The research objective of this collaborative project is advancing our understanding of regenerative repair of bones by introducing a smart implantable microvasculature, mimicking developmental regeneration. The research approaches are: 1) Developing microfabrication technologies for integration of three-dimensional microvasculature; 2)Demonstrating sensing, logic and controllable release with smart micovasculature in-vitro; 3)Modeling growth factor release and cell growth in microvasculature; 4) Testing of implanted smart microvasculature in vivo for bone regeneration.
Intellectual Merit: The project will advance the knowledge of design and microfabrication of smart microvasculature for controlled temporal and spatial release of growth factors, mimicking developmental bone formation. The response of functional hydrogel microstructures in response to physiological stimuli, such as pH and temperature, will be analyzed, during the bone healing process. This will be coupled to modeling effort in predicting growth factor release characteristics from the smart microvasculature, and related cell growth and proliferation to enhance bone regeneration.
Broader Impact: Understanding the process of tissue regeneration as a function of controlled transport of growth factors in space and time is a fundamental challenge in biology. This fundamental research is expected to have direct impact, such as analyte controlled and modulated drug and protein delivery, drug screening, and tissue engineering. The PIs will actively disseminate their research findings to the local community, including high school students and science teachers on the basics of bone biology and miniature implant for assisted regeneration. Also, a high resolution micro-stereolithography service will be established for other user groups to explore the innovative microvasculature design.
Injuries of long bones that fail to heal properly and result in osseous non-union are frequently encountered in orthopedic medicine, and these injuries pose significant medical and socioeconomic problems. While a number of techniques have been developed over the years to treat these injuries, addressing these conditions remains a clinical challenge. The relatively young discipline of Tissue Engineering has endeavored to develop new methods for treating these injuries, utilizing combined knowledge of materials science, engineering, and cell and molecular biology to develop implantable scaffolds to stimulate and aid healing of bone defects. The number of combinations of scaffold materials and designs, coupled with drug, growth factor, and stem cell treatments developed to promote bone healing, is rapidly and constantly growing. One of the challenges for bone tissue engineering is identifying promising scaffold formulations to refine and test in expensive pre-clinical large animal model systems. Ideally, a small animal screening system would aid in testing and refining several different scaffold formulations for healing bone defects in order to identify the most promising designs for further testing in large animals. As part of our project to design novel microvasculature scaffolds for bone tissue engineering, we also developed a novel small animal bone defect model system for testing these scaffolds, and other potential scaffold designs. We defined and established the adult frog, Xenopus laevis, as a small animal model system to test scaffold therapies designed to improve healing in long bone segmental defect non-unions. We were able to utilize the tarsus bone of the Xenopus hindlimb to generate non-healing long bone defects, implant these defects with scaffolds loaded with different growth factors, and assay the ability of the scaffold/growth factorcombinations to heal the osseous defect. We developed protocols to follow the progress of segmental bone defect healing non-invasively, utilizing MRI and ultrasonography. Due in part to the size and location of the tarsus bone in Xenopus, we were able to demonstrate the ability of ultrasonography to follow scaffold-assisted healing of bone defects and predict successful vs. unsuccessful healing outcomes. The ability to use ultrasonography to monitory healing noninvasively in our system will allow us to use fewer animals to evaluate the ability of different scaffold designs to promote bone defect healing. Employingan HDDA (1,6 hexanediol diacrylate) scaffold we developed a therapy that delivers the growth factors bone morphogenetic protein-4 (BMP4) and vascular endothelial growth factor (VEGF), to the bone defect area. We demonstrated that scaffold-assisted delivery of these factors promote healing of the bone defect by cartilage callus formation that eventually undergoes endochondral ossification.
