Oxygen generating bioinks for 3D printed bone implants

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Abstract Musculoskeletal tissue injuries are a leading cause of disability in the United States (US), yet there are only a few viable options for patients suffering from bone degeneration. One of the major challenges in this field is nonunion formation, which is the permanent failure of bone fracture healing. Current therapies such as bone fixation or bone grafting are often ineffective, painful, invasive, costly, and do not result in recovery of full function. To overcome this grand challenge, much research has been dedicated to the development of engineered three- dimensional (3D) bone tissue, which typically is composed of a biomaterial containing human mesenchymal stem cells (hMSCs) for bone formation and endothelial cells for blood vessel formation. Although these approaches accelerate implant anastomosis, it is inherently still associated with a prevascular phase that causes significant amounts of starvation induced cell death. Here, we propose an innovative solution to solve this important problem. We aim to achieve this by developing an oxygen generating biomaterial that can be used to 3D bioprint a vascularized bone implant for critical bone defect treatments. To this end, we set-out to explore two of our recently developed technologies: oxygen generating biomaterials and embedded sacrificial 3D bioprinting. To maintain cell survival during the implant’s pre-anastomosis phase, we will develop hydrophobic micromaterials containing molecules that release oxygen upon hydrolysis, which can be controlled via tuning the micromaterial’s hydrophobicity. These microparticles will be combined with our 3D printable and bone forming nanoparticle incorporated biomaterial matrix (Silicate-nanoparticles/GelMA) that is laden with human mesenchymal stem cells to effectively create an oxygenating bone forming bioink. This bioink will be used as a viscous medium in which a 3D vascular structure will be printed using embedded bioprinting; a novel 3D bioprinting technique that we are pioneering. Specifically, we will endow constructs with a 3D vascular structure of endothelial cell laden alginate bioink. Crosslinking the oxygenating bioink using low levels of UV light will yield a fully solid 3D construct. Upon sacrificing the internal alginate structure, an open 3D vascular network will be instantly formed. The pre-laden endothelial cells will coat the 3D network and thus provide a functional early vascularity that will accelerate anastomosis and thus minimize the implant’s prevascular phase. After in depth in vitro characterization using normoxic and hypoxic cultures, we will investigate the construct’s in vivo behavior using a subcutaneous and a critical defect model.