Microdamage in biological hard tissues and its repair mechanisms

Microdamage often occurs in biological hard tissues which mainly include bone tissue and tooth hard tissue, and it primarily comprises diffuse damage and microcracks. The unique microscopic structures of biological hard tissues directly influence the initiation and progression of microcracks. Mechanical forces, loading methods, macroscopic tissue characteristics, aging-related changes, diseases, and medication factors contribute to the complexity of analysis in studying microdamage of biological hard tissues. A large number of literatures have verified the detection and research methods of microcracks. The mechanisms underlying the absorption and repair of biological hard tissues caused by microdamage are still not completely clear. This article reviews the occurrence and development of various types of microdamage in biological hard tissues from microscopic to macroscopic scales, summarizes research approaches of microdamage, elucidates the mechanisms involved in absorption and repair of microdamage, analyzes existing gaps and controversies in current research findings, and proposes potential directions for future research. The study on microdamage of biological hard tissues is crucial for developing biomimetic materials. Such studies facilitate the prediction, control, prevention, and even restoration of microdamage in these materials.