Qin-Fei Ke

Hybrid nanostructured hydroxyapatite–chitosan composite scaffold: bioinspired fabrication, mechanical properties and biological properties

The fabrication of bone scaffolds with interconnected porous structure, adequate mechanical properties, excellent biocompatibility and osteoinductivity presents a great challenge. Herein, a hybrid nanostructured hydroxyapatite-chitosan (HA-CS) composite scaffold has been fabricated according to the following steps: (i) the deposition of brushite-CS on a CS fibre porous scaffold by a dip-coating method; and (ii) the formation of a hybrid nanostructured HA-CS composite scaffold by the in situ conversion of brushite to HA using a bioinspired mineralization process. The hybrid HA-CS composite scaffold possesses three-dimensional (3D) interconnected pores with pore sizes of 30-80 μm. The HA rods with a length of ∼200 nm and width of ∼50 nm are perpendicularly oriented to the CS fibres. Interestingly, the abovementioned HA rods are composed of many smaller nanorods with a length of ∼40 nm and width of ∼10 nm oriented along the c-axis. The hybrid nanostructured HA-CS composite scaffold exhibits good mechanical properties with a compression strength of 9.41 ± 1.63 MPa and an elastic modulus of 0.17 ± 0.02 GPa, which are well-matched to those of trabecular bone. The influences of the hybrid HA-CS composite scaffold on cells have been investigated using human bone marrow stem cells (hBMSCs) as cell model and the CS fibre porous scaffold as the control sample. The hybrid HA-CS composite scaffold not only supports the adhesion and proliferation of hBMSCs, but also improves the osteoinductivity. The alkaline phosphatase activity and mineralization deposition on the hybrid HA-CS composite scaffold are higher than those on the CS fibre porous scaffold. Moreover, the hybrid HA-CS composite scaffold can promote the formation of new bone in rat calvarial defects as compared with the CS fibre porous scaffold. The excellent biocompatibility, osteoinductivity and mechanical properties suggest that the hybrid nanostructured HA-CS composite scaffold has great potential for bone tissue engineering.

Strontium hydroxyapatite/chitosan nanohybrid scaffolds with enhanced osteoinductivity for bone tissue engineering

For the clinical application of bone tissue engineering with the combination of biomaterials and mesenchymal stem cells (MSCs), bone scaffolds should possess excellent biocompatibility and osteoinductivity to accelerate the repair of bone defects. Herein, strontium hydroxyapatite [SrHAP, Ca10-xSrx(PO4)6(OH)2]/chitosan (CS) nanohybrid scaffolds were fabricated by a freeze-drying method. The SrHAP nanocrystals with the different x values of 0, 1, 5 and 10 are abbreviated to HAP, Sr1HAP, Sr5HAP and Sr10HAP, respectively. With increasing x values from 0 to 10, the crystal cell volumes and axial lengths of SrHAP become gradually large because of the greater ion radius of Sr2+ than Ca2+, while the crystal sizes of SrHAP decrease from 70.4nm to 46.7nm. The SrHAP/CS nanohybrid scaffolds exhibits three-dimensional (3D) interconnected macropores with pore sizes of 100-400μm, and the SrHAP nanocrystals are uniformly dispersed within the scaffolds. In vitro cell experiments reveal that all the HAP/CS, Sr1HAP/CS, Sr5HAP/CS and Sr10HAP/CS nanohybrid scaffolds possess excellent cytocompatibility with the favorable adhesion, spreading and proliferation of human bone marrow mesenchymal stem cells (hBMSCs). The Sr5HAP nanocrystals in the scaffolds do not affect the adhesion, spreading of hBMSCs, but they contribute remarkably to cell proliferation and osteogenic differentiation. As compared with the HAP/CS nanohybrid scaffold, the released Sr2+ ions from the SrHAP/CS nanohybrid scaffolds enhance alkaline phosphatase (ALP) activity, extracellular matrix (ECM) mineralization and osteogenic-related COL-1 and ALP expression levels. Especially, the Sr5HAP/CS nanohybrid scaffolds exhibit the best osteoinductivity among four groups because of the synergetic effect between Ca2+ and Sr2+ ions. Hence, the Sr5HAP/CS nanohybrid scaffolds with excellent cytocompatibility and osteogenic property have promising application for bone tissue engineering.

Fabrication of hydroxyapatite/chitosan porous materials for Pb(II) removal from aqueous solution

Lead is one of the common heavy metal contaminants that pose a significant threat to human health. Herein, a freeze-drying method has been used to fabricate hydroxyapatite/chitosan (HAP/CS) porous materials for the removal of Pb(II) ions from aqueous solutions. The HAP/CS porous materials possessed interconnected three-dimensional macropores with pore sizes of 100–300 μm. Low-crystallinity HAP particles were dispersed uniformly among the porous materials. Adsorption experiments for Pb(II) ions were conducted under flow conditions. The adsorption capacity of the HAP/CS porous material was found to be 264.42 mg g−1, while that of the CS porous material was only 5.67 mg g−1. The better adsorption property of the HAP/CS porous material than the CS porous material was attributed to the presence of HAP particles in the composite material. During the adsorption process, the HAP particles were converted to rod-like lead hydroxyapatite (PbHAP, Pb10(PO4)6(OH)2) particles via a dissolution–precipitation reaction. Adsorption kinetic studies revealed that the adsorption of Pb(II) ions on the HAP/CS porous material exhibited a good fit to the pseudo-second-order kinetic model. Therefore, the HAP/CS porous materials possess a great potential for the removal of Pb(II) ions from aqueous solutions.

Hydroxyapatite coatings with oriented nanoplate arrays: synthesis, formation mechanism and cytocompatibility

Hydroxyapatite (HA) is the main inorganic constituent of natural bones and teeth with c-axis orientation and a(b)-axis orientation, respectively. Designing HA coatings (HACs) with specific orientation and morphology is an important strategy to improve their biological properties. Herein, we report, for the first time, the hydrothermal synthesis of HACs with oriented nanoplate arrays according to the following steps: (i) deposition of brushite/chitosan coatings (BCCs) on Ti6Al4V substrates; and (ii) transformation of HACs with oriented nanoplate arrays from BCCs after hydrothermal treatment with alkaline solutions. After soaking the BCCs in a NaOH solution under hydrothermal conditions, the Ca2+ and PO4 3- ions are released from the coatings because of the dissolution reaction of brushite, and they react with OH- ions to form HA nanoplates. Interestingly, these HA nanoplates with a preferential c-plane orientation are perpendicular to the coating surfaces. Hydrothermal reaction time and Ca/P ratio of BCCs have great effects on the morphologies of HA nanoplates. On increasing the reaction time from 3 h to 3 days or decreasing the Ca/P ratio from 2.0 to 1.0, the widths (or lengths) of HA nanoplates increase gradually. Simulated body fluid immersion (SBF) tests reveal that the HACs with oriented nanoplate arrays can promote the formation of apatite on the surfaces, suggesting their good in vitro bioactivity. Moreover, human bone marrow stromal cells (hBMSCs) have been used as cell models to investigate cytocompatibility of the HACs. The hBMSCs on the HACs have better cell adhesion, spreading, proliferation and osteogenic differentiation than those on Ti6Al4V substrates because the HACs are similar to the minerals of human hard tissues in chemical composition, morphology and crystallographic orientation. Therefore, HACs with oriented nanoplate arrays have great potential for use as implants of human hard tissues.

Synergetic effect between adsorption and photodegradation on nanostructured TiO2/activated carbon fiber felt porous composites for toluene removal

The low quantum efficiency and limited adsorption efficiency of TiO2 makes it only fit for the removal of VOCs with low concentrations. Herein, we for the first time fabricated nanostructured TiO2/activated carbon fiber felt (TiO2/ACFF) porous composites by the in situ deposition of TiO2 microspheres on the carbon fibers in ACFF. Interestingly, the TiO2 microspheres exhibit hierarchical nanostructures constructed by nanocrystals as building blocks. The TiO2/ACFF porous composites possess excellent adsorption and photodegradation properties for toluene because of the synergetic effects between the nanostructured TiO2 and ACFF. The adsorption efficiencies of the TiO2/ACFF porous composites reach approximately 98% at the toluene concentration (<1150ppm) and approximately 77% even at the high concentration of 6900ppm. Moreover, the ACFF in the TiO2/ACFF porous composites significantly enhances photocatalytic property for toluene by hindering the recombination of electron-hole pairs, reducing the TiO2 band gap energy (Eg) to 2.95eV and accelerating toluene adsorption. At the toluene concentrations of 230ppm and 460ppm, the photocatalytic oxidation efficiency of toluene into CO2 arrives at 100% and 81.5%, respectively. Therefore, the TiO2/ACFF porous composites with synergetic adsorption and photocatalytic activities have great potentials for toluene removal.

Fabrication of a chitosan/bioglass three-dimensional porous scaffold for bone tissue engineering applications

Bone defects caused by trauma and disease have become urgent problems. Three-dimensional (3D) porous scaffolds for bone tissue engineering should ideally have an interconnected porous structure, good biocompatibility and mechanical properties similar to those of natural bones. In the present study, a chitosan/bioglass (CS/BG) 3D porous scaffold was constructed by initially preparing a CS fibre 3D porous scaffold by needle-punching, and then depositing BG on the scaffold by dip-coating. The CS/BG 3D porous scaffold had an interconnected porous structure, with a porosity of 77.52% and a pore size around 50 μm. Water absorption values of the CS fibre 3D porous scaffold and the corresponding CS/BG scaffold were 570% and 59%, respectively. The BG present in the latter significantly decreased the swelling of the CS fibres, thus improving the stability of the scaffolds. The CS/BG 3D porous scaffold possessed good mechanical properties, with a compression strength of 7.68 ± 0.38 MPa and an elastic modulus of 0.46 ± 0.02 GPa, which are well-matched to those of trabecular bone. In vitro cell assay results demonstrated that the CS/BG 3D porous scaffold had good biocompatibility, which facilitates the spreading and proliferation of human bone marrow stromal cells (hBMSCs). The CS/BG 3D porous scaffold is thus a suitable material for bone tissue engineering.

Chitosan Wound Dressings Incorporating Exosomes Derived from MicroRNA‐126‐Overexpressing Synovium Mesenchymal Stem Cells Provide Sustained Release of Exosomes and Heal Full‐Thickness Skin Defects in a Diabetic Rat Model

There is a need to find better strategies to promote wound healing, especially of chronic wounds, which remain a challenge. We found that synovium mesenchymal stem cells (SMSCs) have the ability to strongly promote cell proliferation of fibroblasts; however, they are ineffective at promoting angiogenesis. Using gene overexpression technology, we overexpressed microRNA‐126‐3p (miR‐126‐3p) and transferred the angiogenic ability of endothelial progenitor cells to SMSCs, promoting angiogenesis. We tested a therapeutic strategy involving controlled‐release exosomes derived from miR‐126‐3p‐overexpressing SMSCs combined with chitosan. Our in vitro results showed that exosomes derived from miR‐126‐3p‐overexpressing SMSCs (SMSC‐126‐Exos) stimulated the proliferation of human dermal fibroblasts and human dermal microvascular endothelial cells (HMEC‐1) in a dose‐dependent manner. Furthermore, SMSC‐126‐Exos also promoted migration and tube formation of HMEC‐1. Testing this system in a diabetic rat model, we found that this approach resulted in accelerated re‐epithelialization, activated angiogenesis, and promotion of collagen maturity in vivo. These data provide the first evidence of the potential of SMSC‐126‐Exos in treating cutaneous wounds and indicate that modifying the cells—for example, by gene overexpression—and using the exosomes derived from these modified cells provides a potential drug delivery system and could have infinite possibilities for future therapy. Stem Cells Translational Medicine 2017;6:736–747

Hydroxyapatite coatings with oriented nanoplate and nanorod arrays: Fabrication, morphology, cytocompatibility and osteogenic differentiation

Hydroxyapatite (HA) crystals exhibit rod-like shape with c-axis orientation and plate-like shape with a(b)-axis orientation in vertebrate bones and tooth enamel surfaces, respectively. Herein, we report the synthesis of HA coatings with the oriented nanorod arrays (RHACs) and HA coatings with oriented nanoplate arrays (PHACs) by using bioglass coatings as sacrificial templates. After soaking in simulated body fluid (SBF) at 120°C, the bioglass coatings are hydrothermally converted into the HA coatings via a dissolution-precipitation reaction. If the Ca/P ratios in SBF are 2.50 and 1.25, the HA crystals on the coatings are oriented nanorod arrays and oriented nanoplate arrays, respectively. Moreover, the bioglass coatings are treated with SBF at 37°C, plate-like HA coatings with a low crystallinity (SHACs) are prepared. As compared with the Ti6Al4V and SHACs, the human bone marrow stromal cells (hBMSCs) on the RHACs and PHACs have better cell adhesion, spreading, proliferation and osteogenic differentiation because of their moderately hydrophilic surfaces and similar chemical composition, morphology and crystal orientation to human hard tissues. Notably, the morphologies of HA crystals have no obvious effects on cytocompatibility and osteogenic differentiation. Hence, the HA coatings with oriented nanoplate arrays or oriented nanorod arrays have a great potential for orthopedic applications.

Fabrication of silver nanoparticle-doped hydroxyapatite coatings with oriented block arrays for enhancing bactericidal effect and osteoinductivity

Implant-associated infection is a common postoperative complication and remains a serious problem in orthopedic surgery. This work describes the synthesis of silver nanoparticle-doped hydroxyapatite coatings with oriented block arrays (AgNP-BHAC). The resulting nanostructure was investigated using scanning electron microscopy, energy-dispersive spectrometry, transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. AgNP-BHAC exhibited excellent antimicrobial activity toward gram-negative Escherichia coli and gram-positive Staphylococcus aureus owing to the antibacterial effects of the silver nanoparticles. Human bone marrow stromal cells (hBMSC) culture revealed that the AgNP-BHAC exhibited better biocompatibility, and permitted improved cell proliferation, attachment, and osteoinductivity than uncoated Ti-6Al-4V titanium alloy, the favored material for biomedical applications. In summary, this study presents a convenient and effective method for the incorporation of silver into HA coatings with block morphology. This method can be utilized to modify a variety of metallic implant surfaces to improve their antimicrobial effects and reduce potential long-term cytotoxicity.

Bioinspired nanostructured hydroxyapatite/collagen three-dimensional porous scaffolds for bone tissue engineering

During the biomineralization process of bone minerals, amorphous calcium phosphate (ACP) is converted to apatite crystals by using octacalcium phosphate (OCP) and brushite (DCPD) as transitory precursors, resulting in the formation of hybrid nanostructured collagen/apatite composites. Herein, we report, for the first time, the bioinspired synthesis of a collagen/hydroxyapatite (HA) porous scaffold (CHPS) according to the following stages: (i) fabrication of collagen fibre porous scaffold (CFPS) by a needle-punching process; (ii) deposition of brushite/chitosan (DCPD/CS) on CHPS by a dip-coating method; and (iii) formation of CHPS by in situ conversion of DCPD to HA. The CHPS exhibits three-dimensional (3D) interconnected porous structures with pore sizes of around 60 μm. HA crystals distribute homogeneously on the CHPS, and display wheat-like shapes with a length of approximately 200 nm and a width of approximately 80 nm. The in vitro cell tests by using human bone marrow stromal cells (hBMSCs) indicate that the HA crystals in the CHPS not only promote the cell adhesion and proliferation of the hBMSCs, but also stimulate osteogenic differentiation. The in vivo results reveal that the CHPS exhibits better osteoinductivity than the CFPS because of its similar chemical components, crystallinity and crystallographic texture to natural bone. Moreover, the CHPS can stimulate new bone formation in rat critical-sized calvarial defects within 8 weeks. The CHPS possesses a favourable pore structure, and excellent biocompatibility and osteoinductivity, and thus it has great potential applications for bone tissue engineering.