Fine-tuning the degradation of 3D-printed Calcite/Polycaprolactone scaffolds by mineral morphologies for use as bone graft substitute.

Abstract text (incl. figure legends and references)

Introduction&Objective: Gradual degradation of Polycaprolactone (PCL) bone graft substitutes can be adjusted by incorporating calcite particles (CaCO₃) of various morphologies to adapt to parallel regeneration of new bone tissue in vivo. The objective was, if either spherical, scalenohedron or rhombohedral CaCO3 particles incorporated in gamma-sterilized PCL scaffolds are most beneficial for bone graft substitutes. Evaluating the results in descending priority on stable buffer buffering of acidic PCL degradation products, mechanical stability after bulk degradation, and continuous calcium release.

Materials&Methods: Calcite particles were mixed into melted PCL and afterwards processed to a scaffold via fused deposition modelling (FDM). Gamma-sterilized scaffolds and single strands were incubated in 0.9% NaCl, PBS with Lipase and 2.5 M HCl. Calcium release was measured using a colorimetric calcium kit with UV-VIS, while buffer capacity was proven by pH measurements. Mechanical stability was tested via 3-point tension testing. Scaffolds were incubated over 28 days and single strands over 14 daysd at 37°C in 7% CO2, while performing medium change every 3 to 4 days.

Results&Conclusion: While scalenohedron particles cause a very stable calcium release, they are disintegrating the matrix during bulk degradation. In contrast, calcium release of rhombohedron particles decreases after 21 days, while the matrix"s integrity is rather comparable to pure PCL (compare Fig.1 and Fig.2). Furthermore, for comparability to in vitro degradation mechanism, bulk and surface degradation of PCL could be accelerated. It was proven that different morphologies of calcite particles do have a significant impact on the degradation of gamma-sterilized PCL scaffolds, produced by FDM and intended to be used as bone graft substitutes. Trade-off decisions need to be made in order to fine-tune the properties of a suitable bone graft substitute without functional loss.