Editorial for Special Issue on “ In Vivo Animal Models for Bone Tissue Regeneration”

In the field of orthopedic and dentistry, bone destructions/atrophies are common and the result of trauma, infectious diseases, tumors, or congenital disorders. ¹ For many years, physicians are already employing several surgical techniques to treat and restore the functional/esthetic disability as caused by bone defects. However, the complete regeneration of bone defects remains challenging, although several specific bone-grafting techniques have been proposed. ² Therefore, demands for implantation of biomaterials (bone substitutes) have been developed to reach optimal bone regeneration. ³

The currently used bone-grafting materials are focusing on the implementation of new therapeutic/instructive strategies to promote bone regeneration, which is a new paradigm in the field of tissue engineering and regenerative medicine. The recent technologies of tissue engineering are based on the use of cell-based therapy as well as the application of osteoinductive biomolecules to enable predictable bone regeneration.^4,5

The biological process of bone regeneration is complex and still remains largely unknown. It includes three essential phases: inflammation, bone formation, and bone remodeling. ⁶ In the bone formation stage, the majority of bone regeneration is dependent on the phenomena of osteogenesis, osteoinduction, and osteoconduction. These biological phenomena include many interactions between different types of bone cells that are mediated by biomolecules. ⁶ Nevertheless, the challenge in bone tissue engineering is to mimic the regenerative healing process of bone tissue by adding all the biological components in a scaffold to enhance osteogenesis in a bone defect that exceeds the critical size.

For the investigation of bone regeneration with newly developed tissue engineering technologies, in vivo animal experiments that address clinical relevance are of fundamental significance. ⁷ Indeed, several animal models are commonly used to study bone regeneration in healthy conditions. For compromised health condition, specific animal models are well established and characterized to resembling the medical condition being investigated. ⁸ This helps very much to experimentally explore the complex process of bone–material interactions in different medical conditions as in humans. Other advantages of the in vivo animal models are that they allow valuable static and dynamic histological investigations as well as biomechanical testing for bone regeneration. ⁹

The focus of this special issue aims to present a collection of articles that highlight recent progress of various in vivo animal models that identify several biological mechanisms of tissue-engineered biomaterials and their applications in favor of optimal bone regeneration.