The layer-by-layer (LbL) templating technique has attracted significant interest as a simple, highly versatile approach that has been widely used to prepare nanostructured materials with tailored properties. The process involves the sequential deposition of species, such as polymers, nanoparticles, lipids, proteins, and dye molecules, onto various templates, which are subsequently removed to yield free-standing structures. Although fine control of the material properties (e.g., size, composition, thickness, permeability, function) is afforded by the type of species LbL-assembled, the morphology and composition of the templates also play a crucial role in determining the properties, and hence potential applications, of the materials generated. In this review, we focus on the two main classes of templates that have been employed to prepare nanostructured materials: planar and colloidal. The use of porous planar and colloidal substrates in LbL templating synthesis is also presented, as this offers opportunities to fabricate novel materials with advanced structuring. Particular emphasis will be placed on using colloidal templates of different composition (e.g., polymer, inorganic, liquid droplets, gas bubbles) and geometry (e.g., spheres, rods, fibers). The assembly routes employed to prepare a range of nanostructured materials, including films, capsules, nanotubes, nanoporous particles, and macroporous and biomimetic structures, are described, together with the potential applications of the materials in fields such as adsorption/immobilization, catalysis, drug delivery, sensing, separations, and synthesis. Future research directions of the LbL templating technique are also discussed.

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We report the preparation and characterization of light-responsive delivery vehicles, microcapsules composed of multiple polyelectrolyte layers and light-absorbing gold nanoparticles. The nanostructured capsules were loaded with macromolecules (fluorescein isothiocyanate-labeled dextran) by exploiting the pH-dependence of the shell permeability, and the encapsulated material was released on demand upon irradiation with short (10 ns) laser pulses in the near-infrared (1064 nm). In addition, the polyelectrolyte multilayer shell was modified with lipids (dilauroylphosphatidylethanolamine) and then functionalized with ligands (monoclonal immunoglobulin G antibodies) for the purposes of enhanced stability and targeted delivery, respectively. We anticipate that these capsules will find application in a range of areas where controlled delivery is desirable.

This paper provides an overview of our recent work in the area of bioinspired colloidal particles. We highlight how modifying the basic polyelectrolyte multilayer shell with materials such as light-absorbing gold nanoparticles, lipid bilayer membranes, and targeting ligands can functionalize colloids prepared via the layer-by-layer assembly technique. These nanoengineered colloids are expected to show promise in areas ranging from drug and gene delivery to cell membrane modeling.

The interaction between gut microbiota and host plays a central role in health. Dysbiosis, detrimental changes in gut microbiota and inflammation have been reported in non-communicable diseases. While diet has a profound impact on gut microbiota composition and function, the role of food additives such as titanium dioxide (TiO 2 ), prevalent in processed food, is less established. In this project, we investigated the impact of food grade TiO 2 on gut microbiota of mice when orally administered via drinking water. While TiO 2 had minimal impact on the composition of the microbiota in the small intestine and colon, we found that TiO 2 treatment could alter the release of bacterial metabolites in vivo and affect the spatial distribution of commensal bacteria in vitro by promoting biofilm formation. We also found reduced expression of the colonic mucin 2 gene, a key component of the intestinal mucus layer, and increased expression of the beta defensin gene, indicating that TiO 2 significantly impacts gut homeostasis. These changes were associated with colonic inflammation, as shown by decreased crypt length, infiltration of CD8 + T cells, increased macrophages as well as increased expression of inflammatory cytokines. These findings collectively show that TiO 2 is not inert, but rather impairs gut homeostasis which may in turn prime the host for disease development.