Figure 3 ∣. Hollow fibers (HFs) and lab-on-a-chip.

(a) Image (i) and schematic (ii) of the collagen gel HF microfluidic device. (iii) Human kidney-2 cell-laden collagen HF with Ca-alginate core having a diameter of 100 μm (left) and HF having an inner diameter of 50 μm (right) after 10 days of culture. Confocal images of renal tubules in HF are shown at the bottom, which depicts renal tubules with a cross-sectional view (bar = 50 μm) (lower left); 3D reconstructed confocal image (bar = 50 μm) (upper right); and magnified view showing the cell-cell connection (bar = 20 μm) (lower right). Reproduced with permission from Shen C, Zhang G, Wang Q, Meng Q. Fabrication of collagen gel hollow fibers by covalent cross-linking for construction of bioengineering renal tubules. ACS Appl Mater Interf. 2015;7:19789.²⁸ (b) Combining polyethersulfone-polyvinyl pyrrolidone HF and lab-on-a-chip technology. Human proximal tubular epithelial cells are cultured on the coarse inner surface of hollow fibers coated with fibrin that is embedded in a polydimethylsiloxane-glass chamber. (i) Image and (ii) schematic of the lab-on-a-chip HF bioreactor. (iii) Setup for inulin recovery perfusion studies, (iv) normal perfusion culture, and (v) static configuration for urea, creatinine, and glucose transport studies. ECS, extracapillary space surrounding the hollow fibers; ICS, intracapillary of the hollow fibers; PDMA, poly(N,N-dimethylacrylamide); RPTEC, renal proximal tubule epithelial cells. (c) Immunofluorescence and electron microscopic images of the cell-laden HF: (i) transverse section and (ii) cross-section (bar = 500 μm). Close-up views of the (iii) cross-section and (iv) transverse section (confocal image) revealing a cell monolayer in the HF (bar = 100 μm). (v) Scanning electron microscopic image of the cell-laden HF (bar = 200 μm), with (vi) the magnified view showing microvilli expression on the cell surface (bar = 5 μm). (b,c) Reproduced with permission from Ng CP, Zhuang Y, Lin AWH, Teo JCM. A fibrin-based tissue-engineered renal proximal tubule for bioartificial kidney devices: development, characterization and in vitro transport study. Int J Tissue Eng. 2013; article ID 319476.⁴¹ To optimize viewing of this image, please see the online version of this article at http://www.kidney-international.org.