gms | German Medical Science

Objectives: Critical-sized bone defects, caused by trauma or tumor removal, do not heal spontaneously. These bone defects vary in their size or shape thus require individual surgical procedures along with suitable implants to achieve mechanical stabilization and bone healing. Additive manufacturing technologies, such as extrusion-based 3D printing, offer the possibility to fabricate complex and individualized bone scaffolds. The aim of this study was to print scaffolds with osteoinductive properties and a spongiosa-inspired structure. For printing the biocompatible and bioresorbable polymer polycaprolactone (PCL) was used in its pristine form or blended with calcium phosphate nanoparticles (CaP). After printing the scaffolds were seeded with MG63 (osteosarcoma cell line) or human mesenchymal stem cells (hMSC) to analyze their impact on osteogenic differentiation. Mechanical testing was performed to ensure their suitability as load bearing bone implants.

Methods: Annular scaffolds (d: 20 mm, h: 10 mm) were manufactured by extrusion-based 3D printing (BIO X6, Cellink) using pristine PCL or blended with CaP particles (< 150 nm) at a ratio of 80/20%. The scaffold design includes interconnecting pores (d: 2 mm +/- 0.2 mm) which were irregularly distributed to mimic cancellous bone structure. The scaffolds were seeded with 5 x 10^6 MG63 per scaffold, or hMSC and further cultured in osteogenic differentiation medium for 14 days. Biocompatibility and osteoinductive properties of cell-seeded constructs were analyzed using several methods and parameters including assessment of morphology, proliferation (DNA-quantification), and osteogenic differentiation (polymerase chain reaction (PCR), alizarin red staining (ARS), alkaline phosphatase (ALP) assay). Distribution of calcium was assessed by energy dispersive X-ray (EDX) analysis. Compression and tensile force testing were performed to analyze a potential influence from the material composition.

Results and conclusion: Although both MG63 and hMSC attached to the scaffolds, the material composition, PCL versus PCL-CaP, clearly indicated differences in the cell response. While the amount of DNA significantly increased in culture time for MG63 on PCL scaffolds indicating proliferation, the incorporation of CaP in the composite material favored osteogenic gene expression in MG63 cells (collagen type 1 and osteocalcin). ARS confirmed improved calcification processes of cells on PCL-CaP and revealed freely accessible CaP particles at the material surface. EDX analysis further demonstrated a homogeneous distribution of CaP throughout the printed scaffolds.

Mechanical tests revealed bone-like compression strength for both scaffold types, indicating no significant differences in either compression strength or tensile force for PCL-CaP or pure PCL.

In conclusion, this study highlights the suitability of CaP-containing 3D-printed scaffolds in terms of their biocompatibility as well as mechanical and osteoinductive properties.