Biofunctionalized and self-supported polypyrrole frameworks as nanostructured ECM-like biointerfaces

Tuning Au/SiO2 nanostructures from 1D to 3D interconnected nanotube networks using polycarbonate porous templates

We report a simple process, based on the combination of sol-gel deposition and nano-templating with polycarbonate membranes, for the synthesis of 1D to 3D free-standing silica (SiO2) interconnected nanotube (NT) networks. The thickness and porosity of the SiO2 nanotube walls can be, respectively, controlled by adjusting the ethanol amount in the sol-gel reaction mixture and by the addition or not of a porogen agent during the synthesis. Internal functionalization of 1D and 3D porous and non-porous SiO2 NTs by Au nanoparticles (NPs) was then performed using electroless deposition leading to particle sizes ranging from 15 to 20 nm. Characterization of all these systems by SEM-EDX, TEM, ICP and XPS clearly demonstrated the impact of the porosity of SiO2 on the amount and localization of Au NPs. Selective functionalization of the inner or the inner + outer surfaces of SiO2 NTs was achieved by keeping or freeing the SiO2 NTs from the template prior to electroless deposition, respectively. Moreover, UV-visible analysis confirmed plasmon resonance associated with Au NPs in all functionalized systems, paving the way to applications in many fields such as nano-medicine or (photo-)catalysis. In particular, the free-standing interconnected silica-based nanotube systems provide unique features of great interest for use in nanoscale fluidic bioseparation, sensing, and flow (photo)-catalytic chemistry, as demonstrated herein for the photodegradation of methylene blue.

Layer-by-layer assembly in nanochannels: assembly mechanism and applications

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

Enzyme-assisted mineralization of calcium phosphate: exploring confinement for the design of highly crystalline nano-objects

In hard tissues of vertebrates, calcium phosphate (CaP) biomineralization is a fascinating process that combines specific physicochemical and biochemical reactions, resulting in the formation of extracellular matrices with elegant nanoarchitectures. Although several "biomimetic" strategies have been developed for the design of mineralized nanostructured biointerfaces, the control of the crystallization process remains complex. Herein, we report an innovative approach to overcome this challenge by generating, in situ, CaP precursors in a confined medium. For this purpose, we explore a combination of (i) the layer-by-layer assembly, (ii) the template-based method and (iii) the heterogeneous enzymatic catalysis. We show the possibility of embedding active alkaline phosphatase in a nanostructured multilayered film and inducing the nucleation and growth of CaP compounds under different conditions. Importantly, we demonstrate that the modulation of the crystal phase from spheroid-shaped amorphous CaP to crystalline platelet-shaped hydroxyapatite depends on the degree of confinement of active enzymes. This leads to the synthesis of highly anisotropic mineralized nanostructures that are mechanically stable and with controlled dimensions, composition and crystal phase. The present study provides a straightforward, yet powerful, way to design anisotropic nanostructured materials, including a self-supported framework, which may be used in broad biomedical applications.