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 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.     

Fabrication of cancellous-bone-mimicking β-tricalcium phosphate bioceramic scaffolds with tunable architecture and mechanical strength by stereolithography 3D printing

It is highly challenging to fabricate bioceramic scaffolds mimicking architecture and mechanical strength of cancellous bone. Gyroid structure, which is based on triply periodic minimal surface, highly resembles the architecture of cancellous bone. Herein, β-tricalcium phosphate (β-TCP) bioceramic scaffolds with gyroid structure were fabricated by stereolithography (SLA) 3D printing. The SLA 3D printing ensured high precision of ceramic part. The porosity (51–87%), pore size (250 – 2400 µm), pore wall thickness (< 300 µm) and compressive strength (0.6 – 16.8 MPa) of gyroid bioceramic scaffolds were readily adjusted to match various sites of cancellous bone. The gyroid bioceramic scaffolds were more favorable for cell proliferation than the grid-like bioceramic scaffolds. The cancellous-bone-mimicking gyroid bioceramic scaffolds with tunable architecture and mechanical strength were expected to efficiently repair the target bone defects.     

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.     

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.     

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.     

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.     

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.     

Synthesis and characterization of hydroxyapatite/β-tricalcium phosphate nanocomposites using microwave irradiation

Microwave assisted synthesis method is a relatively new approach employed to decrease synthesis time and form a more homogenous structure in biphasic calcium phosphate bioceramics. In this study, nanocrystalline HA/β-TCP composites were prepared by microwave assisted synthesis method and, for comparison reason, by conventional wet chemical methods. The chemical and phase composition, morphology and particle size of powders were characterized by FTIR, XRD and SEM, respectively. The use of microwave irradiation resulted in improved crystallinity. The amount of hydroxyapatite phase in BCP ranged from 5% to 17%. The assessment of bioactivity was done by soaking of powder compacts in simulated body fluid (SBF). The decreasing pH of the solution in the presence of β-TCP indicated its biodegradable behavior. Rod-like hydroxyapatite particles were newly formed during the treatment in SBF for microwave assisted substrate synthesis. In contrast, globular particles precipitate under same conditions if BCP substrates were synthesized using conventional wet chemical methods.     

Effects of Mn-doping on the structure and in vitro degradation of β-tricalcium phosphate

β-tricalcium phosphate (β-TCP) is an ideal biomaterial for the bone repair because of its biocompatibility and biodegradability. In this study, 0 mol%, 5 mol%, 15 mol% and 30%mol bivalent manganese ion (Mn²⁺) doped β-TCP (Mn-TCP) powders were synthesized by a sol-gel method. The amount of the dopants significantly influences the crystallinity and the parameters related with structure of β-TCP, such as the lattice parameters and crystallite dimensions. The particle size and the particle distribution of doped β-TCP powers were evaluated as well. Meanwhile, the as-synthesized powders were consolidated by sintering at 1000 °C in muffle furnace for 5 h to get Mn-TCP porous material and the degradation experiment was carried out in Simulated Body Fluid (SBF) solution for 28 days. Then, Mn-TCP porous material were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). Significantly, there were bone-like apatite materials deposited on the surface of bone-like porous materials. With the increasing doping amount of Mn²⁺, the newly formed apatite-like materials decreased, while the crystallinity increased significantly. Besides, pH results showed that alkaline environment was more favorable for the formation of sedimentary materials.     

Fabrication and characterization of multiwalled carbon nanotube–loaded interconnected porous nanocomposite scaffolds

Novel nanocomposite porous scaffolds based on poly(?-caprolactone) (PCL) and multiwalled carbon nanotubes (MWCNTs) were manufactured by a compression-molding/polymer-leaching approach utilizing cryomilling for homogeneous dispersion of nanotubes and blending of polymers. Addition of MWCNTs to PCL and PCL/polyglycolide (PGA) blends resulted in significant changes to scaffold morphology compared to control samples despite persistent interconnected porosity. Several structures exhibiting rough and nanotextured surfaces were observed. Mean pore sizes were in the range of ～3–5?µm. The nanocomposites presented good mechanical and water uptake properties. The results of this research provide significant insight into a strategy for producing nanocomposite scaffolds with interconnected porosity.     

Preparation and characterization of iron/β-tricalcium phosphate bio-cermets for load-bearing bone substitutes

Ceramic-metal composite materials, namely cermets, are provided with characteristics of both ceramic and metal. Herein, for the first time bio-cermets based on β-tricalcium phosphate (β-TCP) bioceramic with biodegradable iron being reinforcement phase, were fabricated using the powder metallurgic method. The phase composition, microstructure, mechanical properties and in vitro cell behaviors of bio-cermets were investigated. The results revealed that atomic diffusion occurred between the iron and β-TCP matrix during the sintering process. The bio-cermets attained remarkable increase in fracture toughness (1.16–1.55 MPa m^1/2) compared to the β-TCP bioceramic (0.54 MPa m^1/2). The bio-cermets with 10 vol% iron showed the highest compressive strength (640 MPa), significantly higher than that of plain β-TCP bioceramic (285 MPa). The in vitro cell behaviors test indicated that the bio-cermets did not showed any sign of toxicity; the iron ions released from bio-cermets up-regulated bone-related gene expression of bone mesenchymal stem cells. The bio-cermets developed in this study represent potential bone substitutes for application in the load-bearing bone defects.     

Fabrication and properties of porous β-tricalcium phosphate ceramics prepared using a double slip-casting method using slips with different viscosities

A new method to enhance the flexural strength of porous β-tricalcium phosphate (β-TCP) scaffolds was developed. This new method provides better control over the microstructures of the scaffolds and enhances the scaffolds’ mechanical properties. Using this technique, we were able to produce scaffolds with mechanical and structural properties that cannot be attained by either the polymer sponge or slip-casting methods alone or by simply combining the polymer sponge and slip-casting methods. The prepared scaffolds had an open, uniform, interconnected porous structure with a bimodal pore size of 100.0–300.0 μm. The flexural strength of the bimodal porous β-TCP scaffold sintered at 1200 °C was 56.2 MPa and had porosity of 61.4 vol%. The scaffolds obtained provide good mechanical support while maintaining bioactivity, and hence, these bioscaffolds hold promise for applications in hard-tissue engineering.     

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.     

Microstructural,mechanical properties and strengthening mechanism of DLP produced β-tricalcium phosphate scaffolds by incorporation of MgO/ZnO/58S bioglass

The inherent brittleness of bioceramics restricts their applications in load-bearing implant, although they possess good biocompatibility and bioactivity. ZnO, MgO and 58S bioglass (BG) were incorporated as additives to further improve the mechanical properties and biocompatibility of β-TCP and ZnO/MgO/BG-β-TCP composite scaffolds were manufactured via digital light processing (DLP). The composite with the best comprehensive performance was selected for degradation behavior and biocompatibility evaluation. The effects of different proportions of ZnO/MgO/BG on mechanical strength were analyzed and ZnO0·5/MgO1/BG2-β-TCP (ZMBT) samples exhibited superior mechanical strength. The improvement by 272% and 99% respectively was achieved in fracture toughness and compressive strength with the optimal recipe. The enhancement effect is realized through phase transition, alterative sliding actions and transgranular fracture to effectively prevent the load transfer combining the functions of bioglass and metal oxide. ZMBT scaffolds exhibited a more desirable pH environment and an enhanced ability of apatite-mineralization formation, meanwhile Si⁴⁺, Mg²⁺ and Zn²⁺ were gradually released from scaffolds. Furthermore, in vitro evaluation indicated that ZMBT scaffolds presented not only excellent cell attachment, proliferation, alkaline phosphatase (ALP) activity, but they up-regulated osteogenic gene (ALP, OCN, Runx2). These results suggest that the addition of ZnO/MgO/BG to DLP-printed β-TCP scaffolds offer a smart strategy to fabricate porous scaffolds with conspicuously better biological and physicochemical properties including compressive strength, bioactivity, osteogenesis and osteogenesis-related gene expression. Metal-oxide and BG synergistically enhanced the mechanical and biological properties which make the ZMBT scaffolds a strong candidate for bone repair applications.     

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.     

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.     

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.     

Fabrication and characterization of poly(ε-caprolactone)/gelatin nanofibrous scaffolds for retinal tissue engineering

Different ratios of poly(ε-caprolactone) (PCL) and gelatinwere used to fabricate scaffolds for regeneration of retinal pigment epithelium (RPE) layer. Physical and chemical characterizations were performed and the behavior of human RPE cells on the scaffolds was evaluated subsequently. An increase in gelatin content in the scaffold enhanced hydrophilicity, RPE cell attachment, proliferation, and spreading over PCL scaffolds. Granular and cytoplasmic expressions of RPE65 and Cytokeratin 8/18 markers confirmed the presence of RPE cells. It was believed that PCL/gelatin scaffolds could be used as substrates to replace RPE extracellular matrix to facilitate regeneration of RPE layer in retinal diseases.     

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.