Porous Hydroxyapatite Ceramics Research Articles

Self-sacrificing template synthesis of ultralight porous hydroxyapatite microtube-based ceramics for hemoglobin adsorption

Strong and porous hydroxyapatite ceramics are highly desired for biomedical materials. However, 1D hydroxyapatite crystals with enhanced bioactivity, densification, and sinterability are limited in practical application for self-agglomeration and unfavorable 3D morphology. Herein, a sacrificed template approach is developed to prepare ultralight porous hydroxyapatite microtube-based ceramics (HMTC). First, hydroxyapatite microtubes (HMTs) are self-assembled proceeding from nanowires to microtubes through a solvothermal reaction. Then, HMTs are shaped into 3D columns by using chitosan aerogel as a template and sintered at 1300 °C to obtain ultralight porous ceramics. The chitosan template considerably contributes to constructing the macro-meso-microporous architecture of HMTC, thereby benefiting the loading capacity, biomolecule migration, cell proliferation, and other biomedical applications. HMTC exhibits ultralight weight but excellent compressive resistance to bear objects weighing hundreds of times more. HMTC exhibits a high adsorption capacity (311 mg g−1) towards bovine hemoglobin (BHb) at the pH near pI by the driving force of ionic interaction and hydrophobic interaction. The adsorption kinetics and fixed-bed adsorption confirm that the physisorption process is controlled by the intraparticle diffusion of BHb. The excellent protein adsorption performance and good recyclability demonstrate the biological availability of HMTC.

Induced porous structure with a slight change in mechanical properties of hydroxyapatite-based nanocomposites synthesized from waste bovine bone and their bioactivity

Porous hydroxyapatite (HAp) ceramics have been widely used in several biomedical applications. However, efforts to enhance the porous structure in HAp ceramics often lead to a decline in their mechanical properties. In the present study, by adding a small amount of aluminum nitride (AlN) nanoparticles to HAp ceramics, we achieved the formation of porous HAp with a slight change in grain size and mechanical properties. The starting powder of the HAp was obtained from a natural source of bovine bone. The HAp/xAlN nanocomposites were fabricated by a simple conventional technique. The 0.06 mol% AlN-added sample (HAp/0.06AlN) presented the maximum mechanical properties (Vickers hardness = 3.68 GPa, elastic modulus = 94.04 GPa, and fracture toughness = 0.97 MPa∙m1/2) with favorable porosity. Simulated body fluid and cell viability assays showed that all the studied nanocomposites possessed desirable bioactivity with high cell viability. The HAp/0.06AlN samples were coated with antimicrobial agents. The samples coated with silver nitrate (AgNO3) had high antibacterial efficiency against S. aureus (66.2%) and P.aeruginosa (67.3%). Based on the obtained results, the nanocomposites exhibited promising potential for development and utilization in biomedical applications.

Material Design of Porous Hydroxyapatite Ceramics via Inverse Analysis of an Estimation Model for Bone-Forming Ability Based on Machine Learning and Experimental Validation of Biological Hard Tissue Responses.

Hydroxyapatite and β-tricalcium phosphate have been clinically applied as artificial bone materials due to their high biocompatibility. The development of artificial bones requires the verification of safety and efficacy through animal experiments; however, from the viewpoint of animal welfare, it is necessary to reduce the number of animal experiments. In this study, we utilized machine learning to construct a model that estimates the bone-forming ability of bioceramics from material fabrication conditions, material properties, and in vivo experimental conditions. We succeeded in constructing two models: 'Model 1', which predicts material properties from their fabrication conditions, and 'Model 2', which predicts the bone-formation rate from material properties and in vivo experimental conditions. The inclusion of full width at half maximum (FWHM) in the feature of Model 2 showed an improvement in accuracy. Furthermore, the results of the feature importance showed that the FWHMs were the most important. By an inverse analysis of the two models, we proposed candidates for material fabrication conditions to achieve target values of the bone-formation rate. Under the proposed conditions, the material properties of the fabricated material were consistent with the estimated material properties. Furthermore, a comparison between bone-formation rates after 12 weeks of implantation in the porcine tibia and the estimated bone-formation rate. This result showed that the actual bone-formation rates existed within the error range of the estimated bone-formation rates, indicating that machine learning consistently predicts the results of animal experiments using material fabrication conditions. We believe that these findings will lead to the establishment of alternative animal experiments to replace animal experiments in the development of artificial bones.

Magnesium-enhanced porous hydroxyapatite ceramics: Morphometric parameters, physical properties and bioactivity

The application of porous bioactive ceramics as bone substitutes requires their effective osseointegration, which relies on specific physical and biological properties. In this study, we developed porous magnesium-doped hydroxyapatite (MgHA) ceramics with four different magnesium concentrations (0.25, 2, 5 and 10 mol%). The ceramics were prepared through the polymeric replication sponge method and subjected to physical and biological characterizations. Upon sintering, the porous 10 mol% MgHA ceramics exhibited increased densification, which resulted in the highest compressive strength of 2.17 MPa at the lowest porosity of 31 %.The porous samples were analysed via microcomputed tomography. The scaffolds with 0.25 and 10 mol% Mg doping concentrations were selected to elucidate the influence of Mg on morphometric parameters and biological properties at two distinct levels. The high level of Mg doping led to considerable improvements in relative bone volume, connectivity density, trabecular number and trabecular thickness. Cell attachment and proliferation tests using Vero cell lines were conducted on both samples to investigate the correlations between their morphometric parameters and bioactivities. Substantially more cells attached to and proliferated on the surface of the 10 mol% MgHA ceramics compared with those on the ceramics containing 0.25 mol% MgHA. In summary, our study underscores the effectiveness of Mg incorporation in improving the physical and biological properties of porous HA ceramics, which makes them promising candidates for bone substitute applications.

Physicochemical characterization and cell behavior of porous hydroxyapatite ceramics doped with Ag ions: Fluorescence quenching in fluorescence-labeled cells

Mouse preosteoblast cells were found to adhere well to and spread on the surface of porous Ag-doped hydroxyapatite (HAp) ceramics fabricated using a small amount of Ag. Ag particles were deposited on the surfaces of the HAp ceramics fabricated by doping Ag in large amounts. These Ag-doped samples were more hydrophobic owing to the loss of OH ions from HAp lattices with increasing the amount of added Ag. The cells adhered to the hydrophobic surface even in the presence of cytotoxic Ag particles. Consequently, the equilibrium between the hydrophobicity of the surface and cytotoxicity of Ag particles determines cell adhesion. Additionally, fluorescence quenching did not occur in cells stained for nuclei (blue) and fibronectin (red), but in cells stained for actin (red and green), in the presence of Ag particles. Charge transfer from actin protein molecules to Ag particles enabled quenching because the Ag particles exerted the heavy-atom effect.

Study of neck formation and densification in porous hydroxyapatite ceramics using thermal conductivity measurements

Neck formation and densification during sintering have strong effects on the thermal conductivity of a porous ceramic body. This has been described by an analytical model using grain conductivity, grain size, pore fraction and particle – particle contact area as input parameters. It has been tested on hydroxyapatite ceramics sintered with conventional, microwave and spark plasma techniques. The green bodies containing at least 40% porosity yield conductivity values in the range 0.24–0.29 Wm−1K−1. Neck formation in the initial stage of sintering increases the values to above 0.5 Wm−1K−1. Further increase is achieved by densification, well described by Landauer's relation as part of the model with close agreement to experiment for hydroxyapatite ceramics containing 40 to 5% porosity. An evaluation of thermal conductivity for 100% dense hydroxyapatite gives a value of 1.5 Wm−1K−1 which is almost constant between room temperature and 900 °C.

<i>In Vivo</i> Evaluation of Calcium-Phosphate Ceramics with Highly-Interconnected Pores Using Porcine Tibia Defect Model

The aim of this study was to compare the difference in bone formation between hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) ceramics with similar porous structure. Porous HAp and β-TCP ceramics (total porosity: ~70%) with highly-interconnected structure were fabricated by firing calcium-phosphate fiber mixed with carbon beads (~150 μm). The size of highly-interconnected pores was measured by mercury intrusion technique. Each sample (ϕ4 mm × 8 mm) was implanted into the tibial bone defect (ϕ4.2 mm × 8 mm) of a pig (2 years old, male). After 6 weeks of implantation, undecalcified section was prepared and stained with hematoxylin and eosin (HE) stain. New bone area and remaining material area were evaluated.Interconnection sizes of HAp and β-TCP ceramics were 23.0 µm and 15.6 µm, respectively. New bone area of β-TCP ceramics was significantly higher compared to HAp ceramics. Remaining material ratio was 77.1 ± 3.3% for β-TCP ceramics whereas HAp ceramics remained stable. Bone formation in HAp ceramics was inhomogeneous compared to β-TCP ceramics in HE stained section. Although the β-TCP ceramics interconnection size was smaller, higher resorption may have played a positive role in homogeneous bone formation. According to the result of the study, it is suggested that highly-interconnected porous ceramics made by β-TCP could be a suitable material for bone regeneration.

Fabrication of hydroxyapatite porous body with connective pores using the self-networking property of rice starch powder by heat treatment

• Porous hydroxyapatite ceramics was fabricated. • Gelatinization-retrogradation phenomena of starch was used as pore-networking agent. • Randomly-developed open pores were introduced into the hydroxyapatite matrix. • Pore structure was characterized by confocal scanning laser fluorescence microscopy. Hydroxyapatite porous ceramics were fabricated utilizing the property called gelatinization-retrogradation in which starch particles used as a pore-forming agent form a self-network structure by heat treatment. The pore structures in the hydroxyapatite samples were observed by combining the immersion transmission method and a confocal scanning laser fluorescence microscope. The three-dimensional image created by stacking the cross-sectional observation images showed that randomly-developed open pores were introduced into the matrix.

Physicochemical and microstructural properties of porous Zn-doped hydroxyapatite ceramics: cell behavior on their surfaces

Physicochemical and microstructural properties of porous Zn-doped hydroxyapatite ceramics: cell behavior on their surfaces

Trace addition of cellulose nanofiber in gel-casting system for structurally controlled porous ceramics towards superior thermal-insulating property

In present work, structurally controlled porous hydroxyapatite ceramics are fabricated via a novel and facile gel-casting process with trace addition of cellulose nanofiber (CNF). The pore structure with respects to pore size, shape and open/close porosity is selectively controlled by altering the addition amount of CNF and surfactant, as well as forming time. The origin of pore structure controlling is systemically investigated in the point view of chemical/physical interaction between ceramic powder, CNF as well as dispersant, assisted by detailed characterizations as X-ray computer tomography observation, viscosity analysis, and z-potential analysis. Fabricated porous ceramic bodies exhibit superior low thermal conductivity which opens a new avenue for the wide applications of hydroxyapatite ceramics.

Reinforcement of hydroxyapatite ceramics by soaking green samples of tetracalcium phosphate / monetite mixture in aqueous solutions

Porous hydroxyapatite ceramics with enhanced mechanical strength were prepared by sintering a compressed tetracalcium phosphate/monetite (TTCPM) powder precursor at 1150 °C after soaking in water, NaHCO3 solution and simulated body fluid (SBF). The microstructure and compressive strength of the ceramic were compared with the ceramic obtained by sintering an unsoaked green sample of TTCPM (Cpres) and a sample of cement (C) after hardening the TTCPM mixture in SBF. The results showed a strong influence of porosity, chemical and phase purity, as well as the arrangement of the HAP lattice in ceramics on the compressive strength. Similar densification was observed in all soaked green samples (∼77% relative density), in contrast to the unchanged relative densities in the C and Cpres ceramics, which were the same as in the original green samples. More compact, well-sintered grains were found in CpresSBF ceramics (soaked in SBF) with the highest compressive strength (∼165 MPa), which was 2–4 times more than in other samples. The reason for improving the microstructural characteristics and mechanical strength of the ceramic was probably in the suitable morphology of HAP nanoparticles in the green CpresSBF sample, as well as in the composition without secondary phases with higher Mg and Na content.

Gypsum-related compensation of ions uptake by highly porous hydroxyapatite ceramics – Consequences for osteoblasts growth and proliferation

Hydroxyapatites of high calcium and phosphate ions adsorption capacity are highly bioactive. However, they cause the removal of these ions from tissue liquids and cell culture media, thus reducing viability and proliferation potential of osteoblasts. Addition of small amount of gypsum (calcium sulfate dihydrate) to such hydroxyapatite-based composites may help to compensate the ions removal and stimulate the osteoblasts growth and proliferation. Therefore, the aim of this work was to enrich the highly porous hydroxyapatite-based composite with gypsum and verify its effect on ions adsorption as well as osteoblasts viability and proliferation. The results showed that addition of 1.5–1.75% gypsum caused short-term calcium ions compensation in media incubated with the composite and time-shifted increase of osteoblasts proliferation. Moreover, presence of gypsum in the composite increased the content of large pores in SBF-incubated biomaterials with no effect on their microstructure or mechanical parameters. Overall, gypsum addition improves the compatibility of hydroxyapatite-based materials with no critical disadvantages for other properties.

EFFECT OF BALL-MILLING TREATMENT ON SINTERABILITY OF HYDROXYAPATITE CERAMICS INCLUDING BONE MINERALS

Biological apatite found in the bone and teeth of mammals contains various ions, such as Na+, K+, Mg2+, F- and CO32-. We have previously developed porous hydroxyapatite ceramics, containing bone minerals (bone HAp). These ceramics showed great bone-forming ability and bio-resorbability; however, their mechanical strengths were in sufficient for clinical application. Thus, we focused on the refinement of raw material powder to improve the strength of the resulting bone HAp ceramics. In particular, we clarified the effect of ball milling time on sinterability of the bone HAp powder. Among the prepared samples, the most easily sinterable powder was prepared after ball milling for 1 hour. This powder showed the smallest particle size with a particle size distribution that was close to a uniform distribution. The compressive strengths of Bone HAp ceramics from powders prepared by ball-milling for 30 minutes and 1 hour were of 55.7 MPa and 63.1 MPa, respectively.

Hydroxyapatite cages with aligned pores for bone grafting – Seeding of human osteoblast-like cells in vitro and their response in dynamic culture mode

Hydroxyapatite (HA) is a highly regarded synthetic bone graft material. Porous HA ceramics blocks are used to substitute harvested natural bone grafts. Being similar to bone mineral, HA material integrates with the host bone through surface osteointegration and slowly resorb along with the natural bone remodeling process. The blocks in use currently have random and tortuous pore structures. The present work explores the usefulness of cage-like HA ceramic design with end-to-end open pores, with the help of in vitro cell culture methods. Such a structure, on implantation, will take up the blood factors and cells and host the bone remodeling process inside the bulk of the cage, leading to early healing. In the study, HA samples with aligned through-pores were prepared and explored in vitro, with a focus on how the pores host the cells inside and to what level the cells maintain their activity. Human osteoblast-like cells (HOS) were used, at different seeding and culturing approaches. Cell seeding was done through (i) conventional large volume cell suspension, (ii) a confined mini chamber with a limited volume of cell suspension, and (iii) placing a concentrated drop of cell suspension directly on top of the scaffold. The third approach gave the best cell adhesion and proliferation, and hence used for further explorations. A dynamic culture system was designed in-house by bifurcating the cell culture wells using vertical inserts, holding the samples horizontally with their ends open to both sides, and making the media flow across using a rocker platform. The HOS cell adhesion, viability and proliferation were tested in the HA cages, in static and dynamic culture conditions, with conventional porous ceramics as the control. The cell infiltration was deeper and the cell viability over a period of 7 days was significantly higher in dynamic culture conditions in the test samples.

Biocompatible Composite Materials Based on Porous Hydroxyapatite Ceramics and Copolymer of Lactide and Glycolide

The intensive development of reconstructive surgery and traumatology provides a stable demand for new materials for implants. Of particular interest are materials based on hydroxyapatite, which are chemically close to the elemental composition and structure of bone and have similar bioactive properties. The aim of this work was to obtain porous composite materials based on hydroxyapatite and a copolymer of lactide and glycolide with properties suitable for use as a material for bone implants. The phase and elemental composition of composites was investigated by infrared spectroscopy, X-ray diffraction, and X-ray photoelectronic spectroscopy methods, and it was established how the production process affects the composition of materials. Regularities of the formation of porosity by the methods of low-temperature adsorption of nitrogen, immersion in a liquid (determination of the pore space volume), measurement of the diffusion coefficient through the material (Franz cell), and surface properties of composite materials by the Hammett indicator method, by the lying drop method were revealed. Regularities were established between the surface properties and the composition of materials and their biocompatibility determined using monocytes isolated from human peripheral blood.

Effects of molecular weight on macropore sizes and characterization of porous hydroxyapatite ceramics fabricated using polyethylene glycol: mechanisms to generate macropores and tune their sizes

Hydroxyapatite (HAp) is a raw material used to fabricate scaffolds. Scaffolds are required to be porous to facilitate nutrient flow and vascularization. This study aims to produce porous HAp ceramics with macropores (>200 μm) and bioactivity and tune their macropore size. Polyethylene glycol (PEG) with molecular weights of 400, 3,400, and 8,300 was used to generate macropores. The macropore size increased as the molecular weight of PEG increased. In this method, emulsions were formed by hydrophobic PEG binding HAp nanoparticles during chemical syntheses. Water foams, as a core of the emulsion, were transformed into steam, and the steam expanded under heat treatment. Macropores were generated by the evaporation of the steam and consolidation of HAp nanoparticles. The difference in the molecular weight of PEG did not affect cell adhesion to the porous HAp ceramics. Cells adhered well to and spread widely on the HAp ceramics regardless of macropore size.

Osteoinduction in Novel Micropores of Partially Dissolved and Precipitated Hydroxyapatite Block in Scalp of Young Rats.

Osteoinduction in muscles by porous ceramics has been reported to be a real phenomenon. In this study, osteoinduction in connective tissues was found in highly porous hydroxyapatite (HAp) ceramics with large specific surface areas. We have developed the combination method of the partial dissolution-precipitation (PDP) technique involving the stirring-supersonic treatment in 1.7 × 10−2 N HNO3 solution containing Ca2+ and PO43− to improve the surface and the bulk of commercially available synthetic HAp block (82.5% in porosity, 50–300 µm in pore size). The modified HAp was named as a partially dissolved and precipitated HAp (PDP-HAp). The PDP-HAp exhibited the porosities of 85–90%, the macropore sizes of 50–200 µm, and the specific surface areas of 1.0–2.0 m2/g, with microcracks. The aim of this study was to observe bone induction by the PDP-HAp with or without BMP-2 in scalp tissues of four-week-old rats. Young rats were divided into the PDP-HAp alone group and the PDP-HAp/BMP-2 group for a long-term observation. In the PDP-HAp group, bone induction occurred inside the many pores at nine months, and the ratio of induced bone was 12.0%. In the PDP-HAp/BMP-2 group, bone induction occurred in almost all pores at three months, and compact bone was found at nine months. The ratios of induced bone were 77.0% at three months and 86.0% at nine months. We believe that osteoinduction by the PDP-HAp might be different from the process of BMP-loaded HAp-induced bone formation, because the PDP-HAp has osteogenic microporous compartments with partially absorbable HAp crystals. The PDP technique may contribute to create bioceramics with osteoinductive property for bone regenerative medicine.

Porous hydroxyapatite ceramics coated with biomimetic peptides for induced osteogenesis

Biomimetic peptide has attracted extensive attention in bone tissue repairing owing to its excellent biocompatibility and stability. Hydroxyapatite ceramics (HAP) possess both excellent mechanical properties and good biocompatibility. To study the effects of bionic peptide D9KIPKAS(pSer)VPTELSAISRGDS on the interfacial activity and biological properties of hydroxyapatite ceramics, porous HAP ceramics were prepared using ammonium carbonate as a pore-forming agent. To explore the influence of surface modification on the interfacial activity of porous HAP ceramics when applying different methods, surface modification was carried out using physical adsorption (HAP-p-PP2) and a chemically grafted polypeptide (HAP-c-PP2). X-ray diffraction was used to characterize the crystal morphology of the porous HAP ceramics before and after sintering. The results of FTIR and XPS showed that bionic peptides were successfully grafted onto the surface of a porous HAP ceramic. An SEM graph shows the adhesion and spread of BMSCs on the materials. Meanwhile, the results of in vitro cell experiments showed that HAP-c-PP2 can better promote BMSC proliferation. In conclusion, bionic peptide D9KIPKAS(pSer)VPTELSAISRGDS with multifunctional functional groups is more conducive to the adhesion, proliferation and differentiation of BMSCs which can make it play an effective role in osteoinduction in bone tissue engineering.

Design of three‐dimensional interconnected porous hydroxyapatite ceramic‐based composite phase change materials for thermal energy storage

In this article, three-dimensional connected porous hydroxyapatite ceramics (PHCs) were prepared by using the Pickering emulsion template, which possessing controlled pore structure simply by adjusting the solid content from 35 to 55 wt%. The polyethylene glycol (PEG) and PHCs were compounded by vacuum impregnation to acquire composite phase change materials (CPCMs) with admirable shape stability. The SEM and EDS images showed that PEG was successfully adsorbed in the pore, and the results of FT-IR, XRD, TGA, and thermal cycles test, demonstrated the CPCMs possessed satisfactory chemical stability, favorable thermal stability, and wonderful thermal reliability. The maximum package ratio obtained was 66 wt%, which was supported by the PHC sample prepared with a solid content of 40 wt%. Moreover, the phase transition temperature and latent heat during melting and solidification were 53.41°C and 117.5 J/g, 36.49°C and 111.1 J/g, respectively. Therefore, the prepared PCM composites had a controlled pore structure, stable chemical properties, high latent heat, and excellent thermal reliability, making it a reliable application of thermal energy storage.

Fluoride Adsorption on Porous Hydroxyapatite Ceramic Filters: A Study of Kinetics

Batch kinetic tests and continuous-flow column experiments were conducted to study fluoride adsorption on porous hydroxyapatite ceramics. Batch tests showed that fluoride uptake occurred faster for...