Aqueous dispersions of organogel nanoparticles - potential systems for cosmetic and dermo-cosmetic applications

Mechanically Flexible Self-Healing Mg(II)-Metallogel: Approach of Triggering the ROS-Induced Apoptosis in Human Breast Cancer Cells

A self-assembly-directed thixotropic metallohydrogel (i.e., Mg-Tetrakis) of Mg(II)-metal salt and N,N,N',N'-tetrakis(2-hydroxy-ethyl)ethylenediamine (i.e., Tetrakis) was successfully achieved. The organic chemical component N,N,N',N'-tetrakis(2-hydroxy-ethyl)ethylenediamine was used as a low-molecular-weight gelator, and water was employed as the gel-forming solvent. The fabricated supramolecular metallohydrogel promisingly depicted viscoelastic and mechanoelastic behaviors, which are interpreted through various rheological parameters. The thixotropic behavior of the metallohydrogel is also well characterized through this rheological study. Field emission scanning electron microscopy microstructural analyses were performed to visualize the morphological arrangements of the metallohydrogel. The anticancer properties of the synthesized metallogels are investigated through this work. The cytotoxic potential of the metallohydrogel on the MCF-7 breast cancer cell line is critically examined. Reducing the growth of breast cancer cell line MCF-7 through the treatment of gel on the colony formation assay has been explored through the work. The antimigratory potential of the metallohydrogel on the MCF-7 cell was also scrutinized. The anticancer effect of the fabricated metallohydrogel is inspected through various assay formation strategies, like wound healing assay, tumor spheroid inhibition assay, nuclear fragmentation assay, and so on. Quantitative reactive oxygen species analysis of the cancer cells by treatment with the metallohydrogel was also conducted through this study. The mechanistic apoptosis study was executed by studying the expression of various apoptotic markers like BAX, BCL2, PUMA, and NOXA.

Solvent-Directed Bioactive Supramolecular Zinc(II)-Metallogels: Exploring Semiconducting Aptitudes of Fabricating p-n Junction and Schottky Devices

α-Ketoglutaric acid-based supramolecular Zn(II) metallogels in N,N'-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) solvent (i.e., Zn-α-Glu-DMF and Zn-α-Glu-DMSO) were successfully achieved. Zinc(II) acetate salt and α-ketoglutaric acid directed a three-dimensional noncovalent supramolecular network individually entrapped with N,N'-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) solvent to accomplish their respective semisolid flexible metallogel frameworks. The gel features of these synthesized materials were verified by rheological experiments such as amplitude sweep and frequency sweep measurements. The discrete morphological arrangements were analyzed for these metallogel samples through field emission scanning electron microscopic (FESEM) analysis. Highly stacked interconnected blocks of Zn-α-Glu-DMF with hierarchical arrays are found due to the occurrence of diverse noncovalent supramolecular interactions present in the metallogel framework. A distinct spherical shaped microstructure with interconnected hierarchical assembly has been observed for the FESEM pattern of Zn-α-Glu-DMSO. FTIR spectroscopic measurement was carried out to detect some important stretching vibrations of xerogel samples of different metallogels as well as gel-constructing chemical ingredients. A substantial amount of peak shifting of xerogel samples for both metallogels is observed in FTIR analysis, indicating the presence of different noncovalent interactions. ESI-mass analysis portrays a possible metallogel-constructing strategy. The antibacterial potentialities of both metallogels were investigated. These materials exhibited good antimicrobial efficacy toward Gram-positive and Gram-negative bacterial strains (including Escherichia coli, Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, and Salmonella typhimurium). Both synthesized metallogels were successfully implemented to fabricate the photoresponsive semiconducting diode. These materials offer excellent photodiode parameters including an ideality factor and rectification ratio (ON/OFF ratio). Synthesized metallogels are used to successfully fabricate photodiodes with an Al/p-Si/metallogel/Au structure. The ideality factors (η) for Zn-α-Glu-DMF and Zn-α-Glu-DMSO are found as 1.3 and 2.3, respectively, in dark conditions. The rectification ratios for Zn-α-Glu-DMF and Zn-α-Glu-DMSO metallogels are also determined, and these are found as 40 and 10, respectively.

Surfactant-Driven Dynamic Changes in Rheology of Activated Carbon Slurry Electrodes

Carbon black slurry electrodes are an effective means to improve flow battery performance by increasing the active surface area necessary for electrochemical reactions with a cost-effective material. Current challenges with this specific flow battery chemistry include the stability and flowability of the carbon black suspensions, especially in response to formulation choices. Advancing the manufacturing, operation, and performance of these redox flow batteries requires a deeper understanding of how slurry formulation impacts its rheological profile and ultimately battery performance. In response to this need, the linear and nonlinear rheological responses of activated carbon (AC) based slurry electrode materials used in an all-iron flow battery in the presence of a nonionic surfactant (Triton X-100) were measured. Results from these measurements show the slurry is a colloidal gel with elasticity remaining constant despite increasing surfactant concentration until α (= Csurf/CAC) < 0.65. However, at α ≥ 0.65, the slurry abruptly transitions to a fluid with no measurable yield stress. This critical surfactant concentration at which the rheological profile undergoes a dynamic change matches the concentration found previously for gel collapse of this system. Moreover, this transition is accompanied by a complete loss of electrical conductivity. From these data we conclude the site specific adsorption of surfactant molecules often used in slurry formulation has a significant and dramatic impact on the stability and flowability of these suspensions. Work presented herein demonstrates the importance of additive choices when formulating a slurry electrode.

Organogels: "GelVolution" in Topical Drug Delivery - Present and Beyond

Topical drug delivery holds immense significance in dermatological treatments due to its non-invasive nature and direct application to the target site. Organogels, a promising class of topical drug delivery systems, have acquired substantial attention for enhancing drug delivery efficiency. This review article aims to explore the advantages of organogels, including enhanced drug solubility, controlled release, improved skin penetration, non-greasy formulations, and ease of application. The mechanism of organogel permeation into the skin is discussed, along with formulation strategies, which encompass the selection of gelling agents, cogelling agents, and additives while considering the influence of temperature and pH on gel formation. Various types of organogelators and organogels and their properties, such as viscoelasticity, non-birefringence, thermal stability, and optical clarity, are presented. Moreover, the biomedical applications of organogels in targeting skin cancer, anti-inflammatory drug delivery, and antifungal drug delivery are discussed. Characterization parameters, biocompatibility, safety considerations, and future directions in optimizing skin permeation, ensuring long-term stability, addressing regulatory challenges, and exploring potential combination therapies are thoroughly examined. Overall, this review highlights the immense potential of organogels in redefining topical drug delivery and their significant impact on the field of dermatological treatments, thus paving the way for exciting prospects in the domain.

Development of Gelled-Oil Nanoparticles for the Encapsulation and Release of Berberine

In this study, a new drug carrier based on gelled-oil nanoparticles (GNPs) was designed and synthesized for the encapsulation and release of the model hydrophobic drug, berberine chloride (BCl). Two compositions with different oil phases were examined, sesame oil (SO) and cinnamaldehyde (Cin), which were emulsified with water, stabilized with Tween 80 (Tw80), and gelled using an N-alkylated primary oxalamide low-molecular-weight gelator (LMWG) to give stable dispersions of GNPs between 100 and 200 nm in size. The GNP formulation with Cin was significantly favored over SO due to (1) lower gel melting temperatures, (2) higher gel mechanical strength, and (3) significantly higher solubility, encapsulation efficiency, and loading of BCl. Also, the solubility and loading of BCl in Cin were significantly increased (at least 7-fold) with the addition of cinnamic acid. In vitro release studies showed that the release of BCl from the GNPs was independent of gelator concentration and lower than that for BCl solution and the corresponding nanoemulsion (no LWMG). Also, cell internalization studies suggested that the N-alkylated primary oxalamide LMWG did not interfere with the internalization efficiency of BCl into mouse mast cells. Altogether, this work demonstrates the potential use of these new GNP formulations for biomedical studies involving the encapsulation of drugs and nutraceuticals and their controlled release.

Influence of solute association on the phase behavior of 12-hydroxystearic acid/n-alkane solutions

The phase behavior of 12-hydroxystearic acid (12-HSA) in even-numbered alkanes ranging from octane (C₈) to hexatriacontane (C₃₆) was measured by visual observation of liquid + solid to liquid and liquid-liquid to liquid cloud points and liquid + solid to liquid + liquid transitions. In general solid phases were stabilized to low concentration and higher temperature with increasing alkane length. Liquid-liquid immiscibility was observed in larger alkanes starting with octadecane. The liquidus lines of shorter alkanes (octane to hexadecane) showing only liquid to liquid + solid transitions were fit with an attenuated associated solution model based on the Flory-Huggins lattice model assuming that 12-HSA forms a carboxylic acid dimer over all concentrations investigated. The fit results show that 12-HSA forms associated structures with degrees of association ranging from 3.7-4.5 dimers in the neat 12-HSA. At low concentrations, the 12-HSA is dissociated into dimers, however the free energy cost of dissociation stabilizes the solid phase giving a sharp knee at low concentrations. The role of 12-HSA association in its phase behavior and gelation behavior are discussed. More broadly, the importance of solute association in small molecule organogelators and its potential as a molecular design parameter similar to other component thermodynamic parameters, such as melting temperature and heat of fusion, is discussed.

Optimization of folic acid Span 60-organogel to enhance its in vitro and in vivo photoprotection: a comparative study

Aim: The acute effects of UV sunlight exposure were inflammation, erythema, and swelling. The present work aims to formulate a novel organogel preparation that can achieve efficient topical folic acid (FA) delivery to cure inflammation from acute exposure to UV sunlight. Methods: The organogels were prepared by direct melting and stirring on a magnetic stirrer. Photostability and in vivo photoprotection were investigated. Results: Optimized organogel showed more sustained release, more photostability, more effective antioxidant activity, higher in vitro sun protection factor, and greater extent of skin photoprotection from natural sunlight. Conclusion: The present results suggest optimized FA organogel as a promising formulation for effective delivery of FA to the skin maximizing it's in vitro and in vivo performance.

Nanoparticles for Topical Application in the Treatment of Skin Dysfunctions-An Overview of Dermo-Cosmetic and Dermatological Products

Nanomaterials (NM) arouse interest in various fields of science and industry due to their composition-tunable properties and the ease of modification. They appear currently as components of many consumer products such as sunscreen, dressings, sports clothes, surface-cleaning agents, computer devices, paints, as well as pharmaceutical and cosmetics formulations. The use of NPs in products for topical applications improves the permeation/penetration of the bioactive compounds into deeper layers of the skin, providing a depot effect with sustained drug release and specific cellular and subcellular targeting. Nanocarriers provide advances in dermatology and systemic treatments. Examples are a non-invasive method of vaccination, advanced diagnostic techniques, and transdermal drug delivery. The mechanism of action of NPs, efficiency of skin penetration, and potential threat to human health are still open and not fully explained. This review gives a brief outline of the latest nanotechnology achievements in products used in topical applications to prevent and treat skin diseases. We highlighted aspects such as the penetration of NPs through the skin (influence of physical-chemical properties of NPs, the experimental models for skin penetration, methods applied to improve the penetration of NPs through the skin, and methods applied to investigate the skin penetration by NPs). The review summarizes various therapies using NPs to diagnose and treat skin diseases (melanoma, acne, alopecia, vitiligo, psoriasis) and anti-aging and UV-protectant nano-cosmetics.

A Review of Potential Use of Amazonian Oils in the Synthesis of Organogels for Cosmetic Application

New strategies for the delivery of bioactives in the deeper layers of the skin have been studied in recent years, using mainly natural ingredients. Among the strategies are organogels as a promising tool to load bioactives with different physicochemical characteristics, using vegetable oils. Studies have shown satisfactory skin permeation, good physicochemical stability mainly due to its three-dimensional structure, and controlled release using vegetable oils and low-molecular-weight organogelators. Within the universe of natural ingredients, vegetable oils, especially those from the Amazon, have a series of benefits and characteristics that make them unique compared to conventional oils. Several studies have shown that the use of Amazonian oils brings a series of benefits to the skin, among which are an emollient, moisturizing, and nourishing effect. This work shows a compilation of the main Amazonian oils and their nutraceutical and physicochemical characteristics together with the minority polar components, related to health benefits, and their possible effects on the synthesis of organogels for cosmetic purposes.

Gel-in-water nanodispersion for potential application in intravenous delivery of anticancer drugs

Organogels are semi-solid systems that can gel organic liquids at low concentrations. The use of organogels in drug delivery has grown rapidly in the last decade owing to their fibrous microstructure and suitability for different routes of administration. The current study is characterized by nanogel dispersion (NGD) development based on emulsion technology. The efficiency of this organogel based NGD as a carrier for anticancer drugs was assessed both in vitro and in vivo. 12-Hydroxystearic acid formed an organogel with lipiodol and encapsulated the anticancer drug paclitaxel. The gel-in-water (G/W) nanodispersion was prepared via ultrasonication and stabilized by a nonionic surfactant. The results showed that the organogel enabled sustained drug release from G/W nanodispersion over time, along with enhanced cellular uptake. The prepared G/W nanodispersion was found to be biocompatible with mouse hepatocytes and fibroblast cells in vitro, whereas paclitaxel-loaded G/W nanodispersion showed cytotoxicity (p <0.05) against lung cancer (A549) cell lines. Similarly, intravenous administration of paclitaxel-loaded G/W nanodispersion exerts an anticancer effect against lung cancer in vivo, with a significant decrease in tumor volume (p <0.05). Therefore, the proposed G/W nanodispersion could be a promising carrier for chemotherapy agents with sustained drug release and better therapeutic outcomes against cancer.

Nanoparticle platforms for dermal antiaging technologies: Insights in cellular and molecular mechanisms

Aging is a continuous process defined by a progressive functional decline in physiological parameters. Skin, being one of the most vulnerable organs, shows early signs of aging which are predominantly affected by intrinsic factors like hormone, gender, mood, enzymes, and genetic predisposition, and extrinsic factors like exposure to radiation, air pollution, and heat. Visible morphological and anatomical changes associated with skin aging occur due to underlying physiological aberrations governed by numerous complex interactions at cellular and subcellular levels. Nanoparticles are perceived as a powerful tool in the cosmeceutical industry both for augmenting the efficacy of existing agents and as a novel standalone therapy. Both organic and inorganic nanoparticles have been extensively investigated in antiaging applications. The use of nanoparticles helps to enhance the activity of antiaging molecules by selectively targeting cellular and molecular pathways. On the other hand, the nanoparticle platforms also gained increasing popularity as the skin protectant against extrinsic factors such as UV radiation and pollutants. This review comprehensively discusses skin aging and its mechanism by highlighting the impact on cellular, subcellular, and epigenetic elements. Importantly, the review elaborates on the examples of organic and inorganic nanoparticle-based formulations developed for antiaging application and provides mechanistic insights on how they modulate the mechanisms of skin aging. The clinical progress of nanoparticle antiaging technologies and factors that impact clinical translation are also explored. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Preparation, Characterization and Evaluation of Organogel-Based Lipstick Formulations: Application in Cosmetics

1,3:2,4-Dibenzylidene-D-sorbitol (DBS) and 12-hydroxystearic acid (12-HSA) are well-known as low-molecular-weight organogelators (LMOGs) capable of gelling an organic liquid phase. Considering their unique chemical and physical properties, we assessed their potential effects in new lipstick formulations by discrimination testing; in vitro measurements of the sun protection factor (SPF); and thermal, mechanical and texture analyzes. DBS and 12-HSA were used to formulate four types of lipsticks: L1 (1% DBS), L2 (10% 12-HSA), L3 (1.5% DBS) and L4 (control, no LMOGs). The lipsticks were tested for sensory perception with an untrained panel of 16 consumers. LMOG formulations exhibited higher UVA protection factor (UVA-PF) and in vitro SPF, particularly in the 12-HSA-based lipstick. Regarding thermal properties, the 12-HSA-based lipstick and those without LMOGs were more heat-amenable compared to thermoresistant DBS-based lipsticks. The results also showed the viscoelastic and thermally reversible properties of LMOGs and their effect of increasing pay-off values. In general, the texture analysis indicated that 12-HSA-based lipstick was significantly harder to bend compared to control, while the other formulations became softer and easier to bend throughout the stability study. This work suggests the potential use of LMOGs as a structuring agent for lipsticks, paving the way towards more photoprotective and sustainable alternatives.

Olive Oil/Pluronic Oleogels for Skin Delivery of Quercetin: In Vitro Characterization and Ex Vivo Skin Permeability

The main objective of this study was to prepare and characterize oleogel as potential carrier for quercetin skin delivery. The formulations were prepared by adding olive oil (5-30%) to Pluronic F127 hydrogel and were evaluated for particle size, zeta potential, viscosity in vitro quercetin release and stability, and were compared with that of Pluronic F127 hydrogel. The selected formulation was characterized for its interaction possibility, ex vivo skin permeation and skin histological changes and safety. The particle sizes ranged from 345.3 ± 5.3 nm to 401.5 ± 2.8 nm, and possessed negative charges. The viscosities of the formulations were found in the range of 6367-4823 cps with inverse proportionality to olive oil percentage while the higher percentages showed higher quercetin release. Percentages of 25% and 30% olive oil showed instability pattern under the conditions of accelerated stability studies. Differential scanning calorimetry verified the existence of quercetin in micellar aggregation and the network in the case of hydrogel and oleogel respectively. Ex vivo skin permeation showed an improved skin permeation of quercetin when 20% olive oil containing oleogel was used. Skin histology after 10 days of application showed stratum corneum disruption and good safety profile. Based on these findings, the proposed oleogel containing 20% olive oil denotes a potential carrier for topical delivery of quercetin.

Influence of vegetable oils in the rheology, texture profile and sensory properties of cosmetic formulations based on organogel

OBJECTIVE

The knowledge about how ingredients in formulation can influence the texture profile is an important factor on the development of a cosmetic product. In this context, the aim of this work was to evaluate the effect of vegetable oils in the texture profile, rheological and sensorial properties of cosmetic formulations based on organogel.

METHODS

Four organogel-based emulsions were developed and supplemented or not with sunflower, macadamia or olive oils. Analyses of rheological behaviour, texture profile and sensory properties were performed.

RESULTS

The vegetable oils added to formulation did not alter the pseudoplastic rheological behaviour, but increased the area of hysteresis and reduced the work of shear of the formulations. In addition, the sunflower seed oil increased the consistency index and all texture parameters while the macadamia oil reduced firmness and consistency. The cosmetic formulation based on organogel containing the sunflower seed oil showed the highest score on sensory evaluation.

CONCLUSION

The vegetable oils affected the rheology behaviour, texture profile and sensory properties of the formulations under study. However, the influence of sunflower oil in organogel-based cosmetic formulation was more pronounced considering texture profile and the response perceived by subjects in the sensorial analysis.

Spatially Resolved Crosslinking of Hydroxypropyl Cellulose Esters for the Generation of Functional Surface-Attached Organogels

Chemistry, geometric shape and swelling behavior are the key parameters that determine any successful use of man-made polymeric networks (gels). While understanding of the swelling behavior of both water-swellable hydrogels and organogels that swell in organic solvents can be considered well-advanced with respect to fossil fuel-based polymer networks, the understanding, in particular, of wood-derived polymers in such a network architecture is still lacking. In this work, we focus on organogels derived from hydroxypropyl cellulose (HPC) ester. The latter polymer was functionalized with saturated and unsaturated fatty acids, respectively. Due to their tailored chemical constitution, we demonstrated that such polysaccharide can be crosslinked and simultaneously surface-bound by using a photo-induced radical reaction using a photo-initiator. Based on the choice of fatty acid used in the design of the HPC ester, and by controlling the degree of substitution (DS) obtained during the esterification of the polysaccharide, modular manipulation of the physical properties (e.g., polarity) of the resulting gel is possible. Depending on the initiator employed, different wavelengths of light, from UV to visible, can be utilized for the crosslinking reaction, which facilitates the deployment of a range of light sources and different lithographic methods. Additionally, we showed that altering of the illumination time allows to tailor the netpoint density, and thus, the degree of linear deformation in equilibrium and the swelling kinetics. Finally, we performed a proof-of-principle experiment to demonstrate the application of our material for the generation of spatially resolved polymer patches to enrich organic molecules from a solution within a microfluidic channel.

Biocellulose Masks as Delivery Systems: A Novel Methodological Approach to Assure Quality and Safety

Bacterial cellulose (BC) has become of great interest in recent years, as a delivery system in several areas of application, including food, drugs, and cosmetics, thanks to its exclusive advantages, such as high biocompatibility, water holding capacity, and good gas permeability. The novel approach of the authors has led to a protocol for checking the quality and safety of bacterial cellulose matrices in the manufacture of cosmetic masks. Two non-destructive techniques, near-infrared spectroscopy (NIR) and multiple light scattering (MLS), were used to verify different parameters affecting the quality of BC sheets, allowing cellulose masks to be checked over time. NIR spectroscopy allowed for discovering changes in the water content, depending on filling/packaging procedures, like flat-folding. Multiple light scattering was used to ascertain the stability of solutions in contact with masks. From a clinical standpoint, the cutaneous tolerability of biocellulose masks, and their effect on skin parameters, were evaluated through some specific “in vivo” tests. Also, a safety evaluation during application was conducted through different studies: a short-term one after single application, and a long-term one upon continued use.

Colloidal Dispersions of Gelled Lipid Nanoparticles (GLN): Concept and Potential Applications

The interest in using colloidal dispersions of gelled lipid nanoparticles (GLN) for different fields of application has increased in recent years, notably in cosmetic, dermatology, and/or pharmaceutics due to their capacity to immobilize compounds with poor water solubility. The pharmaceutical field desires to achieve lipophilic drug formulations which are able to conserve their stability, although it is well-known that emulsions and solid lipid nanoparticles (SLN) present a lack of stability over time, leading to system destabilization. Furthermore, stable colloidal dispersions of gelled oil particles do not affect the properties of the molecule to be delivered, and they result as an alternative for the previously appointed systems. This review is an attempt to present the reader with an overview of colloidal dispersions of GLN, their concept, formulation methods, as well as the techniques used for their characterization. Moreover, various application fields of organogel dispersions have been illustrated to demonstrate the potential application range of these recent materials.

Evaluation of Organogel Nanoparticles as Drug Delivery System for Lipophilic Compounds

The purpose of the study was to evaluate organogel nanoparticles as a drug delivery system by investigating their stability, according to the formulation strategy, and their release profile. The gelled nanoparticles were prepared by hot emulsification (above the gelation temperature) of an organogel in water, and cooling at room temperature. In the first step, we used DLS and DSC to select the most suitable formulations by optimizing the proportion of ingredients (HSA, PVA, castor oil) to obtain particles of the smallest size and greatest stability. Then, two lipophilic drug models, indomethacin and ketoconazole were entrapped in the nanoparticles made of castor oil gelled by 12-hydroxystearic acid. Thermal studies (DSC) confirmed that there was no significant alteration of gelling due to the entrapped drugs, even at 3% w/w. Very stable dispersions were obtained (>3 months), with gelled oil nanoparticles presenting a mean diameter between 250 and 300 nm. High encapsulation efficiency (>98%) was measured for indomethacin and ketoconazole. The release profile determined by in vitro dialysis showed an immediate release of the drug from the organogel nanoparticles, due to rapid diffusion. The study demonstrates the interest of these gelled oil nanoparticles for the encapsulation and the delivery of lipophilic active compounds.

Acyclovir-loaded sorbitan esters-based organogel: development and rheological characterization

Herein, a nanoemulsion-based organogel (NEOG) system loaded with acyclovir has been developed for the effective treatment of herpes simplex virus infection via topical delivery. Pseudo-ternary phase diagram exhibited increase in non-birefrigent, optically isotropic region of organogel with Smix (K_w) ratio. The NEOG C showed good storage (G') and loss moduli (G″), and more compact network structures. Gel-sol transition temperature (Tg) and fractal dimension (D_f) of NEOG system revealed increased density of the tubular network with K_w. Hence, high gelling ability of the developed NEOG system may attribute to the combination of sustained and site-specific delivery of drugs.

Outstanding drug loading capacity by water stable microporous MOF: a potential drug carrier

A robust, highly water stable, microporous MOF, [Zn₈(O)₂(CDDB)₆(DMF)₄(H₂O)] {where CDDB = 4,4′-(9-H carbazole-3,6-diyl)dibenzoic acid}, was synthesized based on an open N–H site by a solvothermal process and exhibited an outstanding loading capacity and satisfactory release capability for 5-fluorouracil, with a negligible cytotoxicity effect.