A comparable study of polyglycolic acid's degradation on macrophages' activation

Polyglycolic acid (PGA) is a faster biodegradable polymer for various implants, frequently causing different macrophages' activation. In this study, we undertook a comparable study of PGA's degradation on macrophages' activation with different PGA crystallinity (in porous and fibrous 3D scaffolding format) in an in vitro and in vivo model. The incubation medium containing PGA degradation products, with different pH value of 7.1, 6.1 and 3.6, was added to RAW 264.7 macrophages' culture to simulate different degradation phases. The addition of hydrochloric acid with the same pH values in the culture media was used to compare and simplify the acid types' effect on macrophages. The scaffolds were implanted to mouse subcutaneously for 6 weeks. To correlate the degradation rate between the in vitro and in vivo models, PGA scaffolds were grafted by rhodamine-b covalently enabling the detection of PGA degradation through fluorescence intensity decay. It was confirmed that porous PGA degraded faster than fibrous scaffolds due to lower crystallinity. The acidic PGA degradation products (GA) did not promote IL-10 production, but inhibited IL-1β, IL-6 and TNF-α production in 7-days' culture significantly. The use of HCl with the same pH value as PGA degradation products in culture did not produce the same inhibition effect as GA. The mouse model showed that the degradation of PGA scaffolds was accelerated in vivo in the first two weeks, mainly due to tissue ingrowth. The fast degradation of porous scaffolds triggered M1 macrophages into the implantation site, whilst the slow degradation of PGA fibers promoted the polarization of macrophages into M2 pro-healing phenotypes. This study provides a good foundation to study and design biodegradable biomaterials toward immunomodulation.