Bioinspired Wear‐Resistant and Ultradurable Functional Gradient Coatings

Abstract

For mechanically protective coatings, the coating material usually requires sufficient stiffness and strength to resist external forces and meanwhile matched mechanical properties with the underneath substrate to maintain the structural integrity. These requirements generate a conflict that limits the coatings from achieving simultaneous surface properties (e.g., high wear‐resistance) and coating/substrate interfacial durability. Herein this conflict is circumvented by developing a new manufacturing technique for functional gradient coatings (FGCs) with the material composition and mechanical properties gradually varying crossing the coating thickness. The FGC is realized by controlling the spatial distribution of magnetic‐responsive nanoreinforcements inside a polymer matrix through a magnetic actuation process. By concentrating the reinforcements with hybrid sizes at the surface region and continuously diminishing toward the coating/substrate interface, the FGC is demonstrated to exhibit simultaneously high surface hardness, stiffness, and wear‐resistance, as well as superb interfacial durability that outperforms the homogeneous counterparts over an order of magnitude. The concept of FGC represents a mechanically optimized strategy in achieving maximal performances with minimal use and site‐specific distribution of the reinforcements, in accordance with the design principles of many load‐bearing biological materials. The presented manufacturing technique for gradient nanocomposites can be extended to develop various bioinspired heterogeneous materials with desired mechanical performances.

Squid Beak Inspired Cross-Linked Cellulose Nanocrystal Composites

“…Polymer nanocomposites that consist of nanosized fillers embedded within a polymer matrix are frequently utilized in natural systems to create biological materials with a broad range of exceptional physical properties. − Examples of biological nanocomposites include nacre, which demonstrates remarkable toughness, the dermis of the sea cucumber, which shows mechanical adaptability, − and the club of the mantis shrimp, which exhibits exceptional damage tolerance. , Understanding the mechanism of such biological systems allows for the development of new composites that either directly mimic the function and properties of natural materials or employs nature’s design strategies to enhance the performance of synthetic systems. − Such bioinspired nanocomposites have already been designed and used in a number of applications, such as structural materials, − functional coatings, intracortical sensors, and energy-harvesting membranes …”

Core–Shell Magnetic Micropillars for Reprogrammable Actuation

“…The H r was generated by two disk-shaped NdFeB magnets placed in a parallelly repulsive configuration (Figure S1) with the direction of the field controlled by switching the magnetic poles of the magnets. Such a configuration could significantly increase the magnetic field gradient in-between and thus facilitate the nanoparticle migrations in the resin liquid . The intensity of the H r was controlled by adjusting the distance between the two magnets.…”

“…Such a configuration could significantly increase the magnetic field gradient in-between and thus facilitate the nanoparticle migrations in the resin liquid. 73 The intensity of the H r was controlled by adjusting the distance between the two magnets. In the present study, this intermagnet distance was fixed at 10 mm and the core−shell micropillar specimen was attached with either the top or the bottom magnet at the middle region.…”

Augmenting Tendon‐to‐Bone Repair with Functionally Graded Scaffolds

“…Among the various types of scaffolds that have been fabricated and evaluated for tendon-to-bone repair, the most promising ones include gradual variations, either in a stratified or continuous fashion, with respect to composition, structure, mechanical properties, and cell phenotypes (Figure 1C). [23][24][25][26][27][28][29][30] Such biomimetic scaffolds can duplicate various aspects of the native tendon enthesis to promote healing and functional recovery. These materials are typically referred to as functionally graded scaffolds, which are characterized by gradual spatial variations in composition and/or structure to recapitulate the native interface between soft and hard tissues.…”