Functionally graded materials (FGMs) and functionally graded structures (FGSs) are special types of advanced composites with peculiar features and advantages. This article reviews the design criteria of functionally graded additive manufacturing (FGAM), which is capable of fabricating gradient components with versatile functional properties. Conventional geometrical‐based design concepts have limited potential for FGAM and multi‐scale design concepts (from geometrical patterning to microstructural design) are needed to develop gradient components with specific graded properties at different locations. FGMs and FGSs are of great interest to a larger range of industrial sectors and applications including aerospace, automotive, biomedical implants, optoelectronic devices, energy absorbing structures, geological models, and heat exchangers. This review presents an overview of various fabrication ideas and suggestions for future research in terms of design and creation of FGMs and FGSs, benefiting a wide variety of scientific fields.

A biodegradable UV-cured resin has been fabricated via stereolithography apparatus (SLA). The formulation consists of a commercial polyurethane resin as an oligomer, trimethylolpropane trimethacrylate (TEGDMA) as a reactive diluent and phenylbis (2, 4, 6-trimethylbenzoyl)-phosphine oxide (Irgacure 819) as a photoinitiator. The tensile strength of the three-dimensional (3D) printed specimens is 68 MPa, 62% higher than that of the reference specimens (produced by direct casting). The flexural strength and modulus can reach 115 MPa and 5.8 GPa, respectively. A solvent-free method is applied to fabricate graphene-reinforced nanocomposite. Porous bone structures (a jawbone with a square architecture and a sternum with a round architecture) and gyroid scaffold of graphene-reinforced nanocomposite for bone tissue engineering have been 3D printed via SLA. The UV-crosslinkable graphene-reinforced biodegradable nanocomposite using SLA 3D printing technology can potentially remove important cost barriers for personalized biological tissue engineering as compared to the traditional mould-based multistep methods.

A solvent-free method to fabricate graphene-reinforced nanocomposites in net shape via digital light processing (DLP) 3D printing has been developed in this work. The effect of graphene nanofillers on resin viscosity and wettability for various printing parameters has been examined, with a systematic characterization of the mechanical and thermomechanical properties. With the addition of 0.5 wt.% graphene nanoplatelets in the resin, the flexural modulus and fracture toughness have been improved by 14% and 28% from neat resin, respectively. Thermomechanical properties of graphene-reinforced nanocomposites were also enhanced compared with the neat resin, without scarification in their printability. The feasibility of utilizing the DLP method to fabricate a fracture toughness specimen (K_IC test) without complex skill-dependent notch preparation steps was explored, with different notch tip angles printed for net-shaped specimens. This provided a simple and versatile way to perform a quick examination of reinforcing efficiency from nanofillers at very low cost with high resolution and reproducibility. To demonstrate the suitability of current resins for complexly shaped structures, a gyroid scaffold for tissue engineering applications based on current graphene nanocomposite resins has been successfully fabricated via DLP, showing the great potential of current photocurable resins for applications in various fields such as tissue engineering or personalized medical devices without the cost barriers of traditional methods.

The multiplexed luminescence oxygen channeling immunoassay (multi-LOCI) platform we developed recently that combines conventional LOCI and suspension array technology is capable of realizing facile “mix-and-measure” multiplexed assays without tedious washing steps. However, previous work lacks comprehensive studies of the structure–performance relationship of the host–guest-structured barcode, which may obstruct the evolution and further translation of this exciting new technology to practical applications. Accordingly, this work revealed that polyelectrolyte interlayers played a crucial role in tuning the packing density of guest acceptor beads (ABs). More interestingly, we noticed that “sparse” barcodes (barcodes with low ABs packing density) exhibited comparable assay performance with “compact” ones (barcodes with high ABs packing density). The high robustness of barcodes allows for multi-LOCI to be a more universal and flexible assay platform. Furthermore, through optimization of the assay system including the laser power, as well as the concentrations of donor beads and biotinylated detection antibodies, the multi-LOCI platform showed a significant improvement in sensitivity compared with our previous work, with the limit of detection decreasing to as low as ca. 1 pg/mL. Impressively, multi-LOCI that enabled simultaneous detection of multiple analytes exhibited comparable sensitivity with the classical single-plexed LOCI, due to the ingenious structural design of the multi-LOCI barcode and the unique “on-barcode” assay format.