Essential oil impregnated luminescent hydroxyapatite: Antibacterial and cytotoxicity studies

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Supercritical CO2 Impregnation of Clove Extract in Polycarbonate: Effects of Operational Conditions on the Loading and Composition

The development of active packaging for food storage containers is possible through impregnation of natural extracts by supercritical CO2-assisted impregnation processes. The challenge of scCO2-impregnation of natural extracts is to control the total loading and to ensure that the composition of the loaded extract may preserve the properties of the crude extract. This study aimed at investigating the scCO2-impregnation of clove extract (CE) in polycarbonate (PC) to develop antibacterial packaging. A design of experiments was applied to evaluate the influences of temperature (35–60 °C) and pressure (10–30 MPa) on the clove loading (CL%) and on the composition of the loaded extract. The CL% ranged from 6.8 to 18.5%, and the highest CL% was reached at 60 °C and 10 MPa. The composition of the impregnated extract was dependent on the impregnation conditions, and it differed from the crude extract, being richer in eugenol (81.31–86.28% compared to 70.06 in the crude extract). Differential scanning calorimetry showed a high plasticizing effect of CE on PC, and high CL% led to the cracking of the PC surface. Due to the high loading of eugenol, which is responsible for the antibacterial properties of the CE, the impregnated PC is promising for producing antibacterial food containers.

Root-Associated Microbiomes of Panax notoginseng under the Combined Effect of Plant Development and Alpinia officinarum Hance Essential Oil

Essential oils (EOs) have been proposed as an alternative to conventional pesticides to inhibit fungal pathogens. However, the application of EOs is considerably limited due to their highly volatile nature and unpredictable effects on other microbes. In our study, the composition of bacterial and fungal communities from the rhizosphere soil of P. notoginseng under four treatment levels of Alpinia officinarum Hance EO was characterized over several growth stages. Leaf weight varied dramatically among the four EO treatment levels after four months of growth, and the disease index at a low concentration (0.14 mg/g) of EO addition was the lowest among the P. notoginseng growth stages. The content of monomeric saponins was elevated when EO was added. Bacterial and fungal diversity in the absence of plants showed a decreasing trend with increasing levels of EO. Bacterial diversity recovery was more correlated with plant growth than was fungal diversity recovery. Compared with the control (no EO addition), a low concentration of EO significantly accumulated Actinomycota, including Acidothermus, Blastococcus, Catenulispora, Conexibacter, Rhodococcus, and Sinomonas, after one month of plant-microbial interaction. Overall, the results showed that both the plant growth stage and EOs drive changes in the microbial community composition in the rhizosphere of P. notoginseng. Plant development status had a stronger influence on bacterial diversity than on fungal diversity. EO had a more significant effect on fungal community composition, increasing the dominance of Ascomycota when EO concentration was increased. Under the interaction of P. notoginseng growth and EO, a large number of bacterial genera that have been described as plant growth-promoting rhizobacteria (PGPR) responded positively to low concentrations of EO application, suggesting that EO may recruit beneficial microbes in the root zone to cope with pathogens and reduce root rot disease. These results offer novel insights into the relationship between EO application, altered microbial communities in the plant roots, plant growth stage, and disease occurrence.

Evaluation of the antibacterial effect of tea tree oil on Enterococcus faecalis and biofilm in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Tea tree essential oil (TTO) is extracted from the leaves of Melaleuca alternifolia by steam distillation. It is well known for its traditional medicinal uses, particularly for the treatment of bruises, insect bites, skin infections, vertigo, convulsions, toothache, and rheumatism. Earlier research has shown that TTO can effectively inhibit oral microorganisms in the root canals. Enterococcus faecalis (E. faecalis) has been considered to be associated with persistent root canal infections and root canal treatment failure. The biofilm of E. faecalis makes it more vigorous, toxic, and resistant to antibiotics.

AIM OF THE STUDY

In this study, our aim was to evaluate the antimicrobial effects of TTO on planktonic E. faecalis and biofilms compared with 0.2% CHX.

MATERIALS AND METHODS

We explored the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), the bacteriostatic rate by MTT assay, the antimicrobial time by time-kill assay, and the effects on cell integrity, the biomass, and bacterial activity of E. faecalis biofilms. Finally, we investigated the microstructure changes of E. faecalis biofilms using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

RESULTS

The MIC and MBC values were 0.25% and 0.5%, the bacterial inhibition rate, time-kill was dosage dependent, and TTO can effectively destroy membrane integrity. SEM CLSM images revealed that TTO could reduce bacterial aggregation, biofilm thickness and inhibited biofilm formation. The effect of TTO was the same as that of 0.2% CHX at some specific concentrations. In summary, TTO has the potential to be effective against E. faecalis infections.

CONCLUSIONS

TTO was able to inhibit E. faecalis by destroying cell membrane, inhibiting the formation of E. faecalis biofilms, and eliminating mature formed biofilms. In this study, TTO has the potential to be further developed as a novel antibacterial drug.

In Vivo Biological Evaluation of Biodegradable Nanofibrous Membranes Incorporated with Antibiofilm Compounds

Guided bone regeneration involves excluding non-osteogenic cells from the surrounding soft tissues and allowing osteogenic cells originating from native bone to inhabit the defect. The aim of this work was to fabricate, analyze antibiofilm activity and evaluate in vivo biological response of poly (lactic-co-glycolic acid) (PLGA) electrospun membranes incorporated with tea tree oil and furan-2(5H)-one. Samples were exposed to Streptococcus mutans culture and after 48 h incubation, biofilm was evaluated by colony forming units (CFU/mL) followed by scanning electron microscopy. Additionally, seventy-five Balb-C mice were divided into five experimental groups for subcutaneous implantation: tea tree oil loaded PLGA electrospun fiber membrane, furanone loaded PLGA electrospun fiber membrane, neat PLGA electrospun fiber membrane, a commercially available PLGA membrane –Pratix^® and Sham (no-membrane implantation). Post implantation period of each experimental group (1, 3 and 9 weeks), samples were collected and processed for by histological descriptive and semiquantitative evaluation. Results showed a significant reduction of bacterial attachment on tea tree oil and furan-2(5H)-one incorporated membranes. Macrophage counts were significant found in all the materials implanted, although giant cells were predominantly associated with electrospun fiber membranes. The incorporation of antibiofilm compounds in nanofibers membranes did not incite inflammatory response significantly different in comparison with pure PLGA electrospun membranes, indicating its potential for development of novel functionalized membranes targeting the inhibition of bacterial biofilms on membrane-grafting materials.

Essential Oils for Bone Repair and Regeneration-Mechanisms and Applications

Although bone possesses a remarkable capacity for self-remodeling and self-healing of small defects, the continuously increasing growth of bone diseases in the elderly population is becoming a significant burden, affecting individual life quality and society. Conventional treatment options involve surgical procedures for repair and reconstruction, local debridement, autografts or allografts, bone transport, Masquelet's two-stage reconstructions, and vascularized bone transplants. However, as such approaches often lead to disruptions of bone-regeneration processes and microbial contaminations and are often inefficient, researchers focus on developing bone-regenerative strategies and identifying novel therapeutic agents that could aid the bone-healing process. In this regard, plant-derived biocompounds, especially essential oils (EOs), have received great scientific attention in recent years, owing to their antioxidant, anti-inflammatory, and antimicrobial effects. Current studies focus on either the direct application of EOs on bone tissue or the introduction of EOs as bioactive compounds in bone scaffolds or as coatings for bone implants. Some of the EOs investigated involve St. John's wort, rosemary, thyme, ylang, white poplar, eucalyptus, lavender, and grape seed. In this context, the present paper aims to provide an overview of the main mechanisms involved in bone repair and regeneration and the potential of EOs to address and enhance these mechanisms.