Abstract
Hydrogels with organized structure have attracted remarkable attentions for bio-related applications. Among the preparation of hierarchical hydrogel materials, fabrication of hydrogel with multi-layers is an important branch. Although the generation mechanism of layers had been fully discussed, sub-layer structure was not sufficiently studied. In this research, multi-layered chitosan hydrogel with oriented structure was constructed, and the formation mechanism of orientation was proposed, based on gelation behavior and entanglement of polymer chains in the hydrogel-solution system. Employing the layered-oriented characteristic, chitosan hydrogel materials with various shapes and structure can be designed and fabricated.
Highlights
Hydrogels with organized structure have attracted remarkable attentions for bio-related applications
The modulation of CS hydrogel structure relies on the exploration of formation mechanisms
It had been proved that this characteristic enabled the formation of multi-layers[4]. This characteristic endowed the system with directivity, which laid the foundation of orientation
Summary
When the organized stacking of CS-rich micro-zones along the OH2 diffusion direction was achieved, orientation would appear in the hydrogel (Fig. 5d) This was in good agreement with the transition concentration between random network and orientation structure. The gel-sol interface did not advance from the primary hydrogel layer to the bottom of mold at a constant speed (Fig. 4), indicating that gelation rate of every unit decreased. When gelation rate further decreased in stage III, original entanglement in the gap relaxed and eliminated restriction of macromolecular motion in the lower unit This indicated the proper diffusion rate of OH2 is essential for orientation. Longer oriented region could be achieved with higher c(NaOH) in coagulation bath which was in good agreement with the mechanism (Supplementary Fig. S2) From another perspective, entanglements of macromolecular chains between two consecutive units become weaker with longer gelation time. Chitosan rod prepared via this hydrogel had been studied as an internal fracture fixation material, which showed good bending strength[34,35,36,37,38]
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