Despite the unique advantages of optical microscopy for molecular specific high resolution imaging of living structure in both space and time, current applications are mostly limited to research settings. This is due to the aberrations and multiple scattering that is induced by the inhomogeneous refractive boundaries that are inherent to biological systems. However, recent developments in adaptive optics and wavefront shaping have shown that high resolution optical imaging is not fundamentally limited only to the observation of single cells, but can be significantly enhanced to realize deep tissue imaging. To provide insight into how these two closely related fields can expand the limits of bio imaging, we review the recent progresses in their performance and applicable range of studies as well as potential future research directions to push the limits of deep tissue imaging.

Wavefront shaping holds great potential for high-resolution imaging or light delivery either through or deep inside living tissue. However, one of the biggest barriers that must be overcome to unleash the full potential of wavefront shaping for practical biomedical applications is the fact that wavefront shaping, especially based on iterative feedback, requires lengthy measurements to obtain useful correction of the output wavefront. As biological tissues are inherently dynamic, the short decorrelation time sets a limit on the achievable wavefront shaping enhancement. Here we show that for wavefront shaping in thin anisotropic scattering media such as biological tissues, we can optimize the wavefront shaping quality by simply limiting the numerical aperture (NA) of the incident wavefront. Using the same number of controlled modes, and therefore the same wavefront measurement time, we demonstrate that the wavefront shaped focus peak to background ratio can be increased by a factor of 2.1 while the energy delivery throughput can be increased by a factor of 8.9 through 710 µm thick brain tissue by just limiting the incident NA.

The properties of a semipermeable porous membrane, including pore size, pore density, and thickness, play a crucial role in creating a tissue interface in a microphysiological system (MPS) because it dictates multicellular interactions between different compartments. The small pore-sized membrane has been preferentially used in an MPS for stable cell adhesion and the formation of tissue barriers on the membrane. However, it limited the applicability of the MPS because of the hindered cell transmigration via sparse through-holes and the optical translucence caused by light scattering through pores. Thus, there remain unmet challenges to construct a compartmentalized MPS without those drawbacks. Here we report a submicrometer-thickness (∼500 nm) fibrous extracellular matrix (ECM) film selectively condensed on a large pore-sized track-etched (TE) membrane (10 µm-pores) in an MPS device, which enables the generation of functional tissue barriers simultaneously achieving optical transparency, intercellular interactions, and transmigration of cells across the membrane. The condensed ECM fibers uniformly covering the surface and 10 µm-pores of the TE membrane permitted sufficient surface areas where a monolayer of the human induced pluripotent stem cell-derived brain endothelial cells is formed in the MPS device. The functional maturation of the blood–brain barrier (BBB) was proficiently achieved due to astrocytic endfeet sheathing the brain endothelial cells through 10 µm pores of the condensed-ECM-coated TE (cECMTE) membrane. We also demonstrated the extravasation of human metastatic breast tumor cells through the human BBB on the cECMTE membrane. Thus, the cECMTE membrane integrated with an MPS can be used as a versatile platform for studying various intercellular communications and migration, mimicking the physiological barriers of an organ compartment.

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