## 4 Discussion  
The traditional PLA degradation measurement patterns (i.e., weight loss, morphological change) have been widely studied. However, this study was the first to use an MB sensor to monitor PAB degradation wirelessly and passively. In general, the results indicated that incorporating an MB sensor in PAB allowed the degradation behavior to be monitored in vitro. The in vitro weight loss and SEM monitoring of the PAB degradation behavior [32] were used to further elucidate the viability of the MB sensor. A theoretical analysis was also performed to verify the viability of using the MB sensor to monitor the degradation behavior of PAB. About 5 \(\pm\) 0.1 g of PLA was coated on the MB sensor strip. The PAB weight decreased by 0.3 \(\pm\) 0.03 g in the alkaline medium and 0.15 \(\pm\) 0.03 g in the PBS medium over 15 days. SEM images clearly showed the weight loss of PAB in the alkaline medium. In previous studies, [PERSON] [33] used the traditional methods of weight loss, SEM micrographs, thermal analysis, and others to monitor the degradation process of a new PLA braided biomaterial, while [PERSON] et al [12] used the mass, morphology, thermal behavior, and tensile properties of PLA to monitor its surface degradation. The weight loss and SEM imaging results in this study were similar to those described in the above papers. Figure 8: In the alkaline medium (pH = 12): (**a**) the linear increase in the varying value of the output power with an increasing external force (0–100 N) for the three phases; (**b**) the comparison of output power (dbm) for days 0, 7, and 15 at 10, 50, and 100 N.  
Figure 9: In the PBS medium (pH = 7.4): (**a**) a relationship between the varying value of the output power (dbm) and external force (N) on days 0, 7, and 15; (**b**) a detailed comparison of output power at 10, 50, and 100 N for the three days. Figure 7 shows that the varying value of output power had the same trend when PAB was tested in vivo and in vitro. This indicates that biological tissues have almost no effect on the output power. Therefore, the MB sensor can be used in vivo to monitor the degradation behavior of bioimplants in the future. Figures 8 and 9 present the varying values of the output power when PAB was incubated in alkaline (pH = 12) and PBS (pH = 7.4) media for 15 days. On day 0, the output power was lower than that on days 7 and 15. As the degradation time increased, more PLA degraded, and the diameter and weight of PAB were reduced. The external force could cause a large amount of stress on the MB sensor, which could increase its permeability. The output power of PAB with external forces of 10, 50, and 100 N was further studied for the three days, as shown in Figures 8b and 9b. The effect of degradation on the MB sensor at these specific forces was considered. The output power gradually increased from day 0 to day 7 and day 15, but the only difference was the increasing tendency. This can further explain the degradation behavior of the PAB. Thus, the MB sensor could monitor and reflect the degradation behavior under different conditions wirelessly and passively (i.e., medium and external force). The output power shown in Figure 8a was higher than that shown in Figure 9a on days 0, 7, and 15. PAB degraded more quickly in the alkaline medium than in the PBS medium. The different degradation conditions led to different stresses working on the MB sensor. The different degradation conditions also caused different permeabilities in the MB sensor. Furthermore, the change in the PAB diameter could affect the permeability of the MB sensor in the same environment. In this study, the PAB diameter was 15 \(\pm\) 0.05 mm at the beginning of degradation and decreased to 14.92 \(\pm\) 0.02 mm in the alkaline medium and 14.96 \(\pm\) 0.02 mm in the PBS medium over 15 days. Table 2 gives the variation of the PAB diameter in the two media over 15 days, and the varying value of the output power increased. The diameter and weight of PAB gradually decreased with increasing degradation time, as shown in Figure 10a.