Biomineralized Hydrogel with Enhanced Toughness by Chemical Bonding of Alkaline Phosphatase and Vinylphosphonic Acid in Collagen Framework

Alkaline phosphatase (ALP) and phosphoprotein participation in collagen mineralization is one of the most important physiological processes of bone formation. Simulating the natural mineralization process with the involvement of ALP and phosphoproteins is a powerful tool for the preparation of bone repair scaffolds. Searching for compatible approaches to chemically bond ALP with collagen molecules and introducing phosphoprotein-like molecules into a collagen network is the challenge of the day. Here, we synthesized alkaline phosphatase methacrylamide (ALP-MA) via amidation reaction to enable ALP to be grafted uniformly into the photo-cross-linking collagen gel, achieving homogeneous enzymatic mineralization. Furthermore, vinylphosphonic acid (VAP), a phosphoprotein-like molecule containing phosphonate groups, was successfully introduced on collagen molecules through photo-cross-linking, playing the role of a phosphoprotein for inducing mineralized CaP clusters deposited on the collagen backbone. Hence, a hydrogel termed CAV was synthesized via photochemical reaction among collagen methacrylamide (Col-MA), ALP-MA, and VAP (active mineral bonding site) for in situ mineralization. We found that the binding between the collagen network and CaP clusters would lead to the generation of mechanically enhanced mineralized collagen hydrogel. Encapsulated bone marrow stromal cells (BMSCs) exhibited good growth and proliferation in the in situ enzymatic mineralization process. Additionally, the simulated mineralization system is highly favorable for micropatterned structure construction and 3D bioprinting. In brief, we designed a novel approach to effectively simulate the physiological mineralization process of bone formation. The approach, incorporating great photo-cross-linking performance and enzymatic mineralization activity, was beneficial for in situ cell encapsulation and excellent cell-compatible 3D printing, holding great promise for bone tissue engineering research.