In situ imaging of collagen synthesis by osteoprogenitor cells in microporous bacterial cellulose scaffolds.

Microscopy techniques based on laser-induced nonlinear optical processes allow for chemically specific imaging of unmodified samples at high spatial resolution in three dimensions and provide powerful tools for characterization of tissue-engineering constructs. This is highlighted by the simultaneous imaging of scaffold material, cells, and produced extracellular matrix collagen in samples consisting of osteoprogenitor MC3T3-E1 cells seeded on microporous bacterial cellulose (BC), a potential scaffold material for synthesis of osseous tissue. BC and collagen have been visualized by second harmonic generation (SHG) microscopy, and verification of collagen identification on cellulose scaffolds has been carried out on sectioned samples by comparison with the conventional histological staining technique. Both methods showed similar collagen distributions and a clear increase in the amount of collagen when comparing measurements from two time points during growth. For investigations of intact cellulose scaffolds seeded with cells, SHG was combined with simultaneous coherent anti-Stokes Raman scattering (CARS) microscopy for visualization of cell arrangement in three dimensions and to be correlated with the SHG data. Results showed that the osteoprogenitor cells were able to produce collagen already during the first days of growth. Further on, developed collagen fiber networks could be imaged inside compact regions of cells located in the cellulose micropores. Collagen production, the initial step of tissue mineralization, demonstrates the potential of BC as a scaffold material for bone tissue engineering. Furthermore, the noninvasive in situ monitoring of collagen inside compact tissue clearly manifests the benefits of nonlinear microscopy techniques, such as SHG and CARS, for use in tissue engineering.