Gated ion flow in graphene oxide membranes: Cells are adept at fast, gated ion flow through tailored channels, which is key to many biological processes. Xue et al. developed ion transistors from reduced graphene oxide membranes and observed a field-enhanced diffusivity of the ions (see the Perspective by Hinds). By applying electrical gating, the average surface potential on the graphene layer could be controlled, thus altering the energy barrier for ion intercalation into the channel and leading to very high diffusion rates. The authors observed selective ion transport two orders of magnitude faster than the ion diffusion in bulk water. Science , this issue p. 501 ; see also p. 459

A sound demonstration of Klein tunneling: The ability of particles to tunnel through barriers is an important property of quantum mechanical systems, and the extent of the effect is strongly dependent on the properties of the barrier. By contrast, Klein tunneling can exhibit unity transmission that is independent of the width and height of the energy barrier, but direct evidence for this effect remains elusive. Using a phononic system comprising a periodic array of dielectric pillars, Jiang et al. provide evidence for the direct observation of Klein tunneling. Near-unity transmission of acoustic excitations was observed across the barrier independently of its width and height. This ability to tune the effect by controlling the size of the junctions and the frequency of incident waves provides a promising platform to explore complex nontrivial physics and applications in signal processing and information communications. Science , this issue p. 1447

Something repulsive in the Casimir effect: Two uncharged objects (metal plates for instance) will experience an attractive force between them, the magnitude of which increases as they are brought closer together. This force, or Casimir effect, is caused by vacuum fluctuations of the electromagnetic field. Effectively, more modes outside than between the objects results in the objects being pushed together. Zhao et al. show that the extent of the electromagnetic fluctuations can be controlled by coating one of the objects with a dielectric (Teflon), which changes the Casimir effect to a repulsive force at small distances. This then cancels out the force between plates and produces a point of stable equilibrium. Science , this issue p. 984

3D printing, also known as additive manufacturing, holds immense potential for rapid prototyping and customized production of functional health‐related devices. With advancements in polymer chemistry and biomedical engineering, polymeric biomaterials have become integral to 3D‐printed biomedical applications. However, there still exists a bottleneck in the compatibility of polymeric biomaterials with different 3D printing methods, as well as intrinsic challenges such as limited printing resolution and rates. Therefore, this review aims to introduce the current state‐of‐the‐art in 3D‐printed functional polymeric health‐related devices. It begins with an overview of the landscape of 3D printing techniques, followed by an examination of commonly used polymeric biomaterials. Subsequently, examples of 3D‐printed biomedical devices are provided and classified into categories such as biosensors, bioactuators, soft robotics, energy storage systems, self‐powered devices, and data science in bioplotting. The emphasis is on exploring the current capabilities of 3D printing in manufacturing polymeric biomaterials into desired geometries that facilitate device functionality and studying the reasons for material choice. Finally, an outlook with challenges and possible improvements in the near future is presented, projecting the contribution of general 3D printing and polymeric biomaterials in the field of healthcare.