Bi-enzymatic chemo-mechanical feedback loop for continuous self-sustained actuation of conducting polymers

Biomolecular Actuators for Soft Robots

Biomolecules present promising stimuli-responsive mechanisms to revolutionize soft actuators. Proteins, peptides, and nucleic acids foster specific intermolecular interactions, and their boundless sequence design spaces encode precise actuation capabilities. Drawing inspiration from nature, biomolecular actuators harness existing stimuli-responsive properties to meet the needs of diverse applications. This review features biomolecular actuators that respond to a wide variety of stimuli to drive both user-directed and autonomous actuation. We discuss how advances in biomaterial fabrication accelerate prototyping of precise, custom actuators, and we identify biomolecules with untapped actuation potential. Finally, we highlight opportunities for multifunctional and reconfigurable biomolecules to improve the versatility and sustainability of next-generation soft actuators.

Magnetohydrodynamic Enhancement of Biofuel Cell Performance

Biofuel cells have become an interesting alternative for the design of sustainable energy conversion systems with multiple applications ranging from biosensing and bioelectronics to autonomously moving devices. However, as an electrochemical system, their performance is intimately related to mass transport conditions. In this work, the magnetohydrodynamic (MHD) effect is studied as an easy and straightforward alternative to enhance the performance of a biofuel cell based on the enzymes glucose oxidase (GOx) and bilirubin oxidase (BOD). The synergetic effect between the electric and ionic currents, produced by the enzymatic redox reactions, and a magnetic field orthogonal to the surface of the electrodes, leads to the formation of localized magnetohydrodynamic vortexes. Such an integrated convective regime generates an increase of the bioelectrocatalytic current and its concomitant power output in the presence of the external magnetic field. In addition, by fine-tuning the spatial arrangement of the anode and cathode, it is possible to benefit from the sum of anodic and cathodic MHD vortexes, leading to an enhanced power output of up to 300 %.

Fluid mediated communication among flexible micro-posts in chemically reactive solutions

Communication in biological systems typically involves enzymatic reactions that occur within fluids confined between the soft, elastic walls of bio-channels and chambers. Through the inherent transformation of chemical to mechanical energy, the fluids can be driven to flow within the confined domains. Through fluid-structure interactions, the confining walls in turn are deformed by and affect this fluid flow. Imbuing synthetic materials with analogous feedback among chemo-mechanical, hydrodynamic and fluid-structure interactions could enable materials to perform self-driven communication and self-regulation. Herein, we develop computational models to determine how chemo-hydro-mechanical feedback affects interactions in biomimetic arrays of chemically active and passive micro-posts anchored in fluid-filled chambers. Once activated, the enzymatic reactions trigger the latter feedback, which generates a surprising variety of long-range, cooperative motion, including self-oscillations and non-reciprocal interactions, which are vital for propagating coherent, directional signals over net distances in fluids. In particular, the array propagates a distinct message; each post interprets the message; and the system responds with a specific mode of organized, collective behavior. This level of autonomous remote control is relatively rare in synthetic systems, particularly as this system operates without external electronics or power sources and only requires the addition of chemical reactants to function.

Self-Powered Engineering of Cell Membrane Receptors to On-Demand Regulate Cellular Behaviors

On-demand engineering of cell membrane receptors to nongenetically intervene in cellular behaviors is still a challenge. Herein, a membraneless enzyme biofuel cell-based self-powered biosensor (EBFC-SPB) was developed for autonomously and precisely releasing Zn2+ to initiate DNAzyme-based reprogramming of cell membrane receptors, which further mediates signal transduction to regulate cellular behaviors. The critical component of EBFC-SPB is a hydrogel film on a biocathode which is prepared using a Fe3+-cross-linked alginate hydrogel film loaded with Zn2+ ions. In the working mode in the presence of glucose/O2, the hydrogel is decomposed due to the reduction of Fe3+ to Fe2+, accompanied by rapid release of Zn2+ to specifically activate a Zn2+-responsive DNAzyme nanodevice on the cell surface, leading to the dimerization of homologous or nonhomologous receptors to promote or inhibit cell proliferation and migration. This EBFC-SPB platform provides a powerful "sensing-actuating-treating" tool for chemically regulating cellular behaviors, which holds great promise in precision biomedicine.

Degradable π-Conjugated Polymers

The integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.