Spectrophotometric determination of LAP photoinitiator radicalization in ophthalmic applications

The incidence of lamellar corneal transplantations is increasing. While a human donor cornea could potentially be used for up to two recipients, one anterior and one posterior part, it does not change the disparity between available donor grafts and patients needing corneal transplants. Additionally, donor grafts carry the risk of graft rejection due to foreign cellular material and disease transmission. We have investigated acellular synthetic graft materials to eliminate these drawbacks using hydrogel materials and the extrusion bioprinting process. To create these materials with higher moduli, the photocrosslinking process has advantages but needs an appropriate crosslinker material. We have shown that we can determine the presence of the non-radicalized crosslinker lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP) with spectrophotometric methods, using the crosslinker absorbance characteristics. To show non radicalized LAP the measurement is done at 372 nm, and the measured absorbance level depends on the LAP concentration. This allows for a simple evaluation of crosslinked hydrogels to determine any remaining non radicalized LAP and with that potential cytotoxic or other effects of this crosslinking material to correct this situation if necessary.