Nano-sized Hydroxyapatite Research Articles

Sono-synthesis of nanohydroxyapatite: Effects of process parameters

Hydroxyapatite (HA) [Ca10(PO4)6(OH)2] is a bioactive ceramic with excellent osteoconductive properties. This characteristic helps HA to be integrated into the bone without provoking an immune reaction, thus making it a useful biocompatible material for load bearing bone implant. In this study, nanohydroxyapatite (NHA) was synthesised using a precipitation method assisted with ultrasonication. The process parameters such as ultrasonic time (t) (10–30min), ultrasonic amplitude (A) (50–70%), solution temperature (T) (50–90°C), and solution pH (7–9) were varied on the basis of single factor and their effects on NHA synthesis was investigated. Besides that, the effect of calcination on the NHA powder morphology was also studied by varying the calcination time (2, 4 and 6h) and temperature (400, 800 and 1200°C). The characterisations of the synthesised NHA powder were conducted using thermogravimetric analysis (TGA), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM), zeta-sizer and Fourier transform infrared spectroscopy (FTIR). It was found that nano-sized HA particles can be produced at optimum set of process parameters of t=25min, T=90°C, A=65%, and pH=8. Results revealed that the thermal stability, morphology and crystallinity of the NHA powder was further improved by calcinating the powder at optimum temperature and time of 800°C and 2 h, respectively.

NGHIÊN CỨU TỔNG HỢP VÀ ĐẶC TRƯNG HÓA LÍ CỦA BỘT NANO BARI HYDROXYAPATIT

NGHIÊN CỨU TỔNG HỢP VÀ ĐẶC TRƯNG HÓA LÍ CỦA BỘT NANO BARI HYDROXYAPATIT

Synthesis and thermal stability of selenium-doped hydroxyapatite with different substitutions

Selenium (Se) plays a specific role in human health, especially for its antitumor effect. Incorporation of selenium into biocompatible hydroxyapatite (HAP) may endow the materials with novel characteristics. In the current work, a series of seleniumdoped hydroxyapatite (Se-HAP) nanoparticles with different Se/P ratios were synthesized by a modified chemical precipitation. It was revealed that the powders with/without heattreatment were nano-sized needle-like HAP while the heat-treated samples have high crystallinity. The addition of selenium decreases the crystallinity of the synthesized apatite, and also takes a negative effect on the thermal stability of the as-prepared powders. The Se-HAP nanoparticles with Se/P molar ratio not more than 5% sintered at 900°C can achieve good crystallinity and thermal stability.

Laser Annealing for Gas-Dynamical Spraying of HA Coating upon a Titanium Surface

Laser post-heating computer controlled detonation spraying (CCDS) and cold spray (CS) hybrid processes were proposed for fabrication of near sub micron structure coatings of hydroxyapatite (HA) + Ti system. Optical and SEM with energy dispersive X-ray analysis and comparative XRD phase analysis were used to evaluate microstructure. After those hybrid processes, no substantial variation in HA composition was noted by structural and phase examination. Nano-sized HA powders can be recommended for laser annealing CS (LaCS) process. Regimes of laser treatment optimal for increasing the adhesion between the HA and titanium coatings, providing more strength, ductility and decreasing of HA destruction in the coatings were determined.

Surface Modification of Zirconia Substrate by Calcium Phosphate Particles Using Sol-Gel Method.

Surface modification with a biphasic composition of hydroxyapatite (HA) and tricalcium phosphate (TCP) was performed on a zirconia substrate using a sol-gel method. An initial calcium phosphate sol was prepared by mixing a solution of Ca(NO3)2 · 4H20 and (C2H5O)3P(O), while both porous and dense zirconia were used as substrates. The sol-gel coating was performed using a spin coater. The coated porous zirconia substrate was re-sintered at 1350 °C 2 h, while coated dense zirconia substrate was heat-treated at 750 °C 1 h. The microstructure of the resultant HA/TCP coatings was found to be dependent on the type of zirconia substrate used. With porous zirconia as a starting substrate, numerous isolated calcium phosphate particles (TCP and HA) were uniformly dispersed on the surface, and the particle size and covered area were dependent on the viscosity of the calcium phosphate sol. Conversely, when dense zirconia was used as a starting substrate, a thick film of nano-sized HA particles was obtained after heat treatment, however, substantial agglomeration and cracking was also observed.

Comparison of polyethylene glycol effect on hydroxyapatite morphology produced into different methods: sol–gel and precipitation

Hydroxyapatite (HA) can be used as a bioceramic due to its bioactivity and osteoconductive properties. It is clear that the morphology of HA crystal affects on its specifications such as surface and bioactivity. Because of importance of morphology, in the current research nano-sized HA particles were produced using sol–gel and precipitation methods, and to change the morphology, polyethylene glycol (PEG) was used as an organic modifier. The produced samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy and transmission electron microscopy. The results of XRD patterns show that the pure HA can be produced using two methods. Microscopic evaluations prove that the presence of PEG has a significant effect on HA morphology. Indeed, PEG changes the morphology of HA produced by precipitation method to irregular, whereas in sol–gel method its shape leads toward fibrous with high aspect ratio. The exact reason of this variation can be attributed to the difference in mechanism of HA growth in two methods.

Interfacial diffusion reaction and mechanical characterization of 316L stainless steel-hydroxyapatite functionally graded materials for joint prostheses

Functionally graded materials (FGMs) of 316L stainless steel (316L) matrix with the reinforcement of hydroxyapatite (HA) were fabricated successfully by a pressureless sintering technique for bioimplants. Hydroxyapatite content was varied among the layers of FGMs up to 20wt% with 5wt% gradient. Two types of FGMs were prepared with the same composition in the discrete layers. However, micro- and nano-sized hydroxyapatite was used to reinforce the 316L matrix in two different FGMs under similar conditions of compaction and sintering. FGMs with nano-sized HA (nHA) exhibited better densification than the FGMs prepared with micro-sized HA (mHA). The interdiffusion of chromium along the 316L and HA interface was observed, which improved the interfacial bonding and the FGMs properties. The hardness increased due to strong interfacial boundary for second layer, then due to dominant factor of porosity hardness decreased for succeeding layers of FGMs. Potentiodynamic polarization analysis of both FGMs are also presented and discussed in response to the particle size of HA and interfacial phase produced.

Tensile and biocompatibility properties of synthesized nano-hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposite

Ultrahigh molecular weight polyethylene–based nanocomposites reinforced with nano-sized hydroxyapatite particles were fabricated using internal mixer and compression molding with different weight percent of the nano-hydroxyapatite. In this study, first, hydroxyapatite nanoparticles were synthesized by sol–gel. Then, the mechanical and biological properties of nanocomposites were studied by tensile test and proliferation and cell adhesion assays using MG-63 osteoblast cells, respectively. Results of the tensile test showed that incorporation of 50 wt% nano-hydroxyapatite led to a 345.64% and 57.58% increase in Young's modulus and yield strength (compared to the pure ultrahigh molecular weight polyethylene), respectively. The effect of the nano-hydroxyapatite powders on the MG-63 osteoblast cells behavior was compared to those of a composite (positive control) and a negative control samples. Scanning electron microscopy micrographs revealed that cell–biomaterial interaction was carried out on the surface of the nanocomposites with normal phenotypic shape. Results of MTT assay exhibited that all samples are biocompatible.

Influence of Hydroxyapatite Nano-particles on the Mechanical and Tribological Properties of Orthopedic Cement-Based Nano-composites Measured by Nano-indentation and Nano-scratch Experiments

The aim of this study was to examine the mechanical and tribological properties of a commercially available bone cement by incorporating nano-sized hydroxyapatite using nano-indentation and nano-scratch experiments. In order to achieve this goal, the nano-composite cement samples with different amounts of commercial nano-hydroxyapatite (HAc), as a bone compatible nano-filler, were prepared via vacuum mixing method. The results indicated that nano-indentation and nano-scratch experiments are acceptable methods for measuring the mechanical and tribological properties of orthopedic cement-based nano-composites. Moreover, it was found that the nano-composite of 10 wt.% HAc exhibits the optimum performance compared to the other nano-composite samples in terms of mechanical and tribological properties. These findings can play an important role in achieving the goal of clinical and biomechanical function optimization of bone cement, especially in the field of orthopedic surgery.

Continuous microwave flow synthesis of mesoporous hydroxyapatite.

We have successfully used continuous microwave flow synthesis (CMFS) technique for the template free synthesis of mesoporous hydroxyapatite. The continuous microwave flow reactor consisted of a modified 2.45GHz household microwave, peristaltic pumps and a Teflon coil. This cost effective and efficient system was exploited to produce semi-crystalline phase pure nano-sized hydroxyapatite. Effect of microwave power, retention time and the concentration of reactants on the phase purity, degree of crystallinity and surface area of the final product was studied in detail. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to study the phase purity and composition of the product, while transmission electron microscopy (TEM) was used to study the effect of process parameters on the morphology of hydroxyapatite. The TEM analysis confirmed the formation of spherical particles at low microwave power; however the morphology of the particles changed to mesoporous needle and rod-like structure upon exposing the reaction mixture to higher microwave power and longer retention time inside the microwave. The in-vitro ion dissolution behavior of the as synthesized hydroxyapatite was studied by determining the amount of Ca(2+) ion released in SBF solution.

A Titanium Surface-Modified with Nano-Sized Hydroxyapatite and Simvastatin Enhances Bone Formation and Osseintegration.

The aim of the present study was to evaluate whether coating pristine titanium (Ti) with nano-sized hydroxyapatite (HAp) and simvastatin could enhance bone formation and osseointegration in vitro and in vivo because both HAp and simvastatin have the characteristic of osteogenetic induction. Pristine Ti was sequentially surface-treated with NaOH, 1,1-carbonyldiimidazole (CDI), beta-cyclodextrin-immobilized HAp powders (β-CD/HAp), and simvastatin before analysis using scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS), and static contact angle measurement. This revealed that simvastatin was released continually for up 28 days. Modification of the Ti surface with nano-sized HAp and simvastatin (Ti/β-CD/HAp/Sim) discs enhanced the osteogenic differentiation of MC3T3-E1 cells in vitro. Furthermore, Ti/β-CD/HAp/Sim of screw type enhanced bone formation between the screw and the host bone when the screw implanted to the proximal tibia and femoral head of rabbits. These results suggest that surface modification of nano-sized HAp and simvastatin are effective tools for developing attractive dental implants.

Mechanical and tribological properties of hydroxyapatite nanoparticles extracted from natural bovine bone and the bone cement developed by nano-sized bovine hydroxyapatite filler

The aim of this study is twofold. Firstly, it provides a nano-sized hydroxyapatite derived from bovine bone (BHA), as a raw material and natural source of HA, and to obtain the mechanical and tribological properties of sintered BHA ceramic. Secondly, it evaluates the mechanical and tribological properties of a commercially available bone cement by incorporating nano-sized BHA as a bone compatible nano-filler. In order to achieve these two goals, the mechanical and tribological properties of sintered BHA ceramic and nano-composite cements were measured using nano-indentation and nano-scratch experiments. The results indicated that the nano- hydroxyapatite of single phase with high crystallinity and appropriate mechanical and tribological properties could be produced from the natural bovine bone. Moreover, it was found that the nano-composite with 10wt% BHA exhibited a good improvement in mechanical and tribological properties in comparison with other examined PMMA/BHA nano-composites.

Effect of citric acid addition on disaggregation of crystalline hydroxyapatite nanoparticles under calcium-rich conditions

The effect of citric acid (CA) addition on the disaggregation of crystalline hydroxyapatite (HAp) nanoparticles under calcium-rich conditions was investigated in this study. HAp nanoparticles were prepared by a wet chemical precipitation process under calcium-rich conditions, which included an excess amount of calcium ions compared with the stoichiometric Ca/P molar ratio of HAp, with added CA. The formation of calcium citrate under calcium-rich conditions was highly effective for inhibiting the aggregation of nanosize HAp primary particles, and thus highly crystalline and disaggregated HAp nanoparticles were obtained.

Improved sinterability of hydroxyapatite functionally graded materials strengthened with SS316L and CNTs fabricated by pressureless sintering

Recently, functionally graded materials (FGMs) have attracted particular research attention for their potential use in biomedical implants and joint prosthesis. In the present investigation, carbon nanotubes (CNTs) and stainless steel 316L (SS316L) reinforced hydroxyapatite (HA) hybrid FGMs were fabricated by pressureless sintering. Three types of FGMs were successfully fabricated with varying amounts of SS316L (0–40wt%) in the discrete layers, in which SS316L was then combined with micro-sized HA, mixture of micro-sized HA with CNTs and a mixture of (1:1) mass ratio micro and nano-sized HA with CNTs. In the ceramic reinforced composites, it is difficult to surmount the thermal cracks generated during conventional pressureless sintering due to differences in thermal expansion coefficients of metal and ceramic. In this study, the emphasis was on elimination of the cracks generated in FGMs during the pressureless sintering by controlling process parameters such as temperature and time at different sintering stages and binder concentration. The microstructural analysis revealed uniform structure with optimized sintering cycle. No cracks were found around the inter-layer boundaries and within the composite layers. Moreover, improvement in the densification and sintering shrinkage was observed with the addition of CNTs and nano HA.

Preparation and characterization of nano-sized hydroxyapatite/alginate/chitosan composite scaffolds for bone tissue engineering.

The aim of this study was to develop chitosan composite scaffolds with high strength and controlled pore structures by homogenously dispersed nano-sized hydroxyapatite (nano-HAp) powders. In the fabrication of composite scaffolds, nano-HAp powders distributed in an alginate (AG) solution with a pH higher than 10 were mixed with a chitosan (CS) solution and then freeze dried. While the HAp content increased up to 70 wt.%, the compressive strength and the elastic modulus of the composite scaffolds significantly increased from 0.27 MPa and 4.42 MPa to 0.68 MPa and 13.35 MPa, respectively. Higher content of the HAp also helped develop more differentiation and mineralization of the MC3T3-E1 cells on the composite scaffolds. The uniform pore structure and the excellent mechanical properties of the HAp/CS composite scaffolds likely resulted from the use of the AG solution at pH 10 as a dispersant for the nano-HAp powders.

Bioactivity of wound healing using nano bioceramic

A nano-sized hydroxyapatite/zirconia (3 mol-% yttria-stabilised cubic zirconia) bioceramic was fabricated by a hot pressure sintering process in this study. The in vitro biocompatibility of bioceramic was researched, with the aim of validating the effects of incisions in the bodies of 4-month-old rats made with a nano-sized hydroxyapatite–yttria-stabilised cubic zirconia bioceramic scalpel, and to illustrate the incision properties of the tissues. The wound-healing experiment of a nano bioceramic knife was studied, and subcutaneous tissues and musculature samples were obtained and analysed by optical microscopy at 3, 7 and 14 days post-surgery. The effects of the bioceramic on biocompatibility were studied, and the results showed that no wound dehiscence was observed after stitch removal at 14 days after the procedures. The experiments demonstrated that the hydroxyapatite–yttria-stabilised cubic zirconia bioceramic was non-toxic, non-allergenic and possessed bioactive properties.

Blind micro-hole array Ti6Al4V templates for carrying biomaterials fabricated by fiber laser drilling

Blind micro-hole array templates were constructed by laser drilling using a 20W fiber laser on a Ti6Al4V substrate to improve carrying capacity of Ti6Al4V substrate to biomaterials in this study. The influence of laser parameters on the morphology of the blind holes was investigated and the blind micro-hole array templates were fabricated by the optimized laser parameters. Three typical morphologies were generated through adjusting laser parameters. The type II micro-hole characterized by column-shaped entrance and a hemispherical dome bottom is believed to have a suitable morphology, which was produced by the optimized laser parameters, i.e., defocusing distance 0mm, laser average power 16W, laser irradiation time 1ms and repetition rate 25kHz. The blind micro-hole templates with different micro-hole density were constructed by the mentioned-above optimized parameters and then the nano-sized hydroxyapatite (HA) powders were uniformly deposited into the blind micro-hole templates by electrophoretic deposition. Finally, the dynamic behavior of laser-drilling process was analyzed.

Pre-cultivation of adipose tissue-derived microvascular fragments in porous scaffolds does not improve their in vivo vascularisation potential.

Adipose tissue-derived microvascular fragments represent promising vascularisation units for implanted tissue constructs. However, their reassembly into functional microvascular networks takes several days, during which the cells inside the implants are exposed to hypoxia. In the present study, we analysed whether this critical phase may be overcome by pre-cultivation of fragment-seeded scaffolds prior to their implantation. Green fluorescent protein (GFP)-positive microvascular fragments were isolated from epididymal fat pads of male C57BL/6-TgN (ACTB-EGFP) 1Osb/J mice. Nano-size hydroxyapatite particles/poly (ester-urethane) scaffolds were seeded with these fragments and cultivated for 28 days. Subsequently, these scaffolds or control scaffolds, which were freshly seeded with GFP-positive microvascular fragments, were implanted into the dorsal skinfold chamber of C57BL/6 wild-type mice to study their vascularisation and incorporation by means of intravital fluorescence microscopy, histology and immunohistochemistry over 2 weeks. Pre-cultivation of microvascular fragments resulted in the loss of their native vessel morphology. Accordingly, pre-cultivated scaffolds contained a network of individual CD31/GFP-positive endothelial cells with filigrane cell protuberances. After implantation into the dorsal skinfold chamber, these scaffolds exhibited an impaired vascularisation, as indicated by a significantly reduced functional microvessel density and lower fraction of GFP-positive microvessels in their centre when compared to freshly seeded control implants. This was associated with a deteriorated incorporation into the surrounding host tissue. These findings indicate that freshly isolated, non-cultivated microvascular fragments should be preferred as vascularisation units. This would also facilitate their use in clinical practice during intra-operative one-step procedures.

PEGylation of novel hydroxyapatite/PEG/Ag nanocomposite particles to improve its antibacterial efficacy.

Hydroxyapatite (HAp) nanocomposite particles were prepared simply in the presence of polyethylene glycol (PEG) and fabricated with silver via a sol-gel route and the physico-chemical and biological properties of these materials were investigated. The objective of this study is to inspect the crystallinity and antibacterial activity of these composite materials. PEG has been used to greatly promote biocompatibility and biodegradability of HAp. Silver nanoparticles were used for improving its bactericidal efficacy while applying composites. Nano-sized HAp composite particles with PEG and nano-silver was incorporated to increase the crystalline nature of the nanocomposite. The structure of nanocomposite particles was studied by XRD, FTIR, HR-SEM, EDS and TEM analyses. Silver nanoparticles loaded on the synthesized HAp-PEG showed a synergistic antibacterial effect against Gram-negative bacterium Escherichia coli (E. coli). The controlled release of Ag(+) ion from HAp-PEG-Ag nanocomposite has given good antibacterial efficacy evidenced by epi-fluorescence microscopy images during different hours.

Nanocomposite bone scaffolds based on biodegradable polymers and hydroxyapatite.

In tissue engineering, development of an osteoconductive construct that integrates with host tissue remains a challenge. In this work, the effect of bone-like minerals on maturation of pre-osteoblast cells was investigated using polymer-mineral scaffolds composed of poly(propylene fumarate)-co-poly(caprolactone) (PPF-co-PCL) and nano-sized hydroxyapatite (HA). The HA of varying concentrations was added to an injectable formulation of PPF-co-PCL and the change in thermal and mechanical properties of the scaffolds was evaluated. No change in onset of degradation temperature was observed due to the addition of HA, however compressive and tensile moduli of copolymer changed significantly when HA amounts were increased in composite formulation. The change in mechanical properties of copolymer was found to correlate well to HA concentration in the constructs. Electron microscopy revealed mineral nucleation and a change in surface morphology and the presence of calcium and phosphate on surfaces was confirmed using energy dispersive X-ray analysis. To characterize the effect of mineral on attachment and maturation of pre-osteoblasts, W20-17 cells were seeded on HA/copolymer composites. We demonstrated that cells attached more to the surface of HA containing copolymers and their proliferation rate was significantly increased. Thus, these findings suggest that HA/PPF-co-PCL composite scaffolds are capable of inducing maturation of pre-osteoblasts and have the potential for use as scaffold in bone tissue engineering.