Killing Bacteria by Faradaic Processes through Nano-Hydroxyapatite/MoOx Platforms.

Following the secular idea of ″restitutio ad integrum″, regeneration is the pursued option to restore bones lost after a disease; accordingly, complementing antibiotic and regeneration capacity to bone grafts represents a great scientific success. This study is a framework proposal for understanding the antimicrobial effect of biocompatible nano-hydroxyapatite/MoOx (nano-HA/MoOx) platforms on the basis of their electroactive behavior. Through cyclic voltammetry and chronoamperometry measurements, the electron transference capacity of nano-HA and nano-HA/MoOx electrodes was determined in the presence of pathogenic organisms: Pseudomonas aeruginosa and Staphylococcus aureus. Faradaic processes were confirmed and related to the switch of MoO42-/PO43- groups in the original hexagonal nano-HA crystal lattice and to the extent of OH vacancies that act as electron acceptors. Microscopic analysis of bacteria's ultrastructure showed a disruptive effect on the cytoplasmic membrane upon direct contact with the materials, which is not evident in the presence of eukaryotic cells. Experiments support the existence of a type of extracellular electron transfer (EET) process that alters the function of the bacterial cytoplasmic membrane, accelerating their death. Our findings provide strong quantitative support for a drug-independent biocidal physical approach based on EET processes between microorganisms and phosphate ceramics that can be used to combat local orthopedic infections associated with implants.

NIR-Reflective and Hydrophobic Bio-Inspired Nano-Holed Configurations on Titanium Alloy.

Near-infrared (NIR) radiation plays an important role in guided external stimulus therapies; its application in bone-related treatments is becoming more and more frequent. Therefore, metallic biomaterials that exhibit properties activated by NIR are promising for further orthopedic procedures. In this work, we present an adapted electroforming approach to attain a biomorphic nano-holed TiO2 coating on Ti6Al4V alloy. Through a precise control of the anodization conditions, structures revealed the formation of localized nano-pores arranged in a periodic assembly. This specific organization provoked higher stability against thermal oxidation and precise hydrophobic wettability behavior according to Cassie-Baxter's model; both characteristics are a prerequisite to ensure a favorable biological response in an implantable structure for guided bone regeneration. In addition, the periodically arranged sub-wavelength-sized unit cell on the metallic-dielectric structure exhibits a peculiar optical response, which results in higher NIR reflectivity. Accordingly, we have proved that this effect enhances the efficiency of the scattering processes and provokes a significant improvement of light confinement producing a spontaneous NIR fluorescence emission. The combination of the already favorable mechanical and biocompatibility properties of Ti6Al4V, along with suitable thermal stability, wetting, and electro-optical behavior, opens a promising path toward strategic bone therapeutic procedures.

Self-fluorescent antibiotic MoOx-hydroxyapatite: a nano-theranostic platform for bone infection therapies.

Nowadays, the repair of large-size bone defects represents a huge medical challenge. A line of attack is the construction of advanced biomaterials having multifunctional properties. In this work, we show the creation of biocompatible MoOx-hydroxyapatite nanoparticles (nano-HA/MoOx) that simultaneously exhibit self-activated fluorescence and antibiotic skills. Along this text, we demonstrate that the insertion of molybdenum, an essential trace element, into the non-stoichiometric calcium deficient hydroxyapatite lattice generates intrinsic electronic point defects that exacerbate its epifluorescence blue emission and provokes new red emissions, preserving, always, its bioactivity. Furthermore, these point defects, acting as electron acceptors, stimulate the materials' biological redox status and promote the death of pathogen microorganisms after their direct contact. A putative mechanism, by which bacteria lose electrons from their metabolic circuit that alter the function of their cytoplasmic membrane and potentially die, agrees with our results. Our findings highlight the importance of tuning the electronic communications between biomaterial interfaces and biological units, and support the use of self-fluorescent MoOx-hydroxyapatite nanoparticles as fundamental building blocks for new real-time imaging platforms against bone infection.

Multi-drug delivery system based on lipid membrane mimetic coated nano-hydroxyapatite formulations.

Local delivery systems from an osteoconductive biomaterial are suggested as a promising strategy to avoid simultaneously peri-implant traumas and to induce tissue regeneration. In this work, it is detailed the design and construction of a multi-drug delivery formulation based on lipid membrane mimetic coated nano-hydroxyapatite, LMm/nano-HA, as a bone-specific drug delivery approach. The optimal LMm/nano-HA formulation was selected after analysing the lipid/nano-HA interaction by dynamic light scattering (DLS), ζ-potential, transmission electron microscopy (TEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC) and UV-vis spectroscopy. After the initial screening, Ciprofloxacin and Ibuprofen simultaneous -load and -release efficiency from selected LMm/nano-HA was assessed. pH-responsive kinetic profiles of local drug distribution were characterized and compared with currently applied systemic doses. Finally, the systems' biocompatibility and drug released activity were positively validated. The obtained results demonstrated that LMm/nano-HA formulations can represent a valuable multi-modal platform in bone tissue therapies.

Electroactive Mg2+-Hydroxyapatite Nanostructured Networks against Drug-Resistant Bone Infection Strains.

Surface colonization competition between bacteria and host cells is one of the critical factors involved in tissue/implant integration. Current biomaterials are evaluated for their ability both of withstanding favorable responses of host tissue cells and of resisting bacterial contamination. In this work, the antibacterial ability of biocompatible Mg2+-substituted nanostructured hydroxyapatite (HA) was investigated. The densities of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli strains were significantly decreased after culture in the presence of Mg-substituted HA materials in direct correlation with Mg2+-Ca2+ switch in the HA lattice. It was noticed that this decrease was accompanied by a minimal alteration of bacterial environments; therefore, the Mg2+-HA antibacterial effect was associated with the material surface topography and it electroactive behavior. It was observed that 2.23 wt % Mg2+-HA samples exhibited the best antibacterial performance; it decreased 2-fold the initial population of E. coli, P. aeruginosa, and S. aureus at the intermediate concentration (50 mg mL-1 of broth). Our results reinforce the potential of Mg-HA nanostructured materials to be used in antibacterial coatings for implantable devices and/or medicinal materials to prevent bone infection and to promote wound healing.

Structural and Kinetic Visualization of the Protein Corona on Bioceramic Nanoparticles.

Bioceramic nanoparticles exhibit excellent features that enable them to function as an ideal material for hard tissue engineering. However, to fully understand their behavior, it is of crucial importance to understand their behavior within the fluids of the human body. To achieve this goal, we have studied the interaction between hydroxyapatite nanorods (HA) and bovine serum albumin (BSA). First, we describe the surface morphology of the nanoparticle. Then, the main characteristics of the physiological interplay of BSA and the hydroxyapatite nanoparticle are presented by using a battery of techniques: ITC, zeta potential, UV-vis, fluorescence, and CD. Experimental data was analyzed by developing specific approaches to determining important parameters such as rates, affinities, and stochiometries of protein associated with the nanoparticles. ITC has been confirmed as a powerful technique for determining the affinity, binding, and thermodynamics of BSA-nanoparticle interactions. Careful quantitative assessment of the kinetic properties of the adsorption were revealed by UV-vis and fluorescence measurements. Finally, CD measurements highlight the important role of protein flexibility in these kinds of systems.

Manipulation of Mg2+-Ca2+ Switch on the Development of Bone Mimetic Hydroxyapatite.

Ionic substitution can affect essential physicochemical properties leading to a specific biological behavior upon implantation. Therefore, it has been proposed as a tool to increase the biological efficiency of calcium phosphate based materials. In the following study, we have evaluated the contribution of an important cation in nature, Mg2+, into the structure of previously studied biocompatible and biodegradable hydroxyapatite (HA) nanorods and its subsequent effect on its chemical, morphology, and bone mimetic articulation. Mg2+-substituted HA samples were synthesized by an aqueous wet-chemical precipitation method, followed by an hydrothermal treatment involving a Mg2+ precursor that partially replace Ca2+ ions into HA crystal lattice; Mg2+ concentrations were modulated to obtain a nominal composition similar to that exists in calcified tissues. Hydrothermally synthesized Mg2+-substituted HA nanoparticles were characterized by X-ray powder diffraction, FT-NIR and EDX spectroscopies, field emission scanning and high resolution transmission electron microscopies (FE-SEM, H-TEM). Molecular modeling combining ab initio methods and power diffraction data were also performed. Results showed that Mg2+-substitution promoted the formation of calcium deficient HA (cdHA) where Mg2+ replacement is energetically favored at Ca(1) position in a limited and specific amount directing the additional Mg2+ toward the surface of the crystal. The control of Mg2+ incorporation into HA nanorods gave rise to a tailored crystallinity degree, cell parameters, morphology, surface hydration, solubility, and degradation properties in a dose-replacement dependent manner. The obtained materials show qualities that conjugated together to drive an optimal in vitro cellular viability, spreading, and proliferation confirming their biocompatibility. In addition, an improved adhesion of osteoblast was evidenced after Mg2+-Ca2+ substitution.

Albumin-mediated deposition of bone-like apatite onto nano-sized surfaces: Effect of surface reactivity and interfacial hydration.

The bioactivity of an implant is displayed on its ability to induce heterogeneous nucleation of biogenic apatite onto its surface upon immersion in body fluids; forming, through this layer, a stable bond with the host tissue. The present article evaluates the bioactivity of different nanostructured substrates based on synthetic hydroxyapatite (HA) and titania (TiO2) nanoparticles, where we extend the debate regarding the selective roles played by the presence of albumin on the biogenic apatite coating evolution. The substrates bone-bonding potential was evaluated by keeping the materials in contact with Simulated Body Fluid, while the influence of the presence of Bovine Serum Albumin in bioactivity was analyzed by a spectrophotometric technique. Our results show that materials' surface reactivity and their interfacial hydration are responsible for the bonding-site alteration and surface charge density distribution, which in turn, regulate the protein adsorption process. As a matter of fact, variations on the protein adsorbed density have a directly proportional impact on calcium binding sites, which should be responsible for the initiation of the mineralization process, disturbing the deposition of the interfacial calcium phosphate (Ca-P) mineralized coating.

Biomimetic fiber mesh scaffolds based on gelatin and hydroxyapatite nano-rods: Designing intrinsic skills to attain bone reparation abilities.

Intrinsic material skills have a deep effect on the mechanical and biological performance of bone substitutes, as well as on its associated biodegradation properties. In this work we have manipulated the preparation of collagenous derived fiber mesh frameworks to display a specific composition, morphology, open macroporosity, surface roughness and permeability characteristics. Next, the effect of the induced physicochemical attributes on the scaffold's mechanical behavior, bone bonding potential and biodegradability were evaluated. It was found that the scaffold microstructure, their inherent surface roughness, and the compression strength of the gelatin scaffolds can be modulated by the effect of the cross-linking agent and, essentially, by mimicking the nano-scale size of hydroxyapatite in natural bone. A clear effect of bioactive hydroxyapatite nano-rods on the scaffolds skills can be appreciated and it is greater than the effect of the cross-linking agent, offering a huge perspective for the upcoming progress of bone implant technology.

Computational Modeling and Experimental Facts of Mixed Self- Assembly Systems.

The formation of liposomes, nanoparticle micelles, and related systems by mixtures of drugs and/or surfactants is of major relevance for the design of drug delivery systems. We can design new systems using different compounds. Traditionally these systems are created by trial and error using experimental data. However, in most cases measuring all the possible combinations represents a extensive work and almost always unaffordable. In this sense, we can use theoretical concepts and develop computational models to predict different physicochemical properties of self-aggregation processes of mixed molecular systems. In a previous work, we developed a new PT-LFER model (Linear Free Energy Relationships, LFER, combined with Perturbation Theory, PT, ideas) for binary systems. The best PT-LFER model found predicted the effects of 25000 perturbations over nine different properties of binary systems. The present work has two parts. Firstly, we carry out an analysis on the new results on the applications and experimental-theoretical studies of binary selfassembled systems. In the second part, we report for the first time, a new experimental-theoretic study of the NaDC-DTAB binary system. For this purpose, we have combined experimental procedures plus physicochemical thermodynamic framework with the PT-LFER model reported in our previous work.

Models for Self-Assembly of Nanoscale Systems with Biomedical Applications.

BACKGROUND: Understanding the physicochemical basis and the different models of nanosystems is nowadays fundamental in a great number of scientific areas and industrial processes. RESULTS: Here, we focus on nanosystems created by self-assembly, molecular or inorganic. The organization of single units at these scales is a challenging matter in light of the inherently small dimensions involved, the sensitivity of the system to small perturbations, and the problem of scaling up such a process for widespread use and implementation. CONCLUSION: This review examines the different self-assembly routes used to create nanostructures in both the equilibrium and non-equilibrium/dynamic systems and discusses their limits and applications. The connection to biomedicine and pharmaceutical design has been emphasized.

Protective role against hydrogen peroxide and fibroblast stimulation via Ce-doped TiO2 nanostructured materials.

BACKGROUND: Cerium oxide (CeO2) and Ce-doped nanostructured materials (NMs) are being seen as innovative therapeutic tools due to their exceptional antioxidant effects; nevertheless their bio-applications are still in their infancy. METHODS: TiO2, Ce-TiO2 and CeO2-TiO2 NMs were synthesized by a bottom-up microemulsion-mediated strategy and calcined during 7h at 650°C under air flux. The samples were compared to elucidate the physicochemical characteristics that determine cellular uptake, toxicity and the influence of redox balance between the Ce(3+)/Ce(4+) on the cytoprotective role against an exogenous ROS source: H2O2. Fibroblasts were selected as a cell model because of their participation in wound healing and fibrotic diseases. RESULTS: Ce-TiO2 NM obtained via sol-gel reaction chemistry of metallic organic precursors exerts a real cytoprotective effect against H2O2 over fibroblast proliferation, while CeO2 pre-formed nanoparticles incorporated to TiO2 crystalline matrix lead to a harmful CeO2-TiO2 material. TiO2 was processed by the same pathways as Ce-TiO2 and CeO2-TiO2 NM but did not elicit any adverse or protective influence compared to controls. CONCLUSIONS: It was found that the Ce atoms source and its concentration have a clear effect on material's physicochemical properties and its subsequent influence in the cellular response. It can induce a range of biological reactions that vary from cytotoxic to cytoprotective. GENERAL SIGNIFICANCE: Even though there are still some unresolved issues and challenges, the unique physical and chemical properties of Ce-based NMs are fascinating and versatile resources for different biomedical applications.

Self-Assembled Binary Nanoscale Systems: Multioutput Model with LFER-Covariance Perturbation Theory and an Experimental-Computational Study of NaGDC-DDAB Micelles.

Studies of the self-aggregation of binary systems are of both theoretical and practical importance. They provide an opportunity to investigate the influence of the molecular structure of the hydrophobe on the nonideality of mixing. On the other hand, linear free energy relationship (LFER) models, such as Hansch's equations, may be used to predict the properties of chemical compounds such as drugs or surfactants. However, the task becomes more difficult once we want to predict simultaneaously the effect over multiple output properties of binary systems of perturbations under multiple input experimental boundary conditions (b(j)). As a consequence, we need computational chemistry or chemoinformatics models that may help us to predict different properties of the autoaggregation process of mixed surfactants under multiple conditions. In this work, we have developed the first model that combines perturbation theory (PT) and LFER ideas. The model uses as input covariance PT operators (CPTOs). CPTOs are calculated as the difference between covariance ΔCov((i)µ(k)) functions before and after multiple perturbations in the binary system. In turn, covariances calculated as the product of two Box-Jenkins operators (BJO) operators. BJOs are used to measure the deviation of the structure of different chemical compounds from a set of molecules measured under a given subset of experimental conditions. The best CPT-LFER model found predicted the effects of 25,000 perturbations over 9 different properties of binary systems. We also reported experimental studies of different experimental properties of the binary system formed by sodium glycodeoxycholate and didodecyldimethylammonium bromide (NaGDC-DDAB). Last, we used our CPT-LFER model to carry out a 1000 data point simulation of the properties of the NaGDC-DDAB system under different conditions not studied experimentally.

Bone-repair properties of biodegradable hydroxyapatite nano-rod superstructures.

Nano-hydroxyapatite (nano-HAp) materials show an analogous chemical composition to the biogenic mineral components of calcified tissues and depending on their topography they may mimic the specific arrangement of the crystals in bone. In this work, we have evaluated the potential of four synthesized nano-HAp superstructures for the in vitro conditions of bone-repair. Experiments are underway to investigate the effects of the material microstructure, surface roughness and hydrophilicity on their osseo-integration, osteo-conduction and osteo-induction abilities. Materials were tested in the presence of both, rat primary osteoblasts and rabbit mesenchymal stem cells. The following aspects are discussed: (i) cytotoxicity and material degradation; (ii) rat osteoblast spreading, proliferation and differentiation; and (iii) rabbit mesenchymal stem cell adhesion on nano-HAp and nano-HAp/collagen type I coatings. We effectively prepared a material based on biomimetic HAp nano-rods displaying the appropriate surface topography, hydrophilicity and degradation properties to induce the in vitro desired cellular responses for bone bonding and healing. Cells seeded on the selected material readily attached, proliferated and differentiated, as confirmed by cell viability, mitochondrial metabolic activity, alkaline phosphatase (ALP) activity and cytoskeletal integrity analysis by immunofluorescence localization of alpha-smooth muscle actin (α-SMA) protein. These results highlight the influence of material's surface characteristics to determine their tissue regeneration potential and their future use in engineering osteogenic scaffolds for orthopedic implants.

Multiscale Inorganic Hierarchically Materials: Towards an Improved Orthopaedic Regenerative Medicine.

Bone is a biologically and structurally sophisticated multifunctional tissue. It dynamically responds to biochemical, mechanical and electrical clues by remodelling itself and accordingly the maximum strength and toughness are along the lines of the greatest applied stress. The challenge is to develop an orthopaedic biomaterial that imitates the micro- and nano-structural elements and compositions of bone to locally match the properties of the host tissue resulting in a biologically fixed implant. Looking for the ideal implant, the convergence of life and materials sciences occurs. Researchers in many different fields apply their expertise to improve implantable devices and regenerative medicine. Materials of all kinds, but especially hierarchical nano-materials, are being exploited. The application of nano-materials with hierarchical design to calcified tissue reconstructive medicine involve intricate systems including scaffolds with multifaceted shapes that provides temporary mechanical function; materials with nano-topography modifications that guarantee their integration to tissues and that possesses functionalized surfaces to transport biologic factors to stimulate tissue growth in a controlled, safe, and rapid manner. Furthermore materials that should degrade on a timeline coordinated to the time that takes the tissues regrow, are prepared. These implantable devices are multifunctional and for its construction they involve the use of precise strategically techniques together with specific material manufacturing processes that can be integrated to achieve in the design, the required multifunctionality. For such reasons, even though the idea of displacement from synthetic implants and tissue grafts to regenerative-medicine-based tissue reconstruction has been guaranteed for well over a decade, the reality has yet to emerge. In this paper, we examine the recent approaches to create enhanced bioactive materials. Their design and manufacturing procedures as well as the experiments to integrate them into engineer hierarchical inorganic materials for their practical application in calcified tissue reparation are evaluated.

Photoluminescent SBA-16 Rhombic Dodecahedral Particles: Assembly, Characterization, and ab Initio Modeling.

Nowadays, the use of polyhedral instead of spherical particles as building blocks of engineering new materials has become an area of particular effort in the scientific community. Therefore, fabricating in a reproducible manner large amounts of uniform crystal-like particles is a huge challenge. In this work we report a low reagent-consuming binary surfactant templated method mediated by a hydrothermal treatment as a facile and controllable route for the synthesis of crystal-like rombdodecahedral particles exhibiting SBA-16 mesoporosity. It was determined that the hydrothermal treatment conditions were a key point upon the final material morphology, surface area, microporosity, wall thickness, and mesopore width. As a consequence of their internal mesoporosity order, rhombic dodecahedral synthesized particles exhibited highly efficient ultraviolet absorptions and photoluminescence emissions at room temperature. Conducting experimental and theoretical comparative studies allowed us to infer that the presence of intrinsic defects confined into an ordered mesoporous structure plays a very important role in semiconductor materials. The information presented here is expected to be useful, giving new, accurate information, for the construction of novel technological devices.

Analyzing the hydrodynamic and crowding evolution of aqueous hydroxyapatite-gelatin networks: Digging deeper into bone scaffold design variables.

The hydration of the polypeptide network is a determinant factor to be controlled on behalf of the design of precise functional tissue scaffolding. Here we present an exhaustive study of the hydrodynamic and crowding evolution of aqueous gelatin-hydroxyapatite systems with the aim of increasing the knowledge about the biomimesis of collagen mineralization; and how it can be manipulated for the preparation of collagenous derived frameworks with specific morphological characteristics. The solution's density and viscosity evaluation measurements in combination with spectroscopic techniques revealed that there is a progressive association of protein chain that can be influenced by the amount of hydroxyapatite nanorods. Gelatin and additives' concentration effect on the morphology of the gelatin scaffolds was investigated. Transverse and longitudinal sections of the obtained scaffolds were taken and analyzed using optical microscopy. It can be seen that the porous size and shape of gelatin assemblies can be easily adjusted by controlling the gelatin/HAp ratio in the solution used as template in agreement with our statement.

Self-assembly drugs: from micelles to nanomedicine.

Self-assembly has fascinated many scientists over the past few decades. Rapid advances and widespread interest in the study of this subject has led to the synthesis of an ever-increasing number of elegant and intricate functional structures with sizes that approach nano- and mesoscopic dimensions. Today, it has grown into a mature field of modern science whose interfaces with many disciplines have provided invaluable opportunities for crossing boundaries for scientists seeking to design novel molecular materials exhibiting unusual properties, and for researchers investigating the structure and function of biomolecules. Consequently, self-assembly transcends the traditional divisional boundaries of science and represents a highly interdisciplinary field including nanotechnology and nanomedicine. Basically, self-assembly focuses on a wide range of discrete molecules or molecular assemblies and uses physical transformations to achieve its goals. In this Review, we present a comprehensive overview of the advances in the field of drug self-assembly and discuss in detail the synthesis, self-assembly behavior, and physical properties as well as applications. We refer the reader to past reviews dealing with colloidal molecules and colloidal self-assembly. In the first part, we will discuss, compare, and link the various bioinformatic procedures: Molecular Dynamics and Quantitative Structure Activity Relationship. The second section deals with the self-assembly behavior in more detail, in which we focus on several experimental techniques, selected according to the depth of knowledge obtained. The last part will review the advances in drug-protein assembly. Nature provides many examples of proteins that form their substrate binding sites by bringing together the component pieces in a process of self-assembly. We will focus in the understanding of physical properties and applications developing thereof.