Clickable Human Protein-Based Hydrogels for Biomedical Applications

Hydrogels form a class of biomaterials of particular interest to regenerative medicine because of their ability to mimic the extracellular environment in vivo, with the delivery of mechanical support, enhanced permeability to nutrients, and adjustable physicochemical properties. Among the various strategies that have been developed in recent years, human-derived bioactive constituents enable the creation of biocompatible materials free of the immunogenic risk associated with the use of animal-derived additives. In particular, platelet derivatives such as platelet lysate (PL) are a concentrated reservoir of growth factors, cytokines, and bioactive proteins that are commonly recognized to cause cell proliferation, migration, and differentiation. Compared to more traditional platelet-rich plasma (PRP), PL is safer and more standardized because of its cell-free nature and ease of administration in clinical and engineering contexts. In this work, a new fully human hydrogel platform was built based on the combination of HA functionalized with norbornene and PL functionalized with tetrazine. The approach uses the inverse electron demand Diels–Alder (IEDDA) click reaction, which enables the rapid formation of covalent bonds under mild and cytocompatible conditions without the use of photopolymerization and cytotoxic reagents. After the synthesis and purification of both precursors (HA–Nor and PL–Tz), various hydrogel formulations were prepared and characterized for their morphology, mechanical properties through rheological test and physicochemical properties. The results indicated rapid gelation and demonstrated that the appropriate ratios of HA–Nor and PL–Tz concentrations yield stable and controllable hydrogels with a porous microstructure well suited for tissue engineering applications. Rheological experiments showed that the injectable hydrogels exhibited shear-thinning behaviour, and the viscoelastic measurements demonstrated that the elastic moduli increased with precursor concentration. Swelling and degradation experiments using hyaluronidase highlighted the high water uptake ability and the ability to degrade under physiological concentrations of hyaluronidase. Furthermore, protein release kinetics revealed an initial burst followed by extended release, which signaled the potential of the system as a drug delivery vehicle for bioactive agents. In addition, preliminary tests demonstrated the feasibility of 3D printing with the developed formulations, confirming good print fidelity within a support bath. However, challenges remain, particularly the limited stability of the constructs once removed from the bath and the occasional presence of trapped air bubbles, both of which highlight the need for further optimization. Globally, the hydrogel system created through this thesis also emerges as a prospective biomimetic platform for regenerative medicine. The fact that the material is composed solely of human-derived constituents, coupled with the lack of photoinitiators in crosslinking, demonstrates biocompatibility and translatability. These findings provide an opening for further proof-of-concept in vitro and in vivo validated studies for the design of patient-specific scaffolds for healing, regeneration, and therapeutic delivery in multiple areas of regenerative medicine.