Preparation and Characterization of Hydrocolloid Biopolymer-Based Films for Dressing Applications

In this study three types of dressings in the form of thin films were prepared from a mixture of two natural biopolymers, namely gelatin and pectin. The protein and the polysaccharide were chosen because of their hydrosolubility and interactivity, respectively. Glutaraldehyde was also used to crosslink the films.

The physical properties of the resulting films were evaluated through measurements of absorption capacity and water vapor permeability. FTIR and UV spectroscopy were also used to characterize the films.

It was found that crosslinking much increased the absorption capacity, reflecting the strong interactions that developed between gelatin and pectin. It was also found that the water vapor permeability depends greatly on the film thickness and evolves linearly with time.

The FTIR analysis also allowed us to identify the different functional groups through which gelatin and pectin chemically interacted. The quantitative analysis of the residue by means of UV spectroscopy indicated that the films were biodegradable and therefore can be used for biomedical applications.     

Crosslinking structures of gelatin hydrogels crosslinked with genipin or a water‐soluble carbodiimide

It was suggested in our previous studies that carbodiimide‐ and genipin‐crosslinked gelatin hydrogels could be used as bioadhesives to overcome the cytotoxicity problem associated with formaldehyde‐crosslinked gelatin hydrogels. In this study, we investigated the crosslinking structures of carbodiimide‐ and genipin‐crosslinked gelatin hydrogels. We found that crosslinking gelatin hydrogels with carbodiimide or genipin could produce distinct crosslinking structures because of the differences in their crosslinking types. Carbodiimide could form intramolecular crosslinks within a gelatin molecule or short‐range intermolecular crosslinks between two adjacent gelatin molecules. On the basis of gel permeation chromatography, we found that the polymerization of genipin molecules could occur under the conditions used in crosslinking gelatin hydrogels via a possible aldol condensation. Therefore, besides intramolecular and short‐range intermolecular crosslinks, additional long‐range intermolecular crosslinks could be introduced into genipin‐crosslinked gelatin hydrogels. Crosslinking a gelatin hydrogel with carbodiimide was more rapid than crosslinking with genipin. Therefore, the gelation time for the carbodiimide‐crosslinked gelatin hydrogels was significantly shorter than that of the genipin‐crosslinked gelatin hydrogels. However, the cohesive (interconnected) structure of the carbodiimide‐crosslinked gelatin hydrogels was readily broken because, unlike the genipin‐crosslinked gelatin hydrogels, there were simply intramolecular and short‐range intermolecular crosslinks present in the carbodiimide‐crosslinked hydrogel. In the cytotoxicity study, the carbodiimide‐crosslinked gelatin hydrogels were dissolved into small fragments in the cultural medium within 10 min. In contrast, the genipin‐crosslinked gelatin hydrogels remained intact in the medium throughout the entire course of the study. Again, this may be attributed to the differences in their crosslinking structures. The genipin‐crosslinked gelatin hydrogels were less cytotoxic than the carbodiimide‐crosslinked gelatin hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4017–4026, 2004     

Tensile properties,barrier properties,and biodegradation in soil of compression—Molded gelatin‐dialdehyde starch films

Glycerol (Gly)‐plasticized gelatin (Ge) films crosslinked with dialdehyde starch (DAS) as environmentally friendly crosslinking agent were successfully produced by compression molding, demonstrating the capacity of gelatin of being transformed into films by using thermoplastic processes. The effect of DAS content on the color, light transmission, total soluble matter (TSM), water uptake (WU), water vapor permeability (WVP), oxygen permeability (OP) as well as biodegradability during soil burial was investigated. The addition of up to 10 wt % DAS (Ge‐10DAS) generated transparent films, with reduced TMS, WU, WVP, and OP values but higher extensivity than the uncrosslinked counterpart. Further incorporating DAS into plasticized‐gelatin matrix conducted to phase separation with detrimental effect of transparency and tensile properties. DAS‐containing films degraded at slow rate than the uncrosslinked counterpart, suggesting that biotic attack during soil burial is restricted by covalent crosslinking points induced by DAS. Ge‐10DAS films lost about 28% of their initial mass within the first 8 days of exposure to degrading medium; therefore, the material can be classified as rapidly degradable. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of pH-sensitive and antibacterial gelatin/citric acid/Ag nanocomposite hydrogels with potential for biomedical applications

This work aimed to prepare pH-sensitive and antibacterial drug releasing systems through a completely green route. To achieve this, the gelatin natural biopolymer was crosslinked with citric acid in the presence of Ag nanoparticles (NPs). Interestingly, Ag NPs formation and gelatin crosslinking were simultaneously occurred during annealing of samples without need for any toxic chemicals, which were confirmed by FTIR, UV-vis spectra, SEM and TEM observations. In addition, potential of the citric acid crosslinked-gelatin/Ag nanocomposite hydrogels was successfully explored for drug delivery applications using cefixime as a model drug. It was found that these hydrogels have pH-dependent swelling and drug release behavior with higher drug release at pH 7.4 compared to pH 1.2. Also, an antibacterial effect against the E. coli and S. aureus microorganisms was achieved by incorporation of Ag NPs into hydrogels. These hydrogels can be considered as stimuli responsive materials for oral drug delivery and wound dressing applications.     

Rheological Behavior of Polycarbosilane Part II: Effect of Heterometal (Al) Content and Nature of Bonding with Si of Polycarbosilane

A few aluminum containing polycarbosilanes named AlOR-PCS and Alac-PCS have been synthesized by the reaction of aluminum isopropoxide (AlOR) and aluminum acetylacetonate (Alac) with polycarbosilane (PCS), respectively. These materials were characterized by Fourier Transform Spectroscopy (FTIR), Thermo gravimetric Analysis (TGA) and Gel Permeation Chromatography (GPC). The rheological properties of these compounds were studied with respect to time, temperature and atmosphere (inert & air). It has been observed that the increase in metal content enhances the crosslinking of the PCS chains. Under similar conditions, the crosslinking of AlOR-PCS derivatives was found slower than Alac-PCS. GPC analysis of the samples showed the increase in molecular weight of these compounds compared to virgin PCS. TGA showed improved ceramic yield with increasing metal content. Alac-PCS gave higher ceramic yield than AlOR-PCS for similar molar ratios of metal complexes.     

Performance of silane-coupling agent-treated hydroxyapatite/diethylene glycol-based pH-sensitive biocomposite hydrogels

Hydrogels are three-dimensional polymeric networks with segments of hydrophilic groups. Stimuli-responsive hydrogels have played attractive role toward much research due to slight modification of environment by abrupt changes in swelling behavior. In this study, a series of pH-sensitive biocomposite hydrogels were acquired through solvent-free green approach by utilization of diethylene glycol (DEG), citric acid (CA), acrylic acid (AA) and hydroxyapatite (HA). Incorporation of hydroxyapatite (HA) prepared from waste eggshells with ACD resulted in the biocomposite hydrogel (ACD–HA). The synthesized biocomposite hydrogel was examined by various characterization techniques, viz., spectral (FTIR), powder X-ray diffraction (XRD) technique, thermal (TGA and DTG), morphological (SEM) and swelling equilibrium studies. In addition, HA was surface treated with two different silane-based coupling agents, namely 3-aminopropyltrimethoxysilane (AMS) and vinyltriethoxysilane (VES) on the performance properties of biocomposite hydrogels. The results of the studies revealed that VES-treated ACD–HA had superior properties than AMS-treated ACD–HA and untreated ACD–HA on overall properties of biocomposite hydrogels. Hence, the decreasing order of swelling equilibrium behavior in various pH, viz., 4.0, 6.0, 7.4, 8.0, 10.0, has been listed as ACD–HA–VES > ACD–HA–AMS > ACD–HA > ACD. The observations indicated that hydrogels’ adaptability with pH-tuned properties may have greater potential in eco-friendly approaches such as metal ion removal, dye removal and agrochemical release.     

Separation of Uranyl Ions on Starch-Based Functional Hydrogels: Mechanism and Kinetics

In this article, we report the mechanism and kinetics of adsorption of uranyl ions on starch-based functional hydrogels. The hydrogels were prepared from starch in native or hydrolyzed/oxidized form by crosslinking with N,N-methylenebisacrylamide. The hydrogels synthesized from the oxidized starch have carboxylic groups at C-6 position. The effect of the structure and external environmental factors, i.e., contact time, temperature, ion strength, and simulated seawater (0.55 M NaCl and 3 mM NaHCO₃), was investigated on the uranyl adsorption behavior of hydrogels. The adsorption of uranyl ions was rapid as the highest adsorption was observed after 6 h and at 40°C. The sorbents also exhibited appreciable ion uptake even from the simulated seawater. The equilibrium data was analyzed using Langmuir and Freundlich adsorption isotherms and pseudo-first order and pseudo-second order kinetic models. Evidence of adsorption was obtained by characterization of the uranyl ions-loaded hydrogels by FTIR spectroscopy and also by elution with 0.1 N HCl.     

Physical and mechanical properties of highly plasticized pectin/starch films

Blends of citrus pectin and high amylose starch plasticized with glycerine were investigated to determine the effect of compositional variables on film properties. Several films with representative compositions were made from sugar beet and almond pectin, and tested for comparison. The films were cast from water onto glass plates, dried, and removed. Mechanical analysis was done using a Rheometrics RSA II solids analyzer. Increasing the glycerine concentration led to decreases in static modulus, dynamic modulus, and tensile strength, but to increases in elongation. Increasing levels of starch in the blend lowered the effect of glycerine on mechanical properties. Oxygen permeability of the films was extremely low. Sugar-beet pectin and almond pectin gave films with mechanical properties comparable to those made with citrus pectin. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Dissolution and Enzymatic Degradation Studies Before and After Artificial Ageing of Silk‐ or Linen‐Reinforced Gelatin Laminates, 2

Biodegradable laminates based on gelatin and on gelatin/starch blend reinforced with fabrics (silk or linen) were prepared by melt pressing. Due to crosslinking during the thermal treatment and in some cases, to additional crosslinking with methylenedi(p‐phenyl) diisocyanate, the fresh and artificially aged samples demonstrated improved mechanical properties, as reported previously. In Part 1 of this study on the environmental behavior of these new laminated composites, the simple dissolution in a buffer solution or water of fresh and artificially aged samples was considered. During this treatment soluble, i.e., uncrosslinked molecules were removed leaving a product resulting from addition reactions and consequent crosslinking. These processes take place during the melt pressing at 180 °C and cause a decreased solubility of gelatin. The present Part 2 deals with the enzymatic treatment of the same samples. We have implicitly shown that the gelatin moiety of the laminates undergoes proteolysis and that this process depends on the laminate composition. At the end of the treatment the enzymatic buffer solution contains only peptides and virtually no high‐molecular gelatin. The degrees of degradation vs. time dependencies differ for water and enzymatic treatment of the samples, indicating different processes in either treatment. The time‐course curves of the enzymatic treatment of different laminates and the kinetic parameters derived therefrom were analyzed. Thereby the effect of many factors on the accessibility of the gelatin moiety to proteolysis was shown. These factors are: temperature treatment, artificial ageing, the nature of the reinforcing fabrics, the “additional” crosslinking with methylenedi(p‐phenyl) diisocyanate, etc. The gelatin‐linen laminate is the most sensitive to crosslinking. There is a tendency that the crosslinking smears the differences in the time‐course of the absorption behavior curves of the different samples.

Degree of degradation, β′, (related to only the gelatin) vs. time, t, for laminates: (a) uncrosslinked gelatin‐linen; (b) crosslinked gelatin‐linen; (c) uncrosslinked gelatin‐silk; (d) crosslinked gelatin‐silk.     

Synthesis of hybrid crosslinked polyphosphazenes and investigation of their properties

Novel organic/inorganic hybrid polyphosphazenes were prepared by free radical UV copolymerization of linear polyphosphazenes and vinyl monomers. In this work, linear polyphosphazenes grafted by allyl amino and n-butylamino groups have been synthesized via nucleophilic substitution reaction at an anhydrous and anaerobic atmosphere. By regulating the molar ratio of allyl amino and n-butylamino groups, five different linear polyphosphazenes were prepared. The hybrid polyphosphazenes have been crosslinked using the linear polyphosphazenes and vinyl monomers including styrene, methyl methacrylate, and lauryl methacrylate as intermediates via free radical UV copolymerization. By changing the quantity of vinyl monomers participating in the crosslinking reaction, series of hybrid polyphosphazene membranes were obtained. The linear polyphosphazenes have been characterized by Nuclear magnetic resonance, Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Differential scanning calorimeter, Dynamic mechanical analyzer and Drop Shape Analysis (DSA). The hybrid polyphosphazenes have also been studied via FTIR, TGA and DSA. The test results proved that the linear polymers were successfully synthesized. Moreover, the water contact angles showed that the hybrid crosslinked polyphosphazenes had a better hydrophobicity and thermal stability than the linear polyphosphazenes and the hydrophobicity of hybrid membranes have a regular changing tendency with the quantities of UV-monomers and ratio of allylamino. The initial decomposition temperatures of the hybrid polymers also had a regular change due to the difference and quantities of vinyl monomers.     

Identification and quantification of cholesterol oxides in grated cheese and bleached butteroil

Butteroil samples bleached with benzoyl peroxide (BP) and 17 commercial cheeses were screened for oxidized sterols by thin layer chromatography (TLC). Ungrated cheeses made from bleached milk and freshly bleached butteroil contained no detectable oxidized sterols. Oxidized sterols were detected in stored, bleached butteroils and in grated cheeses. Four major oxidation products were the isomeric 5,6-epoxycholesterols and the epimeric 7-hydroxycholesterols identified by TLC, high performance liquid chromatography (HPLC) and mass spectrometry (MS). Additional sterol oxides (tentatively identified and not quantified) present in these samples included low levels of 7-ketocholesterol and cholesta-3,5-dien-7-one. The epimeric 7-hydroxycholesterols were detected in bleached butteroils stored in air (BP-A) and nitrogen (BP-N) for 22 days at 15 C. Butteroil, after 90 days of storage at 15 C, had 30 (BP-N) and 60 (BP-A) μg total oxides/g of bleached oil and, after 1-year at −20 C, had 70 (BP-N) and 180 (BP-A) μg/g butteroil. A grated, unbleached cheese packaged in clear glass contained the most oxidized sterols (44 μg/g). Sterol oxides were not detected in bleached cream using a simulated industrial process.     

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.     

Enhancing mechanical strength of hydrogels via IPN structure

In this investigation, polyacrylamide (PAAm) as the flexible network is introduced to enhance the mechanical strength of hyaluronic acid–gelatin (HA–Gel) hydrogels by interpenetrating polymer network (IPN). The structure, mechanical property, and rheology property of the IPN hydrogels are investigated. It is found that the compressive strength of the HA–Gel/PAAm IPN hydrogels has increased five times higher than that of HA–Gel hydrogels. Rheological test demonstrates that elastic moduli (G′) and viscous moduli (G″) of HA–Gel/PAAm IPN hydrogels increase 100 times higher than those of HA–Gel hydrogels. Moreover, the HA–Gel hydrogels are fractured under the low compressive stress, whereas HA–Gel/PAAm IPN hydrogels are not broken under the high compressive stress. It is envisioned that the IPN hydrogels will be an effective approach to enhance the mechanical strength and broaden the range of hydrogels' applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44503.     

Understanding the in situ crosslinked gelatin hydrogel

The present study focuses on an in‐depth investigation at the molecular level of in situ crosslinked gelatin hydrogel by oxidized carboxymethylcellulose (OCMC), intended for biomedical purposes. The crosslinking parameters, namely the crosslinking temperature, crosslinking time and the amount of crosslinker, were varied. The surface and bulk properties were investigated to construct a representative model postulating the interaction of gelatin and OCMC encompassing their physical and covalent linking which determines the properties of the hydrogel. It was inferred that covalent crosslinking facilitates the interfacial interaction between gelatin and OCMC which beyond 30% OCMC composition is impeded due to depletion: microdomain formation leading to phase separation. This study might enable the fabrication of tunable hydrogel with crosslinking parameters in accordance with its purpose. The preliminary biocompatibility studies of the hydrogel conclude that the crosslinked hydrogel generates favourable conditions for cells to adhere and proliferate showing potential for biomedical purposes. © 2015 Society of Chemical Industry     

Rapid and green functionalization of multi-walled carbon nanotubes by glucose: structural investigation and the preparation of dopamine-based poly(amide-imide) composites

Functionalization of multi-walled carbon nanotubes (MWCNTs) by glucose was performed through esterification reaction. The reaction was carried out in water, in the presence of N,N′-carbonyldiimidazole as a catalyst. Glucose-functionalized MWCNTs (MWCNTs-Gl) were characterized by a set of methods including Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning, and transmission electron microscopy. Thermogravimetric analysis (TGA) results also demonstrated the presence of organic portions of the functionalized MWCNTs. MWCNT-Gl/poly(amide-imide) (PAI) composite films with different MWCNTs-Gl content (5, 10, and 15 wt%) were prepared by ultrasonication-assisted solution blending method. Microscopic observations showed that the dispersion of the MWCNTs-Gl was improved by the organic groups on the MWCNT surface and functional groups on the PAI. TGA results showed that the hybrid films exhibited a good thermal stability. According to mechanical tensile tests, the tensile strength and the Young’s modulus of the MWCNT-Gl/PAI composites were increased with increasing MWCNTs-Gl content.     

A comparative study of grafting steps on the preparation and properties of modified nanosilica for UV-curable coatings

Nanosilica was modified and functionalized with acrylsilane by the “grafting to” method via different grafting steps, i.e., prepared-grafting step and step-wise propagation. The prepared-grafting step was achieved by grafting the nanosilica surface with the prepared acrylsilane, which was obtained by thiol-ene click reaction between 3-mercaptopropyl trimethoxysilane (MPTMS) and trimethylolpropane triacrylate (TMPTA). The step-wise propagation was achieved by first grafting MPTMS onto the nanosilica surface and then using the mercapto groups as initiators to react with TMPTA. The acrylsilane was characterized by FTIR. The modified nanosilica was characterized by FTIR, TGA, and contact angle analysis. It was demonstrated that the thiol-ene click reaction can easily occur between MPTMS and TMPTA. The grafting ratio of modified nanosilica via prepared-grafting step was higher than that of step-wise propagation. The SEM images of fractured films containing modified nanosilica also indicated that the former is more effective than the latter in reducing the self-aggregation of nanosilica. The effects of modified nanosilica on the viscosity and hardness of UV-curable coatings were also investigated.     

Release of fluorescent markers from phase‐separated gelatin‐maltodextrin hydrogels

Genipin‐crosslinked gelatin‐maltodextrin phase‐separated hydrogels consisting of gelatin‐continuous or bicontinuous microstructures were developed to regulate swelling and release behavior of four fluorescent markers of varying molecular weights [(fluorescein (332 Da) and FITC‐dextrans (FD) (4000–250,000 Da)]. Bicontinuous hydrogels showed significantly greater swelling than gelatin‐continuous hydrogels under all conditions (at pH 1.5 and 7.4 and three genipin/gelatin crosslinking ratios) (P < 0.05). With both microstructures, fluorescein showed the largest release rate and total release followed by FD 4000 Da, FD 40,000 Da, and FD 250,000 Da (P < 0.05). Marker molecular weight, pH, and crosslink ratio all affected the rate and amount of release. The mode of transport for the solvent and all markers was Fickian or slightly anomalous, with diffusional exponent (n) values ranging from 0.35 to 0.64. These results demonstrated that with the proper combination of crosslink density, solvent pH, and microstructure, hydrogels with a specified swelling behavior may be developed. This, coupled with a marker of appropriate size, can lead to controllable levels and rates of release. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and conformational study of novel,stable, helical poly(N-propargylamides) containing dipole azobenzene chromophores in the side chains

A series of novel N-propargylamides carrying dipole azobenzene chromophores were synthesized and polymerized with [Rh(nbd)Cl]₂ catalyst to obtain cis-transoid poly(N-propargylamides). The solubility, thermal stability and conformation of these polymers were also studied. The introduction of valeryl group increased the solubility of this kind of poly(N-propargylamides). All the polymers exhibited a good, thermal stability. CD and UV–Vis spectra showed that poly(N-propargylamide) (Poly(V_2b)) took a tight helical structure with predominantly one-handed screw sense. Poly(V_2b) exhibited a good stable helical structure at various temperatures (5–60 °C). It also maintained good helicity in polar solvent. The improved helix stability could be attributed to the enhanced hydrogen bonding strength and steric repulsion between the newly designed azobenzene groups. Furthermore, the electrostatic repulsion between the dipole azobenzene chromophores in the side chains improved the helix stability as well. The backbone of Poly(V_2b) still kept helical sense after the isomerization of trans-azobenzene to the cis form under UV irradiation.     

Low-methoxyl pectin–zeolite hydrogels controlling drug release promote in vitro wound healing

This study presents the design of novel hydrogel films, based on low-methoxyl (LM) pectin and NaA- or ZnA-zeolite particles, to serve as wound dressing materials with controlled drug delivery properties. We studied the effects of the preparation method of hydrogels, the amounts of crosslinker, drug and zeolite, and the type of cation in zeolites on the drug release mechanisms from the hydrogels. Ionic strengths of both film and external medium dictated the drug release behavior of the films, while the other parameters also played essential roles. NaA-zeolite hydrogels prepared using membrane diffusion controlled system, could reach a drug release ratio of 86% within 5 h. The drug-free hydrogels displayed no cytotoxicity while supporting cell proliferation and migration. Our cost-effective LM pectin–zeolite hydrogels promise to be effective wound dressing materials with controlled drug delivery ability, transparency, good swelling properties, ability to hold fluids, good oxygen transmission rate, and biocompatibility. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47640.     

Fabrication of superhydrophobic surfaces via poly(methyl methacrylate)-modified anodic aluminum oxide membrane

Superhydrophobic surfaces were prepared by poly(methyl methacrylate) (PMMA) or polystyrene (PS) modification on an optimized anodic aluminum oxide (AAO) honeycomb-like structure surface. The AAO membrane was initially etched in sodium hydroxide solution to get a hierarchical polygon-cavity structure in micro- and nano-scales, and then, it was coated with the polymer solution. The obtained polymer-modified AAO films show superhydrophobicity with water contact angles of larger than 150°. The intrinsic contact angles of the PMMA and PS are 68° and 94°, respectively. The morphology and components of the micro-/nano-structure were characterized by SEM and XPS, respectively, and the mechanism is discussed. This work provides a simple method to obtain superhydrophobic surfaces by common polymers without the need for low surface energy compounds.