Sunflower Oil and Protein-based Novel Bigels as Matrices for Drug Delivery Applications—Characterization and in vitro Antimicrobial Efficiency

The current study deals with the characterization of sunflower oil- and protein-based bigels for drug delivery applications. Span-40 was used as an organogelator for the preparation of bigels. The bigels were characterized by microscopy, XRD, thermal, texture studies and impedance spectroscopy. The microscopic studies revealed that the droplets were apolar in nature (organogels), while the continuum phase was polar in nature (protein hydrogel matrix). Incorporation of the proteins improved the stability of the bigels. The release of the drugs followed diffusion kinetics. The bigels showed good antimicrobial efficiency against E.coli and were cytocompatible in presence of L929 cells.     

Influence of Aqueous Matrices into Candelilla Wax Organogels Emulsions for Topical Applications

Emulgels and bigels are, respectively, partial and total gelified forms of emulsions that can increase stability and bring different permeation and diffusion properties for traditional oil and water mixtures. This work investigated the stability, rheological behavior, and microstructure of bigels and emulgels through a topical application perspective. Candelilla wax (CW)/sunflower oil (5/95) organogels or pure sunflower oil was used to obtain dilute (5% oily phase) and concentrated (40% oily phase) emulsions. It was used three different aqueous phases with each oily phase and oil load: water, sodium polyacrylate hydrogel, and modified starch hydrogel. Dilute emulsions showed better stability with sodium polyacrylate hydrogel forming oil-in-water bigels and emulgels while concentrated emulsions were stable only in water-in-oil emulgels. Thixotropy, network strength, and thermal stability were modulated by the oily phase and concentration used. Concentrated emulgels showed higher spreadability, but strong temperature-dependency. Diluted emulgels and bigels showed high hydrogel influence on stability and rheological properties observed. The results showed the potential of CW organogels to stabilize and modify sensory attributes in bigels and emulgels for topical applications.     

Development and characterization of gelatin‐based hydrogels,emulsion hydrogels,and bigels: A comparative study

This study was designed to examine the physicochemical and electrical properties of gelatin‐based hydrogels, emulgels, and bigels. The chemical studies suggested an increase in hydrogen bonding in the emulgel and bigel when sesame oil (SO; representative vegetable oil) and SO organogel (OG; representative OG) were incorporated within the gelatin matrix. The emulgel and bigel showed better mechanical properties and higher electrical impedances compared to the hydrogel. The hydrogel showed similar swelling at pH 1.2 and 7.2. The swelling of the emulgel and bigel was higher at pH 7.2. The formulations were found to be highly hemocompatible; this indicated their biocompatible nature. Ciprofloxacin, a model antimicrobial drug, was incorporated within the formulations. The release of the drug was found to be diffusion‐mediated. The antimicrobial efficiency of all of the drug‐loaded formulations was found to be equivalent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41502.     

A Novel Propolis Wax-Based Organogel: Effect of Oil Type on Its Formation,Crystal Structure and Thermal Properties

In this work, the potential application of propolis wax (PW) as a novel organogelator was investigated in different oils (canola, sesame, sunflower and flaxseed oil). PW at 2% (w/w) concentration produced a thick organogel at 5, 10 and 15 °C, with needle‐like crystals, suggesting that PW is a relatively efficient structuring agent for organogel formation. The oil binding capacity of the organogel with canola oil was lower than that of the other organogels, and the gelling time of flaxseed organogel with lower oil viscosity was shorter. The X‐ray diffraction measurements of the crystals showed β′‐form crystals, with no influence of oil type. In FTIR results, no chemical intermolecular interactions that were observed indicated physical bonds in the organogel network. DSC analysis was carried out to obtain greater insight into the thermal behavior of PW organogels. No significant differences were observed. The textural properties of PW organogels were stable over 30 days of storage. Flaxseed oil organogel had the greatest firmness and stickiness. These results showed the effect of oil viscosity on PW gel behavior.     

Thermo‐mechanical properties of candelilla wax and dotriacontane organogels in safflower oil

The thermo‐mechanical properties of organogels developed by a complex mixture of n‐alkanes present in candelilla wax (CW) were investigated and compared with the ones of organogels developed by a pure n‐alkane, dotriacontane (C₃₂). In both cases, the liquid phase used was safflower oil high in triolein (SFO) and the variables studied were two levels of gelator concentration (1 and 3%), cooling rates of 1 and 10 °C/min, and two gel setting temperatures, 5 and 25 °C (T_set). Based on comparisons of the organogels made with C₃₂, the presence of minor molecular components in CW had a profound effect on the crystal habit of the n‐alkanes in CW‐based organogels, and therefore on their physical properties. Thus, independent of the cooling rate and T_set, C₃₂ showed a higher solubility and higher self‐assembly capability in the SFO than CW. Nevertheless, for the same gelator concentration and time‐temperature conditions, C₃₂ organogels had lower G' profiles than CW organogels. Additionally, independent of the type of gelator, more stable organogel structures were developed at T_set = 5 °C and using the lower cooling rate. The rheological behavior of the organogels was explained considering the formation of a rotator phase by the n‐alkanes, its solid‐solid transition, and their dependence as a function of the cooling rate and T_set. The results here obtained showed that it is possible to gelate SFO through organogelation with CW and without the use of trans fats.     

Properties of biodegradable hydrogels prepared by γ irradiation of microbial poly(ϵ-lysine) aqueous solutions

Poly(?-lysine) (PL) hydrogels have been prepared by means of γ irradiation of PL produced by Streptomyces albulus in aqueous solutions. When the dosage of γ irradiation was 70 kGy or more and the concentration of PL in water was 1–7 wt %, transparent hydrogels (opaque hydrogels for 1–3 wt % PL concentration) could be produced. In the case of 70 kGy of γ irradiation and 5 wt % PL concentration, the specific water content (wt of absorbed water/wt of dry hydrogel) of the PL hydrogel was approximately 160. Specific water contents of PL hydrogels decreased markedly with an increase in the dosage of γ irradiation. The specific water contents were increased with an increase in PL concentration in the irradiated solution. This result indicates the presence of a radical scavenger in the PL solution. Swelling equilibria of PL hydrogels were measured in water or in aqueous solutions of various pHs or concentrations of NaCl, Na₂SO₄, and CaCl₂. Under acid conditions, the PL hydrogel swelled due to the ionic repulsion of the protonated amino groups in the PL molecules. The degree of deswelling in electrolyte solution was smaller than that of other ionic hydrogels [poly(γ-glutamic acid), poly(acrylic acid) etc.]. In addition, the enzymatic degradations of PL hydrogel were studied at 40°C and pH 7.0 in an aqueous solution of the neutral protease [Protease A (Amano)] produced from Aspergillus oryzae. The rate of enzymatic degradation of the respective PL hydrogels was much faster than the rate of simple hydrolytic degradation. The rate of enzymatic degradation decreased with the increase in γ-irradiation dose during preparation of the PL hydrogel. © 1995 John Wiley & Sons, Inc.     

Studies on the self‐assembly of neat DBS and DBS/PPG organogels

The self‐assembly behavior of neat 1,3:2,4‐dibenzylidene‐D ‐sorbitol (DBS) and DBS/poly(propylene glycol) (PPG) organogels has been investigated by scanning electron microscopy, polarizing optical microscopy, and rheological measurements. DBS molecules are capable of self‐organizing into fibrils and exhibit the birefringent spherulitic textures during cooling from the melt. On the other hand, DBS can self‐assemble into a fibrillar network in PPG to produce organogels. DBS/PPG organogels also reveal a spherulite‐like morphology. When a small amount of DBS is dispersed into a PPG matrix, we find that the spherulite sizes are much smaller than those of neat DBS. This is because the dilution of DBS causes DBS to self‐assemble in PPG at a lower temperature. Therefore, more nucleation sites and smaller spherulite sizes are found in the DBS/PPG organogel system. The rheological measurements demonstrate that the elastic modulus (G′) in DBS/PPG organogels increases as the DBS concentration increases. However, the increase in G′ is less obvious, as the DBS content exceeds 3 wt %. suggesting that the DBS networks become saturated. Also, it is found that these organogels require a certain period of time to reach thermodynamic equilibrium, depending on DBS concentrations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and Physical Properties of Organogels Developed by Sitosterol and Lecithin with Sunflower Oil

High linoleic acid sunflower oil (HLSO) with various sitosterol (Sit) to lecithin (Lec) mass ratios (i.e., 0:100–100:0) were used to develop organogels at two storage temperatures (T_s: 5 and 25 °C). The results showed that, at 25 °C, the hardness value of organogels obtained from HLSO with both Sit and Lec was higher than that of organogels developed from HLSO with only Sit or Lec. Microscopy revealed that the shapes of the crystals in the organogels varied significantly with the composition of the structurant and the T_s. At both T_s used, the Sit:Lec (80:20) system had a lower degree of supersaturation compared with the (100:0) system. X‐ray diffraction (XRD) revealed that Sit:Lec mass ratio of 70:30, 80:20 and 100:0 had similar short spacings, and the presence of Lec might be adverse to the formation of Sit crystal in oil. Small‐angel X‐ray scattering (SAXS) showed that the layer thickness of Sit/Lec/HLSO organogel was larger than that of Sit/HLSO organogel. It was found that the presence of Lec induced the change of self‐assembly structure of Sit in HLSO and caused the changes of physical properties of organogels obtained.     

Swelling properties of amino acid containing cross-linked polymeric organogels and their respective polyelectrolytic hydrogels with pH and salt responsive property

Amino acid based superabsorbent polymer (SAP) organogel library has been synthesized from Boc-glycine/alanine/valine/leucine/isoleucine/phenylalanine methacryloyl-oxyethyl ester (Boc-Gly/Ala/Val/Leu/Ilu/Phe-HEMA), which can switch over to corresponding hydrogels by simple one step Boc deprotection method. Swelling behaviour of organogels is investigated in various organic solvents (dielectric constant (ε) between 2.25 and 46.7), shows superabsorbent property in nonpolar organic solvents (2.25 ≤ ε ≤ 10.26) and moderate degree of swelling in polar aprotic solvents like acetone, N,N-dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), etc. Swelling property of organogels is greatly influenced by the –R group of pendant amino acids and increases as bulkiness and hydrophobicity of –R increased. Organogels release absorbed volatile organic compounds (VOCs) very rapidly at room temperature and bulkiness of –R group accelerate the deswelling kinetic. Deprotection of Boc groups in the organogel network converts them to superabsorbent cationic polyelectrolyte hydrogels with high degree of swelling (∼518 for hydrogel from leucine) due to the presence of –NH₃⁺ ion functionality, and the swelling ratio of hydrogels is drastically affected by the –R group of amino acids moiety, pH of aqueous medium and ionic strength of the solutions.     

Thermal and Textural Properties of Organogels Developed by Candelilla Wax in Safflower Oil

We investigated organogel formation in dispersions of CW in safflower oil (SFO). Candelilla wax (CW) has as its main component hentriacontane (78.9%), a n-alkane with self assembly properties in organic solvents (i.e., vegetable oils). Results showed that, independent of the cooling rate (i.e., 1 °C/min and 10 °C/min) and gel setting temperature (T _set), the CW organogels observed a thermoreversible behavior. This was evaluated by the behavior of thermal parameters that characterized organogel formation (gelation temperature, T _g; heat of gelation, ΔH_g) and melting (melting temperature, T _p; heat of melting, ΔH_M) after two heating-cooling cycles. For a given CW concentration (i.e., 0.5, 1.0, and 3%), the magnitude of ΔH_M and T _p and the structural organization of the organogel, depended on the cooling rate, the thermodynamic drive force for gelation, and the annealing process occurring at high T_set (i.e., 25 °C). At T _set of 25 °C the microplatelet units that formed the organogel aggregated as a function of storage time, a process that resulted in an increase in organogel hardness. In contrast, at T _set of 5 °C annealing occurred in a limited extent, but gels had higher solid fat content and microplatelet units of a smaller size than the gels obtained at 25 °C. The result was a three-dimensional network with greater hardness than the one obtained at 25 °C. The 3% CW organogels showed no phase separation up to 3 months at room temperature, with textures of potential use by the food industry.     

Comparison of the pomegranate seed oil organogels of carnauba wax and monoglyceride

The aims of this study were to prepare organogels from pomegranate seed oil (PO) with carnauba wax (CW) and monoglyceride (MG), compare the organogels with a commercial margarine (CM) and evaluate 3 months storage stability. At 3% organogelator addition, no gels were formed, while at 7 and 10% additions, the oil binding capacities increased and were always higher in CW organogels, with crystal formation times of 8.0 to 14.0 min. Solid fat content (SFC) of the CW organogels varied between 2.96 and 8.71% at 20°C, while MG gels had 2.89–9.43%, and CM had 29.73% SFC. The peak melting temperatures of the CW organogels ranged from 74.73 to 75.74°C and MG organogels ranged from 11.09 to 50.63°C, whereas CM product exhibited 45.92°C peak melting temperature. The hardness of CW organogels was higher than that of MG organogels. The organogels showed potential as spreadable products. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41343.     

Hydrogels composite of poly(acrylamide‐co‐acrylate) and rice husk ash. I. Synthesis and characterization

Composite hydrogels of poly(acrylamide‐co‐acrylate) with rice husk ash (RHA) were synthesized and studies of the swelling variables were accomplished comparatively with commercial polyacrylamide gel and PAMACRYL, a poly(acrylamide‐co‐acrylate) hydrogel without RHA. FT‐IR and WAXS were the techniques employed for characterizing a series of hydrogel obtained by varying the percentage of RHA (1, 2, 5, 10, and 20 wt %) and the amount of crosslinking agent (0.05, 0.1, and 0.2 mol %) relative to sum of AAm and AAc. Superabsorbent hydrogel with W_eq > 800 g H₂O/g gel was obtained with percentage of 10 wt % of RHA and 0.1 of crosslinking agent mol %. The hydrogel showed to be sensitive to the pH variation and to the presence of salts. The hydrogels, even though submitted through cycles of drying and swelling, preserved their superabsorbent characteristics and demonstrated better water absorbance properties when compared with commercial polyacrylamide gel. The composite hydrogels of poly(acrylamide‐co‐acrylate) with RHA presented good characteristics to be applied as soil conditioner for using in agriculture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and property of starch nanoparticles reinforced aldehyde–hydrazide covalently crosslinked PNIPAM hydrogels

Injectable, de‐crosslinkable, and thermosensitive hydrogels are obtained by hydrazide‐functionalized poly(N‐isopropylacrylamide) and aldehyde‐functionalized dextrin through in situ crosslinked method. Natural based and degradable starch nanoparticles (SNPs) are used as fillers in order to improve mechanical property of hydrogels. Internal morphology, dynamic modulus, thermosensitivity property, de‐crosslinking performance, drug release, and in vitro cytotoxicity of hydrogels are investigated. Results show that SNPs disperse well throughout hydrogel and have no significant influence on gelation time and de‐crosslinking performance. Elasticity property of composite hydrogel prepared from 9.0 wt % precursors with 1.5 wt % fillers is improved significantly by SNPs and maximum storage modulus reaches 399.2 kPa, but 89.6 kPa of unreinforced hydrogels. Hydrogels exhibit good thermosensitive performance at alternating cyclic temperature of 25 and 37 °C. Doxorubicin hydrochloride‐loaded hydrogels can release more than 25 days. No significant cytotoxicity to L929 fibroblast cells is observed through a CCK‐8 assay for hydrogels, precursors, and SNPs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45761.     

Effect of comonomer type and concentration on the equilibrium swelling and volume phase transition temperature of N‐isopropylacrylamide‐based hydrogels

The effect of incorporating a hydrophilic monomer into poly(N‐isopropylacrylamide) (polyNIPA) hydrogels on the equilibrium swelling and the volume phase transition temperature is reported here. A nonionizable monomer (acrylamide) and three ionizable monomers (itaconic acid, 2‐ethoxyethyl monoitaconate, and 2,2‐(2‐ethoxyethyl) monoitaconate) were studied. Hydrogels with larger swelling capacity than that of the polyNIPA hydrogel were obtained. With the exception of the hydrogel containing 2,2‐(2‐ethoxyethyl) monoitaconate, which did not exhibit the de‐swelling phenomena, the rest showed a volume phase transition. The hydrogels containing 85 wt % acrylamide and 15 wt % comonomer presented the higher shrinking ratio. For some compositions, the T_c of the polyNIPA hydrogel was within the desired temperature range (38–41°C) for controlled‐drug delivery in the human body. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

Alcohol-triggered silk fibroin hydrogels having random coil and β-turn structures enhanced for cytocompatible cell response

Alcohol additive is one of the stimulants that induces the fast gelation of silk fibroin solution. Based on our previous report, different alcohol types influence the gelation kinetic and the properties of resulting silk fibroin hydrogels. Here, the effects of alcohol concentrations on the silk fibroin gelation and cell response were reported. All fibroin hydrogels prepared with various alcohol additives showed cell biocompatibility, especially the fibroin hydrogel prepared with 10 wt % n-butanol. Results on the mechanical properties of hydrogels, n-butanol additive enhanced a higher compressive modulus up to ~ 22 times in comparison to non-alcoholic fibroin hydrogel. Fourier transform infrared analysis and peak deconvolution showed a possible formation of more β-turn linkage and random coil structure of fibroin segments in alcoholic fibroin hydrogel. So, the micro-segmental structure of fibroin hydrogel caused the higher compressive modulus, prolonged deformation of the hydrogels, and efficient cell growth on the fibroin hydrogel. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48731.     

Properties and Stability of Hazelnut Oil Organogels with Beeswax and Monoglyceride

The objectives of this study were to produce and characterize hazelnut oil (HO) organogels with beeswax (BW) and monoglyceride (MG) organogelators. Oil binding capacities of most samples were over 99 %. As the organogelator level increased, crystal formation time decreased, but solid fat content (SFC %) was enhanced. Although the highest SFC was 8.52 % among the organogel samples, it was 30.35 % in the commercial shortening (CS) at 20 °C. The peak melting temperature of CS was 41.86 °C, and almost all organogels had very close values to it. Melting enthalpies of the samples ranged from 0.48 to 13.40 J/g. Firmness and stickiness values of all samples were measured each month during 90 days of storage. There was no important change during storage. The organogels were texturally very stable, and were very homogenous and smooth in structure. Polarized light microscopy pictures revealed needle-like crystals for BW and rosette-like aggregates for MG organogels. The X-ray diffraction measurements of the crystals also showed the difference of the two types. There would be some hydrogen bonding in only MG organogels as predicted from the infrared spectra. The organogels were very stable against oxidation during storage. HO organogels can be used as shortening or margarine-like fat stock.     

Intelligent self-healable electroactive carboxymethyl cellulose hydrogel containing conductive polythiophene and acid hydrolyzed cellulose

Self-healable electroactive carboxymethyl cellulose/polythiophene/acid hydrolyzed cellulose (CMC/PTh/AHC) hydrogels were successfully fabricated. AHC particles dispersed well in the CMC matrix improving hydrogels thermal stability. The electro-responsive performance of the hydrogels was investigated with respect to bending angle and bending sensitivity. The results showed that under an applied electric field, the CMC/PTh/AHC hydrogels bend toward a cathode electrode. In addition, the electroactive performance of the hydrogels decreased with increased AHC content. The CMC/PTh/AHC10 (10 wt.% AHC) hydrogel exhibited the shortest induction time (τ_ind) of 3.35 ± 0.56 s. For self-healing, it was found that the hydrogel with addition of 2 wt.% AHC had the highest self-healing efficiency on both tensile strength and elongation at break (93.37 ± 3.17% and 99.35 ± 12.11%, respectively). While the self-healing efficiency on bending angle was 82.73 ± 14.55%. The results demonstrated that the properties of the CMC/PTh/AHC2 hydrogel were close to its original properties after healing for 24 h. The results demonstrated that the CMC/PTh/AHC hydrogel can be utilized as an actuator or artificial muscle using electrical stimulus.     

Influence of Storage on Physicochemical and Volatile Features of Enriched and Aromatized Wax Organogels

In this study, virgin olive oil (VOO) organogels were produced with beeswax (BW) and sunflower wax (SW) and enriched with β‐carotene, vitamin D₃ and E as well as aromatized with strawberry, banana, and butter aromas. The physicochemical, thermal, structural, and sensorial properties of the fresh organogel samples were determined. The peroxide values, antioxidant activities, firmness, and volatile compositions of the fresh samples and those stored for 3 months were also determined. The organogels were not only stable, uniform, and homogenous during the storage period but also the added components did not affect the organogel properties. The panel defined three appearance, four texture, three mouthfeel, four aroma, and four flavor terms to describe the organogels sensorially. Moreover, the added aroma (banana, strawberry, and diacetyl‐butter) components of the fresh and stored organogels were quantified by GC/MS‐SPME. In conclusion, these results demonstrated that beeswax and sunflower wax are very suitable to preserve the aromatic characteristics of these types of spreadable products.     

Cyclic voltammetry investigation of diffusion of ferrocene within propylene carbonate organogel formed by gelator

Propylene carbonate organogel containing LiClO₄ was formed in the presence of gelator bis-(4-stearoylaminophenyl) methane (BSAPM). The electrochemical behavior and diffusion of ferrocene (Fc) and ferricenium (Fc⁺) entrapped within the organogel was investigated by cyclic voltammetry. The Fc molecules still show redox activity within the organogels in comparison with corresponding solutions of propylene carbonate containing LiClO₄. The shape of the cyclic voltammograms of the Fc electrooxidation in organogel was similar to that in corresponding solutions. The results indicated that redox reactions of Fc/Fc⁺ were a quasi-reversible process of diffusion-controlled single electron transfer in organogels. The diffusion coefficients of Fc and Fc⁺ in organogels decreased with an increase of the concentration of gelator BSAPM, but increased with an increase of temperature. The temperature dependence of the diffusion coefficient in organogels followed classical Arrhenius equation. The activation energy in organogels was found of no difference from that in corresponding solutions.