Thymol Loading Research Articles

Evaluation of Preparation, Characterisation and Release Properties of Thymol-Containing Gelatin-Based Hydrogels for Varroosis Control

The aim of this study was to investigate the swelling/degradation behaviour of controlled-release system using gelatin, thymol loading capacity, characterisation, morphology and thymol release level in terms of the recommended therapeutic dose for varroosis control. In this context, a series of hydrogels were first produced using glutaraldehyde (GA) crosslinker and swelling tests were performed. Thymol loading was performed on the appropriate hydrogels with swelling values between 269% and 431%. Thymol loading efficiency was determined between 20.07% and 29.80%. The chemical structures of the hydrogels with and without thymol loading were compared by Fourier transform infrared spectrometry (FT-IR) and it was determined that thymol was loaded into the structure. The morphological structures of thymol loaded and unloaded hydrogels were examined by scanning electron microscopy (SEM). It was observed that the non-thymol loaded hydrogel had larger diameter pores than the thymol loaded hydrogel. A model release environment and measurement system were developed to predict the release type, level and duration of the controlled release system in the hive air environment. In this model release environment, release tests were carried out for four weeks using different thymol application systems and the measurements were compared. As a result, it was determined that the controlled thymol release system developed for the control of varroosis infestation exhibited a more stable release compared to existing application systems.

Controlled release mechanism of thymol loaded into mesoporous silica nanoparticles for active packaging films

In order to overcome the poor water solubility and instability of thymol to enhance its bioavailability, mesoporous silica nanoparticles (MSNPs: SBA-15, SBA-16 and MCM-41) with different pore structures were developed using solution-gel method to carry and release thymol. The N2 adsorption-desorption test showed thymol-loaded MSNPs contained significantly low surface areas, pore sizes and pore volumes. When the ratio of thymol to MSNPs was 3:1, the loading capacity (LC) of MSNPs reached the highest (SBA-15: 35.20%, SBA-16: 30.84%, and MCM-41: 44.23%). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and microstructure characterization confirmed that thymol encapsulation process was successful. TGA results showed that the encapsulation of MSNPs improved thymol stability. The zeta-potential results confirmed that thymol loading increased the intermolecular repulsion of thymol-loaded MSNPs, which was beneficial to its dispersibility in the film. Additionally, thymol release experiment revealed a sustainable release behavior of thymol for MSNPs within 10 d. The release mechanism was adjusted according to the Korsmeyer-Peppas model, which showed thymol obeyed Fickian diffusion process. Notably, both thymol-loaded MSNPs and thymol-loaded MSNPs/potato starch films showed a remarkable antimicrobial efficiency against S. aureus. Therefore, thymol-loaded MSNPs provide feasible guidelines for the development of active packaging films and the on-demand release of active substances.

Preparation of Thymol Nanoliposome and Solid Lipid Nanoparticle and Evaluation of their Inhibitory Effects on Leishmania Major Promastigotes

Introduction: Thymol has an antiprotozoal effect. Nanoparticulate systems are useful carriers for both small and large drug molecules, which can protect them from some chemical and biological damages as well as target drug delivery to specific organs or receptors. In this work, the nano-liposomal system and solid lipid nanoparticles loaded by thymol were prepared and the effectiveness of them were evaluated on Leishmania major promastigotes.
 Methods: Several formulations of nano-liposomes and solid lipid nanoparticles were prepared, and the amount of thymol loading, in-vitro release profile, particle size, and zeta potential were evaluated. Finally, the best formulations were serially diluted and incubated for 24, 48, and 72 hours on Leishmania major promastigotes, which cultured on Novy–MacNeal–Nicolle medium, and the results were analyzed.
 Results: The highest loading of thymol in nano-liposomes (92%) was seen in the formulations made with phosphatidylcholine (Called L3), and among the solid lipid nanoparticles, the formulation prepared with glycerol monostearate (S1) had the most entrapment efficiency of thymol (87%). These formulations were selected to evaluate the release rate of thymol. The results showed that S1 has a slower release rate than L3; this may be due to the presence of Glycerol monostearate in solid lipid nanoparticles structure. The best formulations, L3 and S1, were chosen for anti-Leishmaniosis assessment; which showed that all three forms of free thymol, nanoliposomes, and solid lipid nanoparticles inhibited Leishmania major. The half maximal inhibitory concentration (IC50) of free thymol, nanoliposome, and solid lipid nanoparticles for a 24-hour incubation are 7.8, 62.5, and 125, respectively, which decrease to 7.8, 7.8, and 15.6 for 48 hours and 7.8, 0.49, and 0 for 72 hours of incubation.
 Conclusion: Thymol has a significant effect on the inhibition of Leishmania major promastigotes and usage of thymol in the form of liposomes or solid lipid nanoparticles can sustain the drug release and have a lower IC50 during the longer incubation time.

Alginate carrier as a controlled thymol delivery system: Effect of particle size

Thymol, which possesses outstanding pharmacological activities such as anti-inflammatory, antibacterial, antifungal, and antitumor behavior, has a wide range of applications in medical and food packaging fields. This work aimed to conduct a comparison of alginate microparticles and nanoparticles as thymol delivery systems. Alginate was utilized to prepare nanoparticles of size 62.54 nm and microparticles of size 500–600 μm by emulsification and electrospraying methods, respectively. The effect of thymol loading on the characteristics of both particles demonstrated the significant size reduction and decrease of size distribution in thymol-loaded alginate nano/microparticles upon loading thymol to the alginate nano/microparticles. The chemical properties and thermal stability of the synthesized thymol-loaded alginate carriers were investigated by Fourier Transform Infrared and Differential scanning calorimetry; the results exhibit physical entrapment of thymol within the alginate carriers in the absence of any chemical changes in the carriers’ structure. Encapsulation efficiency and loading capacity for thymol-loaded alginate microparticles were calculated as 88.9% ± 1.1% and 8.23% ± 0.8%, correspondingly, while that of thymol-loaded alginate nanoparticles were reported as 98.7% ± 0.6% and 5.75% ± 0.14%, respectively. In vitro drug release recommended that thymol-loaded alginate nanoparticles released thymol in a more sustainable and controllable manner compared to thymol-loaded alginate microparticles, whereas for both of them, Korsmeyer-Peppas kinetic model can be applied, the trend of the Thymol release from the carriers followed a quasi-Fickian diffusion mechanism. Also, both thymol-loaded carriers represented cell viability of about 98% and good antibacterial properties against E. coli and S. aureus in vitro. The fabricated thymol-loaded Alginate Microparticles and thymol-loaded Alginate Nanoparticles can be deployed as promising drug delivery systems.

Supercritical CO2 Impregnation of Thymol in Thermoplastic Starch-Based Blends: Chemico-Physical Properties and Release Kinetics.

The aim of the present study was to investigate starch-based materials, prepared in an environmentally friendly way and from renewable resources, suitable for the development of biodegradable active food packaging. For this purpose, a bioactive compound (thymol) was incorporated into thermoplastic starch (TPS) and a TPS blend with poly (ε-caprolactone) (TPS–PCL) by the supercritical CO2 (scCO2) impregnation process. Impregnation experiments with scCO2 were carried out at a pressure of 30 MPa and temperatures in the range of 40–100 °C during 1 to 20 h. The structural, morphological, and thermal properties of the obtained materials were comprehensively evaluated. Bioactive component release kinetic studies were performed in water at 6 °C and 25 °C. It was shown that the scCO2 impregnation process could be successfully employed for thymol loading into TPS and TPS–PCL. The process was significantly influenced by the operating temperature and time as well as content of PCL. The samples showed a controlled release of thymol within seven days with a higher amount of released thymol from the TPS–PCL blend. The obtained materials are solvent-free and release the bioactive component in a controlled manner.

A green approach to develop zeolite-thymol antimicrobial composites: analytical characterization and antimicrobial activity evaluation

In this work, the development, analytical characterization and bioactivity of zeolite-thymol composites, obtained using wet, semi-dry and dry processes, were carried out in order to obtain sustainable and powerful antimicrobial additives. FT-IR, XRD, DSC, TGA, SEM and B.E.T. analyses were carried out to gain comprehensive information on the chemical-physical, thermal, and morphological features of the composites. GC-MS analyses allowed quantifying the active molecule loaded in the zeolite, released by the functionalized composites and its stability over time. Among the three procedures, the dry approach allowed to reach the highest thymol loading content and efficiency (49.8 ± 1.6% and 99.6 ± 1.2%, respectively), as well as the highest composite specific surface area value, feature which promises the best interaction between the surface of the composite and the bacterial population. Therefore, the bioactive surface of composites obtained by this solvent-free method was assayed for its antimicrobial activity against four microbial strains belonging to Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans species. The higher antimicrobial activity produced by the solvent-free composite in comparison with that of pure thymol, at the same thymol concentration, was ascribed to the large interfacial contact between the composite and the bacterial target. This feature, together with its enhanced storage stability, suggested that this composite could be employed as effective additives for the development of antimicrobial biointerfaces for food, home and personal care applications.

Utilization of supercritical carbon dioxide for development of antibacterial surgical sutures

Outbreak of surgical infections and bacterial resistance against synthetic antibiotic has prompted research towards development of antibacterial medical devices. For that purpose, absorbable surgical sutures were impregnated with natural compound thymol using an environmentally friendly medium. The supercritical solvent impregnation process was performed at 35 °C and 10 MPa during 1, 2, 3 and 6 h, resulting in thymol loadings of 3.9–5.6%. All tested samples expressed antibacterial activity against E. coli and S. aureus. Release tests in PBS at 37 °C showed that impregnated material released loaded thymol in a gradual manner. While sutures impregnated during 6 h released complete amount of loaded thymol during 6 days, shorter impregnation process resulted in sutures that retained significant thymol amounts (~ 20–40%) after 10 days of release test. The effect of proposed process on final material properties and its application were explained in detail using characterization techniques SEM, FTIR, DSC and DMA.

Electrospun pullulan/PVA nanofibers integrated with thymol-loaded porphyrin metal−organic framework for antibacterial food packaging

Pathogenic microorganisms posed perniciousness for postharvest fruits and vegetables, as well as brought potential risks for human health. In this work, pullulan/polyvinyl alcohol (PUL/PVA) nanofibers incorporated with thymol-loaded porphyrin metal-organic framework nanoparticles (THY@PCN-224 NPs) were developed for antibacterial food packaging. PCN-224 MOFs not only act as thymol loading carriers but also highly produce singlet oxygen (1O2) with bactericidal activity. PUL/PVA nanofiber was a promising sustainable substrate because of its good flexibility, biocompatibility and biodegradability. The loading capacity of PCN-224 for thymol was about 20%. The THY@PCN/PUL/PVA nanofibers exhibited synergistic antibacterial activities against E. coli (~99%) and S. aureus (~98%) under light irradiation. The cell viability assays and fruit preservation study demonstrated good biosafety of the polymeric film. The results suggested that this novel nanofiber has potential application prospects for food packaging.

Functionalization of polyamide microfiltration membranes by supercritical solvent impregnation

The study reports the application of supercritical solvent impregnation to deliver antibacterial substance thymol to the defined polymeric structure of commercial polyamide microfiltration membranes. The process performed at a temperature of 40 °C and pressures of 10, 15, and 20 MPa was characterized by the fast impregnation in the first 30 min with thymol loadings up to 29 wt%. The maximal achieved thymol loading in the process was around 42 wt%, regardless the pressure. The scanning electron and ion microscopy analyses revealed that the membranes’ microstructure was preserved with a thymol content of 20 wt%, while a more prominent swelling effect was observed in samples with 35 wt% of thymol. The cross-flow filtration tests showed that the impregnation process did not harm the membranes’ functionality in samples with 20 wt% of thymol. These membranes exhibited strong anti-biofilm activity, and were less prone to the blockage with bacteria in comparison to neat membranes.

Functional Modification of Cellulose Acetate Microfiltration Membranes by Supercritical Solvent Impregnation.

This study investigates the modification of commercial cellulose acetate microfiltration membranes by supercritical solvent impregnation with thymol to provide them with antibacterial properties. The impregnation process was conducted in a batch mode, and the effect of pressure and processing time on thymol loading was followed. The impact of the modification on the membrane’s microstructure was analyzed using scanning electron and ion-beam microscopy, and membranes’ functionality was tested in a cross-flow filtration system. The antibiofilm properties of the obtained materials were studied against Staphyloccocus aureus and Pseudomonas aeruginosa, while membranes’ blocking in contact with bacteria was examined for S. aureus and Escherichia coli. The results revealed a fast impregnation process with high thymol loadings achievable after just 0.5 h at 15 MPa and 20 MPa. The presence of 20% of thymol provided strong antibiofilm properties against the tested strains without affecting the membrane’s functionality. The study showed that these strong antibacterial properties could be implemented to the commercial membranes’ defined polymeric structure in a short and environmentally friendly process.

Application of Supercritical Solvent Impregnation for Production of Zeolite Modified Starch-Chitosan Polymers with Antibacterial Properties

In the present study, supercritical solvent impregnation (SSI) has been applied to incorporate thymol into bio-composite polymers as a potential active packaging material. Thymol, a natural component with a proven antimicrobial activity, was successfully impregnated into starch-chitosan (SC) and starch-chitosan-zeolite (SCZ) films using supercritical carbon dioxide (scCO2) as a solvent. Experiments were performed at 35 °C, pressures of 15.5 and 30 MPa, and an impregnation time in the range of 4–24 h. The highest impregnation yields of SC films with starch to chitosan mass ratios of 1:1 and 1:2 were 10.80% and 6.48%, respectively. The addition of natural zeolite (15–60%) significantly increased the loading capacity of films enabling thymol incorporation in a quantity of 16.7–27.3%. FTIR and SEM analyses were applied for the characterization of the films. Mechanical properties and water vapor permeability of films before and after the impregnation were tested as well. Thymol release kinetics in deionized water was followed and modeled by the Korsmeyer-Peppas and Weibull model. SCZ films with thymol loading of approximately 24% exhibited strong antibacterial activity against E. coli and methicillin-resistant Staphylococcus (S.) aureus (MRSA).

Preparation, characterization, and permeability of novel poly (lactic acid)-based blends filled with thymol and ZnO

Novel thin sheets based on poly (lactic acid)/poly (caprolactone)/thermoplastic starch ternary blends were fabricated by incorporating thymol, zinc oxide nanoparticles (ZnO-NPs) and thymol/ZnO-NPs at different concentrations (6, 9, 12 wt% thymol and 1, 3, 5 wt% ZnO). The gas/water vapor barrier properties of the nanocomposites comprising the effects of polar and non-polar molecules and their leading mechanisms were thoroughly discussed. Moreover, the localization preference of ZnO-NPs, morphology along with mechanical, and thermal properties of the nanocomposites were investigated. A significant improvement of 58% in the water vapor impermeability by 5 wt% ZnO and 12 wt% thymol loading was achieved. Finally, the fitting of the Maxwell model on the experimental data revealed that this model cannot correctly predict the permeation behavior of ZnO-filled nanocomposites. Results suggested that these nanocomposites could be capable of being used as the packaging materials with high barrier performance.

Drug delivery by micro and meso metal-organic frameworks

Three metal-organic frameworks (MOFs), HKUST-1, MIL-53(Al) and MIL-101(Cr) were synthesized and applied as carriers for Thymol loading. The MOFs and designed drug delivery systems were characterized by scanning electron microscope, N2 sorption isotherm, X-ray diffraction and Fourier transform infrared. Thymol was incorporated by high pressure method into hosts. The amount of encapsulated drug could be calculated using thermogravimetric analysis. The release profile of drug was recorded in buffer media and two pHs (6.9 and7.4) by reading the absorbance of solution in λmax. Higuchi and first order release kinetic models were applied to the experimental data. Then, the effect of MOFs and designed drug delivery systems on human breast and lung cancer cell lines viability was evaluated. In studied weight range٬ the hosts alone revealed no toxicity to cell lines. But, Thymol encapsulated into MOFs indicated more inhibition of cell livability, when compared to the non-encapsulated drug. Among of applied hosts, MIL-53 shows not only high loading capacity but also controlled release. In addition, the inhibition of cell livability is more notably in lung cancer cell line.

Added-value porous materials for controlled thymol release obtained by supercritical CO2 impregnation process

This study explores utilization of biodegradable and biocompatible polymers for controlled release of natural bioactive substance. For that purpose, poly(ε-caprolactone) (PCL) beads, cellulose acetate (CA) film, and poly lactic- co-glycolic acid (PLGA) flakes were impregnated with thymol by employing environmentally friendly process of supercritical carbon dioxide (scCO2) impregnation. At selected pressure and temperature, prolongation of operating time increased thymol loading. Pure scCO2 did not affect CA film with average pore diameter of approximately 3 µm, while it enabled change of PCL beads and PLGA flakes into foams with average pore diameter approximately 175 µm and 87 µm, respectively. Additionally to scCO2, thymol acted as a plasticizer increasing pore size of polymers up to three times. Kinetic of thymol release from selected samples was tested using phosphate buffer saline at 37°C and successfully described with Korsmeyer–Peppas, zero-order, first-order, and Higuchi models. The suggested method of PCL, CA, and PLGA supercritical impregnation led to development of porous, solvent free, added-value materials that release thymol in a controlled manner from 5 h to several days.

Supercritical CO2 - assisted production of PLA and PLGA foams for controlled thymol release

Amorphous, medical grade poly(d,l-lactic acid) (PLA) and poly(d,l-lactic-co-glycolic acid) (PLGA) were used to develop systems for controlled release of a natural bioactive substance - thymol. Supercritical carbon dioxide (scCO2) was successfully used both as an impregnation medium for thymol incorporation into the polymer matrix and a foaming agent in a single-step batch process. Impregnation of samples using low to moderate scCO2 densities (273 kg/m3 and 630 kg/m3) and short processing times (2 h and 4 h) enabled thymol loading of 0.92%–6.62% and formation of microcellular foams upon system depressurization. Thymol effect on structural and thermal properties on foamed samples was proven by FTIR and DSC. The effect of CO2 under elevated pressure on the neat polymers was analysed by high pressure DSC. Foaming of polymers with lower molecular weight by CO2 of higher density yielded foams with smaller pores. All tested foams released thymol in a controlled manner in phosphate buffered saline (PBS) at 37 °C within 3 to 6 weeks. Higher loading and lower cell density favoured thymol release rate, while its concentration in PBS for the tested period depended on foam interaction with the medium. Representative PLGA foam sample with the highest thymol loading (6.62%) showed controlled thymol release within 72 h in mediums having pH values from 1.1 to 7.4.

Porous metal-organic framework (MOF) Carrier for incorporation of volatile antimicrobial essential oil

The increasing demand for safety and quality in food products has stimulated research on developing natural preservatives and their carrier systems as a novel preventive control strategy. In this study, metal-organic framework (MOF) was investigated, for the first time, as a carrier for volatile antimicrobial essential oils. Zinc metal-organic framework (Zn@MOF) was synthesized with zinc nitrate hexahydrate and 2-aminoterephthalic acid in N, N-dimethylformamide (DMF). Thymol was then loaded into the Zn@MOF at a loading rate of 3.96% as measured by thermogravimetric analysis (TGA). The crystal structure of porous MOF was confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Antibacterial activity of thymol loaded Zn@MOF (T-Zn@MOF) with active thymol loading of 0.029 g/100 g was assessed against a three-strain cocktail of E. coli O157:H7 in a tryptic soy broth (TSB). E. coli O157:H7 growth in T-Zn@MOF exhibited growth inhibition without an exponential growth phase after 24 h of incubation, which could be attributed to the sustained release of thymol by incorporating it in the porous Zn@MOF through noncovalent interactions. This research demonstrates that Zn@MOF loaded with the essential oil thymol is an effective antimicrobial and may have potential indirect applications in food.

Utilization of supercritical carbon dioxide in fabrication of cellulose acetate films with anti-biofilm effects against Pseudomonas aeruginosa and Staphylococcus aureus

This study discusses utilization of supercritical carbon dioxide for impregnation of cellulose acetate films with thymol in order to produce material with anti-biofilm activity against Pseudomonas aeruginosa and Staphylococcus aureus. Analysis of anti-biofilm activity of cellulose acetate beads impregnated with thymol suggested that optimal thymol loading was in the range from 26% to 30% for efficient reduction of biofilm formation and eradication of pre-formed biofilms. Polymer films were fabricated by the solvent casting method from polymer solutions of different contents, and loaded with thymol using supercritical carbon dioxide at 15.5 MPa and 35 °C. The film containing 30% of thymol (F1 30%) exhibited substantial anti-adhesion properties inhibiting biofilm formation on its surface and considerably reduced formation of biofilms on the surrounding surfaces (up to 80%) by all tested strains including antibiotic resistant P. aeruginosa DM50 and methicillin-resistant S. aureus.

Development and characterization of novel antimicrobial bilayer films based on Polylactic acid (PLA)/Pickering emulsions

Biodegradable food packaging is sustainable and has a great application prospect. PLA is a promising alternative for petroleum-derived polymers. However, PLA packaging suffers from poor barrier properties compared with petroleum-derived ones. To address this issue, we designed bilayer films based on PLA and Pickering emulsions. The formed bilayer films were compact and uniform and double layers were combined firmly. This strategy enhanced mechanical resistance, ductility and moisture barrier of Pickering emulsion films, and concomitantly enhanced the oxygen barrier for PLA films. Thymol loadings in Pickering emulsion layer endowed them with antimicrobial and antioxidant activity. The release profile of thymol was well fitted with Fick’s second law. The antimicrobial activity of the films depended on film types, and Pickering emulsion layer presented larger inhibition zone than PLA layer, hinting that the films possessed directional releasing role. This study opens a promising route to fabricate bilayer architecture creating synergism of each layer.

Development and characterisation of polylactic acid–gliadin bilayer/trilayer films as carriers of thymol

SummaryBiodegradable food packaging promises a more sustainable future. Poly(lactic acid) (PLA) is a promising alternative for petroleum‐derived polymers. However, PLA films suffer from poor barrier properties compared with petroleum‐derived ones. To address this issue, we designed bilayer and sandwich‐architectured trilayer films based on PLA and gliadin. We reported firstly the direct formation of PLA–gliadin bilayer/trilayer films without surface modification on PLA film. The films were compact and uniform, and double/triple layers were combined firmly, preventing delamination. This strategy enhanced mechanical resistance, ductility and moisture barrier of gliadin films and concomitantly enhanced the oxygen barrier for PLA films. Thymol loadings endowed bilayer/trilayer films with antimicrobial activity and antioxidant activity. The antimicrobial activity of the films depended on film types, and gliadin layer presented larger inhibition zone than PLA layer, hinting that the films possessed directional releasing role. This study opens a promising route to fabricate bilayer/trilayer architecture helping to create synergism of the biopolymers.

Effect of starch xero‐ and aerogels preparation on the supercritical CO2 impregnation of thymol

In this study, for the first time, the supercritical solvent impregnation (SSI) technique has been used to test the incorporation of thymol into starch gels. Corn and tapioca starch hydrogels prepared at different temperatures (70–100°C) were converted to the acetogels and subsequently dried with supercritical CO2 or air to obtain aero‐ or xerogels, respectively. Starch xero‐ and aerogels were impregnated with thymol in a high pressure view cell using supercritical CO2 at 15.5 MPa and 35°C during 24 h. The influence of the botanical origin of starch, temperature for hydrogels preparation (Tgel‐h) and drying method on the gel morphology and thymol impregnation yields was discussed. Determined thymol SSI yields were in the range of 1.15–4.02% for the corn and 0.58–3.63% for the tapioca starch gels. Xerogels had higher thymol loading capacities (1.76–4.02%) than aerogels (0.58–3.31%) at given SSI conditions. Gel morphology and thymol SSI yields were positively affected by the Tgel‐h increase. The xerogel obtained from the corn starch hydrogel prepared at 100°C had the largest specific surface area (5.52 m2/g) and thymol loading capacity (4.02%) at given SSI conditions. These results, along with a simple and low‐cost production, indicated the great potential of the corn starch xerogel for commercial use as a carrier in pharmaceuticals and nutraceuticals.