Triblock copolymer and use therefor

A composition comprising:

• a polyion complex comprising a polyanion selected from the group consisting of poly(acrylic acid), poly(methacrylic acid), poly(sulfonic acid), DNA, RNA and anionic proteins, and a triblock copolymer or salt thereof of following formula:
• wherein each L1 is independently selected from the group consisting of a single bond, —S—(CH2)c—, —S—(CH2)cCO—, —(CH2)cS— and —CO(CH2)cS—, in which c is an integer from 1 to 5;
• each L2 is independently —C1-6 alkylene-NH—(C1-6 alkylene)q-, in which q is the integer 0 or 1;
• and at least 50% of the total number n of R in the formula independently represent residues of cyclic nitroxide radical compounds selected from the group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl-4-yl, 2,2,5,5-tetramethylpyrrolidine-1-oxyl-3-yl, 2,2,5,5-tetramethylpyrroline-1-oxyl-3-yl, 2,4,4-trimethyl-1,3-oxyazolidine-3-oxyl-2-yl, 2,4,4-trimethyl-1,3-thiazolidine-3-oxyl-2-yl and 2,4,4-trimethyl-imidozolidine-3-oxyl-2-yl, with other R if any representing hydrogen atoms, halogen atoms or hydroxy groups, and m is an integer from 20 to 5,000 while each n is independently an integer from 3 to 1,000,
• wherein the polyion complex is in the form of a polyion complex micelle in Na2HPO4 buffer (0.1M) at pH 6.28,
• wherein said composition forms a gel when injected into a living body and said gel is retained in a specific area of the body selected from the group consisting of a periodontal pocket, a cancer lesion and a site affected by arthritis;
• and wherein the composition further provides at least one property selected from the group consisting of suppressing inflammation, scavenging active oxygen, and regulating fluidity.