Two-photon imaging of collagen remodeling in RAFT tissue cultures

Tissue remodeling is associated with both normal and abnormal processes including wound healing, fibrosis and cancer. In skin, abnormal remodeling causes permanent structural changes that can lead to hypertropic scarring and keloid formation. Normal remodeling, although fast and efficient in skin, is still imperfect, and a connective tissue scar remains at the wound site(1). As a result, methods are needed to optimize tissue remodeling in vivo in all cases of wound repair. Since fibroblast-mediated contraction of engineered 3-D collagen based tissues (RAFTs) represents an in vitro model of the tissue contraction and collagen remodeling that occurs in vivo(2), RAFT tissue contraction studies combined with two-photon microscopy (TPM) studies are used to provide information on ways to improve tissue remodeling in vivo. In the RAFT models discussed here, tissue contraction is modulated either by application of exogenous growth factors or photodynamic therapy. During tissue contraction, TPM is used to image changes in Collagen Type I fibers in the RAFT skin models. Tissues are imaged at depth at day 15 after modulation. TPM signal analysis shows that RAFT tissues having the highest collagen density have the fastest rate of decay of fluorescent signal with depth.