Hydrogels obtained from the chemical or physical association of macromolecules are an important area of material science, due to the wide array of design possibilities and countless biomedical applications, for instance as skin substitutes, adhesives, or drug delivery matrices. Through a careful choice of the macromolecules, the molecular associations that maintain the hydrogel 3D network can be selected and tuned. For medical applications, the requirements are more restrictive; particular attention has to be paid to biocompatibility and biodegradability. Thus, biopolymers, inherently more suited for medical applications than their synthetic counterparts, have become a great focus of interest. However, due to their physical and chemical complexity, the properties of natural polymers remain poorly understood. 

We report on hydrogels made from gelatin, in the presence and absence of chitosan, and cross-linked by the enzyme microbial transglutaminase (mTGase). This chemical gelation process was also used in combination with physical gelation, which results from the single-strand to triple-helix transition of gelatin occurring above gelation temperature. An array of techniques – rheology, small-angle neutron scattering, optical rotation and molecular dynamics – was employed to connect the bulk properties to the nanoscale morphology of the gels. The study provides new insight into the synergism between mixed gelation processes in hybrid gels and their impact on cell behaviour.

The systems reported here, based on a sustainable material and an enzymatic cross-linking process, are attractive for biomedical applications, in particular tissue engineering. The type of multi-disciplinary approach proposed here, where the architecture of the gels on the nanoscale, their mechanical behaviour on the macroscale and their biological performance for cell regeneration are examined and correlated, is paramount to achieve a comprehensive understanding of networks properties and rationalise the design of hydrogels with controlled functional properties.

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