The use of stereo lithography (SL) for fabricating complex three-dimensional (3D) tissue engineered scaffolds of aqueous poly(ethylene glycol) (PEG) hydrogel solutions is described. The primary polymer used in the study was PEG-dimethacrylate (PEG-dma) with an average molecular weight (M_W) of 1000 in distilled water with the photoinitiator Irgacure 2959 (I-2959). Successful layered manufacturing (LM) with embedded channel architecture required investigation of the photopolymerization characteristics of the PEG solution (measured as hydrogel thickness or cure depth) as a function of photoinitiator concentration and laser energy dosage for a specific photoinitiator type and polymer concentration in solution. Hydrogel thickness was a strong function of PI concentration and energy dosage. Curves of hydrogel thickness were utilized to successfully plan, perform, and demonstrate layered manufacturing of highly complex hydrogel scaffold structures, including structures with internal channels of various orientations. Successful fabrication of 3D, multi-layered bioactive PEG scaffolds containing cells was accomplished using a slightly modified commercial SL system (with 325 nm wavelength laser) and procedure. Human dermal fibroblast (HDF) cells were encapsulated in PEG hydrogels using small concentrations (～5 mg/ml) of acryloyl-PEG-RGDS (M_W 3400) added to the photopolymerizable PEG solution to promote cell attachment. HDF cells were combined with the PEG solution, photocrosslinked using SL, and successfully shown to survive the fabrication process. The combined use of SL and photocrosslinkable biomaterials such as PEG makes it possible to fabricate complex 3D scaffolds that provide site-specific and tailored mechanical properties (i.e., multiple polymer materials) with a polymer matrix that allows transport of nutrients and waste at the macroscale and facilitates cellular processes at the microscale through precisely placed bioactive agents.
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