Triggerable materials capable of being degraded by selective stimuli stand to transform our capacity to precisely control biomedical device activity and performance while reducing the need for invasive interventions. Here, we describe the development of a modular and tunable light-triggerable hydrogel system capable of interfacing with implantable devices. We apply these materials to two applications in the gastrointestinal (GI) tract: a bariatric balloon and an esophageal stent. We demonstrate biocompatibility and on-demand triggering of the material in vitro, ex vivo, and in vivo. Moreover, we characterize performance of the system in a porcine large animal model with an accompanying ingestible LED. Light-triggerable hydrogels have the potential to be applied broadly throughout the GI tract and other anatomic areas. By demonstrating the first use of light-degradable hydrogels in vivo, we provide biomedical engineers and clinicians with a previously unavailable, safe, dynamically deliverable, and precise tool to design dynamically actuated implantable devices.

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The equality between the spectral, directional emittance and absorptance of an object under local thermal equilibrium is known as Kirchhoff's law of radiation. The breakdown of Kirchhoff's law of radiation is physically allowed by breaking time-reversal symmetry and can open new opportunities for novel non-reciprocal light emitters and absorbers. Large anomalous Hall conductivity and angle recently observed in topological Weyl semimetals, particularly type-I magnetic Weyl semimetals and type-II Weyl semimetals, are expected to create large nonreciprocal electromagnetic wave propagation. In this work, we focus on type-I magnetic Weyl semimetals and show via modeling and simulation that non-reciprocal surface plasmons polaritons can result in pronounced non-reciprocity without an external magnetic field. The modeling in this work begins with a single pair of Weyl nodes, followed by a more realistic model with multiple paired Weyl nodes. Fermi-arc surface states are also taken into account through the surface conductivity. This work points to the promising applicability of topological Weyl semimetals for magneto-optical and energy applications. . These authors contributed equally to this work. Main textKirchhoff's law of radiation establishes the equality between the spectral, directional absorptance ( , ) and the spectral, directional emittance ( , ) of an object in local thermal equilibrium, i.e., ( , ) = ( , ) , where and are the wavelength and the direction of incoming and outgoing radiation, respectively. Fundamentally, Kirchhoff's law of radiation underlies the theoretical efficiency limit in radiative energy conversion since converting absorbed incoming radiation into another form of energy, such as electricity or heat, always entails the outgoing emission at the same wavelength in the same direction from the object, which causes an intrinsic loss 1-3 . It has been argued 2,4,5 that Kirchhoff's law of radiation is not a required condition for the validity of the second law of thermodynamics in systems that exchange radiative energy, but rather a result of the Lorentz reciprocity theorem in which the only assumptions are a linear constitutive relation and symmetric permittivity and permeability tensors 6,7 . Thus, the violation of Kirchhoff's law of radiation, i.e., non-reciprocity in the spectral, directional absorptance and emittance, is physically allowed, and its realization can open new opportunities for novel light emitters and absorbers for a wide range of radiative applications including solar photovoltaics, thermo-photovoltaics, and antennas 1,8 .Non-reciprocity in a medium often arises due to non-zero anti-symmetric off-diagonal elements of the dielectric tensor of the medium, which creates non-reciprocal electromagnetic modes 9 . One way to create the anti-symmetric off-diagonal elements is by inducing magnetic responses either by the Hall response under an external magnetic field or by spontaneous magnetization in materials, namely the anomalous Hall effect 10 . The anomalous Hall effect can origin...

We hypothesized that ingested warm fluids could act as triggers for biomedical devices. We investigated heat dissipation throughout the upper gastrointestinal (GI) tract by administering warm (55°C) water to pigs and identified two zones in which thermal actuation could be applied: esophageal (actuation through warm water ingestion) and extra-esophageal (protected from ingestion of warm liquids and actuatable by endoscopically administered warm fluids). Inspired by a blooming flower, we developed a capsule-sized esophageal system that deploys using elastomeric elements and then recovers its original shape in response to thermal triggering of shape-memory nitinol springs by ingestion of warm water. Degradable millineedles incorporated into the system could deliver model molecules to the esophagus. For the extra-esophageal compartment, we developed a highly flexible macrostructure (mechanical metamaterial) that deforms into a cylindrical shape to safely pass through the esophagus and deploys into a fenestrated spherical shape in the stomach, capable of residing safely in the gastric cavity for weeks. The macrostructure uses thermoresponsive elements that dissociate when triggered with the endoscopic application of warm (55°C) water, allowing safe passage of the components through the GI tract. Our gastric-resident platform acts as a gram-level long-lasting drug delivery dosage form, releasing small-molecule drugs for 2 weeks. We anticipate that temperature-triggered systems could usher the development of the next generation of stents, drug delivery, and sensing systems housed in the GI tract.