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Abstract Eukaryotic cells have evolved membrane-bound organelles, including the endoplasmic reticulum (ER), Golgi, mitochondria, peroxisomes, chloroplasts (in plants and green algae) and lysosomes/vacuoles, for specialized functions. Organelle quality control and their proper interactions are crucial both for normal cell homeostasis and function and for environmental adaption. Dynamic turnover of organelles is tightly controlled, with autophagy playing an essential role. Autophagy is a programmed process for efficient clearing of unwanted or damaged macromolecules or organelles, transporting them to vacuoles for degradation and recycling and thereby enhancing plant environmental plasticity. The specific autophagic engulfment of organelles requires activation of a selective autophagy pathway, recognition of the organelle by a receptor, and selective incorporation of the organelle into autophagosomes. While some of the autophagy machinery and mechanisms for autophagic removal of organelles is conserved across eukaryotes, plants have also developed unique mechanisms and machinery for these pathways. In this review, we discuss recent progress in understanding autophagy regulation in plants, with a focus on autophagic degradation of membrane-bound organelles. We also raise some important outstanding questions to be addressed in the future. 

Biohybrid robots, composed of cellular actuators and synthetic scaffolds, have garnered much attention in recent years owing to the advantages provided by their biological components. In recent years, various forms of biohybrid robots have been developed that are capable of life-like movements, such as walking, swimming, and gripping. Specifically, for walking or crawling biorobots, there is a need for complex functionality and versatile and robust fabrication processes. Here, we designed and fabricated multi-actuator biohybrid walkers with multi-directional walking capabilities in response to noninvasive optical stimulation through a scalable modular biofabrication process. Our new fabrication approach provides a constant mechanical strain throughout the cellular differentiation and maturation process. This maximizes the myotube formation and alignment, limits passive bending, and produces higher active forces. These demonstrations of the new fabrication process and bioactuator designs can pave the way for advanced multi-cellular biohybrid robots and enhance our understanding of the emergent behaviors of these multi-cellular engineered living systems. 

Biohybrid centimeter-scale robots developed from optoelectronics and optogenetic muscles can be controlled wirelessly. 

Tissue-on-chip systems represent promising platforms for monitoring and controlling tissue functions in vitro for various purposes in biomedical research. The two-dimensional (2D) layouts of these constructs constrain the types of interactions that can be studied and limit their relevance to three-dimensional (3D) tissues. The development of 3D electronic scaffolds and microphysiological devices with geometries and functions tailored to realistic 3D tissues has the potential to create important possibilities in advanced sensing and control. This study presents classes of compliant 3D frameworks that incorporate microscale strain sensors for high-sensitivity measurements of contractile forces of engineered optogenetic muscle tissue rings, supported by quantitative simulations. Compared with traditional approaches based on optical microscopy, these 3D mechanical frameworks and sensing systems can measure not only motions but also contractile forces with high accuracy and high temporal resolution. Results of active tension force measurements of engineered muscle rings under different stimulation conditions in long-term monitoring settings for over 5 wk and in response to various chemical and drug doses demonstrate the utility of such platforms in sensing and modulation of muscle and other tissues. Possibilities for applications range from drug screening and disease modeling to biohybrid robotic engineering.

 

Biohybrid robots, or bio‐bots, integrate living and synthetic materials following a synergistic strategy to acquire some of the unique properties of biological organisms, like adaptability or bio‐sensing, which are difficult to obtain exclusively using artificial materials. Skeletal muscle is one of the preferred candidates to power bio‐bots, enabling a wide variety of movements from walking to swimming. Conductive nanocomposites, like gold nanoparticles or graphene, can provide benefits to muscle cells by improving the scaffolds’ mechanical and conductive properties. Here, boron nitride nanotubes (BNNTs), with piezoelectric properties, are integrated in muscle‐based bio‐bots and an improvement in their force output and motion speed is demonstrated. A full characterization of the BNNTs is provided, and their piezoelectric behavior with piezometer and dynamometer measurements is confirmed. It is hypothesized that the improved performance is a result of an electric field generated by the nanocomposites due to stresses produced by the cells during differentiation. This hypothesis is backed with finite element simulations supporting that this stress can generate a non‐zero electric field within the matrix. With this work, it is shown that the integration of nanocomposite into muscle‐based bio‐bots can improve their performance, paving the way toward stronger and faster bio‐hybrid robots.

 

The intriguing opportunities enabled by the use of living components in biological machines have spurred the development of a variety of muscle‐powered biohybrid robots in recent years. Among them, several generations of tissue‐engineered biohybrid walkers have been established as reliable platforms to study untethered locomotion. However, despite these advances, such technology is not mature yet, and major challenges remain. Herein, steps are taken to address two of them: the lack of systematic design approaches, common to biohybrid robotics in general, and in the case of biohybrid walkers specifically, the lack of maneuverability. A dual‐ring biobot is presented which is computationally designed and selected to exhibit robust forward motion and rotational steering. This dual‐ring biobot consists of two independent muscle actuators and a four‐legged scaffold asymmetric in the fore/aft direction. The integration of multiple muscles within its body architecture, combined with differential electrical stimulation, allows the robot to maneuver. The dual‐ring robot design is then fabricated and experimentally tested, confirming computational predictions and turning abilities. Overall, a design approach based on modeling, simulation, and fabrication exemplified in this versatile robot represents a route to efficiently engineer complex biological machines with adaptive functionalities.