Abstract: Methods and systems of osteoarthritis treatment. One method includes providing a cartilage hydrogel, the cartilage hydrogel including piezoelectric nano-fibers of Poly-L-lactide (PLLA). The method also includes injecting the cartilage hydrogel into a cartilage defect. The method also includes applying an ultrasonic treatment to the cartilage defect. The method also includes, in response to applying the ultrasonic treatment to the cartilage defect, converting a mechanical impact of the ultrasonic treatment into an electrical charge from the piezoelectric nano-fibers of PLLA and providing, in response to the electrical charge from the piezoelectric nano-fibers of PLLA, chondrogenesis differentiation for cartilage regeneration for the cartilage defect.

Abstract: A facepiece respirator configured to be worn by a user. The facepiece respirator includes including a first layer and a second layer coupled to the first layer. The first layer is positionable adjacent the user. A filtering layer is positioned between the first and second layer, and the filtering layer includes a piezoelectric film.