Light-Harvesting Artificial Cells Containing Cyanobacteria for CO2 Fixation and Further Metabolism Mimicking

The bottom-up constructed artificial cells help to understand the cell working mechanism and provide the evolution clues for organisms. The energy supply and metabolism mimicry are the key issues in the field of artificial cells. Herein, an artificial cell containing cyanobacteria capable of light harvesting and carbon dioxide fixation is demonstrated to produce glucose molecules by converting light energy into chemical energy. Two downstream “metabolic” pathways starting from glucose molecules are investigated. One involves enzyme cascade reaction to produce H₂O₂ (assisted by glucose oxidase) first, followed by converting Amplex red to resorufin (assisted by horseradish peroxidase). The other pathway is more biologically relevant. Glucose molecules are dehydrogenated to transfer hydrogens to nicotinamide adenine dinucleotide (NAD⁺) for the production of nicotinamide adenine dinucleotide hydride (NADH) molecules in the presence of glucose dehydrogenase. Further, NADH molecules are oxidized into NAD⁺ by pyruvate catalyzed by lactate dehydrogenase, meanwhile, lactate is obtained. Therefore, the cascade cycling of NADH/NAD⁺ is built. The artificial cells built here pave the way for investigating more complicated energy-supplied metabolism inside artificial cells.     

Chemical durability of a superconducting oxide YBa2Cu3Ox in aqueous solutions of varying pH values

The chemical durability of a superconducting oxide YBa₂Cu₃O _x in the aqueous solution was investigated as a function of pH value by measuring the amount of leaching of the cations in the solution by inductively coupled plasma (ICP) analysis. The chemical durability of YBa₂Cu₃O _x was very low in highly acidic solutions of pH ca, 1, where the cations were dissolved in the same cation ratio as that of the compound. In an ion-exchanged water and NaOH solution, barium ions were leached out preferentially and almost no yttrium and copper ions were leached out. When NH₄OH was used as a basic reagent, the amounts of barium ions leached out were higher than in the NaOH solution of the same pH value and the dissolution of copper ions was observed, unlike in the NaOH solution of the same pH value. These observations were explained in terms of the chemical stability of individual oxide components.     

Rapid screening of potential metallic glasses for biomedical applications

This paper presents a rapid screening process to select potential titanium and zirconium based metallic glasses (MGs) for bio-material applications. Electrochemical activity of 7 MGs including 6 bulk metallic glasses and 1 thin-film deposited MG in simulation body and human serum is first inspected. A low-voltage potential state test is also developed to simulate the cell membrane potential that the implant MGs will suffer. Results show that the MGs composed of Ti₆₅Si₁₅Ta₁₀Zr₁₀ and Ta₅₇Zr₂₃Cu₁₂Ti₈ exhibit excellent electrochemical stability in both simulation body fluid and human serum. In addition, the copper content in the MGs plays an important role on the electrochemical activity. MGs with the copper content higher than 17.5% show significant electrochemical responses. The cytotoxicity of the solid MG samples and the corrosion released ions are also evaluated by an in-vitro MTT test utilizing the murine bone marrow stem cells. Results indicate that all the solid MG samples show no acute cytotoxicity yet the corrosion released ions show significant toxicity for murine bone marrow stem cells. The rapid screening process developed in the present study suggests that the Ti₆₅Si₁₅Ta₁₀Zr₁₀ metallic glass has high potential for biomedical applications due to its good electrochemical stability and very low cytotoxicity.     

Osteoblast-like cell responses to silicate ions released from 45S5-type bioactive glass and siloxane-doped vaterite

Silicate ions released from bioactive glasses and ceramics have been reported to stimulate osteogenic cell functions. Here, we evaluated osteoblast-like cell reactions to silicate ions released from two different types of materials, 45S5 bioactive glass (BG) and siloxane-doped vaterite (SiV), to investigate the influence of the ionic structure of silicate ions on osteoblast-like cell properties. BG and SiV powders were prepared by using melt-quenching and carbonation methods, respectively. Aminopropyltriethoxysilane was used as a siloxane source of SiV. MC3T3-E1 and SaOS-2 cells were cultured in media containing dissolved BG or SiV ions (10–50 ppm of Si). Cell proliferation (metabolic activity), differentiation (alkaline phosphatase activity) and mineralisation (Ca deposition) were examined. ²⁹Si NMR spectra demonstrated that Q^0,1 species and T^0–3 species were released from BG and SiV, respectively. Proliferation and mineralisation of the two types of cells were influenced by silicate ions released from BG and SiV in a concentration-dependent manner. In particular, there were significant differences (P < 0.05) in the degree of proliferation and Ca deposition levels in SaOS-2 cells treated with dissolved BG and SiV ions. Furthermore, Ca deposition in SaOS-2 cells was influenced by both the presence of silicate ions and the duration of exposure of cells to them. The structure of silicate ions influenced the proliferation and mineralisation of SaOS-2 cells incubated for different time periods in culture media containing different Si concentrations. Understanding the effect of Si on bone cell behaviour will enable a design-led approach to further BG optimisation.     

Preliminary evaluation of the in vitro cytotoxicity of PMMA-co-EHA bone cement

This work reports a preliminary in vitro cytotoxicity assessment of new poly (methyl methacrylate)-co-ethyl hexylacrylate (PMMA-co-EHA) bone cement by evaluating the effect of its leachables on the viability of human osteoblast-like cells (MG63 line) and their progression through the cell cycle. MG63 cells were exposed to 72 h-extract dilutions of PMMA-co-EHA and their viability was tested using the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Also, putative changes in the progression of cells through the cell cycle were monitored using flow cytometry. For that the relative nuclear DNA content and the ratio of cells at G₁:S:G₂ stages of the cell cycle were measured after three exposure periods (24, 48 and 72 h). The obtained results revealed a dose-dependent influence of the cement extract in MG63 cell metabolism when compared to cells cultivated in a culture medium only. The MTT assay showed that a moderate number of cells died after exposure to the most concentrated extract. The cell cycle analysis revealed that leachables of PMMA-co-EHA led to significant changes in cellular proliferation, with cells exposed for 48 h to the most concentrated extract being arrested in the S phase of the cell cycle. However, despite the initial period of cytotoxicity, the obtained results suggest that after 72 h of exposure, the surviving cells are able to recover from this arresting condition and continue to proliferate. Therefore, this preliminary study indicates that, at the biological level, PMMA-co-EHA may have potential of being used as a bone cement matrix. However, a more detailed research work is needed to fully understand the factors responsible for the initial cytotoxicity observed.     

Synthesis and cytocompatibility of manganese (II) and iron (III) substituted hydroxyapatite nanoparticles

Manganese (II) and iron (III) substituted hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) nanoparticles were synthesized using wet chemical method. All samples were single-phase, non-stoichiometric and B-type carbonated hydroxyapatite. Compared with pure HA, Mn²⁺ substituted (MnHA) and Fe³⁺ doped HA (FeHA) did not demonstrate significant structure deviation. Since ion exchange mechanism was applied for the synthesis process, the morphology and particle size were not significantly affected: all samples were elongated spheroids of around 70 nm. The presence of Fe and Mn was confirmed by energy dispersive X-ray spectroscopy (EDX) while the concentrations were quantified by inductively coupled plasma (ICP). Fe³⁺ ions were more active than Mn²⁺ ions in replacing Ca²⁺ ions in HA lattice structure. The magnetic property of HA was modified by substitution with Fe. The Fe5 (Fe_added/Ca_added = 5% by molar ratio) was paramagnetic while pure HA was diamagnetic. Results of extraction assay from cells cultured in extracted medium for 72 h suggested that both MnHA and FeHA were non-cytotoxic to osteoblast cells. Meanwhile, the presence of Fe³⁺ ions in HA demonstrated significant positive effect on osteoblast cells, where the cell number on Fe5 pellets was twice that of pure HA and MnHA samples.     

Synergistic effects of bioactive ions and micro/nano-topography on the attachment,proliferation and differentiation of murine osteoblasts (MC3T3)

Surface topography and chemical nature of biological materials play an important role in regulating cell behaviors. For the intention of improving the biological performance of Ti₆Al₄V, the hierarchical micro/nano-topographies containing bioactive ions (Ca²⁺ and Mg²⁺) were fabricated in this study. Briefly, the hierarchical micro/nano-topography was constructed on Ti₆Al₄V surface via sandblasting, acid etching and alkali-hydrothermal treatment. Then Na⁺ existing in the nano-topography was replaced by Ca²⁺ and Mg²⁺ through hydrothermal reaction. The surface topographies and chemical nature of native and treated samples were characterized using laser scanning microscope, X-ray Photoelectron Spectroscopy and field emission scanning electron microscopy with the energy-dispersive spectroscopy. Surface wettability was measured with a contact angle goniometer. A series of biological tests were carried out to evaluate the synergistic effects of bioactive ions and micro/nano-topography on the attachment, proliferation and differentiation of murine osteoblastic MC3T3 cells. The results of in vitro tests indicated that Ca²⁺ and Mg²⁺ in the titanium alloy surface had an affirmative effect on cells attachment, proliferation and differentiation. Cells grown onto micro/nano-structured surface with Ca²⁺ implantation exhibited significantly higher differentiation levels of alkaline phosphatase activity and mineralization compared to that on micro/nano-structured surface with Mg²⁺ implantation. This study provided a novel method to construct a favorable biological environment between tissues and implants.     

Rattle‐Type Fe3O4@SiO2 Hollow Mesoporous Spheres as Carriers for Drug Delivery

Rattle‐type Fe₃O₄@SiO₂ hollow mesoporous spheres with different particle sizes, different mesoporous shell thicknesses, and different levels of Fe₃O₄ content are prepared by using carbon spheres as templates. The effects of particle size and concentration of Fe₃O₄@SiO₂ hollow mesoporous spheres on cell uptake and their in vitro cytotoxicity to HeLa cells are evaluated. The spheres exhibit relatively fast cell uptake. Concentrations of up to 150 µg mL^?1 show no cytotoxicity, whereas a concentration of 200 µg mL^?1 shows a small amount of cytotoxicity after 48 h of incubation. Doxorubicin hydrochloride (DOX), an anticancer drug, is loaded into the Fe₃O₄@SiO₂ hollow mesoporous spheres, and the DOX‐loaded spheres exhibit a somewhat higher cytotoxicity than free DOX. These results indicate the potential of Fe₃O₄@SiO₂ hollow mesoporous spheres for drug loading and delivery into cancer cells to induce cell death.     

Comparative study of synthesized silver and gold nanoparticles using leaves extract of <Emphasis Type="Italic">Bauhinia tomentosa</Emphasis> Linn and their anticancer efficacy

Nanotechnology is an emerging field in science and technology, which can be applied to synthesize new materials at the nanoscale level. The present investigation aimed at comparing the synthesis, characterization and in vitro anticancer efficacy of synthesized silver and gold nanoparticles using leaves extract of Bauhinia tomentosa Linn. Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were synthesized using aqueous extract of leaves with solution of silver nitrate (AgNO₃, 1 mM) and chloroauric acid (HAuCl₄?3H₂O, 1 mM), respectively. The synthesized nanoparticles were characterized using UV–visible spectrophotometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, X-ray diffraction, thermogravimetric analysis and cyclic voltammetry, which confirmed the reduction of Ag⁺ ions to Ag⁰ and Au³⁺ ions to Au ⁰ . The in vitro anticancer efficacy of AgNPs, AuNPs and aqueous extract of leaves confirmed by MTT assay exhibited IC₅₀ concentrations of 28.125, 46.875 and 50 μg ml^?1 for lung A-549 cells, 103.125, 34.375 and 53.125 μg ml^?1 for HEp-2 cells and 62.5, 23.4 and 13.26 μg ml^?1 for MCF-7 cells, respectively. The concentrations indicate that both silver and gold nanoparticles as well as aqueous extract of leaves exhibited high anticancer efficacy.     

Metal ion effects on different types of cell line,metal ion incorporation into L929 and MC3T3-E1 cells,and activation of macrophage-like J774.1 cells

V ions showed high cytotoxicity for mouse fibroblast L929, osteoblastic MC3T3-E1, and macrophage-like J774.1 cells compared with Pb, Cu, Ni, Co, Zn, and Mo ions. The quantities of metal ions incorporated into the L929 and MC3T3-E1 cells increased with increasing metal concentration in the medium, depending on the metal ion type. In particular, the quantities of V incorporated into the cells were markedly higher than those of other metals. It was suggested that the cytotoxicity of a metal ion changes with the quantity of the metal ion incorporated into cells. It was also considered that V ions are incorporated into cells through xanthine derived from fetal bovine serum by high-performance liquid chromatography (HPLC). The strong interaction of Co, Ni and Mo with amino acids was analyzed by HPLC. The rate of increase of nitric oxide (NO) concentration released with the activation of the mouse macrophage-like J774.1 cells increased at a concentration of V ions ten times lower than that of Ni ions. The release of the cytokine tumor necrosis factor-α (TNF-α) from the J774.1 cells started at approximately 0.5 ppm V; interleukin-6 (IL-6) and transforming growth factor-β (TGF-β) showed a marked increase in the rate of increase at more than 1 ppm V. No increase in the concentration of IL-1α, IL-8, IL-15 or granulocyte macrophage-colony stimulating factor (GM-CSF) was observed for V and Ni ions.     

Toxicity of Silver Nanoparticles in Macrophages

Silver nanoparticles (nanosilver) are broadly used today in textiles, food packaging, household devices and bioapplications, prompting a better understanding of their toxicity and biological interactions. In particular, the cytotoxicity of nanosilver with respect to mammalian cells remains unclear, because such investigations can be biased by the nanosilver coatings and the lack of particle size control. Here, nanosilver of well‐defined size (5.7 to 20.4 nm) supported on inert nanostructured silica is produced using flame aerosol technology. The cytotoxicity of the prepared nanosilver with respect to murine macrophages is assessed in vitro because these cells are among the first to confront nanosilver upon its intake by mammals. The silica support facilitates the dispersion and stabilization of the prepared nanosilver in biological suspensions, and no other coating or functionalization is applied that could interfere with the biointeractions of nanosilver. Detailed characterization of the particles by X‐ray diffraction and electron microscopy reveals that the size of the nanosilver is well controlled. Smaller nanosilver particles release or leach larger fractions of their mass as Ag⁺ ions upon dispersion in water. This strongly influences the cytotoxicity of the nanosilver when incubated with murine macrophages. The size of the nanosilver dictates its mode of cytotoxicity (Ag⁺ ion‐specific and/or particle‐specific). The toxicity of small nanosilver (<10 nm) is mostly mediated by the released Ag⁺ ions. The influence of such ions on the toxicity of nanosilver decreases with increasing nanosilver size (>10 nm). Direct silver nanoparticle–macrophage interactions dominate the nanosilver toxicity at sizes larger than 10 nm.     

In vitro response of primary rat osteoblasts to titania/hydroxyapatite coatings compared with transformed human osteoblast-like cells

The biocompatibility of titania/hydroxyapatite (TiO₂HA) composite coatings, at different ratio obtained by sol–gel process, was investigated studying the behavior of primary cultures of rat osteoblastic cells, isolated by femoral trabecular bone tissue. Moreover, the results have been compared with the response of human osteoblast-like MG63 cell line. Cytotoxicity of coatings was assessed by lactate dehydrogenase activity (LDH). The cellular behavior was analyzed by the cell proliferation (MTT test), cell morphology (SEM) and the biochemical markers evaluation of osteoblastic phenotype, such as alkaline phosphatase activity (ALP) and osteocalcin production. The results showed that TiO₂/HA coatings have no toxic effects and seemed to be a good support for cell adhesion and proliferation. Moreover, these materials allowed the differentiation of osteoblasts, stimulating the expression of alkaline phosphatase activity. The responses of the primary rat osteoblasts and human osteoblast-like MG63 cell line grown onto these coatings were similar in terms of proliferation and ALP activity. Differences were found considering the osteocalcin production. The results show that these coatings, thanks to their chemical composition and the deposition technique, are very promising for the potential orthopedic and dental applications.     

Multifunctional Upconversion Mesoporous Silica Nanostructures for Dual Modal Imaging and In Vivo Drug Delivery

Incorporating the agents for magnetic resonance imaging (MRI), optical imaging, and therapy in one nanostructured matrix to construct multifunctional nanomedical platform has attracted great attention for simultaneous diagnostic and therapeutic applications. In this work, a facile methodology is developed to construct a multifunctional anticancer drug nanocarrier by combining the special advantages of upconversion nanoparticles and mesoporous silica. β‐NaYF₄:Yb³⁺, Er³⁺@β‐NaGdF₄:Yb³⁺ is chosen as it can provide the dual modality of upconversion luminescence and MRI. Then mesoporous silica is directly coated onto the upconversion nanoparticles to form discrete, monodisperse, highly uniform, and core–shell structured nanospheres (labeled as UCNPs@mSiO₂), which are subsequently functionalized with hydrophilic polymer poly(ethylene glycol) (PEG) to improve the colloidal stability and biocompatibility. The obtained multifunctional nanocomposites can be used as an anticancer drug delivery carrier and applied for imaging. The anticancer drug doxorubicin (DOX) is absorbed into UCNPs@mSiO₂‐PEG nanospheres and released in a pH‐sensitive pattern. In vitro cell cytotoxicity tests on cancer cells verify that the DOX‐loaded UCNPs@mSiO₂‐PEG has comparable cytotoxicity with free DOX at the same concentration of DOX. In addition, the T₁‐weighted MRI that measures in aqueous solutions reveals that the contrast brightening increases with the concentration of Gd³⁺ component. Upconversion luminescence images of UCNPs@mSiO₂‐PEG uptaken by cells show green emission under 980 nm infrared laser excitation. Finally, the nanocomposites show low systematic toxicity and high in vivo antitumor therapy efficacy. These findings highlight the fascinating features of upconversion‐mesoporous nanocomposites as multimodality imaging contrast agents and nanocarrier for drug molecules.     

Ion release from three lead-free piezoelectric ceramics and their physical and cytotoxicity characteristics

The ions released from the polarized potassium sodium niobate (KNN), lithium-doped potassium sodium niobate (LKNN) and barium titanate (BT) specimens after soaking in a normal saline up to 28 days were monitored. The cytotoxicity of ion released products was evaluated. The cytotoxicity testing on these three lead-free piezoelectric ceramics exhibited low toxicity. However, the decrease of biaxial strength for KNN and the decrease of piezoelectric charge coefficient d₃₃ for LKNN were noted after soaking in saline solution. Such decreases can be related to the release of ions from the surface of the KNN and LKNN specimens during soaking in saline solution.     

Precipitation of carbonate crystal on surface active glasses

Anions, such as CO₃ ^2– and SO₄ ^2– ions, in industrial wastewater can cause serious scale problem in drainage pipes and vessels, when combined with other metal ions in the water. In this study, it was attempted to remove CO₃ ^2– ions from an aqueous solution by using surface active glasses. Glasses with various compositions of SiO₂-Na₂O-B₂O₃-RO (R = Mg, Ca, Sr, Ba) system were reacted in a CO₃ ^2– ion-containing solution with various pH, then the glass surfaces were analyzed by XRD and SEM, and CO₃ ^2– ions in the reacted solution were also measured. CO₃ ^2– ions in the solution were combined with alkaline earth metal ions, which were leached out of the glass, and were precipitated on the glass surface as carbonate crystals. In this way, the carbonate ions could be removed from the solution. The removal capacity of CO₃ ^2– ions is closely related to the surface reactivity of the glass and solubility product constants of the newly formed carbonate crystals. Glass containing either SrO or BaO showed a strong uptake capacity of CO₃ ^2– ions from the solution.     

Hydrothermal precipitation of hydroxyapatite on anodic titanium oxide films containing Ca and P

Highly-crystallized hydroxyapatite (HA) can be precipitated during heat treatment in high-pressure steam at 300 °C on an anodic titanium oxide film containing Ca and P (AOFCP), which has been electrochemically formed on a titanium substrate prior to the hydrothermal treatment. Factors affecting the precipitation, such as a percentage of distilled water in the autoclave and additives in the AOFCP, were evaluated by scanning electron microscopy. Ca²⁺ and PO^3– ₄ ions were leached from the AOFCP into a water layer covering the film surface, and nucleate HA heterogeneously on the porous TiO₂ matrix of the AOFCP which was made by the ion leaching. The morphology of the precipitated crystals was significantly affected by the water volume ratio because the concentrations of the Ca²⁺ and PO₄ ^3– ions varied depending on the thickness of the water layer. The amount of the precipitation decreased on the AOFCP which was formed in the solution containing a small amount of Mg²⁺ ions or formed on Ti-6Al-4V alloy instead of titanium.     

Effects of fluoridation of porcine hydroxyapatite on osteoblastic activity of human MG63 cells

Abstract

Biological hydroxyapatite, derived from animal bones, is the most widely used bone substitute in orthopedic and dental treatments. Fluorine is the trace element involved in bone remodeling and has been confirmed to promote osteogenesis when administered at the appropriate dose. To take advantage of this knowledge, fluorinated porcine hydroxyapatite (FPHA) incorporating increasing levels of fluoride was derived from cancellous porcine bone through straightforward chemical and thermal treatments. Physiochemical characteristics, including crystalline phases, functional groups and dissolution behavior, were investigated on this novel FPHA. Human osteoblast-like MG63 cells were cultured on the FPHA to examine cell attachment, cytoskeleton, proliferation and osteoblastic differentiation for in vitro cellular evaluation. Results suggest that fluoride ions released from the FPHA play a significant role in stimulating osteoblastic activity in vitro, and appropriate level of fluoridation (1.5 to 3.1 atomic percents of fluorine) for the FPHA could be selected with high potential for use as a bone substitute.     

Fatigue limit and crack arrest in alkali-containing silicate glasses

Crack growth, including fatigue limit and crack arrest, have been investigated for glasses of the systemsxNa₂O-11Al₂O₃-(89-x)SiO₂,xNa₂O-(100-x)SiO₂ andxNa₂O-7CaO-(93−x)SiO₂ in water as well as in acid and alkaline solutions. From studies of the dependence of the crack arrest on the alkali content of the glass, the kind of alkali (K⁺, Na⁺, Li⁺), the pH of the corrosive medium, the ageing time and ageing loading in conjunction with measuring the alkali leaching behaviour, the basic mechanism of crack arrest and fatigue limit can be concluded. Owing to load- and medium-dependent diffusion processes, a crack-growth retarding leached layer at the crack is generated with modified strength and crack growth properties compared to the bulk properties. In high alkali-containing glasses the process is additionally stimulated by stresses produced in the leached layer at the crack tip and at the crack surfaces.     

In vitro biocompatibility of modified potassium fluorrichterite and potassium fluorrichterite-fluorapatite glass–ceramics

Potassium fluorrichterite (KNaCaMg₅Si₈O₂₂F₂) glass–ceramics were modified by either increasing the concentration of calcium in the glass (GC5), or by the addition of P₂O₅ to produce potassium fluorrichterite-fluorapatite (GP2). The solubility of the stoichiometric composition (GST), GC5 and GP2 were measured using the standard test described in ISO 6872:1995 (Dental Ceramics). Ion release profiles were determined for Si, Ca, Mg, Na, K and P using inductively coupled plasma mass spectrometry and fluoride ion (F⁻) concentration was measured using an ion-selective electrode. The cytotoxicity of all compositions was assessed using cultured rat osteosarcoma cells (ROS, 17/2.8). Cell response was qualitatively assessed using scanning electron microscopy (SEM) and quantitatively using the Alamar blue assay. GST was the least soluble and also released the lowest concentration of ions following immersion in water. Of the modified compositions, GC5 demonstrated intermediate solubility but the greatest ion release while GP2 exhibited the highest solubility. This was most likely due to GC5 having the greatest proportion of residual glass following crystallisation. The mass loss exhibited by GP2 may have been due in part to the partial disintegration of the surface of specimens during solubility testing. SEM demonstrated that all compositions supported the growth of healthy ROS cells on their surfaces, and this data was further supported by the quantitative Alamar blue assay.     

Effect of particle size on in vitro cytotoxicity of titania and alumina nanoparticles

Aluminium oxide (Al₂O₃) and titanium dioxide (TiO₂) nanoparticles (NPs) have been widely used in nanotechnology-based products. Recently, researchers and the public have raised concerns about the adverse effects of these NPs in biological systems, particularly in humans. The aim of this study was to investigate the possible adverse effects of these two common metal oxide NPs on human lung epithelium cells (A549) and to investigate NP size-dependent effects on these cells, considering both the primary and hydrodynamic particle size. NPs were found to inhibit cell viability and proliferation at the highest concentration level (10?mg/mL) included in this study, as measured by a clonogenic assay. Moreover, cell viability, proliferation and metabolism were impaired to a greater extent by the smaller NPs (5?nm TiO₂ and 10?nm Al₂O₃) relative to the larger particles (200?nm TiO₂ and 50?nm Al₂O₃) included in this study, as measured by cell proliferation and metabolism. Notably, the observed cytotoxic effects correlated to the primary size, rather than the hydrodynamic size. Similarly, NP cytotoxicity was found to be correlated with the NP surface area. These findings highlight the importance of including primary size and surface area information in NP characterisation in cytotoxicity studies.