Aggregation Of Silica Nanoparticles Research Articles

Extracellular vesicles promote silica nanoparticle aggregation that inhibits silica-induced cytotoxicity

Amorphous silica has been approved as a food and pharmaceutical additive. However, its potential to enhance the carcinogenicity of epithelial cells is incontrovertible. With their expanded surface area per unit mass and distinctive cellular incorporation, nano-sized silica particles (nSPs) exhibit heightened cytotoxicity compared to micrometer-sized counterparts. The precise effect of nSPs on the generation of small extracellular vesicles (sEVs) within endosomes after cellular uptake remains unclear. In the present study, we explored the secretion of sEVs from cells and their functional implications following exposure to nSPs. Our findings demonstrate that nSP50 exposure not only induced epithelial-mesenchymal transition (EMT) but also promoted the maturation of multivesicular endosomes (MVEs) along with the secretion of sEVs in A549 cells. Inhibition of sEV secretion using GW4869 and apoptosis activator 2 exacerbated nSP50-induced EMT, indicating that sEV secretion may suppress EMT. Analysis of the function of sEV in a cell-free system revealed that co-incubation of sEVs with nSP50 led to the formation of micrometer-sized aggregates, which exhibited limited uptake efficiency within A549 cells. These results strongly suggest that the secretion of sEVs plays a protective role against the cytotoxicity attributed to nSP50 exposure.

Mitigating CO2 emanations within the marine concrete industry with different structures of silica nanoparticles

The extensive utilization of marine concrete results in a significant consumption of cement, thereby leading to an increase in CO2 emanations. Enhancing the potency and longevity of marine concrete serves as an efficacious approach to mitigate CO2 emanations. The objective of this investigation was to introduce colloidal silica nanoparticles with distinct three-dimensional structures (MCM-41, SBA-15, and DFNS) for the purpose of enhancing the mechanical functionality and longevity of remarkable sulfate persistence Portland cement. Meantime, the incorporation of silica nanoparticles with distinct three-dimensional architectures (DFNS, MCM-41, and SBA-15) into marine cement mortar was carried out, and an investigation was conducted on the aggregation of silica nanoparticles, as well as the humidifying process and micro-process of the mortar. According to the findings, the addition of silica NPs improved the resilience, mechanical traits, and longevity of the marine cement cases. When the inclusion of silica nanoparticles with varying three-dimensional structures (DFNS, MCM-41, and SBA-15) was implemented, a decrease in both the chloride diffusion coefficient and porosity was observed. The compressive intensity of cement mortar was enhanced in the presence of DFNS, MCM-41, and SBA-15 when compared to control samples, following a rehabilitating period of 5, 15, and 30 days. These advancements in intensity and longevity suggest that DFNS exhibits considerable potential in mitigating CO2 emanations within the marine concrete industry.

Microfluidic assembly of silica nanoparticles within emulsion droplets: Considering the rheological behavior of the dispersed phase

Microfluidic assembly of nanoparticles (NPs) is advantageous in various fields, such as drug delivery and synthesis of photonic crystals and catalysts. The present study uses a flow-focusing microfluidic device to encapsulate silica NPs as water-in-oil (W/O) emulsions. Hence, water-based nanofluids with silica NPs are prepared, and nanofluid droplets are generated at different capillary numbers, flow rate ratios, and nanoparticle concentrations. Although most previous studies neglect the effect of the rheology of nanofluids on droplet formation, this study reveals its significance for determining droplet formation regimes as well as the size and production rates of droplets. As the nanofluid concentration increases, smaller droplets are generated in general with higher production rates. Also, droplet formation regimes are affected by nanoparticle concentrations such that an unusual mode of droplet formation, the binary dripping regime, appears at high concentrations of silica NPs. With the privilege of a computational fluid dynamics (CFD) analysis, it is revealed that the rheological behavior of the employed nanofluids is responsible for these observations. The viscosity of the employed nanofluids significantly affects the duration of the growth stage during droplet formation. As the nanoparticle concentration increases, viscous dissipation increases, which leads to generating smaller droplets with higher production rates. Compared to the interfacial tension, the rheological behavior of the employed nanofluids is more prevailing for determining droplet formation characteristics. This study highlights the rheology effects on the microfluidic generation of nanofluid droplets for the first time and has the potential to push the frontiers of knowledge in colloid science.

The influence of the aqueous media acidity on the electrokinetic potential, aggregation and adsorption properties of silica nanoparticles synthesized from metallurgical wastes

The main physicochemical characteristics of silica nanoparticles synthesized using such metallurgical wastes as copper-smelting slags and microsilica were analyzed and compared to fumed silica A-60. For silicas in the aqueous media, electrokinetic potential, morphology, particle size distribution, and adsorption activity with respect to low molecular weight solutes vs. the pH values were studied using quasi-elastic light scattering, scanning electron and optical microscopies, potentiometry, and infrared (IR) spectroscopy. It was found that the absolute value of the zeta potential for all the studied silicas does not exceed 30 mV that indicates certain instability of the aqueous suspensions. The value of the isoelectric point is within 2.98–3.30, at which the effective diameter of the particles has a maximum value. It has been determined that the synthesized silica has a sufficiently high sorption activity with respect to Methylene Blue and Congo Red at Qmax = 15 mg/g for MB and Qmax = 20 mg/g for CR. The efficiency of the dye adsorption greatly depends on the aqueous medium acidity since the maximum Methylene Blue extraction is observed in strongly alkaline media in contrast to Congo Red demonstrating maximal adsorption in strongly acidic media. According to the IR spectra, several possible mechanisms of interactions of dyes with the silica particles are considered, and the most probable scheme of such interaction is proposed.

Dispersion of silica nanoparticles in water/ethanol/PEG mixtures for stimuli-responsive aggregation to prepare improved fused silica glass

The preparation of bulk-fused silica glass using stimuli-responsive silica nanoparticle (SiNP) aggregation methods is a promising research topic. For instance, the use of a SiNP/polyethylene glycol (PEG)/polyvinyl butyral (PVB) system for thermoplastic nanocomposite preparation, followed by heat-treatment sintering, has emerged as a highly precise and scalable method for obtaining fused silica glass with a short processing time. In this study, transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and rheological analysis were used to investigate the dispersion of SiNPs in water, ethanol, water/ethanol, and water/ethanol/PEG mixtures. Furthermore, we investigated the effect of the different solvents on regulating external stimuli in the preparation of a SiNP slurry. Our results indicate that water/ethanol mixtures have a greater ability to obtain dispersed and thin slurries than water or ethanol alone, while the inclusion of PEG can further enhance this effect.The feedstocks obtained by this method is favorable for obtaining defect-free fused silica glass. In addition, agglomerates formed by SiNPs in a liquid environment can be rearranged and partially disassembled under the action of mechanical (shear) forces. Finally, optical profilometry tests showed that the sintered fused silica glass exhibited good surface quality replication, with a roughness Sa of only 148 nm. The finding in this study provides an idea for the preparation of commercial slurry for sintering fused silica glass.

In Situ and Ex Situ Studies of Ring-Like Assembly of Silica Nanoparticles in the Presence of Poly(propylene oxide)-Poly(ethylene oxide) Block Copolymers.

Block copolymer-mediated self-assembly of colloidal nanoparticles has attracted great attention for fabricating various nanoparticle arrays. We have previously shown that silica nanoparticles (SNPs) assemble into ring-like nanostructures in the presence of temperature-responsive block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (PEOVE-PMOVE) in an aqueous phase. The ring-like nanostructures formed within an aggregate of PEOVE-PMOVE when the temperature was increased to 45 °C, at which the polymer is amphiphilic. Herein, we report that SNPs assemble into ring-like nanostructures even with a different temperature-responsive, amphiphilic block copolymer poly(propylene oxide)-block-poly(ethylene oxide) (PPO-PEO) at 45 °C. Field-emission scanning electron microscopy for SNP assemblies that were spin-coated on a substrate indicated that SNP first assembled into chain-like nanostructures and then bent into closed loops over several days. In contrast, in situ small-angle X-ray diffraction measurements revealed the formation of SNP nanorings within 75 s at 45 °C in the liquid phase. These results indicated that ring-like assembly of SNPs occurs quickly in the liquid phase, but the slow formation of Si-O-Si bonds between SNPs leads to their structure being destroyed by spin-coating. Intriguingly, SNPs with a diameter of 15 nm form a well-defined nanoring structure, with five SNPs located at the vertex points of a regular pentagon. Additionally, small-angle neutron scattering, where the contrast of the solvent (a mixture of H2O and D2O) matches that of SNPs, clarified that SNPs are contained within the spherical micelle formed from PPO-PEO. This work offers a facile and versatile approach to preparing ring-like arrays from inorganic colloidal nanoparticles, leading to applications including sensing, catalysis, and nanoelectronics.

PH-controlled release feature of chitosan assembled silica nanoparticles containing nano-formulated curcumin over in vitro gastric and physiological condition

Low water solubility leading to poor bioavailability has an impact on the decreasing of curcumin uptake in the body, resulting in a deficiency of its medicinal benefits. This study aims to overcome the limitations of curcumin by formulating a nano-emulsion called curcumin emulsion (CE). Furthermore, in order to improve the physicochemical properties and drug release features, the CE was encapsulated within chitosan-assembled mesoporous silica nanoparticles (Chi@SiO2@CE). This material was prepared using a one-pot method and was characterized by Attenuated-total reflectance (ATR-FTIR), Particle Size Analyzer (PSA), Thermogravimetric analysis (TGA), N2 adsorption-desorption, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Additionally, antioxidant activity and in vitro drug release were also conducted. The study demonstrated that CE has strong antioxidant activity (IC50 = 14.14 μM) compared to curcumin alone. Additionally, the Chi@SiO2@CE exhibited pH-controlled release behavior, with less than 20% release of curcumin under an artificial gastric environment and 50% release under pH 7.4 conditions within 24 h. Therefore, this research suggest that Chi@SiO2@CE material has potential as a pH-responsive drug delivery material.

Synergistic Role of Temperature and Salinity in Aggregation of Nonionic Surfactant-Coated Silica Nanoparticles.

The adsorption of nonionic surfactants onto hydrophilic nanoparticles (NPs) is anticipated to increase their stability in aqueous medium. While nonionic surfactants show salinity- and temperature-dependent bulk phase behavior in water, the effects of these two solvent parameters on surfactant adsorption and self-assembly onto NPs are poorly understood. In this study, we combine adsorption isotherms, dispersion transmittance, and small-angle neutron scattering (SANS) to investigate the effects of salinity and temperature on the adsorption of pentaethylene glycol monododecyl ether (C12E5) surfactant on silica NPs. We find an increase in the amount of surfactant adsorbed onto the NPs with increasing temperature and salinity. Based on SANS measurements and corresponding analysis using computational reverse-engineering analysis of scattering experiments (CREASE), we show that the increase in salinity and temperature results in the aggregation of silica NPs. We further demonstrate the non-monotonic changes in viscosity for the C12E5-silica NP mixture with increasing temperature and salinity and correlate the observations to the aggregated state of NPs. The study provides a fundamental understanding of the configuration and phase transition of the surfactant-coated NPs and presents a strategy to manipulate the viscosity of such dispersion using temperature as a stimulus.

Low Fouling Nanostructured Cellulose Membranes for Ultrafiltration in Wastewater Treatment

Ultrafiltration (UF) is a common technique used in wastewater treatments. However, the issue of membrane fouling in UF can greatly hinder the effectiveness of the treatments. This study demonstrated a low-fouling composite cellulose membrane system based on microfibrillated cellulose (MFC) and silica nanoparticle additives. The incorporation of 'non-spherical' silica nanoparticles was found to exhibit better structural integration in the membrane (i.e., minimal aggregation of silica nanoparticles in the membrane scaffold) as compared to spherical silica. The resulting composite membranes were tested for UF using local wastewater, where the best-performing membrane exhibited higher permeation flux than commercial polyvinylidene difluoride (PVDF) and polyether sulfone (PES) membranes while maintaining a high separation efficiency (~99.6%) and good flux recovery ratio (>90%). The analysis of the fouling behavior using different models suggested that the processes of cake layer formation and pore-constriction were probably two dominant fouling mechanisms, likely due to the presence of humic substances in wastewater. The demonstrated cellulose composite membrane system showed low-fouling and high restoration capability by a simple hydraulic cleaning method due to the super hydrophilic nature of the cellulose scaffold containing silica nanoparticles.

Green synthesis and characterization of UKMRC-8 rice husk-derived mesoporous silica nanoparticle for agricultural application

Agriculture plays a crucial role in safeguarding food security, more so as the world population increases gradually. A productive agricultural system is supported by seed, soil, fertiliser and good management practices. Food productivity directly correlates to the generation of solid wastes and utilization of agrochemicals, both of which negatively impact the environment. The rice and paddy industry significantly adds to the growing menace of waste management. In low and middle-income countries, rice husk (RH) is an underutilized agro-waste discarded in landfills or burned in-situ. RH holds enormous potential in the development of value-added nanomaterials for agricultural applications. In this study, a simple and inexpensive sol–gel method is described to extract mesoporous silica nanoparticles (MSNs) from UKMRC8 RH using the bottom-up approach. RHs treated with hydrochloric acid were calcinated to obtain rice husk ash (RHA) with high silica purity (> 98% wt), as determined by the X-ray fluorescence analysis (XRF). Calcination at 650 °C for four hours in a box furnace yielded RHA that was devoid of metal impurities and organic matter. The X-ray diffraction pattern showed a broad peak at 2θ≈20–22 °C and was free from any other sharp peaks, indicating the amorphous property of the RHA. Scanning electron micrographs (SEM) showed clusters of spherically shaped uniform aggregates of silica nanoparticles (NPs) while transmission electron microscopy analysis indicated an average particle size of < 20 nm. Besides Energy Dispersive X-Ray which validated the chemical constituent of the silica NPs, the Fourier transform infrared (FT-IR) spectra showed peaks at 796.4 cm−1 and 1052 cm−1 corresponding to O–Si–O symmetric stretching vibration and O–Si–O asymmetric stretching, respectively. The Brunauer–Emmet–Teller (BET) analysis indicated an average pore size = 8.5 nm while the specific surface area and the pore volume were 300.2015 m2/g and 0.659078 cm3/g, respectively. In conclusion, agrowaste-derived MSN was synthesized using a simple and economical sol–gel method without the addition of surfactant reagents for controlled formation at the structural level. Owing to the MSNs’ excellent physical properties, the method established herein, could be used singly (without any modifications) for the functionalization of a myriad of agrochemicals.

A supraparticle-based biomimetic cascade catalyst for continuous flow reaction

Robust millimeter-sized spherical particles with controlled compositions and microstructures hold promises of important practical applications especially in relation to continuous flow cascade catalysis. However, the efficient fabrication methods for producing such particles remain scare. Here, we demonstrate a liquid marble approach to fabricate robust mm-sized porous supraparticles (SPs) through the bottom-up assembly of silica nanoparticles in the presence of strength additive or surface interactions, without the need for the specific liquid-repellent surfaces used by the existing methods. As the proof of the concept, our method was exemplified by fabricating biomimetic cascade catalysts through assembly of two types of well-defined catalytically active nanoparticles. The obtained SP-based cascade catalysts work well in industrially preferred fixed-bed reactors, exhibiting excellent catalysis efficiency, controlled reaction kinetics, high enantioselectivity (99% ee) and outstanding stability (200~500 h) in the cascades of ketone hydrogenation-kinetic resolution and amine racemization-kinetic resolution. The excellent catalytic performances are attributed to the structural features, reconciling close proximity of different catalytic sites and their sufficient spatial isolation.

Multi-angle holographic characterization of individual fractal aggregates.

Holographic particle characterization uses quantitative analysis of holographic microscopy data to precisely and rapidly measure the diameter and refractive index of individual colloidal spheres in their native media. When this technique is applied to inhomogeneous or aspherical particles, the measured diameter and refractive index represent properties of an effective sphere enclosing each particle. Effective-sphere analysis has been applied successfully to populations of fractal aggregates, yielding an overall fractal dimension for the population as a whole. Here, we demonstrate that holographic characterization also can measure the fractal dimensions of an individual fractal cluster by probing how its effective diameter and refractive index change as it undergoes rotational diffusion. This procedure probes the structure of a cluster from multiple angles and thus constitutes a form of tomography. Here we demonstrate and validate this effective-sphere interpretation of aspherical particles' holograms through experimental studies on aggregates of silica nanoparticles grown under a range of conditions.

Reversible assembly of silica nanoparticles at water-hydrocarbon interfaces controlled by SDS surfactant.

Achieving reversible and tunable assembly of silica nanoparticles at liquid-liquid interfaces is vital for a wide range of scientific and technological applications including sustainable subsurface energy applications, catalysis, drug delivery and material synthesis. In this study, we report the mechanisms controlling the assembly of silica nanoparticles (dia. 50 nm and 100 nm) at water-heptane and water-toluene interfaces using sodium dodecyl sulfate (SDS) surfactant with concentrations ranging from 0.001-0.1 wt% using operando ultrasmall/small-angle X-ray scattering, cryogenic scanning electron microscopy imaging and classical molecular dynamics simulations. The results show that the assembly of silica nanoparticles at water-hydrocarbon interfaces can be tuned by controlling the concentrations of SDS. Silica nanoparticles are found to: (a) dominate the interfaces in the absence of interfacial SDS molecules, (b) coexist with SDS at the interfaces at low surfactant concentration of 0.001 wt% and (c) migrate toward the aqueous phase at a high SDS concentration of 0.1 wt%. Energetic analyses suggest that the van der Waals and electrostatic interactions between silica nanoparticles and SDS surfactants increase with SDS concentration. However, the favorable van der Waals and electrostatic interactions between the silica nanoparticles and toluene or heptane decrease with increasing SDS concentration. As a result, the silica nanoparticles migrate away from the water-hydrocarbon interface and towards bulk water at higher SDS concentrations. These calibrated investigations reveal the mechanistic basis for tuning silica nanoparticle assembly at complex interfaces.

Quadrature moment simulation of silica nanoparticles aggregation and breakage in chemical mechanical polishing

Chemical mechanical polishing (CMP), a wafer surface planarization method, is critical in the semiconductor industry because uniform and scratch-free processing is required for a highly integrated circuit on the wafer surface. Thus, the prediction of aggregated particle size during CMP helps achieve stable and precise processing during experimental circumstances. Herein, silica nanoparticle aggregation simulation during CMP process-based Quadrature Method of Moments (QMOM) was first described using ANSYS Fluent as a computational fluid dynamics (CFD) tool. Experiments were also implemented in a 10,000 class cleanroom using a CMP polisher actually used in the semiconductor industry. Moreover, a comparison of experimental particle size measured through zeta-potential and particle size analyzer and simulated Sauter mean diameter (D32) showed that the experimental data agreed well with the simulation results.

Polarization-dependent refractive index analysis for nanoporous microcavities by ray tracing of a propagating electromagnetic field

In this study, we demonstrated an accurate estimation of the refractive index in nanoporous structures using a novel hybrid simulation method that combines electromagnetic field analysis and ray tracing based on wave optics and ray optics. A novel theoretical model for the refractive index in a nanoporous structure was developed using a simulation of the effective medium approximation (EMA) and screening effect with consideration of polarization dependence. The optical properties were then experimentally evaluated on aggregates of silica nanoparticles. Based on the measured properties, nanoparticles were predicted to have sufficient transparency for the optical cavity. A nanoporous microdisk laser was thus fabricated with laser dye to demonstrate that the nanoporous microdisk was capable of lasing. The microdisk functioned sufficiently as an optical cavity and had well-matched characteristics. This study provides a novel viewpoint of polarization dependence to estimate the refractive index of nanoporous materials by combining numerical simulations and experiments.

Enhanced catalytic stability of acid phosphatase immobilized in the mesospaces of a SiO2-nanoparticles assembly for catalytic hydrolysis of organophosphates

Abstract Acid phosphatase (APase) was immobilized in discrete mesospaces of an assembly of silica nanoparticles (SiO2NPA) to be used as a heterogeneous catalyst for the hydrolysis of organophosphates often found as pesticide residues in agricultural products. APase immobilized in SiO2NPA exhibited higher catalytic activity than APase supported on conventional porous supports for the hydrolysis of p-nitrophenyl phosphate (p-NPP) with quantitative yield of p-nitrophenol below pH 5.5 due to the efficient diffusion of substrates in the SiO2NPA. Especially, a heterogeneous catalyst prepared by the co-accumulation method, in which silica nanoparticles (SiO2NPs) dispersion containing APase was simply dried to assemble a composite catalyst (APase/SiO2NPA), exhibited four times faster rate for the hydrolysis of p-NPP than the catalyst prepared by the equilibrium adsorption of APase in pre-assembled SiO2NPA. The catalytic stability of immobilized APase above pH 6.0 was enhanced by surface modification of SiO2NPs with 3-aminopropyltriethoxysilane (APase/SiO2NPA-NH2) due to the strong electrostatic interaction between APase and the protonated amino groups at the pH condition. Such stability enhancement was hardly obtained by cross-linking treatment of SiO2NPA to improve the robustness. These results suggest that electrostatic interaction between APase and SiO2NPs is crucial to enhance catalytic stability in the wide range of pH as well as preparation methods for the stable encapsulation.

Crack propagation behaviors in a nanoparticle‐filled rubber studied by in situ tensile electron microscopy

AbstractAlthough fracture resistance is critical for rubber materials, the fracture mechanisms are poorly understood from a microscopic perspective. In this study, a crack propagation process in rubber with silica nanoparticles, which is commonly used to enhance the mechanical properties of rubber materials, was successfully observed in situ with nanoscale resolution using transmission electron microscopy (TEM). The consecutive time‐sliced TEM images clarified that the crack tip propagated along the interfaces between the rubber matrix and aggregates of silica nanoparticles (rubber‐aggregate interfaces). Moreover, the path and propagation rate of the crack were significantly affected by the heterogeneous distribution of the silica aggregates, which resulted in a “stick–slip” propagation behavior of the crack tip. Detailed spatial strain analysis revealed that the local maximum principal strain () around the crack tip was nonuniform. The crack tip propagated through regions with large , delaminating the rubber‐aggregate interfaces. This study successfully demonstrated that the heterogeneous distribution of nanoparticles significantly affects the fracture behavior of nanoparticle‐filled rubbers.

Fiber template approach toward preparing one-dimensional silica nanostructure with rough surface

Silica nanofibers were grown on the surface of chitosan nanofibers used as templates by coating the surface with silica derived from the hydrolysis and condensation of tetraethoxysilane using ammonium hydroxide as a catalyst. This was followed by the decomposition of the chitosan template. The relationship between different processing factors (type of templates as well as amounts of catalyst and template) and the formation of silica nanofibers was examined. Varying the processing factors was found to be effective in controlling the morphology of the silica nanofibers. The use of chitosan nanofibers effectively led to the formation of one-dimensional silica nanofibers as the positively charged chitosan nanofibers promoted the deposition of the negatively charged silica nanoparticles through electrostatic attractive forces. Therefore, the chitosan nanofibers acted as good deposition sites for interacting with silica nanoparticles. Although a large amount of catalyst promoted the sol-gel reaction, the silica nanoparticles grew excessively in the solvent. Therefore, the surface structure of the prepared silica nanofibers could be controlled by varying the amount of chitosan template as this also varied the formation mechanism of the silica nanofibers. The resultant samples had a rough silica wall composed of densely assembled silica nanoparticles, with a high specific surface area (338 m2/g).

Understanding the temperature induced aggregation of silica nanoparticles decorated with temperature-responsive polymers: Can a small step in the chemical structure make a giant leap for a phase transition?

Temperature-responsive nanomaterials have gained increasing interest over the past decade due their ability to undergo conformational changes in situ, in response to a change in temperature. One class of temperature-responsive polymers are those with lower critical solution temperature, which phase separate in aqueous solution above a critical temperature. When these temperature-responsive polymers are grafted to a solid nanoparticle, a change in their surface properties occurs above this critical temperature, from hydrophilic to more hydrophobic, giving them a propensity to aggregate. This study explores the temperature induced aggregation of silica nanoparticles functionalised with two isomeric temperature-responsive polymers with lower critical solution temperature (LCST) behavior, namely poly(N-isopropyl acrylamide) (PNIPAM), and poly(2-n-propyl-2-oxazoline) (PNPOZ) with similar molecular weights (5000 Da) and grafting density. These nanoparticles exhibited striking differences in the temperature of aggregation, which is consistent with LCST of each polymer. Using a combination of small-angle neutron scattering (SANS) and dynamic light scattering (DLS), we probed subtle differences in the aggregation mechanism for PNIPAM- and PNPOZ-decorated silica nanoparticles. The nanoparticles decorated with PNIPAM and PNPOZ show similar aggregation mechanism that was independent of polymer structure, whereby aggregation starts by the formation of small aggregates. A further increase in temperature leads to interaction between these aggregates and results in full-scale aggregation and subsequent phase separation.

Hydrogel-Tissue Adhesion Using Blood Coagulation Induced by Silica Nanoparticle Coatings.

The fixation of hydrogels to biological tissues is a major challenge conditioning the development of implants and surgical techniques. Here, coatings of procoagulant nanoparticles are devised which use the presence of blood to create adhesion between hydrogels and soft internal organs. Those nanostructured coatings are simply adsorbed at the hydrogel surfaces and can rapidly activate the formation of an interfacial blood clot acting as an adhesive joint. This concept is demonstrated on pig liver capsules with model poly(ethylene-glycol) membranes that are intrinsically poorly adhesive. In the absence of blood, ex vivo peeling tests show that coatings with aggregates of bare silica nanoparticles induce a 2- to 4-fold increase in adhesion energy as compared to the uncoated membrane (3 ± 2 J m-2). This effect is found to scale with the specific surface area of the coating. The highest adhesion energies produced by these nanoparticle-coated membranes (10 ± 5 J m-2) approach the value obtained with cyanoacrylate glue (33 ± 11 J m-2) for which tearing of the tissue is observed. Ex vivo pull-off tests show an adhesion strength of coated membranes around 5 ± 1 kPa, which is significantly reduced when operating in vivo (1.0 ± 0.5 kPa). Nevertheless, when blood is introduced at the interface, the in vivo adhesion strength can be improved remarkably with silica coatings, reaching 4 ± 2 kPa after 40 min contact. In addition, these silica-coated membranes can seal and stop the bleeding produced by liver biopsies very rapidly (<30 s). Such a combination of coagulation and particle bridging opens promising routes for better biointegrated hydrogel implants and improved surgical adhesives, hemostats, and sealants.