IN2SIGHT: a microstructured window for label-free non-linear imaging in vivo.

Tissue histopathology, reliant on costly and time-consuming hematoxylin and eosin (H&E) staining of thin tissue slices, faces limitations. Label-free non-linear optical microscopy in vivo presents a solution, allowing work on fresh samples. Implantable microstructures prove effective for systematic longitudinal in vivo studies of immunological responses to biomaterials using label-free non-linear optical microscopy. Employing two-photon laser polymerization, we implanted a matrix of 3D lattices in the chorioallantoic membrane of chicken embryos, establishing a 3D reference frame for cell counting. H&E analysis is compared to label-free in vivo non-linear excitation imaging for cell quantification and identifying granulocytes, collagen, and microvessels. Preliminary results in higher animal models demonstrate the transformative potential of this approach, offering an alternative to conventional histopathology for validating biomaterials in in vivo longitudinal studies.