by Birgitte McDonagh
Cartilage is sensitive to electrical stimuli. Nanoampere currents can stimulate growth of aggrecan and collagen: two crucial molecules for load bearing properties in cartilage. Medical devices that can generate a small electrical current are therefore seen as a promising solution to regenerate damaged cartilage.
Piezoelectric materials have been investigated as a source for nanoampere currents. Materials that are piezoelectric generate an electrical current when they are subjected to mechanical stress and can be a suitable constituent of a medical device for cartilage regeneration. However, common piezoelectric materials (such as lead zirconate titanate, polyvinylidene fluoride and zinc oxide) suffer from lack of biodegradability and from toxicity.
A recent paper published in Science demonstrates promising data on how a piezoelectric device can stimulate cartilage regeneration in rabbits through exercise. The novelty is based on production of a piezoelectric nanofiber film made from biodegradable poly-L-lactic acid (PLLA). The 3-dimensional scaffold was built up of consecutive layers of piezoelectric PLLA-films and collagen hydrogels. In addition to being an adhesive layer between the piezoelectric PLLA, collagen hydrogels were chosen to add volume to the 3D-scaffold and to promote cell ingrowth.
The scaffolds were tested in vivo in rabbits. First, a critical-sized osteochondral defect was created in the knee, followed by implantation of the piezoelectric 3D-scaffold. Rabbits were trained to exercise on treadmills for 20 minutes per day, to induce mechanical stress to the implanted scaffolds. The regeneration of the osteochondral defect was evaluated after 1 and 2 months after implantation surgery. The authors report that less regeneration was observed in the sham and control groups compared to the experimental group with piezoelectric 3D scaffolds with exercise. The subchondral bone volume increased in the experimental group compared to any other control groups.
The authors suggest that the system developed and described in the paper could serve as a battery-free biodegradable stimulator, but that more data on understanding the effects piezoelectric stimulation has on different signalling pathways are needed.
Liu et al, Exercise- induced piezoelectric stimulation for cartilage regeneration in rabbits, Science Translational medicine, Vol. 14., No 627, 2022, https://www.science.org/doi/10.1126/scitranslmed.abi7282