Degradation of silica particles functionalised with essential oil components under simulated physiological conditions

Surface Modification of Mesoporous Silica Nanoparticles for Application in Targeted Delivery Systems of Antitumour Drugs

The problem of tumour therapy has attracted the attention of many researchers for many decades. One of the promising strategies for the development of new dosage forms to improve oncology treatment efficacy and minimise side effects is the development of nanoparticle-based targeted transport systems for anticancer drugs. Among inorganic nanoparticles, mesoporous silica deserves special attention due to its outstanding surface properties and drug-loading capability. This review analyses the various factors affecting the cytotoxicity, cellular uptake, and biocompatibility of mesoporous silica nanoparticles (MSNs), constituting a key aspect in the development of safe and effective drug delivery systems. Special attention is paid to technological approaches to chemically modifying MSNs to alter their surface properties. The stimuli that regulate drug release from nanoparticles are also discussed, contributing to the effective control of the delivery process in the body. The findings emphasise the importance of modifying MSNs with different surface functional groups, bio-recognisable molecules, and polymers for their potential use in anticancer drug delivery systems.

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.

Mesoporous Silica Nanoparticles as a Gene Delivery Platform for Cancer Therapy

Cancer remains a major global health challenge. Traditional chemotherapy often results in side effects and drug resistance, necessitating the development of alternative treatment strategies such as gene therapy. Mesoporous silica nanoparticles (MSNs) offer many advantages as a gene delivery carrier, including high loading capacity, controlled drug release, and easy surface functionalization. MSNs are biodegradable and biocompatible, making them promising candidates for drug delivery applications. Recent studies demonstrating the use of MSNs for the delivery of therapeutic nucleic acids to cancer cells have been reviewed, along with their potential as a tool for cancer therapy. The major challenges and future interventions of MSNs as gene delivery carriers for cancer therapy are discussed.

Nutrient molecule corona: An update for nanomaterial-food component interactions

The adsorption of biological molecules to nanomaterials (NMs) will significantly impact NMs' behavior in complex microenvironments. Previously we proposed the need to consider the interactions between food components and NMs for the evaluation of oral toxicity of NMs. This review updated this concept as nutrient molecule corona, that the adsorption of nutrient molecules alters the uptake of nutrient molecules and/or NMs, as well as the signaling pathways to induce a combined toxicity due to the biologically active nature of nutrient molecules. Even with the presence of protein corona, nutrient molecules may still bind to NMs to change the identities of NMs in vivo. Furthermore, this review proposed the binding of excessive nutrient molecules to NMs to induce a combined toxicity under pathological conditions such as metabolic diseases. The structures of nutrient molecules and physicochemical properties of NMs determine nutrient molecule corona formation, and these aspects should be considered to limit the unwanted effects brought by nutrient molecule corona. In conclusion, similar to other biological molecule corona, the formation of nutrient molecule corona due to the presence of food components or excessive nutrient molecules in pathophysiological microenvironments will alter the behaviors of NMs.

In vivo toxicity assessment of eugenol and vanillin-functionalised silica particles using Caenorhabditis elegans

The toxicological properties of different silica particles functionalised with essential oil components (EOCs) were herein assessed using the in vivo model C. elegans. In particular, the effects of the acute and long-term exposure to three silica particle types (SAS, MCM-41 micro, MCM-41 nano), either bare or functionalised with eugenol or vanillin, were evaluated on different biological parameters of nematodes. Acute exposure to the different particles did not reduce nematodes survival, brood growth or locomotion, but reproduction was impaired by all the materials, except for vanillin-functionalised MCM-41 nano. Moreover, long-term exposure to particles led to strongly inhibited nematodes growth and reproduction. The eugenol-functionalised particles exhibited higher functionalisation yields and had the strongest effects during acute and long-term exposures. Overall, the vanillin-functionalised particles displayed milder acute toxic effects on reproduction than pristine materials, but severer toxicological responses for the 96-hour exposure assays. Our findings suggest that the EOC type anchored to silica surfaces and functionalisation yield are crucial for determining the toxicological effects of particles on C. elegans. The results obtained with this alternative in vivo model can help to anticipate potential toxic responses to these new materials for human health and the environment.

Preparation and Enhanced Antimicrobial Activity of Thymol Immobilized on Different Silica Nanoparticles with Application in Apple Juice

In order to diminish the application limitations of essential oils (EOs) as natural antimicrobial components in the food industry, novel antimicrobial materials were designed and prepared by immobilization of thymol derivatives on silica particles with different morphologies (hollow mesoporous silica nanoparticles, MCM-41, amorphous silica). The structural characteristics of antimicrobial materials were estimated by FESEM, FT-IR, TGA, N2 adsorption-desorption, and small-angle XRD, and the results revealed that both mesoporous silica nanoparticles maintained the orderly structures and had good immobilization yield. Furthermore, the antibacterial performance tests showed that mesoporous silica nanoparticles greatly enhanced the antimicrobial activity of thymol against two representative foodborne bacteria (Escherichia coli and Staphylococcus aureus), and the application of the antimicrobial support was tested in apple juices inoculated with E. coli. The MBC of functionalized mesoporous silica supports was established to be below 0.1 mg/mL against E. coli and S. aureus, which is much lower than that of free thymol (0.3 mg/mL and 0.5 mg/mL against E. coli and S. aureus, respectively). In addition, at a range from 0.05 mg/mL to 0.2 mg/mL, immobilized hollow mesoporous silica nanoparticles (HMSNs) can inhibit the growth of E. coli in apple juice and maintain good sensory properties during 7 days of storage.

In vitro toxicological evaluation of mesoporous silica microparticles functionalised with carvacrol and thymol

The cytotoxicity of carvacrol- and thymol-functionalised mesoporous silica microparticles (MCM-41) was assessed in the human hepatocarcinoma cell line (HepG2). Cell viability, lactate dehydrogenase (LDH) activity, reactive oxygen species (ROS) production, mitochondrial membrane potential (ΔΨm), lipid peroxidation (LPO) and apoptosis/necrosis analyses were used as endpoints. The results showed that both materials induced cytotoxicity in a time- and concentration-dependent manner, and were more cytotoxic than free essential oil components and bare MCM-41. This effect was caused by cell-particle interactions and not by degradation products released to the culture media, as demonstrated in the extract dilution assays. LDH release was a less sensitive endpoint than the MTT (thiazolyl blue tetrazolium bromide) assay, which suggests the impairment of the mitochondrial function as the primary cytotoxic mechanism. In vitro tests on specialised cell functions showed that exposure to sublethal concentrations of these materials did not induce ROS formation during 2 h of exposure, but produced LPO and ΔΨm alterations in a concentration-dependent manner when cells were exposed for 24 h. The obtained results generally support the hypothesis that the carvacrol- and thymol-functionalised MCM-41 microparticles induced toxicity in HepG2 cells by an oxidative stress-related mechanism that resulted in apoptosis through the mitochondrial pathway.

Variation in dissolution behavior among different nanoforms and its implication for grouping approaches in inhalation toxicity

Different nanoforms (NF) of the same substance each need to be registered under REACH, but similarities in physiological interaction -among them biodissolution- can justify read-across within a group of NFs, thereby reducing the need to perform animal studies. Here we focused on the endpoint of inhalation toxicity and explored how differences in physical parameters of 17 NFs of silica, and organic and inorganic pigments impact dissolution rates, half-times, and transformation under both pH 7.4 lung lining conditions and pH 4.5 lysosomal conditions. We benchmarked our observations against well-known TiO₂, BaSO₄ and ZnO nanomaterials, representing very slow, partial and quick dissolution respectively. By automated image evaluation, structural transformations were observed for dissolution rates in the order of 0.1 to 10 ng/cm²/h, but did not provide additional decision criteria on the similarity of NFs. Dissolution half-times spanned nearly five orders of magnitude, mostly dictated by the substance and simulant fluid, but modulated up to ten-fold by the subtle differences between NFs. Physiological time scales and benchmark materials help to frame the biologically relevant range, proposed as 1 h to 1 y. NFs of ZnO, Ag, SiO₂, BaSO₄ were in this range. We proposed numerical rules of pairwise similarity within a group, of which the worst case NF would be further assessed by in vivo inhalation studies. These rules divided the colloidal silica NFs into two separate candidate groups, one with Al-doping, one without. Shape or silane surface treatment were less important. The dissolution halftimes of many organic and inorganic pigment NFs were longer than the biologically relevant range, such that dissolution behavior is not an obstacle for their groupings.

The assembly of silica species with alkylamines: Mechanism of wastewater-free synthesis and the application of gel as a catalyst

Silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) could assemble with alkylamines to form silica gel. Herein, it was evidenced that part of the added amines, including butylamine (BA), octylamine (OA) or dodecylamine (DA), was protonated in the mixture of water and ethanol. Therefore, besides the hydrogen bonding between neutral silica species and the micelles composed of the non-protonated amines (Tanev and Pinnavaia, 1995), there existed strong electrostatic attraction between negatively charged silica species and the micelles composed of the protonated amines. This coexisting assembly mechanism could explain why the uncalcined BA- and OA-gels were millimeter-sized small blocks with large porosities and synthesized without waste water emission, while the uncalcined DA-gel was almost non-porous and formed via precipitation from its reaction medium. The uncalcined BA gel was proved to be efficient as a solid basic catalyst, replacing the commonly used ammonia solution which is easily volatilized and has a pungent smell, for the hydrolysis and condensation of TEOS to prepare silica microspheres.

Evaluation of the influence of food intake on the incorporation and excretion kinetics of mesoporous silica particles in C.elegans

The effect of the presence of food on the incorporation and excretion of silica particles was studied in this work using the biological model Caenorhabditis elegans and image analysis techniques. The experiment was based on two 24-hour phases: exposure and depuration. During exposure, nematodes were maintained for 24 h in liquid medium with silica particles, but some with and others without food. During depuration, nematodes were transferred to medium without particles. Nematodes were analysed by an image analysis in both phases to quantify the properties of particle distributions in nematodes' bodies with time. No differences were found in the proportion of nematodes carrying particles in the exposure phase when food was present. However in the depuration phase, lack of food generated a high proportion of particle carriers. Particle distribution properties were also similar in the exposure phase. Nevertheless, lack of food produced particle accumulation due to decelerated excretion because digestive tube relaxed under these conditions. Thus after the depuration phase, lack of food led particles to persist in digestive tubes. According to these results, intake of silica particles had no retention effects when a food flux was provided, but particles were not easily excreted when the food flux was interrupted.

Comparative cytotoxic study of silica materials functionalised with essential oil components in HepG2 cells

This work evaluated the cytotoxic effect of different EOCs-functionalised silica particle types. The in vitro toxicity of eugenol and vanillin-immobilised SAS, MCM-41 microparticles and MCM-41 nanoparticles was evaluated on HepG2 cells, and compared to free EOCs and pristine materials. The results revealed that free essential oil components and bare silica had a mild cytotoxic effect on HepG2 cells. However, the comparative study showed that free eugenol and vanillin had a milder cytotoxic effect than the equivalent concentrations of immobilised components on the different silica particles, while differences in cell viability between the bare and functionalised particles relied on the type of analysed material. The most cytotoxic materials were eugenol and vanillin-functionalised MCM-41 micro with IC₅₀ values of 0.19 and 0.17 mg/mL, respectively, at 48 h exposure. Differences in cytotoxicity between functionalised particles may be attributed to the density of the functional components on their surface as a result of the functionalisation reaction performance for different materials. The study of the physico-chemical properties of particles demonstrated that cationic nature and increased hydrophobicity could be responsible for promoting cell-particle interactions for the eugenol and vanillin functionalised silica particles, enhancing their cytotoxic behaviour.