Highly porous titanium (Ti) scaffolds with bioactive microporous hydroxyapatite/TiO2 hybrid coating layer

Highly porous Ti scaffolds with a bioactive microporous hydroxyapatite (HA)/TiO₂ hybrid coating layer were fabricated using the sponge replication process and micro-arc oxidation (MAO) treatment to produce the porous Ti scaffold and hybrid coating layer, respectively. In particular, the morphology and chemical composition of the hybrid coating layer were controlled by carrying out the MAO treatment in electrolyte solutions containing various concentrations of HA, ranging from 0 to 30 wt.%. The fabricated sample showed high porosity of approximately 70 vol.% with interconnected pores and reasonably high compressive strength of 18 ± 0.3 MPa. Furthermore, the surfaces could be coated successfully with a bioactive microporous HA/TiO₂ hybrid layer. The amount of HA particles in the hybrid coating layer increased with increasing HA content in the electrolyte solution, while preserving the microporous morphology. This hybrid coating improved the osteoblastic activity of the porous Ti scaffolds significantly.     

Fabrication of porous titanium scaffolds with high compressive strength using camphene-based freeze casting

We herein report the fabrication of highly porous titanium (Ti) scaffolds with unusually high compressive strength by freezing a titanium hydride (TiH₂)/camphene slurries at 42 °C. As the freezing time was increased from 1 to 7 days, the pore size obtained was increased significantly from 143 to 271 μm due to the continual overgrowth of camphene dendrites. However, interestingly, the formation of the micro-pores inside the Ti walls was suppressed at longer freezing time. This resulted in a significant increase in compressive strength up to 110 ± 17 MPa with a porosity of 64%. It is believed that this unusually high compressive strength with large interconnected pores makes this material suitable for applications as load-bearing parts.     

Development of highly porous titanium scaffolds by selective laser melting

The selective laser melting (SLM) of the TiH₂-Ti blended powder was performed in the present work. Porous titanium scaffolds characterized by high porosity (∼ 70%), interconnected Ti walls and open porous structures with macroscopic pores (in a range of ∼ 200 to ∼ 500 μm) were successfully prepared at a laser power of 1000 W and a scan speed of 0.02 m/s. The effects of componential and processing conditions in terms of TiH₂ content and scan speed on the microstructural development of porous titanium (porosity and pores size) were investigated. Reasonable mechanisms for pores formation during SLM apart from microstructural evolutions were proposed.     

Porous titanium (Ti) scaffolds by freezing TiH2/camphene slurries

Porous titanium (Ti) scaffolds with interconnected pores were fabricated by freezing titanium hydride (TiH₂)/camphene slurries at 33 °C for 24 h, followed by freeze-drying and subsequent heat-treatment at 1300 °C for 2 h in vacuum. All of the fabricated samples revealed highly porous structures having large pores up to 100 μm in size surrounded by Ti metal walls without any secondary phases. When the initial TiH₂ content was increased from 15 to 25 vol.%, the porosity was decreased from 63 to 49%, while the compressive strength was significantly improved from 81 to 253 MPa.     

Nanostructured bioactive glass coating on porous hydroxyapatite scaffold for strength enhancement

Many attempts have been focused on preparing highly porous scaffolds with appropriate mechanical strength. This paper has developed a new route to enhance the compressive strength of porous HA (hydroxyapatite) scaffold (porosity: ∼ 83%, mean pore size:∼ 800 μm). Briefly this route included nanostructure coating of bioactive glass on struts of porous HA. Coating microstructure consisted of the grains with the range between 91 and 320 nm and micron size pores that could be detected by SEM observation. This simple method improved the compressive strength of highly porous HA from 0.22 to 1.49 MPa. The obtained scaffolds provided good mechanical support while maintaining bioactivity so they could be used as tissue engineering scaffolds for low-load bearing applications.     

Highly porous hydroxyapatite scaffolds with elongated pores using stretched polymeric sponges as novel template

This study reports a simple way of improving the compressive strength of highly porous hydroxyapatite (HA) scaffolds by adopting elongated polymeric sponges as a novel template. In this method, as-received polymeric sponges with isotropic pores were stretched uniaxially to 50% elongation at 200 °C for 2 h, and then coated with a HA slurry. The HA-coated sponges were heat-treated at 800 °C for 3 h to remove the polymeric sponges and at 1250 °C for 3 h to sinter the HA walls. The fabricated samples showed a highly anisotropic pore structure with elongated pores parallel to the direction of the elongation of the polymeric sponge. This simple method allowed a highly porous scaffold to have a high compressive strength of 3.8 ± 0.1 MPa at a porosity of 76% when tested parallel to the direction of pore elongation.     

Improving the strength and biocompatibility of porous titanium scaffolds by creating elongated pores coated with a bioactive, nanoporous TiO2 layer

This paper reports a novel way of improving the mechanical properties and biocompatibility of porous Ti scaffolds using a combination of the modified sponge replication method and anodization process. The use of a stretched polymeric sponge as a novel template allowed the creation of elongated pores in a porous Ti scaffold, which, accordingly, led to a high compressive strength of 24.2 ± 2.08 MPa at a porosity of approximately 70 vol%. Furthermore, the surfaces of the Ti walls were coated successfully with a bioactive nanoporous TiO₂ layer using the anodization process, which enhanced the biocompatibility remarkably, as assessed by the attachment of MC3T3-E1 cells.     

Fabrication and characterization of novel hydroxyapatite/porous carbon composite scaffolds

Novel hydroxyapatite (HA)/porous carbon composite scaffolds were prepared by applying sonoelectrodeposition and a subsequent hydrothermal treatment to previous carbonized phenolic resin coated polyurethane sponges. The interconnected pore network and morphology of HA/porous carbon composite scaffolds were determined by scanning electron microscope (SEM), and the whole surface of porous carbons were evenly coated with the deposited HA layer which was confirmed by EDS and XRD. The porosity (83.5 ± 0.3%) and the bulk density (0.297 ± 0.009 g·cm⁻³) of HA/porous carbon scaffolds were detected by the Archimedes method. The compressive and flexural strength of the scaffolds is 1.187 ± 0.064 MPa and 0.607 ± 0.268 MPa, respectively. Compared with the polymeric surface of 24-well cell culture plates, these novel scaffolds significantly promote the proliferation of human osteoblast-like MG-63 cells, indicating that this novel HA/porous carbon composite scaffold could be used for in vitro 3D culture of osteoblasts.     

Fabrication of porous titanium scaffold with controlled porous structure and net-shape using magnesium as spacer

This paper reports a new approach to fabricating biocompatible porous titanium with controlled pore structure and net-shape. The method is based on using sacrificial Mg particles as space holders to produce compacts that are mechanically stable and machinable. Using magnesium granules and Ti powder, Ti/Mg compacts with transverse rupture strength (~ 85 MPa) sufficient for machining were fabricated by warm compaction, and a complex-shape Ti scaffold was eventually produced by removal of Mg granules from the net-shape compact. The pores with the average size of 132–262 μm were well distributed and interconnected. Due to anisotropy and alignment of the pores the compressive strength varied with the direction of compression. In the case of pores aligned with the direction of compression, the compressive strength values (59–280 MPa) high enough for applications in load bearing implants were achieved. To verify the possibility of controlled net-shape, conventional machining process was performed on Ti/Mg compact. Compact with screw shape and porous Ti scaffold with hemispherical cup shape were fabricated by the results. Finally, it was demonstrated by cell tests using MC3T3-E1 cell line that the porous Ti scaffolds fabricated by this technique are biocompatible.     

Fabrication of titanium scaffolds with porosity and pore size gradients by sequential freeze casting

This paper reports a novel method for producing porous Ti scaffolds with a gradient in porosity and pore size using the freeze casting method, in which TiH₂/camphene slurries with various TiH₂ contents (40, 25, and 10 vol.%) were cast sequentially into a mold, followed by freeze drying and heat-treatment in a vacuum at 1300 °C for 3 h. This simple sequential freeze casting method produced good bonding between the layers with different porosities of 35, 53, and 75 vol.% obtained using the TiH₂ contents of 40, 25 and 10 vol.%, respectively. In addition, the pore size could be increased significantly by increasing the freezing time. The pore sizes obtained in the regions produced using 40, 25, and 10 vol.% TiH₂ after freezing for 7 days were 96, 166, and 270 μm, respectively.     

Development of macroporous calcium phosphate scaffold processed via microwave rapid drying

Porous hydroxyapatite (HA) scaffold has great potential in bone tissue engineering applications. A new method to fabricate macroporous calcium phosphate (CP) scaffold via microwave irradiation, followed by conventional sintering to form HA scaffold was developed. Incorporation of trisodium citrate dihydrate and citric acid in the CP mixture gave macroporous scaffolds upon microwave rapid drying. In this work, a mixture of β-tricalcium phosphate (β-TCP), calcium carbonate (CaCO₃), trisodium citrate dihydrate, citric acid and double distilled de-ionised water (DDI) was exposed to microwave radiation to form a macroporous structure. Based on gross eye examinations, addition of trisodium citrate at 30 and 40 wt.% in the CP mixture (β-TCP and CaCO₃) without citric acid indicates increasing order of pore volume where the highest porosity yield was observed at 40 wt.% of trisodium citrate addition and the pore size was detected at several millimeters. Therefore, optimization of pore size was performed by adding 3–7 wt.% of citric acid in the CP mixture which was separately mixed with 30 and 40 wt.% of trisodium citrate for comparison purposes. Fabricated scaffolds were calcined at 600 °C and washed with DDI water to remove the sodium hydroxycarbonate and sintered at 1250 °C to form HA phase as confirmed in the X-ray diffraction (XRD) results. Based on Archimedes method, HA scaffolds prepared from 40 wt.% of trisodium citrate with 3–7 wt.% of citric acid added CP mixture have an open and interconnected porous structure ranging from 51 to 53 vol.% and observation using Scanning electron microscope (SEM) showed the pore size distribution between 100 and 500 μm. The cytotoxicity tests revealed that the porous HA scaffolds have no cytotoxic potential on MG63 osteoblast-like cells which might allow for their use as biomaterials.     

Synthesis and bioactivity of porous Ti alloy prepared by foaming with TiH2

A novel porous Ti–6Al–4V with an open cell structure was fabricated by powder metallurgy process with the addition of TiH₂ as the pore forming and active agent. Control of porosity of porous Ti alloy made it possible to obtain the porous Ti with the Young's modulus value of 5.8–9.5 GPa, which was similar to that of human cancellous bone. This kind of porous Ti alloy with good biomechanical properties is potential to alleviate the problem of mechanical mismatch between the bone and the Ti implant. The porous Ti alloy prepared by the addition of TiH₂ as foaming agent had a uniform distribution of pores with pore size of 90–190 μm and porosity of 43–59%. In order to improve the biological properties, the duplex titania/apatite coatings were applied onto the surface of porous Ti alloy. The titania coating was deposited by chemical treatment and the apatite coating was subsequently applied by immersing the samples in a simulated body fluid. Results showed that a homogeneous nanocrystallite titania coating with a thickness of 0.8 μm was formed on the surface of the Ti alloy after chemical treatment. The carbonate-containing apatite coating with a thickness of 1 μm was deposited on the surface of titania coating after immersion in simulated body fluid for 7 days. The nucleation of the carbonate-containing apatite can be induced from the electrostatic interaction between the OH-containing groups on the surface of titania coating and the calcium and phosphate ions in the metastable simulated body fluid on those specific superficial sites. The growth kinetics of the coatings was also discussed. Cell culture test showed the well stretched and proliferated cells on the surface of the sample, indicating the good biocompatibility of porous Ti alloy.     

Hydroxyapatite (HA) bone scaffolds with controlled macrochannel pores

Hydroxyapatite (HA) macrochanneled porous scaffolds, with a controlled pore structure, were fabricated via a combination of the extrusion and lamination processes. The scaffold was architectured by aligning and laminating the extruded HA and carbon filaments. The macrochannel pores were formed by removing the carbon filaments after thermal treatments (binder removal and sintering). The porosity of the scaffolds was varied between 48 and 73% with a controlled pore size of ∼450 μm, by adjusting the fractions of HA and carbon filaments. As the porosity was increased from 48 to 73%, the compressive strength decreased from 11.5 to 3.2 MPa. However, the osteoblast-like cell responses on the scaffold, such as the proliferation rate and alkaline phosphatase (ALP) activity, were significantly enhanced as the porosity was increased.     

Processing of porous Ti and Ti5Mn foams by spark plasma sintering

Titanium and its alloys are one of the best metallic biomaterials to be used for implant application. In this study, porous Ti and Ti5Mn alloy with different porosities were successfully synthesized by powder metallurgy process with the addition of NH₄HCO₃ as space holder and TiH₂ as foaming agent. The consolidation of powder was achieved by spark plasma sintering process (SPS) at 16 MPa and pressureless conditions. The morphology of porous structure was investigated by using scanning electron microscopy (SEM) and X-ray micro-tomography (μ-CT). Nano-indentation tester was used to evaluate Young’s modulus of the porous Ti and Ti5Mn alloy. Experimental results showed that pure Ti sample, which sintered under pressure of 16 MPa, full relative density was achieved even at a relative low sintering temperature 750 °C; however, in the case of pressureless condition at sintering temperature 1000 °C the porosity was 53% and Young’s modulus was 40 GPa. The Ti5Mn alloy indicated a good pore distribution, and the porosity decreased from 56% to 21% by increasing the sintering temperature from 950 °C to 1100 °C. Young’s modulus was increased from 35 GPa to 51.83 GPa with increasing of the sintering temperatures from 950 °C to 1100 °C.     

Fabrication of biocompatible titanium scaffolds using space holder technique

Open-pore titanium scaffolds were fabricated by sintering of compressed mixtures of TiH_1.924 and urea. Spherical and irregular shaped space holders were used to investigate the effect of pore shape on cellular behavior. After removal of the space holder, the shape of the spacers was replicated to the pores. Average diameter of the pores was in the range of 300–600?μm. SEM images showed that titanium hydride resulted in higher surface roughness and larger micro porosities than pure titanium. In vitro evaluations were carried out by using MTT assay, measuring alkaline phosphatase activity and alizarin red staining in flow perfusion bioreactor for cell culture. Observations revealed excellent attachment and proliferation of G-292 cells to the highly porous scaffolds fabricated with titanium hydride and urea of this research.     

Fabrication of bioactive composite by developing PLLA onto the framework of sintered HA scaffold

Composite porous scaffolds of hydroxyapatite (HA)/poly-l-lactide (PLLA) were fabricated by a two-step immersing replication method. Structure and mechanical properties of both the single HA scaffold and the composite HA/PLLA scaffold were determined. The bioactivity of the scaffolds was evaluated by soaking in a simulated body fluid (SBF), and the formation of the apatite layer was determined by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Energy-Dispersive Spectrometer (EDS). The results showed that without changing the highly interconnected porous structure, the HA/PLLA composite scaffold was mechanically enhanced to a great deal of extent compared with single HA scaffold. On the other hand, it is also suggested that the HA/PLLA scaffold was bioactive as it induced the formation of apatite on the surface of the composite scaffolds after soaking in SBF for 7 days.     

Novel,simple and reproducible method for preparation of composite hierarchal porous structure scaffolds

Demand to develop a simple and adaptable method for preparation the hierarchical porous scaffolds for bone tissue regeneration is ever increasing. This study presents a novel and reproducible method for preparing the scaffolds with pores structure spanning from nano, micro to macro scale. A macroporous Sr-Hardystonite (Sr–Ca₂ZnSi₂O₇, Sr–HT) scaffold with the average pore size of ~ 1200 μm and porosity of ~ 95% was prepared using polymer sponge method. The struts of the scaffold were coated with a viscous paste consisted of salt (NaCl) particles and polycaprolactone (PCL) to provide a layer with thickness of ~ 300–800 μm. A hierarchical porous scaffold was obtained with macro, micro and nanopores in the range of 400–900 μm, 1–120 μm and 40–290 nm, after salt leaching process. These scales could be easily adjusted based on the starting foam physical characteristics, salt particle size, viscosity of the paste and salt/PCL weight ratio.     

One-step synthesis of petal-like apatite/titania composite coating on a titanium by micro-arc oxidation

Petal-like apatite/titania (TiO₂) coating was prepared on commercially pure titanium (Ti) by micro-arc oxidation in electrolyte containing calcium and phosphate for the first time. The surface morphology, crystalline structure, chemical composition and binding state of the apatite/TiO₂ composite coating were characterized. The coating consists of a double-layer (apatite layer and TiO₂ layer) structure. The average thickness of the inner TiO₂ layer and the outer apatite layer is about 6 μm and 16 μm respectively. The outer apatite layer is porous and exhibits petal-like pattern. The apatite layer consists of hydroxyapatite (HA) and carbonate-apatite and the inner TiO₂ layer consists of anatase and rutile.     

Polyurethane (PU) scaffolds prepared by solvent casting/particulate leaching (SCPL) combined with centrifugation

This article reports an enhanced solvent casting/particulate (salt) leaching (SCPL) method developed for preparing three-dimensional porous polyurethane (PU) scaffolds for cardiac tissue engineering. The solvent for the preparation of the PU scaffolds was a mixture of dimethylformamide (DFM) and tetrahydrofuran (THF). The enhanced method involved the combination of a conventional SCPL method and a step of centrifugation, with the centrifugation being employed to improve the pore uniformity and the pore interconnectivity of scaffolds. Highly porous three-dimensional scaffolds with a well interconnected porous structure could be achieved at the polymer solution concentration of up to 20% by air or vacuum drying to remove the solvent. When the salt particle sizes of 212–295, 295–425, or 425–531 µm and a 15% w/v polymer solution concentration were used, the porosity of the scaffolds was between 83–92% and the compression moduli of the scaffolds were between 13 kPa and 28 kPa. Type I collagen acidic solution was introduced into the pores of a PU scaffold to coat the collagen onto the pore walls throughout the whole PU scaffold. The human aortic endothelial cells (HAECs) cultured in the collagen-coated PU scaffold for 2 weeks were observed by scanning electron microscopy (SEM). It was shown that the enhanced SCPL method and the collagen coating resulted in a spatially uniform distribution of cells throughout the collagen-coated PU scaffold.     

Attachment of stem cells on porous chitosan scaffold crosslinked by Na5P3O10

In this study, porous chitosan scaffolds were prepared by freeze-dried method using Na₅P₃O₁₀ as a crosslinking agent. The three-dimensional pore structure of the scaffold was interconnected with a mean pore size about 40 to 100 μm. The remained weight of crosslinked scaffold was about 76% after being exposed to PBS for 30 days. Mouse embryonic stem (E. S.) cells could grow on these crosslinked scaffolds. E. S. cells differentiated to other cells after 21 days of culturing on the scaffolds. The growth rate of E. S. cells was improved by post surface treatment of the scaffolds with collagen. However, there was no significant increase in growth rate of E. S. cells when scaffolds were surface treated with argon plasma. These porous chitosan scaffolds present a promising approach for tissue engineering applications.