Figure 9: Description of Double Crosslinking Reaction.

(A) On the left, the ionic interaction between TPP and Chitosan is described; later a crosslinking between Chitosan and HA is created through the TPP, on the right, in the last step the crosslinking between HA and DVS is obtained. (B) Diffusion and formation of double-crosslinked core-shell. Schematical representation of the crosslinking at the interface between the core and shell structure. (C) A schematical explanation of the process by the phase diagram change. Starting by the considerations reported in Fig. 3 about the reactive groups, this representation reports details about the thermodynamic involved in the proposed coacervation process. I- After the preparation of the primary emulsion, disperse phase contains a homogeneous solution. Therefore, the working point represented in the phase diagram is located in the region of complete miscibility between water and Chitosan. II- Solution containing the coacervate is added to the primary emulsion, promoting the dilution of the disperse phase, promoting the supersaturation of the solute in the disperse phase and inducing the precipitation of the chitosan. At the same time keeping constant the temperature, Acetic acid continues to evaporate producing the further shifting of the working point into the miscibility gap. This last step will complete the formation of the chitosan template and the HA coacervation; III- In the final phase, a controlled cooling step is performed to increase the miscibility gap able to promote a faster supersaturation and to enhance the stability of the nanoparticle’s architecture.