3D-printed PCL scaffolds: optimising material selection for specific bone regeneration applications

Significant clinical challenges are posed by large bone defects, necessitating the use of scaffolds that combine mechanical stability with osteoinductive properties. While polycaprolactone (PCL) lends itself well to 3D printing, its limited bioactivity means it needs to be modified with bioactive additives. Various additives have been proposed to enhance PCL scaffolds, but a systematic comparative evaluation of their mechanical and biological effects is lacking. This hinders the optimal selection of materials for specific applications. In this study, we compared the effects of four additives-silver nanoparticles (AgNPs), osteogenon (OST), zinc oxide (ZnO) and vitroceramic calcium phosphate (CaPNPs)-when incorporated at a concentration of 0.5 wt% into 3D-printed PCL scaffolds. We comprehensively evaluated the mechanical properties, thermal characteristics, and osteoblast biocompatibility using tensile testing, differential scanning calorimetry, and SaOS-2 cell culture assays (MTT test, activity of alkaline phosphatase, production of collagen I and fluorescent staining with acridine orange or phalloidin). ZnO modification significantly enhanced the mechanical properties (834% strain at break versus 658% for pure PCL and an increased Young's modulus), as well as supporting cell viability (87 and 85%). Meanwhile, CaPNPs demonstrated the highest level of early-stage cell viability (103% after 24 h), although this was not statistically significant. All additives exhibited non-cytotoxic profiles with >80% cell viability and demonstrated time-dependent increases in alkaline phosphatase activity, but further evaluation for clinical application is essential. These findings provide evidence-based guidance for selecting PCL scaffold additives based on specific application requirements: ZnO is optimal for mechanically demanding applications, while CaPNPs could be optimal for facilitating rapid cell integration.