The ratios of EDC and NHS to BSA-FITC were assessed at 25:75, 50:50, and 75:25, as shown in Figure and. Amongst all three conditions, when EDC/NHS was less than BSA-FITC, at a ratio of 25:75, the SNRs were significantly reduced across all dry times. This was expected, as less EDC/NHS to BSA-FITC resulted in overall reduced covalent crosslinking. The majority of the BSA-FITC were subsequently printed solely with physical immobilization through force application, and not all the BSA-FITC proteins were covalently crosslinked, making the cross-linking non-uniform. When EDC/NHS levels were higher than BSA-FITC levels in the bioink ratio 75:25, initial SNRs after 1min airdrying were the highest among the three conditions, but then significantly reduced when airdrying time increased. This is because EDC/NHS is highly reactive, and as such, having higher levels of EDC/NHS caused either protein aggregation or salt formation, when left to airdry longer than 1min. This is further shown in pockets with high fluorescent intensities within each square at the longer airdrying times, indicative of the formation of circular aggregates (Figure ). As highlighted in the FMEA, protein aggregation and salt formation from EDC/NHS reactivity are challenging to control. These issues lead to inconsistent fluorescence images, contributing to the high-risk RPN for the bioink formulation step of μCP. The %CVs for all conditions remained above 10% for inter-assay measurements, indicating nonrepeatable and non-reproducible signals, which are unsuitable for industry applications (Table ).