Preparing Alginate Hydrogels with BMP-2

RGD-functionalized alginate (FMC BioPolymer) was reconstituted in MEM alpha (Thermo Fisher Scientific) to create a 2% w/v solution, as described previously.^{19 (link)} Recombinant human bone morphogenetic protein 2 (BMP-2, Pfizer Inc.) was reconstituted in a solution of 0.1% rat serum albumin (Sigma–Aldrich) in 4 mM hydrochloric acid and mixed with the alginate solution to yield 2 or 5 μg BMP-2 per 150 μl of final solution. This alginate/BMP-2 solution was gelled with the addition of calcium sulfate (Sigma–Aldrich) at a 1:25 volume ratio. Hydrogels were prepared under sterile conditions inside a laminar flow hood and stored overnight at 4°C before use in surgery the next day.