Design and 3D Printing of Hydrogel Scaffolds with Fractal Geometries

Structures that exhibit fractal geometries are typically self-similar and iterative. Fractal patterns appear in nature as approximations of mathematical abstractions, yet exist as artifacts of specific processes having reached optimized conditions in the presence of various forces and movements. In this paper, we focus on 3D printing of fractal geometry using computer designed and user adjusted patterns. Various biocompatible hydrogel structures were printed from a photopolymerizable poly(ethylene glycol) diacrylate via maskless stereolithography. This digital micromirror device based projection printing platform is capable of imbuing fractal topographic patterns into a more cell accommodating medium. Several fractal structures were printed mimicking the energy and material pattern optimization achieved by fractal geometries found in nature. The resulting structures were confirmed with bright-field and SEM microscopy. Complex geometries were obtained at many angles, and various heights that exhibited self-similar geometries. The surfaces of the hydrogel structures were conjugated with fibronectin cell adhesion protein and then seeded with cells. Fluorescent staining of actin and nuclei for both murine myoblast cells and human mesenchymal stem cells were conducted to determine the feasibility of these designed cell adhesive topographies to influence aggregate cells. This flexible and versatile platform can be extended to fabricate other complex biomimetic designs for biological applications, such as tissue engineering.