Development of a novel bioengineered tissue model and its application in the investigation of the depth selectivity of polarization-gating

Recently, there has been significant interest in using polarization gating to selectively probe superficial tissue to facilitate the diagnosis of epithelial neoplasia. Thus, understanding the propagation of polarized light in tissue in general and the mechanisms of polarization gating in particular are crucial for biomedical optics applications. However, these investigations have been impeded in part by the lack of realistic tissue models that can replicate both the morphological complexity and the optical properties of biological tissue. Here we report the development of a novel bioengineered connective tissue model to study light transport in tissue. This tissue model was fabricated by combination of scaffolding and crosslinking techniques. It demonstrates great similarity to real connective tissue in its optical properties and microarchitecture. Moreover, the physical and optical properties of the model can be reproducibly controlled. As an example, we demonstrated the application of this tissue model in our investigation of the depth sensitivity of polarization-gating. Specifically, we studied the effects of epithelium and connective tissue on the penetration depth of differential polarization signals. Our results indicate that the penetration depth in both epithelial and connective tissues primarily depends on the optical thickness of the tissue: the polarization gated signal probes the superficial layer of tissue up to the optical depth of ∼ 2. The corresponding physical penetration depth depends on the specific tissue type and in the connective tissue is about 6-7 times shorter than in the epithelium (∼ 40-50 microns and ∼ 200 - 300 microns, respectively).