Modelling and optimization of NaOH-etched 3-D printed PCL for enhanced cellular attachment and growth with minimal loss of mechanical strength.

Despite having gained success in achieving intricate geometries for bone-graft fabrication, 3D printing technology still lacks good implant-tissue bonding. This can be addressed with alkaline surface post-treatment of 3D printed grafts, which improves the surface morphology and cellular response (attachment and proliferation), as shown in this study of polycaprolactone (PCL). The parameters for process optimization were NaOH-concentration, reaction temperature, and treatment time. Along with the hydrolysis reaction, its morphological implications at micro-level was also studied here for the first time. The modified surface was characterized by measuring surface porosity, surface roughness, and cellular response. A kinetic model was developed to correlate surface porosity with concentration, temperature and time. The concept of treatment intensity is introduced, which is a lumped parameter consisting of the product of the three governing parameters, which shows a concentration-temperature-time equivalency. With the increase in treatment intensity, surface porosity increased to ~60%, the surface roughness (RMS value) increased to ~700 nm, and cellular response improved till surface porosity reaches ~35%. This study establishes the importance of NaOH-PCL interaction and proposes that the surface reaction mechanism studied here can be exploited to enhance the in-vivo performance of bone grafts.