Preparation and characterisation of HA/TCP biphasic porous ceramic scaffolds with pore-oriented structure

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic scaffolds with a uniform unidirectional pore structure were successfully fabricated by an ice-templating method by using Ca-deficient HA whiskers and phosphate bioglass. HA whiskers showed good dispersibility in the slurry and favoured the formation of interconnected pores in the scaffolds. Addition of bioglass powders enhanced the material sintering process and the phase transformation of Ca-deficient HA to β-TCP. Calcium-phosphate-based scaffolds with a composition from HA to an HA/β-TCP complex could be obtained by controlling the freezing moulding system and slurry composition. The fabricated scaffolds had a porosity of 75–85%, compressive strength of 0.5–1.0 MPa, and a pore size range of 130–200 µm.     

3D-printed barium strontium titanate-based piezoelectric scaffolds for bone tissue engineering

In order to promote bone healing, new generations of biomaterials are under development. These biomaterials should demonstrate proper biological and mechanical properties preferably similar to the natural bone tissue. In this research, 3D-printed barium strontium titanate (BST)/β-tricalcium phosphate (β-TCP) composite scaffolds have been synthesized as an alternative strategy for bone regeneration to not only induce appropriate bioactive characteristics but also piezoelectric behavior. The physical, chemical and biological performance of the scaffolds have been examined in terms of mechanical, dielectric properties, apatite-forming ability, Alizarin Red Staining (ARS), Alkaline Phosphatase activity (ALP), and cytotoxicity. The samples composed of 60% BST and 40% β-TCP showed the highest compressive strength, bending module, elastic modulus and the Young's modulus. The dielectric constant increased with further addition of the BST phase in the constructs. Scanning Electron Microscope (SEM) and energy dispersive X-ray (EDX) analyses showed that 60% BST/40% β-TCP sample had the highest amount of bone-like apatite formation after 28 days in simulated body fluid (SBF). Moreover, the results of ARS proved that 60% BST/40% β-TCP composite could present higher quantities of mineral deposition. The ALP activity of osteosarcoma cells on 60% BST/40% β-TCP sample showed higher activities compare with the other composites. None of the samples demonstrated any sign of toxicity using MTT test. It can be suggested that BST/β-TCP composite scaffolds can be potentially used as the next generation of bone tissue engineering scaffold materials.     

A Novel Biphasic Bone Scaffold: β-Calcium Phosphate and Amorphous Calcium Polyphosphate

Calcium polyphosphate (CPP) was added to hydroxyapatite (HA) to develop a novel biphasic calcium phosphate (BCP). The effects of varying CPP dosage on the sintering property, the mechanical strength, and the phase compositions of HA were investigated. Results showed that CPP reacted with HA and produced β-calcium phosphate (β-TCP) and H₂O and that an excessive dosage of CPP (>10 wt%) obtained a novel BCP of β-TCP/amorphous-CPP, while a lesser dosage of CPP (<10 wt%) obtained a traditional BCP (HA/β-TCP). The porous β-TCP/amorphous-CPP scaffolds (porosity of 66.7%, pore diameter of 150–450 μm, and compressive strength of 6.70±1.5 MPa) were fabricated and their in vitro degradation results showed a significant improvement of degradation with the addition of CPP.     

Effects of formaldehyde solution and nanoparticles on mechanical properties and biodegradation of gelatin/nano β-TCP scaffolds

In this study, gelatin/beta tricalcium phosphate (β-TCP) nanocomposite scaffolds were prepared by solvent casting method. The cross-linking method was carried out by adding formaldehyde to gelatin. The microparticles of sodium chloride were used as porogen agent. Characterization of nano β-TCP was performed using XRD, FTIR, and SEM. Results showed that the size of the particles is about 100 nm with spherical morphology. In addition, the scaffold characterization was carried out using FTIR and SEM techniques. Observations showed a porous texture with pore size between 100 and 400 μm. The biodegradability and bioactivity evaluations of the scaffolds were done by immersing them in a simulated body fluid solution for different time periods. The biodegradability studies demonstrated a reduction in the degradation rate of gelatin/β-TCP nanocomposite scaffolds due to the presence of β-TCP nanoparticles. The obtained results of bioactivity tests confirmed the formation of apatite layer on the surface of the scaffolds. Furthermore, the effects of porosity, cross-linking agent, and β-TCP nanoparticles on the bending and compressive properties of the composite scaffolds were examined. According to the mechanical examinations of the scaffolds, the best bending and compressive properties occurred in the presence of 10 and 20 wt% of β-TCP nanoparticles, respectively. The appropriate mechanical properties and biodegradation rate for tissue engineering applications obtained at 1 g of the formaldehyde solution.     

Fabrication of doped β-tricalcium phosphate bioceramics by Direct Ink Writing for bone repair applications

β-tricalcium phosphate (β-TCP, β-Ca₃(PO₄)₂) is one of the most attractive biomaterials for bone regeneration and β-TCP macroporous scaffolds are very promising for both cell proliferation and mechanical support. The Additive Manufacturing (AM) process called Direct Ink Writing (DIW), based on the extrusion of a concentrated ceramic slurry, is particularly adapted to resolve the main drawbacks associated with conventional shaping of ceramic scaffolds. In this work, co-doped β-TCP powders were synthetized and used to print macroporous scaffolds by DIW. Doped β-TCP powders have been proved to exhibit higher thermal stability, densification and mechanical properties compared to undoped β-TCP. Two co-doped compositions were produced via the aqueous precipitation technique combining magnesium, strontium, silver and copper cations: Mg-Sr (2.0–2.0 mol%) and Mg-Sr-Ag-Cu (2.0–2.0–0.1–0.1 mol%). DIW slurries were optimized with undoped and co-doped β-TCP with the use of a dispersant and a carboxymethylcellulose and polyethyleneimine mixture to obtain aqueous slurries filled with 42 vol% of powder. Complete rheological characterizations were realized to assess the suitability of the β-TCP slurries for the DIW process (shear-thinning and thixotropic behaviour). The whole processing chain including printing, osmotic drying (PEG 10000) and sintering (1100 °C, 3 h) was optimized to successfully print co-doped β-TCP macroporous scaffolds. Characterizations after sintering showed a reduction of macropores and microcracks using co-doped β-TCP powders as well as improved compressive strengths and densities compared to undoped β-TCP. A significant enhancement of compressive strength values was obtained compared to literature data.     

EELS characterisation of β-tricalcium phosphate and hydroxyapatite

Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are of great interest due to their potential application as bone-replacement materials. In particular, composites made of a mixture of these Ca-phosphates revealed improved mechanical properties; however, the reason for this improvement is unknown. Future development and properties enhancement of such bioceramics is linked to the possibility to characterise their particular microstructure. In this context, the ability to quickly identify individual grains of HA and β-TCP within these composites will allow acquiring information about the phase distributions and the phase-boundary microstructure. The aim of the present study is, therefore, to demonstrate that electron energy-loss spectroscopy (EELS) can be successfully employed to differentiate between individual grains of HA and β-TCP. In particular, the analysis of the near-edge structure of the oxygen K-ionisation edge allows detection of a characteristic signal at ca. 536 eV that can be employed as an identification tool for HA. EELS investigations were performed first on as-received and calcined (1000 °C) HA and β-TCP powders and subsequently on pure bulk HA and β-TCP samples sintered at 1250 °C. Finally, this method was successfully applied to a HA/β-TCP (50/50 wt.%) composite sintered at 1250 °C.     

Phase Transition from α-TCP into β-TCP in TCP/HA Composites

The phase transition from α-tricalcium phosphate (α-TCP) into β-tricalcium phosphate (β-TCP) in tricalcium phosphate/hydroxyapatite (TCP/HA) composites was investigated by X-ray diffraction, differential scanning calorimetry, thermogravimetry and scanning electron microscopy in this study. The current experimental results indicated that the calcining temperature for the complete phase transition from α-TCP into β-TCP increased with the increasing HA content in the composite. HA/β-TCP biphasic composites with initial Ca/P molar ratios of 1.571, 1.600 and 1.636 were synthesized. The particle coarsening occurred significantly in the process of calcination.     

Study of biodegradable ceramic bone graft substitute

Abstract

The aim of the present study was to obtain a biodegradable porous calcium phosphate implants as a synthetic bone graft substitute. The calcium phosphate used in the present study consisted of hydroxyapatite (HA) and dicalcium phosphate anhydrous (DCP). Porous bioceramic was fabricated by a foam casting method. By polyurethane foam and slurry containing HA/DCP (3 : 1 weight ratio) powder, water and additives a high porous structure with ～70% was created. The X-ray diffractometry revealed that the β-tricalcium phosphate (β-TCP) formation is major phase. Surface morphology analysis and porosity evaluations were performed. The variation in the compressive strength, elastic modulus and dissolution behaviour of immersed synthetic bone graft in simulated physiological solution investigated.     

Inorganic calcium filled bacterial cellulose based hydrogel scaffold: novel biomaterial for bone tissue regeneration

Abstract

This work emphasizes the structural, physio-chemical characterization and cell biological efficiency analysis of novel inorganic calcium (only calcium phosphate and in combination of calcium phosphate & CaCO₃) filled bacterial cellulose (BC) based hydrogel scaffolds. FTIR and TG analysis indicates the presence of BC and inorganic calcium within the hydrogel scaffolds. SEM establishes the porous structures (50–200 µm). Swelling study indicates significant swelling ability in both calcium phosphate filled and calcium phosphate & CaCO₃ filled hydrogel scaffolds. Compressive strength (0.24–0.60?MPa) of the calcium filled hydrogel scaffolds are similar like trabecular bone. Significant cell viability (Lep-3) was further noticed until 72,120 and 168?h.     

Fabrication and characterization of honeycomb β-tricalcium phosphate scaffolds through an extrusion technique

In this study, for the first time honeycomb β-tricalcium phosphate (β-TCP) scaffolds were fabricated through an extrusion technique. The physicochemical properties and cell behaviors of the honeycomb β-TCP scaffolds were investigated. The results showed that scaffolds were characterized by ordered channel-like macropores and unidirectional interconnection. The pore structure and mechanical strength could be tailored by changing the parameters of extrusion molds. The pore size of scaffolds was in the range of 400–800 µm approximately, while their compressive strength parallel to the pore direction and porosity ranged from 14 to 20 MPa and 60–70%, respectively. The in vitro cell behavior demonstrated that cells could well attach on the surfaces and grow into the inner channel-like pores of thescaffolds; the scaffolds with higher porosity showed better cell proliferation but poorer cell differentiation. The honeycomb scaffolds fabricated by extrusion technique are potential candidate for bone tissue engineering.     

3D printing of bioactive macro/microporous continuous carbon fibre reinforced hydroxyapatite composite scaffolds with synchronously enhanced strength and toughness

Continuous carbon fibre (CF) reinforced HA (CF/HA) composite scaffolds were prepared using a self-designed and manufactured 3D printer. The optimised design of nozzle structure and the tailored viscoelastic property of HA inks ensured compound extrusion of monofilament and multifilament CF with HA rod. The composite scaffolds designed using the CAD programme and sintered via a suitable process exhibited a hierarchical macro/microporous structure and contained approximately 50% HA and 50% β-TCP. The continuous CF synchronously enhanced the strength and toughness of the scaffolds. The compressive strengths of 1CF/HA and 5CF/HA were 11.4 ± 1.7 MPa and 16.3 ± 2.6 MPa, respectively, which were approximately double and triple compared with that of HA scaffolds. The fracture toughness of 1CF/HA was approximately double that of HA scaffolds and close to that of cortical bone. In vitro and in vivo studies demonstrated that 1CF/HA also had apatite formation capability and adequate bone regeneration capacity.     

Dissolution properties of different compositions of biphasic calcium phosphate bimodal porous ceramics following immersion in simulated body fluid solution

Biphasic calcium phosphate (BCP) bimodal porous ceramics were prepared from a mixture of fine powders of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) with varying HAp/β-TCP ratios. Two types of HAp powders and one type of β-TCP powder were used to produce porous BCP bioceramics with HAp/β-TCP weight ratios of 20/80, 40/60, and 80/20. Dissolution tests were performed to compare the dissolution properties of BCP-based bioceramics with different structural properties. Porous ceramic samples of approximately 0.5 g were individually soaked in 30 ml of simulated body fluid (SBF) solution at 36.5 °C for 1, 3, 7 and 10 days, respectively. The calcium content of the SBF solution was analyzed by ICP. The porous bodies were filtered, dried, and characterized using SEM, XRD, and FT-IR. The results indicate that the sample structural properties seem to have a greater effect than the storage environment on the dissolution properties.     

Novel hydrogels of PVP–CMC and their swelling effect on viscoelastic properties

Polyvinylpyrrolidone (PVP) and carboxymethyl cellulose (CMC) mixed hydrogels were prepared by heat treatment. The physical characteristics of the hydrogels were studied by Fourier transform infrared spectroscopy and scanning electron microscopy. The swelling study of the hydrogels in water shows remarkable water absorption property. The swelling effect on the rheological behavior of PVP‐, PVP–CMC‐, and CMC‐based hydrogels was investigated to judge its application on uneven surface of body. The rheological properties (storage modulus, loss modulus, and complex viscosity) of samples before drying and swelled (15, 30, and 60 min) were measured against angular frequency and composition. The hydrogel containing PVP/CMC ratio of 20 : 80 appeared to be the best hydrogel from rheological and water absorbent points of view. These properties and low cost of the materials utilized in this work suggest that this hydrogel is a viable alternative product for dressing materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Indirect fabrication of hydroxyapatite/β-tricalcium phosphate scaffold for osseous tissue formation using additive manufacturing technology

Patient specific HA/β-TCP scaffold were fabricated using an indirect fabrication approach which involves the application of rapid prototyping technology. β-TCP powder with 10, 20 and 30 % HA concentrations were analyzed for different sintering temperatures. Scaffolds were evaluated by Scanning Electron Microscopy, X-ray diffraction, compression tests, Fourier transform infrared spectroscopy and cytotoxicity tests using human osteosarcoma cell line. Results include HA/β-TCP scaffold porosity, volumetric shrinkage, mechanical properties, bonding, structural phase change and cytotoxicity.     

Effect of the HA/β-TCP Ratio on the Biological Performance of Calcium Phosphate Ceramic Coatings Fabricated by a Room-Temperature Powder Spray in Vacuum

Four calcium phosphate ceramic coatings, the less soluble hydroxyapatite (HA) coating, the more soluble β-tricalcium phosphate (β-TCP) coating, and two biphasic calcium phosphate (BCP) coatings with HA/β-TCP ratios of 70/30 and 30/70 were fabricated by spraying each corresponding powder onto a titanium substrate at room temperature (RT) in a vacuum, in order to investigate the effect of the HA/β-TCP ratio on the dissolution behavior and the cellular responses of the coating. No secondary phases, except for HA and β-TCP, were observed for the coatings in the X-ray diffraction results. The coating compositions were almost the same as those of the starting powders because the coating was conducted at RT. Microscopic examination of the coatings revealed crack-free and dense microstructures. The BCP coatings exhibited dissolution rates intermediate between those of the pure HA and β-TCP coatings. The dissolution rate of the coatings was largely dependent on their HA/β-TCP ratio. The cell proliferation and differentiation results indicated that the cellular responses of the coatings were not proportional to their dissolution rates. The 3HA–7TCP (HA/β-TCP ratio of 30/70) coating exhibited an optimal dissolution rate for excellent biological performance.     

Properties of calcium phosphates ceramic composites derived from natural materials

In this study, ceramics containing mixed phases of hydroxyapatite/beta-tricalcium phosphate (HA/β-TCP) were fabricated by a solid-state reaction technique. The HA powder was synthesized from cockle shells while the β-TCP powder was synthesized from egg shells. Pure HA and β-TCP fine powders were successfully obtained. The HA and β-TCP were mixed and subjected to a thermal treatment up to 1100 °C. To form the mixed phase ceramics, the resulting powders were sintered at 1350 °C. Effects of HA concentration on the properties of the studied ceramic were investigated. X-ray diffraction analysis revealed that all samples presented multiphase of calcium phosphate compounds. Average grain size of the ceramics decreased with the HA additive content. The 75 wt% HA ceramic showed the maximum hardness value (5.5 GPa) which is high when compared with many calcium phosphate ceramics. In vitro bioactivity test indicated that apatite forming increased with the HA additive content. To increase antibacterial activity, selected ceramics were coated with AgNO₃. Antibacterial test suggested that an Ag compound coating on the ceramics could improve the antibacterial ability of the studied ceramics. In addition, the antibacterial ability for the Ag coated ceramics depended on the porosity of the ceramics.     

β-Tricalcium phosphate/ԑ-polycaprolactone composite scaffolds with a controllable gradient: Fabrication and characterization

β-tricalcium phosphate (β-TCP)/ԑ-polycaprolactone (PCL) composite scaffolds with a controllable gradient were developed with a two-step process: fabrication of the β-TCP scaffolds using digital light processing (DLP) 3D printing and then immersion of the β-TCP scaffolds into a PCL melt for different times. The gradient structure was controlled by the immersion time of the β-TCP scaffolds in the molten PCL. The composite scaffolds with a gradient exhibited a substantially higher compressive strength and toughness than the bare β-TCP scaffolds. Moreover, the increase in infiltration time also enhanced the compressive strength and toughness of the composite scaffolds because the infiltration thickness increased with infiltration time. The gradient structure resulted in a gradient degradation and may provide a better response to time-varying mechanical properties than pure β-TCP scaffolds during its absorption process. Therefore, composite scaffolds with a gradient are promising candidates for load-bearing bones or large segmental bone repair.     

β-TCP scaffold coated with PCL as biodegradable materials for dental applications

Requirements for an ideal scaffold include biocompatibility, biodegradability, mechanical strength and sufficient porosity and pore dimensions. Beta tricalcium phosphate (β-TCP) has competent biocompatibility and biodegradability, but has low mechanical strength because of its porous structure. Polycaprolactone (PCL) is a biodegradable polymer with elastic characteristics and good biocompatibility. In this study, β-TCP/PCL composites were prepared in different ratio and their morphology, phase content, mechanical properties, biodegradation and biocompatibility were investigated. After coating, surfaces of β-TCP scaffolds were covered with the PCL while some of the pores were partially clogged. The compression and bending strength of β-TCP scaffolds were significantly enhanced by PCL coating. The degradation rate of the scaffold in Tris buffer was reduced with higher content of the PCL coating. MTT and ALP assays showed that the osteoblast cells could proliferate and differentiate on PCL coated scaffolds as well as on bare β-TCP scaffolds. Based on the comprehensive analysis achieved in this study, it is concluded that the β-TCP/PCL composite scaffold fabricated with 40% β-TCP and 5% PCL exhibits optimum properties suitable for dental applications.     

Research of phase transformation induced biodegradable properties on hydroxyapatite and tricalcium phosphate based bioceramic

Biodegradable calcium phosphate composites consisting of tricalcium phosphate (α-TCP) and hydroxyapatite (HA) were prepared using a two-step sintering method. The ratio of α-TCP/HA was controlled by modulating the sintering temperature. The initial calcination process at 800 °C causes HA dehydroxylation and induces the early transformation of HA into α-TCP in subsequent sintering processes. At the optimum sintering temperature of 1300 °C, the material is comprised of a moderate ratio of α-TCP to HA (3:7) and possesses a hardness of 5.0 GPa. The high temperature phase transformation from HA to α-TCP accompanied by bonded water loss, which results in the formation of nano-pores within the α-TCP matrix, hardly deteriorated the mechanical strength of the composite. This pore-containing structure also provided a convincing evidence for the origin of the high degradability of α-TCP in a biological environment.     

Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation

This study focused on the effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate. Chemical precipitation was used to prepare Sr-doped hydroxyapatite (HA) precursor powders. The phase transformation of the as-prepared samples during sintering was analyzed. The powders were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Quantitative analysis of the phase content and fine structure was performed by Rietveld refinement. Sr doping was found to facilitate the phase transformation from HA to beta-tricalcium phosphate (β-TCP) at 1000 °C. The β-TCP content increased with increasing Sr content, causing a decline in the ratio of HA to β-TCP. With Sr contents of ≤5 mol%, HA remained the major phase in the biphasic mixtures; in contrast, with Sr contents of ≥15 mol%, the mass fraction of β-TCP exceeded 50%. The incorporation of Sr²⁺ into HA and β-TCP caused the lattice parameters of both phases to increase. Additionally, Sr incorporation slightly enhanced the binding energy of Ca. The study confirmed that Sr doping could be used to modulate the phase fractions of HA and β-TCP. The effective partial substitution of Sr in both HA and β-TCP makes these materials promising for bone repair.