The goal of tissue engineering scaffolds is to simulate the physiological microenvironment, in which the electrical microenvironment is an important part. Hydrogel is an ideal material for tissue engineering scaffolds because of its soft, porous, water-bearing, and other extracellular matrix-like properties. However, the hydrogel matrix is usually not conductive and can hinder the communication of electrical signals between cells, which promotes researchers' attention to conductive hydrogels. Conductive hydrogels can promote the communication of electrical signals between cells and simulate the physiological microenvironment of electroactive tissues. Hydrogel formation is an important step for the application of hydrogels in tissue engineering. In situ forming of injectable hydrogels and customized forming of three-dimensional (3D) printing hydrogels represent two most potential advanced forming processes, respectively. In this review, we discuss (i) the classification, properties, and advantages of conductive hydrogels, (ii) the latest development of conductive hydrogels applied in myocardial, nerve, and bone tissue engineering, (iii) advanced forming processes, including injectable conductive hydrogels in situ and customized 3D printed conductive hydrogels, (iv) the challenges and opportunities of conductive hydrogels for tissue engineering. Impact Statement: Biomimetic construction of electro-microenvironment is a challenge of tissue engineering. The development of conductive hydrogels provides possibility for the construction of biomimetic electro-microenvironment. However, the importance of conductive hydrogels in tissue engineering has not received enough attention so far. Herein, various conductive hydrogels and their tissue engineering applications are systematically reviewed. Two potential methods of conductive hydrogel forming, in situ forming of injectable conductive hydrogels and customized forming of three-dimensional printing conductive hydrogels, are introduced. The current challenges and future development directions of conductive hydrogels are comprehensively overviewed. This review provides a guideline for tissue engineering applications of conductive hydrogels.

Inspired by electrically active tissues, conductive materials have been extensively developed for electrically active tissue engineering scaffolds. In addition to excellent conductivity, nanocomposite conductive materials can also provide nanoscale structure similar to the natural extracellular microenvironment. Recently, the combination of three-dimensional (3D) printing and nanotechnology has opened up a new era of conductive tissue engineering scaffolds exhibiting optimized properties and multifunctionality. Furthermore, in the case of two-dimensional (2D) conductive film scaffolds such as periosteum, nerve membrane, skin repair, etc., the traditional preparation process, such as solvent casting, produces 2D films with defects of unequal bubbles and thickness frequently. In this study, poly-l-lactide (PLLA) conductive scaffolds incorporated with polypyrrole (PPy) nanoparticles, which have multiscale structure similar to natural tissue, were prepared by combining extrusion-based low-temperature deposition 3D printing with freeze-drying. Furthermore, we creatively integrated the advantages of 3D printing and solvent casting and successfully developed a 2D conductive film scaffold with no bubbles, uniform thickness, and good structural stability. Subsequently, the effects of concentration and morphology of PPy nanoparticles on electrical properties and mechanical properties of 3D conductive scaffolds and 2D conductive films scaffolds have been studied, which provided a new idea for the design of both 2D and 3D electroactive tissue engineering scaffolds.

Herein, we have fabricated a novel robust self-healing magnetic double-network hydrogel by multiple interactions between bondable magnetic Fe₃O₄ and chitosan–polyolefin matrix, and the hydrogel also exhibits an excellent magnetogenic effect and MR imageability. The practical potential of the magnetic double-network hydrogel is further revealed by its 3D-printing performance.

Hydrogel is one of the hottest biomaterials in recent years. Especially, magnetic hydrogels (MHs) prepared by combining unique magnetic nanoparticles (MNPs) with hydrogels have attracted wide attention due to their excellent biocompatibility, mechanical properties, absorbability and rich magnetic properties (magnetocaloric, magnetic resonance imaging and intelligent response, etc.). However, the current literature mainly focuses on the application of MHs, without fully understanding the relationship between the design strategies and applications of each function in MHs. This review highlights six major functional properties of MHs, including mechanical properties, adsorption, magnetocaloric effect, magnetic resonance (MR) imaging, intelligent response and biocompatibility. Principles and design strategies of each performance are thoroughly analyzed. Furthermore, the latest applications of MHs in biomedicine, soft actuators, environmental protection, chemistry and engineering in recent 5 years are introduced from the perspective of each function. In the carefully selected representative cases, the design strategies and application principle of multi‐functional MHs are detailed, respectively. The classical fabrication processing of MHs is summarized. At last, we discuss the unmet needs and potential future challenges in MHs development and highlight its emerging strategies.