were selected "off-the-shelf" based on the ingenuity of the surgeons. [1] During the last century, significant medical and technological progress has paved the way for the field of biomaterials research and the emergence of a biomaterials industry. Various synthetic or natural biomaterials have been developed which have enabled treatment of a wide range of medical conditions. Nevertheless, biomaterials are being considered for increasingly complex indications, which has increased the requirements for biomaterials considerably during the past decades. [2] Consequently, challenging-or even contradictorycombinations of biomaterial properties are often required which cannot be met by conventional biomaterials. For instance, biomaterials are desired which combine injectability, mechanical strength, and degradability with toughness to avoid mechanical damage following crack propagation. To meet these strict requirements, biomaterials are needed which can adapt to the implantation site and are able to heal themselves upon mechanical damage. While the majority of synthetic biomaterials does not recover from mechanical damage, natural tissues display a remarkable capacity for self-healing such as the spontaneous self-repair of bone fractures or ruptured skin. This self-healing ability is the ultimate solution of nature for continued survival based Biomaterials are being applied in increasingly complex areas such as tissue engineering, bioprinting, and regenerative medicine. For these applications, challenging-or even contradictory-combinations of biomaterial properties are often required which cannot be met by conventional biomaterials. During the past decade, several new concepts have been developed to render biomaterials self-healing, thereby offering new opportunities to improve the functionality of traditional biomaterials in terms of their mechanical, handling, and biological properties. Consequently, various types of self-healing polymeric, ceramic, or composite biomaterials have been developed. Nevertheless, despite the rapid emergence of the field of self-healing biomaterials, this field of research has not been reviewed during the recent years. Therefore, this article provides a critical overview of recent progress in the field of self-healing biomaterials research by discussing both extrinsic and intrinsic self-healing systems. While the extrinsic self-healing section focuses on self-healing dental materials and orthopedic bone cements that rely on release of healing liquids from embedded microcapsules, the section on intrinsic self-healing materials mainly discusses concepts for self-healing of polymeric biomaterials that are either hydrated (hydrogels) or nonhydrated (e.g., films and coatings). Finally, benefits of the self-healing feature for biomaterials are discussed, and directions for future research and developments are outlined.
