Inorganic phosphate in growing calcium carbonate abalone shell suggests a shared mineral ancestral precursor.

The presence of phosphate from different origins (inorganic, bioorganic) is found more and more in calcium carbonate-based biominerals. Phosphate is often described as being responsible for the stabilization of the transient amorphous calcium carbonate phase. In order to specify the composition of the mineral phase deposited at the onset of carbonated shell formation, the present study investigates, down to the nanoscale, the growing shell from the European abalone Haliotis tuberculata, using a combination of solid state nuclear magnetic resonance, scanning transmission electron microscope and spatially-resolved electron energy loss spectroscopy techniques. We show the co-occurrence of inorganic phosphate with calcium and carbonate throughout the early stages of abalone shell formation. One possible hypothesis is that this first-formed mixed mineral phase represents the vestige of a shared ancestral mineral precursor that appeared early during Evolution. In addition, our findings strengthen the idea that the final crystalline phase (calcium carbonate or phosphate) depends strongly on the nature of the mineral-associated proteins in vivo.

Strontium Calcium Phosphate Nanotubes as Bioinspired Building Blocks for Bone Regeneration.

Calcium phosphate (CaP)-based ceramics are the most investigated materials for bone repairing and regeneration. However, the clinical performance of commercial ceramics is still far from that of the native tissue, which remains as the gold standard. Thus, reproducing the structural architecture and composition of bone matrix should trigger biomimetic response in synthetic materials. Here, we propose an innovative strategy based on the use of track-etched membranes as physical confinement to produce collagen-free strontium-substituted CaP nanotubes that tend to mimic the building block of bone, i.e., the mineralized collagen fibrils. A combination of high-resolution microscopic and spectroscopic techniques revealed the underlying mechanisms driving the nanotube formation. Under confinement, poorly crystalline apatite platelets assembled into tubes that resembled the mineralized collagen fibrils in terms of diameter and structure of bioapatite. Furthermore, the synergetic effect of Sr2+ and confinement gave rise to the stabilization of amorphous strontium CaP nanotubes. The nanotubes were tested in long-term culture of osteoblasts, supporting their maturation and mineralization without eliciting any cytotoxicity. Sr2+ released from the particles reduced the differentiation and activity of osteoclasts in a Sr2+ concentration-dependent manner. Their bioactivity was evaluated in a serum-like solution, showing that the particles spatially guided the biomimetic remineralization. Further, these effects were achieved at strikingly low concentrations of Sr2+ that is crucial to avoid side effects. Overall, these results open simple and promising pathways to develop a new generation of CaP multifunctional ceramics that are active in tissue regeneration and able to simultaneously induce biomimetic remineralization and control the imbalanced osteoclast activity responsible for bone density loss.

Phosphatidylserine controls calcium phosphate nucleation and growth on lipid monolayers: A physicochemical understanding of matrix vesicle-driven biomineralization.

Bone biomineralization is an exquisite process by which a hierarchically organized mineral matrix is formed. Growing evidence has uncovered the involvement of one class of extracellular vesicles, named matrix vesicles (MVs), in the formation and delivery of the first mineral nuclei to direct collagen mineralization. MVs are released by mineralization-competent cells equipped with a specific biochemical machinery to initiate mineral formation. However, little is known about the mechanisms by which MVs can trigger this process. Here, we present a combination of in situ investigations and ex vivo analysis of MVs extracted from growing-femurs of chicken embryos to investigate the role played by phosphatidylserine (PS) in the formation of mineral nuclei. By using self-assembled Langmuir monolayers, we reconstructed the nucleation core - a PS-enriched motif thought to trigger mineral formation in the lumen of MVs. In situ infrared spectroscopy of Langmuir monolayers and ex situ analysis by transmission electron microscopy evidenced that mineralization was achieved in supersaturated solutions only when PS was present. PS nucleated amorphous calcium phosphate that converted into biomimetic apatite. By using monolayers containing lipids extracted from native MVs, mineral formation was also evidenced in a manner that resembles the artificial PS-enriched monolayers. PS-enrichment in lipid monolayers creates nanodomains for local increase of supersaturation, leading to the nucleation of ACP at the interface through a multistep process. We posited that PS-mediated nucleation could be a predominant mechanism to produce the very first mineral nuclei during MV-driven bone/cartilage biomineralization.

Characterization of the in Vitro Osteogenic Response to Submicron TiO2 Particles of Varying Structure and Crystallinity.

Titanium oxide (TiO2) nano-/microparticles have been widely used in orthopedic and dental sciences because of their excellent mechanical properties, chemical stability, and ability to promote the osseointegration of implants. However, how the structure and crystallinity of TiO2 particles may affect their osteogenic activity remains elusive. Herein, we evaluated the osteogenic response to submicron amorphous, anatase, and rutile TiO2 particles with controlled size and morphology. First, the ability of TiO2 particles to precipitate apatite was assessed in an acellular medium by using a simulated body fluid (SBF). Three days after the addition to SBF, anatase and rutile TiO2 particles induced the precipitation of aggregates of nanoparticles with a platelike morphology, typical for biomimetic apatite. Conversely, amorphous TiO2 particles induced the precipitation of particles with poor Ca/P atomic ratio only after 14 days of exposure to SBF. Next, the osteogenic response to TiO2 particles was assessed in vitro by incubating MC3T3-E1 preosteoblasts with the particles. The viability and mineralization efficiency of osteoblastic cells were maintained in the presence of all the tested TiO2 particles despite the differences in the induction of apatite precipitation in SBF by TiO2 particles with different structures. Analysis of the particles' surface charge and of the proteins adsorbed onto the particles from the culture media suggested that all the tested TiO2 particles acquired a similar biological identity in the culture media. We posited that this phenomenon attenuated potential differences in osteoblast response to amorphous, anatase, and rutile particles. Our study provides an important insight into the complex relationship between the physicochemical properties and function of TiO2 particles and sheds light on their safe use in medicine.

Synthesis of Sr-morin complex and its in vitro response: decrease in osteoclast differentiation while sustaining osteoblast mineralization ability.

Strontium ranelate (SrR) has been used as the ultimate choice for osteoporosis treatment. However, the development of more tolerable and bioactive Sr2+ carriers is still a need. The design of Sr2+-based platforms has moved towards the obtention of anion carriers that can also exhibit a positive effect on bone metabolism. In this sense, we used morin, a natural flavonoid, as a new arrangement for Sr2+ carriage in the synthesis of an Sr2+ complex. It has been claimed that phenolic compounds promote bone health. Therefore, we hypothesized that the association of Sr2+ with morin could improve its anabolic effects. Complexes with the general formula [(C15H9O7)Sr(H2O)2]Cl·3H2O were synthesized and characterized by elemental analysis, thermogravimetry, UV-Vis and infrared absorption spectroscopies and 1H-nuclear magnetic resonance. We showed that the complexation between morin and Sr2+ occurred among the 3-OH and 4C[double bond, length as m-dash]O groups of morin. Preosteoclasts cultures with the Sr-morin complex exhibited a reduced osteoclast differentiation rate and sustained osteoblast mineralization ability. The response of Sr-morin was higher than that observed for SrR at the same concentration range. Considering the above-mentioned observations, the Sr-morin complex could be an interesting approach to be further exploited not only as an alternative treatment for osteoporosis but also in the design of materials for faster osteointegration.

The role played by modified bioinspired surfaces in interfacial properties of biomaterials.

The success of a biomaterial relies on an appropriate interaction between the surface of that biomaterial and the surrounding environment; more specifically, the success of a biomaterial depends on how fluids, proteins, and cells interact with the foreign material. For this reason, the surface properties of biomaterial, such as composition, charge, wettability, and roughness, must be optimized for a desired application to be achieved. In this review we highlight different bioinspired approaches that are used to manipulate and fine-tune the interfacial properties of biomaterials. Inspired by noteworthy natural processes, researchers have developed materials with a functional anatomy that range from hierarchical hybrid structures to self-cleaning interfaces. In this review we focus on (1) the creation of particles and modified surfaces inspired by the structure and composition of biogenic mineralized tissues, (2) the development of biofunctional coatings, (3) materials inspired by biomembranes and proteins, and (4) the design of superwettable materials. Our intention is to point out different bioinspired methodologies that have been used to design materials for biomedical applications and to discuss how interfacial properties modified by manipulation of these materials determine their final biological response. Our objective is to present future research directions and to highlight the potential of bioinspired materials. We hope this review will provide an understanding of the interplay between interfacial properties and biological response so that successful biomaterials can be achieved.

Biomedical applications of nanotechnology.

The ability to investigate substances at the molecular level has boosted the search for materials with outstanding properties for use in medicine. The application of these novel materials has generated the new research field of nanobiotechnology, which plays a central role in disease diagnosis, drug design and delivery, and implants. In this review, we provide an overview of the use of metallic and metal oxide nanoparticles, carbon-nanotubes, liposomes, and nanopatterned flat surfaces for specific biomedical applications. The chemical and physical properties of the surface of these materials allow their use in diagnosis, biosensing and bioimaging devices, drug delivery systems, and bone substitute implants. The toxicology of these particles is also discussed in the light of a new field referred to as nanotoxicology that studies the surface effects emerging from nanostructured materials.