Fig. 2

Methods for preparing synthetic polymer scaffolds. 1D/2D Scaffolds a. In photolithography b a substrate is covered with a light-sensitive organic material termed a positive or negative photoresist. The photoresist is then exposed to a specific pattern of intense UV radiation. With positive photoresist, UV light causes the exposed photoresist to become soluble, allowing removal with solutions known as developers. For a negative photoresist, UV light causes the exposed regions to become insoluble, and the shielded photoresist is removed with developers. The remaining photoresist is removed by etching to create the desired scaffold. In soft lithography c a pattern master and a stamp pattern the substrate. Masters are commonly produced using photolithography, or through electron beam lithography if greater resolution is desired. The masters are used to form the stamps, often using an elastomeric polymer. The stamp is then pressed into a solution to create the desired pattern on the substrate. In nanoimprint lithography d a silicon stamp (of the inverse pattern) is used to imprint a pattern into the desired substrate at a specific temperature and pressure. The mold is then removed leaving the model fiber system on the desired substrate. In microphotopatterning e a thin hydrogel is spin-coated onto a prepared glass-bottom dish. The hydrogel is ablated using a multiphoton microscope in prescribed regions of interest created using microscope-specific imaging software. Next, the ablated regions are functionalized using ECM proteins, commonly fibronectin, to allow cell adhesion to the patterns. 3D Scaffolds f. In electrospinning g a positively charged polymer solution is extruded through an orifice, where it forms a jet. The jet elongates toward a grounded collector, the solvent evaporates, and polymer fibers are drawn out towards the collector. In melt electrospinning writing h, the polymer is melted rather than in solution. The melted polymer is extruded through a high-voltage electric field toward a grounded, motorized stage to collect the scaffold. In meltblowing i a melted polymer is extruded through die heads known as spinnerets, where hot air jets attenuate the polymer melt into fibers that form a sheet of fabric as they cool and crystalize