A fused loop of an elongated material, such as a surgical suture, and apparatus for making the loop are described. Portions of one or more segments of elongated material may be fused in an ultrasonic welding process to form a welded joint. Multiple materials each with different a different melting point may be used for one or more fibers within the elongated material. The elongated material may include a sheath, which may be used to protect a core within the elongated material. A fused region of the fused loop may be formed when a material with a lower melting temperature, compared to one or more other materials in the elongated material, is caused to melt. A related ultrasonic welding apparatus may include a temperature sensor for control of the welding process.