Biomimetic Silica Nanocapsules for Tunable Sustained Release and Cargo Protection

MOF-based stimuli-responsive controlled release nanopesticide: mini review

By releasing an adequate amount of active ingredients when triggered by environmental and biological factors, the nanopesticides that respond to stimuli can enhance the efficacy of pesticides and contribute to the betterment of both the environment and food safety. The versatile nature and highly porous structure of metal-organic frameworks (MOFs) have recently garnered significant interest as drug carriers for various applications. In recent years, there has been significant progress in the development of metal-organic frameworks as nanocarriers for pesticide applications. This review focuses on the advancements, challenges, and potential future enhancements in the design of metal-organic frameworks as nanocarriers in the field of pesticides. We explore the various stimuli-responsive metal-organic frameworks carriers, particularly focusing on zeolitic imidazolate framework-8 (ZIF-8), which have been successfully activated by external stimuli such as pH-responsive or multiple stimuli-responsive mechanisms. In conclusion, this paper presents the existing issues and future prospects of metal-organic frameworks-based nanopesticides with stimuli-responsive controlled release.

Steric Effects in the Deposition Mode and Drug-Delivering Efficiency of Nanocapsule-Based Multilayer Films

Using surface-initiated atom transfer radical polymerization (ATRP), block polymers with a series of quaternization degrees were coated on the surface of silica nanocapsules (SNCs) by the "grafting-from" technique. Molnupiravir, an antiviral medicine urgently approved for the treatment of SARS-CoV-2, was encapsulated in polymer-coated SNCs and further incorporated into well-defined films with polystyrene sulfonate (PSS) homopolymers by layer-by-layer (LBL) self-assembly via electrostatic interactions. We investigated the impact of the quaternization degree of the polymers and steric hindrance of functional groups on the growth mode, swelling/deswelling transition, and drug-delivering efficiency of the obtained LBL films. The SNCs were derived from coronas of parent block polymers of matched molecular weights-poly(N-isopropylacrylamide)-block-poly(N,N-dimethylaminoethyl methacrylate) (PNIPAM-b-PDMAEMA)-by quaternization with methyl sulfate. As revealed by the data results, SNCs with coronas with higher quaternization degrees resulted in a larger layering distance of the film structure because of weaker ionic pairing (due to the presence of a bulky methyl spacer) between SNCs and PSS. Interestingly, when comparing the drug release profile of the encapsulated drugs from SNC-based films, the release rate was slower in the case of capsule coronas with higher quaternization degrees because of the larger diffusion distance of the encapsulated drugs and stronger hydrophobic-hydrophobic interactions between SNCs and drug molecules.

Investigation of the Mechanism of SiO2 Particle and Capsule Formation at the Oil-Water Interface of Dye-Stabilized Emulsions

In a previous contribution we described the formation of silica nanostructures in dye-stabilized nanoemulsions from tetraethyl orthosilicate droplets in water. Depending on the type of dye, either capsules (crystal violet, CV) or nanoparticles (congo red, CR) are formed. The thorough study of the sol-gel process uses a combination of time- and/or temperature-resolved small-angle X-ray scattering, transmission electron microscopy, and ¹H NMR spectroscopy to elucidate the detailed kinetics and mechanism of structure formation. In both cases, small nuclei of 1.5-2 nm are formed, followed by either a fast cluster-cluster (CV) or a much slower monomer-cluster aggregation (CR). The former leads to a cross-linked network and finally to patchy capsules, while the latter leads to individual nanoparticles (SNPs). From an Avrami plot it can be deduced that the SNPs are formed by an interface-controlled one-dimensional growth process. The mechanisms are based on the different local environments at the oil-water interface, which is either slightly acidic (CV) or fairly basic (CR). The kinetics differ by a factor between 3 and 20 and are presumably caused by the different mobility of the catalyzing species H⁺ or OH^-.

A Comparison of Environmental Impact of Various Silicas Using a Green Chemistry Evaluator

To answer questions surrounding the sustainability of silica production, MilliporeSigma's DOZN 2.0 Green Chemistry Evaluator was employed as it provides quantitative values based on the 12 principles of Green Chemistry. As a first study using DOZN 2.0 to evaluate the greenness of nanomaterials, a range of silica types were considered and their greenness scores compared. These included low- and high-value silicas, both commercial and emerging, such as precipitated, gel, fumed, colloidal, mesoporous, and bioinspired silicas. When surveying these different types of silicas, it became clear that while low value silicas have excellent greenness scores, high-value silicas perform poorly on this scale. This highlighted the tension between high-value silicas that are desired for emerging markets and the sustainability of their synthesis. The calculations were able to quantify the issues pertaining to the energy-intensive reactions and subsequent removal of soft templates for the sol-gel processes. The importance of avoiding problematic solvents during processes and particularly releasing them as waste was identified. The calculations were also able to compare the amount of waste generated as well as their hazardous nature. The effects of synthesis conditions on greenness scores were also investigated in order to better understand the relationship between the production process and their sustainability.

Facile bioinspired synthesis of iron oxide encapsulating silica nanocapsules

Iron oxide nanoparticles have been extensively studied for a wide variety of applications. However, there remains a challenge in developing hierarchical magnetic iron oxide nanoparticles as existing synthetic techniques require harsh, toxic chemical conditions and high temperatures or give poorly defined product with weak magnetic properties. In addition, drug loading is limited to post-loading methods such as chemical conjugation or surface adsorption that have poor loading efficiency and are prone to premature drug release. We report a facile biomimetic method for making iron oxide nanoparticle-loaded silica nanocapsules based on a bimodal catalytic peptide surfactant stabilized nanoemulsion template. Iron oxide nanoparticles can be preloaded into the oil phase of the nanoemulsion at tunable concentrations, and the excellent surface activity of the designed bimodal peptide in combination with sufficient electrostatic repulsion promotes the stability of the nanoemulsions. Biosilicification induced by the catalytic peptide module leads to the formation of silica shell nanocapsules containing a magnetic oil core. The bioinspired silica nanocapsules encapsulating iron oxide nanoparticles demonstrate the next-generation of magnetic nanostructures for drug delivery applications.

Biomimetic core-shell silica nanoparticles using a dual-functional peptide

Biomimetic nanomaterials have attracted tremendous research interest in the past decade. We recently developed biomimetic core-shell nanoparticles - silica nanocapsules, using a designer dual-functional peptide SurSi under room temperature, neutral pH and without use of any toxic reagents or chemicals. The SurSi peptide is designed capable of not only stabilizing nanoemulsions because of its excellent surface activity, but also inducing the formation of silica through biosilicification at an oil-water interface. However, it remains challenging to precisely control the peptide-induced nucleation and biosilicification specifically at the oil-water interface, thus forming oil-core silica-shell nanocapsules with uniform size and monodispersity. In this study, the fundamental mechanism of silica formation through a peptide catalyzed biosilicification was systematically investigated, so that the formation of oil-core silica-shell nanocapsules can be precisely controlled. The SurSi peptide induced hydrolysis and nucleation of biomineralized silica particles were monitored to study the biosilicification kinetics. Effects of pH, SurSi peptide concentration and pre-hydrolysis of silica precursors were also studied to optimize the formation of biomimetic silica nanocapsules. The fundamental understanding achieved through these systematic studies provides valuable insights for making core-shell nanoparticles via controlling nucleation and reaction at interfaces.

Development of High-Drug-Loading Nanoparticles

Formulating drugs into nanoparticles offers many attractive advantages over free drugs including improved bioavailability, minimized toxic side effects, enhanced drug delivery, feasibility of incorporating other functions such as controlled release, imaging agents for imaging, targeting delivery, and loading more than one drug for combination therapies. One of the key parameters is drug loading, which is defined as the mass ratio of drug to drug-loaded nanoparticles. Currently, most nanoparticle systems have relatively low drug loading (<10 wt%), and developing methods to increase drug loading remains a challenge. This Minireview presents an overview of recent research on developing nanoparticles with high drug loading (>10 wt%) from the perspective of synthesis strategies, including post-loading, co-loading, and pre-loading. Based on these three different strategies, various nanoparticle systems with different materials and drugs are summarized and discussed in terms of their synthesis methods, drug loadings, encapsulation efficiencies, release profiles, stabilities, and their applications in drug delivery. The advantages and disadvantages of these strategies are presented with an objective of providing useful design rules for future development of high-drug-loading nanoparticles.

In situ replacement of Cu-DEN: an approach for preparing a more noble metal nanocatalyst for catalytic use

The advantage of dendritic monodisperse macromolecules’ dual templating ability was useful in the formation of silica-supported copper nanoparticles Cu_n@SiO₂NPs.

Evaluation of baiting fipronil-loaded silica nanocapsules against termite colonies in fields

Various pesticide nanocarriers have been developed. However, their pest-control applications remain limited in laboratories. Herein, we developed silica nanocapsules encapsulating fipronil (SNC) and their engineered form, poly(ethyleneimine)-coated SNC (SNC-PEI), based on recombinant catalytic modular protein D4S2 and used them against termite colonies Coptotermes lacteus in fields. To achieve this, an integrated biomolecular bioprocess was developed to produce D4S2 for manufacturing SNC containing fipronil with high encapsulation efficiency of approximately 97% at benign reaction conditions and at scales sufficient for the field applications. PEI coating was achieved via electrostatic interactions to yield SNC-PEI with a slower release of fipronil than SNC without coating. As a proof-of-concept, bait toxicants containing varied fipronil concentrations were formulated and exposed to nine termite mounds, aiming to prolong fipronil release hence allowing sufficient time for termites to relocate the baits into and distribute throughout the colony, and to eliminate that colony. Some baits were relocated into the mounds, but colonies were not eliminated due to several reasons. We caution others interested in producing bait toxicants to be aware of the multilevel resistance mechanisms of the Coptotermes spp. “superorganism”.

Bioinspired Core-Shell Nanoparticles for Hydrophobic Drug Delivery

A large range of nanoparticles have been developed to encapsulate hydrophobic drugs. However, drug loading is usually less than 10 % or even 1 %. Now, core-shell nanoparticles are fabricated having exceptionally high drug loading up to 65 % (drug weight/the total weight of drug-loaded nanoparticles) and high encapsulation efficiencies (>99 %) based on modular biomolecule templating. Bifunctional amphiphilic peptides are designed to not only stabilize hydrophobic drug nanoparticles but also induce biosilicification at the nanodrug particle surface thus forming drug-core silica-shell nanocomposites. This platform technology is highly versatile for encapsulating various hydrophobic cargos. Furthermore, the high drug loading nanoparticles lead to better in vitro cytotoxic effects and in vivo suppression of tumor growth, highlighting the significance of using high drug-loading nanoparticles.