Slight alterations in nanoparticles’ surface properties can significantly influence the corona composition which may alter their interaction with the biological milieu. Size and porosity of silica nanoparticles (SNPs) are known to be predominant factors influencing their dose-dependent toxicity. Little is known however about the extent and type of protein adsorption on SNPs as a function of physicochemical properties and the role this might play on mechanisms of cellular uptake and toxicity. In this work we investigated the influence of size and porosity of SNPs on protein adsorption, cellular uptake, and toxicity in RAW 264.7 macrophages. Toxicity of the SNPs was found to be concentration dependent, and the formation of the protein corona mitigated toxicity for all particles. Detailed analysis of the amount of proteins recovered from each nanoparticle revealed similarities in the protein adsorption profile as a function of size and porosity. The mechanism of uptake was highly dependent on size rather than porosity or the adsorbed proteins.

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Design and development of silica nanoparticles (SiO2 NPs) with a controlled degradation profile promises effective drug delivery with a predetermined carrier elimination profile. In this research, we fabricated a series of redox-responsive polysulfide-based biodegradable SiO2 NPs with low polydispersity and with variations in size (average diameters of 58 ± 7, 108 ± 11, 110 ± 9, 124 ± 9, and 332 ± 6 nm), porosity, and composition (disulfide vs tetrasulfide bonds). The degradation kinetics of the nanoparticles was analyzed in the presence of 8 mM glutathione (GSH), mimicking the intracellular reducing condition. Results indicate that porosity and core composition play the predominant roles in the degradation rate of these nanoparticles. The 108 nm mesoporous disulfide-based nanoparticles showed the highest degradation rate among all the synthesized nanoparticles. Transmission electron microscopy (TEM) reveals that nonporous nanoparticles undergo surface erosion, while porous nanoparticles undergo both surface and bulk erosion under reducing environment. The cytotoxicity of these nanoparticles in RAW 264.7 macrophages was evaluated. Results show that all these nanoparticles with the IC50 values ranging from 233 ± 42 to 705 ± 17 μg mL−1 do not have cytotoxic effect in macrophages at concentrations less than 125 μg mL−1. The degradation products of these nanoparticles collected within 15 days did not show cytotoxicity in the same macrophage cell line after 24 h of incubation. In vitro doxorubicin (DOX) release was examined in 108 nm mesoporous disulfide-based nanoparticles in the absence and presence of 8 mM GSH. It was shown that drug release depends on intracellular reducing conditions. Due to their ease of synthesis and scale up, robust structure, and the ability to control size, composition, release, and elimination, biodegradable SiO2 NPs provide an alternative platform for delivery of bioactive and imaging agents.

Tunable glutathione (GSH)-sensitive hollow mesoporous silica nanoparticles (HMSiO NPs) were developed using a structural difference-based selective etching strategy. These organosilica hollow nanoparticles contained disulfide linkages (S-S) in the outer shell which were degraded by GSH. The particles were compared with their nonGSH-sensitive tetraethyl orthosilicate (TEOS) HMSiO counterparts in terms of their synthesis method, characterization, doxorubicin (DOX) release profile, and in vitro cytotoxicity in MCF-7 breast cancer cells. Transmission electron microscopy (TEM) of the particles indicated that the fabricated HMSiO NPs had an average diameter of 130 ± 5 nm. Thermogravimetric analysis (TGA) revealed that GSH-sensitive particles had approximately 5.3% more weight loss than TEOS HMSiO NPs. Zeta potential of these redox-responsive particles was -23 ± 1 mV at pH 6 in deionized (DI) water. Nitrogen adsorption-desorption isotherm revealed that the surface area of the hollow mesoporous nanoreservoirs was roughly 446 ± 6 m g and the average diameter of the pores was 2.3 ± 0.5 nm. TEM images suggest that the nanoparticles started to lose mass integrity from Day 1. The particles showed a high loading capacity for DOX (8.9 ± 0.5%) as a model drug, due to the large voids existing in the hollow structures. Approximately 58% of the incorporated DOX released within 14 days in phosphate buffered saline (PBS) at pH 6 and in the presence of 10 mM of GSH, mimicking intracellular tumor microenvironment while release from TEOS HMSiO NPs was only c.a. 18%. The uptake of these hollow nanospheres by MCF-7 cells and RAW 264.7 macrophages was evaluated using TEM and confocal microscopy. The nanospheres were shown to accumulate in the endolysosomal compartments after incubation for 24 h with the maximum uptake of c.a. 2.1 ± 0.3% and 5.2 ± 0.4%, respectively. Cytotoxicity of the nanospheres was investigated using CCK-8 assay. Results indicate that intact hollow particles (both GSH-sensitive and TEOS HMSiO NPs) were nontoxic to MCF-7 cells after incubation for 24 h within the concentration range of 0-1000 μg ml. DOX-loaded GSH-sensitive nanospheres containing 6 μg ml of DOX killed c.a. 51% of MCF-7 cells after 24 h while TEOS HMSiO NPs killed c.a. 20% with the difference being statistically significant. Finally, cytotoxicity data in RAW 264.7 macrophages and NIH 3 T3 fibroblasts shows that intact GSH-sensitive HMSiO NPs did not show any toxic effects on these cells with the concentrations equal or <125 μg ml.

Careful evaluation of the toxicological response of engineered nanomaterials (ENMs) as a function of physicochemical properties can aid in the design of safe platforms for biomedical applications including drug delivery. Typically, in vitro ENM cytotoxicity assessments are performed under conventional static cell culture conditions. However, such conditions do not take into account the sedimentation rate of ENMs. Herein, we synthesized four types of similar size silica nanoparticles (SNPs) with modified surface roughness, charge, and density and characterized their cytotoxicity under static and dynamic conditions. Influence of particle density on sedimentation and diffusion velocities were studied by comparing solid dense silica nanoparticles of approximately 350 nm in diameter with hollow rattle shape particles of similar size. Surface roughness and charge had negligible impact on sedimentation and diffusion velocities. Lower cellular uptake and toxicity was observed by rattle particles and under dynamic conditions. Dosimetry of ENMs are primarily reported by particle concentration, assuming homogeneous distribution of nanoparticles in cell culture media. However, under static conditions, nanoparticles tend to sediment at a higher rate due to gravitational forces and hence increase effective doses of nanoparticles exposed to cells. By introducing shear flow to SNP suspensions, we reduced sedimentation and nonhomogeneous particle distribution. These results have implications for design of in vitro cytotoxicity assessment of ENMs and suggest that among other factors, sedimentation of nanoparticles in toxicity assessment should be carefully considered.

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Silica nanoparticles (SNPs) are attractive for applications for the delivery of drugs and as imaging agents due to their ease of synthesis and scale up, robust structure, and controllable size and composition. Degradability is one important factor that limits biomedical applications of SNPs. With this in mind, we designed, prepared and characterized novel hydrolysable organosilica nanoparticles (ICPTES-Sorbitol SNPs). These particles were prepared by co-condensation of tetraethoxysilane with a bridged sorbitol-based silsesquioxane precursor containing carbamate linkages. The non-porous spherical ICPTES-Sorbitol SNPs became porous after they were placed in an aqueous environment as a result of the hydrolysis of carbamate bonds and were completely degraded upon prolonged exposure to water. The rate of degradation depended on the pH of the solution, with nanoparticles degrading slower at pH 2 than at pH 4 or pH 7. The degradation was demonstrated by transmission electron microscopy, nitrogen desorption analysis and solution analytical techniques such as ICP-MS and molybdenum blue assay, which was also used to follow the dissolution of ICPTES-Sorbitol SNPs.

Poly(amido amine) (PAMAM) dendrimers have shown transepithelial transport across intestinal epithelial barrier in rats and across Caco-2 cell monolayers. Caco-2 models innately lack mucous barriers, and rat isolated intestinal tissue has been shown to overestimate human permeability. This study is the first report of transport of PAMAM dendrimers across isolated human intestinal epithelium. It was observed that FITC labeled G4-NH2 and G3.5-COOH PAMAM dendrimers at 1 mM concentration do not have a statistically higher permeability compared to free FITC controls in isolated human jejunum and colonic tissues. Mannitol permeability was increased at 10 mM concentrations of G3.5-COOH and G4-NH2 dendrimers. Significant histological changes in human colonic and jejunal tissues were observed at G3.5-COOH and G4-NH2 concentrations of 10 mM implying that dose limiting toxicity may occur at similar concentrations in vivo. The permeability through human isolated intestinal tissue in this study was compared to previous rat and Caco-2 permeability data. This study implicates that PAMAM dendrimer oral drug delivery may be feasible, but it may be limited to highly potent drugs.