Mueller matrix analysis of a biologically sourced engineered tissue construct as polarimetric phantom.

Significance: The polarimetric properties of biological tissues are often difficult to ascertain independent of their complex structural and organizational features. Conventional polarimetric tissue phantoms have well-characterized optical properties but are overly simplified. We demonstrate that an innovative, biologically sourced, engineered tissue construct better recapitulates the desired structural and polarimetric properties of native collagenous tissues, with the added benefit of potential tunability of the polarimetric response. We bridge the gap between non-biological polarimetric phantoms and native tissues.

Aim: We aim to evaluate a synthesized tissue construct for its effectiveness as a phantom that mimics the polarimetric properties in typical collagenous tissues.

Approach: We use a fibroblast-derived, ring-shaped engineered tissue construct as an innovative tissue phantom for polarimetric imaging. We perform polarimetry measurements and subsequent analysis using the Mueller matrix decomposition and Mueller matrix transformation methods. Scalar polarimetric parameters of the engineered tissue are analyzed at different time points for both a control group and for those treated with the transforming growth factor $\left(\mathrm{TGF}\right)\text{-}\beta 1$ . Second-harmonic generation (SHG) imaging and three-dimensional collagen fiber organization analysis are also applied.

Results: We identify linear retardance and circular depolarization as the parameters that are most sensitive to the tissue culture time and the addition of $\mathrm{TGF}\text{-}\beta 1$ . Aside from a statistically significant increase over time, the behavior of linear retardance and circular depolarization indicates that the addition of $\mathrm{TGF}\text{-}\beta 1$ accelerates the growth of the engineered tissue, which is consistent with expectations. We also find through SHG images that collagen fiber organization becomes more aligned over time but is not susceptible to the addition of $\mathrm{TGF}\text{-}\beta 1$ .

Conclusions: The engineered tissue construct exhibits changes in polarimetric properties, especially linear retardance and circular depolarization, over culture time and under $\mathrm{TGF}\text{-}\beta 1$ treatments. This tissue construct has the potential to act as a controlled modular optical phantom for polarimetric-based methods.