## 5. Degradable Devices  
Based on the degradable materials introduced above, researchers have successfully developed a variety of degradable implantable devices [165; 166; 167]. [PERSON] used degradable Mg metal and poly (glycerol sebacate) (PGS) dielectric layer to prepare two core components of the LC resonant wireless sensor, namely the inductor and the capacitor, respectively [115]. Meanwhile, materials such as poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/PHV) and poly-L-lactic acid (PLLA) were used for encapsulation and electrical isolation, endowing the sensor with both flexibility and complete degradability. This sensor can easily wrap around arteries with a diameter of less than 1 mm and can completely degrade 12 weeks after being implanted in rats, thus avoiding the need for a second surgery. The [PERSON] team also developed an all-degradable LC resonant pressure sensor [79]. In this sensor, a laser-cut magnesium metal coil was used as the inductive device, zinc foil was used as the flexible electrode, and poly (lactic-co-glycolic acid) (PLGA) was used as the dielectric layer. By constructing a specific-shaped cavity structure, the deformation degree of the top electrode was effectively increased under a given applied pressure, thereby improving the sensitivity of the device. In addition, Si\({}_{3}\)N\({}_{4}\) and wax were used as bioabsorbable biofluid barriers to reduce the impact of the in vivo liquid environment on the sensor (Figure 4a). This sensor remained stable during a four-day operation and exhibited the characteristics of low noise interference. Figure 4. (**a**) The explosion view diagram of this device highlights the pressure sensing window of the sensor and the relationship between the resonant frequency and the pressure that varies over time. (**b**) Optical microscope images of the sensor and circuit diagrams of the Wheatstone bridge, consisting of strain gauges, temperature gauges, a voltage source and a meter that compensates for temperature-induced variations in the piezoresistivity of strain gauges. R represents the gauge resistance. (**c**) The highly flexible eb-MEMS platform is demonstrated, with a particular emphasis on CMOS electronic devices, resistors, capacitors, and the bioabsorbable polymer substrate. Meanwhile, the integration of this platform on the myocardial surface is presented. (**d**) Schematic diagram of the metagels wireless intracranial physiological sensor using ultrasonic reflection and its structure under the microscope. Photos of metagel degradation were displayed after one month in PBS solution at 37 \({}^{\circ}\)C (The dotted line depicts the shape of the meta-image). In addition, [PERSON] exploited the degradable property of ultrathin silicon to develop an amorphous silica adhesive layer formed by calcining polydimethylsiloxane (PDMS), which was used to bond a pair of silicon-on-insulator (SOI) wafers to form a pressure sensor [168] (Figure 4b). This sensor used four silicon nanomembranes as the pressure/temperature sensitive regions to measure the intracranial pressure and temperature of rats. Through dissolution kinetics characterization, it was found that this sensor device could completely dissolve within 290 days without significantly affecting the performance of the sensor. The dissolved silicic acid was excreted from the body through the kidneys. Analogous to this type of system is MEMS. Leveraging specialized manufacturing processes and packaging strategies, degradable MEMS systems can be integrated onto flexible substrates. As depicted in the figure, a differential uniaxial accelerometer based on a biodegradable PAP substrate is introduced [169]. Herein, a suspended rectangular film measuring 200 \(\upmu\)m \(\times\) 420 \(\upmu\)m \(\times\) 2 \(\upmu\)m functions as the mass block; a set of suspended serpentine structures with a cross-sectional area of 3 \(\upmu\)m \(\times\) 2 \(\upmu\)m and a length of 2 mm act as the spring system; moreover, there are suspended interdigitated electrodes for capacitive sensing (Figure 4c).