A new piezoelectric actuator induces bone formation in vivo: a preliminary study

Abstract

This in vivo study presents the preliminary results of the use of a novel piezoelectric actuator for orthopedic application. The innovative use of the converse piezoelectric effect to mechanically stimulate bone was achieved with polyvinylidene fluoride actuators implanted in osteotomy cuts in sheep femur and tibia. The biological response around the osteotomies was assessed through histology and histomorphometry in nondecalcified sections and histochemistry and immunohistochemistry in decalcified sections, namely, through Masson's trichrome, and labeling of osteopontin, proliferating cell nuclear antigen, and tartrate-resistant acid phosphatase. After one-month implantation, total bone area and new bone area were significantly higher around actuators when compared to static controls. Bone deposition rate was also significantly higher in the mechanically stimulated areas. In these areas, osteopontin increased expression was observed. The present in vivo study suggests that piezoelectric materials and the converse piezoelectric effect may be used to effectively stimulate bone growth.

Figure 1

Location of the actuators within the bone. The figure shows example of bone section prior to inclusion: (a) section of tibia—scale bar 1 cm; (b) shows how the areas for histomorphometry were distributed; Z1 corresponds to the film clamped region—scale bar 2 cm.

Figure 2

Postoperative radiograph thirty days after implantation showing the six actuators in place (four in the femur, two in the tibia). There are neither signs of periostal or peri-implantar reaction nor signs of infection in neighboring soft tissues.

Figure 3

Low-magnification picture of histological section where it is evident the fibrous tissue around the implant (arrows). Scale bar represents 4 mm.

Figure 4

Total bone area measured around actuators and static controls, expressed in percentage. Bars represent means and error bars standard deviation.

Figure 5

Microphotograph of nondecalcified sections. On top, (a) shows Z3 areas of actuator and (b) shows static control, both implanted in the same position in tibia. On bottom, Z2 areas showing increase labeled area in (c) femoral actuator when compared to contra lateral (d) static control. A fibrous capsule (FC) was present on the bone/film interface. Scale bar represents 200 μm.

Figure 6

Total bone area measured around actuators and static controls, organized by areas Z1 to Z4. Bars represent means and error bars standard deviation.

Figure 7

Microphotograph of decalcified sections, osteopontin (white arrows) and PCNA expression. Picture shows Z3 areas of femoral: (a) actuator and (b) static control, suggesting more extensive osteopontin labeling around actuator. Double Fast-Red and DAB immunohistochemistry staining for osteopontin and PCNA, respectively. Scale bar represents 100 μm.