Progress and Opportunities in Soft Photonics and Biologically Inspired Optics

Optical components made fully or partially from reconfigurable, stimuli‐responsive, soft solids or fluids—collectively referred to as soft photonics—are poised to form the platform for tunable optical devices with unprecedented functionality and performance characteristics. Currently, however, soft solid and fluid material systems still represent an underutilized class of materials in the optical engineers' toolbox. This is in part due to challenges in fabrication, integration, and structural control on the nano‐ and microscale associated with the application of soft components in optics. These challenges might be addressed with the help of a resourceful ally: nature. Organisms from many different phyla have evolved an impressive arsenal of light manipulation strategies that rely on the ability to generate and dynamically reconfigure hierarchically structured, complex optical material designs, often involving soft or fluid components. A comprehensive understanding of design concepts, structure formation principles, material integration, and control mechanisms employed in biological photonic systems will allow this study to challenge current paradigms in optical technology. This review provides an overview of recent developments in the fields of soft photonics and biologically inspired optics, emphasizes the ties between the two fields, and outlines future opportunities that result from advancements in soft and bioinspired photonics.     

Cobweb-Inspired Microenvironment-Targeting Nanosystem with Sequential Multiple-Stage Stimulus-Response Capacity for Ischaemic Tissue Repair

Myocardial ischaemia is pathologically complicated; various changes in intracellular and extracellular microenvironments make it essential to develop a smart drug system with multiple stimulus responses to adapt to the complex process. Inspired by the cobweb, this study designs a microreticular nanosystem that adheres to tissue and is sequentially responsive to multiple stimuli in the ischaemic microenvironment. The nanosystem is fabricated from hyaluronic acid (HA), ROS-responsive B-PDEA, and hypoxia-sensitive VEGF-expressing plasmids (EPODNA) through electrostatic interactions. After intramyocardial injection, the tissue-adhesive property of the nanosystem will significantly decrease its acute loss from the injection site. Extracellularly, the microreticular nanosystem first responds to activated hyaluronidase (hyal), releasing HA for microenvironment regulation and B-PDEA/DNA nanoparticles (NP) with high transfection efficiency for cardiac cells. Intracellularly, ROS sequentially induced B-PDEA/DNA NP dissociation, consuming some ROS to attenuate oxidative stress and releasing DNA to promote its expression. Meanwhile, local hypoxia significantly activates VEGF expression in plasmids for myocardial revascularization and repair. The function of the microreticular nanosystem is systematically evaluated in vitro. In a rat model of myocardial infarction, treatment with the microreticular nanosystem significantly promotes functional and structural improvements. Collectively, the study provides a promising smart nanosystem to promote tissue repair after complex damage.     

Bioinspired MXene-Based Piezoresistive Sensor with Two-stage Enhancement for Motion Capture (Adv. Funct. Mater. 18/2023)

Structured piezoresistive membranes are compelling building blocks for wearable bioelectronics. However, the poor structural compressibility of conventional microstructures leads to rapid saturation of detection range and low sensitivity of piezoresistive devices, limiting their commercial applications. Herein, a bioinspired MXene-based piezoresistive device is reported, which can effectively boost the sensitivity while broadening the response range by architecting intermittent villus-like microstructures. Benefitting from the two-stage amplification effect of this intermittent architecture, the developed MXene-based piezoresistive bioelectronics exhibit a high sensitivity of 461 kPa⁻¹ and a broad pressure detection range of up to 311 kPa, which are about 20 and 5 times higher than that of the homogeneous microstructures, respectively. Cooperating with the deep-learning algorithm, the designed bioelectronics can effectively capture complex human movements and precisely identify human motion with a high recognition accuracy of 99%. Evidently, this intermittent architecture of biomimetic strategy may pave a promising avenue to overcome the limitation of rapid saturation and low sensitivity in piezoresistive bioelectronics, and provide a general way to promote its large-scale applications.     

Bioinspired Amyloid Fibril-Based Hydrogel with Engineering Programable Functionalities for Diverse Applications

Natural proteins display organized hierarchical structures and tailored functionalities that cannot be achieved by synthetic approaches, highlighting the increased interest in developing protein-based materials. Protein self-assembly allows fabricating sophisticated supramolecular structures from relatively simple building blocks, a strategy naturally employed by amyloid proteins and intrinsically disordered proteins. However, the design of self-assembled bioinspired materials with multi functionalities is still challenging. Inspired by the natural self-assembly proteins (such as mussel foot proteins and amyloid proteins), a temperature-inducible engineering programable hydrogel-like amyloid nanostructure is developed by using a genetically modular fusion approach. The resulting hydrogel-like assemblies display outstanding adhesive capacity, high stability, and broad substrate universality. The employed SpyCatcher/SpyTag system allows modifying the hydrogel-like assemblies with any functional proteins of interest. Owing to their strong adhesive capacity and functional flexibility, such amyloid fibril-based hydrogel shows advantages in the immobilization of diverse enzymes for highly efficient biocatalysis, fabrication of multi-layered functional coatings, and construction of functionalized 3D scaffold for cell culture. Overall, a modular and straightforward approach is established to obtain a genetically programable nanostructure platform. The novel hydrogel-like assemblies described here may be potentially applied to but not limited to synthetic biology, surface/interface engineering, and tissue engineering.     

Bioinspired Poly(vinyl alcohol) Film Actuator Powered by Water Evaporation under Ambient Conditions

Soft humidity‐responsive materials are highly desirable for applications such as actuators, sensors, generators, and soft robots. However, it remains a huge challenge to develop a durable, cost‐effective, fast responsive version of such a smart material powered by water evaporation at ambient conditions. Herein, this challenge is addressed to demonstrate sustained response to humidity gradient from ambient water evaporation by using common poly(vinyl alcohol) (PVA) film as an actuator. The resultant PVA film displays strong mechanical properties in both dry and wet conditions, which cause rapid adsorption and desorption of water vapor to drive the film undergoing swift locomotion with flipping frequency of up to 65 r min^‐1. Based on these features, a mimosa inspired humidity‐responsive actuator is developed which is far superior in response speed and durability than real mimosa. Furthermore, it is demonstrated that the film actuator can convert water evaporation energy into electricity when attached to a piezoelectric element.     

Parallel bioinspired algorithms for NP complete graph problems

It is no longer believed that DNA computing will outperform digital computers when it comes to the computation of intractable problems. In this paper, we emphasise the in silico implementation of DNA-inspired algorithms as the only way to compete with other algorithms for solving NP-complete problems. For this, we provide sticker algorithms for some of the most representative NP-complete graph problems. The simple data structures and bit-vertical operations make them suitable for some parallel architectures. The parallel algorithms might solve either moderate-size problems in an exact manner or, when combined with a heuristic, large problems in polynomial time.     

Synthesis of Biomimetic Superhydrophobic Surface through Electrochemical Deposition on Porous Alumina

The superhydrophobicity of plant leaves is a benefit of the hierarchical structures of their surfaces. These structures have been imitated in the creation of synthetic surfaces. In this paper, a novel process for fabrication of biomimetic hierarchical structures by electrochemical deposition of a metal on porous alumina is described. An aluminum specimen was anodically oxidized to obtain a porous alumina template, which was used as an electrode to fabricate a surface with micro structures through electrochemical deposition of a metal such as nickel and copper after the enlargement of pores. Astonishingly, a hierarchical structure with nanometer pillars and micrometer clusters was synthesized in the pores of the template. The nanometer pillars were determined by the nanometer pores. The formation of micrometer clusters was related to the thin walls of the pores and the crystallization of the metal on a flat surface. From the as-prepared biomimetic surfaces, lotus-leaf-like superhydrophobic surfaces with nickel and copper deposition were achieved.     

Structural Design Elements in Biological Materials: Application to Bioinspiration

Eight structural elements in biological materials are identified as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the field of biological materials science as they can serve as a toolbox for rationalizing the complex mechanical behavior of structural biological materials and for systematizing the development of bioinspired designs for structural applications. They are employed to improve the mechanical properties, namely strength, wear resistance, stiffness, flexibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, weight reduction). The structural elements identified are: fibrous, helical, gradient, layered, tubular, cellular, suture, and overlapping. For each of the structural design elements, critical design parameters are presented along with constitutive equations with a focus on mechanical properties. Additionally, example organisms from varying biological classes are presented for each case to display the wide variety of environments where each of these elements is present. Examples of current bioinspired materials are also introduced for each element.