Biomechanical characterization of a fibrinogen-blood hydrogel for human dental pulp regeneration

In dental practice, Regenerative Endodontic Treatment (RET) is applied as an alternative to classical endodontic treatments of immature necrotic teeth. This procedure, also known as dental pulp revitalization, relies on the formation of a blood clot inside the root canal leading to the formation of a reparative vascularized tissue similar to dental pulp, which would provide vitality to the affected tooth. Despite the benefit of this technique, it lacks reproducibility due to the fast degradation and poor mechanical properties of blood clots. This work presents a method for constructing a fibrinogen-blood hydrogel that mimics the viscoelastic properties of human dental pulp while preserving the biological properties of blood for application in RET. By varying the blood and fibrinogen concentrations, gels with different biomechanical and biological properties were obtained. Rheology and atomic force microscopy (AFM) were combined to study the viscoelastic properties. AFM was used to evaluate the elasticity of human dental pulp. The degradation and swelling rates were assessed by measuring weight changes. The biomimetic properties of the gels were demonstrated by studying the cell survival and proliferation of dental pulp cells (DPCs) for 14 days. The formation of an extracellular matrix (ECM) was assessed by multiphoton microscopy (MPM). The angiogenic potential was evaluated by an ex vivo aortic ring assay, in which the endothelial cells were observed by histological staining after migration. The results show that the Fbg-blood gel prepared with 9 mg ml^-1 fibrinogen and 50% blood of the Fbg solution volume has similar elasticity to human dental pulp and adequate degradation and swelling rates. It also allows cell survival and ECM secretion and enhances endothelial cell migration and formation of neovessel-like structures.