Water-responsive (WR) materials that reversibly deform in response to humidity changes show great potential for developing muscle-like actuators for miniature and biomimetic robotics. Here, it is presented that Bacillus (B.) subtilis' peptidoglycan (PG) exhibits WR actuation energy and power densities reaching 72.6 MJ m −3 and 9.1 MW m −3 , respectively, orders of magnitude higher than those of frequently used actuators, such as piezoelectric actuators and dielectric elastomers. PG can deform as much as 27.2% within 110 ms, and its actuation pressure reaches ≈354.6 MPa. Surprisingly, PG exhibits an energy conversion efficiency of ≈66.8%, which can be attributed to its super-viscous nanoconfined water that efficiently translates the movement of water molecules to PG's mechanical deformation. Using PG, WR composites that can be integrated into a range of engineering structures are developed, including a robotic gripper and linear actuators, which illustrate the possibilities of using PG as building blocks for high-efficiency WR actuators. IntroductionDespite more than a century of research, mechanical actuators, which typically transduce electrical fields, [1] chemical energy, [2] heat, [3,4] and pressurized gas/liquid [5] into motions, still cannot

High Energy and Power Density Peptidoglycan Muscles Biological organisms have developed water‐responsive materials that dramatically deform in response to humidity fluctuations and evaporation. In article number 2104697 , Xi Chen and co‐workers discover that peptidoglycan actuates more energetically and efficiently than existing actuators and it can be used to power micro‐ and macro‐structures. Image credit: Ella Maru Studio.

Every animal secretes mucus, placing them among the most diverse biological materials. Mucus hydrogels are complex mixtures of water, ions, carbohydrates, and proteins. Uncertainty surrounding their composition and how interactions between components contribute to mucus function complicates efforts to exploit their properties. There is substantial interest in commercializing mucus from the garden snail,Cornu aspersum, for skincare, drug delivery, tissue engineering, and composite materials.C. asperumsecretes three mucus — one shielding the animal from environmental threats, one adhesive mucus from the pedal surface of the foot, and another pedal mucus that is lubricating. It remains a mystery how compositional differences account for their substantially different properties. Here, we characterize mucus proteins, glycosylation, ion content, and mechanical properties to understand structure-function relationships through an integrative ″mucomics″ approach. We identify new macromolecular components of these hydrogels, including a novel protein class termed Conserved Anterior Mollusk Proteins (CAMPs). Revealing differences betweenC. aspersummucus shows how considering structure at all levels can inform the design of mucus-inspired materials.