Hydrogels find widespread applications in biomedical engineering due to their hydrated environment and tunable properties (e.g., mechanical, chemical, biocompatible) similar to the native extracellular matrix (ECM). However, challenges still exist regarding utilizing hydrogels in applications such as engineering 3D tissue constructs and active targeting in drug delivery, due to the lack of controllability, actuation, and quick‐response properties. Recently, magnetic hydrogels have emerged as a novel biocomposite for their active response properties and extended applications. In this review, the state‐of‐the‐art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed. The applications of magnetic hydrogels in biomedical engineering are also reviewed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators. Concluding remarks and perspectives for the future development of magnetic hydrogels are addressed.

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Directed assembly of nano and microscale particles is of great interest and has widespread applications in various fields including electronics, nanomaterials and tissue engineering. Bottom-up tissue engineering is motivated by the occurrence of repeating functional units in vivo. The bottom-up approach requires novel techniques to assemble engineered functional units as building blocks at a high speed with spatial control over three-dimensional (3D) micro-architecture. Here, we report a magnetic assembler that utilizes nanoparticles and microscale hydrogels as building blocks to create 3D complex multi-layer constructs via external magnetic fields using different concentrations of magnetic nanoparticles. This approach holds potential for 3D assembly processes that could be utilized in various tissue engineering and regenerative medicine applications.

Our understanding of how capillary blood flow and oxygen distribute across cortical layers to meet the local metabolic demand is incomplete. We addressed this question by using two-photon imaging of resting-state microvascular oxygen partial pressure (PO2) and flow in the whisker barrel cortex in awake mice. Our measurements in layers I-V show that the capillary red-blood-cell flux and oxygenation heterogeneity, and the intracapillary resistance to oxygen delivery, all decrease with depth, reaching a minimum around layer IV, while the depth-dependent oxygen extraction fraction is increased in layer IV, where oxygen demand is presumably the highest. Our findings suggest that more homogeneous distribution of the physiological observables relevant to oxygen transport to tissue is an important part of the microvascular network adaptation to local brain metabolism. These results will inform the biophysical models of layer-specific cerebral oxygen delivery and consumption and improve our understanding of the diseases that affect cerebral microcirculation.