Formation of a DNA/N‐dodecylated chitosan complex and salt‐induced gene delivery

An N‐dodecylated chitosan (CS‐12) was synthesized from dodecyl bromide and chitosan and was assembled with DNA to form a polyelectrolyte complex (DNA/CS‐12 PEC). UV was used to examine the thermal stability of DNA embedded in PEC. The results indicate that the incorporation of dodecylated chitosan can enhance the thermal stability of DNA. The analysis of AFM image shows that PEC develops a globule‐like structure composed of 40–115 DNA molecules. Dissociation of PEC was investigated by the addition of low molecular weight electrolytes. The added small molecular salts dissociate the PEC, inducing DNA to release. The ability of Mg²⁺ to dissociate PEC is greater compared to that of Na⁺ and K⁺. From AFM images, it can be visualized that DNA remains intact and undamaged due to the protection from DNase offered by alkylated chitosan. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3391–3395, 2001     

Development of gelatin/chitosan/PVA hydrogels: Thermal stability,water state,viscoelasticity, and cytotoxicity assays

Gelatin/chitosan/poly(vinyl alcohol) (PVA) hydrogels were fabricated with different polymer ratio using the freeze-drying process. The thermal stability, water state, rheological, and cytotoxic properties of the hydrogels were evaluated. Thermogravimetric/differential scanning calorimetry analyses showed a decomposition onset temperature below 242.7 ± 2.7 °C. The samples did not show statistical differences (p < 0.05) on the onset temperature values. Nonfreezing water reached a constant value around of 1 g water/g polymer. Freezing water increased linearly with the increase of the water content independently of the polymer ratio. The hydrogels showed an equilibrium water content from 9 to 13 times their mass. The hydrogels exhibited a solid-viscoelastic behavior. The elastic modulus was higher with the increase of chitosan concentration (G′ = 22 170 ± 85 Pa) independently of the temperature (5–55 °C). In vitro assay showed that hydrogels are nontoxic in the HT29-MTX-E12 cell line. These results indicate that the gelatin/chitosan/PVA hydrogels could be considered for biomedical applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47149.     

Grafting of poly(3‐hydroxyalkanoate) and linoleic acid onto chitosan

Poly(3‐hydroxy octanoate) (PHO), poly(3‐hydroxy butyrate‐co‐3‐hydroxyvalerate) (PHBV), and linoleic acid were grafted onto chitosan via condensation reactions between carboxylic acids and amine groups. Unreacted PHAs and linoleic acid were eliminated via chloroform extraction and for elimination of unreacted chitosan were used 2 wt % of HOAc solution. The pure chitosan graft copolymers were isolated and then characterized by FTIR, ¹³C‐NMR (in solid state), DSC, and TGA. Microbial polyester percentage grafted onto chitosan backbone was varying from 7 to 52 wt % as a function of molecular weight of PHAs, namely as a function of steric effect. Solubility tests were also performed. Graft copolymers were soluble, partially soluble or insoluble in 2 wt % of HOAc depending on the amount of free primary amine groups on chitosan backbone or degree of grafting percent. Thermal analysis of PHO‐g‐Chitosan graft copolymers indicated that the plastizer effect of PHO by means that they showed melting transitions T_ms at 80, 100, and 113°C or a broad T_ms between 60.5–124.5°C and 75–125°C while pure chitosan showed a sharp T_m at 123°C. In comparison of the solubility and thermal properties of graft copolymers, linoleic acid derivatives of chitosan were used. Thus, the grafting of poly(3‐hydroxyalkanoate) and linoleic acid onto chitosan decrease the thermal stability of chitosan backbone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:81–89, 2007     

Design of robust and photoluminescence‐responsive materials based on poly(methacrylic acid‐co‐m‐phenylenediamine) with graphene oxide composite hydrogels and its adsorption

A promising strategy to design crosslinked photoluminescent hydrogel (PL hydrogel) is to synthesize the covalently bonded polymer chains by thermal polymerization. A proper ratio of methacrylic acid and m‐phenylenediamine was used to prepare the PL hydrogel, and doping with graphene oxide and carboxymethyl chitosan improves the structure of the gel. The green and efficient hydrothermal synthesis realized a high polymerization and a short reaction time. Meanwhile, a series of properties were investigated for several combinations of hydrogels. Ultraviolet spectra, fluorescence spectra, and particle size distributions were used to characterize the PL composites. Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, thermogravimetric analysis, rheological studies, and stress–strain tests were conducted to characterize the morphology, structure, and performance of the compound hydrogel. The adsorption properties of the PL hydrogel were characterized in adsorption tests. The results indicated that the PL hydrogel exhibited a favorable luminescence property, a certain degree of mechanical strength, and good adsorption performance. The prepared PL hydrogel has potential applications in adsorption and visual detection. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46354.     

Medicated wound dressings based on poly(vinyl alcohol)/poly(N‐vinyl pyrrolidone)/chitosan hydrogels

Poly(vinyl alcohol)/poly(N‐vinyl pyrrolidone) (PVP)/chitosan hydrogels were prepared by a low‐temperature treatment and subsequent ⁶⁰Co γ‐ray irradiation and then were medicated with ciprofloxacin lactate (an antibiotic) and chitosan oligomer (molecular weight = 3000 g/mol). The gel content, swelling ratio, tensile strength, and crystallinity of the hydrogels were determined. The effects of the chitosan molecular weight, the low‐temperature treatment procedure, and the radiation dosage on the hydrogel properties were examined. The molecular weight of chitosan was lowered by the irradiation, but its basic polysaccharide structure was not destroyed. Repeating the low‐temperature treatment and γ‐ray irradiation caused effective physical crosslinking and chemical crosslinking, respectively, and contributed to the mechanical strength of the final hydrogels. The incorporation of PVP and chitosan resulted in a significant improvement in the equilibrium swelling ratio and elongation ratio of the prepared hydrogels. The ciprofloxacin lactate and chitosan oligomer were soaked into the hydrogels. Their in vitro release behaviors were examined, and they were found to follow diffusion‐controlled kinetics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2453–2463, 2006     

Use of rheological compatibility criteria to study SBS modified asphalts

Polymer‐modified asphalts (PMAs) were prepared using Bachaquero asphalt and styrene–butadiene–styrene (SBS) type copolymers. Their rheological behavior was compared to that of unmodified asphalt and of a compatible commercial PMA. Materials were submitted to frequency sweeps between 10^?1 and 10² rad/s from 0 to 50°C. Storage stability tests were performed for 72 h at 160°C. Ring and ball softening points from the top and the bottom of the blends were compared and were used along with fluorescence microscopy to evaluate stability. Samples prepared with styrene–ethylene–butylene–styrene (SEBS) showed improved compatibility and stability as compared with SBS‐modified asphalts, probably because of a higher stability to thermal degradation from the absence of double bonds. An additional improvement in stability and compatibility was observed for SEBS functionalized with maleic anhydride (SEBS‐g‐MAH)–modified blends. Better compatibility, however, did not improve rheological behavior at low temperatures. The systems studied are so complex from a chemical point of view that the rheological criteria normally used to predict compatibility of polyblends did not give enough information regarding the compatibility of the modified asphalts. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1772–1782, 2003     

Swelling behavior of polyelectrolyte complex hydrogels composed of chitosan and hyaluronic acid

Polyelectrolyte complex (PEC) hydrogels composed of various weight ratios of chitosan and hyaluronic acid were prepared. The PEC hydrogels were formed by the reaction of the oppositely charged chitosan polymers. The PEC films swelled in water rapidly, reaching equilibrium within 30 min, and exhibited relatively high swelling ratios, 243–322%, at 25°C. The swelling ratio increased with increasing temperature. The transport phenomena of all PEC samples were non‐Fickian and diffusion and relaxation controlled. The diffusion coefficients of the PEC films ranged from 2.22 × 10^?6 to 10.05 × 10^?6 cm²/s. The activation energy of the polyelectrolyte complexes ranged from 37.14 to 54.58 kJ/mol and proved to be hydrophilic. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1097–1101, 2004     

Preparation and characterization of methoxy‐poly(ethylene glycol) side chain grafted onto chitosan as a wound dressing film

Chitosan has received extensive attention as a biomedical material; however, the poor solubility of chitosan is the major limiting factor in its utilization. In this study, chitosan‐based biomaterials with improved aqueous solubility were synthesized. Two molecular weights (750 Da and 2000 Da) of methoxypoly(ethylene glycol) (mPEG) were grafted onto chitosan (mPEG‐g‐chitosan) to form a ～100‐μm‐thick plastic film as a wound dressing. The chemical structures of the mPEG‐g‐chitosan copolymers were confirmed using Fourier transform infrared spectroscopy (FTIR), and the thermal properties were characterized using thermogravimetry analysis (TGA). Their microstructures were observed using scanning electron microscopy (SEM). The other properties were analyzed via the swelling ratio, tensile strength, elongation, and water vapor transmission rate (WVTR). Biocompatibility evaluations through biodegradability, cytotoxicity, and antimicrobial effect studies were also performed. The obtained mPEG‐g‐chitosan copolymers were soluble in slightly acidic aqueous solutions (pH～6.5) at a concentration of 10 wt %. The optimal mPEG‐g‐chitosan hydrogels had swelling ratios greater than 100% and WVTRs greater than 2000 g/m²/day. Their performance against Staphylococcus aureus will be subjected to further improvements with respect to medical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42340.     

Novel bioresorbable hydrogels prepared from chitosan‐graft‐polylactide copolymers

A series of biodegradable chitosan‐graft‐polylactide (CS‐g‐PLA) copolymers were prepared by grafting of poly(L ‐lactide) (PLLA) or poly(D ‐lactide) (PDLA) precursor to the backbone of chitosan using N,N′‐carbonyldiimidazole as coupling agent. The composition of the copolymers was varied by adjusting the chain length of PLA as well as the ratio of chitosan to PLA. The copolymers synthesized via this ‘graft‐onto’ method present interesting properties as shown by NMR and infrared spectroscopy, gel permeation chromatography and solubility tests. Hydrogels were prepared by mixing water‐soluble CS‐g‐PLLA and CS‐g‐PDLA solutions. Gelation was assigned to stereocomplexation between PLLA and PDLA blocks as evidenced by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. Thymopentin (TP5) was taken as a model drug to evaluate the potential of these CS‐g‐PLA hydrogels as drug carriers. An initial burst and a final release up to 82% of TP5 were observed from high‐performance liquid chromatography analysis. Copyright © 2011 Society of Chemical Industry     

Viscoelastic sol–gel state of the chitosan and alginate solution mixture

The rheological behavior of chitosan/alginate solutions was investigated in relation to gelation and polyelectrolyte complex (PEC) formation. Before mixing, the chitosan and the alginate solutions were both homogeneous fluids. However, heterogeneity developed after mixing, accompanied by a serious increase of viscosity. To determine the sol–gel state of the solutions, the viscoelastic variables, such as the dynamic storage modulus (G′) and loss modulus (G″), the loss tangent, and the viscoelastic exponents for G′ and G″, were obtained. Depending on the concentration, the chitosan/alginate solutions revealed unexpected rheological behavior. At a polymer concentration of 1.0 wt %, the chitosan/alginate solution was in a viscoelastic gel state, whereas, at higher concentrations, viscoelastic sol properties were dominant. A viscoelastic gel state for the chitosan/alginate solution was induced based on the weak formation of fiber‐shaped precipitates of a PEC at a low polymer concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1408–1414, 2007     

Genipin‐cross‐linked chitosan‐based hydrogels: Reaction kinetics and structure‐related characteristics

The main aim of this work is the synthesis and characterization of cross‐linked chitosan systems. Chitosan hydrogels can be prepared by physical or chemical cross‐linking of polymer chains. Chemical cross‐linking, leading to the creation of hydrogel networks possessing improved mechanical properties and chemical stability, can be achieved using either synthetic agents or natural‐based agents. In this work, the cross‐linker Genipin, a naturally derived compound, was selected because of the lower acute toxicity compared to many other commonly used synthetic cross‐linking reagents. In particular, the chemical stabilization of chitosan through genipin cross‐linking molecules was performed and characterized by calorimetric analyses (differential scanning calorimetry), swelling measurements in different pHs, and ionic strength. The reaction kinetics was carried out by means of rheological measurements, and both the activation energy (E_a) and the reaction order (m) were calculated. The hydrogel analyses were carried out at different concentrations of genipin (GN1 and GN2). The results were used to evaluate the possibility to use the chemical cross‐linked chitosan–genipin hydrogel for biomedical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42256.     

Thermal and rheological properties of poly(vinyl alcohol) and water‐soluble chitosan hydrogels prepared by a combination of γ‐ray irradiation and freeze thawing

Poly(vinyl alcohol) (PVA)/water‐soluble chitosan (ws‐chitosan) hydrogels were prepared by a combination of γ‐irradiation and freeze thawing. The thermal and rheological properties of these hydrogels were compared with those of hydrogels prepared by pure irradiation and pure freeze thawing. Irradiation reduced the crystallinity of PVA, whereas freeze thawing increased it. Hydrogels made by freeze thawing followed by irradiation had higher degrees of crystallinity and higher melting temperatures than those made by irradiation followed by freeze thawing. ws‐Chitosan disrupted the ordered association of PVA molecules and decreased the thermal stability of both physical blends and hydrogels. All the hydrogels showed shear‐thinning behavior in the frequency range of 0.2–100 rad/s. Hydrogels made by freeze thawing dissolved into sol solutions at about 80°C, whereas those made by irradiation showed no temperature dependence up to 100°C. The chemical crosslinking density of the hydrogels made by irradiation followed by freeze thawing was much greater than that of hydrogels made by freeze thawing followed by irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

pH‐ and thermal characteristics of graft hydrogels based on chitosan and poly(dimethylsiloxane)

Graft copolymerization of epoxy‐terminated poly(dimethylsiloxane) (PDMS) onto chitosan was reacted without using a catalyst. pH‐sensitive hydrogels were obtained that are based on two different components: a natural polymer and a synthetic polymer. These PDMS substitutents provide the basis for hydrophobic interactions that contribute to the formation of hydrogels. Various graft hydrogels were prepared from different weight ratios of chitosan and PDMS. Swelling behavior of these hydrogels was studied by immersion of the gels in various buffer solution. Photocrosslinked hydrogels exhibited a high equilibrium water content (EWC). Particularly, the sample CP31 of the highest chitosan–PDMS weight ratio showed the highest EWC in time‐dependent, temperature‐dependent, and pH‐dependent swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2661–2666, 2002     

Thiolated chitosans: In vitro comparison of mucoadhesive properties

The aim of this study was to compare the mucoadhesive properties of thiolated chitosans with regard to their molecular mass and type of immobilized thiol ligand. Mediated by a carbodiimide, aromatic‐ and aliphatic‐thiol‐bearing compounds were covalently attached to low‐ and medium‐molecular‐mass chitosan. All synthesized conjugates displayed on average 320 ± 50 μmol of immobilized free thiol groups per gram of polymer. The rheological synergy was observed by the mixture of equal volumes of polymer with mucin solution. Because of the increase in viscosity of the conjugate/mucin mixture, the self‐crosslinking properties and the interaction of thiomers with the mucus layer could be confirmed. Further mucoadhesion of the chitosan conjugates was evaluated in vitro with the rotating cylinder method and tensile studies on excised porcine intestinal mucosa. The results show a significantly enhanced residence time (p < 0.05) on the mucosa of all thiolated chitosans compared to the unmodified polymer. Among all of the conjugates tested, the following rank order of mucoadhesion could be determined: Chitosan–thiobutylamidine > Chitosan–4‐mercaptobenzoic acid > Chitosan–glutathione > Chitosan–6‐mercaptonicotinic acid > Chitosan–N‐acetyl cysteine > Chitosan–thioglycolic acid > Unmodified chitosan. The charge, pK_a, and reactivity of the attached compounds were found to be important factors influencing the mucoadhesive potential of the polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Swelling characteristics and in vitro drug release study with pH‐ and thermally sensitive hydrogels based on modified chitosan

The grafting of a poly(ethylene glycol) diacrylate macromer onto a chitosan backbone was carried out with different macromer concentrations. The grafting was achieved by (NH₄)₂Ce(NO₃)₆‐induced free‐radical poly merization. Biodegradable, pH‐ and thermally responsive hydrogels of poly(ethylene glycol)‐g‐chitosan crosslinked with a lower amount of glutaraldehyde were prepared for controlled drug release studies. Both the graft copolymers and the hydrogels were characterized with Fourier transform infrared, elemental analysis, and scanning electron microscopy. The obtained hydrogels were subjected to equilibrium swelling studies at different temperatures (25, 37, and 45°C) in buffer solutions of pHs 2.1 and 7.4 (similar to those of gastric and intestinal fluids, respectively). 5‐Fluorouracil was entrapped in these hydrogels, and equilibrium swelling studies were carried out for the drug‐entrapped gels at pHs 2.1 and 7.4 and 37°C. The in vitro release profile of the drug was established at 37°C and pHs 2.1 and 7.4. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 977–985, 2006     

Effective removal of a cobalt‐tetrasulfonated phthalocyanine dye from an aqueous solution with a novel modified chitosan‐based superabsorbent hydrogel

Industrial wastewaters from the Merox process are heavily polluted by toxic cobalt‐tetrasulfonated phthalocyanine (CoTsPc) dye catalyst, and in this article, we describe the synthesis of novel chitosan hydrogels and their adsorption capabilities against CoTsPc as biosorbents. In this study, novel chitosan hydrogels were crosslinked by 3,3′,4,4′‐tetracarboxybenzophenone dianhydride and used for the first time. The adsorption capacities of the hydrogels were significantly improved, and they exhibited excellent sorption behavior with ammonium sulfate modification. The adsorption behavior was observed to be pH dependent, and the optimum pH was found to be 8. Moreover, the swelling studies indicated that the hydrogels are superabsorbent. The reusability of these dye‐adsorbent hydrogels was also evaluated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46167.     

Polydimethylsiloxane-modified chitosan I. Synthesis and structural characterisation of graft and crosslinked copolymers

Graft and crosslinked polydimethylsiloxane (PDMS)-chitosan copolymers were prepared through the reaction between mono and difunctional glycidoxypropyl-terminated PDMSs and chitosan. The transformation of amino groups of chitosan through the reaction with epoxy groups was confirmed by FT-IR and ¹³C cross-polarization (CP) magic-angle spinning (MAS)-NMR analysis. Chitosan-based materials modified with about 40% and 60% hydrophobic polydimethylsiloxane were obtained, respectively. As proved by wide angle X-ray analysis, the crystallinity of chitosan was strongly decreased through the incorporation of PDMS sequences. However, both graft and crosslinked copolymers still present a partial crystalline structure. Their X-ray patterns are not only different as compared to chitosan but also as compared to each other. For the graft copolymer, three diffraction peaks were observed at 2θ = 8.4°, 11.2° and 21.2°, indicating the formation of a new partially crystalline phase and the modification of the interplanar distances for the phases similar to chitosan. The crosslinked copolymer is even less crystalline, the peak around 2θ = 20° being strongly decreased. Different thermal behaviour of siloxane modified chitosan was registered for graft and crosslinked copolymers; the graft sample is less stable than chitosan, while the crosslinked copolymer showed an intermediate stability between chitosan and polydimethylsiloxane precursors.     

Poly(2‐hydroxyethyl methacrylate)/boric acid composite hydrogel as soft contact lens material: Thermal,optical, rheological,and enhanced antibacterial properties

The present work proposes to fabricate a composite hydrogel material that well characterized, transparent, biocompatible, and self‐antibacterial as potential soft contact lens material. For this purpose, poly(2‐hydroxyethyl methacrylate) (PHEMA)/boric acid (BA) composite hydrogels were successfully prepared by chemical crosslinking with BA through in situ polymerization using different BA ratios between 1 and 10% w/w. Afterward, the compositions, thermal stability, transparence, oxygen permeability, water uptake capacity, swelling ratio as well as morphological and rheological properties, in vitro degradability, in vitro cytotoxicity, and antibacterial properties of the all prepared materials were analyzed using a series of different techniques. The thermal stability, hydrophilicity, water uptake, oxygen permeability gradually increased depending ratio of BA, which is desirable for biomaterial. While the transparence and refractive index decreased, the composite hydrogels, except for BA content of 10 wt %, maintained enough transparency to be used for contact lens. In addition, PHEMA/BA composite hydrogels exhibited good cytocompatibility (PHEMA‐1%BA and PHEMA‐3%BA) and excellent antibacterial activity against Gram‐positive (Staphylococcus aureus and Enterococcus faecium) and Gram‐negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Overall, the results demonstrated that the obtained PHEMA/BA composite hydrogels could be considered as self‐antibacterial contact lens and a potential composite biomaterial for other applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46575.     

Determination of the competitive adsorption of heavy metal ions on poly(n‐vinyl‐2‐pyrrolidone/acrylic acid) hydrogels by differential pulse polarography

Poly(N‐vinyl‐2‐pyrrolidone) and poly(N‐vinyl‐2‐pyrrolidone/acrylic acid) hydrogels were prepared by gamma irradiation for the removal of heavy metal ions (i.e., lead, copper, zinc, and cadmium) from aqueous solutions containing different amounts of these ions (2.5–10 mg/L) and at different pH values (1–13). The observed affinity order in adsorption of these metal ions on the hydrogels was Zn(II) > Pb(II) > Cu(II) > Cd(II) under competitive conditions. The optimal pH range for the heavy metal ions was from 7 to 9. The adsorption of the heavy metal ions decreased with increasing temperature in both water and synthetic seawater conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2013–2018, 2003     

Star‐shaped polycaprolactone/chitosan composite hydrogels: fabrication and characterization

Star‐shaped polycaprolactone (stPCL)/chitosan composite hydrogel was fabricated by simply melt/solution blending between chitosan/dicarboxylic acid solution and melted stPCL, using 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and N‐hydroxysuccinimide as conjugating agents to obtain a composite hydrogel. Here, stPCL and modified stPCL were investigated. The stPCL was modified to have a carboxyl‐terminated chain (stPCL‐COOH). The composite hydrogels were transparent. The network structure of the composite hydrogels was investigated. stPCL‐OH had no chemical bond to the chitosan network but stPCL‐COOH could co‐crosslink with the chitosan network. The porous structure and porosity of the composite hydrogels were similar to those of chitosan hydrogel. However, the hydrophobicity of stPCL resulted in a lower swelling ratio compared to chitosan hydrogel. The rheological analysis of the composite hydrogel exhibited a stable crosslinked network. Compression testing of the composite hydrogel obtained from stPCL‐COOH at a mole ratio of stPCL‐COOH and chitosan of 1:1 had optimum compressive mechanical properties comparable to chitosan hydrogel due to a synergistic effect of the flexibility in stPCL and the co‐crosslinking of stPCL‐COOH with the chitosan network. © 2020 Society of Chemical Industry