Novel Strategy for Bone Tissue Engineering Using Nanofibrous Osteogenic Collagen Peptides
Abstract
Bone loss caused by combat trauma, cancer, and congenital defects is a major cause of disability and human suffering. For example, delayed healing or non-union, which occurs in 5%-10% of all bone fractures and 20% of high-impact fractures, prolongs patient morbidity, causes substantial pain, and is associated with a significantly higher rate of healthcare resource use per patient. To treat these patients, over 0.5 million bone surgeries (grafting, bone excision, surgical fracture repair) are conducted annually at a cost of approximately $2.5 billion. Bone autografts, where healthy bone is removed from a donor site in the patient and implanted at the site of injury, is the current standard of treatment. However, this approach is limited by the availability of grafting bone as well as donor site morbidity. Another approach is to use allografts (cadaveric bone products), but these generally have poor regenerative activity and, if not properly processed, can transmit disease. The limitations of current treatments have stimulated development of tissue engineering (TE) strategies for bone regeneration using a variety of synthetic biodegradable scaffolds. The ideal TE scaffold should be able to attract bone precursor cells to the site of regeneration and provide an environment that supports new bone formation. In healthy bone, this environment is composed of collagen nanofibers that attract bone precursor cells and stimulate their osteogenic activity. Bone precursor cells recognize these collagen nanofibers using specific cell surface receptors. Two receptors have been described that each recognize a separate part of the collagen molecule, beta1 integrin and discoidin domain receptor 2 (DDR2). TE scaffolds were developed by other groups containing beta1 integrin-binding collagen sequences, but these scaffolds have only weak bone-forming activity. We showed that the second collagen receptor, DDR2, is essential for normal bone development and regeneration; humans and mice lacking this receptor exhibit severe defects in bone development and DDR2-deficient mice do not heal injured bones. Synthetic DDR2-binding collagen peptides stimulate precursor cells to form bone and, significantly, when these peptides are combined with beta1 integrin-binding peptides, bone formation is synergistically stimulated. Because DDR2 and beta1 integrin-binding peptides are both components of fibrillar collagens, we think it logical to present them to cells in a microenvironment that resembles the physical structure of native collagen. To this end, we developed a technique to fabricate nanofibrous scaffolds having a similar physical structure to nanofibrous collagen (fiber diameter approximately 200 nanometers = 0.0002 mm). Based on these findings, we propose the following hypothesis to be tested in this proposal: (1) DDR2 is a critical factor for bone regeneration that functions in skeletal progenitor cells to stimulate bone regeneration by functioning together with collagen-binding integrins and (2) increasing DDR2 activity using nanofibrous scaffolds containing DDR2-activating peptides alone or together with integrin-activating peptides will positively stimulate bone regeneration to promote healing of large craniofacial defects. This hypothesis will be addressed by achieving the following two aims: Aim 1 will determine how DDR2 functions during bone regeneration in mice using two different injury models, a cranial defect where healing of a small hole in the skull is measured and a leg fracture defect. These studies will identify bone cells requiring DDR2 for their normal regenerative functions and determine how DDR2 interacts with beta1 integrin to optimally stimulate bone formation after cells are treated with DDR2 and integrin-activating peptides. In Aim 2, nanofibrous TE scaffolds will be developed containing DDR2-binding collagen peptides, beta1 integrin-binding peptides and combinations. These scaffolds will be fabricated usin
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010571
Entities
People
- Renny T Franceschi
Organizations
- United States Army
- University of Michigan