Preparation of nanometer-scale rod array of hydroxyapatite crystal

Biomaterial Cues Regulated Differentiation of Neural Stem Cells into GABAergic Neurons through Ca2+/c-Jun/TLX3 Signaling Promoted by Hydroxyapatite Nanorods

Directed differentiation enables the production of a specific cell type by manipulating signals in development. However, there is a lack of effective means to accelerate the regeneration of neurons of particular subtypes for pathogenesis and clinical therapy. In this study, we find that hydroxyapatite (HAp) nanorods promote neural differentiation of neural stem cells due to their chemical compositions. Lysosome-mediated degradation of HAp nanorods elevates intracellular calcium concentrations and accelerates GABAergic neurogenesis. As a mechanism, the enhanced activity of a Ca²⁺ peak initiated by HAp nanorods leads to the activation of c-Jun and thus suppresses the expression of GABAergic/glutamatergic selection gene TLX3. We demonstrate the capability of HAp nanorods in promoting the differentiation into GABAergic neurons at both molecular and cellular function levels. Given that GABAergic neurons are responsible for various physiological and pathological processes, our findings open up enormous opportunities in efficient and precise stem cell therapy of neurodegenerative diseases.

Role of citrate in the formation of enamel-like calcium phosphate oriented nanorod arrays

The effect of citrate on the formation of oriented fluoride doped hydroxyapatite nanorods grown on an amorphous calcium phosphate substrate was investigated.

Pulp Regeneration Concepts for Nonvital Teeth: From Tissue Engineering to Clinical Approaches

Following the basis of tissue engineering (Cells-Scaffold-Bioactive molecules), regenerative endodontic has emerged as a new concept of dental treatment. Clinical procedures have been proposed by endodontic practitioners willing to promote regenerative therapy. Preserving pulp vitality was a first approach. Later procedures aimed to regenerate a vascularized pulp in necrotic root canals. However, there is still no protocol allowing an effective regeneration of necrotic pulp tissue either in immature or mature teeth. This review explores in vitro and preclinical concepts developed during the last decade, especially the potential use of stem cells, bioactive molecules, and scaffolds, and makes a comparison with the goals achieved so far in clinical practice. Regeneration of pulp-like tissue has been shown in various experimental conditions. However, the appropriate techniques are currently in a developmental stage. The ideal combination of scaffolds and growth factors to obtain a complete regeneration of the pulp-dentin complex is still unknown. The use of stem cells, especially from pulp origin, sounds promising for pulp regeneration therapy, but it has not been applied so far for clinical endodontics, in case of necrotic teeth. The gap observed between the hope raised from in vitro experiments and the reality of endodontic treatments suggests that clinical success may be achieved without external stem cell application. Therefore, procedures using the concept of cell homing, through evoked bleeding that permit to recreate a living tissue that mimics the original pulp has been proposed. Perspectives for pulp tissue engineering in the near future include a better control of clinical parameters and pragmatic approach of the experimental results (autologous stem cells from cell homing, controlled release of growth factors). In the coming years, this therapeutic strategy will probably become a clinical reality, even for mature necrotic teeth.

Structural and Chemical Analysis of Hydroxyapatite (HA)-Boron Nitride (BN) Nanocomposites Sintered Under Different Atmospheric Conditions

Calcium phosphate derivatives have been widely employed in medical and dental applications for hard tissue repair, as they are the main inorganic constitution of hard tissue; such as bones and teeth. Owing to their excellent osteoconductive and bioactive properties, hydroxyapatite- (HA) based ceramics are the best candidates of this group for medical, bioscience, and dental applications. However, when replacing a bone or tooth, HA is not able to sustain similar mechanical properties. In this study, to improve the mechanical properties, nanoscale hexagonal boron nitride with different compositional percentages was added to the nano HA to form composites. The effect of compositional changes and sintering parameters on microstructural and morphological properties of the ceramic composites was comparatively investigated. Detailed chemical characterization of the composite materials was carried out using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy, whereas scanning electron microscopy and atomic force microscopy investigations were employed to monitor morphological and surface features. Additional transmission electron microscopy investigations were carried out to reveal the nanostructure and crystal structure of the composites.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

Synthesis and characterization of amino acid-functionalized calcium phosphate nanoparticles for siRNA delivery

Small interfering RNAs (siRNA) are short nucleic acid fragments of about 20-27 nucleotides, which can inhibit the expression of specific genes. siRNA based RNAi technology has emerged as a promising method for the treatment of a variety of diseases. However, a major limitation in the therapeutic use of siRNA is its rapid degradation in plasma and cellular cytoplasm, resulting in short half-life. In addition, as siRNA molecules cannot penetrate into the cell efficiently, it is required to use a carrier system for its delivery. In this work, chemically and morphologically different calcium phosphate (CaP) nanoparticles, including spherical-like hydroxyapatite (HA-s), needle-like hydroxyapatite (HA-n) and calcium deficient hydroxyapatite (CDHA) nanoparticles were synthesized by the sol-gel technique and the effects of particle characteristics on the binding capacity of siRNA were investigated. In order to enhance the gene loading efficiency, the nanoparticles were functionalized with arginine and the morphological and their structural characteristics were analyzed. The addition of arginine did not significantly change the particle sizes; however, it provided a significantly increased binding of siRNA for all types of CaP nanoparticles, as revealed by spectrophotometric measurements analysis. Arginine functionalized HA-n nanoparticles showed the best binding behavior with siRNA among the other nanoparticles due to its high, positive zeta potential (+18.8mV) and high surface area of Ca⁺⁺ rich "c" plane. MTT cytotoxicity assays demonstrated that all the nanoparticles tested herein were biocompatible. Our results suggest that high siRNA entrapment in each of the three modified non-toxic CaP nanoparticles make them promising candidates as a non-viral vector for delivering therapeutic siRNA molecules to treat cancer.

Artificial enamel induced by phase transformation of amorphous nanoparticles

Human tooth enamel has tightly packed c-axis-oriented hydroxyapatite (HAP: Ca10(PO4)6(OH)2) nanorods with high elastic modulus. Fabrication of an enamel architecture in vitro supports the repair of teeth using HAP; however, existing methods require complex and laborious steps to form an enamel-like structure. Here we present a very simple and effective technique for forming artificial enamel in near-physiological solution using a substrate composed of amorphous calcium phosphate (ACP) nanoparticles. Without any functionalized modification of the substrate surface, faint dissolution and successive phase transformation automatically induce formation of an intermediate layer of low-crystalline HAP nanoparticles, on which highly oriented HAP nanorods grow by geometrical selection. We also show that an enamel structure forms on a substrate of amorphous calcium carbonate when the surface nanoparticles react so as to form an intermediate layer similar to that in ACP. Our results demonstrate that there is a wide range of substrate choices for nanorod array formation. Contrary to current understanding, a stable surface designed in nanoscale is not essential for the growth of arranged guest crystals. Reactive amorphous nanoparticles and their transformation efficiently induce a nanorod array structure.

Aligned hydroxyapatite nano-crystal formation on a polyamide surface

Highly aligned n-HA arrays were fabricated on polyamide matrix. The oriented nHA crystals show excellent cell response and the mechanism of how these structures form was explored.

Large-Scale Automated Production of Highly Ordered Ultralong Hydroxyapatite Nanowires and Construction of Various Fire-Resistant Flexible Ordered Architectures

Practical applications of nanostructured materials have been largely limited by the difficulties in controllable and scaled-up synthesis, large-sized highly ordered self-assembly, and macroscopic processing of nanostructures. Hydroxyapatite (HAP), the major inorganic component of human bone and tooth, is an important biomaterial with high biocompatibility, bioactivity, and high thermal stability. Large-sized highly ordered HAP nanostructures are of great significance for applications in various fields and for understanding the formation mechanisms of bone and tooth. However, the synthesis of large-sized highly ordered HAP nanostructures remains a great challenge, especially for the preparation of large-sized highly ordered ultralong HAP nanowires because ultralong HAP nanowires are easily tangled and aggregated. Herein, we report our three main research findings: (1) the large-scale synthesis of highly flexible ultralong HAP nanowires with lengths up to >100 μm and aspect ratios up to >10000; (2) the demonstration of a strategy for the rapid automated production of highly flexible, fire-resistant, large-sized, self-assembled highly ordered ultralong HAP nanowires (SHOUHNs) at room temperature; and (3) the successful construction of various flexible fire-resistant HAP ordered architectures using the SHOUHNs, such as high-strength highly flexible nanostructured ropes (nanoropes), highly flexible textiles, and 3-D printed well-defined highly ordered patterns. The SHOUHNs are successively formed from the nanoscale to the microscale then to the macroscale, and the ordering direction of the ordered HAP structure is controllable. These ordered HAP architectures made from the SHOUHNs, such as highly flexible textiles, may be engineered into advanced functional products for applications in various fields, for example, fireproof clothing.

Preparation of Porous Chitosan-Siloxane Hybrids Coated with Hydroxyapatite Particles

This paper describes the apatite deposition of chitosan-silicate porous hybrids derived from chitosan and γ-glycidoxypropyltrimethoxysilane (GPTMS) in alkaline phosphate solution. The preparation of porous hybrids with needle-like apatite on their surfaces is described. Following apatite deposition the porous hybrids maintained high porosity. The enzymatic degradation rate was low even after 6 months and the porous hybrids were very flexible and cut easily using surgical scissors.

Heterogeneous structure and in vitro degradation behavior of wet-chemically derived nanocrystalline silicon-containing hydroxyapatite particles

Nanocrystalline hydroxyapatite (HAp) and silicon-containing hydroxyapatite (SiHAp) particles were synthesized by a wet-chemical procedure and their heterogeneous structures involving a disordered phase were analyzed in detail by X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The effects of heterogeneous structure on in vitro biodegradability and the biologically active Ca(II)- and Si(IV)-releasing property of SiHAp particles were discussed. The (29)Si NMR analysis revealed that the Si(IV) was incorporated in the HAp lattice in the form of Q(0)(SiO(4)(4-)orHSiO(4)(3-)) species, accompanied by the formation of condensed silicate units outside the HAp lattice structure, where the fraction and amount of Q(0) species in the HAp lattice depends on the Si content. The (31)P and (1)H NMR results agreed well with the XRD, TEM and FTIR results. NMR quantitative analysis results were explained by using a core-shell model assuming a simplified hexagonal shape of HAp covered with a disordered layer, where Si(IV) in Q(0) was incorporated in the HAp lattice and a disordered phase consisted of hydrated calcium phosphates involving polymeric silicate species and carbonate anions. With the increase in the Si content in the HAp lattice, the in vitro degradation rate of the SiHAps increased, while their crystallite size stayed nearly unchanged. The biologically active Ca(II)- and Si(IV)-releasing ability of the SiHAps was remarkably enhanced at the initial stage of reactions by an increase in the amount of Si(IV) incorporated in the HAp lattice but also by an increase of the amount of polymeric silicate species incorporated in the disordered phase.

Protein-mediated enamel mineralization

Enamel is a hard nanocomposite bioceramic with significant resilience that protects the mammalian tooth from external physical and chemical damages. The remarkable mechanical properties of enamel are associated with its hierarchical structural organization and its thorough connection with underlying dentin. This dynamic mineralizing system offers scientists a wealth of information that allows the study of basic principels of organic matrix-mediated biomineralization and can potentially be utilized in the fields of material science and engineering for development and design of biomimetic materials. This chapter will provide a brief overview of enamel hierarchical structure and properties and the process and stages of amelogenesis. Particular emphasis is given to current knowledge of extracellular matrix protein and proteinases, and the structural chemistry of the matrix components and their putative functions. The chapter will conclude by discussing the potential of enamel for regrowth.

Amelogenin-assisted ex vivo remineralization of human enamel: Effects of supersaturation degree and fluoride concentration

The formation of organized nanocrystals that resemble enamel is crucial for successful enamel remineralization. Calcium, phosphate and fluoride ions, and amelogenin are important ingredients for the formation of organized hydroxyapatite (HAP) crystals in vitro. However, the effects of these remineralization agents on the enamel crystal morphology have not been thoroughly studied. The objective of this study was to investigate the effects of fluoride ions, supersaturation degree and amelogenin on the crystal morphology and organization of ex vivo remineralized human enamel. Extracted third molars were sliced thin and acid-etched to provide the enamel surface for immersion in different remineralization solutions. The crystal morphology and mineral phase of the remineralized enamel surface were analyzed by field emission-scanning electron microscopy, attenuated total reflection-Fourier transformed infrared and X-ray diffraction. The concentration of fluoride and the supersaturation degree of hydroxyapatite had significant effects on the crystal morphology and crystal organization, which varied from plate-like loose crystals to rod-like densely packed nanocrystal arrays. Densely packed arrays of fluoridated hydroxyapatite nanorods were observed under the following conditions: σ(HAP)=10.2±2.0 with 1.5±0.5 mg l(-1) fluoride and 40±10 μg ml(-1) amelogenin, pH 6.8±0.4. A phase diagram summarizes the conditions that form dense or loose hydroxyapatite nanocrystal structures. This study provides the basis for the development of novel dental materials for caries management.

Amelogenin as a Promoter of Nucleation and Crystal Growth of Apatite

Human dental enamel forms over a period of 2 - 4 years by substituting the enamel matrix, a protein gel mostly composed of a single protein, amelogenin with fibrous apatite nanocrystals. Self-assembly of amelogenin and the products of its selective proteolytic digestion are presumed to direct the growth of apatite fibers and their organization into bundles that eventually comprise the mature enamel, the hardest tissue in the mammalian body. This work aimed to establish the physicochemical and biochemical conditions for the growth of apatite crystals under the control of a recombinant amelogenin matrix (rH174) in combination with a programmable titration system. The growth of apatite substrates was initiated in the presence of self-assembling amelogenin particles. A series of constant titration rate experiments was performed that allowed for a gradual increase of the calcium and/or phosphate concentrations in the protein suspensions. We observed a significant amount of apatite crystals formed on the substrates following the titration of rH174 sols that comprised the initial supersaturation ratio equal to zero. The protein layers adsorbed onto the substrate apatite crystals were shown to act as promoters of nucleation and growth of calcium phosphates subsequently grown on the substrate surface. Nucleation lag time experiments have showed that rH174 tends to accelerate precipitation from metastable calcium phosphate solutions in proportion to its concentration. Despite their mainly hydrophobic nature, amelogenin nanospheres, the size and surface charge properties of which were analyzed using dynamic light scattering, acted as a nucleating agent for the crystallization of apatite. The biomimetic experimental setting applied in this study proves as convenient for gaining insight into the fundamental nature of the process of amelogenesis.

Synthesis of nanobioglass and formation of apatite rods to occlude exposed dentine tubules and eliminate hypersensitivity

The occlusion of patent dentine tubules may reduce or eliminate hypersensitivity by restricting dentinal fluid movement. The efficacy of a novel sol-gel nanobioglass and a melt-derived bioglass to occlude tubules and promote apatite formation was tested by mechanically brushing a slurry of bioglass powder and human saliva onto dentine possessing exposed tubules. Scanning electron microscopy, focused ion beam and energy-dispersive X-ray spectroscopy were used to characterize the powders and assess tubule occlusion. Melt-derived bioglass possessed an irregular particle morphology and had a mean size of 3.30 +/- 0.42 microm. The sol-gel bioglass particles were spherical, with a mean size of 0.65 +/- 0.19 microm. Dentine treated with melt-derived bioglass exhibited a tightly adherent continuous apatite layer. Treatment with nanobioglass resulted in particle deposition within tubules and formation of apatite rods which were tightly adherent to tubule walls and continuous to a measured depth of 270 microm.

Synthesis of dental enamel-like hydroxyapatite through solution mediated solid-state conversion

An ordered dental enamel-like structure of hydroxyapatite (HAp) was achieved through a solution mediated solid-state conversion process with organic phosphate surfactant and gelatin as the mediating agent. Transmission electron microscopy (TEM) tests demonstrated uniform sizes in the obtained apatite nanorods which arranged in parallel to each other along the c-axis and formed organized microarchitectural units over 10 microm in size. The sizes of the synthetic hydroxyapatite nanorods were similar to that observed in enamel from human teeth. The formation and regulation of the orientation and size of HAp nanorods might lead to a better understanding of the biomineralization process for the preparation of high performance biomaterials.

Nanodimensional and Nanocrystalline Apatites and Other Calcium Orthophosphates in Biomedical Engineering, Biology and Medicine

Recent developments in biomineralization have already demonstrated that nanosized particles play an important role in the formation of hard tissues of animals. Namely, the basic inorganic building blocks of bones and teeth of mammals are nanodimensional and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds nanocrystals of a biological apatite were found to be combined into self-assembled structures under the control of various bioorganic matrixes. In addition, the structures of both dental enamel and bones could be mimicked by an oriented aggregation of nanosized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nanodimensional and nanocrystalline calcium orthophosphates for a clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various types of cells were detected on smaller crystals of calcium orthophosphates. Thus, the nanodimensional and nanocrystalline forms of calcium orthophosphates have a great potential to revolutionize the field of hard tissue engineering starting from bone repair and augmentation to the controlled drug delivery devices. This paper reviews current state of knowledge and recent developments of this subject starting from the synthesis and characterization to biomedical and clinical applications. More to the point, this review provides possible directions of future research and development.