On the Processability and Antibacterial Activity of Silver Nitrate Nanocomposites Manufactured by Stereolithography

This study investigates the level of multifunctionality that might be achieved with the implementation of silver nitrate (AgNO₃) to UV-curable resins during stereolithography. To achieve that it sets improved mechanical response and antibacterial activity of the additively manufactured nanocomposites as two objectives to be achieved without disturbing the printing quality. The resins containing 0.1, 0.3, 0.5, 1, 3, and 5 wt % AgNO₃ were mixed via high shear mixing under 6000 rpm. A desktop-scale SLA machine and a postcure UV device were employed for the manufacturing of nanocomposite specimens. The level of printing quality was evaluated by SEM analysis focusing on the layer-by-layer printing marks that were highly disturbed after 1 wt % particle loading. Potential chemical effects causing this disappearance were investigated with UV-visible spectroscopy and FTIR analysis. Results suggested that some of the provided UV energy was used for the conversion of silver cations of silver nitrate to AgNPs during the polymerization reaction. Such a reduction reaction was found to decrease the degree of monomer conversion with increasing particle amount, which was confirmed by the FTIR analyses. Results of mechanical tests assisted by a detailed fractographic analysis also confirmed that 1 wt % was a particle agglomeration threshold above which the mechanical response was highly deteriorated. The maximum mechanical performance with a 20% improvement in elastic modulus and yield strength values was noted for 0.5 wt % case. The antibacterial activity tests were then performed on 0.3, 0.5, and 1 wt % samples according to ISO 22196. The results suggested that antibacterial activity was maximum for 1 wt % particle containing nanocomposites. Hence, the aim of a stronger, antibacterial yet adaptable nanocomposite material design was achieved at 0.5 wt % silver nitrate loading.