Amphiphilic block polymers having nitroxide radicals (TEMPO) self-assemble in water to form nanoparticles. This is a new nanomedicine that avoids the adverse effects of conventional antioxidants, which destroy the intracellular redox environment, and makes it possible to treat various oxidative-stress-related diseases such as cerebral or cardiovascular ischemia-reperfusions, Alzheimer’s disease and cancer. In addition, we have designed a gelation function in these materials and developed them as a material for anti-tissue adhesion agents and periodontal diseases. Additionally, we succeeded in enhancing cultured cell functions using an antioxidant biointerface.