Extra-cellular Matrix-based Hydrogels for Personalized Guided Bone Regeneration

Objectives: Extra-cellular matrix-based tissue engineering scaffolds are currently of greater interest due to the existence of tunable platforms that create tailored properties to match a specific tissue or a disease state. We have created a toolbox of the collagen-elastin-like polypeptide (ELP) and collagen-ELP-Bioglass hydrogels that can have tunable properties (dependent on composition, pH, and temperature) usable for specific tissue microenvironment. Here, we are showing composition-dependent tunability of hydrogels to have different mechanical properties, aiding in vitro and in vivo bone regeneration. Methods: Varying concentrations of rat-tail collagen I (Corning), ELP (made in-house from recombinant E. coli) and 45S5 Bioglass (Mo-Sci) were used to make hydrogels for maximizing mechanical properties, and determining optimal composition using response surface methodology (RSM). Physical characteristics (swelling behavior, morphology, and chemical interactions) and in vitro osteogenic differentiation of mesenchymal stem cells (MSCs) for the composite hydrogels were characterized. In vivo subcutaneous biocompatibility, degradation, and regeneration in critical-sized cranial defect were tested in Sprague Dawley rats using the composite hydrogels loaded with or without MSCs. Results: Mechanical properties varied depending on composition. RSM provided a toolbox to optimize a range of tensile and compressive mechanical properties. An optimal composition (6mg/mL collagen+18mg/mL ELP+ 6.6mg/mL Bioglass) with maximized compressive properties was less hydrophilic, porous with rough nano-fibrous morphology, and showed physical and chemical interactions within the components. In vitro testing showed greater cell attachment, spreading, differentiation, and mineralization. The optimized composite hydrogel with or without MSCs showed no localized or systemic toxicity and was present in vivo at the implantation site (subcutaneous and cranial) up to three weeks. MSC-loaded composite hydrogel showed better quality and quantity of newly formed bone in vivo after eight weeks. Conclusions: Our results show smart collagen-ELP-Bioglass hydrogels possess optimal mechanical, physical, and degradation characteristics to support in vitro and in vivo bone regeneration for non-load bearing applications.