In vivo degradation and neovascularization of silk fibroin implants monitored by multiple modes ultrasound for surgical applications

Background In this paper we aimed to investigate the neovascularization and biodegradation of the silk fibroin in vivo using multiple modes ultrasound, including two-dimensional, three-dimensional and contrast-enhanced ultrasound by quantifying the echo intensity, volume and contrast enhancement of the silk fibroin implants. Method A total of 56 male Wistar rats were randomly divided into two groups and 4%(w/v) silk hydrogels were injected subcutaneously at hind limb or upper back of the rats respectively to compare the biodegradation rate in different sites of the body. The implants were observed at day 0, 4, 8, 12, 16, 18, 20 with multiple modes ultrasound. Results The echo intensity of silk fibroin implants increased and the volume decreased gradually, and complete degradation was confirmed 18 and 20 days after subcutaneous implantation at the upper back and at the hind limb respectively. This demonstrated that the silk fibroin embedded in the upper back degraded slightly faster than that in the hind limb. Additionally, the neovascularization revealed by the contrast enhancement values of CEUS showed that there was a relatively low enhancement (< 5 dB) during day 4 to day 16, followed by moderate enhancement at day 18 (5–20 dB), and a significant enhancement at day 20 (> 40 dB). Conclusion This study suggests that multiple modes ultrasound imaging could be an ideal method to evaluate the degradation and neovascularization of biomaterial implants in vivo for surgical applications.