Inner strut morphology is the key parameter in producing highly porous and mechanically stable poly(e-caprolactone) scaffolds via selective laser sintering

Selective laser sintering (SLS) is an established method to produce dimensionally accurate scaffolds for tissue engineering (TE) applications, especially in bone. In this context, the FDA-approved, biodegradable polymer poly(e-caprolactone) (PCL) has been suggested as a suitable scaffold material. However, PCL scaffold mechanical stability - an attribute of particular importance in the field of bone TE - was not considered as a primary target for SLS process parameters optimization so far. Here, we investigated the influence of SLS process parameters on the sintered scaffolds with the aim of producing highly porous (>70% porosity) PCL scaffolds with sub-mm geometrical features for bone TE. Specifically, we studied the influence of laser power, beam compensation and laser beam diameter on the dimensional accuracy and mechanical stiffness of the produced PCL scaffolds. We found that the ratio between the diameter of the molten cross-section within scaffold struts and the outer strut diameter (including partially sintered particles) depended on the SLS process parameters. By maximizing this ratio, the mechanical stability could be optimized. The comparison with in silico predictions of scaffold mechanical stiffness revealed that the diameter of the molten cross-section within struts and not the strut diameter controlled the mechanical behaviour of the scaffold. These observations should be considered when evaluating the quality of the sintering process based on dimensional accuracy, especially for features <1 mm. Based on these findings, we suggested an approach to evaluate the sintering outcome and to define SLS process parameters that enable the production of highly porous scaffolds that are both dimensionally accurate and mechanically stable. Moreover, the cytocompatibility of PCL scaffolds was evaluated by elution tests with primary human mesenchymal stromal cells. No evidence of cytotoxicity was found in any of the investigated scaffolds, confirming the suitability of SLS as production technique of PCL scaffolds for bone TE over a wide range of SLS process parameters.