Silica-rich regenerated cellulose fibers enabled by delayed dissolution of silica nanoparticles in strong alkali using zinc oxide

Silica nanoparticles (SNPs) dissolve in alkaline media, which limits their use in certain applications. Here, we report a delayed dissolution of SNPs in strong alkali induced by zinc oxide (ZnO), an additive which also limits gelation of alkaline cellulose solutions. This allows incorporating high solid content of silica (30 wt%) in cellulose solutions with retention of their predominant viscous behavior long enough (ca. 180 min) to enable fiber wet spinning. We show that without addition of ZnO, silica dissolves completely, resulting in strong gelation of cellulose solutions that become unsuitable for wet spinning. With an increase of silica concentration, gelation of the solutions occurs faster. Employing ZnO, silica-rich regenerated cellulose fibers were successfully spun, possessing uniform cross sections and smooth surface structure without defects. These findings are useful in advancing the development of functional man-made cellulose fibers with incorporated silica, e.g., fibers with flame retardant or self-cleaning properties.

Formation of Supported Lipid Bilayers Derived from Vesicles of Various Compositional Complexity on Conducting Polymer/Silica Substrates

Supported lipid bilayers (SLBs) serve important roles as minimalistic models of cellular membranes in multiple diagnostic and pharmaceutical applications as well as in the strive to gain fundamental insights about their complex biological function. To further expand the utility of SLBs, there is a need to go beyond simple lipid compositions to thereby better mimic the complexity of native cell membranes, while simultaneously retaining their compatibility with a versatile range of analytical platforms. To meet this demand, we have in this work explored SLB formation on PEDOT:PSS/silica nanoparticle composite films and mesoporous silica films, both capable of transporting ions to an underlying conducting PEDOT:PSS film. The SLB formation process was evaluated by using the quartz crystal microbalance with dissipation (QCM-D) monitoring, total internal reflection fluorescence (TIRF) microscopy, and fluorescence recovery after photobleaching (FRAP) for membranes made of pure synthetic lipids with or without the reconstituted membrane protein β-secretase 1 (BACE1) as well as cell-derived native lipid vesicles containing overexpressed BACE1. The mesoporous silica thin film was superior to the PEDOT:PSS/silica nanoparticle composite, providing successful formation of bilayers with high lateral mobility and low defect density even for the most complex native cell membranes.

Contrasting Anti-obesity Effects of Smectite Clays and Mesoporous Silica in Sprague-Dawley Rats

Porous colloids have been shown to exert unique bioactivities for mediating lipid (fat) metabolism and thereby offer significant potential as anti-obesity therapies. In this study, we compare the capacity for two classes of colloids, that is, smectite clays (Laponite XLG, LAP; montmorillonite, MMT) and mesoporous silica (SBA-15 ordered silica; MPS), to impede intestinal lipid hydrolysis and provoke lipid and carbohydrate excretion through adsorption within their particle matrices. A two-stage in vitro gastrointestinal lipolysis model revealed the capacity for both smectite clays and MPS to inhibit the rate and extent of lipase-mediated digestion under simulated fed state conditions. Each system adsorbed more than its own weight of organic media (i.e., lipid and carbohydrates) after 60 min lipolysis, with MMT adsorbing >10% of all available organics through the indiscriminate adsorption of fatty acids and glycerides. When co-administered with a high-fat diet (HFD) to Sprague-Dawley rats, treatment with MMT and MPS significantly reduced normalized rodent weight gain compared to a negative control, validating their potential to restrict energy intake and serve as anti-obesity therapies. However, in vitro-in vivo correlations revealed poor associations between in vitro digestion parameters and normalized weight gain, indicating that additional/alternate anti-obesity mechanisms may exist in vivo, while also highlighting the need for improved in vitro assessment methodologies. Despite this, the current findings emphasize the potential for porous colloids to restrict weight gain and promote anti-obesity effects to subjects exposed to a HFD and should therefore drive the development of next-generation food-grade biomaterials for the treatment and prevention of obesity.

Enhancing the Cellular Uptake and Antibacterial Activity of Rifampicin through Encapsulation in Mesoporous Silica Nanoparticles

An urgent demand exists for the development of novel delivery systems that efficiently transport antibacterial agents across cellular membranes for the eradication of intracellular pathogens. In this study, the clinically relevant poorly water-soluble antibiotic, rifampicin, was confined within mesoporous silica nanoparticles (MSN) to investigate their ability to serve as an efficacious nanocarrier system against small colony variants of Staphylococcus aureus (SCV S. aureus) hosted within Caco-2 cells. The surface chemistry and particle size of MSN were varied through modifications during synthesis, where 40 nm particles with high silanol group densities promoted enhanced cellular uptake. Extensive biophysical analysis was performed, using quartz crystal microbalance with dissipation (QCM-D) and total internal reflection fluorescence (TIRF) microscopy, to elucidate the mechanism of MSN adsorption onto semi-native supported lipid bilayers (snSLB) and, thus, uncover potential cellular uptake mechanisms of MSN into Caco-2 cells. Such studies revealed that MSN with reduced silanol group densities were prone to greater particle aggregation on snSLB, which was expected to restrict endocytosis. MSN adsorption and uptake into Caco-2 cells correlated well with antibacterial efficacy against SCV S. aureus, with 40 nm hydrophilic particles triggering a ~2.5-log greater reduction in colony forming units, compared to the pure rifampicin. Thus, this study provides evidence for the potential to design silica nanocarrier systems with controlled surface chemistries that can be used to re-sensitise intracellular bacteria to antibiotics by delivering them to the site of infection.

Microporosity, Pore Size, and Diffusional Path Length Modulate Lipolysis Kinetics of Triglycerides Adsorbed onto SBA-15 Mesoporous Silica Particles

Understanding lipase-mediated hydrolysis mechanisms within solid-state nanocarriers is fundamental for the rational design of lipid-based formulations. In this study, SBA-15 ordered mesoporous silica (MPS) particles were engineered with well-controlled nanostructural properties to systematically elucidate the role of intrawall microporosity, mesopore size, and particle structure on lipase activity. The microporosity and diffusional path length were shown to be key modulators for lipase-provoked hydrolysis of medium chain triglycerides confined within MPS, with small changes in the pore size, between 9 and 13 nm, showing now a clear correlation to lipase activity. Lipid speciation within MPS after lipolysis, obtained through ¹H NMR, indicated that free fatty acids preferentially adsorbed to rod-shaped MPS (RodMPS) particles with high microporosity. MPS that formed aggregated spindle-like structures (AggMPS) had intrinsically reduced microporosity, which was hypothesized to limit lipase/lipid diffusion to and from the MPS pores and thus retard lipolysis kinetics. A linear correlation between the microporosity and the extent of lipase-provoked hydrolysis was observed within both AggMPS and RodMPS, ultimately indicating that the intricate interplay between the microporosity and lipid/lipase diffusion can be harnessed to optimize lipolysis kinetics for silica-lipid hybrid carriers. The new insights derived in this study are integral to the future development of solid-state lipid-based nanocarriers that control the lipase activity for improving the absorption of poorly soluble bio-active compounds.