Graphene-oxide-modified β-tricalcium phosphate bioceramics stimulate in vitro and in vivo osteogenesis

Graphene oxide (GO) has attracted much interest for applications in bone tissue engineering; however, until now, the interaction between GO and stem cells, and the in vivo bone-forming ability of GO have not been explored. The aim of this study was to produce GO-modified β-tricalcium phosphate (β-TCP-GRA) bioceramics and then explore the material’s osteogenic capacity in vitro and in vivo, as well as unravel some of the molecular mechanisms behind this. β-TCP-GRA disks and scaffolds were successfully prepared by a simple GO/water suspension soaking method in combination with heat treatment. These scaffolds were found to significantly enhance the proliferation, alkaline phosphatase activity, and osteogenic gene expression of human bone marrow stromal cells (hBMSCs), when compared with β-TCP without GO modification (controls). Activation of the Wnt/β-catenin signaling pathway in hBMSCs appears to be the mechanism behind this osteogenic induction by β-TCP-GRA. β-TCP-GRA scaffolds led to an increased rate of in vivo new bone formation compared to β-TCP controls, indicative of the stimulatory effect of GO on in vivo osteogenesis, making GO modification of β-TCP a very promising method for applications in bone tissue engineering, in particular for the regeneration of large bone defects.     

Clarifying the effect of sintering conditions on the microstructure and mechanical properties of β-tricalcium phosphate

The effect of the sintering conditions (temperature and time) on the microstructure (density and grain size) and mechanical properties (hardness, elastic modulus, and strength) of β-tricalcium phosphate (β-TCP) bioceramics fabricated from Ca-deficient commercial powders is analyzed. Contrary to current general opinion, it is demonstrated that the optimal sintering temperature to maximize the mechanical performance of this β-TCP material is not necessarily below the β ? α transformation temperature (1125 °C). In particular, optimal performance was achieved in samples sintered at 1200 °C for 3 h, since it was not until higher temperatures or longer sintering times that microcracking develops and mechanical properties are degraded. It is argued that the residual stresses developed during this reversible transformation do not lead to microcrack propagation until sufficiently large starting flaws develop in the microstructure as a consequence of grain growth. Implications of these findings for the processing routes to improve sintering of this important bioceramic are discussed.     

Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.     

Influences of gallium substitution on the phase stability,mechanical strength and cellular response of β-tricalcium phosphate bioceramics

β-tricalcium phosphate (β-TCP), a well-accepted synthetic bone grafting biomaterial, is confronted with limitations of poor phase stability and lacking the capacity to mediate the biological functions. In the current study, gallium (Ga) was substituted for calcium in the β-TCP, and the influences of Ga substitution on the phase stability, compressive strength and cellular response of β-TCP bioceramics were investigated. The results indicated that substitution of at least 2.5 mol% Ga for calcium prevented the β-TCP from transforming into α-TCP at 1250 °C. The β-TCP bioceramics substituted with 2.5 mol% Ga attained the highest compressive strength. The β-TCP bioceramics substituted with 2.5 and 5 mol% Ga showed good cytocompatibility, and suppressed in vitro osteoclastic activity as well as osteoblastic differentiation. Considering the favorable mechanical strength and the inhibitory effect on the osteoclastic activity, the β-TCP bioceramics substituted with 2.5 mol% Ga are promising for treating the bone defect in the pathological state of excessively rapid bone resorption.     

Novel method for the synthesis of a β-tricalcium phosphate coating on a zirconia implant

A novel method for the synthesis of a thin β-tricalcium phosphate (β-TCP) coating on zirconia implants has been developed. The synthesis procedure involves two steps: (i) rapid wet-chemical deposition of a biomimetic CaP coating and (ii) subsequent post-deposition processing of the biomimetic CaP coating, which includes a heat treatment at 900 °C followed by a short sonication in a water bath. The obtained β-TCP coating showed a uniform and dense morphology with a thickness of ≈500 nm and displayed a roughness in the nanometre range (R_a = 28 nm). The β-TCP coating demonstrated an apatite-mineralization ability in a simulated body fluid and enhanced the adsorption of serum proteins on the zirconia. Moreover, the β-TCP coating adhered firmly to the zirconia substrate, developing a notable scratch resistance (L_c = 97 N) and tensile strength (52 MPa) and showed strong resistance towards mechanical forces present during implantation of the coated zirconia implant into the artificial bone.     

Fabrication and characterization of porous β-tricalcium phosphate scaffolds coated with alginate

All porous materials have a common limitation which is lack of strength due to the porosity. In this study, two different methods have been used to produce porous β-tricalcium phosphate (β-TCP) scaffolds: liquid-nitrogen freeze casting and a combination of the direct-foaming and sacrificial-template methods. Among these two methods, porous β-TCP scaffolds with acceptable pore size and compressive strength and defined pore-channel interconnectivity were successfully fabricated by the combined direct-foaming and sacrificial-template method. The average pore size of the scaffolds was in the range of 100–150 µm and the porosity was around 70%. Coating with 4 wt% alginate on porous β-TCP scaffolds led to higher compressive strength and low porosity. In order to make a chemical link between the β-TCP scaffolds and the alginate coating, silane coupling agent was used. Treated β-TCP scaffold showed improvements in compressive strength of up to 38% compared to the pure β-TCP scaffold and 11% compared to coated β-TCP scaffold.     

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.     

Improvements in phase stability and densification of β-tricalcium phosphate bioceramics by strontium-containing phosphate-based glass additive

β-tricalcium phosphate (β-TCP), which transforms to α-TCP at around 1125?°C, is characterized by poor sinterability. In this study, for the first time strontium-containing phosphate-based glass (SPG) was used as a sintering additive for β-TCP, which was sintered at 1250?°C. The results indicated that the SPG additive allowed for liquid-state sintering of β-TCP, thereby noticeably promoting the densification of β-TCP bioceramics. In the sintering process SPG reacted with β-TCP, and the metal ions from SPG were substituted for the calcium ions of β-TCP. The SPG additive effectively inhibited the phase transformation of β-TCP to α-TCP in the bioceramics. The compressive strength of porous β-TCP bioceramics was markedly increased by introducing 10?wt% SPG. The SPG is considered as an effective sintering additive to improve the phase stability and mechanical strength of porous β-TCP bioceramics.     

Preparation of biphasic hydroxyapatite/ β-tricalcium phosphate foam using the replication technique

Biphasic hydroxyapatite/β-tricalcium phosphate foams were prepared using the replication technique starting from a precipitated hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAP) powder, and sodium glycerophosphate (GP). The effect of the grinding time, solid loading, dispersant amount, and etching, replication, and sintering processes were investigated. The SEM, OEM and FTIR analyses proved that the surface of the polyurethane template must be treated with NaOH solution to make it more hydrophilic prior to the coating process. With a solid loading of 40 wt-%, the slurries prepared from the precipitated hydroxyapatite presented a shear thinning behavior, which was useful for the coating process. The SEM analysis of the foams showed that the optimum number of coating layers to obtain foam with an identical structure with the template was limited to three. The use of GP and the optimized preparation parameters helped to decrease the consolidation temperature of the ceramic foams to 1000 °C. The XRD and FTIR analyses of the prepared foams showed that the thermal treatment of the GP and the HAP mixture led to a partial decomposition of the HAP to tricalcium phosphate. The fitting of the XRD patterns and the obtained lattice parameters proved that the decomposition was accompanied by the insertion of sodium from GP toward the lattice of tricalcium phosphate and the formation of Na-β-tricalcium. The results of the SEM analysis, the pore size distribution and the mechanical strength showed that the presence of the Na-β-tricalcium reduced the pore size distribution from 500-2700 to 100–1700 μm, decreased slightly the total porosity from 80 vol-% to 70 vol-%; and improved the mechanical strength of the obtained foam from 1.56 MPa to 2.60 MPa.     

Effect of graphite particles as additive on the curing behaviour of β-tricalcium phosphate suspensions and scaffold fabrication by digital light processing

Reducing the viscosity of high solid-loading ceramic suspensions and controlling the resolution of ceramic green parts produced by digital light processing (DLP) 3D printing are two important concerns in the ceramic additive manufacturing industry. The presence of ceramic particles within a photopolymerizable system leads to light scattering that reduces the resolution of the ceramic green scaffolds. This study introduced a graphite additive to solve these problems and focused on the effects of graphite concentration on the viscosity, curing behaviour and scaffold fabrication of β-TCP ceramic suspensions. As a result, it was found that an appropriate addition of graphite reduced the viscosity of the ceramic suspensions, and the light scattering decreased with the increase of graphite concentration. Both the cure depth (C_d) and excess width (C_ex) also decreased with the increase of graphite concentration. But, graphite has a larger effect on the width curing than depth curing.     

Gelatin-layered and multi-sized porous β-tricalcium phosphate for tissue engineering scaffold

The multi-sized porous β-tricalcium phosphate scaffolds were fabricated by freeze drying followed by slurry coating using a multi-sized porous sponge as a template. Then, gelatin was dip coated on the multi-sized porous β-tricalcium phosphate scaffolds under vacuum. The mechanical and biological properties of the fabricated scaffolds were evaluated and compared to the uniformly sized porous scaffolds and scaffolds that were not coated by gelatin. The compressive strength was tested by a universal testing machine, and the cell viability and differentiation behavior were measured using a cell counting kit and alkaline phosphatase activity using the MC3T3-E1 cells. In comparison, the gelatin-coated multi-sized porous β-tricalcium phosphate scaffold showed enhanced compressive strength. After 14 days, the multi-sized pores were shown to affect cell differentiation, and gelatin coatings were shown to affect the cell viability and differentiation. The results of this study demonstrated that the multi-sized porous β-tricalcium phosphate scaffold coated by gelatin enhanced the mechanical and biological strengths.     

Effects of Sr2+/Zn2+ co-substitution on crystal structure and properties of nano-β-tricalcium phosphate

The incorporation of therapeutic ions like Sr²⁺, Si⁴⁺, Zn²⁺ and Li⁺ into biomaterials has become a promising approach to promote bone regeneration. However, the effects of Sr²⁺ and Zn²⁺ co-substitution on the crystal structure and properties of β-tricalcium phosphate (β-TCP) have not been elucidated well. In this study, Sr²⁺/Zn²⁺ co-substituted β-tricalcium phosphate (SrZnTCP) nano-powders with different extents of substitution (0–4.8 mol%) were synthesized by poly(ethylene glycol)-assisted co-precipitation and subsequent heat treatment. The as-synthesized SrZnTCP nano-powders were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, Rietveld refinement and differential scanning calorimetry. The results showed that the conversion of calcium-deficient apatite to β-TCP was achieved after heat-treatment above 800 °C. The a-axis and c-axis lattice parameters gradually decreased with increasing level of Sr²⁺/Zn²⁺ co-substitution in β-TCP lattice. Sr²⁺ and Zn²⁺ preferentially occupied the ninefold coordinated Ca (4) sites and the sixfold coordinated Ca (5) sites, respectively. The co-substitution of Sr²⁺ and Zn²⁺ for Ca²⁺ significantly improved the thermal stability of β-TCP. The release rate of Zn²⁺ from SrZnTCP depended on Ca²⁺ concentration over 63-day immersion in PBS solution while that of Sr²⁺ was not affected by Ca²⁺ concentration. The amount of Sr²⁺ released increased with increasing Sr²⁺ content in SrZnTCP. Collectively, SrZnTCP showed great promise as a Sr²⁺/Zn²⁺-releasing biomaterial for bone repair, although no obvious mineralization was observed on β-TCP and SrZnTCP disc samples during 56 days of immersion in simulated body fluid.     

Enhancement of mechanical strength and osteogenesis,and inhibition of osteoclastic activity for β-tricalcium phosphate bioceramics by incorporating calcium silicate and magnesium-strontium phosphate

β-tricalcium phosphate bioceramics suffer from a drawback of poor mechanical strength and a scarcity of capacity to regulate biological performances. In the current study, the overall performances of β-tricalcium phosphate (TCP) bioceramics were improved by incorporating calcium silicate (CS) and magnesium-strontium phosphate (MSP). During the sintering process, the MSP stabilized the β phase of TCP, and the formation of MSP melt ensured effective liquid-sintering of TCP, thus conducing to lower porosity of TCP/MSP and TCP/CS/MSP bioceramics. In comparison with the TCP bioceramics, the TCP/CS and TCP/MSP bioceramics showed lower compressive strength, while the TCP/CS/MSP bioceramics attained noticeably higher compressive strength. Due to the sustained release of therapeutical ions, the TCP/CS bioceramics enhanced in vitro early-stage osteoblastic differentiation, but compromised cell proliferation; both the TCP/MSP and TCP/CS/MSP bioceramics enhanced cell proliferation and osteoblastic differentiation, and restrained osteoclastic activities. Collectively, the TCP/CS/MSP bioceramics with optimal overall performances are promising for efficaciously treating the defects of osteoporotic bone.     

Fabrication and characterization of porous biphasic β-tricalcium phosphate/carbonate apatite alginate coated scaffolds

In this research, biphasic β-tricalcium phosphate/carbonate apatite (β-TCP/CO₃Ap) scaffolds incorporated with alginate were fabricated. Sodium alginate was extracted from local brown seaweed, Sargassum polycystum via calcium alginate process. Biphasic β-TCP/CO₃Ap scaffolds were fabricated by polymer reticulate method. β-TCP slurry was infiltrated into the polyurethane foam (PU) foam, then sintered up to 1300?°C, soaked for 4?h and immediately quenched in still air to form biphasic β-TCP/α-TCP scaffold. Biphasic β-TCP/α-TCP scaffold was then transformed to biphasic β-TCP/CO₃Ap scaffold by dissolution-precipitation reaction with 1?M of NaHCO₃ at 170?°C for 1, 3 and 5 days. Biphasic β-TCP/CO₃Ap scaffold from 5 days dissolution-precipitation reaction was chosen to incorporate with 1%, 3% and 5% of sodium alginate, respectively, as it has the highest composition of CO₃Ap phase. FTIR and FESEM analysis confirmed the presence of characteristic functional groups of sodium alginate. Mechanical strength of biphasic β-TCP/CO₃Ap scaffold improved by increasing the concentration of sodium alginate. The highest mechanical strength achieved was 26.38 kPa for biphasic β-TCP/CO₃Ap scaffold with 5% sodium alginate coating and it was chosen to further study with the addition of 1%, 3% and 5% microspheres. FESEM analysis confirmed the attachment of microspheres on the surface of alginate/biphasic β-TCP/CO₃Ap scaffold was successful.     

Improvement of mechanical properties of macroporous β-tricalcium phosphate bioceramic scaffolds with uniform and interconnected pore structures

The biocompatible and degradable macroporous bioceramic scaffolds with high mechanical properties and interconnected porous structures play an important role in hard tissue regeneration and bone tissue engineering applications. In this study, the improvement of mechanical properties of macroporous β-tricalcium phosphate [β-Ca₃(PO₄)₂, β-TCP] bioceramic scaffolds with uniform macropore size and interconnected pores were fabricated by impregnation of the synthesized β-TCP nano-powder slurry into polymeric frames. The microstructures, mechanical properties and in vitro degradation of the fabricated samples were investigated. For a comparison, β-TCP scaffolds were also fabricated from commercial micro-size powders under the same conditions. The resultant scaffolds showed porosities ∼65% with uniform macropore size ranging from 400 to 550 μm and interconnected pore size ∼100 μm. The compressive strength of the samples fabricated from nano-size powders reached 10.87 MPa, which was almost twice as high as those fabricated from commercial micro-size powders, and was comparable to the high-end value (2–10 MPa) of human cancellous bone. Furthermore, the degradation of the β-TCP bioceramics fabricated from nano-size powders was apparently lower than those fabricated from commercial micro-size powders, suggesting the possible control of the degradation of the scaffolds by regulating initial powder size. Regarding the excellent mechanical properties and porous structures, the obtained macroporous β-TCP bioceramic scaffolds can be used in hard tissue regeneration and bone tissue engineering applications.     

Effects of the structure of CeCu catalysts on the catalytic combustion of toluene in air

CeCu composite oxide catalysts were prepared by a hard-template method (CeCu-HT) and a complex method (CeCu-CA). The prepared CeCu composite oxide catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) analyses. The catalytic properties of the prepared CeCu composite oxide catalysts were also investigated by the catalytic combustion of toluene in air. XRD results showed that the synthesized CeCu composite oxide catalysts had different phase components and crystallinities but similar CeO₂CuO solid solution phases. Low-angle XRD, TEM, and BET results indicated that the prepared CeCu-HT catalyst had a developed ordered mesoporous structure and a large specific surface area of 206.1 m² g^?1. Toluene catalytic combustion results indicated that the CeCu-HT catalyst had higher toluene catalytic combustion activity in air than the CeCu-CA catalyst. The minimum reaction temperature at which toluene conversion exceeded 90% for toluene catalytic combustion on the CeCu-HT catalyst was 225 °C. The toluene catalytic combustion conversion on the CeCu-HT catalyst at 240 °C exceeded 99.3% with decreased toluene concentration in air to below 70 ppm. On the other hand, the toluene catalytic combustion conversion on the CeCu-CA catalyst was only 92% even when the reaction temperature reached 280 °C. The differences between the toluene catalytic combustion performances of the CeCu composite oxide catalysts prepared by different methods can be attributed to their discrepant compositions and structures.     

The biological properties of carbon nanofibers decorated with β-tricalcium phosphate nanoparticles

Carbon nanofibers decorated with β-tricalcium phosphate (β-TCP) nanoparticles (β-TCP/CNFs) have been prepared by sintering electrospun polyacrylonitrile fibers with calcium nitrate tetrahydrate as the calcium source and triethyl phosphate as the phosphorus source. Microstructure and phase composition analysis indicate that the resulting materials are composed of β-TCP nanoparticles and CNFs. And the long β-TCP/CNFs can be cut into organism-eliminable short CNFs gradually in hydrochloric acid solution due to the solubilization of β-TCP nanoparticles. The materials exhibit good biocompatibility, and have comparable effect on cell growth with pure CNFs, with their tuning ability in degradation.     

Mechanochemically synthesized phase stable and biocompatible β-tricalcium phosphate from avian eggshell for the development of tissue ingrowth system

Bioceramics obtained from naturally derived materials are gaining much interest as implants for bone and dental defects. The present study aims to synthesize phase stable β-tricalcium phosphate (β-TCP) from avian eggshell assisted with ball milling process followed by a wet chemical precipitation method (Group CPM). The effect of mechanical stimulation on phase conversion of CaO was also studied. The study was carried alongside the powders synthesized from chemical precursors (Group CPS) as well as eggshell derived powders without ball milling process (Group CPN). The phase behaviour and surface morphology were studied by XRD, FT-IR, and SEM analysis. Scaffolds were fabricated using sponge replication method to simulate a potential bone graft analogue. The cytocompatibility study was performed by human adipose-derived stem cells (ADSCs) over a period of 21 days by live-dead assay and Alamar blue dye reduction assay. The process of mechanically stimulating CaO precursor through extensive milling plays a major role on phase stabilization of β-TCP, as compared to the mixed phases of Hydroxyapatite (HAp) and β-TCP formed from unmilled CaO. Group CPN scaffolds were found to be biologically equivalent to group CPS scaffolds. This novel route, aided with ball-milling process for the synthesis of β-TCP from naturally occurring eggshell waste seems promising enough to replace commercially available β-TCP produced from harmful nitrate precursors and has the capability to develop implantable biomaterial for tissue regeneration.     

DLP printed β-tricalcium phosphate functionalized ceramic scaffolds promoted angiogenesis and osteogenesis in long bone defects

Nowadays, the repair of long bone defects remains a clinical challenge mainly due to poor oxygen and nutrients delivery. In this study, β-tricalcium phosphate (β-TCP) porous ceramic scaffolds were prepared by digital light processing (DLP) and gradient sintering process. The functionalization of scaffolds was achieved by loading hyaluronic acid-dopamine (HA-DA) coating or sphingosine 1-phosphate/hyaluronic acid-dopamine (S1P/HA-DA) coating, which solved the problem of oxygen and nutrients delivery to a certain extent by promoting blood vessels growth. Cytocompatibility assay, qRT-PCR, Alkaline phosphatase (ALP) staining and quantitative analysis demonstrated that the S1P/HA-DA/TCP scaffolds significantly promoted the proliferation and osteogenic differentiation of mouse bone marrow mesenchymal stem cells (mBMSCs). Long bone defects (22 mm), rarely reported in previous studies, were constructed on the radius of rabbits. Animal experiments showed excellent early angiogenesis and bone repair in HA-DA/TCP and S1P/HA-DA/TCP groups. In particular, the S1P/HA-DA/TCP scaffolds enhanced bone regeneration and osseointegration. Overall, these functionalized scaffolds had an effective repair on long bone defects that would have great potential for clinical applications.