The extraordinary properties of biological materials often result from their sophisticated hierarchical structures. Through multilevel and cross-scale structural designs, biological materials offset the weakness of their individual building blocks and enhance performance at multiple length scales to match the multifunctional needs of organisms. One essential merit of hierarchical structure is that it can optimize the interfacial features of the “building blocks” at different length scales, from the molecular level to the macroscale. Understanding the roles of biological material interfaces (BMIs) on the determination of properties and functions of biological materials has become a growing interdisciplinary research area in recent years. A pivotal aim of these studies is to use BMIs as inspiration for developing bioinspired and biomimetic materials and devices with advanced structures and functions. Given these considerations, this review aims to comprehensively discuss the structure–property–function relationships of BMIs in nature. We particularly focus on the discussion of BMIs and their inspired materials from mechanical and optical perspectives because these two directions are the most well-investigated and closely related. The challenges and directions of design and fabrication of BMI-inspired mechanical and optical materials are also discussed. This review is expected to garner interest from advanced material communities as well as environmental, nanotechnology, food processing, and engineering fields.

Fiber microactuators are interesting in wide variety of emerging fields, including artificial muscles, biosensors, and wearable devices. In the present study, a robust, fast‐responsive, and humidity‐induced silk fiber microactuator is developed by integrating force‐reeling and yarn‐spinning techniques. The shape gradient, together with hierarchical rough surface, allows these silk fiber microactuators to respond rapidly to humidity. The silk fiber microactuator can reach maximum rotation speed of 6179.3° s−1 in 4.8 s. Such a response speed (1030 rotations per minute) is comparable with the most advanced microactuators. Moreover, this microactuator generates 2.1 W kg−1 of average actuation power, which is twice higher than fiber actuators constructed by cocoon silks. The actuating powers of silk fiber microactuators can be precisely programmed by controlling the number of fibers used. Lastly, theory predicts the observed performance merits of silk fiber microactuators toward inspiring the rational design of water‐induced microactuators.

Ductile and damage-tolerant fibers (DDTFs) are desired in aerospace engineering, mechanical engineering, and biomedical engineering because of their ability to prevent the catastrophic sudden structural/mechanical failure. However, in practice, design and fabrication of DDTFs remain a major challenge due to finite fiber size and limited processing techniques. In this regard, animal silks can provide inspirations. They are hierarchically structured protein fibers with an elegant trade-off of mechanical strength, extensibility and damage tolerance, making them one of the toughest materials known. In this article, we confirmed that nanofibril organization could improve the ductility and damage-tolerance of silk fibers through restricted fibril shearing, controlled slippage and cleavage. Inspired by these strategies, we further established a rational strategy to produce polyamide DDTFs by combining electrospinning and yarn-spinning techniques. The resultant polymeric DDTFs show a silklike fracture resistance behavior, indicating potential applications in smart textile, biomedicine, and mechanical engineering.

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Knowledge learned from nature demonstrates that system performance can be enhanced and optimized by hierarchical structural design which has dramatically expanded implications for synthetic materials, from design to implementation. In recent years, numerous bioinspired and biomimetic strategies are devoted to design energy storage and harvesting devices. For these devices, efficient and stable electrode/electrolyte interfaces, modified interactions, and new functions are desired, which remain a challenge to fully meet the requirement of the rapidly developed electronic industry. This review, taking lithium batteries, nanogenerators and solar cells as examples, provides a summary and discussion of how the bio‐inspired strategies can influence the electrode/device design and the corresponding interface interactions. By applying and learning from biological materials, natural hierarchical structure, surface topography, and biochemical process, enhanced performance and stability for energy devices can be achieved. Future research expectations in this field and energy management are also discussed.