Self-Assembled Hydrogel Fiber Bundles from Oppositely Charged Polyelectrolytes Mimic Micro-/Nanoscale Hierarchy of Collagen

Fiber bundles are present in many tissues throughout the body. In most cases,
collagen subunits spontaneously self-assemble into a fibrilar structure that
provides ductility to bone and constitutes the basis of muscle contraction.
Translating these natural architectural features into a biomimetic scaffold still
remains a great challenge. Here, a simple strategy is proposed to engineer
biomimetic fiber bundles that replicate the self-assembly and hierarchy of
natural collagen fibers. The electrostatic interaction of methacrylated gellan
gum with a countercharged chitosan polymer leads to the complexation of the
polyelectrolytes. When directed through a polydimethylsiloxane channel, the
polyelectrolytes form a hierarchical fibrous hydrogel demonstrating nanoscale
periodic light/dark bands similar to D-periodic bands in native collagen and
align parallel fibrils at microscale. Importantly, collagen-mimicking hydrogel
fibers exhibit robust mechanical properties (MPa scale) at a single fiber bundle
level and enable encapsulation of cells inside the fibers under cell-friendly mild
conditions. Presence of carboxyl- (in gellan gum) or amino- (in chitosan) functionalities
further enables controlled peptide functionalization such as Arginylglycylaspartic
acid (RGD) for biochemical mimicry (cell adhesion sites) of native
collagen. This biomimetic-aligned fibrous hydrogel system can potentially be
used as a scaffold for tissue engineering as well as a drug/gene delivery vehicle.