Development of bioresorbable Mg-substituted tricalcium phosphate scaffolds for bone tissue engineering

Mg-substituted tricalcium phosphate (β-TCMP) samples were prepared either by the solid-state reaction of CaHPO₄ (DCPA), CaCO₃ and MgO powder at 1000 °C, or by a two-step process: wet precipitation of a precursor and further calcination of the precursor. The transition temperature from β-Tricalcium Phosphate (TCP) to α-TCP increases with the increase of Mg²⁺ content in β-TCMP samples. A β-TCMP sample with 3 mol% Mg²⁺ has a β-TCP to α-TCP transition temperature above 1300 °C, which was then used to fabricate various β-TCMP scaffolds in this study. Interconnected porous β-TCMP ceramics, with pore size > 100 μm and relative density of ~ 81% to 84%, were developed by a replication method using polyurethane foam as a template; micropores were also found in the scaffold struts. β-TCMP ceramics with a porous structure in the center and a dense shell-like structure outside, mimicking human bone, were fabricated by a molding method. Dense β-TCMP ceramic rings were also produced with an average compressive strength of 129 MPa.     

Preparation of a–b plane oriented Nb-doped Bi4Ti3O12 ceramics by magnetic alignment via gelcasting

Highly a–b plane grain-oriented Nb-doped Bi₄Ti₃O₁₂ ceramics (Bi₄Ti_2.96Nb_0.04O₁₂, BINT) were successfully prepared by magnetic alignment (MA) via gelcasting technique using only conventional solid-state-synthesized starting powder. The micro-size BINT particles with irregular shape were aligned in slurry by strong magnetic force and then in situ locked by polymerization via gelcasting technique in 30 min in a 10 T magnetic field. Highly a–b plane orientation parallel to the magnetic field direction (//B) was obviously observed in the green compact (f_(200)/(020) = 0.41) and sintered sample (f_(200)/(020) = 0.67). The sintered sample contained plate-like grains and reached 97% theoretical density. Compared to the controlled sample without magnetic alignment, the magnetically aligned sample shows enhanced dielectric constant in //B direction (160 versus 120 at room temperature and 350 versus 250 at 580 °C). This method, using typical gelcasting technique in a strong magnetic field, readily applicable to prepare other ceramics and is expected to facilitate the mass preparation of large and dense grain-oriented ceramic components.     

Microstructure and properties of porous silicon nitride ceramics prepared by gel-casting and gas pressure sintering

Wave-transparent porous Si₃N₄ ceramics were prepared by gel-casting and gas pressure sintering, and the effects of solid loading on microstructure, mechanical and dielectric properties were investigated. Microstructures with interlocked elongated β-Si₃N₄ grains and uniformly distributed pores were observed, while both the β-Si₃N₄ phase content and grain aspect ratio reduced as the solid loading increased due to the restrained anisotropic growth of β-Si₃N₄ grains. As the solid loading increased from 30 to 45 vol.%, the porosity of ceramics declined from 57.6% to 36.4%. The flexural strength increased linearly from 108.3 to 235.1 MPa, and the dielectric constant and loss tangent of ceramics increased from 2.63 and 2.85 × 10⁻³ to 3.68 and 3.56 × 10⁻³ (10 GHz), respectively.     

Enhanced sintering ability of biphasic calcium phosphate by polymers used for bone scaffold fabrication

Biphasic calcium phosphate (BCP), which is composed of hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] and β-tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂], is usually difficult to densify into a solid state with selective laser sintering (SLS) due to the short sintering time. In this study, the sintering ability of BCP ceramics was significantly improved by adding a small amount of polymers, by which a liquid phase was introduced during the sintering process. The effects of the polymer content, laser power and HAP/β-TCP ratios on the microstructure, chemical composition and mechanical properties of the BCP scaffolds were investigated. The results showed that the BCP scaffolds became increasingly more compact with the increase of the poly(l-lactic acid) (PLLA) content (0–1 wt.%) and laser power (6–10 W). The fracture toughness and micro-hardness of the sintered scaffolds were also improved. Moreover, PLLA could be gradually decomposed in the late sintering stages and eliminated from the final BCP scaffolds if the PLLA content was below a certain value (approximately 1 wt.% in this case). The added PLLA could not be completely eliminated when its content was further increased to 1.5 wt.% or higher because an unexpected carbon phase was detected in the sintered scaffolds. Furthermore, many pores were observed due to the removal of PLLA. Micro-cracks and micro-pores occurred when the laser power was too high (12 W). These defects resulted in a deterioration of the mechanical properties. The hardness and fracture toughness reached maximum values of 490.3 ± 10 HV and 1.72 ± 0.10 MPa m^1/2, respectively, with a PLLA content of approximately 1 wt.% and laser power of approximately 10 W. Poly(l-lactic-co-glycolic acid) (PLGA) showed similar effects on the sintering process of BCP ceramics. Rectangular, porous BCP scaffolds were fabricated based on the optimum values of the polymer content and laser power. This work may provide an experimental basis for improving the mechanical properties of BCP bone scaffolds fabricated with SLS.     

Fabrication of biodegradable nano-sized β-TCP/Mg composite by a novel melt shearing technology

Biodegradable magnesium-matrix composites have attracted increasing interest for application in implant material fields. In this study, a new type of nano-sized β-tricalcium phosphate (β-TCP)/Mg–3Zn–Ca composite was proposed and produced using a novel melt shearing technology combined with high-pressure die casting (HPDC) process. The effect of the mixing methods on the distribution of β-TCP particles was investigated. Microstructure evolution during solidification process was analysed and the mechanical properties of the composite were also evaluated. Compared with the conventional mechanical stirring, the agglomerate phenomenon of the β-TCP particles in the matrix can be decreased by using the high shear unit and further decreased by melt shearing in the MCAST unit. The results also showed that the main constitutes in the matrix of the β-TCP/Mg–3Zn–1Ca composite are α-Mg and Ca₂Mg₆Zn₃ phase and most of the β-TCP particles are adjacent to the eutectic Ca₂Mg₆Zn₃ phase around the grain boundary. The average Vickers hardness, yield strength (0.2% YS), ultimate tensile strength (UTS), elastic modulus and elongation of as-cast of this composite are 79.0, 125.4 MPa, 150.0 MPa, 45.3 GPa and 2.85%, respectively.     

Lovastatin release from polycaprolactone coated β-tricalcium phosphate: Effects of pH,concentration and drug–polymer interactions

The approach of local drug delivery from polymeric coating is currently getting significant attention for both soft and hard tissue engineering applications for sustained and controlled release. The chemistry of the polymer and the drug, and their interactions influence the release kinetics to a great extent. Here, we examine lovastatin release behaviour from polycaprolactone (PCL) coating on β-tricalcium phosphate (β-TCP). Lovastatin was incorporated into biodegradable water insoluble PCL coating. A burst and uncontrolled lovastatin release was observed from bare β-TCP, whereas controlled and sustained release was observed from PCL coating. A higher lovastatin release was observed pH 7.4 as compared to pH 5.0. Effect of PCL concentration on lovastatin release was opposite at pH 7.4 and 5.0. At pH 5.0 lovastatin release was decreased with increasing PCL concentration, whereas release was increased with increasing PCL concentration at pH 7.4. High Ca^2 + ion concentration due to high solubility of β-TCP and degradation of PCL coating were observed at pH 5.0 compared to no detectable Ca^2 + ion release and visible degradation of PCL coating at pH 7.4. The hydrophilic–hydrophobic and hydrophobic–hydrophobic interactions between lovastatin and PCL were found to be the key factors controlling the diffusion dominated release kinetics of lovastatin from PCL coating over dissolution and degradation processes. Understanding the lovastatin release chemistry from PCL will be beneficial for designing drug delivery devices from polymeric coating or scaffolds.     

Clinical evaluation of β-TCP in the treatment of lacunar bone defects: A prospective,randomized controlled study

The aim of this study was to investigate the potential wide application of beta tricalcium phosphate (β-TCP) only for bone defects as compared to allograft. 95 patients with a solitary bone cyst were randomly assigned to the treatment. A new radiographic scoring system was employed to calculate the biodegradation of bone graft and to evaluate the influence of multiple factors. At an average of 28.43 months after surgery, a radiographic semi-quantitative analysis revealed that the degradation rates of β-TCP and the allograft were comparable (p > 0.05). Age, complication, packing methods and granule diameters have a significant influence on β-TCP degradation. The loose packing method and 3–5 mm granule size should be employed in clinical practice. A histological analysis of biopsy showed that β-TCP supported the growth of fibrous tissue, vascular tissue, as well as bone tissue into the implants. The results proved that single β-TCP is an advantageous alternative to allografts for lacunar bone defect repair and would well guide the design and clinical application of the β-TCP.     

Preparation and characterization of novel bioactive α-Tricalcium Phosphate doped with Dicalcium Silicate ceramics

This work describes the evaluation of pure α-Tricalcium Phosphate (TCP) and silica containing TCP ceramics in the system Dicalcium Silicate–Tricalcium Phosphate (C₂S–TCP) as a potential substrate for bone tissue engineering. The ceramics were soaked in dynamic simulated body fluid (SBF) for 2 weeks and characterized by SEM-WDS, XRD, and TEM analysis, and the results indicated that a carbonated hydroxyapatite (CHA) was formed on the surface of the ceramics. In addition, cell attachment assay showed that the ceramics supported the adult mesenchymal stem cells of human origin (hMSCs-A) adhesion and spreading, and the cells established close contacts with the ceramics after 24 h of culture. Also, cellular assays have shown a greater ability of hMSCs-A to express markers of the osteoblast phenotype (ALP, Col I, OC) in the C₂S doped α-TCP ceramics, indicating osteoblastic differentiation as a result of the increased concentration of silicon in solid solution in α-TCP. These findings indicate that the C₂S doped α-TCP ceramics possess good bioactivity, and biocompatibility, and might be promising for bone implant material.     

Transmission electron microscopic investigation of the β1→β phase transformation in a Mg–Dy–Nd alloy

The phase transformation of β₁→β in a Mg–Dy–Nd alloy was studied by TEM. The β₁ phase, forming as plates parallel to {11?00}_α, has an f.c.c structure, with a ～ 0.74 nm, and an orientation relationship that may be described by (11?1)_β1//(112?0)_α, (110)_β1//(0001)_α. The equilibrium phase β, forming as plates parallel to {11?00}_α, has an ordered f.c.c structure, with a ～ 2.223 nm, and the orientation relationship between β and the matrix phase is identical to that observed between β₁ and matrix phase. Both phases are interconnected according to the orientation relationship: (11?1)_β//(11?1)_β1 and (110)_β//(110)_β1.     

Fabrication and mechanical properties of β-TCP pieces by gel-casting method

In the present work, dense β-TCP ceramics were fabricated by gel-casting method. The effects of the solids loading on the rheological behavior of β-TCP slurries were investigated. When the concentration of the slurries was increased from 40 to 60 vol.%, the compressive strength of green pieces was raised from 12.4 ± 1.1 to 41.2 ± 2.3 MPa, and flexural strength from 9.4 ± 0.4 to 16.3 ± 0.9 MPa. The density of the final specimens was 97.4% of the theoretical density after pressureless sintering at 1100 °C. The compressive strength, flexural strength, elasticity modulus and the fracture toughness of the sintered pieces were 291 ± 15 MPa, 93.0 ± 8.7 Mpa, 72.4 ± 7.5 GPa and 0.92 ±0.04 Mpa·m^0.5 respectively. SEM images show a compact and uniform microstructure; XRD and FTIR determined the phase and the radical before and after sintering.     

Microstructure,mechanical property and corrosion behavior of co-continuous β-TCP/MgCa composite manufactured by suction casting

The co-continuous β-TCP/MgCa composite was fabricated by infiltrating MgCa alloy into porous β-TCP using suction casting technique. The microstructure, mechanical property and corrosion behaviors of the composite have been evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical testing, electrochemical and immersion tests. It was shown that the composite structure was compact and the interfacial combination between MgCa alloy and β-TCP scaffold was very well. The composite had an ultimate compressive strength of (147 ± 13) MPa, which was near with the natural bone (2–180 MPa) and about 1000-fold higher than that of the original porous β-TCP scaffold, but it still retained over half of the strength of the MgCa bulk alloy. The electrochemical and immersion tests indicated that the corrosion resistance of the composite was better than that of the MgCa bulk alloy, and the corrosion rate of the MgCa matrix alloy was quicker than that of the porous scaffold for the composite. The corrosion products of the composite surface were mainly Mg(OH)₂, hydroxyapatite (HA) and Ca₃(PO₄)₂.     

Coating and spark plasma sintering of nano-sized TiN on Y-α-sialon

TiN coating on Y-α-sialon was accomplished by depositing TiO₂ on their particle surfaces through controlled hydrolysis of TiCl₄ and Ti(O-i-C₃H₇)₄ and subsequent nitridation with NH₃ gas at 1000 °C. TiN particles covering Y-α-sialon were about 20 nm in size. Spark plasma sintering (SPS) of TiN/Y-α-sialon particles produced composite ceramics with continuous TiN networks at 1400 °C, but with TiN grains isolated in elongated β-sialon grains at 1600 °C. The relative density and Vickers hardness of TiN/sialon ceramics SPSed at 1400–1600 °C containing 25 vol.% TiN were measured. The electrical resistivity was in a wide range of 10⁻⁴ to 10⁰ Ω cm for the ceramics sintered at 1400 °C, but lowered to the order of magnitude of 10⁻¹ and 10⁵ Ω cm at higher temperatures ≥1500 °C. It was found that the complete transition to β-sialon increased the resistivity to 10³ to 10⁵ Ω cm, due to breaking up continuous TiN layers by elongated β-sialon grains.     

The influences of B dopant on the crystal structure and nucleation ability of TiCx in the Al melt

The influences of B dopant on the crystal structure of TiC_x and nucleation efficiency on α-Al are investigated in this paper. It was found that B solute atoms in the melt easily diffused into the crystal lattice of TiC_x, meanwhile the f.c.c. crystal structure was preserved according to the EDS and TEM analysis. The doping effect of B in TiC_x was reflected on the X-ray diffraction (XRD) patterns, in which the diffraction peak of (2 0 0) plane rose correspondingly. TiC_x showed strong (1 1 1) orientation, but shifted to strong (2 0 0) after trace B doped. Furthermore, the grain refining ability of TiC_x with strong (2 0 0) orientation induced by B dopant on commercial pure Al was improved obviously and the excellent refining performance was kept in a long holding time, which indicated that the structural stability of TiC_x was enhanced after B doped.     

Microstructural study of a titanium-based biocomposite produced by the powder metallurgy process with TiH2 and nanometric β-TCP powders

A titanium-based composite with Ca-P phases was prepared in situ by powder metallurgy processing with TiH₂ and nanometric β-TCP powders. Crystal phases of the as-fabricated composite are found to be α-Ti, CaTiO₃ and Ti_xP_y phase(s). The Ti_xP_y and CaTiO₃ phases resulted from the reaction between titanium and β-TCP at about 1135 °C. The composite presented a mean compressive strength of 635 MPa and a lower contact angle than pure titanium.     

Effect of aligning magnetic field on the magnetic and calorimetric properties of ferrimagnetic bioactive glass ceramics for the hyperthermia treatment of cancer

The magnetic and heat generating properties of the ferrimagnetic zinc-ferrite containing bioactive glass ceramics have been enhanced by aligning magnetic field, without any compositional or micro-structural changes in the material. The glass ceramics were heated to 600 °C and cooled in an aligning magnetic field of 1 T. Magnetically aligned samples were compared with the non-aligned samples. VSM measurements taken at 500 Oe showed that coercive force, remanance magnetization and hysteresis area increased for the aligned samples. This occurred because the aligning magnetic field setup an easy axis for the magnetic domains. After cooling, the domains were trapped and became stable along the direction of aligning field. Now stronger magnetic field was required to turn the domains away from their aligned positions. Thus magnetic properties were enhanced by the aligning magnetic field and it led to enhance the heat generation under magnetic induction furnace operating at 500 Oe and 60 kHz for 2 min. Data showed that maximum specific power loss and temperature increase after 2 min were 4.4 W/g and 6.3 °C respectively for the aligned sample of maximum zinc-ferrite crystalline content having pseudo single domain crystalline structure. The glass ceramics were immersed in simulated body fluid over weeks. FTIR, SEM and EDX results indicated the growth of precipitated Hydroxyapatite suggesting the bioactivity of the materials.     

Magnesium substitution in brushite cements

The use of magnesium-doped ceramics has been described to modify brushite cements and improve their biological behavior. However, few studies have analyzed the efficiency of this approach to induce magnesium substitution in brushite crystals. Mg-doped ceramics composed of Mg-substituted β-TCP, stanfieldite and/or farringtonite were reacted with primary monocalcium phosphate (MCP) in the presence of water. The cement setting reaction has resulted in the formation of brushite and newberyite within the cement matrix. Interestingly, the combination of SAED and EDX analyses of single crystal has indicated the occurrence of magnesium substitution within brushite crystals. Moreover, the effect of magnesium ions on the structure, and mechanical and setting properties of the new cements was characterized as well as the release of Ca^2 + and Mg^2 + ions. Further research would enhance the efficiency of the system to incorporate larger amounts of magnesium ions within brushite crystals.     

Effects on high magnetic fields on the microstructure of Al-Al2Cu eutectic

Effect of a high magnetic field on the Al-Al₂Cu eutectic growth has been investigated. It has been found that the application of the magnetic field has aligned the eutectic grains with the < 001>-crystal direction of the Al₂Cu phase along the magnetic field. Moreover, it has been proved experimentally that the Al₂Cu crystal owns the remarkable magnetocrystalline anisotropy. Therefore, the alignment of the Al-Al₂Cu eutectic under the magnetic field may be attributed to the orientation of the Al₂Cu crystal.     

Radiation synthesis of gelatin/CM-chitosan/β-tricalcium phosphate composite scaffold for bone tissue engineering

A series of biodegradable composite scaffolds was fabricated from an aqueous solution of gelatin, carboxymethyl chitosan (CM-chitosan) and β-tricalcium phosphate (β-TCP) by radiation-induced crosslinking at ambient temperature. Ultrasonic treatment on the polymer solutions significantly influenced the distribution of β-TCP particles. An ultrasonic time of 20 min, followed by 30 kGy irradiation induced a crosslinked scaffold with homogeneous distribution of β-TCP particles, interconnected porous structure, sound swelling capacity and mechanical strength. Fourier Transform Infrared Spectroscopy and X-ray Diffraction analysis indicated that β-TCP successfully incorporated with the network of gelatin and CM-chitosan. In vivo implantation of the scaffold into the mandible of beagle dog revealed that the scaffolds had excellent biocompatibility and the presence of β-TCP can accelerate bone regeneration. The comprehensive results of this study paved way for the application of gelatin/CM-chitosan/β-TCP composite scaffolds as candidate of bone tissue engineering material.     

Electromechanical properties of [0 0 1], [0 1 1] and [1 1 1] oriented Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 crystals under uniaxial stress

The electric field and the stress induced strain and polarization responses of [0 0 1], [0 1 1] and [1 1 1] oriented Pb(Mg_1/3Nb_2/3)O₃–0.32PbTiO₃ (PMN–0.32PT) relaxor ferroelectric single crystals have been systematically investigated by experimental study. The responses of [0 0 1] oriented single crystal to stress cycle and electric field are explained by polarization rotation and phase transformations mechanism. However, the responses of [0 1 1] and [1 1 1] oriented single crystal should be explained by domain switching. The differences of strain and polarization between the minimum and maximal values of electric field in [0 0 1] orientation firstly increase then decrease with enhancing of compressive stress.     

Selective laser sintering of β-TCP/nano-58S composite scaffolds with improved mechanical properties

Nano-sized 58S bioactive glass (nano-58S) as the dispersed phase was added to β-tricalcium phosphate (β-TCP) to reinforce the mechanical properties, and then the β-TCP/nano-58S composite scaffolds were prepared via selective laser sintering (SLS). The effects of nano-58S on microstructure, mechanical properties, bioactivity, and biocompatibility of the composite scaffolds were evaluated. The results showed that nano-58S was homogeneously dispersed in the β-TCP matrix and the mechanical properties were gradually improved when the amount of nano-58S was no more than a certain value (15 wt.%). However, exceeding this value, nano-58S became the continuous phase and exhibited the brittleness of bioactive glass. Accordingly, the mechanical properties gradually decreased. The maximum fracture toughness and compressive strength were 1.347 ± 0.025 MPa · m^1/2 and 18.2 ± 0.62 MPa, respectively. In vitro tests in the simulated body fluid (SBF) demonstrated that the apatite-like layer formed faster on the composite scaffolds than on the scaffold without nano-58S, indicating that the nano-58S glass could enhance the bioactivity of the composite scaffolds. The MG-63 cells culture experiment proved that nano-58S glass could further facilitate the growth of human osteoblastic cells.