which uses the compensation method. The hydrogel sensor itself is part of a feedback circuit comprising a proportional-integral controller and an actuator in the feedback loop. In our approach, the hydrogel volume is kept constant at the steady state during the whole measuring process. This is accomplished by applying an appropriate counter pressure that compensates the swelling pressure of the hydrogel and, thus, its attempt to swell or shrink. This counter pressure is a direct measure of the applied pH-value even though the hydrogel remains under isochoric conditions. Here, the novel closed-loop sensor approach and sensor technology are described, as well as measurement results that confirm the applicability of the compensation method to hydrogel sensors are shown.

Two-dimensional array Debye ring diffraction protein recognition sensing

We attach 2-D colloidal arrays onto the surface of hydrogels containing biotin. The hydrogel volume shrinks with increasing concentrations of avidin due to the formation of avidin-biotin crosslinks. This causes the Debye diffraction ring diameter to increase, and the 2-D diffraction wavelength to blue-shift.

An overlap‐volume‐histogram based method for rectal dose prediction and automated treatment planning in the external beam prostate radiotherapy following hydrogel injection

Hydrogel injected between the rectum and prostate prior to radiotherapy provides a possible means of increased dose sparing to the rectum. Here the authors evaluate the overlap volume histogram (OVH) metric as a means to predict the rectal dose following hydrogel injection. Whether OVH predicted dose can serve as the dose objective or constraint for automated treatment planning was also investigated. Treatment planning was performed on 21 prostate cancer patients both pre- and posthydrogel injection, with five-field IMRT delivering 78 Gy to the planning target volume (PTV). The authors quantify the geometrical relationship between the rectum and the prostate PTV using an OVH metric which determines the fractional volume of the rectum that is within a specified distance of the PTV. For an OVH distance the authors selected, L(20), the PTV expansion distance at which 20% of the rectum overlaps. The authors calculated the rectal dose, D(20), received by 20% of the rectum volume on the dose volume histogram. Linear regression was used to examine the correlation between the L(20) and D(20), and between ΔL(20) and ΔD(20) (i.e., the change of L(20) and D(20) posthydrogel injection). Additionally, rectal dose D(15), D(25), D(35), D(50), and bladder dose D(15) were predicted from the OVH (L(15), L(25), L(35), L(50), for rectum and L(15) for bladder) by the L(x)-D(x) linear regression. The predicted doses were applied to the objectives for automated treatment planning of ten plans from five patients. Automatically generated plans were compared with plans manually generated on trial-and-error basis. The rectal L(20) was increased and dose D(20) decreased due to the enlarged separation of rectum caused by the hydrogel injection. Linear regression showed an inverse linear correlation between L(20) and D(20), and between ΔL(20) and ΔD(20) (r(2) = 0.77, 0.60, respectively; p < 0.0001). The increase in rectal sparing (ΔD(20)) is only weakly correlated with the volume of injected hydrogel (r(2) = 0.17; p = 0.07), indicating OVH is a more predictive indicator of rectal sparing than the volume of hydrogel itself. Application of the predicted rectum and bladder doses to automated planning produced acceptable treatment plans, with rectal dose reduced for eight of ten plans. The OVH metric can predict the rectal dose in the external beam prostate radiotherapy for patients with hydrogel injection. The predicted doses can be applied to the objectives of optimization in automated treatment planning to produce acceptable treatment plans.

Rapid pH-dependent phase transition and elasticity of stimuli-responsive cationic poly(N,N-dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli-responsive hydrogels prepared from poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH-dependent swelling and elasticity, a series of cationic hydrogels based on N,N-dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH-dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH-dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10- to 40-fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry

Biodegradable thermosensitive hydrogel for SAHA and DDP delivery: therapeutic effects on oral squamous cell carcinoma xenografts.

BackgroundOSCC is one of the most common malignancies and numerous clinical agents currently applied in combinative chemotherapy. Here we reported a novel therapeutic strategy, SAHA and DDP-loaded PECE (SAHA-DDP/PECE), can improve the therapeutic effects of intratumorally chemotherapy on OSCC cell xenografts.Objective/PurposeThe objective of this study was to evaluate the therapeutic efficacy of the SAHA-DDP/PECE in situ controlled drug delivery system on OSCC cell xenografts.MethodsA biodegradable and thermosensitive hydrogel was successfully developed to load SAHA and DDP. Tumor-beared mice were intratumorally administered with SAHA-DDP/PECE at 50 mg/kg (SAHA) +2 mg/kg (DDP) in 100 ul PECE hydrogel every two weeks, SAHA-DDP at 50 mg/kg(SAHA) +2 mg/kg(DDP) in NS, 2 mg/kg DDP solution, 50 mg/kg SAHA solution, equal volume of PECE hydrogel, or equal volume of NS on the same schedule, respectively. The antineoplastic actions of SAHA and DDP alone and in combination were evaluated using the determination of tumor volume, immunohistochemistry, western blot, and TUNEL analysis.ResultsThe hydrogel system was a free-flowing sol at 10°C, become gel at body temperature, and could sustain more than 14 days in situ. SAHA-DDP/PECE was subsequently injected into tumor OSCC tumor-beared mice. The results demonstrated that such a strategy as this allows the carrier system to show a sustained release of SAHA and DDP in vivo, and could improved therapeutic effects compared with a simple additive therapeutic effect of SAHA and DDP on mouse model.ConclusionsOur research indicated that the novel SAHA-DDP/PECE system based on biodegradable PECE copolymer enhanced the therapeutic effects and could diminished the side effects of SAHA/DDP. The present work might be of great importance to the further exploration of the potential application of SAHA/DDP-hydrogel controlled drug release system in the treatment of OSCC.

Smart surfaces: reversible switching of a polymeric hydrogel topography

Patterns imprinted on smart surfaces are fabricated by direct laser interference patterning (DLIP) of thick films based on poly(N-isopropylacrylamide) (PNIPAM) doped with suitable dyes. Optical and atomic force (AFM) microscopy images reveal that the pattern imprinted on the dry hydrogel film (line-arrays) becomes flat due to swelling of the hydrogel upon immersion in water. The pattern re-emerges after drying the hydrogel. Heating the hydrogel above the phase transition temperature of PNIPAM (ca. 32 °C) also restores the pattern by hydrogel volume collapse. This behaviour suggests that this patterning technique would allow us to produce surfaces useful for technological application.

Remotely triggered release from composite hydrogel sponges

A thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel crosslinked with methylene bisacrylamide (MBA), with the ability to undergo a volume change of approximately 50%, was used to fabricate a hydrogel “sponge” with oil microdrops encapsulated within its structure by the polymerization of an O/W emulsion. By adding 1.5 wt.% of iron oxide nanoparticles to the hydrogel structure it is possible to trigger the hydrogel volume change remotely by exposing the composite to an alternating magnetic field in the radiofrequency range, which heats up the nanoparticles. The increase of the hydrogel temperature leads to its shrinking and subsequently the encapsulated oil droplets are squeezed out. It was shown that the oil is released gradually during cyclic volume change (repeated heating and cooling) and the amount of oil content released during the first 8–15 shrinking cycles was in the range 1–3% v/v per cycle. The total amount of the released oil phase was in the range 18–24% v/v and it was found to be affected by the size of the encapsulated microdroplets, with the larger ones being squeezed out preferentially.

Periodicity-Controlled Two-Dimensional Crystalline Colloidal Arrays

We developed a convenient and fast approach to preparing close-packed two-dimensional (2-D) particle arrays on mercury surfaces. Addition of cosolvents, such as alcohols, to aqueous colloidal particle suspensions induces spreading and self-assembly of the particles into 2-D arrays on top of the mercury surface. We can fabricate large-area close-packed 2-D arrays (>70 cm(2)) within 30 s. We attached these 2-D arrays to functional hydrogel films such that the 2-D array spacings were altered by the hydrogel volume response to the environment. We directly observed the hydrogel volume induced 2-D array spacing changes by using confocal laser scanning microscopy to monitor the spacings of fluorescent polystyrene particle 2-D arrays in response to changes in pH, solvent composition, temperature, etc.

Osteogenic Differentiation and Ectopic Bone Formation of Canine Bone Marrow-Derived Mesenchymal Stem Cells in Injectable Thermo-Responsive Polymer Hydrogel

This study describes an injectable, thermo-responsive hyaluronic acid-g-chitosan-g-poly(N-isopropylacrylamide) (HA-CPN) copolymer for bone tissue engineering. The wettability, temperature-dependent change of water content, and volume of HA-CPN hydrogel were measured, together with its biocompatibility in vitro and in vivo. The dried hydrogel morphology shows a three-dimensional, porous structure with interconnected pores. Canine bone marrow-derived mesenchymal stem cells (cBMSCs) were encapsulated in HA-CPN hydrogel and osteoinduction was assessed by comparing samples with different osteogenic differentiation induction times but with the same total cell culture time. Cell proliferation and time-dependent osteogenic differentiation, evident from secretion of extracellular matrix and formation of mineral deposits, were observed. The cells showed better proliferation in HA-CPN hydrogel than on tissue culture polystyrene after osteo-induced for 21 days and higher alkaline phosphatase activity regardless of osteo-induction times. Mineralization extent of cBMSCs in HA-CPN followed by Alizarin red stains showed positive stained nodules after osteo-induced longer than 7 days. The cells/hydrogel construct also showed increased mechanical strength and elasticity after osteogenic differentiation, and the increase could be correlated with osteo-induction time. In vivo studies confirmed the biocompatibility and bioresorption of the HA-CPN hydrogel and ectopic bone formation when the hydrogel was used as a cell carrier for osteo-induced cBMSCs and implanted in nude mice subcutaneously. Taken together, the results indicate the feasibility and efficacy of HA-CPN hydrogel as an injectable bone tissue engineering scaffold with cBMSCs.

2-D Array Photonic Crystal Sensing Motif

We have developed the first high-diffraction-efficiency two-dimensional (2-D) photonic crystals for molecular recognition and chemical sensing applications. We prepared close-packed 2-D polystyrene particle arrays by self-assembly of spreading particle monolayers on mercury surfaces. The 2-D particle arrays amazingly diffract 80% of the incident light. When a 2-D array was transferred onto a hydrogel thin film showing a hydrogel volume change in response to a specific analyte, the array spacing was altered, shifting the 2-D array diffraction wavelength. These 2-D array photonic crystals exhibit ultrahigh diffraction efficiencies that enable them to be used for visual determination of analyte concentrations.

A modified Boltzmann sigmoidal model for the phase transition of smart gels

Smart gels are soft polymeric systems that exhibit a reversible phase transition when exposed to environmental stimuli. A modified Boltzmann sigmoidal equation is proposed to model the phase transition behavior of smart gels. The equation can be solved through nonlinear conventional mathematical techniques by determining the hydrogel volume as a function of a particular stimulus. The theoretical results are in good agreement with the experimental data and are similar to those obtained from multiphysical mathematical models. Moreover, for all of the adjusted parameters, error probabilities approaching zero were obtained.

Photonic crystal hydrogel material for the sensing of toxic mercury ions (Hg2+) in water

We report the development of a new photonic crystal hydrogel for the sensing of highly toxic mercury ion (Hg2+) in water. This new sensing material optically reports the Hg2+ concentration in watervia diffraction of visible light from polymerized crystalline colloidal array (PCCA). The PCCA consists of light diffracting crystalline colloidal array (CCA) of monodisperse, highly charged polystyrene particles, which are polymerized within the polyacrylamide hydrogel. The changes in hydrogel surroundings trigger the volume change of hydrogel, which alters the lattice spacing of CCA and hence shifts the diffraction wavelength of light. The ions responsive urease coupled PCCA (UPCCA) hydrolyzes the urea and produces the HCO3− and NH4+ ions inside the hydrogel. These ions induce the charge-screening of the polyacrylamide carboxylates by decreasing the electrostatic repulsion between carboxylates and the polyacrylamide backbone relaxes, causing the shrinkage of hydrogel. Hence the UPCCA exhibits the blue shift of the diffracted wavelength. Hg2+ being the principal inhibitor of the urease-urea hydrolysis perturbs urea hydrolysis by the UPCCA when UPCCA is exposed to Hg2+ along with urea and hence suppresses the production of ions. This intervenes the shrinkage of hydrogel and does not allow the hydrogel to shrink as it shrinks in absence of Hg2+. Therefore the PCCA net blue shift decreases in the presence of Hg2+ along with urea compared to only urea. The extent of this hydrogel volume change is a function of Hg2+ concentrations. This UPCCA photonic crystal sensor detects ultra low (1 ppb) concentration of Hg2+ in water, exhibits reversibility and displays very high selectivity towards Hg2+. The uncompetitive inhibition nature of the urease enzyme, when it is covalently attached in the polymer hydrogel backbone, is the driving force for the very high selectivity and reversibility of the UPCCA sensor.

Facile formation of dynamic hydrogel microspheres for triggered growth factor delivery

Dynamic hydrogels have emerged as an important class of biomaterials for temporal control over growth factor delivery. In this study we formed dynamic hydrogel microspheres from protein–polymer conjugates using an aqueous two-phase suspension polymerization process. This polymerization process enabled rapid microsphere formation without the use of an organic phase, surfactants, mechanical strain or toxic radical initiators. The microspheres’ size distribution was modulated by varying the protein–polymer conformation in the pre-polymer solution. Notably, the protein’s ligand-induced, nanometer-scale conformational change translated to maximum hydrogel volume changes of 76±10%. The magnitude of the microspheres’ volume change was tuned by varying the crosslinking time and ligand identity. After characterizing the microspheres’ dynamic properties, we encapsulated two important therapeutic proteins, vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2), in the hydrogel microspheres and characterized how the microspheres’ dynamic properties controlled their release. Significantly, the aqueous two-phase suspension polymerization process enabled high encapsulation efficiencies (65.8±4.8% and 79.5±3.0% for VEGF and BMP-2, respectively). Also, the microspheres’ ligand-induced volume change triggered VEGF and BMP-2 release at specific, predetermined times. There are hundreds of proteins that undergo well-characterized conformational changes that could be processed into hydrogel microspheres via aqueous two-phase suspension polymerizations. Therefore, this approach could be used to form dynamic, growth-factor-releasing hydrogel microspheres that respond to a broad range of specific biochemical ligands.

Development of a Gastroretentive Drug Delivery System based on Superporous Hydrogel

Purpose: The aim of this work was to synthesize superporous hydrogels of rosiglitazone using chitosan and to study its swelling behaviour for application as a gastroretentive drug delivery system. Methods: Chitosan superporous hydrogels were synthesized using glyoxal as a crosslinking agent by gas blowing method. The effect of pH and ionic strength on the swelling ratio was determined. Swelling reversibility studies were also carried out. Fourier transform infrared (FTIR) analysis was undertaken to characterize the superporous hydrogels while dissolution studies were carried out to assess release characteristics. Results: Swelling was highly dependent on the extent of crosslinking. The higher the amount of crosslinking agent, the lower the swelling ratio. Higher ionic strength in pH 1.2 solution led to a decrease in swelling ratio. The superporous hydrogels were highly sensitive to pH of swelling medium, and showed reversible swelling and de-swelling behaviour while still maintaining their mechanical stability. Apparent density was dependent on the volume of the superporous hydrogels and decreased with increasing crosslink density. Degradation kinetics showed that chitosan superporous hydrogels had good water retention capability. Drug release was inversely related to the amount of crosslinking agent and fitted best to the Korsmeyer-Peppas model. Conclusion: The studies showed that chitosan-based superporous hydrogels can be used as a gastroretentive drug delivery system in view of their swelling characteristics in acidic pH. Keywords: Gastroretentive, Porous hydrogels, Chitosan, Swelling, Rosiglitazone

Nanoscale Characterization of the Equilibrium and Kinetic Response of Hydrogel Structures

The use of hydrogel nanostructured patterns and films in biomedical micro- and nanodevices requires the ability to analyze and understand their response properties at the nanoscale. Herein, the thermoresponse behavior of atom transfer radical polymerization (ATRP) grown poly(ethylene glycol) n dimethacrylate (PEGnDMA) cross-linked poly(N-isopropyl acrylamide) (PNIPAAm) hydrogel thin films over gold was studied. By controlling the mesh size of the hydrogel matrix through tuning the cross-linking density (i.e., using different molecular weight cross-linker and/or various amounts of cross-linker), the hydrogel volume swelling ratio was tailored for response applications. Thermoresponsive patterns exhibited a broad lower critical solution temperature (LCST) swelling transition, while rms roughness analysis of the hydrogel surface showed a sharp LCST transition. Mass and viscoelastic property changes were monitored using quartz crystal microbalance with dissipation (QCM-D), and the rapid response behavior of the thin hydrogel films was observed. The tunable response behavior along with the controlled growth of the hydrogel achieved via ATRP at the nanoscale make them applicable as functional components in diagnostic and therapeutic devices.

INFLUENCE OF POLY(ETHYLENE GLYCOL) ON PROPERTIES OF PAMPS/PAM DOUBLE NETWORK HYDROGELS

Double network (DN) hydrogels composing of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first network (FN) and poly(acrylamide) (PAM) as the second network (SeN),which were prepared by ultraviolet irradiation polymerization,were modified by poly( ethylene glycol) ( PEG). By adding PEG into single network (SN) hydrogels,many tiny meshes have been made in the network structures; meanwhile the PAM particles of SeN are in different sizes. DN hydrogels modified by PEG become tougher and softer than those without PEG. The swelling behavior was measured gravimetrically at 28℃. The absorbed amount of acrylamide (AM) in SN hydrogels was measured by brominate titration. The structures of different SN hydrogels were successfully characterized by scanning electron microscopy ( SEM). The compressive and tensile properties were examined by using Zwick /Roell tester. The results showed that:this PEG modified DN hydrogels exhibited higher swelling ratio than that of unmodified DN hydrogels,the former was twice times higher than the latter. Interestingly,the volume of DN hydrogels became larger with the gradual increasing amount of PEG in the hydrogels,likewise,the transmittance of DN hydrogels with various PEG amounts became lower. Modified SN hydrogels prefer to absorb AM,because the small meshes,which are in the network of hydrogels,enhance the absorbability of water and AM. Pictures of SEM demonstrate apparently that many small meshes of about 0. 05 ～ 10 μm are in the network structures and the thickness of mesh walls ranges from 0. 02 μm to 0. 2 μm. However,in the unmodified SN hydrogels no obvious meshes were found and the thickness of mesh walls is about 3 μm. Some compressive and tensile properties were enhanced,for example when the PEG = 1. 0 g,the compressive strain of modified DN hydrogels was 90% ,while that of the unmodified ones was 80%. Twice times higher tensile strain than that of unmodified DN hydrogels indicated that modified DN hydrogels had become tougher and softer.