Metamaterials are engineered materials that possess unique properties not typically found in natural substances. Unlike conventional materials where behavior is primarily dictated by their chemical composition, metamaterials exhibit performance characteristics that are largely influenced by their physical structure. The specific design, shape, arrangement, and size of their microscopic components play a crucial role in determining how they respond to external stimuli, enabling functionalities that go beyond those supportable by traditional materials.

The metamaterial created by Kong and his research team combines exceptional stability with a level of deformability rarely seen in soft structures. According to the researchers, this feat of engineering is unprecedented, as the metamaterial not only displays remarkable strength—able to withstand compressive loads exceeding ten times its own weight—but also performs admirably under extreme conditions, such as temperatures well beyond typical physiological ranges and in harsh chemical environments.

In the design process, the team successfully integrated a phenomenon known as multistability into the structure of the metamaterial. Multistability refers to the ability to exist in multiple stable states simultaneously. By incorporating geometric features like trapezoidal support segments and reinforced beams, Kong’s team created energy barriers that effectively lock the material into its new shape even after the external actuation force has been removed. This significant characteristic enables the metamaterial to maintain its form and function without continuous energy application, thus presenting novel opportunities for its use in medical devices subjected to varying conditions within the body.

The soft architecture of the metamaterial addresses critical medical safety issues, notably the complications associated with conventional implantable and ingestible devices. Rigid components typically pose risks such as gastric ulcers, puncture wounds, and other inflammatory conditions. The innovative design of this new metamaterial alleviates such concerns, paving the way for safer medical interventions that minimize the occurrence of adverse reactions when devices are housed within the human body.

Utilizing cutting-edge 3D printing technology, Kong and his team crafted intricate molds that form interconnected microarchitectures consisting of tilted beams and supporting elements. This innovative design allows the metamaterial to switch rapidly between open and closed configurations (referred to as “off” and “on” states), ensuring that the transformed shape is sustained even after magnetization is withdrawn. The aggregation of numerous unit cells as structural “building blocks” results in a three-dimensional construct capable of not only changing shape but also generating complicated peristaltic motions. This attribute enables the metamaterial to propel and channel fluids in a controlled manner when influenced by a magnetic field.

Notably, the metamaterial’s performance remains steadfast even after prolonged exposure to mechanical stress and acidic environments, emulating the adverse conditions that devices face within the human stomach. Such resilience is crucial for the reliability of ingestible and implantable devices, signaling a significant advancement in materials science that can cater to the unique requirements of biomedical applications.

Kong, who holds the position of assistant professor of mechanical engineering at Rice’s George R. Brown School of Engineering, emphasizes the transformative implications of their work. “The metamaterial allows for remote control over the size and shape of devices within the body,” he stated, highlighting its potential to revolutionize medical practices. “This may one day enable targeted drug delivery, control over device locations, or induce mechanical forces deep inside the body when necessary.”

Looking ahead, the research team is currently applying the principles of this metamaterial to create ingestible systems aimed at addressing significant health issues, such as obesity in humans, or enhancing the well-being of marine mammals. Furthermore, Kong and his group are collaborating with surgical experts at the Texas Medical Center to design sophisticated wireless fluidic control systems that seek to fulfill previously unmet clinical needs.

The implications of this research extend far beyond the laboratory. By exploring the intersection of materials science, engineering, and medicine, Kong and his team are positioned at the forefront of innovation. As their metamaterial advances toward practical applications, the potential for impactful healthcare solutions grows, ushering in a new era where the physical characteristics of devices can be dynamically controlled to meet patient needs more effectively.

The first author of the study, Taylor Greenwood, was Kong’s first graduate student and has since graduated to begin a faculty position at Brigham Young University. The collaborative effort also included contributions from fellow graduate students Brian Elder and Jared Anklam, alongside postdoctoral researchers Jian Teng and Saebom Lee. This ambitious study has received backing from notable institutions, including the National Institutes of Health and the Office of Naval Research, underlining the research’s significance in advancing scientific knowledge and its potential applications in medicine.

In conclusion, this innovative work at Rice University signifies more than just a technical achievement. It fosters hope for future medical technologies that are tailored to be safer, more efficient, and responsive to the complex demands of human anatomy. The journey from theoretical material science to practical application in healthcare has made a considerable leap, showcasing the boundless possibilities that lie ahead in this exciting field of research.

Subject of Research: Metamaterials with Remote Control Capabilities
Article Title: Soft multistable magnetic-responsive metamaterials
News Publication Date: 16-Jul-2025
Web References: DOI
References: Science Advances Article
Image Credits: Jorge Vidal/Rice University

Keywords

Metamaterials, Soft Materials, Biomedical Engineering, Remote-Control Systems, 3D Printing, Multistability, Medical Devices, Mechanical Engineering.

Traditional bio-batteries have long held appeal due to their inherent biocompatibility, adaptability to physiological environments, and potential for powering implantable devices without toxic byproducts. However, the challenges of miniaturization, portability, and integration with existing technology have stymied broad application. Addressing these limitations, the team designed a bio-battery platform leveraging Shewanella oneidensis MR-1, a bacterium known for its exceptional ability to transfer electrons extracellularly, thereby facilitating electron flow for bioelectric power generation.

Central to their design is the 3-D printing of living hydrogels, a soft, flexible matrix composed predominantly of alginate in which the bacteria are encapsulated. This approach preserves bacterial viability and metabolic function while permitting precise control over the device’s architecture. The hydrogel bio-anode incorporates the metabolically active bacteria, while the complementary bio-cathode consists of a ferricyanide-containing alginate hydrogel. These electrodes are separated by a Nafion ion-exchange membrane, mirroring the structural principles found in advanced lithium-ion battery technologies but adapted for biologically active components.

The bio-battery itself possesses a compact footprint of 20 millimeters in diameter and a height of just over three millimeters, underscoring its suitability for portable and implantable bio-devices. The metabolic activity of the encapsulated bacteria generates electrical current autonomously, enabling the battery to self-charge for up to ten cycles. Furthermore, it demonstrates excellent coulombic efficiency exceeding 99.5% over 50 charge-discharge cycles, indicating minimal energy loss during operation—a hallmark of mature electrochemical energy systems.

Crucially, the viability of Shewanella oneidensis MR-1 within the hydrogel matrix remains remarkably high throughout the battery’s operational lifespan, with over 70% survival maintained during multiple cycles and near-complete viability (97.6%) at the end of use. This preservation of the living components is vital for the bio-battery’s sustained performance and paves the way for longer-lasting bioenergetic devices, unlike conventional batteries that suffer from irreversible chemical degradation.

Although the power and energy densities of this bio-battery—0.4 mAh per gram capacity, approximately 8.31 microwatts per square centimeter of power, and 0.008 watt-hours per liter energy density—do not currently rival those of traditional lithium-ion batteries, the remarkable sustainability advantages are undeniable. By circumventing the need for rare or hazardous materials such as cobalt, lithium, manganese, or organic solvents, this technology positions itself as an environmentally friendly alternative that mitigates ecological and supply risks inherent in current energy storage solutions.

The potential biomedical applications for such a miniaturized bio-battery are wide-ranging and transformative. The team demonstrated its ability to deliver controlled electrical stimulation to biological tissues, particularly focusing on the sciatic and vagus nerves—two critical neural pathways involved in sensory, motor, and autonomic functions. The bio-battery’s capacity for precise modulation of bioelectrical signals introduces new prospects for non-invasive nerve stimulation therapies, potentially aiding conditions such as chronic pain, epilepsy, or cardiac arrhythmias without the drawbacks of conventional electrical stimulators.

Fundamentally, the bio-battery acts not just as a power source but as a biological interface capable of integrating living systems with electronic devices. The ability to 3-D print customized geometries facilitates tailoring to specific anatomical or functional requirements. Such versatility could enable patient-specific implants or wearable therapy devices that dynamically respond to physiological cues.

The use of Shewanella species as the electroactive agent within the hydrogel is particularly strategic. Known for their electrochemical robustness and environmental resilience, these bacteria efficiently shuttle electrons to external acceptors without requiring electrodes with complex surface modifications. Their encapsulation within a biocompatible alginate network ensures containment and viability while allowing nutrient and ion exchange necessary for sustained metabolic function.

Moreover, the ion-exchange Nafion membrane, a polymer widely used in fuel cells and battery separators, optimizes ion transport between anode and cathode compartments. This design aspect enhances the bio-battery’s electrochemical performance and stability, borrowing mature material science principles to augment living system functionality.

As neuromodulation and biosensing technologies gain momentum within personalized medicine, the integration of such bio-batteries as self-sufficient power modules can address key challenges related to device miniaturization, longevity, and biocompatibility. Unlike traditional batteries prone to leakage, bulk, and toxic breakdown products, bio-batteries based on living hydrogels offer a paradigm shift towards safer, adaptive, and sustainable bioelectronics.

This pioneering work also expands the scientific frontier of engineered living materials, blending synthetic biology, electrochemistry, and advanced manufacturing. By marrying microbial metabolism with precise 3-D fabrication techniques, the research embodies a new class of biohybrid systems capable of energy generation, sensing, and actuation in physiological environments.

In conclusion, the emergence of 3-D printable living hydrogel bio-batteries signifies a milestone in sustainable biomedical engineering. The demonstrated miniaturization, high viability of electroactive microbes, efficient electrochemical cycling, and practical nerve stimulation applications collectively suggest broad potential for future development. Beyond medical devices, these living bio-energy systems could inspire environmentally responsible power solutions for diverse portable electronics and biosensors. Continued exploration and optimization could lead to commercially viable bio-batteries that harmonize energy technology with living systems and ecological imperatives.

Subject of Research: Not applicable

Article Title: 3-D Printable Living Hydrogels as Portable Bio-energy Devices

News Publication Date: 5-Mar-2025

Web References:
10.1002/adma.202419249

Image Credits: SIAT

Keywords: bio-battery, living hydrogels, 3-D bioprinting, electroactive bacteria, Shewanella oneidensis MR-1, portable energy devices, nerve stimulation, bioelectrical stimulation, sustainable energy, implantable devices, biohybrid systems, metabolic energy generation