Essentially, they examined the type of spider silk found in spider webs, noted the periodic bulges in it, and created a print head that could produce corrugated ABS filaments.

As far as I could tell from the article, they haven't yet done anything with the corrugated ABS filaments other than string them up around the room where they exhibit the robotic printer/extruder. I imagine the next step is to perform tensile strength tests and flexing strength tests against an ABS monofilament with a round cross section of equal area to the corrugated multifilament.