Hydroxyapatite Nanotubes Research Articles

Preparation and Characterization of Hydroxyapatite Nanotubes

As the key mineral component of human bones, hydroxyapatite (HA) has grasped much attention due to its outstanding biocompatibility, bioactivity and osteoconductive properties. Among different morphologies of HA materials, the special structure and good performance of HA nanotubes has been the focus of many scientific researchers. HA nanomaterials with hollow tube shapes have a relatively high surface area, low density and good mechanical property. However, the simple and convenient procedure to synthesize well distributed HA nanotubes is still rare. In this article, HA nanotubes with tens of nanometers in diameter and hundreds of microns in length were successfully synthesized via a simple solvothermal route. Calcium oleate and sodium hexametaphosphate are selected as the calcium source and phosphorus source, respectively. The surface structure of the HA nanotubes was observed under a scanning electron microscope. The synthesized HA nanotubes can be used in the area of adsorption, drug delivery and treatment of disease.

Tubular nanomaterials for bone tissue engineering.

Nanomaterial composition, morphology, and mechanical performance are critical parameters for tissue engineering. Within this rapidly expanding space, tubular nanomaterials (TNs), including carbon nanotubes (CNTs), titanium oxide nanotubes (TNTs), halloysite nanotubes (HNTs), silica nanotubes (SiNTs), and hydroxyapatite nanotubes (HANTs) have shown significant potential across a broad range of applications due to their high surface area, versatile surface chemistry, well-defined mechanical properties, excellent biocompatibility, and monodispersity. These include drug delivery vectors, imaging contrast agents, and scaffolds for bone tissue engineering. This review is centered on the recent developments in TN-based biomaterials for structural tissue engineering, with a strong focus on bone tissue regeneration. It includes a detailed literature review on TN-based orthopedic coatings for metallic implants and composite scaffolds to enhance in vivo bone regeneration.

Sodium Alginate Modified Hydroxyapatite Nanotubes as a Novel Ecofriendly Additive for Preparation of Polyethersulfone Hybrid Ultrafiltration Membranes

Background:: Hydrophilic nanomaterials have been extensively exploited their applications in the field of hybrid water treatment membranes. However, some of the modification process to nanomaterials may be complicated, and the nonselective pores caused by the poor compatibility between nanoparticles and the polymer matrix impair the rejection efficiency for ultrafiltration application. Thus, it is highly desirable to develop a kind of effective nano dopant with favorable compatibility by a facile way for the preparation of ultrafiltration membranes. Objective:: The aim of this study was to fabricate a novel environmentally friendly and low-cost nano additive with good compatibility for the preparation of ultrafiltration membranes. Methods:: Hydroxyapatite nanotubes were prepared via a biomimetic process, and then SA was coated on the surface of hydroxyapatite nanotubes. Subsequently, a series of hybrid ultrafiltration membranes were fabricated with different amounts of modified HANTs and polyethersulfone (PES). Results:: Exhaustive characterizations were conducted for the membranes, including hydrophilicity, porosity, mean pore size, morphologies and UF performance test. The highest water flux of the hybrid membranes displayed 1.9 times that of the original PES membrane. Meanwhile, the hybrid membrane with 0.2% hydroxyapatite nanotubes obtained elevated antifouling ability, achieving a flux recovery ratio of 85.6%. Conclusion:: The facile coating of SA endowed the nanotubes improved hydrophilicity and meanwhile enhanced the compatibility between PES and HANTs. This work provides a facile way in the construction of green nanofillers and promising results in the preparation of hybrid UF membranes.

Combined strategy of blending and surface modification as an effective route to prepare antifouling ultrafiltration membranes

Ultrafiltration (UF) membranes blended with hydrophilic nanomaterials usually exhibit preferable overall performance including the membrane permeability and antifouling capability. However, the improvement in antifouling performance may be not outstanding due to the small amount of nanomaterial distributed near the membrane surface and the limited improvement in membrane hydrophilicity. Notably, excess addition of nanomaterials may lead to the decline in membrane permeability. In order to solve the above problem, we integrated the strategy of blending and surface modification to construct novel hybrid UF membranes. Novel nanohybrid was prepared via tannic acid (TA) coating on hydroxyapatite nanotubes (HANTs) and the subsequent grafting of zwitterionic polyethylenimine (ZPEI). The prepared nanohybrid (HANTs@TA-ZPEI) was incorporated with the polysulfone containing tertiary amine groups to fabricate hybrid membranes via the solution blending and the subsequent immersion-precipitation phase inversion process. Then the matrix was modified with zwitterions via the reaction of tertiary amine group with 1, 3-propane sultone. UF tests were conducted using the bovine serum albumin (BSA) and humic acid (HA) as the representative foulants. Results showed that both the permeability and the antifouling performance of the membranes achieved favorable promotion. Thereinto, the water flux of M-B0.4-Z membrane (pre blended with 0.4 wt% HANTs@TA-ZPEI in the casting solution and post-surface modified) exhibited 2.6 times that of the pristine membrane and the flux recovery ratio (FRR) for BSA and HA attained 93.4% and 96.1%, respectively. By the combination of blending and surface modification, both the membrane permeability and fouling resistant properties could attain remarkable promotion, which exerted the advantages of two methods and made up the deficiency of single blending method.

Sequential release of immunomodulatory cytokines binding on nano-hydroxyapatite coated titanium surface for regulating macrophage polarization and bone regeneration

Inflammation occurs when the material is implanted into the body. As one of the important immune cells in the regulation of inflammation, macrophages are able to remove pathogens and necrotic cells, and polarize to different phenotypes to regulate inflammatory response for tissue regeneration. Therefore, it is known that the sequential release of immunomodulatory cytokines from the surface of titanium (Ti) implants can regulate the polarization of macrophages and promote osseointegration of implants. In order to control the switch of macrophage phenotypes at desired time, we fabricated hydroxyapatite (HAp) nanotube arrays coating on Ti surface, by acid-etching, alkali-heating and HAp coating sequentially. Then we loaded the interleukin-4 (IL-4) encapsulated by poly (lactic-co-glycolic acid) (PLGA) on the bottom of the nanotube and the interferon-γ (IFN-γ) encapsulated by sodium hyaluronate (SH) on the top of the nanotube. Based on the physical and chemical properties of PLGA and SH and the spatial distribution of loaded cytokines, we hypothesized that the programmed release of IFN-γ and IL-4, which made the phenotypic transition of macrophages at a specific time, so as to regulate inflammation and promote osteogenic repair. Our hypothesis created a new type of drug sustained release system, which has high research value for improving the osseointegration of implants.

Development of highly permeable and antifouling ultrafiltration membranes based on the synergistic effect of carboxylated polysulfone and bio-inspired co-deposition modified hydroxyapatite nanotubes

Hybridization has become a powerful toolbox for developing ultrafiltration membranes with superior properties. However, it remains challenging to give full play to the utility of nanofillers because of poor bonding strength between polymers and inorganic nanomaterials. Herein, hydroxyapatite nanotubes (HANTs) were modified via bio-inspired polydopamine (PDA) and polyethylenimine (PEI) co-deposition. Meanwhile, polysulfone with carboxylation degree of 30% (PSF-COOH-30%) was synthesized by nucleophilic substitution reaction and employed as the membrane matrix. The results showed that when 0.3 wt% HANTs@PDA/PEI was incorporated, the pure water flux of the hybrid membrane achieved about 3.2 times that of the unfilled membrane and the rejection rate of bovine serum albumin (BSA) and humic acid (HA) remained 94.5% and 97.8%, respectively. Meanwhile, the flux recovery ratio for BSA and HA solutions (1 g/L) reached 90.8% and 93.7%, respectively. Specifically, the superiority of UF performance benefited from the synergistic effect of both the carboxylated polymer and the nanofiller. On one hand, the incorporation of HANTs@PDA/PEI promoted the formation of more porous membrane structure and improved the hydrophilicity of the membrane. On the other hand, due to the existence of COOH, the electrostatic repulsion between the membranes and contaminants enhanced the fouling resistance for BSA and HA. Conspicuously, the ease and versatility of co-deposition provide new ideas in the construction of nanohybrid and the favorable improvement renders that appropriate combination of polymer and additive is an effective way for developing future ultrafiltration membranes.

Magnetic hydroxyapatite nanotubes on micro-arc oxidized titanium for drug loading

A novel coating which comprised magnetic hydroxyapatite (HA) nanotubes as an outer layer and porous TiO2 as the inner layer was fabricated on Ti by a hybrid process of micro arc oxidation (MAO), hydrothermal treatment (HT) and electrochemical treatment (ET). The microstructure of HA nanorods after HT was investigated, and their morphology evolution from nanorods to nanotubes by prolonging ET was observed. The formation mechanism of HA nanotubes was explored, and magnetism property of the composite coating was evaluated. Monocrystallized HA nanorods doped with 1.19 At% Fe were initially formed on microporous TiO2 by MAO and HT, and they had a mean diameter of 300 nm. The mismatching between Ca and Fe ions induced some lattice distortions on the basal-faceted surfaces of HA. During ET process, Na+ and H+ ions should concentrate on the negatively charged basal planes of HA inducing further lattice distortion and local dissolution. By prolonging the ET process, dissolution of basal planes increased, resulting in the formation of HA nanotubes with an average outer diameter of about 300 nm, and wall thickness of about 30 nm. The composite coating showed magnetism behavior with a value of 0.3 emu g−1 at applied field of 4 T. A strategy to fabricate a magnetic HA nanotube coating on Ti was given, and the unique nanostructure should have a potential application in drug loading.

Silver nano-particle coated hydroxyapatite nano-composite membrane for the treatment of palm oil mill effluent

Nano-composite ultra-filtration membranes were developed for the treatment of Palm Oil Mill Effluent (POME). Silver nano-particle was synthesized and was used to coat hydroxyapatite nanotubes. This coated nano-filler was used as filler for the polyphenylsulfone (PPSU) membrane. The filler composition in the membrane was varied from 0 to 2.5 wt% to investigate the effect of fillers on the separation properties of the membrane. Both dead-end and cross-flow techniques were used for the separation. Characterization techniques such as contact angle analysis, particle size analyzer, XRD, SEM were used to analyze both nanoparticles as well as the nano-composite membranes. Parameters like COD, BOD, turbidity, suspended solids, pH, conductivity and TDS of the permeate were studied. Change in intrinsic membrane resistance with respect to filler composition was also studied. Based on the results the membrane having a filler composition of 2% was found to be exhibiting excellent properties compared to other membranes in terms of separation performances. The rejection percentage of PPSU membrane with a filler content of 2% was 89.74%. The composite membrane had shown promising results by removing all the organic matter present in the POME and can be further developed into a pilot plant.

Fabrication of hybrid ultrafiltration membranes with improved water separation properties by incorporating environmentally friendly taurine modified hydroxyapatite nanotubes

In this work, hydroxyapatite nanotubes (HANTs) were explored as a novel environment-friendly additive for the fabrication of ultrafiltration (UF) membranes. Hydrophilic modification was conducted to the prepared HANTs, which includes the polydopamine (PDA) coating and the following grafting of taurine (TA), a kind of amino acid with -SO3H group. Subsequently, the modified HANTs (HANTs-DA-TA) were mixed with polyethersulfone (PES) to fabricate nanocomposite UF membranes. The prepared membranes were fully characterized, including the porosity, hydrophilicity, membrane morphology, and practical UF capability. The fabricated PES/HANTs-DA-TA membranes exhibited remarkably elevated water flux (up to 439 L m−2 h−1), which was ~2.6 times that of PES membrane (169 L m−2 h−1), whereas the rejection of PES/HANTs-DA-TA membranes was still kept at a high state. The improved flux mainly benefited from the more porous membrane structure, declined skin layer thickness, and the enhanced hydrophilicity. Meanwhile, the PES/HANTs-DA-TA membranes exhibited increased antifouling capability and the highest flux recovery ratio (FRR) reached 77.9% due to the improved surface hydrophilicity. Furthermore, the short rod-like nano hydroxyapatite (HA) was prepared and functionalized the same way as the HANTs-DA-TA. It was found that compared to rod-like HA, the tubular nano HA was more efficient in facilitating the membrane permeation due to the superiority of nanotubular structure. This work reveals that as a novel green additive, the HANTs have great application potential in fabricating water treatment membranes and can be employed for further studies.

The hydroxyapatite nanotube as a promoter to optimize the HDS reaction of NiMo/TiO2 catalyst

A composite containing TiO2 whiskers (TiO2(w)) and hydroxyapatite nanotube (nHA) with mosaic structure functioned as a support was successfully synthesized by a facile route. The TiO2(w) was prepared from potassium titanate and the novel single-crystalline hydroxyapatite nanotubes were synthesized via a distinctive biomimetic route. Properties of support and catalyst were characterized by SEM, TEM, XRD, FT-IR of adsorbed pyridine (in situ FT-IR), BET, TPR, and NH3-TPD. Catalytic activity of NiMo/TiO2(w)-nHA, and the effect of nHA contents on hydrodesulfurization (HDS) activity was performed. Results indicated the incorporation of nHA can weaken the Lewis acidity of TiO2 supports and decrease acidity of the NiMo/TiO2(w)-nHA catalyst. The addition of moderate nHA has weak influence on the textural and structural properties of the catalyst. NiMo/TiO2(w)-nHA exhibits higher HDS catalytic activity than that of NiMo/TiO2(w) catalyst under mild conditions of low temperature and pressure (280°C and 2MPa), and the catalytic performance of NiMo/TiO2(w)-nHA-0.1 is the best. The synergistic effects between TiO2(w) and nHA and acidity regulation contribute to improve the HDS catalytic activity of the nHA-doped samples.

Facile preparation of hydroxyapatite nanotubes assisted by needle-like calcium carbonate

Hydroxyapatite (HA) is a famous biomaterial and its performance depends greatly on its morphology and 3D architecture. So the synthesis for HA with specific structures has been widely paid attention. In this research, a cost-effective way to prepare HA nanotubes with no post-processing template removal step was presented through Kirkendall effect-assisted ion-exchange process by using inexpensive needle-like CaCO3 nanoparticles as templates and calcium sources. The effects of reaction time, temperature and pH value on the formation of HA nanotubes were investigated. The as-prepared HA nanotube products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET). It was found that HA nanotubes had uniform tubular hollow structures with big openings, a length of 2–4μm, the average inner diameters at the two ends of 300–400nm and 150–250nm, respectively, as well as a wall thickness of approximately 35nm and a specific surface area of 60m2/g.

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

Uniform single-crystalline hydroxyapatite nanotubes with hexagonal facets are synthesized via a distinctive organoamines-assisted biomimetic route. These novel HA nanotubes exhibit exceptional performance in stimulating osteoblast proliferation, which gives them intriguing potential for bone repair.

Mechanical properties and biomedical applications of a nanotube hydroxyapatite-reduced graphene oxide composite

As a result of the growing interest in the biological and mechanical performance of hydroxyapatite (HA)–graphene nano-sheets (GNs) composite systems, reduced graphene oxide (rGO) reinforced hydroxyapatite nano-tube (nHA) composites were synthesized in situ using a simple hydrothermal method in a mixed solvent system of ethylene glycol (EG), N,N-dimethylformamide (DMF) and water, without using any of the typical reducing agents. The consolidation process was performed by hot isostatic pressing (HIP) at 1150°C and 160MPa. The composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, enabling confirmation of the synthesis and reduction of the nHA and rGO, respectively. The structure of the synthesized powder and cell attachment on the sintered sample was confirmed by field emission scanning electron microscopy (FESEM). The effects of the rGO on the mechanical properties and the in vitro biocompatibility of the nHA based ceramic composites were investigated. The elastic modulus and fracture toughness of the sintered samples increased with the increase of the rGO content when compared to the pure nHA by 86% and 40%, respectively. Cell culture and viability test results showed that the addition of the rGO promotes osteoblast adhesion and proliferation, thereby increasing the biocompatibility of the nHA–rGO composite.

Synthesis of hydroxyapatite nanotubes for biomedical applications

Single phase, stoichiometrically pure, hollow nanotubes of hydroxyapatite have been synthesized and single-particle analysis has been performed to successfully prove the sole formation of Ca10(PO4)6(OH)2 phase. The facile synthesis involves a sol–gel process under neutral conditions in the presence of a sacrifical anodic alumina template. The structures formed are hollow nanotubes that have been characterized by XRD, SEM, TEM, SAED, EELS, EDS and BET measurements. The diameter of the resulting tubes is in the range of 140–350nm, length is on the order of a few microns and the wall thickness of the tubes was found to be ca. 30nm. Moreover these tubes had a large BET surface area of 115m2/g and were found to be biocompatible. They displayed inertness in the presence of NIH 3T3 mouse fibroblast cells as dictated by an MTT assay.

A novel preparation of magnetic hydroxyapatite nanotubes

We report here the novel preparation of magnetic hydroxyapatite nanotubes (MHAnt). Poly(caprolactone) (PCL)–magnetite nanoparticles (MNPs) composite nanofiber was used as a template for the MHAnt. The surface of the composite nanofiber was activated in an alkaline solution and then an apatite mineral phase was deposited through a series of solution-mediated processes. After heat-treatment at 500°C, a hollow tube of HA-MNPs was created in which HA formed an outer shell and most of the MNPs lined the inner shell surface. The inner shell size was about 650nm and the shell thickness was about 137nm. The developed MHAnt showed a saturation magnetization of 27.20emu/g, exhibiting a ferromagnetic property. The newly developed MHAnt may be useful in biomedical applications such as hyperthermia treatment of bone cancer.

Production of a biomimetic apatite nanotube mesh via biotemplating a polymer nanofiber mesh

Here, we report the preparation of hydroxyapatite nanotubes for specific use as bone regeneration material. The nanofiber mesh of a polymer (polycaprolactone) used as a template was mineralized within solutions via a biomimetic process. A subsequent heat-treatment (over 500 °C) completely eliminated the inner polymer, resulting in preserving the surface mineral phase in the form of nanotubes. The nanotubes had diameters of hundreds of nanometers with nonwoven mesh, replicating the initial nanofiber template. Furthermore, the nanotubes revealed a phase of poorly crystallized apatite, mimicking biological bone mineral. The developed biomimetic apatite nanotubes may be useful for bone regeneration as a new type of biomaterial.

Polymeric micelle-templated synthesis of hydroxyapatite hollow nanoparticles for a drug delivery system

Hydroxyapatite (HA) hollow nanoparticles (HNPs) have great potential in nanoscaled delivery devices due to their small size, excellent biocompatibility and expected high capacity. However, the preparation of HA HNPs for their application in a drug delivery system has rarely been reported because HA has a complicated crystal structure and it is difficult to obtain stable HA HNPs with hollows that are only nanoscaled in size. In the present study, HA HNPs were successfully produced through a novel polymeric micelle-templating method. The micelles were structured with completely insoluble Pluronic P123 molecules at cloud point as the core and Tween-60 molecules as the shell by the hydrophobic interaction of the alkyl chains with the insoluble P123 core. The morphology of the HA HNPs could be transformed from nanospheres to nanotubes by adding citric acid as a cosurfactant. The prepared HA HNPs had a much higher drug payload than traditional nanoparticles, using vancomycin as the model drug. Most importantly, the HA nanotubes were coupled with a layer of citrate molecules on the HA surfaces, which could further improve the drug load efficiency and could form an excellent pH-controlled open/closed gate for drug release with the addition of cationic polyelectrolytes.

Direct Electrochemistry of Hemoglobin Immobilized on Colloidal Gold‐Hydroxyapatite Nanocomposite for Electrocatalytic Detection of Hydrogen Peroxide

AbstractA novel nanocomposite of colloidal gold (GNPs) and hydroxyapatite nanotubes (Hap) was prepared for immobilization of a redox protein, hemoglobin (Hb), on glassy carbon electrode. The immobilized Hb showed fast direct electron transfer and excellent electrocatalytic behavior toward reduction of hydrogen peroxide. A synergic effect between GNPs and Hap for accelerating the surface electron transfer of Hb was observed, which led to a pair of redox peaks with a formal potential of (−340±2) mV at pH 7.0, and a new biosensor for hydrogen peroxide with a linear range from 0.5 to 25 μM and a limit of detection of 0.2 μM at 3σ. Owing to the good biocompatibility of the nanocomposite, the biosensor exhibited good stability and acceptable reproducibility. The as‐prepared nanocomposite film provided a good matrix for protein immobilization and biosensor preparation.

Sol–gel auto-combustion synthesis of hydroxyapatite nanotubes array in porous alumina template

In this paper, an array of highly ordered hydroxyapatite (HAP) nanotubes was synthesized by sol–gel auto-combustion method with porous anodic aluminum oxide (AAO) template for the first time. Based on thermogravimetry (DTA/TG), Fourier transform infrared (FTIR) and X-ray diffraction (XRD), the dried gel, derived from the sol solution with Ca(NO 3) 2·4H 2O and PO(CH 3O) 3 as precursors and ethylene glycol as the polymeric matrix, exhibited a typical self-propagating combustion behavior at low temperature, directly resulting in hexagonal crystalline HAP materials. The resultant HAP arrays fabricated from the above sol–gel in the AAO template were uniformly distributed, highly ordered nanotubes with uniform length and diameter according to the observations of scanning electron microscopy (SEM) and transmission electron microscope (TEM). The electron diffraction (ED), XRD and X-ray photoelectron spectroscopy (XPS) survey proved the formation of HAP phase with polycrystalline structure in the AAO template. Based on these results, a potential mechanism of “an auto-combustion from dried gel to nanoparticles and a subsequent in situ reaction from nanoparticles to nanotubes” was proposed.