Synthesis of PEG-Laminin Hydrogels

PEG-LM hydrogels were synthesized as previously described in refs. 52 (link) and 53 (link). Briefly, full-length LM111 (Trevigen, Gaithersburg, MD, USA) was conjugated with acrylate-PEG-hydroxysuccinimide (10 kDa; Creative PEGWorks, Chapel Hill, NC, USA) to produce a PEGylated-LM solution. PEG-LM was dialyzed against PBS to remove any unreacted acrylate-PEG-hydroxysuccinimide, and the final LM concentration in the resulting PEG-LM conjugate precursor solution was determined via absorbance reading at 280 nm. Hydrogels were synthesized by combining 500 μg/ml PEG-LM precursor solution with varying amounts of 8-arm PEG acrylate (20 kDa; Creative PEGWorks) in chamber slides (Millicell EZ Slide; MilliporeSigma, Burlington, MA, USA) and polymerized in the presence of a photoinitiator (0.1% w/v; Irgacure 2959; BASF, Ludwigshafen, Germany) upon UV exposure (3–4 mW × cm⁻²). Hydrogels were produced at either 4% (w/v; soft 0.3 kPa) or 20% (stiff, 20 kPa; Fig. 1C, D).