Femtosecond lasers are improving fabrication of tissue scaffolds and implants without needing nonbiocompatible photoinitiators or chemical cross-linking materials typically used in 3D printing. Direct micropatterning leveraging multiphoton absorption (MPA) of ultrafast laser light has been demonstrated by Tufts University (Medford, MA) researchers within an elastomeric silk fibroin hydrogel formula that is transparent to visible light, allows initiation of MPA at low powers (a few nanojoules) without self-focusing, is biocompatible and biodegradable, and allows laser light to create 10- to 400-μm-diameter voids (with a 5 μm lateral resolution) over a large 3D volume in the hydrogel through penetration depths up to 1 cm—1.5 orders of magnitude deeper than other biocompatible materials.
To fabricate complex features or voids within the hydrogel that function as tissue scaffolds for cell growth, the < 2 nJ output of an 810 nm, 80 MHz repetition-rate, 100 fs pulse-width femtosecond laser was input to a microscope objective and focused into the silk hydrogel fixed to a three-axis translation stage. Test patterns such as a 200-μm-diameter, two-turn helix and a blood-vessel-like branching structure beginning 300 μm deep and extending 100 μm in length were easily fabricated (in volumes up to 100 cm3) by scanning the stage at speeds between 50 and 100 μm/s. Typical fabrication time for the helix or vessel structure is around 1 hr., depending on the shape/size of object. Reference: M. B. Applegate et al., Proc. Nat. Acad. Sci., 112, 39, 12052–12057 (Sept. 29, 2015).