## 4 Biosensors in the Field of Healthcare
### Future Direction--State-of-the-Art for Cardiovascular Smart Stents/Grafts  
NIH and thrombosis continue to be primary threats to the failure of CVD and PVD stents and grafts. Restenosis commonly occurs in nearly 10% of patients with DES and as high as 50% in vascular grafts [81; 160]. Restenosis, which can sometimes be silent and asymptomatic, is associated with irreversible health conditions such as morbidity and mortality. Often these complications mandate the patient to be readmitted to the hospital for a second operation. For example, undergoing another PCI procedure or re-establishing AV access. Repeated procedures afflict patients and cause further deterioration to their physical and mental health. Furthermore, they increase the burden on the healthcare system in multiple aspects. This includes the strain on medical staff and the substantial spending to correct complications that arise from current therapeutic solutions. Therefore, the transition to implantable smart devices has become essential for enhancing health and improving societal well-being. The employment of miniaturised implantable bioelectronics, biosensors, and wireless technology in CVD and PVD will permit the early detection of the onset of the disease and enable wireless pre-emptive treatment at an early stage. Early diagnosis and remote treatment would entirely reshape the healthcare system. Yet, the development of smart stents and grafts for early diagnosis and therapy is still ongoing. Some solutions have been achieved, but they are limited by drawbacks that prevent their use in humans. There have been several attempts to integrate and incorporate sensors into cardiovascular implants to overcome challenges facing both patients and healthcare providers (Figure 9). Specifically, the miniaturisation of microelectronics must be overcome. Here, we review some of these studies. [PERSON] et al. developed a self-reporting stent to monitor the re-endothelialisation process using piezoelectric microcantilevers. These were integrated at multiple locations on the surface of a stent. [PERSON] et al. hypothesised that the incomplete coverage of stent struts by endothelial cells leads to late thrombosis [161]. The real-time monitoring of this healing process would allow physicians to personalise anti-platelet prescriptions based on patient needs [162]. However, the technology's inability to differentiate between various cell types or circulating substances, such as fibrin, clots, or endothelial cells, made it impractical. On the other hand, [PERSON] et al. and his team developed an antenna stent by integrating a Micro-Electro-Mechanical System (MEMS) capacitive pressure sensor at one end. Combining pressure sensors with the stent forms an inductor-capacitor tank, which yields a resonant frequency, which reflects the blood pressure within the stent. Fluctuations in blood pressures indicate that ISR has occurred [163]. Furthermore, they adopted the commercially available double-J ureteral stent to enable the continuous monitoring of renal hypertension (hydronephrosis). This innovative approach is achieved by incorporating an inductive antenna with an integrated capacitive micro-pressure sensor to the wall of a ureteral stent [164; 165]. Both of their approaches for CVD and CKD smart stents are effective for only the early detection of the onset of restenosis and cannot support wireless treatment. Therefore, this technology does not protect patients from illness, requires hospital visits, and leaves the healthcare cost burden unresolved. In addition, another unique design of a smart stent, called the helix-like stent antenna, has been developed by [PERSON] et al. to serve as a whole stent antenna with two sensors integrated at both ends and one radiofrequency microprocess at one end. Pressure sensors at both ends measure the blood pressure and flow and transfer acquired data from the internal radiofrequency integrated circuit and antenna stent to an external antenna [166].