Ultrasonically induced electrical potentials in PLLA film and bone

Abstract

Osteosynthesis materials are used for the fixed treatment of serious bone fractures. Titanium and bioabsorbable poly-L-lactic acid (PLLA) are often used. PLLA is known to have piezoelectricity, and its contribution to bone fracture healing has been discussed. On the other hand, bone fracture healing using low-intensity-pulsed-ultra-sound (LIPUS) is also popular although the initial mechanism (how bones sense ultrasound) is still unclear. One key factor is the weak piezoelectricity of bone. If ultrasound was able to induce higher electrical potentials in PLLA than in bone, the combination treatment of PLLA and LIPUS would be effective for bone fracture healing. Then, we experimentally investigated the piezoelectricity of PLLA and bone in the MHz range. First, we fabricated an ultrasonic receiver using a cortical bone plate (thickness 1 mm) covered by a stretched PLLA film (thickness 50 mm) as a piezoelectric material. Second, we irradiated ultrasound in the MHz range to the receiver and measured electrical potentials as the output of the receiver. As a result, the average electrical potentials were about 1.4 times higher than those of a receiver made of bone without the PLLA film. This result indicates that ultrasonically induced potentials around bone may increase by the PLLA film.