Since their initial development in 2012, triboelectric nanogenerators (TENGs) have gained popularity worldwide as a desired option for harnessing energy. The urgent demand for TENGs is attributed to their novel structural design, low cost, and use of large-scale materials. The output performance of a TENG depends on the surface charge density of the friction layers. Several recycled and biowaste materials have been explored as friction layers to enhance the output performance of TENGs. Natural and oceanic biomaterials have also been investigated as alternatives for improving the performance of TENG devices. Moreover, structural innovations have been made in TENGs to develop highly efficient devices. This review summarizes the recent developments in recycling and biowaste materials for TENG devices. The potential of natural and oceanic biowaste materials is also discussed. Finally, future outlooks for the structural developments in TENG devices are presented.

This study aimed to examine the effect of a mild elevation in serum cholesterol level in a porcine coronary overstretch restenosis model using a balloon angioplasty catheter or drug-eluting coronary stent. Pigs were divided into two groups and were fed a commercial normal diet (CND, n = 4) or a high-fat diet (HFD, n = 4) for 5 weeks. Coronary overstretch injury by balloon angioplasty or stent implantation was induced in the left anterior descending and left circumflex artery after 1 week of feeding. Histopathological analysis was performed at 4 weeks after coronary injury. During the experiment, the total cholesterol level in the HFD group increased by approximately 44.9% (from 65.9 ± 3.21 mg/dL at baseline to 95.5 ± 9.94 mg/dL at 5 weeks). The lumen area in the CND group was reduced in comparison with that in the HFD group after balloon angioplasty. After stent implantation, the injury score showed no significant difference. There were significant differences in the neointimal area (2.7 ± 0.33 mm2 in the CND group vs. 3.3 ± 0.34 mm2 in the HFD group, p<0.05), lumen area (2.6 ± 0.54 mm2 in the CND group vs. 2.0 ± 0.33 mm2 in the HFD group, p<0.05), and percent area stenosis (52.0 ± 7.96% in the CND group vs. 62.4 ± 5.15% in the HFD group, p<0.05). Body weight change was not different between the two groups. Increased serum cholesterol level activated vascular smooth muscle cell proliferation in the porcine coronary overstretch model.