Early-stage macroporosity enhancement in calcium phosphate cements by inclusion of poly(N-vinylpyrrolidone) particles as a porogen

Abstract

The incorporation of poly(DL-lactic-co-glycolic acid) (PLGA) particles into calcium phosphate cements (CPCs) is an effective strategy to enhance CPC macroporosity and degradation. However, bone regeneration is hindered until hydrolytic PLGA degradation starts a few weeks after implantation. Additionally, CPC and CPC/PLGA injectability and cohesion are suboptimal. In the current study, poly(N-vinylpyrrolidone) (PVP), a water-soluble polymer, was incorporated as a porogen in CPC and CPC/PLGA composites to enhance handling properties and early-stage macroporosity formation. Further, the effect of PVP molecular weight (Mw) and particle size was studied. The results showed that PVP incorporation increased both injectability and cohesion of the CPC pastes, especially with addition of high Mw PVP. Moreover, the in vitro degradation studies revealed that incorporation of PVP induced an initial mass loss during the first week of incubation. In combination with PLGA, small PVP particles induced a higher mass loss at an early stage than large PVP particles, but this effect was no longer apparent after 4 weeks of incubation. In contrast, the incorporation of low Mw PVP had a stronger effect on in vitro degradation in the long term compared to high Mw. Finally, the presence of PLGA porogens appeared to be necessary for adequate CPC degradation.