| Background:With increasing application of implantable electronic devices in clinical medicine, the clinical diagnosis and treatment has been developed largely. The implantable medical electronic devices are hindered by problems in accuracy, security, portability and durability. Despite the rapid development of microelectronics, the battery technology for microelectronics is progressing slowly and power supply becomes a major obstacle to the development of implantable medical electronic devices.Since last decade, energy harvesting has become a focus of research interests. As a result, it has become a new strategy to scavenge and convert the energy of the human body into electric energy as power supply for implantable medical electronic devices by using piezoelectric devices.The mechanical energy generated by cardiac motion has the advantages of life-long durability and large amount. Harvesting the biomechanical energy of heart and converting it into electric energy for cardiac pacemaker by using piezoelectric technology is a new strategy for integrating piezoelectric technology with implantable medical electronic devices. Given the motion and shape of the heart, the piezoelectric devices must have good stretchability and flexibility and should not cause any damage or extra burden to the heart.This study was undertaken to validate the stretchability and flexibility of an ultra-flexible piezoelectric device with in vivo testing and to provide experimental data for further researches.Methods:The experimental rabbits are randomly divided into the experimental and control groups, each group containing 20 animals. In animals of the experimental group, ultra-flexible piezoelectric devices were sutured on the surface of the heart under general anesthesia and thoracotomy. In animals of the control group only thoracotomy was performed, without suturing ultra-flexible devices. Parameters and vital signs including the body weight, heart rate, respiratory rate, systolic blood pressure and the physical properties of the ultra-flexible devices were recorded before and after sternal closure, at 1 day, 1 week, 2, 3 and 4 weeks postoperatively. Temporal trends of these parameters were compared and analyzed with linear mixed modeling. All devices were explanted at the end of the in vivo testing and examined with optical microscope and scanning electron microscope(SEM). Histological stains with hematoxylin and eosin(H-E), Masson, TUNEL and CD 68 were used to detect the changes in the myocardium of animals after sacrifice.Results:The energy harvesting performance and micro-specialty of all ultra-flexible piezoelectric devices were remained intact after the mechanical model experiments. All animals in the experimental and control groups were alive by the end of the in vivo testing(1 month). Before anesthesia, there were no significant differences in weight(2.88 ± 0.20 vs. 2.90 ± 0.25 kg, p = 0.78), heart rate(227.0 ± 12.7 vs. 232.0 ± 10.4 beats per minute, bpm, p = 0.19), respiratory rate(50.0 ± 4.9 vs. 51.0 ± 5.3 times per minute, p = 0.39) and systolic blood pressure(106.0 ± 9.2 vs. 107.6 ± 8.4 mm Hg, p = 0.58) between the experimental and control groups. At postoperative 1 day, 1 week, 2, 3 and 4 weeks, there were also no statistical differences in the weight, heart rate, respiratory rate and systolic blood pressure between animals of the two groups: at postoperative 1 day: weight, p = 0.82; heart rate, p = 0.62; respiratory rate, p = 0.38; systolic blood pressure, p = 0.63; at 1 week postoperatively: weight, p = 0.67; heart rate, p = 0.21; respiratory rate, p = 0.95; systolic blood pressure, p = 0.24; at 2 weeks postoperatively: weight, p = 0.47; heart rate, p = 0.94; respiratory rate, p = 0.38; systolic blood pressure, p = 0.54; at postoperative 3 weeks: weight, p = 0.11; heart rate, p = 0.61; respiratory rate, p = 0.28; systolic blood pressure, p = 0.55; at 4 weeks postoperative: weight, p = 0.60; heart rate, p = 0.22; respiratory rate, p = 0.71; systolic blood pressure, p = 0.83.Linear mixed model estimates revealed that there were no statistical differences in the weight(p = 0.54), heart rate(p = 0.47), systolic blood pressure(p = 0.86) and respiratory rate(p = 0.46) between the animals of the experimental and control groups.In the experimental group, the ultra-flexible piezoelectric devices were functioning well at 1 day, 1 week and 2 weeks postoperatively(p = 1.00). However, 2 devices failure occurred at postoperative 3 weeks(p = 0.49). Thereafter no additional device failure was observed till 4 weeks postoperatively. Upon explantation at 4 weeks, optical microscopy and scanning electron microscopy(SEM) showed that the microstructure of all of these devices was intact(p = 1.00). The 2 damaged devices at 3 postoperative weeks were caused by dislocation of the welding point connecting the film and the wire.Histological stains detected no lesions of the myocardium in the animals of the experimental and control groups with hematoxylin and eosin(H-E), Masson, TUNEL and CD 68.Conclusions:The results of the mechanical model experiments and in vivo testing confirmed the stretchability, flexibility and energy harvesting performance demonstrated by the ultra-flexible piezoelectric devices. The ultra-flexible piezoelectric devices did not cause damages to the physiological function and the myocardium, which proved its biocompatibility, flexibility and in vivo performance. This study implies that implantable ultra-flexible piezoelectric devices may provide new method for harvesting energy of the human body and represent a new strategy of power supply for implantable electric devices. |
