Polyelectrolyte complex hydrogel composed of chitosan and poly(γ‐glutamic acid) for biological application: Preparation,physical properties,and cytocompatibility

Polyelectrolyte complex (PEC) hydrogels composed of chitosan as a cationic polyelectrolyte and poly (γ‐glutamic acid) (γ‐PGA) as an anionic polyelectrolyte were prepared from PEC dispersions based on a chitosan solution to which different amounts of γ‐PGA solutions were added to charge equivalency. The chemical structures of the PEC hydrogels were investigated by Fourier transform infrared spectroscopy. The physical properties, fixed charge concentration, crystallinity, mechanical properties, micromorphology, and swelling properties of the PEC hydrogels were also investigated. The total fixed charge concentration of the PEC hydrogels varied as a function of pH on the pK intervals between chitosan (pK = 6.5) and γ‐PGA (pK = 2.27). The isoelectric points (IEP) were shifted to a lower pH with a higher weight ratio of γ‐PGA to chitosan. The elastic modulus was decreased with the weight ratio increasing from 0 : 1 to 1 : 1 (γ‐PGA/chitosan) by ionic crosslinking between the amino groups of chitosan and the carboxyl groups of γ‐PGA. The results of the swelling study showed that the swelling properties of PEC hydrogels were more affected by the change in the elastic restoring force than by the change in the fixed charge concentration depending on the pH. Also, the cytotoxicity of the PEC hydrogels was investigated using normal human dermal fibroblast (NHDF) cell lines, and the results showed the PEC hydrogels were not toxic. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:386–394, 2007     

Gelation and crosslinking characteristics of photopolymerized poly(ethylene glycol) hydrogels

The gelation and crosslinking features of poly(ethylene glycol) (PEG) hydrogels were scrutinized through the UV polymerization processes of poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) mixtures. The real‐time evolutions of the elastic moduli of the prepolymerized mixtures with different crosslinking ratios of PEGMA and PEGDMA and the photoinitiator concentrations were measured during photopolymerization. The rheological properties were compared with other properties of the PEG hydrogels, including the relative changes in the C?C amounts in the mixtures before and after UV irradiation, water swelling ratio, gel fraction, mesh size, and mechanical hardness. As the portion of PEGDMA as a crosslinker increased, the final elastic modulus and gel fraction increased, whereas the swelling ratio and scratch penetration depth at the hydrogel film surface decreased because of the formation of compact networks inside the hydrogels. These results indicate that there was a good correlation between the rheological analysis for predicting the crosslinking transition during photopolymerization and the macroscopic properties of the crosslinked hydrogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41939.     

Controlled mechanical and swelling properties of poly(vinyl alcohol)/sodium alginate blend hydrogels prepared by freeze–thaw followed by Ca2+ crosslinking

Poly(vinyl alcohol) (PVA)/sodium alginate (SA) blend hydrogels have immense potential for use as functional biomaterials. Understanding of influences of processing parameters and compositions on mechanical and swelling properties of PVA/SA blend hydrogels is very important. In this work, PVA/SA blend hydrogels with different SA contents were prepared by applying freeze–thaw method first to induce physical crosslinking of PVA chains and then followed by Ca²⁺ crosslinking SA chains to form interpenetrating networks of PVA and SA. The effects of number of freeze–thaw cycles, SA content and Ca²⁺ concentration on mechanical properties, swelling kinetics, and pH‐sensitivity of the blend hydrogels were investigated. The results showed that the blend hydrogels have porous sponge structure. Gel fraction, which is related to crosslink density of the blend hydrogels, increased with the increase of freeze–thaw cycles and strongly depended on SA content. The SA content exerts a significant effect on mechanical properties, swelling kinetics, and pH‐sensitivity of the blend hydrogels. The number of freeze–thaw cycles has marked impact on mechanical properties, but no obvious effect on the pH‐sensitivity of the PVA/SA blend hydrogels. Concentration of CaCl₂ aqueous solution also influences mechanical properties and pH‐sensitivity of the blend hydrogel. By altering composition and processing parameters such as freeze–thaw cycles and concentration of CaCl₂ aqueous solution, the mechanical properties and pH‐sensitivity of PVA/SA blend hydrogels can be tightly controlled. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical properties of poly(N‐isopropyl‐acrylamide‐co‐itaconic acid) hydrogels

Hydrogels of N‐isopropylacrylamide and itaconic acid were synthesized with different monomer ratios and with two crosslinking agent concentrations. The different xerogels were immersed in water and the swelling process was conducted up to equilibrium conditions at two temperatures (22 and 37°C). These temperatures are lower and higher than the transition temperature shown by PNIPA hydrogels. The mechanical properties of the different solvated hydrogels were examined by oscillatory shear measurements at 22 and 37°C. The copolymer volume fraction and the elastic storage modulus of the hydrogels decreased as the itaconic acid percentage in the copolymer increased. This behavior was attributed to the higher hydrophilic character of the itaconic acid comonomer. Effective crosslinking density, molar mass between crosslinks, and the polymer–solvent interaction parameter were determined from the experimental values of the elastic storage moduli and the copolymer volume fractions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2540–2545, 2002     

Preparation of biodegradable crosslinking agents and application in PVP hydrogel

Firstly, biodegradable crosslinking agents (BCA) were synthesized by ring‐opening polymerization reaction of lactide, four kinds of which with different molecular weights were got by means of changing the ratio of DL ‐lactide(LA) and glycerol(GL). Then a series of poly(N‐vinyl pyrrolidone) (PVP) hydrogels were prepared successfully by radical polymerization of BCA and N‐vinyl pyrrolidone(NVP). Both the ratio of NVP/BCA and the molecular weight of BCA were used to control the performance of PVP hydrogels, which were measured in terms of the ratio of swelling, contact angle, mechanical properties, and biodegradability in vitro. This study showed that increasing both the ratio of NVP/BCA and the molecular weight of BCA resulted in a low crosslinking density of the hydrogels. The crosslinking density played an important role in determining the properties of biodegradable PVP hydrogels. Both the ratio of NVP/BCA and the molecular weight of BCA contributed to high ratio of swelling. A smaller amount of crosslinking agent caused a lower contact angle, while the molecular weight of BCA had little effect on it. In terms of mechanics of hydrogels on both dry and wet conditions, tensile modulus decreased along with decreasing BCA, while the extension at break increased at the beginning and decreased at the end. In the end, measured by mass loss, biodegradability in vitro of hydrogels had two stages: an initial stage with approximately constant loss of mass (stage 1) followed by a stage with rapid mass loss (stage 2). Both increased content and molecular weight of BCA improved the degradation rate of the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1515–1521, 2006     

Comparison the properties of PVA/Na+‐MMT nanocomposite hydrogels prepared by physical and physicochemical crosslinking

A novel physicochemical crosslinked nanocomposite hydrogel based on polyvinyl alcohol (PVA) and natural Na‐montmorillonite (Na⁺‐MMT) was synthesized by chemical crosslinking of nanocomposite hydrogel followed by a freezing‐thawing process. The effects of physical crosslinking, as well as physicochemical crosslinking, on the structure, morphology, and properties (thermal, mechanical, swelling, and deswelling) of nanocomposite hydrogels were investigated and compared with each other. The structure and morphology of nanocomposites were studied by Fourier transform infrared, X‐ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy techniques. The thermal and mechanical properties of nanocomposites that were affected by physical and physicochemical crosslinking were evaluated by thermogravimetric analysis, differential scanning calorimeter, dynamic mechanical analysis, hardness test, and Water vapor transmission rate (WVTR) experiments. The results showed that the physicochemical crosslinking of a PVA nanocomposite leads to a reduction in crystallinity and melting temperature, as well as an increase in the Hardness and WVTR compared to a physically crosslinked PVA nanocomposite hydrogel. The swelling and deswelling experiments were performed using a gravimetric method, and it was shown that controlled crosslinking of PVA nanocomposite hydrogel with glutaraldehyde causes the swelling ratio to increase and the cumulative amount of water loss to decrease. The swelling (sorption) and deswelling (desorption) kinetics data for physically and physicochemical crosslinking of nanocomposite hydrogels were fitted with a fickian model. It is concluded that through control crosslinking of PVA nanocomposite can lead to a hydrogel with higher swelling capacity than that is in conventional PVA nanocomposite hydrogel. POLYM. COMPOS., 37:897–906, 2016. © 2014 Society of Plastics Engineers     

Tunable elasticity and thermodynamic parameters of hydroxypropyl methacrylate‐based gels with varying extents of monomer concentration: Statistical mechanics treatments of physical observations

The present article reports the scaling laws relating the preparation conditions with the equilibrium swelling degree and the crosslinking density of a new family of hydroxyl functional hydrogels (Hgs) prepared by free radical crosslinking polymerization of hydroxypropyl methacrylate (HPMA) in aqueous solution with tetraethylene glycol dimethacrylate (TEGDMA) as crosslinker. For comparison of physical properties, chemical and mechanical stability, HPMA cryogels (Cgs) were also prepared using the cryotropic gelation technique by conducting the gelation reactions at subzero temperatures. The measurements of the equilibrium swelling degree and the elastic properties of poly(hydroxypropyl methacrylate) (PHPMA) gel samples having different initial monomer concentration were treated according to the scaling theory to explain the rubbery behavior of the resulting Hgs. The obtained scaling relation between the reduced modulus and the swelling degree indicated limiting chain extensibility which is neglected in the Flory–Rehner theory. The effective crosslink density and polymer–solvent interaction parameter of PHPMA Hgs were used to interpret the observed deviation. Results showed that the properties of PHPMA Hgs and Cgs can be controlled by varying the HPMA and TEGDMA content. Increase of total monomer concentrations causes a pronounced decrease in the equilibrium swelling degree, and an increase in the elastic response of PHPMA Hgs and Cgs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45889.     

Hybrid double‐network hydrogel based on poly(aspartic acid) and poly(acryl amide) with improved mechanical properties

Hydrogels usually have a smaller mechanical strength and toughness than generic polymeric materials. Therefore, many studies report improvements for mechanical properties of hydrogels by preparing double‐network hydrogels, nanocomposite hydrogels, and nanostructured hydrogels. In this study, interpenetrating‐type dually‐crosslinked hydrogels were prepared via free radical crosslinking polymerization of acrylamide monomers in the presence of poly(aspartic acid) and subsequent immersion in a metal ion containing aqueous solution to induce extra physical crosslinking through ionic or coordination bonding. Using this approach, the mechanical properties of inherently weak and brittle homopolymer gels could be improved via interpenetrating the double network formed by both covalent bonding and metal coordination‐assisted reversible physical crosslinks. The preparation, swelling behavior, morphology, and mechanical properties of these hydrogels are presented. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45925.     

Evaluation of two chemical crosslinking methods of poly(vinyl alcohol) hydrogels for injectable nucleus pulposus replacement

Low back pain caused by intervertebral disc degeneration is one of the most common spinal disorders among patients seeking medical treatment. The most common surgical treatments are spinal fusion and total disc arthroplasty, both of which are very invasive surgical procedures. Nucleus pulposus replacement is an earlier stage intervention for disc degeneration. One of the material classes being studied for this application is hydrogels: a three‐dimensional hydrated network of polymer(s), which mimics the mechanical and physiological properties of the nucleus. Poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), and poly(ethylene glycol) (PEG) hydrogels have previously been shown to be great candidate materials for injectable nucleus pulposus replacement, but have experienced issues with swelling and mass retention. The addition of chemical crosslinking to the PVA/PVP/PEG hydrogel system will allow tailoring of the swelling, mechanical, injectability, and mass loss properties of the hydrogel network. Two chemical crosslinking methods were evaluated for the PVA/PVP/PEG hydrogel system by characterizing the hydrogels with compression, swelling, and spectroscopy experiments. The results of these experiments led to the selection of the difunctional crosslinking strategy using PEG functionalized with terminal epoxide group (PEG diglycidyl ether) as the preferred crosslinking method. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40843.     

Preparation and characterization of pH‐sensitive hydrogels based on chitosan,itaconic acid and methacrylic acid

Novel pH‐sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were prepared in two steps. Chitosan was first ionically crosslinked with itaconic acid, after which a free radical polymerization and crosslinking of the chitosan/itaconic acid network was performed by adding methacrylic acid and a crosslinker in order to achieve better mechanical properties and tunable swelling. The samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, X‐ray diffraction, dynamic mechanical analysis and the swelling ratios of the hydrogels at various pH values (2.0–8.0). The hydrogel composition is found to have a great impact on the hydrogel structure, mechanical and thermal properties, morphology and swelling kinetics. The highly porous morphology of the gels is probably connected with the bulky chitosan/itaconic acid network which reduces the degree of crosslinking in the second step of the synthesis due to steric hindrances. The gels demonstrate substantial change in buffer absorbency with change of pH, low for acid buffers and the higher for pH values above 6 where the swelling is considerably slow, thus suggesting their strong candidature for use as oral drug‐delivery systems in the lower parts of the gastrointestinal tract and for drugs that require longer release times. Copyright © 2010 Society of Chemical Industry     

聚丙烯酸/氧化石墨烯自修复水凝胶的合成及性能

通过改进的Hummers方法成功制备了氧化石墨烯(GO)。以Fe3+为交联剂、丙烯酸(AA)为单体、GO为增强剂,采用原位聚合法制备了聚丙烯酸(PAA)/GO自修复水凝胶。考查了不同GO含量下,PAA/GO自修复水凝胶的溶胀性能,并探讨了GO含量、Fe3+含量和H2O含量对PAA/GO自修复水凝胶力学性能的影响,研究了PAA/GO自修复水凝胶的自修复性能。结果表明,Fe3+含量、GO含量和H2O单体含量分别为0.5 %（摩尔分数）、0.5 %（质量分数,下同）、80 %时,具有最佳力学性能（其拉伸强度为743.5 kPa,断裂伸长率为2940.5 %）;GO含量为0.25 %时,PAA/GO自修复水凝胶的吸水性能最大;PAA/GO自修复水凝胶具有优异的自修复性能。     

Evaluation of the influence of spirulina microalgae on the drug delivery characteristics of genipin cross-linked chitosan hydrogels

Abstract

Chitosan-spirulina hydrogels were prepared by crosslinking of chitosan with genipin, in presence of spirulina microalgae. The swelling ratios and kinetic parameters of the hydrogels in distilled water, pH:2 and pH:7.4 solutions and the drug 5-Fluorouracil delivery capacities of the hydrogels were determined by gravimetric and spectrophotometric analyses, respectively and the results were statistically evaluated. The morphological structures, thermal and mechanical properties of the hydrogels were investigated using related techniques. Furthermore, cytotoxicity test was performed for assessment of biocompability of the hydrogels.The all results indicate that spirulina significantly improves the drug delivery properties of the genipine cross-linked hydrogels.     

Mechanical characteristics of poly(2‐hydroxyethyl methacrylate) hydrogels crosslinked with various difunctional compounds

Poly(2‐hydroxyethyl methacrylate) hydrogels were prepared in the presence of 30 wt% water using two series of crosslinking agents including divinylic (ethyleneglycol dimethacrylate, 1,4‐butanediol dimethacrylate, 2,3‐dihydroxybutanediol 1,4‐dimethacrylate) and diallylic (1,5‐hexadiene‐3,4‐diol and 1,5‐hexadiene) compounds, over a concentration range between 0.1 and 5 mol%. The resulting polymers were swollen in water to yield homogeneous transparent hydrogels. These hydrogels were characterised in terms of equilibrium swelling in water, tensile properties and compression stress–strain measurements. The influences of the nature and the concentration of crosslinking agent on the swelling behaviour and the mechanical properties of these hydrogels were investigated. The crosslinking efficiency of two representative agents (ethyleneglycol dimethacrylate and 1,5‐hexadiene‐3,4‐diol) was quantified by compression experiments. A much lower crosslinking efficiency (0.013) was observed for 1,5‐hexadiene‐3,4‐diol than for ethyleneglycol dimethacrylate (0.336). It is suggested that the low crosslinking efficiency of diallylic agents is responsible for a trend in properties different from that displayed by the gels crosslinked with dimethacrylates. A comparison was made to the similar effect observed previously in heterogeneous PHEMA hydrogels. © 2001 Society of Chemical Industry     

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     

Enzymatic and ionic crosslinked gelatin/K‐carrageenan IPN hydrogels as potential biomaterials

Hydrogels of a natural origin have attracted considerable attention in the field of tissue engineering due to their resemblance to ECM, defined degradability and compatibility with biological systems. In this study, we introduced carrageenan into a gelatin network, creating IPN hydrogels through biological methods of enzymatic and ionic crosslinking. Their gelation processes were monitored and confirmed by rheology analysis. The combination of biochemical and physical crosslinking processes enables the formation of biohydrogels with tunable mechanical properties, swelling ratios and degradation behaviors while maintaining the biocompatibilities of natural materials. The mechanical strength increased with an increase in carrageenan content while swelling ratio and degradability decreased correspondingly. In addition, the IPN hydrogels were shown to support adhesion and proliferation of L929 cell line. All the results highlighted the use of biological crosslinked gelatin‐carrageenan IPN hydrogels in the context of tissue engineering. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 10.1002/app.40975.     

Preparation and characterization of polyacrylic acid‐poly(vinyl alcohol)‐based interpenetrating hydrogels

Some structural features of hydrogels from poly(acrylic acid) (PAAc) of various crosslinking degrees have been investigated through mechanical and swelling measurements. Interpenetrating polymer hydrogels (IPHs) of poly(vinyl alcohol) (PVA) and PAAc have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N,N‐methylenebisacrylamide in the presence of PVA. The application of freeze–thaw (F–T) cycles leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and viscoelastic properties of the IPHs were evaluated as a function of the content of crosslinker and the application of one F–T cycle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5789–5794, 2006     

Investigation of mechanical and thermodynamic properties of pH‐sensitive poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with different crosslinking agents

pH‐sensitive poly(N,N‐dimethylaminoethyl methacrylate) hydrogels were synthesized by free‐radical crosslinking polymerization using two different crosslinking agents; tetraethylene glycol dimethacrylate (TEGMA) and N,N′‐methylenebis(acrylamide) (BAAm). The influence of the polymerization factors such as the type of the crosslinking agent and the gel preparation concentration on the swelling behavior, the gel strength, the effective crosslinking density and the average chain length between the crosslink points for the resulting hydrogels was investigated. The results of the equilibrium swelling measurements in water showed that the linear swelling ratio of the resulting hydrogels increases with increasing gel preparation concentration. The swelling ratio of PDMAEMA hydrogels crosslinked with BAAm is larger than those for hydrogels crosslinked with TEGMA over the entire range of the polymer network concentration. The hydrogels exhibit very sharp pH‐sensitive phase transition in a very narrow range of pH between 7.7 and 8.0. From the mechanical measurements, it was also found that the linear swelling ratio of resulting hydrogels depends on the crosslinking density and also the type of the crosslinker used in the preparation. The resulting hydrogels are thought to be good candidates for pH‐sensitive drug delivery systems. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Effect of polymer solution concentration on the swelling and mechanical properties of glycol chitosan superporous hydrogels

This study examined the effect of the polymer solution concentration on the swelling and mechanical properties of glycol chitosan (GCS) superporous hydrogels (SPHs). GCS SPHs were synthesized using a gas blowing method using glyoxal as the crosslinking agent at different polymer solution concentrations. A small change in the GCS solution concentration resulted in a remarkable change in compression strength and swelling kinetics without any significant loss in equilibrium water imbibing capacity. The increase in mechanical strength accompanied by the decrease in swelling kinetics was caused by the generation of smaller pores during the gelation process of the reactant systems associated with a higher polymer solution viscosity. The apparent diffusion coefficients for a variety of GCS/simulated gastric fluid solution systems were determined from the theoretical fitting of experimental dynamic swelling data, explaining the effects of the solution concentration and crosslinking density on the swelling kinetics. The diffusion coefficients determined in this study are expected to be used as the basic information in estimating the swelling kinetics of samples in different dimension. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

亲水-疏水PVP-semi-IPN-PCL水凝胶的制备与溶胀性能

N-乙烯基吡咯烷酮（NVP）在聚己内酯（PCL）的乙酸乙酯溶液中进行自由基聚合,制备了亲水-疏水性聚乙烯吡咯烷酮（PVP）/聚己内酯（PCL）半互穿网络水凝胶（PVP-semi-IPN-PCL）。凝胶中PCL的熔融温度T_m无明显变化,而T_m吸热峰形状随PVP含量变化。凝胶平衡溶胀率（ESR）随PVP含量的升高而增大,结合水量的增大尤其显著。由于“笼蔽效应”,低浓度引发剂时,偶氮二异丁睛（AIBN）引发制备的凝胶ESR低于过氧化苯甲酰（BPO）引发剂。交联剂浓度较低时,以戊二醛交联形成凝胶的ESR较N,N-亚甲基双丙烯酰胺（NMBA）交联形成的凝胶大。浓度较高时,戊二醛交联凝胶ESR较NMBA低。PVP含量（质量）分别为20%、40%、60%、80%时,凝胶溶胀动力学Fick模型中的n值分别为0.854、0.471、0.466、0.253,说明在合适的PVP含量时,凝胶的溶胀动力学符合Fick模型。     

Fabrication and characterization of microgel-impregnated, thermosensitive PNIPAAm hydrogels

Poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate (PNIPAAm/PEG-DA) microgels were used as an additive during the polymerization and/or crosslinking of PNIPAAm hydrogels to improve their thermosensitive properties. The influence of this additive on the property of resulting PNIPAAm hydrogels was investigated and characterized. The interior morphology by scanning electron microscopy (SEM) revealed that microgel impregnated PNIPAAm hydrogels have tighter and constrained porous network structures, although large cavities of 30-40 μm in diameter, occupied by the microgels were sporadically distributed in this constrained network. Differential scanning calorimetry (DSC) studies did not show apparent difference in lower critical solution temperature (LCST) between normal and microgel-impregnated PNIPAAm hydrogels. The incorporating of PNIPAAm/PEG-DA microgels, however, significantly improved mechanical properties of modified hydrogels when comparing with a normal PNIPAAm hydrogel, although the tendency was not strictly proportional to the microgel amount. Based on the temperature-induced swelling ratio data as well as response kinetics, microgel-impregnated hydrogels exhibited improved thermosensitive characteristics in terms of higher equilibrium swelling ratio as well as faster response rates and the level of improvement depended on the amount of microgel impregnated.