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Layered Double Hydroxides (LDHs) are inorganic compounds of relevance to various domains, where their surface reactivity and/or intercalation capacities can be advantageously exploited for the retention/release of ionic and molecular species. In this study, we have explored specifically the applicability in the field of bone regeneration of one LDH composition, denoted "MgFeCO3", of which components are already present in vivo, so as to convey a biocompatibility character. The propensity to be used as a bone substitute depends, however, on their ability to allow the fabrication of 3D constructs able to be implanted in bone sites. In this work, we display two appealing approaches for the processing of MgFeCO3 LDH particles to prepare (i) porous 3D scaffolds by freeze-casting, involving an alginate biopolymeric matrix, and (ii) pure MgFeCO3 LDH monoliths by Spark Plasma Sintering (SPS) at low temperature. We then explored the capacity of such LDH particles or monoliths to interact quantitatively with molecular moieties/drugs in view of their local release. The experimental data were complemented by computational chemistry calculations (Monte Carlo) to examine in more detail the mineral–organic interactions at play. Finally, preliminary in vitro tests on osteoblastic MG63 cells confirmed the high biocompatible character of this LDH composition. It was confirmed that (i) thermodynamically metastable LDH could be successfully consolidated into a monolith through SPS, (ii) the LDH particles could be incorporated into a polymer matrix through freeze casting, and (iii) the LDH in the consolidated monolith could incorporate and release drug molecules in a controlled manner. In other words, our results indicate that the MgFeCO3 LDH (pyroaurite structure) may be seen as a new promising compound for the setup of bone substitute biomaterials with tailorable drug delivery capacity, including for personalized medicine. [ABSTRACT FROM AUTHOR]

Biomimetic apatites exhibit a high reactivity allowing ion substitutions to modulate their in vivo response. We developed a novel approach combining several bioactive ions in a spatially controlled way in view of subsequent releases to address the sequence of events occurring after implantation, including potential microorganisms' colonization. Innovative micron-sized core-shell particles were designed with an external shell enriched with an antibacterial ion and an internal core substituted with a pro-angiogenic or osteogenic ion. After developing the proof of concept, two ions were particularly considered, Ag+ in the outer shell and Cu2+ in the inner core. In vitro evaluations confirmed the cytocompatibility through Ag-/Cu-substituting and the antibacterial properties provided by Ag+. Then, these multifunctional "smart" particles were embedded in a polymeric matrix by freeze-casting to prepare 3D porous scaffolds for bone engineering. This approach envisions the development of a new generation of scaffolds with tailored sequential properties for optimal bone regeneration. [ABSTRACT FROM AUTHOR]

Calcium carbonates and in particular amorphous calcium carbonate (ACC) are of great interest for bone substitution, due to their excellent biocompatibility and ability to release some of the bone mineral constitutive ions. Despite thorough investigations on the ACC precipitation mechanism in the presence of a wide variety of additives to stabilise it, their influence on the composition and structuration of the resulting ACC is rarely finely characterised. In this article, pyrophosphate (Py) was studied as an additive, due to its calcite inhibitor role and the good bioactive properties it demonstrated in vitro and in vivo. A series of pyrophosphate-stabilised ACC (PyACC) powders were synthesised by co-precipitation in water with various amounts of Py, and the structure, composition and multiscale organisation of the resulting compounds were thoroughly characterised. XRD, FTIR spectroscopy and FEG-SEM showed a reduction of the amount and size of calcite crystallites when increasing the Py content, crystallites co-existing with an increasing quantity of the amorphous phase, up to obtaining fully amorphous materials above a certain Py amount. Beyond the stabilising role of Py, and considering SAXS, PDF and solid-state NMR analyses, we proposed an experimental model for PyACC based on a vaterite-like (or proto-vaterite) cluster of 1 nm surrounded by a 2 nm-outer shell containing pyrophosphate ions and pseudo-structural water stabilising the cluster. This comprehensive study and the resulting model are predominant prerequisites to understand the underlying mechanisms of PyACC evolution and could contribute to the rational design of tunable amorphous and bioinspired inorganic bone substitute materials. [ABSTRACT FROM AUTHOR]

This paper focuses on an integrative "bricks-and-mortar" approach involving bioactive glass nanoparticles (bricks) covalently functionalized with a customized polymer (mortar) combined with the freeze-casting process. With the aim of obtaining a macroporous composite for bone substitution, composed of a spatially homogeneous assembly of nanoscale objects, we establish a method for the systematic elaboration of nanocomposite scaffolds. It was implemented through several steps from the synthesis of functionalized poly-(d,l-lactide) (PDLLA) and SiO2–CaO binary bioactive glass nanoparticles (diameter around 164 nm) to the unidirectional freeze-casting process. The different stages include the first description of controlled PDLLA (Mn 8400 g·mol–1) grafting onto bioactive glass nanoparticle surfaces, their fine characterization and grafting quantification, and their mixing with free PDLLA chains (83 400 g·mol–1) during suspension formulation. This paper emphasizes the effect of the working temperature during the freeze-casting process on the multiscale spatial organization of resulting scaffolds such as the porosity morphology (lamellar and tubular), size (from 30 to 380 μm), anisotropy, and orientation. In addition to porosity, our results demonstrate a rosary-like organization of PDLLA-grafted nanoparticles in pore walls. The higher homogeneity in the spatial distribution of grafted nanoparticles over the height of scaffolds and at a micron scale confirms the validity of the "bricks-and-mortar" concept to prevent or limit aggregation. In particular, this study highlights the correlation between nanoparticle functionalization and mechanical properties, especially the recovery rate after compression tests. These results lay the foundation for the development of tunable materials for bone substitution, via potential enhancement of bioactivity and cell colonization. [ABSTRACT FROM AUTHOR]

α-Canaphite (CaNa2P2O7·4H2O) is a layered calcium disodium pyrophosphate tetrahydrate phase of significant geological and potential biological interest. This study overcomes the lack of a reliable protocol to synthesize pure α-canaphite by using a novel simple and reproducible approach of double decomposition in solution at room temperature. The pure α-canaphite is then characterized from the atomic to the macroscopic level using a multitool and multiscale advanced characterization strategy, providing for the first time full resolution of the α-canaphite monoclinic structure, including the hydrogen bonding network. Synchrotron X-ray diffraction and neutron diffraction are combined with multinuclear solid state NMR experimental data and computational modeling via DFT/GIPAW calculations. Among the main characteristics of the α-canaphite structure are some strong hydrogen bonds and one of the four water molecules showing a different coordination scheme. This peculiar water molecule could be the last to leave the collapsed structure on heating, leading eventually to anhydrous α-CaNa2P2O7 and could also be involved in the internal hydrolysis of pyrophosphate ions as it is the closest water molecule to the pyrophosphate ions. Relating such detailed structural data on α-canaphite to its physico-chemical properties is of major interest considering the possible roles of canaphite for biomedical applications. The vibrational spectra of α-canaphite (deuterated or not) are analyzed and Raman spectroscopy appears to be a promising tool for the identification/diagnosis of such microcrystals in vitro, in vivo or ex vivo. [ABSTRACT FROM AUTHOR]

The development of amorphous phosphate-based materials is of major interest in the field of biomaterials science, and especially for bone substitution applications. In this context, we herein report the synthesis of gel-derived hydrated amorphous calcium/sodium ortho/pyrophosphate materials at ambient temperature and in water. For the first time, such materials have been obtained in a large range of tunable orthophosphate/pyrophosphate molar ratios. Multi-scale characterization was carried out thanks to various techniques, including advanced multinuclear solid state NMR. It allowed the quantification of each ionic/molecular species leading to a general formula for these materials: [(Ca2+ y Na+ z H+ 3+ x -2y-z)(PO 4 3−) 1-x (P 2 O 7 4−) x ](H 2 O) u. Beyond this formula, the analyses suggest that these amorphous solids are formed by the aggregation of colloids and that surface water and sodium could play a role in the cohesion of the whole material. Although the full comprehension of mechanisms of formation and structure is still to be investigated in detail, the straightforward synthesis of these new amorphous materials opens up many perspectives in the field of materials for bone substitution and regeneration. The metastability of amorphous phosphate-based materials with various chain length often improves their (bio)chemical reactivity. However, the control of the ratio of the different phosphate entities has not been yet described especially for small ions (pyrophosphate/orthophosphate) and using soft chemistry, whereas it opens the way for the tuning of enzyme- and/or pH-driven degradation and biological properties. Our study focuses on elaboration of amorphous gel-derived hydrated calcium/sodium ortho/pyrophosphate solids at 70 °C with a large range of orthophosphate/pyrophosphate ratios. Multi-scale characterization was carried out using various techniques such as advanced multinuclear SSNMR (31P, 23Na, 1H, 43Ca). Analyses suggest that these solids are formed by colloids aggregation and that the location of mobile water and sodium could play a role in the material cohesion. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Peri-implant infection is rapidly becoming an – if not the most – important clinical challenge for indwelling medical devices. To alleviate the global rise in antibiotic use for the treatment of such infections, a plethora of biomaterials/bioengineering-based antimicrobial strategies are emerging to restrict or ideally to eliminate microbial adhesion and biofilm formation on implant surfaces. Yet, the development of such approaches faces specific challenges, like biocompatibility concerns, reduced antimicrobial effectiveness, long-term stability issues and antibiotic resistance development, which limit translation to the clinic. This review provides insights into the antimicrobial activity of current state-of-the-art biomaterial-based approaches to address the aforementioned issues. Translational research strategies and regulatory framework are also emphasised as key elements facilitating clinical implementation of anti-infective biomaterials. This review closes with the vision that the integration of computational tools and experimental databases using artificial intelligence (AI) would provide new insights for the accelerated development of next-generation biomaterial-based antimicrobial strategies. [ABSTRACT FROM AUTHOR]

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO 2 -CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.

This paper presents a series of acidoswitchable NLO-phores combining the 9-methylbenzimidazolo[2,3-b]oxazolidine core with various pi systems such as phenylethenyl, phenylethynyl, and naphthylethenyl. All the prepared derivatives are shown to display acidochromic behavior at ambient temperature. The remarkable contrast in the NLO response along the reversible transformations observed in HRS experiments is rationalized by high level theoretical calculations.