The Use of Porous Silica Particles as Carriers for a Smart Delivery of Antimicrobial Essential Oils in Food Applications.

The objective of this study was to design, develop, and quantify the effectiveness of a simple method to facilitate the smart delivery of antimicrobial essential oils (EOs) via their absorption into a chemically bound high surface area support material. To this end, Santa Barbara Amorphous 15 (SBA-15) was functionalized by means of a post-synthetic reaction using (3-aminopropyl)triethoxysilane (APTES) to create an amine-terminated SBA-15 (SBA-APTES), and functionalization was confirmed by FTIR, TGA, and N2 isotherm analysis. Amine-modified SBA-15 was then grafted to a 3-glycidyloxypropyltrimethoxysilane (GPTS)-modified silicon (Si) surface (Si-GPTS), and subsequent attachment to the GPTS-modified surface was confirmed through XPS, dynamic contact angle, and SEM analysis. The smart delivery devices (SBA-15 and SBA-APTES) were then loaded with antimicrobial oregano essential oil (OEO) and the antimicrobial activity was assessed against common food spoilage microorganisms Escherichia coli, Bacillus cereus, Staphylococcus aureus, and Pseudomonas fluorescens. Antimicrobial activity results indicate that both SBA-OEO and SBA-APTES-OEO have good antimicrobial activity and that functionalization of bare SBA-15 with APTES has no effect on antimicrobial activity (P > 0.05) compared to SBA-OEO. Moreover, it appears that direct surface coating of the modified SBA to a surface substrate may not provide a significant quantity of oil needed to elicit an antimicrobial response. Nevertheless, given the strong absorption properties of SBA materials, good antimicrobial activity, and the GRAS nature of SBA-OEO and SBA-APTES-OEO, the results found in this study open potential applications of the functionalized carrier materials.

Precise Definition of a "Monolayer Point" in Polymer Brush Films for Fabricating Highly Coherent TiO2 Thin Films by Vapor-Phase Infiltration.

In this work, we show that in order to fabricate coherent titania (TiO2) films with precise thickness control, it is critical to generate a complete polymer brush monolayer. To date, demonstrations of such dense polymer monolayer formation that can be utilized for inorganic infiltration have been elusive. We describe a versatile bottom-up approach to covalently and rapidly (60 s processing) graft hydroxyl-terminated poly(2-vinyl pyridine) (P2VP-OH) polymers on silicon substrates. P2VP-OH monolayer films of varying thicknesses can subsequently be used to fabricate high-quality TiO2 films. Our innovative strategy is based upon room-temperature titanium vapor-phase infiltration of the grafted P2VP-OH polymer brushes that can produce TiO2 nanofilms of 2-4 nm thicknesses. Crucial parameters are explored, including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with high coverage and uniformity across wafer-scale areas (>2 cm2). Additionally, we compare the P2VP-OH polymer systems with another reactive polymer, poly(methyl methacrylate)-OH, and a relatively nonreactive polymer, poly(styrene)-OH. Furthermore, we prove the latter to be effective for surface blocking and deactivation. We show a simple process to graft monolayers for polymers that are weakly interacting with one another but more challenging for reactive systems. Our methodology provides new insight into the rapid grafting of polymer brushes and their ability to form TiO2 films. We believe that the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area-selective deposition, solar cell absorber layers, and antimicrobial surface coatings.

The use of hydrophobic amino acids in protecting spray dried trehalose formulations against moisture-induced changes.

Trehalose is commonly used as a protein stabilizer in spray dried protein formulations delivered via the pulmonary route. Spray dried trehalose formulations are highly hygroscopic, which makes them prone to deliquescence and recrystallization when exposed to moisture, leading to impairment in aerosolization performance. The main aim of this study was to investigate and compare the effect of hydrophobic amino acids (i.e. L-leucine and L-isoleucine) in enhancing aerosolization performance and in mitigating moisture-induced changes in spray dried trehalose formulations. Trehalose was spray dried with 20-60% w/w of amino acid (i.e. L-leucine or L-isoleucine). The spray dried formulations were stored at 25 °C/50% RH for 28 days. Solid state characterization and in vitro aerosolization performance studies were performed on the spray dried formulations before and after storage. The addition of 20-60% w/w of amino acid (i.e. L-leucine or L-isoleucine) improved the emitted fractions of spray dried trehalose formulations from a dry powder inhaler. However, ≥ 40% w/w of L-leucine/L-isoleucine was needed to prevent recrystallization of trehalose in the formulations when exposed to 25 °C/50% RH for 28 days. X-ray photoelectron spectroscopy (XPS) demonstrated that samples with 40-60% w/w L-isoleucine had more amino acid on the surfaces of the particles compared to their L-leucine counterparts. This may explain the greater ability of the L-isoleucine (40-60% w/w) samples to cope with elevated humidity compared to L-leucine samples of the same concentrations, as observed in the dynamic vapour sorption (DVS) studies. In conclusion, this study demonstrated that both L-leucine and L-isoleucine were effective in enhancing aerosolization performance and mitigating moisture-induced reduction in aerosolization performance in spray dried trehalose formulations. L-isoleucine proved to be superior to L-leucine in terms of its moisture protectant effect when incorporated at the same concentration in the formulations.