Synthesis of an elastic β‐cyclodextrin hydrogel cage by hydroxyethyl cellulose

Current cyclodextrin (CD) hydrogels have disadvantages, including a limited CD content, long reaction time, and complicated chemical reactions. To overcome these, a one‐pot reaction was adopted, and a concept of a β‐CD hydrogel cage was proposed. Hydroxyethyl cellulose (HEC) was used as the raw material with the adjustment of the stoichiometric relationship among the crosslinking agent of epichlorohydrin, alkali environment, and β‐CD amount, and an elastic β‐CD hydrogel cage system was established. After the β‐CD was caged, the contents of active β‐CD in hydrogel products reached 74.45 and 69.14 wt % by weight measurement and photometric titration, respectively. Furthermore, compared to the pure HEC hydrogel, the hydrogel mechanical strength improved obviously after the β‐CD was caged, and we obtained a faster water swelling rate at the same time. Finally, a hydrophobic molecule of phenolphthalein (PP) was used to evaluated the activity of caged β‐CD in the hydrogel. In addition, the absorption and release of PP by an elastic β‐CD hydrogel cage at certain time intervals were also studied. The results demonstrate that the β‐CD hydrogel cage was used as a functional molecule carrier to quickly absorb and sustain the release of PP. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44388.     

Multifunctional gentamicin supplementation of poly(γ‐glutamic acid)‐based hydrogels for wound dressing application

The process of wound healing is composed of coagulation, inflammation, fibroplasia, collagenation, epithelization, and wound contraction. The wound dressing should protect the wound from bacterial infection, maintain a moist healing environment, and promote cell migration to reconstruct damaged tissue, and be easy to apply and remove to improve patient comfort. The purpose of our study was to develop multifunctional hydrogels composed of genipin‐crosslinked biodegradable biomaterials of poly(γ‐glutamic acid) and gelatin, encapsulating gentamicin to accelerate wound healing. The results of swelling ratio measurements clearly indicate that hydrogel composition of poly(γ‐glutamic acid)–gelatin had a higher swelling ratio and lower peel adhesion properties than gelatin hydrogel alone. In an in vitro study, the gentamicin incorporated in prepared hydrogels effectively inhibited target microorganisms and produced a higher expression of Type I collagen in fibroblast cells. Confocal laser scanning microscopy revealed that the fibroblast cells cultured in the hydrogel membranes produced fibroblast cell migration and showed a continuous lined cytoskeletal distributing status. In the in vivo study, it was found that the gentamicin incorporated in genipin‐crosslinked γ‐PGA–gelatin wound dressing demonstrates the potential of such biologically functionalized dressing to accelerate wound closure and, hence, its potential clinical usefulness. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Adsorption and drug release based on β‐cyclodextrin‐grafted hydroxyapatite composite

In this study, β‐cyclodextrin (β‐CD) was covalently grafted on hydroxyapatite (HA) using a coupling agent to improve the drug loading capacity and prolong the drug release. The binding of β‐CD on the HA surface was confirmed by Fourier transformation infrared spectroscopy, thermal gravimetric analysis, and X‐ray powder diffraction. The adsorption capacity of ofloxacin on β‐CD‐grafted hydroxyapatite (β‐CD‐g‐HA) composite was found to be 30 mg g^?1 at 37°C and 24 h. The adsorption process is spontaneous, given the negative values of free energy change. Compared with the release of ofloxacin loaded on HA, the release of ofloxacin loaded on β‐CD‐g‐HA was slowed down 28% and 21% in pH 2.0 and pH 7.4 buffer media at 2 h, respectively. Biocompatibility of β‐CD‐g‐HA was assessed by MTT assay, and the result showed that it had no cytotoxicity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

β‐cyclodextrin/poly(vinyl alcohol) hydrogels containing phenylpropionic acid and naphthylamine: dual pH‐sensitive release

Hydrogel composed of β‐cyclodextrin (β‐CD) and poly(vinyl alcohol) was prepared in a strong alkaline condition using epichlorohydrin as a crosslinker. Phenylpropionic acid (PPA) and naphthylamine (NA) were loaded in the cavities of β‐CD residues to endow the hydrogel with a dual pH‐sensitive characteristic. In release experiments using fluorescein isothiocyanate‐dextran (FITC‐dextran) as a dye, PPA/NA‐loaded hydrogel exhibited an extensive release not only in acidic conditions (e.g. pH 3.0) but also in alkaline conditions (e.g. pH 9.0). PPA and NA will be highly ionized at the alkaline and the acidic pH and they could promote swelling of the hydrogel, causing an extensive release at those pH values. However, the release was suppressed at mid pH values (e.g. pH 5.0 and pH 7.4), possibly due to the formation of salt bridges between PPA^? and NA⁺. In fact, the degree of swelling at mid pH was lower than that observed at strong acidic pH and alkaline pH. According to SEM images, the pore size and the texture compactness of hydrogels which had been subjected to swelling at different pH values could also account for the dual pH‐sensitive releases. The hydrogels exhibited dual pH sensitivities in terms of FITC‐dextran release and swelling. These hydrogels might be used as a pH‐sensitive vehicle for water‐soluble drugs. © 2013 Society of Chemical Industry     

In situ incorporation of monodisperse drug nanoparticles into hydrogel scaffolds for hydrophobic drug release

The effective and locally sustained delivery of hydrophobic drug with hydrogels as carriers is still a challenge owing to the inherent incompatibility of hydrophilic hydrogel network and hydrophobic drug. One promising approach is to use porous hydrogels to encapsulate and deliver hydrophobic drug in the form of nanoparticles to the disease sites. However, this approach is currently limited by the inability to load concentrated hydrophobic drug nanoparticles into the hydrogels because of the severe nanoparticle aggregation during the loading process. In this article, we firstly designed and fabricated efficient drug nanoparticles embedded hydrogels for hydrophobic drug delivery by incorporating monodisperse silybin (hydrophobic drug for liver protection) nanoparticles into acrylated hyaluronic acid (HA‐AC) based hydrogels through in situ cross‐linking. The silybin nanoparticles embedded hydrogel scaffolds proved to be a good sustained release system with a long period of 36 h. The drug release from this hybrid hydrogels could be modulated by tuning HA‐AC concentration, cross‐linking ratio, chain length of cross‐linker and drug loading amount. The different kinetic models were applied, and it was observed that the release profile of silybin best followed the Hixson‐Crowell model for the release of drug from the hydrogels embedding silybin nanoparticles. It could be envisioned that this process would significantly advance the potential applications of hydrogel scaffolds mediated hydrophobic drug delivery in clinical therapies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43111.     

Sustained delivery of hydrocortisone acetate by CS/N‐vinyl‐2‐pyrrolidone/CaCO3 microparticle hybrid hydrogels

The goal of this research is to develop a composite hydrogel system for sustained release of therapeutic agents. The hybrid hydrogels were prepared by radiation crosslinking on aqueous solution of Chitosan (CS)/N‐vinyl‐2‐pyrrolidone (NVP) with different loads of CaCO₃ in the presence of hydrocortisone acetate (HCA), an anti‐inflammatory drugs. Physical characteristics of CS/NVP/CaCO₃ were studied using X‐ray diffraction (XRD) and infrared spectrophotometery (IR). The porous structure of resulted hydrogel was confirmed by SEM micrographs. The effect of doses and calcium carbonate amount on the swelling of the hydrogels was investigated. The ability of the prepared CS/NVP/CaCO₃‐based hybrid hydrogels to be used as drug carriers for anti‐inflammatory‐specific drug delivery system was estimated using HCA as a model drug. POLYM. COMPOS., 35:1176–1183, 2014. © 2013 Society of Plastics Engineers     

Biomineralized hyaluronic acid/poly(vinylphosphonic acid) hydrogel for bone tissue regeneration

Novel biomineralized hydrogels composed of hyaluronic acid (HA) and vinyl phosphonic acid (VPAc) were designed with the aim of developing a biomimetic hydrogel system to improve bone regeneration by local delivery of a protein drug including bone morphogenetic proteins. We synthesized crosslinked hydrogels composed of methacrylated HA and poly(VPAc) [P(VPAc)], which serves as a binding site for calcium ions during the mineralization process. The HA/P(VPAc) hydrogels were biomineralized by a urea‐mediation method to create functional polymer hydrogels that can deliver the protein drug and mimic the bone extracellular matrix. The water content of the hydrogels was influenced by the HA/P(VPAc) composition, crosslinking density, biomineralization, and ionic strength of the swelling media. All HA/P(VPAc) hydrogels maintained more than 84% water content. Enzymatic degradation of HA/P(VPAc) hydrogels was dependent on the concentration of hyaluronidase and the crosslinking density of the polymer network within the hydrogel. In addition, the release behavior of bovine serum albumin from the HA/PVPAc hydrogels was mainly influenced by the drug loading content, water content, and biomineralization of the hydrogels. In a cytotoxicity study, the HA/P(VPAc) and biomineralized HA/P(VPAc) hydrogels did not significantly affect cell viability. These results suggest that biomineralized HA/P(VPAc) hydrogels can be tailored to create a biomimetic hydrogel system that promotes bone tissue repair and regeneration by local delivery of protein drugs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41194.     

Carbon nanotube‐hybridized supramolecular hydrogel based on PEO‐b‐PPO‐b‐PEO/α‐cyclodextrin as a potential biomaterial

In virtue of the potential biomedical application of carbon nanotube (CNT), the CNT was hybridized into a supramolecular hydrogel based on the selective inclusion of α‐cyclodextrin (α‐CD) onto poly(ethylene oxide) (PEO) segments of a triblock copolymer, i.e., PEO‐block‐poly(propylene oxide)‐block‐PEO. Different from the previous report, the content of α‐CD, in contrast to that of ethylene oxide unit, was decreased to decrease the network density in hydrogel and hence improve the diffusion of encapsulated substances. As a result, the modulus of the hydrogels climbed slightly after introducing CNT. Furthermore, as the essential properties for wound dressing, the antimicrobial activity, the skin‐adhesion, and water‐retention of such supramolecular hybrid hydrogels were also verified. On the other hand, the supramolecular hybrid hydrogels inherited the shear‐thinning property and are suitable as an injectable biomaterial. The cell viability assay confirmed the equivalent cytotoxicity of the supramolecular hybrid hydrogels to that of the native hydrogels without CNT. Consequently, such CNT‐hybridized supramolecular hydrogel shows a great potential in the biomedical application. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dual‐responsive semi‐interpenetrating network beads based on calcium alginate/poly(N‐isopropylacrylamide)/poly(sodium acrylate) for sustained drug release

To improve the mechanical strength of natural hydrogels and to obtain a sustained drug‐delivery device, temperature‐/pH‐sensitive hydrogel beads composed of calcium alginate (Ca‐alginate) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared in the presence of poly(sodium acrylate) (PAANa) with ultrahigh molecular weight (M_η ≥ 1.0 × 10⁷) as a strengthening agent. The influence of PAANa content on the properties, including the beads stability, swelling, and drug‐release behaviors, of the hydrogels was evaluated. Scanning electron microscopy and oscillation experiments were used to analyze the structure and mechanical stability of the hydrogel beads, respectively. The results show that stability of the obtained Ca‐alginate/PNIPAAm hydrogel beads strengthened by PAANa the alginate/poly(N‐isopropyl acrylamide) hydrogel bead (SANBs) was significantly improved compared to that of the beads without PAANa (NANBs) at pH 7.4. The swelling behavior and drug‐release capability of the SANBs were markedly dependent on the PAANa content and on the environmental temperature and pH. The bead sample with a higher percentage of PAANa exhibited a lower swelling rate and slower drug release. The drug release profiles from SANBs were further studied in simulated intestinal fluid, and the results demonstrated here suggest that SANBs could serve as a potential candidate for controlled drug delivery in vivo. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Sustained release of potassium diclofenac from a pH‐responsive hydrogel based on gum arabic conjugates into simulated intestinal fluid

This work describes the preparation, the swelling properties and the potassium diclofenac (KDF) release profile of hydrogels of gum arabic (GA), N′,N′‐dimethylacrylamide, and methacrylic acid. In order to convert GA into a hydrogel, the polysaccharide was vinyl‐modified with glycidyl methacrylate. The hydrogels showed pH‐responsive swelling changes, which were more expressive in the basic environment. Release data of KDF were adjusted to a diffusion‐based kinetic model that provides an important insight on affinity of the drug for hydrogel and solvent, which may be the leading parameter for release of guest molecules from polymers. The KDF release from the hydrogels into simulated intestinal fluid decreases when the amount of modified GA increases. This was demonstrated to be due to the higher affinity of KDF for GA‐richer hydrogel, which makes the anti‐inflammatory release less favorable. The analysis of released drug half‐time (t_1/2 = 16.10 and 21.51 h) indicated sustained release characteristics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43319.     

Effect of drug loading on the properties of temperature‐responsive polyester–poly(ethylene glycol)–polyester hydrogels

Hydrogels that can undergo gelation upon injection in vivo are promising systems for the site‐specific delivery of drugs. In particular, some thermo‐responsive gels require no chemical additives but simply gel in response to a change from a lower temperature to physiological temperature (37 °C). The gelation mechanism does not involve covalent bonds, and it is possible that incorporation of drugs into the hydrogel could disrupt gelation. We investigated the incorporation of drugs into thermo‐responsive hydrogels based on poly(?‐caprolactone‐co‐lactide)‐block‐poly(ethylene glycol)‐block‐poly(?‐caprolactone‐co‐lactide) (PCLA–PEG–PCLA). Significant differences in properties and in the response to incorporation of the anti‐inflammatory drug celecoxib (CXB) were observed as the PEG block length was varied from 1500 to 3000 g mol^?1. Linear viscoelastic moduli of a PCLA–PEG–PCLA hydrogel containing a 2000 g mol^?1 PEG block were least affected by the incorporation of CXB and this gel also exhibited the slowest release of CXB, so the incorporation of phenylbutazone, methotrexate, ibuprofen, diclofenac and etodolac was also investigated for this hydrogel. Different drugs resulted in varying degrees of syneresis of the hydrogels, suggesting that they interact with the polymer networks in different ways. In addition, the drugs had varying effects on the viscoelastic and compressive moduli of the gels. The results showed that the effects of drug loading on the properties of thermo‐responsive hydrogels can be substantial and depend on the drug. For applications such as intra‐articular drug delivery, in which the mechanical properties of the hydrogel are important, these effects should thus be studied on a case‐by‐case basis. © 2019 Society of Chemical Industry     

Fabrication of citric acid crosslinked β‐cyclodextrin/hydroxyethylcellulose hydrogel films for controlled delivery of poorly soluble drugs

β‐cyclodextrin grafted hydroxyethylcellulose (βCD‐g‐HEC) hydrogel films were prepared for the controlled release of poorly soluble model drug (ketoconazole) using citric acid as crosslinking agent. The active βCD and carboxyl content of the hydrogel films were determined by phenolphthalein assay and acid–base titration. The films were characterized by solid state ¹³C NMR, ATR–FTIR, thermogravimetric analysis, and differential scanning calorimetric, and analyzed for tensile strength, swelling ratio, drug loading, release, hemocompatibility, in vitro cytotoxicity, and implantation test. An increase in the concentration of βCD in feed increased the active βCD content of the hydrogel films but reduced their extent of interpolymer crosslinking. The βCD‐g‐HEC hydrogel films with high active βCD content showed maximum drug loading whereas those with high crosslinking density were capable of controlling the drug release for long duration. Hemolysis assay and in vitro cytotoxicity study revealed the biocompatible nature of the hydrogel films whereas implantation test indicated their minimal inflammatory effect. From the overall results, βCD‐g‐HEC hydrogel films were found to be better alternative to the previously reported βCD‐HPMC and βCD‐CMC hydrogel films for enhanced loading and long‐term release, respectively, of the poorly soluble drugs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46452.     

Chitosan and chitosan/β‐cyclodextrin microspheres as sustained‐release drug carriers

The main aim of this study was to compare two microspheres, chitosan (CTS) and CTS/β‐cyclodextrin (β‐CD), made by spray‐drying, as pulmonary sustained drug‐delivery carriers. Theophylline (TH) was used as a model drug. The characteristics of the microspheres and in vitro release were studied. The yield of CTS/β‐CD microspheres was 46.1%, which was higher than that of the CTS microspheres (36.5%). The drug loads of the CTS and CTS/β‐CD microspheres were 22.7 and 21.1%, respectively, whereas the encapsulation efficiencies were 90.7 and 91.4%, respectively. The distribution of 50% [(diameter) d (0.5)] of the CTS microspheres was below 6.49 μm and that of the CTS/β‐CD microspheres was below 4.90 μm. Scanning electron microscopy showed that both microspheres yielded a spherical shape with smooth or wrinkled surfaces. Fourier transform infrared spectroscopy demonstrated that the carbonyl group of TH formed hydrogen bonds with the amide group of CTS and the hydroxyl group of β‐CD. The swelling ability of the two microspheres was more than three times their weight, and their humidity rates attained equilibrium within 24 h. The ciliary beat movement times of CTS and CTS/β‐CD microspheres were 493.00 and 512.33 min, respectively, which indicated that the two microspheres effectively reduced the ciliotoxicity and possessed better adaptability. In vitro release of TH from CTS/β‐CD microspheres was slower than that from CTS microspheres at pH 6.8 and provided a sustained release of 72.0% within 12 h. The results suggest that CTS/β‐CD microspheres are a promising carrier for sustained release for pulmonary delivery. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1183–1190, 2007     

Novel thermosensitive hydrogel composites based on poly(d,l‐lactide‐co‐glycolide) nanoparticles embedded in poly(n‐isopropyl acrylamide) with sustained drug‐release behavior

To reach sustained drug release, a new composite drug‐delivery system consisting of poly(d,l ‐lactide‐co‐glycolide) (PLGA) nanoparticles (NPs) embedded in thermosensitive poly(N‐isopropyl acrylamide) (PNIPAAm) hydrogels was developed. The PNIPAAm hydrogels were synthesized by free‐radical polymerization and were crosslinked with poly(ethylene glycol) diacrylate, and the PLGA NPs were prepared by a water‐in‐oil‐in‐water double‐emulsion solvent‐evaporation method. The release behavior of the composite hydrogels loaded with albumin–fluorescein isothiocyanate conjugate was studied and compared with that of the drug‐loaded neat hydrogel and PLGA NPs. The results indicate that we could best control the release rate of the drug by loading it to the PLGA NPs and then embedding the whole system in the PNIPAAm hydrogels. The developed composite hydrogel systems showed near zero‐order drug‐release kinetics along with a reduction or omission of initial burst release. The differential scanning calorimetry results reveal that the lower critical solution temperature of the developed composite systems remained almost unchanged (<1°C increase only). Such a characteristic indicated that the thermosensitivity of the PNIPAAm hydrogel was not distinctively affected by the addition of PLGA NPs. In conclusion, an approach was demonstrated for the successful preparation of a new hybrid hydrogel system having improved drug‐release behavior with retained thermosensitivity. The developed systems have enormous potential for many biotechnological applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40625.     

Synthesis and properties of hydrogels of poly(acrylic‐co‐acroloyl β‐cyclodextrin)

Novel acrylic monomers (β‐CD‐A and β‐CD‐6‐EA) containing β‐cyclodextrin (β‐CD) with different extent of substitution were prepared by using dicyclohexylcarbodiimide (DCC) as a condensation agent at room temperature. Two kinds of functional hydrogels were also synthesized by copolymerization of β‐CD‐A and β‐CD‐6‐EA with acrylic acid (AAc) using a redox initiator system in aqueous solution. The nuclear magnetic resonance (¹H NMR), infrared spectroscopy (IR), thermogravimetric analysis (TGA) were employed to character the molecular structures of β‐CD modified monomers and their copolymers. The swelling experiments indicate that the hydrogels with different equilibrium swelling ratio (ESR) possess obvious pH‐sensitivity and distinct dynamic swelling behavior. Using an anti‐cancer drug, chlorambucil (CHL), able to form complexes with β‐CD in water, as a model compound, the controlled drug release behaviors of these hydrogels were investigated. The release behavior of CHL from two kinds of hydrogels synthesized reveals that the release rate of CHL can be effectively controlled by pH values, cross‐linking density, and β‐CD content. In addition, it is found that the β‐CD with the proper frame and concentration can increase release efficiency of CHL from the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of a temperature‐sensitive nonwoven poly(propylene) with increased affinity for guest molecules

A temperature‐sensitive hydrogel with the capability of inclusion complex formation with guest molecules was successfully grafted onto the surface of nonwoven polypropylene (nonwoven PP). This was carried out by the use of N‐isopropylacrylamide monomer and a modified cyclodextrin (acrylamidomethyl‐β‐cyclodextrin (β‐CD‐NMA)). Fourier‐transform infra red (FT‐IR) and elemental analyses confirmed the presence of poly(N‐isopropylacrylamide) (PNIPAAm) and β‐CD‐NMA components on the surface of the textile. Equilibrium swelling ratio measurements showed that the grafted hydrogel maintained its temperature‐sensitive property compared to a nongrafted hydrogel. The effect of β‐CD‐NMA and crosslink agent concentrations on the grafting yield was studied. The β‐CD‐NMA content into the PNIPPAM‐ β‐CD‐NMA grafted nonwoven PP (PNIPAAm‐β‐CD‐NMA‐PP) was estimated by FT‐IR through a new procedure. The estimated amounts of β‐CD‐NMA in PNIPAAm‐β‐CD‐NMA‐PP were determined to be 0.9, 1.9 mg g^?1 for 0.019M and 0.049M concentrations of β‐CD‐NMA in monomer solution, respectively. The PNIPAAm‐β‐CD‐NMA‐PP showed a remarkable increase in absorbance affinity of 8‐anilino‐1‐naphthalenesulfonic acid ammonium salt at 20°C from 0.93 to 3.33 µmol g^?1 compared to PNIPAAm‐PP. Furthermore, the results showed a temperature‐sensitive loading affinity for PNIPAAm‐β‐CD‐NMA‐PP in absorbance of guest molecules due to the presence of β‐CD‐NMA. The use of hydrophobic guest molecules such as fragrance oils and antibiotics in modified fabrics can provide new applications in textile and pharmaceutical industry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40497.     

Hydrogels based on copolymers of 2‐hydroxyethylmethacrylate and 2‐hydroxyethylacrylate as a delivery system for proteins: Interactions with lysozyme

Hydrogels have attracted considerable attention due to numerous applications, in particular as contact lenses and carriers for sustained drug delivery. The aim of the present work is to characterize the interactions of copolymer hydrogels consisted of 2‐hydroxyethylmethacrylate (HEMA) and 2‐hydroxyethylacrylate (HEA) with a small protein (lysozyme) and to assess the potential applications of these hydrogels as a drug delivery system for sustained release of protein‐based therapeutics. Physicochemical properties of protein‐loaded hydrogels, as well as lysozyme in vitro loading and release and the conformation of the protein released from hydrogels were studied. The effect of copolymer composition on the protein deposition on hydrogels and protein aggregation in the presence of hydrogels was also assessed. The results show that introduction of HEA into the copolymeric hydrogels enhances their suitability as a delivery system for proteins. Copolymerisation of HEMA and HEA allows controlling the physicochemical properties of hydrogels and the protein release rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44768.     

Theophylline‐loaded pectin‐based hydrogels. I. Effect of medium pH and preparation conditions on drug release profile

In this study, a series of theophylline‐loaded calcium pectin gel films were prepared in three different Ca⁺² concentrations with three different methods for wound dressing applications. Drug release performance of the films were investigated in four different medium pH in order to mimic wound healing pH conditions. Hydrogel films were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy and atomic force microscopy. Their absorbency (fluid handling), swelling behavior, dehydration rate, dispersion characteristic, dressing pH determination, water vapor permeability, oxygen permeability, surface contact angle, flexibility, Shore A hardness, mean mass per unit area and thickness were determined. The effect of the hydrogels on wound healing was evaluated with an in vitro wound healing assay. After evaluating all data, we suggested that the hydrogel film prepared with swelling method using 7% or 10% crosslinker and dried at 26 °C is more suitable for controlled drug release process. We showed that between pH 3.25 and 7.12 the form of the hydrogel did not change, and drug release was continuous. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46731.     

Thermoreversible hydrogel. XVII. Investigation of the drug release behavior for [N‐isopropylacrylamide‐co‐trimethyl acrylamidopropyl ammonium iodide‐co‐3‐dimethyl (methacryloyloxyethyl) ammonium propane sulfonate] copolymeric hydrogels

A series of copolymeric hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm), trimethyl acrylamidopropyl ammonium iodide (TMAAI), and 3‐dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS). Results showed that the swelling ratios of these copolymeric hydrogels increased with an increase of TMAAI content. The drug release behavior of the ionic thermosensitive hydrogels related to their ionicity and drug types. Results indicated that the release ratio of caffeine in the hydrogels was not affected by the ionicity of hydrogels, but increased with increasing of the swelling ratio. The anionic solute (phenol red) strongly interacted with cationic hydrogel (very large K_d), so the phenol red release ratio in cationic gels was very low. On the other hand, CV was adsorbed only on the skin layer of the cationic hydrogel because of the charge repulsion, and released rapidly. Therefore the release ratio was highest for cationic hydrogel to cationic drug. In addition, the partition coefficients (K_d) and the drug delivery behavior of the present gels were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1592–1598, 2002     

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