Less is more: innovative cationic initiators effective in visible light for 3D printing

Herein, we present completely new structures of photoinitiators - iodonium salts of biphenyl derivatives. The structures of the compounds were designed to, the absorbance of the initiators matched the characteristics of the emission spectra of 3D printers and at the same time to ensure that the absorbance characteristics did not generate the intensive color of the compounds (less is more). Spectroscopic and cytotoxicity studies were also conducted. Their potential to initiate cationic and radical photopolymerization was tested using Real-Time FT-IR method. These initiators have been proven to efficiently initiate cationic and radical photopolymerisation processes using UV or Vis-LEDs. This makes the specially developed compositions with these initiators suitable for dental applications, for the preparation of dental composites. A cytotoxicity test of the developed cured compositions was carried out using 3 cell lines: CHO, FB1, FB2. The data obtained show that the compositions have low toxicity and all meet the requirements suggested for biological/dental applications in the ISO 10993-5 regulations to have a cell viability of not <70%. In addition, the same compositions are suitable for photo-curable 3D printing. Moreover, the biphenyl derivatives efficiently initiate the cationic photopolymerisation of the vinyl monomer and are suitable for obtaining prints with good resolution (which is impossible for the commercially available SpeedCure 938 initiator). Finally, hardness and elasticity at microscale of the developed compositions and composites with the biphenyl derivative initiator were carried out. It was shown that the efficiency of the curing has an effect on the hardness and elasticity values achieved. • New iodonium salts efficiently initiate photopolymerization in visible light. • Developed initiators are less toxic than the commercial SpeedCure 938. • Compositions with new initiators are suitable for 3D printing and dentistry. • Initiators enable high-resolution 3D prints with improved performance. • Mechanical properties of composites depend on curing efficiency.