Hydroxyapatite gels and nanocrystals prepared through a sol–gel process

Mechanical and Biocompatibility Properties of Sintered Titanium Powder for Mimetic 3D-Printed Bone Scaffolds

A composite comprising Ti and NaCl powders was sintered similar to a three-dimensional (3D)-printed patient-customized artificial bone scaffold. Additionally, a proper microstructure of the mimetic scaffold and the optimum processing parameters for its development were analyzed. The mechanical properties of the metal-based porous-structured framework used as an artificial bone scaffold were an optimum replacement for the human bone. Thus, it was confirmed that patient-customized scaffolds could be manufactured via 3D printing. The 3D-printed mimetic specimens were fabricated by a powder-sintering method using Ti for the metal parts, NaCl as the pore former, and polylactic acid as the biodegradable binder. Scanning electron microscopy (SEM) images showed that pores were formed homogeneously, while X-ray computed tomography confirmed that open pores were generated. The porosity and pore size distribution were measured using a mercury porosimeter, while the flexural strength and flexural elastic modulus were calculated using the three-point bending test. Based on these measurements, a pore-former content of 15 vol % optimized the density and flexural strength to 2.52 g cm^-2 and 283 MPa, respectively, similar to those of the actual iliac bone. According to the 3D-printing production method, a selective laser-sintering process was applied for the fabrication of the mimetic specimen, and it was determined that the microstructure and properties similar to those of previous metal specimens could be achieved in the as-prepared specimen. Additionally, a decellularized extracellular matrix (dECM) was used to coat the surfaces and interiors of the specimens for evaluating their biocompatibilities. SEM image analysis indicated that the adipose-derived stem cells grew evenly inside the pores of the coated specimens, as compared with the bulky Ti specimens without the dECM coating. The doubling time at 65% was measured at 72, 75, and 83 h for specimens with pore-former contents of 5, 10, and 15 vol %, respectively. The doubling time without the pore former was 116 h. As compared with the specimens without the pore former (73 h), 15% of the dECM-coated specimens showed a doubling time of 64%, measured at 47 h.

A review on bovine hydroxyapatite; extraction and characterization

High rate of bone grafting surgeries emphasizes the need for optimal bone substitutes. Biomaterials mimicking the interconnected porous structure of the original bone with osteoconductive and osteoinductive capabilities have long been considered. Hydroxyapatite (HA), as the main inorganic part of natural bone, has exhibited excellent regenerative properties in bone tissue engineering. This manuscript reviews the HA extraction methods from bovine bone, as one of the principal biosources. Essential points in the extraction process have also been highlighted. Characterization of the produced HA through gold standard methods such as XRD, FTIR, electron microscopies (SEM and TEM), mechanical/thermodynamic tests, and bioactivity analysis has been explained in detail. Finally, future perspectives for development of HA constructs are mentioned.

Synthesis and Characterization of Photoluminescent Ce(III) and Ce(IV) Substituted Hydroxyapatite Nanomaterials by Co-Precipitation Method: Cytotoxicity and Biocompatibility Evaluation

Improved compounds of Ce(III) and Ce(IV)-doped hydroxyapatite (Ca_10-xCe_x(PO₄)₆(OH)₂) with different concentrations such as x = 0.5, 1, 2.5, 5, and 10%, obtained by the simple co-precipitation method were synthesized. The cerium (3⁺) and cerium (4⁺)-doped hydroxyapatite were evaluated for biocompatibility and fluorescence properties. It was found that the cerium-HAp powders were non-toxic, even at higher level of concentration. The synthesized powders were further characterized by FTIR spectrometry, UV-Vis spectroscopy, XRD diffraction, SEM and TEM analysis. Therefore, the present study proves that the developed cerium (3⁺) and cerium (4⁺)-doped hydroxyapatite, respectively can be widely used as luminescent labeling materials, with improved biological properties.

Peptide Self-Assembly into Hydrogels for Biomedical Applications Related to Hydroxyapatite

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the growth of hydroxyapatite (HAp) as well as its encapsulation. Newly designed materials offer great perspectives for applications in the regeneration of hard tissues such as bones, teeth, and cartilage. Furthermore, development of drug delivery systems based on HAp and peptide self-assembly is attracting attention.

Recent progress on fabrication and drug delivery applications of nanostructured hydroxyapatite

Through this brief review, we provide a comprehensive historical background of the development of nanostructured hydroxyapatite (nHAp), and its application potentials for controlled drug delivery, drug conjugation, and other biomedical treatments. Aspects associated with efficient utilization of hydroxyapatite (HAp) nanostructures such as their synthesis, interaction with drug molecules, and other concerns, which need to be resolved before they could be used as a potential drug carrier in body system, are discussed. This review focuses on the evolution of perceptions, practices, and accomplishments in providing improved delivery systems for drugs until date. The pioneering developments that have presaged today's fascinating state of the art drug delivery systems based on HAp and HAp-based composite nanostructures are also discussed. Special emphasis has been given to describe the application and effectiveness of modified HAp as drug carrier agent for different diseases such as bone-related disorders, carriers for antibiotics, anti-inflammatory, carcinogenic drugs, medical imaging, and protein delivery agents. As only a very few published works made comprehensive evaluation of HAp nanostructures for drug delivery applications, we try to cover the three major areas: concepts, practices and achievements, and applications, which have been consolidated and patented for their practical usage. The review covers a broad spectrum of nHAp and HAp modified inorganic drug carriers, emphasizing some of their specific aspects those needed to be considered for future drug delivery applications. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease Nanotechnology Approaches to Biology > Cells at the Nanoscale.

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.

Synthesis, characterization and the formation mechanism of magnesium- and strontium-substituted hydroxyapatite

The hydroxyapatite crystals grow in different ways when the calcium is substituted by strontium or magnesium.

Bioactivation of calcium deficient hydroxyapatite with foamed gelatin gel. A new injectable self-setting bone analogue

An alternative approach to bone repair for less invasive surgical techniques, involves the development of biomaterials directly injectable into the injury sites and able to replicate a spatially organized platform with features of bone tissue. Here, the preparation and characterization of an innovative injectable bone analogue made of calcium deficient hydroxyapatite and foamed gelatin is presented. The biopolymer features and the cement self-setting reaction were investigated by rheological analysis. The porous architecture, the evolution of surface morphology and the grains dimension were analyzed with electron microscopy (SEM/ESEM/TEM). The physico-chemical properties were characterized by X-ray diffraction and FTIR analysis. Moreover, an injection test was carried out to prove the positive effect of gelatin on the flow ensuing that cement is fully injectable. The cement mechanical properties are adequate to function as temporary substrate for bone tissue regeneration. Furthermore, MG63 cells and bone marrow-derived human mesenchymal stem cells (hMSCs) were able to migrate and proliferate inside the pores, and hMSCs differentiated to the osteoblastic phenotype. The results are paving the way for an injectable bone substitute with properties that mimic natural bone tissue allowing the successful use as bone filler for craniofacial and orthopedic reconstructions in regenerative medicine.

Hollow hydroxyapatite spheres fabrication with three-dimensional hydrogel template

Flower-like porous hollow HAp spheres were obtained by diffusion of phosphate ions into PAAm hydrogels containing calcium ions by both an electrophoresis approach and an ion diffusion method.

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.

Microwave-assisted synthesis of biocompatible europium-doped calcium hydroxyapatite and fluoroapatite luminescent nanospindles functionalized with poly(acrylic acid)

Europium-doped calcium hydroxyapatite and fluoroapatite nanophosphors functionalized with poly(acrylic acid) (PAA) have been synthesized through a one-pot microwave-assisted hydrothermal method from aqueous basic solutions containing calcium nitrate, sodium phosphate monobasic, and PAA, as well as sodium fluoride in the case of the fluoroapatite particles. In both cases a spindlelike morphology was obtained, resulting from an aggregation process of smaller subunits which also gave rise to high specific surface area. The size of the nanospindles was 191 (32) × 40 (5) nm for calcium hydroxyapatite and 152 (24) × 38 (6) nm for calcium fluoroapatite. The luminescent nanoparticles showed the typical red luminescence of Eu(3+), which was more efficient for the fluoroapatite particles than for the hydroxyapatite. This is attributed to the presence of OH(-) quenchers in the latter. The nanophosphors showed negligible toxicity for Vero cells. Both PAA-functionalized nanophosphors showed a very high (up to at least 1 week) colloidal stability in 2-(N-morpholino)ethanesulfonic acid (MES) at pH 6.5, which is a commonly used buffer for physiological pH. All these features make both kinds of apatite-based nanoparticles promising tools for biomedical applications, such as luminescent biolabels and tracking devices in drug delivery systems.

Design of injectable organic-inorganic hybrid for bone tissue repair

Injectable bone substitutes are rapidly gained success in tissue engineering applications for their less invasive surgical aspect. Here, the design and the characterization of a novel degradable paste of PCL reinforced with nanocrystals of hydroxyapatite have been presented aiming to mimic natural tissue. Nanohydroxyapatite has been successfully synthesized via sol-gel technique. Dynamic and steady state viscoelastic properties of the solutions and paste were investigated to control the kinetic of phase transition. Correspondingly, the morphology and composition were characterized via TEM, EDAX, and thermal analysis. Injection test underlines the completely ability of the paste of being injected without altering its features. Preliminary biological study showed that the composite paste is not cytotoxic. The synergistic rheological and biological properties, combined with the positive effect of chemical synthesis method indicate that the composite paste is very suitable as local bone substitute in low-load areas.

INCORPORATION OF IRON INTO NANO HYDROXYAPATITE PARTICLES SYNTHESIZED BY THE MICROWAVE PROCESS

This research focuses on understanding the nature of the Fe ions substituted in hydroxyapatite ((HAP) Ca 10-x Fe x( PO 4)6( OH )2-xÿx: x = 0, 0.2 and 0.4) powder synthesized at temperatures between 500°C and 1000°C and their crystallization. The DSC scan indicates a solid state phase transition at about 757°C for the as-prepared powder HAP. The transformation of HAP to β-tricalcium phosphate (β- TCP , β- Ca 3( PO 4)2) is seen when the powder were heated to 750°C. The sizes of the crystallites were determined to be about 46–51 nm, 33–40 nm and 33–59 nm for Fe content of 0, 0.2 and 0.4 mol%, respectively. The ESR parameters for the Fe 3+ ions, g = 4.23 and 8.93 indicated that the ions were subjected to a rhombic ion crystal field within the HAP structures. The g values of ~2.01 indicated that the particles were super-paramagnetic and ferromagnetic iron nanoparticles, having an average size about 0.2–0.5 μm in length.

Direct cytotoxicity evaluation of 63S bioactive glass and bone-derived hydroxyapatite particles using yeast model and human chondrocyte cells by microcalorimetry

In this study, the cytotoxicity evaluation of prepared 63S bioactive glass and bone-derived hydroxyapatite particles with yeast and human chondrocyte cells was carried out using isothermal micro-nano calorimetry (IMNC), which is a new method for studying cell/biomaterial interactions. Bioactive glass particles were made via sol-gel method and hydroxyapatite was obtained from bovine bone. Elemental analysis was carried out by XRF and EDXRF. Amorphous structure of the glass and completely crystalline structure of HA were detected by XRD analysis. Finally, the cytotoxicity of bioactive glass and bone-derived HA particles with yeast and cultured human chondrocyte cells was evaluated using IMNC. The results confirmed the viability, growth and proliferation of human chondrocyte cells in contact with 63S bioactive glass, and bone-derived HA particles. Also the results indicated that yeast model which is much easier to handle, can be considered as a good proxy and can provide a rapid primary estimate of the ranges to be used in assays involving human cells. All of these results confirmed that IMNC is a convenient method which caters to measuring the cell-biomaterial interactions alongside the current methods.

High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering

The synthesis of high-strength, completely dense nanograined hydroxyapatite (bioceramic) monoliths is a challenge as high temperatures or long sintering times are often required. In this study, nanorods of hydroxyapatite (HA) and calcium-deficient HA (made using a novel continuous hydrothermal flow synthesis method) were consolidated using spark plasma sintering (SPS) up to full theoretical density in ∼5 min at temperatures up to 1000°C. After significant optimization of the SPS heating and loading cycles, fully dense HA discs were obtained which were translucent, suggesting very high densities. Significantly high three-point flexural strength values for such materials (up to 158 MPa) were measured. Freeze-fracturing of disks followed by scanning electron microscopy investigation revealed selected samples possessed sub-200 nm sized grains and no visible pores, suggesting they were fully dense.

pH impact on the sol-gel preparation of calcium hydroxyapatite, Ca10(PO4)6(OH)2, using a novel complexing agent, DCTA

Aqueous sol-gel chemistry routes — based on ammonium hydrogen phosphate as the phosphorus precursor, calcium acetate monohydrate as the source of calcium ions, and 1,2-diaminocyclohexanetetraacetic acid monohydrate (DCTA) as the complexing agent — have been used to prepare calcium hydroxyapatite (HA). The sol-gel process was performed in aqueous solution at different pH values followed by calcination of the dry precursor gels for 5 h at 1000°C. Phase transformations, composition, and structural changes in the polycrystalline samples were studied by thermoanalytical methods (TG/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD), and scanning electron microscopy (SEM). It was shown that pH adjustment has significant impact on the apatite formation process and on the morphology and phase purity of the ceramic samples.

Tailoring the microstructure of sol-gel derived hydroxyapatite/zirconia nanocrystalline composites

In this study, we tailor the microstructure of hydroxyapatite/zirconia nanocrystalline composites by optimizing processing parameters, namely, introducing an atmosphere of water vapor during sintering in order to control the thermal stability of hydroxyapatite, and a modified sol-gel process that yields to an excellent intergranular distribution of zirconia phase dispersed intergranularly within the hydroxyapatite matrix. In terms of mechanical behavior, SEM images of fissure deflection and the presence of monoclinic ZrO2 content on cracked surface indicate that both toughening mechanisms, stress-induced tetragonal to monoclinic phase transformation and deflection, are active for toughness enhancement.

Fabrication, chemical composition change and phase evolution of biomorphic hydroxyapatite

Biomorphous, highly porous hydroxyapatite (HA) ceramics have been prepared by a combination of a novel biotemplating process and a sol-gel method, using natural plants like cane and pine as biotemplates. A HA sol was first synthesized from triethylphosphate and calcium nitrate used as the phosphorus and calcium precursors, respectively, and infiltrated into the biotemplates, and subsequently they were sintered at elevated temperatures to obtain porous HA ceramics. The microstructural changes, phase and chemical composition evolutions during the biotemplate-to-HA conversion were investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy. The XRD and FT-IR analysis revealed that the dominant phase of the product was HA, which contained a small amount of mixed A/B-type carbonated HA, closely resembling that of human bone apatite. Moreover, the appearance of a small amount of secondary phase CaCO(3) seemed unavoidable. The HA was not transformed to the other calcium phosphate phases up to 1400 degrees C, but it contained a trace amount of CaO when sintered at above 1100 degrees C. The possible transformation mechanism was proposed. The SEM observation and mechanical property test showed that as-produced HA ceramics retained the macro-/micro-porous structures of the biotemplates with high precision, and possessed acceptable mechanical strength, which is suggested to be potential scaffolds for bone tissue engineering.

Formation of hydroxyapatite-layer on glass plate and its removal–regeneration properties for aqueous cadmium

A glass plate was coated with calcium hydroxyapatite (CaHAp) by a dip-coating method and employed for the removal of aqueous cadmium. Sol obtained from alcoholic solution of (NH(4))(2)HPO(4) and Ca(NO(3))(2) x 4H(2)O was employed for the precursor of the CaHAp layer. The preparation of CaHAp from the sol needed a rather low calcination temperature of 573 K and the resulting solid mainly contained CaHAp. It was shown that the glass plate coated with CaHAp with the sol could be employed for the removal of aqueous cadmium. Furthermore, it was found that cadmium immobilized on the coated plate could be regenerated into weak acidic solution. A dissolution-precipitation mechanism was suggested for the removal-regeneration of aqueous cadmium.

Preparation of alkaline earth phosphates with sol containing sodium alginate and sodium diphosphate

Magnesium hydrogen phosphate, calcium hydroxyapatite, and strontium hydroxyapatite were successfully prepared from sol consisting of sodium alginate and Na4P2O7 with Mg2+, Ca2+, and Sr2+ in the corresponding nitrates, respectively. It is revealed that the order of the addition of those substrates and the role of sodium alginate are important factors for the preparation of desired phosphate compounds. According to the previous paper on the preparation of calcium hydroxyapatite, sodium alginate was mixed with aqueous Na4P2O7, followed by the addition of the aqueous divalent cations, resulting in the poor formation of the target phosphates. However, as a revised sol-gel technique, sodium alginate was added to the mixture of Na4P2O7 and aqueous Mg2+ and Sr2+, resulting in a rather favorable formation of MgHPO4 and strontium hydroxyapatite, respectively, while the sol thus obtained was stable within a few days. However for aqueous Ca2+, calcium hydroxyapatite could not be obtained through the revised sol-gel technique. In the preparation of magnesium hydrogen phosphate, sodium alginate contributes mainly to the sol formation of the precursor. The ion exchange between Na+ in sodium alginate and aqueous Ca2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na4P2O7 and aqueous Sr2+ afforded strontium hydroxyapatite at the specific ratio of those three substrates. The structure of calcium and strontium phosphates prepared from the revised sol-gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na4P2O7 and the corresponding divalent cations.

Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis

Nano-particle hydroxyapatite (HA) rods, were rapidly synthesised using a three pump continuous hydrothermal process (using a water feed at up to 400 degrees C and at 24 MPa): the product was obtained as a highly crystalline and phase pure material, without the need for an ageing step or subsequent heat treatment.