•The MSNPs reinforced bioceramics scaffolds were fabricated by SLS.•Mechanical properties of composite scaffolds were improved by MSNPs.•Reinforcing mechanisms were crack bridging, crack deflection and MSNPs pull-out.•These mechanisms were attribute to the sliding and elastic deformation of MSNPs.•The scaffolds with MSNPs exhibited favorable biocompatibility.The inherent brittleness of bioceramics restricts their applications in load bearing implant, although they possess good biocompatibility and bioactivity. In this study, molybdenum disulfide nanoplatelets (MSNPs) were used to reinforce bioceramics (Mg2SiO4/CaSiO3) scaffolds fabricated by selective laser sintering (SLS). The fracture mode of scaffolds was transformed from transgranular to mixed trans- and intergranular. It could be explained that MSNPs could slide easily due to their weak interlayer van der Waals interactions and provide elastic deformation due to their high elastic modulus. Such sliding action and elastic deformation synergistically induced crack bridging, crack deflection, pull-out and break of MSNPs. Those effects effectively increased the fracture energy dissipation and strain capacity as well as changed the fracture mode, contributing to high fracture toughness and compression strength. Additionally, the scaffolds with MSNPs not only formed a bioactive apatite layer in simulated body fluid, but also supported cell adhesion and proliferation.Download high-res image (390KB)Download full-size image

Strontium (Sr), a bioactive element in natural bone, plays a crucial role in stimulating bone remodeling and inhibiting bone resorption. In this study, strontium oxide (SrO) was incorporated into biosilicate (Mg2SiO4/CaSiO3) scaffolds to improve the biological properties. The results revealed that SrO significantly enhanced cell adhesion, proliferation and the alkaline phosphatase (ALP) activity of the scaffolds. It could be explained that Sr2+ can stimulate osteoblast-related gene expression (osteocalcin, type I collagen, Runx2, etc.) and inhibit osteoclast differentiation. Moreover, the doped scaffolds could degrade continuously and form a dense apatite layer in SBF (simulated body fluid). Besides, the doped scaffolds possessed stable mechanical properties. However, excessive SrO led to a decrease in the strength of the scaffolds, which could be ascribed to the occurrence of unit cell volume expansion caused by the substitution of Sr2+ for Ca2+ in the CaSiO3 lattice. Our research indicated that the SrO doped biosilicate scaffolds have great potential for application in bone regeneration.

•GNPs reinforced Di scaffolds were fabricated by SLS.•The mechanical properties of composite scaffolds were improved by GNPs.•The strengthening and toughening mechanisms were investigated.•GNPs added composite scaffolds exhibited good bioactivity and biocompatibility.Diopside (Di) is ideally suited for tissue engineering applications because of its good bioactivity and biocompatibility, while the low mechanical properties, such as strength and toughness, have hindered its application under load-bearing conditions. In this study, Di scaffolds fabricated by selective laser sintering (SLS) were reinforced with graphene nanoplatelets (GNPs). The mechanism of GNPs on mechanical properties of Di scaffolds was researched. The results showed that the compressive strength and fracture toughness of 1 wt % GNPs/Di scaffold were improved by 102% and 34%, respectively, compared with those of Di scaffold without GNPs. It may be ascribed to the uniform distribution of GNPs in the Di matrix and the grain refinement. Moreover, there exist crack bridging, crack deflection, crack branching and GNPs pullout mechanisms. Furthermore, continuous apatite layers were formed on the scaffolds in SBF solution and MG-63 cells presented good attachment and spreading on the scaffolds in vitro.Fig. 5 SEM images of fractured surfaces for 1 wt % GNPs/Di scaffold: (a) good distribution of GNPs in the scaffold; (b) high magnification image of the fracture surface of the scaffold showing GNPs pull out; (c) GNPs running along the grain boundaries of the Di matrix.Download high-res image (164KB)Download full-size image

Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a membrane protein primarily located in the nuclear membrane and cell membrane. Several groups reported that NGX6 gene was down-regulated in nasopharyngeal carcinoma (NPC), gastric cancer, lung cancer, liver cancer, and colorectal cancer and even less in the carcinomas with metastasis. Current studies have demonstrated that NGX6 possesses various biological functions, such as regulating protein expression of related genes, involving cell signal transduction pathways, negatively controlling cell cycle progression, inhibiting angiogenesis, and increasing the sensitivity of patients to anti-cancer drugs. Some factors regulating the expression level of NGX6 gene also have been studied. The methylation of promoter of NGX6 and histone H3K9 negatively regulates its expression, similar to the function of transcription factor special protein-1 (Sp1). However, the regulatory factor early growth response gene 1 (Egr-1) is provided with positive regulation function. This review will summarize the progress of those studies on NGX6 and elucidate the potential application of NGX6 for some malignant diseases.

Polyglycolide (PGA) is considered an attractive candidate for bone regeneration because of its good biodegradability and biocompatibility. However, its insufficient mechanical strength and inadequate bioactivity limit its applications. In this study, diopside (DIOP) was incorporated into PGA scaffolds to enhance the mechanical and biological properties. The porous scaffolds were fabricated via selective laser sintering (SLS). The effect of the DIOP content on the microstructure, mechanical properties, bioactivity as well as cytocompatibility of the porous scaffolds was studied. The results showed that DIOP particles were homogenously distributed within the PGA matrix, which contained up to 10 wt%. This led to an improvement of 171.2% in compressive strength and 46.2% in compressive modulus. In vitro studies demonstrated that the highest apatite forming ability was obtained on the scaffold surfaces with the highest amount of DIOP after soaking in simulated body fluid (SBF), suggesting that the bioactivity of the scaffolds increased with increasing DIOP. In addition, a cytocompatibility study showed that the scaffolds exhibited a higher degree of cell attachment, growth and differentiation than the pure PGA scaffolds. These indicated that the PGA scaffolds modified with DIOP possessed suitable properties which could be used for bone tissue regeneration.

In this study, graphene oxide (GO) is incorporated into poly(vinyl alcohol) (PVA) for the purpose of improving the mechanical properties. Nanocomposite scaffolds with an interconnected porous structure are fabricated by selective laser sintering (SLS). The results indicate that the highest improvements in the mechanical properties are obtained, that is, a 60%, 152% and 69% improvement of compressive strength, Young's modulus and tensile strength is achieved at the GO loading of 2.5 wt%, respectively. The reason can be attributed to the enhanced load transfer due to the homogeneous dispersion of GO sheets and the strong hydrogen bonding interactions between GO and the PVA matrix. The agglomerates and restacking of GO sheets occur on further increasing the GO loading, which leads to the decrease in the mechanical properties. In addition, osteoblast-like cells attach and grow well on the surface of scaffolds, and proliferate with increasing time of culture. The GO/PVA nanocomposite scaffolds are potential candidates for bone tissue engineering.

Akermanite possesses excellent biocompatibility and biodegradability, while low fracture toughness and brittleness have limited its use in load bearing sites of bone tissue. In this work, nano-titania (nano-TiO2) was dispersed into the ceramic-matrix to enhance the mechanical properties of porous akermanite scaffolds fabricated with selective laser sintering (SLS). The fabrication process, microstructure and mechanical and biological properties were investigated. The results showed that the nano-TiO2 particles were dispersed both within the akermanite grains and along the grain boundaries. The grain size of akermanite was refined due to the pinning effect of the nano-TiO2 particles on the grain boundaries. The crack deflection around the nano-TiO2 particles was observed due to the mismatch of thermal expansion coefficients between TiO2 and akermanite. The fracture mode changed from intergranular fracture to more and more transgranular fracture as the concentration of nano-TiO2 increased from 0 to 5 wt%. Meanwhile, the fracture toughness, Vickers hardness, compressive strength and stiffness were significantly increased with increasing nano-TiO2. The improvement of mechanical properties was due to the grain size refinement, the crack deflection, as well as the fracture mode transition. The bone like apatite was formed on the scaffolds in simulated body fluid (SBF). The human osteoblast-like MG-63 cells (MG-63 cells) adhered and grew well on the scaffolds. The porous akermanite scaffolds reinforced with nano-TiO2 have considerable potential for application in bone tissue engineering.

The calcium sulfate (CaSO4) bone scaffolds with high porosity and interconnectivity and controllable pore size were prepared by using selective laser sintering. The phase composition, micro morphology and biocompatibility were investigated by using X-ray diffraction, scanning electron microscopy and microculture tetrazolium test. The results showed that the CaSO4 powders fused better and a more compact structure was built due to the decrease of holes in the scaffold at laser power of 7 W compared with 6 W or lower. At this time, both compressive strength and fracture toughness were optimal. While CaSO4 decomposed and resulted in the mechanical properties decreasing when laser power further increased. Consequently, the mechanical properties of the scaffolds decreased. Moreover, the osteoblast-like cells attached on the scaffolds were obtained by cell culture in vitro. The results revealed that the cells could adhere and grow well on the scaffolds.

The poor mechanical properties of akermanite (AKM), especially fracture toughness, limits its applications in bone tissue engineering, although it possesses favorable biological performance. In this research, silicon carbide whiskers (SiCw) are added in order to reinforce AKM scaffolds with controllable porous structures fabricated by selective laser sintering (SLS). The mechanical properties, microstructure and toughening mechanisms are analyzed. The results indicate that the compressive strength and fracture toughness increases with increasing SiCw from 5 to 20 wt.%, and then decreases when more SiCw are incorporated. The strengthening and toughening mechanisms are attributed to interface debonding, whisker fracture and whisker pull-out, and the main fracture mode becomes transgranular fracture. Moreover, the phase composition of SiCw remains constant, confirmed by X-ray diffraction (XRD) analysis. The bioactivity and degradation behaviour of the scaffolds were evaluated by soaking them in simulated body fluid (SBF). The results show that the composite scaffolds with 20 wt.% SiCw exhibits good apatite-mineralization ability and a moderate degradation rate in SBF medium. Moreover, scanning electron microscopy (SEM) analysis, MTT assay and alizarin red staining of human bone marrow stromal cells (hBMSCs) seeded scaffolds confirm the stem cell attachment, viability, proliferation and differentiation on the scaffolds. Thus, the overall study proves that SiCw reinforced AKM scaffolds have the potential to be used in bone tissue engineering.

Nasopharyngeal carcinoma (NPC) is the most common cancer originating in the nasopharynx, and is extremely common in southern regions of China. Although the standard combination of radiotherapy and chemotherapy has improved the efficiency in patients with NPC, relapse and early metastasis are still the common causes of mortality. Cancer stem-like cells (CSCs) or tumor initial cells are hypothesized to be involved in cancer metastasis and recurrence. Over the past decade, increasing numbers of studies have been carried out to identify CSCs from human NPC cells and tissues. The present paper will summarize the investigations on nasopharyngeal CSCs, including isolation, characteristics, and therapeutic approaches. Although there are still numerous challenges to translate basic research into clinical applications, understanding the molecular details of CSCs is essential for developing effective strategies to prevent the recurrence and metastasis of NPC.

Calcium phosphate ceramics are considered as the most promising materials for bone tissue engineering due to their excellent biocompatibility and bioactivity. In the paper, porous calcium phosphate scaffolds were prepared via selective laser sintering with various weight ratios of TCP/HAP (0/100, 10/90, 30/70, 50/50, 70/30 and 100/0) powders. Furthermore the effect of phase composition on biological and mechanical properties of the scaffold was investigated. The results showed that both the fracture toughness and compressive strength increased with increasing content of TCP from 0 to 30 wt.%, and then dropped with a further increasing content of TCP. The scaffold made of TCP/HAP with a ratio of 30/70 exhibited the optimum fracture toughness (1.33 MPa m1/2) and compressive strength (18.35 MPa). After the scaffolds were soaked in SBF for 7 days, the apatite agglomerates formed on the surface of the scaffolds and the dissolution rate of the scaffolds increased with the increasing content of the TCP. In vitro cell culture indicated that a balance between biological stability and biodegradation rate was helpful for cell adherence and proliferation. It was concluded that the scaffold sintered with TCP/HAP(30/70) performed with optimum mechanical and biological properties.Highlights► Porous ceramic scaffolds with different ratios of TCP/HAP were fabricated by SLS. ► BCP scaffolds exhibit better mechanical properties than HAP or TCP scaffolds. ► The bioactivity of scaffolds can be controlled by adjusting the TCP/HAP ratio. ► TCP/HAP(30/70) exhibit optimal comprehensive properties.

•Small amount of PLLA/PLGA was added into the BCP bone scaffold fabrication.•BCP scaffold becomes more compact by introducing transient liquid phase of polymers.•Hardness and fracture toughness are optimal with 1 wt.% PLLA/PLGA.•PLLA/PLGA provides a liquid phase at the early stage of sintering.•PLLA/PLGA decomposes and is oxidized completely, then excluded from the final products.Biphasic calcium phosphate (BCP), which is composed of hydroxyapatite [HAP, Ca10(PO4)6(OH)2] and β-tricalcium phosphate [β-TCP, β-Ca3(PO4)2], is usually difficult to densify into a solid state with selective laser sintering (SLS) due to the short sintering time. In this study, the sintering ability of BCP ceramics was significantly improved by adding a small amount of polymers, by which a liquid phase was introduced during the sintering process. The effects of the polymer content, laser power and HAP/β-TCP ratios on the microstructure, chemical composition and mechanical properties of the BCP scaffolds were investigated. The results showed that the BCP scaffolds became increasingly more compact with the increase of the poly(l-lactic acid) (PLLA) content (0–1 wt.%) and laser power (6–10 W). The fracture toughness and micro-hardness of the sintered scaffolds were also improved. Moreover, PLLA could be gradually decomposed in the late sintering stages and eliminated from the final BCP scaffolds if the PLLA content was below a certain value (approximately 1 wt.% in this case). The added PLLA could not be completely eliminated when its content was further increased to 1.5 wt.% or higher because an unexpected carbon phase was detected in the sintered scaffolds. Furthermore, many pores were observed due to the removal of PLLA. Micro-cracks and micro-pores occurred when the laser power was too high (12 W). These defects resulted in a deterioration of the mechanical properties. The hardness and fracture toughness reached maximum values of 490.3 ± 10 HV and 1.72 ± 0.10 MPa m1/2, respectively, with a PLLA content of approximately 1 wt.% and laser power of approximately 10 W. Poly(l-lactic-co-glycolic acid) (PLGA) showed similar effects on the sintering process of BCP ceramics. Rectangular, porous BCP scaffolds were fabricated based on the optimum values of the polymer content and laser power. This work may provide an experimental basis for improving the mechanical properties of BCP bone scaffolds fabricated with SLS.

Poly(lactide-co-glycolide) (PLGA)/nano-hydroxyapatite (nano-HAP) composite porous scaffolds with well-controlled pore architectures as well as high exposure of the bioactive ceramics to the scaffold surface were fabricated via selective laser sintering. Neat PLGA and the composite of PLGA/nano-HAP were used to obtain suitable process parameters. The effects of nano-HAP content on the microstructure and mechanical properties were investigated. The testing results showed that the compressive strength and modulus of the scaffolds were highly enhanced when the nano-HAP content reached from 0 to 20 wt%, while the mechanical properties experienced a sharp dropped with the nano-HAP content further increased. This might be due to the large reduction in polymer which decreased the interface bond strength between particles. It suggests that the introduction of nano-HAP as a reinforcing phase can improve the mechanical properties of the polymer porous scaffolds. The novel developed scaffolds may serve as a three-dimensional bone substrate in tissue engineering.

The sintering processing of hydroxyapatite (HAP) powder was studied using selective laser sintering for bone tissue engineering. The effect of laser energy density on the microstructure, phase composition and mechanical properties of the sintered samples was investigated. The results indicate that the average grain size increases from 0.211 ± 0.039 to 0.979 ± 0.133 μm with increasing the laser energy density from 2.0 to 5.0 J/mm2. The maximum value of Vickers hardness and fracture toughness were 4.0 ± 0.13 Gpa and 1.28 ± 0.033 MPam1/2, respectively, when the laser energy density was 4.0 J/mm2. The XRD results indicated that the nano-HAP was decomposed into TCP with the laser energy density of above 4.0 J/mm2. In vitro bioactivity after soaking in simulated body fluid (SBF) for 3 ∼ 12 days showed that a bone-like apatite layer on the surface of the sintered samples. It indicated that the HAP scaffold possesses favorable mechanical properties and bioactivity, and may be used for bone tissue engineering.