Conjugation of PDLA onto MgO Microspheres: Comparison between Solution Grafting and Melt Grafting Methods

Magnesium oxide (MgO) is known for its bioactivity and osteoconductivity when incprporated into biodegradable polylactide (PLA), while the weak interfacial bonding between MgO microspheres (mMPs) and PLA often leads to suboptimal composite properties with uncontrollable functionality. The conjugation of mMPs with PLA may offer a good way to enhance their compatibility. In this study, we systematically investigated two grafting techniques, solution grafting (Sol) and melt grafting (Mel) to decorate poly(D-lactic acid) (PDLA) on mMPs pre-treatmented by prioritized hydration to obtain Sol MPs and Mel MPs, in order to optimize the grafting efficiency and improve their controllability in the properties including crystal structure and surface morphology. Meanwhile, the Sol method shows an improved grafting ratio (2.9 times higher) compared to the Mel method. The conjugation of mMPs with PDLA effectively neutralized the rapid pH increase along degradation of pure mMPs, which could be used for sustainable delivery of Mg2+ ion release. Moreover, Sol MPs exhibited the lowest degradation rate constant, which could be well fitted by the first order dynamic model, suggesting a transformation of the mMPs degradation mode from bulk degradation to surface degradation. This change in biodegradation mode was beneficial for decreasing the over-basic effect caused by the quick degradation of pure mMPs, thus extending their application in development of PDLA/MgO composites towards tissue engineering or regenerative medicine.