Aerosol-based fabrication of biocompatible organic-inorganic nanocomposites

A scalable on-demand platform to assemble base nanocarriers for combination cancer therapy

Chemophototherapy is an advanced cancer therapeutic that uses photothermal nanocarriers (NCs) responsive to near-infrared (NIR) light. For the past decade, chemophototherapy has been investigated intensively for clinical translation, and continuous-flow production of biofunctional compounds (NCs, drugs, probes, nanocomposites) has received increasing attention for future therapeutics. However, in situ supply of a stimuli-responsive inorganic core and subsequent tight drug loading on the core are challenging tasks in the practical use of on-demand nanomedicines. Thus, in this study, we designed and evaluated both in vitro and in vivo models of an aero-hydro-aero single-pass production system for chemophotothermally active NCs. We prepare tightly-drug-loadable cores (titanium peroxide [yTiO2] nanovesicles [NVs]) using hydrogen flame pyrolysis of vaporized TiCl4 (aero) and successive ultrasonic H2O2 treatment (hydro). The NVs formed were incorporated with graphene oxide (GO), doxorubicin (D), and polyethylene glycol (P) in a spray to form GO-yTiO2@DP NCs (aero). The NVs' tight DP loading and endothermic effect induced greater, sustained D release and tumor-selective distribution, even for hyperthermic activity. The results showed the route developed may be a stepping stone to scalable, reconfigurable production for on-demand chemophotothermal therapeutics.

Photoinduced Rapid Transformation from Au Nanoagglomerates to Drug-Conjugated Au Nanovesicles

Gold (Au) agglomerates (AGs) are reassembled using Triton X-100 (T) and doxorubicin (D) dissolved in ethanol under 185 nm photoirradiation to form TAuD nanovesicles (NVs) under ambient gas flow conditions. The positively charged Au particles are then electrostatically conjugated with the anionic chains of TD components via a flowing drop (FD) reaction. Photoirradiation of the droplets in a tubular reactor continues the photophysicochemical reactions, resulting in the reassembly of Au AGs and TD into TAuD NVs. The fabricated NVs are electrostatically collected onto a polished aluminum rod in a single-pass configuration. The dispersion of NVs is employed for bioassays to confirm uptake by cells and accumulation in tumors. The chemo-photothermal activity is determined both in vitro and in vivo. Different combinations of components are also used to fabricate NVs using the FD reaction, and these NVs are suitable for gene delivery as well. This newly designed gaseous single-pass process results in the reassembly of Au AGs for incorporation with TD without the need of batch wet chemical reactions, modifications, separations, or purifications. Thus, this process offers an efficient platform for preparing biofunctional Au nanostructures that requires neither complex physicochemical steps nor special storage techniques.

In vitro exposure of simulated meat-cooking fumes to assess adverse biological effects

The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is considered as a human carcinogenic or mutagenic compound that is produced from the co-condensation of creatinine and amino acids as meats cook at high temperatures. The cooking of meats at high temperatures produces fumes, and these fumes can be suspended as aerosols via the vapor-to-particle (or -droplet) process in a temperature gradient field. Size distributions of the aerosols included a significant portion of nano- and submicron-sized particles, and these can be directly deposited in the lungs and on skin by particle transport phenomena near cooking areas. In this study, for the first time, PhIP-incorporated oleic acid (OA, simulating cooking oil) (PhIP@OA) particles, including individual particulate PhIP as simulated fumes from meat cooking, were constantly produced via collison atomization and subsequent drying processes. The aerosol particles were then dispersed in phosphate-buffered saline for cytotoxicity and senescence-associated β-galactosidase assays, which were compared with dissolved PhIP in dimethyl sulfoxide. PhIP and PhIP@OA did not show significant cytotoxic effects on SHSY5Y, MRC5, and human dermal fibroblast cells compared with the dissolved PhIP but clearly induced premature senescence activities that may be caused by a limited release of PhIP molecules from the particulate PhIP.

Use of aerosol route to fabricate positively charged Au/Fe3O4 Janus nanoparticles as multifunctional nanoplatforms

Gold (Au)-decorated iron oxide (Fe₃O₄), Au/Fe₃O₄, Janus nanoparticles were fabricated via the continuous route for aerosol Au incorporation with Fe₃O₄ domains synthesized in an aqueous medium as multifunctional nanoplatforms. The fabricated nanoparticles were subsequently exposed to 185-nm UV light to generate positive charges on Au surfaces, and their activities were tested in computed tomography (CT) and magnetic resonance (MR) imaging, gene-delivery and photothermal therapy. No additional polymeric coatings of the Janus particles also had a unique ability to suppress inflammatory responses in macrophages challenged with lipopolysaccharide, which may be due to the absence of amine groups.

Multifunctional metal-polymer nanoagglomerates from single-pass aerosol self-assembly

In this study, gold (Au)-iron (Fe) nanoagglomerates were capped by a polymer mixture (PM) consisting of poly(lactide-co-glycolic acid), protamine sulfate, and poly-l-lysine via floating self-assembly in a single-pass aerosol configuration as multibiofunctional nanoplatforms. The Au-Fe nanoagglomerates were directly injected into PM droplets (PM dissolved in dichloromethane) in a collison atomizer and subsequently heat-treated to liberate the solvent from the droplets, resulting in the formation of PM-capped Au-Fe nanoagglomerates. Measured in vitro, the cytotoxicities of the nanoagglomerates (>98.5% cell viability) showed no significant differences compared with PM particles alone (>98.8%), thus implying that the nanoagglomerates are suitable for further testing of biofunctionalities. Measurements of gene delivery performance revealed that the incorporation of the Au-Fe nanoagglomerates enhanced the gene delivery performance (3.2 × 10⁶ RLU mg⁻¹) of the PM particles alone (2.1 × 10⁶ RLU mg⁻¹), which may have been caused by the PM structural change from a spherical to a hairy structure (i.e., the change followed the agglomerated backbone). Combining the X-ray-absorbing ability of Au and the magnetic property of Fe led to magnetic resonance (MR)-computed tomography (CT) contrast ability in a phantom; and the signal intensities [which reached 64 s⁻¹T₂-relaxation in MR and 194 Hounsfield units (HUs) in CT at 6.0 mg mL⁻¹] depended on particle concentration (0.5–6.0 mg mL⁻¹).

Triple Hit with Drug Carriers: pH- and Temperature-Responsive Theranostics for Multimodal Chemo- and Photothermal Therapy and Diagnostic Applications

Currently there is a strong need for new drug delivery systems, which enable targeted and controlled function in delivering drugs while satisfying highly sensitive imaging modality for early detection of the disease symptoms and damaged sites. To meet these criteria we develop a system that integrates therapeutic and diagnostic capabilities (theranostics). Importantly, therapeutic efficacy of the system is enhanced by exploiting synergies between nanoparticles, drug, and hyperthermia. At the core of our innovation is near-infrared (NIR) responsive gold nanorods (Au) coated with drug reservoirs--mesoporous silica shell (mSi)--that is capped with thermoresponsive polymer. Such design of theranostics allows the detection of the system using computed tomography (CT), while finely controlled release of the drug is achieved by external trigger, NIR light irradiation--ON/OFF switch. Doxorubicin (DOX) was loaded into mSi formed on the gold core (Au@mSi-DOX). Pores were then capped with the temperature-sensitive poly(N-isopropylacrylamide)-based N-butyl imidazolium copolymer (poly(NIPAAm-co-BVIm)) resulting in a hybrid system-Au@mSi-DOX@P. A 5 min exposure to NIR induces polymer transition, which triggers the drug release (pores opening), increases local temperature above 43 °C (hyperthermia), and upregulates particle uptake (polymer becomes hydrophilic). The DOX release is also triggered by drop in pH enabling localized drug release when particles are taken up by cancer cells. Importantly, the synergies between chemo- and photothermal therapy for DOX-loaded theranostics were confirmed. Furthermore, higher X-ray attenuation value of the theranostics was confirmed via X-ray CT test indicating that the nanoparticles act as contrast agent and can be detected by CT.

UV aerosol synthesis: a one-step route to silica, organic-silica and surfactant/silica nanostructured materials

A flame-free UV-mediated aerosol technology opens the way for the fabrication of organic–inorganic powder products in a single operation and ambient temperature.

Reducing the cytotoxicity of inhalable engineered nanoparticles via in situ passivation with biocompatible materials

The cytotoxicity of model welding nanoparticles was modulated through in situ passivation with soluble biocompatible materials. A passivation process consisting of a spark discharge particle generator coupled to a collison atomizer as a co-flow or counter-flow configuration was used to incorporate the model nanoparticles with chitosan. The tested model welding nanoparticles are inhaled and that A549 cells are a human lung epithelial cell line. Measurements of in vitro cytotoxicity in A549 cells revealed that the passivated nanoparticles had a lower cytotoxicity (>65% in average cell viability, counter-flow) than the untreated model nanoparticles. Moreover, the co-flow incorporation between the nanoparticles and chitosan induced passivation of the nanoparticles, and the average cell viability increased by >80% compared to the model welding nanoparticles. As a more convenient way (additional chitosan generation and incorporation devices may not be required), other passivation strategies through a modification of the welding rod with chitosan adhesive and graphite paste did also enhance average cell viability (>58%). The approach outlined in this work is potentially generalizable as a new platform, using only biocompatible materials in situ, to treat nanoparticles before they are inhaled.

Photoionization of nanosized aerosol gold agglomerates and their deposition to form nanoscale islands on substrates

Positively charged gold nanoparticles can be produced in the aerosol state by ultraviolet irradiation of aerosols at wavelengths above the gold ionization energy. Spark-discharge-generated aerosol gold nanoparticles were mobility-classified, neutralized, and then exposed to ultraviolet irradiation at 185 nm. The charge states were determined using a tandem differential mobility analyzer system, and the results revealed that there was no significant dependence of charging probability upon mobility diameter between 4 and 60 nm (1.55 ± 0.26 in positive elementary charge), probably because of the agglomerated nature of the particles. The ionized particles could be deposited to form nanoscale island patterns on a substrate without the use of templates.

Chitosan-Conjugated Dendritic Ag Nanopowders for Photothermal Therapy Applications

We report the development of Ag nanodendrites where ultrafine Pd particles served as seeds for the subsequent deposition of Ag on their surfaces. By applying chitosan as both a reductant and a stabilizer, chitosan-conjugated Ag dendritic nanopowders were continuously synthesized using a serial system consisting of a spark discharge, an ultrasound-assisted polyol cell, and a collison atomizer with a heated tubular reactor. The resulting materials were then employed to kill cancerous cells photothermally. A spark discharge between Pd electrodes was employed to vaporize Pd components into a N₂ flow, and finally Pd particles were injected into an ultrasound irradiating Ag polyol cell to initiate Ag deposition on incoming Pd primary particles (∼4 nm in lateral dimension). The chitosan-conjugated Ag nanodendrites (∼240 nm in lateral dimension) were formed through collison atomization, and the nanodendrites were employed as sensitizers for photothermal cancerous cell killing under near-infrared irradiation in vitro.

Au-TiO(2) nanoscale heterodimers synthesis from an ambient spark discharge for efficient photocatalytic and photothermal activity

Ultrafine Au particles incorporating TiO2 heterodimers were synthesized using an ambient heterogeneous spark discharge and the resultant materials were employed both in oxidizing photocatalytically CO gas and killing photothermally cancerous cells. Ti-Au spark configuration was employed to vaporize Ti and Au components into an airflow and finally ultrafine Au particles (∼2 nm in lateral dimension) were incorporated with TiO2 nanoparticles in the form of Au-TiO2 heterodimers (∼38 nm in lateral dimension) with enhanced photocatalytic (in CO oxidation) and photothermal activity (in cancerous cell killing) under visible light. We propose that the localized surface plasmon resonance of ultrafine Au particles on TiO2 supports, induced by the visible light, would promote the adsorption-oxidation of CO and photothermal killing of HeLa cells. The present strategy may be suitable to fabricate other Au-metal oxide nanocomposites for catalytic and biomedical applications.

Gas-phase self-assembly of highly ordered titania@graphene nanoflakes for enhancement in photocatalytic activity

The gas-phase self-assembly of reduced graphene oxide (rGO) nanoflakes with highly ordered ultrafine titania (TiO2) particles was performed and the resultant hybrid material displayed an enhanced photocatalytic performance, both in producing hydrogen and in degrading dyes. Freshly synthesized TiO2 nanoparticles (∼35 nm in equivalent mobility diameter) were quantitatively incorporated with nanoscale rGO (∼36 nm in equivalent mobility diameter) in the form of TiO2/rGO hybrid nanoflakes (∼31 nm in equivalent mobility diameter). The TiO2/rGO hybrid flakes were finally employed to evaluate its photocatalytic activity, and it was found that the ability to achieve hydrogen production and dye degradation was greater than that of a hybridized material from commercial p25-TiO2 and large rGO. This gas-phase self-assembly also enhanced the photocatalytic activity by applying different spark configurations to prepare ZnO, Au, or Ag particles incorporated with rGO nanoflakes.

An aerosol-seed-assisted hybrid chemical route to synthesize anisotropic bimetallic nanoparticles

Herein we report the development of anisotropic bimetallic nanoparticles where aerosol gold nanoparticles served as the seeds for the continuous deposition of silver atoms on their surfaces. Initially, aerosol gold nanoparticles were formed by spark discharge and then injected into a silver precursor solution in an impinging device. The gold nanoparticles acted as the seed particles, and catalyzed the reduction of the added silver ions in the presence of ultrasound to yield bimetallic (gold core-silver shell) anisotropic nanoparticles.