## 4 Electroceticals--Intelligent Environments  
### Pacemaker  
The heart is an electrical system that can regulate the speed and timing of the heartbeat. Heart chambers contract and expand to push blood flow through the blood nozzles. This is how the heart produces rhythms--heartbeat. Sometimes, the heartbeat is not systematic, i.e., in an unsynchronized fashion, and is known as heart failure. Cardio resynchronization therapy is the only chance to eliminate heart failure, and sometimes it may not. A smart biomedical implant, i.e., the biventricular pacemaker, is a device that is implanted under the skin, with two or three wires passing through the veins leading to the heart muscle [52; 53]. The biventricular pacemaker has wires in the heart's left and right lower chambers and tunes the impulses to make the heart muscle contract better and improve the overall pumping function. Suppose the heart goes into cardiac arrest and is in a dangerous rhythm. In that case, the implantable cardioverter-defibrillator produces impulsive currents to the heart muscle to return to a normal heart function. The biventricular pacemaker and implantable cardioverter-defibrillator functions are integrated into a single device that is implanted beneath the skin in the chest. This device has shown a reduced risk of patients with cardiac arrest in heart failure. However, generating impulse-based shocks from time to time under cardiac arrest is most important. If not so, the patient may face serious risks. There are limitations in existing pacemaker devices' energy supply systems, such as miniaturizing energy storage devices, the battery should supply energy in time, a longer period, etc. The energy storage systems such as lithium-ion batteries efficiently work for a limited time due to their limited charge density and internal resistance. Therefore, the technological innovation in vivo energy harvesters driven by biomedical energy is necessary to supply continuous, uninterrupted power to the titanium packaged implantable devices [54; 55; 56]. There is ongoing research on bioenergy-driven energy supply systems for heart implants. For example, self-rechargeable cardiac pacemaker systems with triboelectric nanogenerators, thermoelectric energy harvesters, piezoelectric energy harvesters, etc., have been successfully developed [52; 54; 55; 56; 57]. Recently, a high-performance inertia-driven triboelectric nanogenerator based on body motion and gravity with the size of a commercial coin has been introduced [57]. [PERSON] et al. demonstrated the nanogenerator integrated cardiac pacemaker system and conformed self-rechargeable cardiac pacemaker system's ventricle pacing and sensing operation mode. Self-powered biomedical implants based on piezoelectric harvesters are among the potential candidates that allow and generate electricity from cardiac motion. In this context, researchers have started with lead-based ceramic piezoelectric generators. However, lead-based systems are toxic and susceptible to cracks. Alternatively, polyvinylidene fluoride trichloroethylene-based films were produced as cardiac energy harvesters. Later on, biocompatible and flexible piezoelectric polymer-based nanogenerators were realized as a battery-free heart pacemaker system that could generate electricity from the cardiac motion of the left ventricle [58]. These piezoelectric polymer-based nanogenerators are produced from polyvinylidene fluoride composite nanofibers, zinc oxide, and reduced graphene oxide hybrid nanofillers. The results revealed that these composite fibrous-based nanogenerators produce energy of about 487 \(\upmu\)J. They suggested that this is a viable candidate for implantable applications, and energy is sufficient for pacing the human heart and leads [58]. The developed bioenergy-driven energy supply devices have possessed several potential advantages, such as extending the implantable pacemaker device's operation time inside the body and reducing the high risk of repeated surgery.