We developed microfluidic-based pure chitosan microfibers (∼1 meter long, 70–150 μm diameter) for liver tissue engineering applications. Despite the potential of the chitosan for creating bio-artificial liver chips, its major limitation is the inability to fabricate pure chitosan-based microstructures with controlled shapes because of the mechanical weakness of the pure chitosan. Previous studies have shown that chitosan micro/nanofibers can be fabricated by using chemicals and electrospinning techniques. However, there is no paper regarding pure chitosan-based microfibers in a microfluidic device. This paper suggests a unique method to fabricate pure chitosan microfibers without any chemical additive. We also analyzed the chemical, mechanical, and diffusion properties of pure chitosan microfibers. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectrometry and electron spectroscopy for chemical analysis (ESCA) were used to analyze the chemical composition of the synthesized chitosan microfibers. We measured the mechanical axial-force and diffusion coefficient in pure chitosan-based microfibers using fluorescence recovery after photobleaching (FRAP) techniques. Furthermore, to evaluate the capability of the microfibers for liver tissue formation, hepatoma HepG2 cells were seeded onto the chitosan microfibers. The functionality of these hepatic cells cultured on chitosan microfibers was analyzed by measuring albumin secretion and urea synthesis. Therefore, this pure chitosan-based microfiber chip could be a potentially useful method for liver tissue engineering applications.

Mutations in cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-regulated chloride channel, cause cystic fibrosis. To investigate interactions of CFTR in living cells, we measured the diffusion of quantum dot-labeled CFTR molecules by single particle tracking. In multiple cell lines, including airway epithelia, CFTR diffused little in the plasma membrane, generally not moving beyond 100–200 nm. However, CFTR became mobile over micrometer distances after 1) truncations of the carboxy terminus, which contains a C-terminal PDZ (PSD95/Dlg/ZO-1) binding motif; 2) blocking PDZ binding by C-terminal green fluorescent protein fusion; 3) disrupting CFTR association with actin by expression of a mutant EBP50/NHERF1 lacking its ezrin binding domain; or 4) skeletal disruption by latrunculin. CFTR also became mobile when the cytoskeletal adaptor protein binding capacity was saturated by overexpressing CFTR or its C terminus. Our data demonstrate remarkable and previously unrecognized immobilization of CFTR in the plasma membrane and provide direct evidence that C-terminal coupling to the actin skeleton via EBP50/ezrin is responsible for its immobility.