Tissue-engineered constructs of human oral mucosa examined by Raman spectroscopy

A noninvasive quality monitoring of tissue-engineered constructs is a required component of any successful tissue-engineering technique. During a 2-week production period, ex vivo produced oral mucosa-equivalent constructs (EVPOMEs) may encounter adverse culturing conditions that might compromise their quality and render them ineffective. We demonstrate the application of near-infrared Raman spectroscopy to in vitro monitoring of EVPOMEs during their manufacturing process, with the ultimate goal of applying this technology in situ to monitor the grafted EVPOMEs. We identify Raman spectroscopic failure indicators for less-than optimal EVPOMEs that are stressed by higher temperature and exposure to higher than normal concentration of calcium ions. Raman spectra of EVPOMEs exposed to thermal and calcium stress showed correlation of the band height ratio of CH(2) deformation to phenylalanine ring breathing modes, providing a Raman metric to distinguish between viable and nonviable constructs. We compared these results to histology and glucose consumption measurements, demonstrating that Raman spectroscopy is more sensitive and specific to changes in proteins' secondary structure not visible by H&E histology. We also exposed the EVPOMEs to rapamycin, a cell growth inhibitor and cell proliferation capacity preserver, and distinguished between EVPOMEs pretreated with 2 nM rapamycin and controls, using the ratio of the Amide III envelope to the phenylalanine band as an indicator.