Comparative Study on Bioactive Filler/Biopolymer Scaffolds for Potential Application in Supporting Bone Tissue Regeneration

The combination of biopolymers and bioactive inorganic particles for bone tissue regeneration has been investigated in the last decades. However, several studies report discordant results on the specific synergistic effect of the compounds. A comparative study on porous scaffolds obtained by the combination of the most promising biopolymers and bioactive inorganic particles is herein reported. Specifically, porous scaffolds have been fabricated by the Thermally Induced Phase Separation method using poly(3-hydroxybutyrate-co-3-hydroxyval- erate) (PHBV), poly(lactic acid) (PLA), and poly(caprolactone) (PCL) compounded with hydroxyapatite (HAp), calcium silicate (CS), or a Mg- and Sr-rich bioglass (BG) with a nominal composition of 2.3% Na2O, 2.3% K2O, 25.6% CaO, 10.0% MgO, 10.0% SrO, 2.6% P2O5, and 47.2% SiO2. Morphological analyses revealed the formation of highly interconnected and aligned open pores. Both thermal investigations and compressive tests highlight the close similarity between PLA- and PHBV-based scaffolds in terms of the amorphous structure and stiffness when the fillers are added. On the other hand, the addition of amorphous BG in semicrystalline PCL shows a decrease of the crystallinity degree of the polymer and a consequent decrease of the compressive modulus. Preliminary in vitro investigations (direct and indirect contact tests) carried out on the composite systems revealed that all the prepared materials provide an appropriate environment for NIH 3T3 cell adhesion and proliferation, showing a total lack of cytotoxicity. The addition of all the inorganic fillers has an overall positive effect on cell proliferation, viability (Neutral Red uptake), and metabolic activity (MTT test). Interestingly, this effect is particularly evident whenever BG is added. The combination of both amorphous BGs with amorphous polymers, such as PLA and PHBV, seems to be responsible for creating the best microenvironmental cue for NIH 3T3 cell attachment and proliferation.