Correction: Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions.

Correction for 'Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions' by Thomas Degabriel, Elodie Colaço et al., Phys. Chem. Chem. Phys., 2018, 20, 12898-12907, https://doi.org/10.1039/C7CP08054A.

Embedding Collagen in Multilayers for Enzyme-Assisted Mineralization: A Promising Way to Direct Crystallization in Confinement.

The biogenic calcium phosphate (CaP) crystallization is a process that offers elegant materials design strategies to achieve bioactive and biomechanical challenges. Indeed, many biomimetic approaches have been developed for this process in order to produce mineralized structures with controlled crystallinity and shape. Herein, we propose an advanced biomimetic approach for the design of ordered hybrid mineralized nano-objects with highly anisotropic features. For this purpose, we explore the combination of three key concepts in biomineralization that provide a unique environment to control CaP nucleation and growth: (i) self-assembly and self-organization of biomacromolecules, (ii) enzymatic heterogeneous catalysis, and (iii) mineralization in confinement. We use track-etched templates that display a high density of aligned monodisperse pores so that each nanopore may serve as a miniaturized mineralization bioreactor. We enhance the control of the crystallization in these systems by coassembling type I collagen and enzymes within the nanopores, which allows us to tune the main characteristics of the mineralized nano-objects. Indeed, the synergy between the gradual release of one of the mineral ion precursors by the enzyme and the role of the collagen in the regulation of the mineralization allowed to control their morphology, chemical composition, crystal phase, and mechanical stability. Moreover, we provide clear insight into the prominent role of collagen in the mineralization process in confinement. In the absence of collagen, the fraction of crystalline nano-objects increases to the detriment of amorphous ones when increasing the degree of confinement. By contrast, the presence of collagen-based multilayers disturbs the influence of confinement on the mineralization: platelet-like crystalline hydroxyapatite form, independently of the degree of confinement. This suggests that the incorporation of collagen is an efficient way to supplement the lack of confinement while reinforcing mechanical stability to the highly anisotropic materials. From a bioengineering perspective, this biomineralization-inspired approach opens up new horizons for the design of anisotropic mineralized nano-objects that are highly sought after to develop biomaterials or tend to replicate the complex structure of native mineralized extracellular matrices.

Hierarchical Collagen-Hydroxyapatite Nanostructures Designed through Layer-by-Layer Assembly of Crystal-Decorated Fibrils.

A comprehensive understanding of the mechanism by which type I collagen (Col) interacts with hydroxyapatite nanoparticles (Hap NPs) in aqueous solutions is a pivotal step for guiding the design of biologically relevant nanocomposites with controlled hierarchical structure. In this paper we use a variety of Hap NPs differing by their shape (rod vs platelet) and their size (∼30 vs ∼130 nm) and investigate their mechanism(s) of interaction with collagen. The addition of collagen to the Hap suspensions induces different effects that strongly depend on the nanoparticle type. Interestingly, the use of small rods, typically with ∼30 nm of length (R30), leads to the formation of assembled collagen fibrils decorated with Hap nanocrystals which, in turn, self-assemble progressively to form larger fibrillar Hap-Col composite. The crystals decorating collagen provide "intrinsic" negative charges to the fibrillar objects that allow their incorporation in three-dimensional structure using layer-by-layer (LbL) assembly. This offers a straightforward way to construct a collagen-based hybrid material with well-defined hierarchy under near-physiological conditions. In situ, QCM-D monitoring revealed the buildup of soft and highly hydrated hybrid (PAH/R30-Col)n multilayers for which the mechanism of growth was very different from that observed for polyelectrolytes and nanoparticles without collagen (PAH/R30). The LbL assembly of crystal-decorated collagen yields a hierarchical nanostructured film whose thickness and roughness can be modulated by the addition of salt and incorporate fibrillar objects of about 400 nm in width and few micrometers in length, as probed by AFM. The approach described in this work provides a relevant way to better control the (supra)molecular assembly of Col and Hap NPs with the perspective of developing hierarchical Hap-Col nanocomposites with tuned properties for various biomedical applications.

Factors impacting the aggregation/agglomeration and photocatalytic activity of highly crystalline spheroid- and rod-shaped TiO2 nanoparticles in aqueous solutions.

We investigate the characteristics, fate and photocatalytic activity of spheroid- and rod-shaped TiO2 nano-crystals in aqueous solutions to better understand their behaviour in media of biological and environmental interest. For this purpose, the potential of a solvothermal method in synthesizing highly crystalline nanoparticles and tuning their sizes/shapes is explored. Spheroid- and rod-shaped nanoparticles are successfully obtained with different aspect ratios, while keeping their structures as well as their cross-sectional areas identical. The aggregation/agglomeration of these nanostructures in aqueous solutions shows an obvious shape effect, revealing critical coagulation concentrations (CCCs) significantly lower for the rods compared to the spheroids (aspect ratio ∼ 2-3). This trend is observed in both NaCl and CaCl2 electrolytes at pH values above and below the pHPZC of TiO2 nanoparticles. The photocatalytic activity of the spheroids is unexpectedly superior to that of the rods at NaCl and CaCl2 concentrations over a range of 2 to 100 and 1 to 50 mM, respectively. Our results show that an increase in the chloride concentration leads to an inhibition of the photocatalytic activity rate, with a more pronounced impact for the rods. In contrast, the size of aggregates/agglomerates has only a little effect on the photocatalytic properties of both nano-crystals.

Layer-by-Layer Assembly of Nanosized Membrane Fractions for the Assessment of Cytochrome P450 Xenobiotic Metabolism.

Herein, we report the use of sequential layer-by-layer (LbL) assembly to design nanostructured films made of recombinant bacterial membrane fractions (MF), which overexpress cytochrome P450 (CYP) and cytochrome P450 reductase. The ability to incorporate MF in LbL multilayered films is demonstrated by an in situ quartz crystal microbalance with dissipation monitoring using poly-l-lysine or poly-l-ornithine as a polycation. Results show that MF preserve a remarkable CYP1A2 catalytic property in the adsorbed phase. Moreover, atomic force microscopy images reveal that MF mostly adopt a flattened conformation in the adsorbed phase with an extensive tendency to aggregate within the multilayered films, which is more pronounced when increasing the number of bilayers. Interestingly, this behavior seems to enhance the ability of embedded MF to remain active after repeated uses. The proposed strategy constitutes a practical alternative for the immobilization of active CYP enzymes. Besides their fundamental interest, MF-based multilayers are useful nano-objects for the creation of new biomimetic reactors for the assessment of xenobiotic metabolism.