3D-printable biodegradable hybrids based on ABA-triblock copolymers synthesised by RAFT polymerisation

There is an unmet clinical need for advanced biomaterials that can promote bone regeneration through three-dimensional (3D) scaffold architectures. Hybrid inorganic/organic biomaterials are promising due to their nanoscale interactions between amorphous polymeric and silica networks, which can provide resistance to cyclic loading and tuneable biodegradability. Our aim was to develop novel biodegradable silica/polymer scaffolds based on P(MMA-co-TMSPMA)-b-PCL-b-P(MMA-co-TMSPMA) triblock copolymers as the organic component. Triblock copolymers produced by RAFT polymerisation were chosen over linear polymers to balance controlled biodegradation with mechanical strength. Optimal compositions were 70 wt% nominal organic content using triblock copolymers synthesised from the 5 kDa PCL based RAFT agent, which exhibited the highest yield strength (compression) of 58 MPa (true stress) at 5% strain. Scaffolds with interconnected pore sizes of 250-300 µm were 3D printed from the hybrid ink via direct ink writing (DIW). Optimal printability was achieved for triblock copolymers with molecular masses between 15 000 and 17 000 g mol^-1 (using PCL of 5 kDa) and they exhibited mechanical properties and porosity comparable to those of trabecular bone, e.g., a yield strength of 10 ± 0.5 MPa at a yield strain of 4 ± 0.3%, and showed ∼23% degradation over two months. In vitro studies confirmed that the scaffolds were not toxic to human bone marrow stromal cells.