Microfluidic synthesis of a cell adhesive Janus polyurethane microfiberElectronic supplementary information (ESI) available: Supplementary figures S1–S4. See DOI: 10.1039/b901308c.

We present a simple synthetic approach for the preparation of cell attachable Janus polyurethane (PU) microfibers in a microfluidic system. The synthesis was performed by using laminar flows of multiple streams with spontaneous formation of carbon dioxide bubbles resulting in an asymmetrically porous PU microfiber. The fabricated asymmetric microfiber (Janus microfiber) provides two distinctive properties: one is a porous region to promote the cellular adhesion and the other is a nonporous region rendering the mechanical strength of the scaffold. The Janus microfibers show dramatic improvement of cell adhesion, proliferation, and viability over a culture period. Cells cultured on the fibers easily bridged gaps between microfibers by joining together to form a cell sheet. The maximum distance between fibers that fibroblasts bridged is approximately 200 µm over 15 days. The Janus microfiber can be used for not only an alternative 2D cell culture plate but also as a novel 3D scaffold for tissue engineering without any need for elegant surface modification for enhancing cell adhesions. [ABSTRACT FROM AUTHOR]