Bi-/multi-modal pore formation of PLGA/hydroxyapatite composite scaffolds by heterogeneous nucleation in supercritical CO2 foaming

Scaffolds with multimodal pore structure are essential to cells differentiation and proliferation in bone tissue engineering. Bi-/multi-modal porous PLGA/hydroxyapatite composite scaffolds were prepared by supercritical CO2 foaming in which hydroxyapatite acted as heterogeneous nucleation agent. Bimodal porous scaffolds were prepared under certain conditions, i.e. hydroxyapatite addition of 5%, depressurization rate of 0.3 MPa·min− 1, soaking temperature of 55 °C, and pressure of 9 MPa. And scaffolds presented specific structure of small pores (122 μm ± 66 μm) in the cellular walls of large pores (552 μm ± 127 μm). Furthermore, multimodal porous PLGA scaffolds with micro-pores (37 μm ± 11 μm) were obtained at low soaking pressure of 7.5 MPa. The interconnected porosity of scaffolds ranged from (52.53 ± 2.69)% to (83.08 ± 2.42)% by adjusting depressurization rate, while compression modulus satisfied the requirement of bone tissue engineering. Solvent-free CO2 foaming method is promising to fabricate bi-/multi-modal porous scaffolds in one step, and bioactive particles for osteogenesis could serve as nucleation agents.