Novel Graphene Planar Architecture with Ultrahigh Stretchability and Sensitivity

Graphene (GNP) reinforced 3D printing nanocomposites: An advanced structural perspective

The influence of macro-micro structural design on the mechanical response of structural nanocomposites is substantial. The advancement of additive manufacturing especially three-dimensional (3-D) printing technology offers a promising avenue for the efficient and precise fabrication of multi-functional low-weight and high-strength nanocomposites. In contemporary discourse, there is a notable emphasis on carbon-based nanomaterials as nanofillers for structural composites due to their substantial specific surface area and exceptional load-bearing ability in mechanical structures. Notably, graphene, a distinctive two-dimensional (2-D) nanomaterial, exhibits very large elastic modulus and ultimate strength as well as remarkable plasticity. The utilization of graphene nanoparticles (GNPs) in the field of 3-D printing enables the production of intricate three-dimensional structures of varying sizes and configurations. This is achieved through the macro-assembly process, which facilitates the creation of a well-organized distribution of graphene and the establishment of a comprehensive physical network through precise micro-regulation. This paper presents an overview of multiscale structural composites that are strengthened by the incorporation of graphene and prepared by 3-D printing. The composites discussed in this study encompass graphene-polymer composites, graphene-ceramic composites, and graphene-metal composites. Furthermore, an analysis of the present obstacles and potential future advancements in this rapidly expanding domain is anticipated.

Graphene nanoribbon woven fabric against the impact of a cylindrical projectile

Graphene nanoribbon woven fabrics (GNWFs) with excellent mechanical properties are promising for ballistic armor materials. The dynamic response of single-layer and bilayer GNWFs under nano-projectile impact at high-speed (4-5 km s-1) is investigated by molecular dynamics simulations. Results show that the woven structure is determined by the bandwidth and gap spacing, which influences the deformation/fracture and motion coupling effects of the crossed nanoribbons and the ballistic performance of GNWF. Owing to the perturbation of the van der Waals (vdW) interface between nanoribbons, the specific penetration energy of GNWFs reaches 16.02 MJ kg-1, which is much higher than that of single-layer graphene (10.80 MJ kg-1) and bilayer graphene (10.07 MJ kg-1). The peculiarities of woven structure minimize the damage of GNWFs, on the one hand, the reversibility of vdW interactions and the entanglement of nanoribbons provide GNWFs a certain self-healing ability. On the other hand, the porous nanostructure of twist-stacked bilayer GNWFs tends to be uniform and dense with the twist angle, which improves the impact resistance. This study provides more understanding of the ballistic properties of GNWFs and the design of nano-fabrics based on two-dimensional materials.

Graphene Flake Self-Assembly Enhancement via Stretchable Platforms and External Mechanical Stimuli

While the green production and application of 2D functional nanomaterials, such as graphene flakes, in films for stretchable and wearable technologies is a promising platform for advanced technologies, there are still challenges involved in the processing of the deposited material to improve properties such as electrical conductivity. In applications such as wearable biomedical and flexible energy devices, the widely used flexible and stretchable substrate materials are incompatible with high-temperature processing traditionally employed to improve the electrical properties, which necessitates alternative manufacturing approaches and new steps for enhancing the film functionality. We hypothesize that a mechanical stimulus, in the form of substrate straining, may provide such a low-energy approach for modifying deposited film properties through increased flake packing and reorientation. To this end, graphene flakes were exfoliated using an unexplored combination of ethanol and cellulose acetate butyrate for morphological and percolative electrical characterization prior to application on polydimethylsiloxane (PDMS) substrates as a flexible and stretchable electrically conductive platform. The deposited percolative free-standing films on PDMS were characterized via in situ resistance strain monitoring and surface morphology measurements over numerous strain cycles, with parameters extracted describing the dynamic modulation of the film's electrical properties. A reduction in the film resistance and strain gauge factor was found to correlate with the surface roughness and densification of a sample's (sub)surface and the applied strain. High surface roughness samples exhibited enhanced reduction in resistance as well as increased sensitivity to strain compared to samples with low surface roughness, corresponding to surface smoothing, which is related to the dynamic settling of graphene flakes on the substrate surface. This procedure of incorporating strain as a mechanical stimulus may find application as a manufacturing tool/step for the routine fabrication of stretchable and wearable devices, as a low energy and compatible approach, for enhancing the properties of such devices for either high sensitivity or low sensitivity of electrical resistance to substrate strain.

Recent advances of polymer-based piezoelectric composites for biomedical applications

Over the past decades, electronics have become central to many aspects of biomedicine and wearable device technologies as a promising personalized healthcare platform. Lead-free piezoelectric materials for converting mechanical into electrical energy through piezoelectric transduction are of significant value in a diverse range of technological applications. Organic piezoelectric biomaterials have attracted widespread attention as the functional materials in the biomedical devices due to their advantages of excellent biocompatibility. They include synthetic and biological polymers. Many biopolymers have been discovered to possess piezoelectricity in an appreciable amount, however their investigation is still preliminary. Due to their piezoelectric properties, better known synthetic fluorinated polymers have been intensively investigated and applied in biomedical applications including controlled drug delivery systems, tissue engineering, microfluidic and artificial muscle actuators, among others. Piezoelectric polymers, especially poly (vinylidene fluoride) (PVDF) and its copolymers are increasingly receiving interest as smart biomaterials due to their ability to convert physiological movements to electrical signals when in a controllable and reproducible manner. Despite possessing the greatest piezoelectric coefficients among all piezoelectric polymers, it is often desirable to increase the electrical outputs. The most promising routes toward significant improvements in the piezoelectric response and energy-harvesting performance of such materials is loading them with various inorganic nanofillers and/or applying some modification during the fabrication process. This paper offers a comprehensive review of the principles, properties, and applications of organic piezoelectric biomaterials (polymers and polymer/ceramic composites) with special attention on PVDF-based polymers and their composites in sensors, drug delivery and tissue engineering. Subsequently focuses on the most common fabrication routes to produce piezoelectric scaffolds, tissue and sensors which is electrospinning process. Promising upcoming strategies and new piezoelectric materials and fabrication techniques for these applications are presented to enable a future integration among these applications.