The high brittleness and low strength of bioactive ceramics have severely restricted their application in bone repair despite the fact that they have been regarded as one of the most promising biomaterials. In the last few years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have gained increasing attention owing to their favorable biocompatibility, large surface specific area and super mechanical properties. These qualities make LDNs potential nanofillers in reinforcing bioactive ceramics. In this review, the types, characteristics and applications of the commonly used LDNs in ceramic composites are summarized. In addition, the fabrication methods for LDNs/ceramic composites, such as hot pressing, spark plasma sintering and selective laser sintering, are systematically reviewed and compared. Emphases are placed on how to obtain the uniform dispersion of LDNs in a ceramic matrix and maintain the structural stability of LDNs during the high-temperature fabrication process of ceramics. The reinforcing mechanisms of LDNs in ceramic composites are then discussed in-depth. The in vitro and in vivo studies of LDNs/ceramic in bone repair are also summarized and discussed. Finally, new developments and potential applications of LDNs/ceramic composites are further discussed with reference to experimental and theoretical studies.Statement of SignificanceDespite bioactive ceramics having been regarded as promising biomaterials, their high brittleness and low strength severely restrict their application in bone scaffolds. In recent years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have shown great potential in reinforcing bioactive ceramics owing to their unique structures and properties. However, so far it has been difficult to maintain the structural stability of LDNs during fabrication of LDNs/ceramic composites, due to the lengthy, high-temperature process involved. This review presents a comprehensive overview of the developments and applications of LDNs in bioactive ceramics. The newly-developed fabrication methods for LDNs/ceramic composites, the reinforcing mechanisms and the in vitro and in vivo performance of LDNs are also summarized and discussed in detail.Download high-res image (235KB)Download full-size image

•A mesoporous silica composite scaffold was fabricated by selective laser sintering.•Experimental results show that the composite scaffold stimulates cell behaviors.•The composite scaffold had good bioactivity.•The biomineralization mechanism of the composite scaffold was investigated.•The addition of SBA15 improved the mechanical properties of the scaffold.Mesoporous structure is beneficial to cellular response due to the large specific surface area and high pore volume. In this study, mesoporous silica (SBA15) was incorporated into poly-l-lactic acid (PLLA) to construct composite scaffold by selective laser sintering. The results showed that SBA15 facilitated cells proliferation, which was mainly attributed to its unique intrinsic mesoporous structure and the released bioactive silicon. Moreover, the hydrolyzate of soluble mesoporous silica can adsorb ions to form nucleation sites that promote biomineralization, leading to improve biological activity of the composite scaffold. In addition, the compressive strength, compressive modulus and Vickers hardness of the scaffold were increased by 47.6%, 35.5% and 29.53% respectively with 1.5 wt.% SBA15. It was found that the particle enhancement of uniform distributed SBA15 accounted for the mechanic reinforcement of the composite scaffold. It indicated that the PLLA-SBA15 composite scaffold had potential applications in bone tissue engineering.Download high-res image (196KB)Download full-size image

•Alloying Sn and laser rapid melting were applied to slow down the degradation rate of Mg.•With Sn content increasing, the grain sizes decreased, while the new Mg2Sn phase increased.•The effects of grain sizes and Mg2Sn phase volume fraction on the degradation rate were studied.•The hardening mechanisms were investigated.Mg is a potentially biomaterial for bone implant due to its biodegradability and biomechanical compatibility. However, the too fast degradation rate limits its clinical application. In the study, both alloying treatment and laser rapid melting were applied to slow down its degradation rate. The microstructure, mechanical properties and degradation behavior of the MgxSn (x = 0–7 wt %) alloys were investigated. With Sn content increasing, the grain sizes decreased, while the new Mg2Sn phase increased. The refined grain slowed the degradation rate due to the reduced segregation. While the Mg2Sn phase accelerated the degradation rate owing to the couple galvanic corrosion. Thus, the optimal degradation behavior was obtained with a balanced grain size and Mg2Sn phase volume fraction. Besides, the compression strength increased firstly (up to 5 wt %) and then decreased with Sn increasing.

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.

•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.