Role of Molecular Chemistry of Degradable pHEMA Hydrogels in Three-Dimensional Biomimetic Mineralization

Three-dimensional (3D) biomimetic mineralization is highly desired for soft biomaterials such as collagen to create useful hybrid biomaterials for orthopedic tissue engineering. Here, we apply an approach of current-mediated ion diffusion, as a feasible means of 3D biomimetic mineralization, to a series of generic, hydrolytically degradable poly­(2-hydroxyethyl methacrylate) hydrogels with various molecular structures, imparted by the introduction of the comonomers, acrylic acid and 2-hydroxyethyl methacrylamide. This approach enables us to create a wide range of nanoscale single crystals of calcium phosphate within the hydrogels as characterized by high-resolution transmission electron microscopy (TEM). Molecular chemistry of the hydrogels, coupled with pH and gel strength, plays a crucial role in formation of the minerals. Both brushite (CaHPO₄·2H₂O) and octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O) are observed in pHEMA homo hydrogel. Both octacalcium phosphate and monetite (CaHPO₄) are seen in a copolymer hydrogel, poly­(2-hydrogelethyl methacrylate-co-acrylic acid). In another copolymer hydrogel (poly­(2-hydroxyethyl methacrylate-co-2-hydroxyethyl methacrylamide), both hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and monetite (CaHPO₄) are observed. All these nanocrystals are essential to bone regeneration. They organize themselves primarily as nanoscale fibers, sheets, needles, and clusters. These nanoarchitectures are important to bone-cell attachment, proliferation, migration, and differentiation, and dictate the ingrowth of new bone tissues

Graphene Oxide: An All-in-One Processing Additive for 3D Printing

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing

Robust Bioinspired Graphene Film via π–π Cross-linking

Graphene composite films inspired by nacre are the subject of ongoing research efforts to optimize their properties for applications in flexible energy devices. Noncovalent interactions do not cause interruption of the delocalized conjugated π-electron system, thus preserving graphene’s excellent properties. Herein, we synthesized a conjugated molecule with pyrene groups on both ends of a long linear chain (AP-DSS) from 1-amino­pyrene (AP) and disuccin­imidyl suberate (DSS). The AP-DSS molecules are used to cross-link adjacent graphene nanosheets via π–π interfacial interactions to improve properties of graphene films. The tensile strength and toughness of resultant graphene films were 4.1 and 6.4 times higher, respectively, than that of pure rGO film. More remarkably, the electrical conductivity showed a simultaneous improvement, which is rare to be achieved in other kinds of covalent or noncovalent functionalization. Such integration demonstrates the advantage of this work to previously reported noncovalent functionalization of graphene

Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures

Robust underwater oil-repellent materials combining high mechanical strength and durability with superwettability and low oil adhesion are needed to build oil-repellent devices able to work in water, to manipulate droplet behavior, etc. However, combining all of these properties within a single, durable material remains a challenge. Herein, we fabricate a robust underwater oil-resistant material (Al2O3) with all of the above properties by gel casting. The micro/nanoceramic particles distributed on the surface endow the material with excellent underwater superoleophobicity (∼160°) and low oil adhesion (<4 μN). In addition, the substrate exhibits typical ceramic characteristics such as good antiacid/alkali properties, high salt resistance, and high load tolerance. These excellent properties make the material not only applicable to various liquid environments but also resistant to the impact of particles and other physical damage. More importantly, the substrate could still exhibit underwater superoleophobicity after being worn under specific conditions, as wear will create new surfaces with similar particle size distribution. This approach is easily scalable for mass production, which could open a pathway for the fabrication of practical underwater long-lasting functional interfacial materials

Metal-Organic Framework ZIF‑8 Films As Low‑κ Dielectrics in Microelectronics

ZIF-8 films were deposited on silicon wafers and characterized to assess their potential as future insulators (low-κ dielectrics) in microelectronics. Scanning electron microscopy and gas adsorption monitored by spectroscopic ellipsometry confirmed the good coalescence of the crystals, the absence of intergranular voids, and the hydrophobicity of the pores. Mechanical properties were assessed by nanoindentation and tape tests, confirming sufficient rigidity for chip manufacturing processes (elastic modulus >3 GPa) and the good adhesion to the support. The dielectric constant was measured by impedance analysis at different frequencies and temperatures, indicating that κ was only 2.33 (±0.05) at 100 kHz, a result of low polarizability and density in the films. Intensity voltage curves showed that the leakage current was only 10^–8 A cm² at 1 MV cm^–1, and the breakdown voltage was above 2 MV cm^–1. In conclusion, metal-organic framework ZIF-8 films were experimentally found to be promising candidates as low-κ dielectrics in microelectronic chip devices. This opens a new direction for research into the application of metal-organic frameworks

Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures

Robust underwater oil-repellent materials combining high mechanical strength and durability with superwettability and low oil adhesion are needed to build oil-repellent devices able to work in water, to manipulate droplet behavior, etc. However, combining all of these properties within a single, durable material remains a challenge. Herein, we fabricate a robust underwater oil-resistant material (Al2O3) with all of the above properties by gel casting. The micro/nanoceramic particles distributed on the surface endow the material with excellent underwater superoleophobicity (∼160°) and low oil adhesion (<4 μN). In addition, the substrate exhibits typical ceramic characteristics such as good antiacid/alkali properties, high salt resistance, and high load tolerance. These excellent properties make the material not only applicable to various liquid environments but also resistant to the impact of particles and other physical damage. More importantly, the substrate could still exhibit underwater superoleophobicity after being worn under specific conditions, as wear will create new surfaces with similar particle size distribution. This approach is easily scalable for mass production, which could open a pathway for the fabrication of practical underwater long-lasting functional interfacial materials

Activation Energy Paths for Graphene Nucleation and Growth on Cu

The synthesis of wafer-scale single crystal graphene remains a challenge toward the utilization of its intrinsic properties in electronics. Until now, the large-area chemical vapor deposition of graphene has yielded a polycrystalline material, where grain boundaries are detrimental to its electrical properties. Here, we study the physicochemical mechanisms underlying the nucleation and growth kinetics of graphene on copper, providing new insights necessary for the engineering synthesis of wafer-scale single crystals. Graphene arises from the crystallization of a supersaturated fraction of carbon-adatom species, and its nucleation density is the result of competition between the mobility of the carbon-adatom species and their desorption rate. As the energetics of these phenomena varies with temperature, the nucleation activation energies can span over a wide range (1–3 eV) leading to a rational prediction of the individual nuclei size and density distribution. The growth-limiting step was found to be the attachment of carbon-adatom species to the graphene edges, which was independent of the Cu crystalline orientation