Calcium Phosphate-Based Biomaterials for Bone Repair

Traumatic, tumoral, and infectious bone defects are common in clinics, and create a big burden on patient's families and society. Calcium phosphate (CaP)-based biomaterials have superior properties and have been widely used for bone defect repair, due to their similarities to the inorganic components of human bones. The biological performance of CaPs, as a determining factor for their applications, are dependent on their physicochemical properties. Hydroxyapatite (HAP) as the most thermally stable crystalline phase of CaP is mostly used in the form of ceramics or composites scaffolds with polymers. Nanostructured CaPs with large surface areas are suitable for drug/gene delivery systems. Additionally, CaP scaffolds with hierarchical nano-/microstructures have demonstrated excellent ability in promoting bone regeneration. This review focuses on the relationships and interactions between the physicochemical/biological properties of CaP biomaterials and their species, sizes, and morphologies in bone regeneration, including synthesis strategies, structure control, biological behavior, and the mechanisms of CaP in promoting osteogenesis. This review will be helpful for scientists and engineers to further understand CaP-based biomaterials (CaPs), and be useful in developing new high-performance biomaterials for bone repair.

Wet End Chemical Properties of a New Kind of Fire-Resistant Paper Pulp Based on Ultralong Hydroxyapatite Nanowires

In 2014, a new type of the fire-resistant paper based on ultralong hydroxyapatite (HAP) nanowires was reported by the author’s research group, which had superior properties and promising applications in various fields, such as high-temperature resistance, fire retardance, heat insulation, electrical insulation, energy, environmental protection, and biomedicine. The wet end chemical properties of the fire-resistant paper pulp are very important for papermaking and mechanical performance of the paper, which play a guiding role in the practical production of the fire-resistant paper. In this paper, the wet end chemical properties of a new kind of fire-resistant paper pulp based on ultralong HAP nanowires are studied for the first time by focusing on the wet end chemical parameters, the effects of these parameters on the properties such as flocculation, retention, draining, and white water circulation of the fire-resistant paper pulp, and their effects on the properties of the as-prepared fire-resistant paper. The experimental results indicated that the wet end chemical properties of the new kind of fire-resistant paper pulp based on ultralong HAP nanowires were unique and entirely different from those of the traditional paper pulp based on plant fibers. The wet end chemical properties of the fire-resistant paper pulp were significantly influenced by the inorganic adhesive and its content, which affected the runnability of the paper machine and the properties of the as-prepared fire-resistant paper. The flocculation properties of the fire-resistant paper pulp based on ultralong HAP nanowires were affected by the conductivity and Zeta potential. The addition of the inorganic adhesive in the fire-resistant paper pulp based on ultralong HAP nanowires could significantly increase the conductivity of the fire-resistant paper pulp, reduce the particle size of paper pulp floccules, and increase the tensile strength of the fire-resistant paper. In addition, the fire-resistant paper pulp based on ultralong HAP nanowires in the presence of inorganic adhesive exhibited excellent antibacterial performance. This work will contribute to and accelerate the commercialization process and applications of the new type of the fire-resistant paper based on ultralong HAP nanowires.

A scalable, low-cost and green strategy for the synthesis of ultralong hydroxyapatite nanowires using peanut oil

A scalable green and low-cost synthesis of ultralong hydroxyapatite nanowires using peanut oil is reported, which can be scaled up for large-scale low-cost production of ultralong hydroxyapatite nanowires and the fire-resistant inorganic paper.

Superamphiphobic coatings with antifouling and nonflammable properties using functionalized hydroxyapatite

Functional superamphiphobic coatings have attracted much attention due to their promising application prospects in oil transportation and anti-contamination, which call for the requirements of flame retardancy.

A facile one-step preparation of Ca10(PO4)6(OH)2/Li-BioMOFs resin nanocomposites with Glycyrrhiza glabra (licorice) root juice as green capping agent and mechanical properties study

The Ca₁₀(PO₄)₆(OH)₂/Li-BioMOFs resin nanocomposites were prepared and introduced as a new dental resin nanocomposite. Ca₁₀(PO₄)₆(OH)₂/Li-BioMOFs resin nanocomposites were synthesized with individual mechanical properties in the presence of lecithin as a biostabilizer. The hydrothermal synthesis of hydroxyapatite (HAp) nanostructures occurred in the presence of Glycyrrhiza glabra (liquorice) root juice that acts not only as a green capping agent but also as a reductant compound with a high steric hindrance agent. Results showed that the mechanical properties of nano-Ca₁₀(PO₄)₆(OH)₂ structures with a concentration of 60 ppm Li-BioMOF were increased by ∼132.5 MPa and 11.5 GPa for the flexural and Young's modulus, respectively. Based on the optical absorption ultraviolet-visible spectrum, the HAp nanocrystallites had a direct bandgap energy of 4.2 eV. The structural, morphological, and mechanical properties of the as-prepared nanoparticles were characterized with the FT-IR (Fourier-transform infra-red), UV-Vis (ultraviolet visible) spectrums, X-ray diffraction, SEM (scanning electron microscopy), and TEM (transmission electron microscopy) images, and atomic force microscopy (AFM). It is suggested that HAp structures loaded on the Li-BioMOFs are as a suitable and novel substrate which can be considered as a promising biomaterial in dental resin nanocomposites significantly improved the strength and modulus.

Rapid regeneration of enamel-like-oriented inorganic crystals by using rotary evaporation

Enamel, the hardest tissue in the human body, has excellent mechanical properties, mainly due to its highly ordered spatial structure. Fabricating enamel-like structure is still a challenge today. In this work, a simple and highly efficient method was introduced, using the silk fibroin as a template to regulate calcium- and phosphate- supersaturated solution to regenerate enamel-like hydroxyapatite crystals on various substrates (enamel, dentin, titanium, and polyethylene) under rotary evaporation. The enamel-like zinc oxide nanorod array structure was also successfully synthesized using the aforementioned method. This strategy provides a new approach to design and fabricate mineral crystals with particular orientation coatings for materials.

One-dimensional hydroxyapatite materials: preparation and applications

As one of the biominerals, hydroxyapatite (HAP) plays important roles in biology, and inspires researchers to investigate HAP-based materials for the applications in various biomedical fields. Among them, one-dimensional (1-D) micro-/nanostructured HAP materials have attracted great interest in the last decades. This review summarizes the preparation and applications of 1-D HAP materials, and discusses different aspects of 1-D HAP materials. Various synthetic methods have been developed to prepare 1-D HAP materials with different morphologies, sizes, surface properties and crystallinities. In addition, elements-substituted 1-D HAP materials and composites have also been prepared. Surfactants and additives are usually adopted to control the nucleation and growth of 1-D HAP materials, but the related mechanisms are not very clear yet. The applications of 1-D HAP materials have been widely investigated, and the biomedical applications show great prospect but still need further improvements. A new kind of highly flexible fire-resistant inorganic paper made of ultralong HAP nanowires has been developed and is a promising alternative of the traditional cellulose paper for valuable archives and important documents. Regardless of the advances, further studies should be made for preparing 1-D HAP materials with controlled structures, sizes and morphologies and for boosting their various applications.

A New Kind of Fireproof, Flexible, Inorganic, Nanocomposite Paper and Its Application to the Protection Layer in Flame-Retardant Fiber-Optic Cables

An innovative method for making a new kind of highly flexible, fireproof, inorganic, nanocomposite paper made from glass fibers (GFs) coated with network-structured hydroxyapatite ultralong nanowires (NS-HANWs) is reported. The NS-HANW/GF paper is fireproof, high-temperature resistant, highly flexible, highly exquisite, and smooth, which is comparable to high-quality advanced coated paper. The most incredible characteristic of the NS-HANW/GF paper is its incombustibility. The as-prepared NS-HANW/GF paper, with the addition of optimized inorganic additives, has high mechanical properties (tensile strength ≈16 MPa) and the tensile strength is nearly 15 times that of GF paper. In addition, the NS-HANW/GF paper exhibits a high biocompatibility, owing to the coating effect of NS-HANWs on GFs. Thermal analysis indicates that the NS-HANW/GF paper has high thermal stability at high temperatures up to 1000 °C. Competitive to conventional insulation materials, the NS-HANW/GF paper exhibits a low thermal conductivity and excellent heat insulation performance. Experiments show that the NS-HANW/GF paper is promising for application in the protection layer of fire-retardant fiber-optic cable. The NS-HANW/GF paper can also be used as printing, copying, or writing paper; nonflammable China paper; fire-retardant wallpaper; specialty fireproof paper; and so on.

Controlled synthesis and transformation of nano-hydroxyapatite with tailored morphologies for biomedical applications

Controllable nucleation, growth and transformation of nano-scaled hydroxyapatite from spherical to needle-like shapes with excellent dispersibility.

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.

Hydrothermally processed 1D hydroxyapatite: Mechanism of formation and biocompatibility studies

Recent developments in bone tissue engineering have led to an increased interest in one-dimensional (1D) hydroxyapatite (HA) nano- and micro-structures such as wires, ribbons and tubes. They have been proposed for use as cell substrates, reinforcing phases in composites and carriers for biologically active substances. Here we demonstrate the synthesis of 1D HA structures using an optimized, urea-assisted, high-yield hydrothermal batch process. The one-pot process, yielding HA structures composed of bundles of ribbons and wires, was typified by the simultaneous occurrence of a multitude of intermediate reactions, failing to meet the uniformity criteria over particle morphology and size. To overcome these issues, the preparation procedure was divided to two stages: dicalcium phosphate platelets synthesized in the first step were used as a precursor for the synthesis of 1D HA in the second stage. Despite the elongated particle morphologies, both the precursor and the final product exhibited excellent biocompatibility and caused no reduction of viability when tested against osteoblastic MC3T3-E1 cells in 2D culture up to the concentration of 2.6mg/cm(2). X-ray powder diffraction combined with a range of electron microscopies and laser diffraction analyses was used to elucidate the formation mechanism and the microstructure of the final particles. The two-step synthesis involved a more direct transformation of DCP to 1D HA with the average diameter of 37nm and the aspect ratio exceeding 100:1. The comparison of crystalline domain sizes along different crystallographic directions showed no signs of significant anisotropy, while indicating that individual nanowires are ordered in bundles in the b crystallographic direction of the P63/m space group of HA. Intermediate processes, e.g., dehydration of dicalcium phosphate, are critical for the formation of 1D HA alongside other key aspects of this phase transformation, it must be investigated in more detail in the continuous design of smart HA micro- and nano-structures with advanced therapeutic potentials.

An overview of chitin or chitosan/nano ceramic composite scaffolds for bone tissue engineering

Chitin and chitosan based nanocomposite scaffolds have been widely used for bone tissue engineering. These chitin and chitosan based scaffolds were reinforced with nanocomponents viz Hydroxyapatite (HAp), Bioglass ceramic (BGC), Silicon dioxide (SiO₂), Titanium dioxide (TiO₂) and Zirconium oxide (ZrO₂) to develop nanocomposite scaffolds. Plenty of works have been reported on the applications and characteristics of the nanoceramic composites however, compiling the work done in this field and presenting it in a single article is a thrust area. This review is written with an aim to fill this gap and focus on the preparations and applications of chitin or chitosan/nHAp, chitin or chitosan/nBGC, chitin or chitosan/nSiO₂, chitin or chitosan/nTiO₂ and chitin or chitosan/nZrO₂ in the field of bone tissue engineering in detail. Many reports so far exemplify the importance of ceramics in bone regeneration. The effect of nanoceramics over native ceramics in developing composites, its role in osteogenesis etc. are the gist of this review.

DNA-templated microwave-hydrothermal synthesis of nanostructured hydroxyapatite for storing and sustained release of an antibacterial protein

Hydroxyapatite nanostructured materials are prepared by a DNA-templated microwave-hydrothermal method and used for IgY loading/release and antibacterial study.

Highly porous ceramics based on ultralong hydroxyapatite nanowires

Highly porous ceramics with high biocompatibility are prepared using ultralong hydroxyapatite nanowires and palmitic acid spheres.

Sonochemical synthesis of hydroxyapatite nanoflowers using creatine phosphate disodium salt as an organic phosphorus source and their application in protein adsorption

Hydroxyapatite nanosheets-assembled nanoflowers are sonochemically synthesized using creatine phosphate, which have excellent cytocompatibility and relatively high protein adsorption ability.

Microwave-Assisted Hydrothermal Rapid Synthesis of Calcium Phosphates: Structural Control and Application in Protein Adsorption

Synthetic calcium phosphate (CaP)-based materials have attracted much attention in the biomedical field. In this study, we have investigated the effect of pH values on CaP nanostructures prepared using a microwave-assisted hydrothermal method. The hierarchical nanosheet-assembled hydroxyapatite (HAP) nanostructure was prepared under weak acidic conditions (pH 5), while the HAP nanorod was prepared under neutral (pH 7) and weak alkali (pH 9) condition. However, when the pH value increases to 11, a mixed product of HAP nanorod and tri-calcium phosphate nanoparticle was obtained. The results indicated that the pH value of the initial reaction solution played an important role in the phase and structure of the CaP. Furthermore, the protein adsorption and release performance of the as-prepared CaP nanostructures were investigated by using hemoglobin (Hb) as a model protein. The sample that was prepared at pH = 11 and consisted of mixed morphologies of nanorods and nanoprisms showed a higher Hb protein adsorption capacity than the sample prepared at pH 5, which could be explained by its smaller size and dispersed structure. The results revealed the relatively high protein adsorption capacity of the as-prepared CaP nanostructures, which show promise for applications in various biomedical fields such as drug delivery and protein adsorption.

Solvothermal synthesis of hydroxyapatite nanostructures with various morphologies using adenosine 5′-monophosphate sodium salt as an organic phosphorus source

Hydroxyapatite nanostructures with various morphologies are synthesized using adenosine 5′-monophosphate sodium salt as an organic phosphorus source.

Facile synthesis of dental enamel-like hydroxyapatite nanorod arrays via hydrothermal transformation of hillebrandite nanobelts

Biomimetic dental enamel-like hydroxyapatite (HAp) nanorod arrays were facilely synthesized via hydrothermal treatment of the hillebrandite nanobelts as hard-templates in trisodium phosphate aqueous solution.

Ln3+-doped hydroxyapatite nanocrystals: controllable synthesis and cell imaging

A series of novel HAp:Ln³⁺ (Ln = Eu or Tb) nanocrystals with tunable aspect ratios were prepared via facile hydrothermal synthetic routes and utilized for biological imaging applications.

Hydroxyapatite-magnetite-MWCNT nanocomposite as a biocompatible multifunctional drug delivery system for bone tissue engineering

New magnetic hydroxyapatite-based nanomaterials as bone-specific systems for controlled drug delivery have been synthesized. The synthesized hydroxyapatite, HA, decorated with magnetite nanoparticles by a deposition method (HA/Fe3O4) and the nanocomposite system obtained using magnetic multi-walled carbon nanotubes (HA/MWCNT/Fe3O4) as a filler for HA have been characterized by chemical and morphological analyses, and their biological behavior was investigated. The systems have also been doped with clodronate in order to combine the effect of bone biomineralization induced by hydroxyapatite-based composites with the decrease of osteoclast formation induced by the drug. An analysis of the preosteoclastic RAW264.7 cell proliferation by MTT assay confirmed the high biocompatibility of the three systems. TRAP staining of RAW 264.7 conditioned with sRAKL to induce osteoclastogenesis, cultured in the presence of the systems doped and undoped with clodronate, showed the inhibitory effect of clodronate after we counted the MNC TRAP(+)cells but only in the osteoclast formation; in particular, the system HA/Fe3O4-Clo exerted a high inhibitory effect compared to the drug alone. These results demonstrate that the synthesized nanocomposites are a biocompatible magnetic drug delivery system and can represent a useful multimodal platform for applications in bone tissue engineering.

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Electrodeposition of nanostructured bioactive hydroxyapatite-heparin composite coatings on titanium for dental implant applications

In this paper we describe the one-pot fabrication of hydroxyapatite (HA)-heparin composites by electrodeposition onto Ti substrates and their characterisation in terms of structure, morphology, heparin content and bioactivity. HA coatings are well known and widely applied osteointegration enhancers, but post-implant healing rate in dental applications is still suboptimal: e.g. coagulation control plays a key role and the incorporation of an anticoagulant is considered a highly desirable option. In this study, we have developed an improved, simple and robust growth procedure for single-phase, pure HA-heparin films of thickness 1/3 μm. HA-heparin, forming nanowires, has the ideal morphology for bone mineralisation. Staining assays revealed homogeneous incorporation of sizable amounts of heparin in the composite films. The bioactivities of the HA and HA-heparin coatings on Ti were compared by HeLa cell proliferation/viability tests and found to be enhanced by the presence of the anticoagulant.

Organoamine-assisted biomimetic synthesis of faceted hexagonal hydroxyapatite nanotubes with prominent stimulation activity for osteoblast proliferation

Uniform single-crystalline hydroxyapatite nanotubes are synthesized via a distinctive organoamines-assisted biomimetic route, and exhibit exceptional performance in stimulating osteoblast proliferation.

Synthesis methods for nanosized hydroxyapatite with diverse structures

Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Calcium phosphate hybrid nanoparticles: self-assembly formation, characterization, and application as an anticancer drug nanocarrier

Calcium phosphate hybrid nanoparticles (CaP-HNPs) have been synthesized in aqueous solution through self-assembly by using two oppositely charged polyelectrolytes (poly(diallyldimethylammonium chloride) (PDADMAC) and poly(acrylate sodium) (PAS)) as dual templates. First, the PAS/Ca(2+) and PDADMAC/PO4(3-) complexes form through electrostatic interactions and then two complexes self-assemble into CaP-HNPs after mixing them together. The as-prepared CaP-HNPs exhibit a spherical morphology with a narrow size distribution, good dispersibility, and high colloidal stability in water. The CaP-HNPs are explored as a nanocarrier for the anticancer drug docetaxel (Dtxl). The CaP-HNPs show excellent biocompatibility, high drug-loading capacity, pH-sensitive drug-release behavior, and high anticancer effect after being loaded with Dtxl. Therefore, the as-prepared CaP-HNPs are promising drug nanocarriers for cancer therapy.