A fluid coupler comprises a ball valve a through hole provided between a female coupler body and a valve holding casing connected to the female coupler body and surrounding the ball. A trap pipe is connected to the bottom portion of the bowl portion. Such polypeptides may be used therapeutically for stimulating wound healing and for vascular tissue repair. The invention further provides photochromic materials of specified structure, photochromic compositions, photochromic articles and optical elements that include the photochromic materials.