japanese hip society

[Purpose] The bioinertness paradigm has so far dominated the field of artificial hip joints, with biomaterials being selected because of their stable molecular structure and structural stability in the human body. However, a deeper understanding of how implant surfaces interact with cells and bacteria at the molecular scale could greatly advance biomedical science research, enable new visions, and produce new biomaterials and intelligent biomedical devices. Surface chemistry remains the “missing key” in searching for biomaterials with long-term therapeutic functions in the human milieu. This presentation assesses some basic aspects of surface chemistry in hip implants and proposes using nitrogen surface chemistry to advance total hip arthroplasty into a new dimension, where it has the ability not only to improve the patient’s quality of life, but also to conquer bone and joint diseases.[Methods] In vitro tests of antibacterial, antifungal, and osteogenic behaviors of oxide and non-oxide (nitrogen-containing bioactive) compounds are performed together with analyses of retrieved implants.[Results] A comparison between oxide and non-oxide bioceramic surfaces at their biological interface with eukaryotic and prokaryotic cells was made with taking alumina (Al₂O₃) and silicon nitride (Si₃N₄) bioceramics, both in bulk and coating on metal surfaces, as paradigmatic examples of these two categories, respectively. Unlike oxide surfaces, the nitrogen moieties produced by hydrolysis at the Si₃N₄ surface promoted the formation of osseous tissue while concurrently lysing invasive pathogens.[Discussion] Promptly activated in aqueous environment, the unique surface chemistry of Si₃N₄ mimics iNOS in poisoning Gram-positive and Gram-negative bacteria, while performing as eNOS in regulating osteoblast differentiation and stimulating the synthesis of osseous tissue. This peculiar property of Si₃N₄ bioceramics represents a therapeutic advantage in counteracting joint diseases arising from imbalanced ionic states. [Conclusion] The role of surface hydrolysis and related kinetics on cell fate and metabolism on Si₃N₄ bioceramics might represent the overcoming of the long-stated “bioinert” approach and give way to the new concept of “self-disinfecting” and “self-healing” biomedical devices.