Bimodal Plasmonic Devices Reveal Extensive Collagen Deposition in Mesenchymal Stem Cells Cultured on 3D Self‐Assembled Peptide Scaffolds via a Birefringence‐Induced Colorimetric Response

Tissue engineering holds promise for the treatment of osteoarthritis (OA), where protective hydrogel scaffolds have been combined with mesenchymal stem cells (MSCs) to promote chondrogenesis. Quantification of chondrogenesis by MSCs in 3D culture requires the imaging and detection of deposited extracellular matrix (ECM) components like collagen and proteoglycans. ECM protein quantification should be performed in a non-destructive, label-free, and simple manner. Here, we demonstrate a nanoplasmonic colorimetric device for the imaging of collagen requiring only a simple optical microscope. MSCs were encapsulated in the hydrogel-forming peptide Fmoc-diphenylalanine (Fmoc-FF) with arginine glycine aspartic acid (RGD) added. We showed, by colorimetric histology, that increased concentrations of RGD resulted in a significant increase in collagen deposition after 21 days. Traditional techniques such as immunohistological staining were not able to detect any RGD dependent increases in ECM deposition. Through an in-depth biophysical analysis we were able to correlate elevated RGD with enhanced cell-viability, collagen deposition, and reduced hydrogel stability. In summary, plasmon-enhanced colorimetric histology provides a non-destructive, label-free means to image collagen without resorting to destructive sample processing and complex immunohistological staining. This approach holds broad potential for routine quantification of collagen-rich biomaterials, promising widespread applications across research and clinical settings.