What are hydrogels?
Hydrogels are polymer networks infiltrated with water. Examples include fruit jellies, and human tissues. Biological hydrogels constitute the major components of the human body.
What are hydrogel machines?
Owing to their superior softness, wetness, responsiveness, and biocompatibility, hydrogels are being intensively investigated for versatile functions in devices and machines including sensors, actuators, coatings, optics, electronics, and water harvesters. A nascent field named hydrogel machines rapidly evolves, exploiting hydrogels as key components for devices and machines.
Hydrogels are polymer networks infiltrated with water. Examples include fruit jellies, and human tissues. Biological hydrogels constitute the major components of the human body.
What are hydrogel machines?
Owing to their superior softness, wetness, responsiveness, and biocompatibility, hydrogels are being intensively investigated for versatile functions in devices and machines including sensors, actuators, coatings, optics, electronics, and water harvesters. A nascent field named hydrogel machines rapidly evolves, exploiting hydrogels as key components for devices and machines.
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By leveraging hydrogel technologies, I am developing three types of hydrogel machines.
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Living Materials & Devices
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Motivation
Living systems, such as bacteria, yeasts, and mammalian cells, can be genetically programmed with synthetic circuits that execute sensing, computing, memory, and response functions. Integrating these functional living components into materials and devices will provide powerful tools for scientific research and enable new technological applications. However, it has been a grand challenge to maintain the viability, functionality, and safety of living components in freestanding materials and devices, which frequently undergo deformations during applications. What we did We designed a set of living materials and devices based on hydrogel–elastomer hybrids and hydrogel 3D printing that host various types of genetically engineered bacterial cells. The hydrogel provides sustainable supplies of water and nutrients to living bacterial cells, and the cells can communicate and process signals in a programmable manner.
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Ingestible Devices
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Motivation
Devices that interact with living organisms are typically made of metals, silicon, ceramics, and plastics. Implantation of such devices for long-term monitoring or treatment generally requires invasive procedures. Hydrogels offer new opportunities for human-machine interactions due to their superior mechanical compliance and biocompatibility. Additionally, oral administration, coupled with gastric residency, serves as a non-invasive alternative to implantation. Achieving gastric residency with hydrogels requires the hydrogels to swell very rapidly and to withstand gastric mechanical forces over time. However, high swelling ratio, high swelling speed, and long-term robustness do not coexist in existing hydrogels. What we did We introduced a hydrogel device that can be ingested as a standard-sized pill, swell rapidly into a large soft sphere, and maintain robustness under repeated mechanical loads in the stomach for up to one month. Large animal tests supported the exceptional performance of the ingestible hydrogel device for long-term gastric retention and physiological monitoring.
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Hydrogel Optics
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Motivation
Holistic study of neural dynamics in behaving subjects often demands simultaneous recording of neural activity across multiple organs in the nervous system. However, currently available silica-based techniques for the chronic recording of activity of specific neuronal ensembles are unsuitable for mobile regions of the nervous system such as the brain stem or spinal cord due to the rigidity of the probes. What we did Here we present a stretchable optical photometry platform based on hydrogels that allows chronic optical recording of neural activity across multiple regions of the nervous system in freely moving rodents during behavioral assays. We anticipate that the hydrogel photometry probes will facilitate investigation of neural circuits across central and peripheral nervous systems in freely moving subjects.
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Anti-Fatigue Hydrogels
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Motivation
The emerging applications of hydrogels in devices and machines require hydrogels to maintain robustness under cyclic mechanical loads. Whereas hydrogels have been made tough to resist fracture under a single cycle of mechanical load, these toughened gels still suffer from fatigue fracture under multiple cycles of loads. The reported fatigue threshold for synthetic hydrogels is on the order of 1 to 100 J/m2.
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