Advances of Hydrogel-Based Bioprinting for Cartilage Tissue Engineering

Bioprinting has gained immense attention and achieved the revolutionized progress for application in the multifunctional tissue regeneration. On account of the precise structural fabrication and mimicking complexity, hydrogel-based bio-inks are widely adopted for cartilage tissue engineering. Although more and more researchers have reported a number of literatures in this field, many challenges that should be addressed for the development of three-dimensional (3D) bioprinting constructs still exist. Herein, this review is mainly focused on the introduction of various natural polymers and synthetic polymers in hydrogel-based bioprinted scaffolds, which are systematically discussed via emphasizing on the fabrication condition, mechanical property, biocompatibility, biodegradability, and biological performance for cartilage tissue repair. Further, this review describes the opportunities and challenges of this 3D bioprinting technique to construct complex bio-inks with adjustable mechanical and biological integrity, and meanwhile, the current possible solutions are also conducted for providing some suggestive ideas on developing more advanced bioprinting products from the bench to the clinic.

Effects of the Interface between Inorganic and Organic Components in a Bi2Te3–Polypyrrole Bulk Composite on Its Thermoelectric Performance

We provided a method to hybridize Bi2Te3 with polypyrrole, thus forming an inorganic/organic bulk composite (Bi2Te3–polypyrrole), in which the effects of energy band junction and phonon scattering were expected to occur at the interface of the two components. Bi2Te3–polypyrrole exhibited a considerably high Seebeck coefficient compared to pristine Bi2Te3, and thus it recorded a somewhat increased power factor despite the loss in electrical conductivity caused by the organic component, polypyrrole. Bi2Te3–polypyrrole also exhibited much lower thermal conductivity than pristine Bi2Te3 because of the phonon scattering effect at the interface. We successfully brought about the decoupling phenomenon of electrical and thermal properties by devising an inorganic/organic composite and adjusting its fabrication condition, thereby optimizing its thermoelectric performance, which is considered the predominant property for n-type binary Bi2Te3 reported so far.

Influences of Process Parameters on the Microstructure and Mechanical Properties of CoCrFeNiTi Based High-Entropy Alloy in a Laser Powder Bed Fusion Process

Recently, high-entropy alloys (HEAs) have attracted much attention because of their superior properties, such as high strength and corrosion resistance. This study aimed to investigate the influences of process parameters on the microstructure and mechanical properties of CoCrFe NiTiMo HEAs using a laser-based powder bed fusion (LPBF) process. In terms of laser power and scan speed, a process map was constructed by evaluating the density and surface roughness of the as-built specimen to optimize the process parameters of the products. The mechanical properties of the as-built specimens fabricated at the optimum fabrication condition derived from the process map were evaluated. Consequently, the optimum laser power and scan speed could be obtained using the process map evaluated by density and surface roughness. The as-built specimen fabricated at the optimum fabrication condition presented a relative density of more than 99.8%. The microstructure of the as-built specimen exhibited anisotropy along the build direction. The tensile strength and elongation of the as-built specimen were around 1150 MPa and more than 20%, respectively.

Photostable and Uniform CH3NH3PbI3 Perovskite Film Prepared via Stoichiometric Modification and Solvent Engineering

Solution-processed organometal halide perovskites (OMHPs) have been widely used in optoelectronic devices, and have exhibited brilliant performance. One of their generally recognized advantages is their easy fabrication procedure. However, such a procedure also brings uncertainty about the opto-electric properties of the final samples and devices, including morphology, stability, coverage ratio, and defect concentration. Normally, one needs to find a balanced condition, because there is a competitive relation between these parameters. In this work, we fabricated CH3NH3PbI3 films by carefully changing the ratio of the PbI2 to CH3NH3I, and found that the stoichiometric and solvent engineering not only determined the photoluminescence efficiency and defects in the materials, but also affected the photostability, morphology, and coverage ratio. Combining solvent engineering and the substitution of PbI2 by Pb(Ac)2, we obtained an optimized fabrication condition, providing uniform CH3NH3PbI3 films with both high photoluminescence efficiency and high photostability under either I-rich or Pb-rich conditions. These results provide an optimized fabrication procedure for CH3NH3PbI3 and other OMHP films, which is crucial for the performance of perovskite-based solar cells and light emitting devices.

A void behavior in a complex-shaped composite structure

Voids or porosities have been one of the biggest headaches in composite fabricators and are still a challenging issue. In this study, void behavior in a low pressurized area of the laminate during cure is identified and analyzed. And, the influence of material’s cure rate difference on laminate inner quality is evaluated and verified through material evaluation and test article fabrication with subsequent non-destructive and destructive inspection. When there is a surface film on outer layer of the laminate, it is confirmed that surface film acts as barrier layer to prevent void evacuation and keep voids locked in laminate during cure. And, under the same fabrication condition and process variables, except for a layer of surface film, trapped void have been properly evacuated and test article exhibited good inner quality.