Application of piezoelectric nanogenerator in medicine: bio-experiment and theoretical exploration

Background: A large number of wearable and implantable electronic medical devices are widely used in clinic and playing an increasingly important role in diagnosis and treatment, but the limited battery capacity restricts their service life and function expansion. Piezoelectric nanogenerators can convert mechanical energy into electrical energy. Our experiment tries to find out if the piezoelectric nanogenerator fixed to the surface of the heart can convert the natural contractions and relaxations of the heart into stable electric energy for electronic medical devices such as pacemakers.

Methods: We used Chinese miniature pig and prepared with standard open chest procedure. Then we fixed two opposite edges of the rectangular nanogenerator at the following three positions of the heart respectively to detect the electric voltage output: Position A, right ventricular surface, near the atrioventricular groove, parallel to the long axis of the heart; Position B, right ventricular surface, parallel to the atrioventricular groove; and Position C, left ventricular surface, near cardiac apex, parallel to the left anterior descending branch. Then we selected the place which has the highest voltage output to fix both ends of the nanogenerator and closed the chest of pig. We recorded the voltage output of nanogenerator under closed chest condition (natural condition) and compared the result with open chest condition. Finally we used Dopamine (positive inotropic agents) and Esmolol (negative inotropic agents) respectively to detect the relation between voltage output of nanogenerator and myocardial contractility.

Results: With its both ends fixed on the surface of the heart, the piezoelectric nanogenerator produced stable voltage output from the mechanical contractions of the heart. Piezoelectric nanogenerator which was fixed at Position A produced the highest voltage output (3.1 V), compared with those fixed at Position B or Position C. The voltage is enough for the pacemaker's operation. The voltage output of piezoelectric nanogenerator at the natural condition (closed chest) was the same as the open chest condition and made a light emitting diode (LED) light continue to shine, which further confirmed its clinical application value. The voltage output of piezoelectric nanogenerator is positively correlated with the myocardial contractile force. The voltage output increased after we used positive inotropic agents and decreased after we used negative inotropic agents.

Conclusions: Piezoelectric nanogenerators can convert the kinetic energy of the heart during the contractions and relaxations of the muscles to electric energy. The output voltage was stable in three positions on the surface of the heart. The highest voltage appeared on the surface of right ventricle, near atrioventricular groove, parallel to the long axis direction of the heart, which can be the potential new energy source for pacemakers. Piezoelectric nanogenerator can be used as cardiac function monitor in the future for its voltage output is positively correlated with myocardial contractile force.