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.     

New 3D stratified Si-Ca-P porous scaffolds obtained by sol-gel and polymer replica method: Microstructural,mineralogical and chemical characterization

The aim of this research was to develop and characterize a novel stratified porous scaffold for future uses in bone tissue engineering. In this study, a calcium silicophosphate porous scaffold, with nominal composition 29.32 wt% SiO₂ – 67.8 wt% CaO – 2.88 wt% P₂O₅, was produced using the sol-gel and polymer replication methods. Polyurethane sponges were used as templates which were impregnated with a homogeneous sol solution and sintered at 950 °C and 1400 °C during 8 h. The characteristics of the 3D stratified porous scaffolds were investigated by Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectrometry, Diametric Compression of Discs Test and Hg porosimetry techniques. The result showed highly porous stratified calcium silicophosphate scaffolds with micro and macropores interconnected. Also, the material has a diametrical strength dependent on the number of layers of the stratified scaffolds and the sintering temperature.     

Bone scaffolds from electrospun fiber mats of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and their blend

In the present contribution, electrospinning was used to fabricate ultrafine fiber mats from poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-2-hydroxyvalerate) (PHBV), and their 50/50 w/w blend for potential use as bone scaffolds. Cytotoxicity evaluation of these as-spun fiber mats with human osteoblasts (SaOS-2) and mouse fibroblasts (L929) indicated biocompatibility of these materials to both types of cells. The potential for use of these fiber mats as bone scaffolds was further assessed in vitro in terms of the attachment, the proliferation, and the alkaline phosphatase (ALP) activity of SaOS-2 that were seeded or cultured at different times. The cells appeared to adhere well on all types of the fibrous scaffolds after 16 h of cell seeding. During the early stage of the proliferation period (i.e., from ∼24 to 72 h in culture), the viability of the cells increased considerably and appeared to be unchanged with further increase in the time in culture. In comparison with the corresponding solution-cast film scaffolds, all of the fibrous scaffolds exhibited much better support for cell attachment and proliferation. Lastly, among the various fibrous scaffolds investigated, the electrospun fiber mat of the 50/50 w/w PHB/PHBV blend showed the highest ALP activity. These results implied a high potential for use of these electrospun fiber mats as bone scaffolds.     

Physico-chemical and biological studies on three-dimensional porous silk/spray-dried mesoporous bioactive glass scaffolds

The incorporation of a bioactive inorganic phase in polymeric scaffolds is a good strategy for the improvement of the bioactivity and the mechanical properties, which represent crucial features in the field of bone tissue engineering. In this study, spray-dried mesoporous bioactive glass particles (SD-MBG), belonging to the binary system of SiO₂-CaO (80:20 mol%), were used to prepare composite scaffolds by freeze-drying technique, using a silk fibroin matrix. The physico-chemical and biological properties of the scaffolds were extensively studied. The scaffolds showed a highly interconnected porosity with a mean pore size in the range of 150 µm for both pure silk and silk/SD-MBG scaffolds. The elastic moduli of the silk and silk/SD-MBG scaffolds were 1.1±0.2 MPa and 6.9±1.0 MPa and compressive strength were 0.5±0.05 MPa and 0.9±0.2 MPa, respectively, showing a noticeable increase of the mechanical properties of the composite scaffolds compared to the silk ones. The contact angle value decreased from 105.3° to 71.2° with the incorporation of SD-MBG particles. Moreover, the SD-MBG incorporation countered the lack of bioactivity of the silk scaffolds inducing the precipitation of hydroxyapatite layer on their surface already after 1 day of incubation in simulated body fluid. The composite scaffolds showed good biocompatibility and a good alkaline phosphatase activity toward human mesenchymal stromal cells, showing the ability for their use as three-dimensional constructs for bone tissue engineering.     

Natural origin hydroxyapatite scaffold as potential bone tissue engineering substitute

Fish scales derived natural hydroxyapatite (FS-HAp) scaffolds were prepared through solvent casting technique, which could mimic the structure of cortical and cancellous bone tissues of body system. The hydroxyapatite (HAp) biomaterial was synthesized by thermal decomposition of chemically treated fish scales. Fabricated scaffolds were characterized through morphological analysis, volumetric shrinkage, mechanical tests, and in vitro, in vivo biological studies. The projected scaffolds successfully mimic the cancellous/cortical bone system in terms of structure, porosity, mechanical strength, and exhibit excellent bioactive behavior. The FS-HAp scaffolds manifest good mechanical behaviors with Vickers Hardness (HV) of ~0.78 GPa, 0.52 GPa compressive stress, 190 MPa tensile stress and ~35% porosity on sintering at 1200 °C. In vitro and in vivo studies suggest these nontoxic HAp scaffolds graft with osteoconductive support, facilitating new cell growth on the developed scaffold surface. The graded grafts have a great potential for application as traumatized tissue augmentation substitute, and ideal for load-bearing bone applications.     

Structure control of hydroxyapatite ceramics via an electric field assisted freeze casting method

Using H₂O₂ aqueous solution as pore-forming agent, hydroxyapatite (HA) porous scaffolds with both lamellar and spherical pores were fabricated by a freeze casting method. The highest porosity was obtained in HA scaffolds prepared using 5 vol% H₂O₂ aqueous solution. The relationship between the electric field intensity and the properties of HA scaffolds was investigated. Results showed that when the electric field intensity was increased from 0 to 90 kV/m, the average diameters of lamellar and spherical pores of HA scaffold were increased from 460 μm to 810 μm, and from 320 μm to 420 μm, respectively. Vitro cellular assay indicated that HA scaffold with both the lamellar and the spherical pores has a better biocompatibility, compared with that with single pores.     

Influence of the calcination temperature on morphological and mechanical properties of highly porous hydroxyapatite scaffolds

Bone tissue engineering is a promising approach for bone replacement or augmentation. However, the achievement of a high performing scaffold is still undergoing. In this work, the optimum calcination temperature value of the starting powder for the preparation of highly porous hydroxyapatite scaffold, fabricated by the sponge replica method, was assessed. Hydroxyapatite nanopowder was synthesized by the precipitation method and the influence of four calcinations temperatures (600, 700, 800 and 900 °C) on either powder characteristics or scaffold properties were exhaustively examined. Powder composition and grain size were determined by XRD, TEM and BET analyses. Composition, morphology, porosity, shrinkage and mechanical strength of the sintered scaffolds were determined by XRD, FT-IR, weight and dimension measurements and compression tests. The results showed that increasing the calcination temperature, the grain size of the HA powder increases and a higher grain size leads to a more resistant HA scaffold. The 900 °C calcinations temperature provide the best performing scaffold without inducing any phase transformation. The study here reported highlighted that the calcinations treatment is essential to fabricate high resistant HA scaffolds.     

Porous β-Ca2SiO4 ceramic scaffolds for bone tissue engineering: In vitro and in vivo characterization

The biodegradable ceramic scaffolds with desirable pore size, porosity and mechanical properties play a crucial role in bone tissue engineering and bone transplantation. A novel porous β-dicalcium silicate (β-Ca₂SiO₄) ceramic scaffold was prepared by sintering the green body consisting of CaCO₃ and SiO₂ at 1300 °C, which generated interconnected pore network with proper pore size of about 300 μm and high compressive strength (28.13±5.37–10.36±0.83 MPa) following the porosity from 53.54±5.37% to 71.44±0.83%. Porous β-Ca₂SiO₄ ceramic scaffolds displayed a good biocompatibility, since human osteoblast-like MG-63 cells and goat bone mesenchymal stem cells (BMSCs) proliferated continuously on the scaffolds after 7 d culture. The porous β-Ca₂SiO₄ ceramic scaffolds revealed well apatite-forming ability when incubated in the simulated body fluid (SBF). According to the histological test, the degradation of porous β-Ca₂SiO₄ ceramic scaffolds and the new bone tissue generation in vivo were observed following 9 weeks implantation in nude mice. These results suggested that the porous β-Ca₂SiO₄ ceramic scaffolds could be potentially applied in bone tissue engineering.     

Surface modification of poly-l-lactic acid fibrous scaffolds by a molecular-designed multi-walled carbon nanotube multilayer for enhancing cell interactions

We presented a molecular-designed multi-walled carbon nanotube (MWCNT) layer-by-layer (LbL) multilayer on poly-l-lactic acid (PLLA) electrospun fibers for engineering cell/CNT interfaces. A stable, positively charged monolayer was created on the fiber surface by the aminolysis reaction of poly(ethylene imine) (PEI) with PLLA, followed by alternate deposition in negatively charged MWCNT and positively charged chitosan (CS). Thermogravimetric analysis indicated a sustained growth of the MWCNT during the self-assembly process. The interactions between MWCNT and polycation crucially affected the specific structure and properties of the MWCNT multilayer. MWCNT/PEI electrostatic interactions reduced the gap between MWCNTs and improved the π → π¹ transitions. However, the CS chains tended to be more serpentine than the chains of PEI molecules, which might have hindered the π → π¹ transitions. On the other hand, the electrostatic interactions might have enhanced the disorder grade of the MWCNT structure, as indicated by Raman analysis. The scaffolds maintained their fibrous and porous structure after MWCNT multilayer modification and supported fibroblast growth. The MWCNT multilayer induced cell migration toward the interior of the scaffolds. Therefore, we created a simple yet efficient method of building a CNT multilayer on three-dimensional (3D) fibrous scaffolds for enhancing cell-matrix interactions.     

Reinforcement with reduced graphene oxide of bioactive glass scaffolds fabricated by robocasting

45S5 bioactive glass composite scaffolds reinforced with reduced graphene oxide (rGO) were fabricated for the first time by robocasting (direct-writing) technique. Composite scaffolds with 0–3 vol.% content of rGO platelets were printed, and then consolidated by pressureless sintering at 550 or 1000 °C in Ar atmosphere. It was found that the addition of rGO platelets up to 1.5 vol.% content enhanced the mechanical performance of the 45S5 bioactive glass scaffolds in terms of strength and toughness. Best performance was obtained for 1 vol.% rGO, which yielded an enhancement of the fracture toughness of ∼850 and 380% for sintering temperatures of 550 and 1000 °C, respectively, while the compressive strength increased by ∼290 and 75%. rGO addition thus emerges as a promising approach for the fabrication of novel bioglass scaffolds with improved mechanical performance without deterioration of their bioactivity, which may then find use in load-bearing bone tissue engineering applications.     

A novel foam-like silane modified alumina scaffold coated with nano-hydroxyapatite–poly(ε-caprolactone fumarate) composite layer

Although alumina scaffolds with biodegradable polymer coating can overcome the limitations of conventional ceramic bone substitutes, the bioactivity potential of these scaffolds needs to be enhanced. In this study, the macroporous alumina scaffolds with the defined pore-channel interconnectivity were successfully prepared by the foam replication method. The average pore size of the scaffolds was in the range 200–900 μm with around 82% porosity. The average Young's modulus of alumina scaffolds was 2.8 GPa. Coating of nano-hydroxyapatite (nano-HA) in poly(ε-caprolactone fumarate) (PCLF) as a carrier on the surface of alumina scaffold was performed. The nano-HA powder was synthesized successfully by the sol–gel method. The crystallite and particle sizes of HA powders were in nano range and confirmed by the Scherrer equation from X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The PCLF was synthesized and characterized by fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). In order to make a chemical link between the alumina scaffolds and the coating, a silane coupling agent was used. The results showed that using of 1 g Methacryloxypropyl trimethoxysilane in 100 g solvent is sufficient for making a thin interface layer between the scaffold and the polymer. The coating process was performed by immersion of scaffolds in the solutions with different percents of nano-HA. The morphology and chemical structure of the coated scaffolds were investigated by SEM and FTIR. SEM images demonstrated that the scaffolds were constituted of interconnected and homogeneously distributed pores. Also, HA distribution and agglomerates on the surface of scaffolds were enhanced by increasing the nano-HA percent in the coating solutions.     

Direct-write assembly of silicate and borate bioactive glass scaffolds for bone repair

Silicate (13-93) and borate (13-93B3) bioactive glass scaffolds were created by robotic deposition (robocasting) of organic solvent-based suspensions and evaluated in vitro for potential application in bone repair. Suspensions (inks) were developed, characterized, and deposited layer-by-layer to form three-dimensional scaffolds with a grid-like microstructure (porosity ≈50%; pore width 420 ± 30 μm). The mechanical response of the scaffolds was tested in compression, and the conversion of the glass to hydroxyapatite (HA)-like material in a simulated body fluid (SBF) was evaluated. As fabricated, the 13-93 scaffolds had a compressive strength 142 ± 20 MPa, comparable to the strength of human cortical bone, while the strength of the 13-93B3 scaffolds (65 ± 11 MPa), was far higher than that for trabecular bone. When immersed in SBF, the borate 13-93B3 scaffolds converted faster than the silicate 13-93 scaffolds to an HA-like material, but they also showed a sharper decrease in strength with immersion time. Based on their high compressive strength and bioactivity, the scaffolds fabricated in this work by robocasting could have potential application in the repair of load-bearing bone.     

A novel approach for the fabrication of carbon nanofibre/ceramic porous structures

This paper describes the fabrication of hybrid ceramic/carbon scaffolds in which carbon nanofibres and multi-walled carbon nanotubes fully cover the internal walls of a microporous ceramic structure that provides mechanical stability. Freeze casting is used to fabricate a porous, lamellar ceramic (Al₂O₃) structure with aligned pores whose width can be controlled between 10 and 90 μm. Subsequently, a two step chemical vapour deposition process that uses iron as a catalyst is used to grow the carbon nanostructures inside the scaffold. This catalyst remains in the scaffold after the growth process. The formation of the alumina scaffold and the influence of its structure on the growth of nanofibres and tubes are investigated. A set of growth conditions is determined to produce a dense covering of the internal walls of the porous ceramic with the carbon nanostructures. The limiting pore size for this process is located around 25 μm.     

Mechanical properties of porous ceramic scaffolds: Influence of internal dimensions

Highly porous ceramic scaffolds have been fabricated from a 70% SiO₂–30% CaO glass powder using stereolithography and the lost-mould process combined with gel-casting. After sintering at 1200 °C the glass crystallised to a structure of wollastonite and pseudowollastonite grains in a glassy matrix with a bulk porosity of 1.3%. All scaffolds had a simple cubic strut structure with an internal porosity of approximately 42% and internal pore dimensions in the range 300–600 μm. The mean crushing strength of the scaffolds is in the range 10–25 MPa with the largest pore sizes showing the weakest strengths. The variability of scaffold strengths has been characterised using Weibull statistics and each set of scaffolds showed a Weibull modulus of m≈3 independent of pore size. The equivalent strength of the struts within the porous ceramics was estimated to be in the range 40–80 MPa using the models of the Gibson and Ashby. These strengths were found to scale with specimen size consistent with the Weibull modulus obtained from compression tests. Using a Weibull analysis, these strengths are shown to be in accordance with the strength of 3-point bend specimens of the bulk glass material fabricated using identical methods. The strength and Weibull modulus of these scaffolds are comparable to those reported for other porous ceramic scaffold materials of similar porosity made by different fabrication routes.     

Electrospun polylactide/silk fibroin–gelatin composite tubular scaffolds for small‐diameter tissue engineering blood vessels

Many synthetic scaffolds have been used as vascular substitutes for clinical use. However, many of these scaffolds may not show suitable properties when they are exposed to physiologic vascular environments, and they may fail eventually because of some unexpected conditions. Electrospinning technology offers the potential for controlling the composition, structure, and mechanical properties of scaffolds. In this study, a tubular scaffold (inner diameter = 4.5 mm) composed of a polylactide (PLA) fiber outside layer and a silk fibroin (SF)–gelatin fiber inner layer (PLA/SF–gelatin) was fabricated by electrospinning. The morphological, biomechanical, and biological properties of the composite scaffold were examined. The PLA/SF–gelatin composite tubular scaffold possessed a porous structure; the porosity of the scaffold reached 82 ± 2%. The composite scaffold achieved the appropriate breaking strength (1.28 ± 0.21 MPa) and adequate pliability (elasticity up to 41.11 ± 2.17% strain) and possessed a fine suture retention strength (1.07 ± 0.07 N). The burst pressure of the composite scaffold was 111.4 ± 2.6 kPa, which was much higher than the native vessels. A mitochondrial metabolic assay and scanning electron microscopy observations indicated that both 3T3 mouse fibroblasts and human umbilical vein endothelial cells grew and proliferated well on the composite scaffold in vitro after they were cultured for some days. The PLA/SF–gelatin composite tubular scaffolds presented appropriate characteristics to be considered as candidate scaffolds for blood vessel tissue engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Loadable TiO2 scaffolds—A correlation study between processing parameters,micro CT analysis and mechanical strength

It was shown in the present study that it is possible to produce TiO₂ scaffolds with both high mechanical strength and high porosity by using the polymer sponge method. TiO₂ scaffolds with porosity above 85% exceeded 1 MPa in compressive strength. TiO₂ scaffolds with equally high compressive strength having a fully open porosity close to 90% is not previously been reported in the literature. Reduction of porosity leads to even further reinforce the scaffolds’ mechanical structure. A statistical correlation study with 160 tested scaffolds defined the most important manufacturing steps and the governing morphological characteristics for the scaffold's increased mechanical strength. The key manufacturing factors were a holding phase during sintering time for more than 30 h (at 1500 °C) and multiple coatings of the scaffold's structure. The crucial parameters for high mechanical strength were the fractal dimensions of the struts, object surface/volume ratio, density and overall porosity.     

Effect of layer printing delay on mechanical properties and dimensional accuracy of 3D printed porous prototypes in bone tissue engineering

Recent advancements in computational design and additive manufacturing have enabled the fabrication of 3D prototypes with controlled architecture resembling the natural bone. Powder-based three-dimensional printing (3DP) is a versatile method for production of synthetic scaffolds using sequential layering process. The quality of 3D printed products by this method is controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The X-direction printed scaffolds with a pore size of 0.8 mm and a layer thickness of 0.1125 mm were subjected to the depowdering step. The effects of four layer printing delays of 50, 100, 300 and 500 ms on the physical and mechanical properties of printed scaffolds were investigated. The compressive strength, toughness and tangent modulus of samples printed with a delay of 300 ms were observed to be higher than other samples. Furthermore, the results of SEM and μCT analyses showed that samples printed with a delay of 300 ms have higher dimensional accuracy and are significantly closer to CAD software based designs with predefined 0.8 mm macro-pore and 0.6 mm strut size.     

In vitro behaviour of sol-gel interconnected porous scaffolds of doped wollastonite

Using the sol-gel method, two different three-dimensional (3D) porous interconnected scaffolds were prepared, whose compositions were MgO-K₂O-CaO-SiO₂ (MgO-K₂O-wollastonite) and Na₂O-K₂O-CaO-SiO₂ (Na₂O-K₂O-wollastonite). Scaffold sintering was performed at 950 °C for 8 h. The scaffolds were obtained and soaked in simulated body fluid for different times (6 h, 3 d, 7 d and 14 d) to study their in vitro behaviour. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed the presence of both a hydroxyapatite-like microstructure and a nanostructure on the surface of 3D scaffolds. The presence of Na and K in the scaffolds resulted in the precipitation of a hierarchical hydroxyapatite-like layer composed of nanorods, approximately 200–400 nm in size. The presence of Mg and K ions in the composition caused the precipitation of particles with a nanorod morphology, approximately 50–100 nm in size. The addition of Na, K and Mg, K to the wollastonite resulted in scaffolds with mechanical strengths of 0.03 and 0.02 MPa, respectively.     

Microwave-assisted hydroconversions of demineralized coal liquefaction residues from Shenfu and Shengli coals

Microwave-assisted hydroconversions of demineralized coal liquefaction residues (DCLRs) from Shenfu (SF) and Shengli coals were investigated using methanol or ethanol as the solvent for both reaction and extraction. The results show that the solubilities of hydroconverted DCLRs in methanol under 0.7 MPa of initial hydrogen pressure (IHP) follow the order: non-catalytic hydroconversion = activated carbon-catalyzed hydroconversion < Pd/C-catalyzed hydroconversion < Ni-catalyzed hydroconversion; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol increases with raising temperature up to 140 °C and with increase in IHP; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol under 0.7 MPa of IHP at 130 °C is higher than that in ethanol. The molecular compositions of the extractable fractions were analyzed with GC/MS and the structural features of some extractable and inextractable fractions were characterized with FTIR.     

Structural and optical properties of solvothermally synthesized ZnS nano-materials using Na2S·9H2O and ZnSO4·7H2O precursors

Hexagonal wurtzite (HWZ) ZnS nanorods were formed in specimens with a S/Zn ratio of 1.3, synthesized at temperatures ≥200 °C in a solution containing 80 vol% water and 20 vol% of ethylenediamine (EN). In contrast, HWZ ZnS nanoparticles were formed in specimens synthesized at temperatures lower than 200 °C. Also, cubic zinc blende (CZB) ZnS nanoparticles were formed in specimen synthesized in water. The absorption peak for the HWZ nanorods and CZB ZnS nanoparticles was at wavelength of 325 nm and 339 nm, respectively, indicating that the band gap energy of the former is larger than that of the latter. Moreover, the HWZ ZnS exhibited two emission peaks at 474 nm and 580 nm. The peak at 474 nm is attributed to Zn vacancies but the origin of the peak at 580 nm remains undetermined. Since the intensity of the emission peak at 580 nm was significantly higher for the HWZ nanoparticles than for nanorods, this peak might be associated with defects in the HWZ ZnS nanoparticles.