Reconstruction of orofacial skeletal defects represents a major clinical challenge, with over 1 million surgical procedures performed each year. New strategies of regenerating bone are needed because of limitations with existing techniques. We and others have shown that cells expanded from human and animal bone marrow aspirates, as well as osteoblasts harvested from bone fragments, are capable of forming new bone in-vivo. However, the rate and extent of differentiation and degree of new bone formation are unpredictable, and dependent upon factors in the cellular microenvironment, which clearly include the supporting biomaterial. In the first cycle of this grant, we developed biomimetic materials based on the 3D self-assembly of biological minerals onto organic templates. We demonstrated that the in-vitro (cell adhesion, proliferation, cytoskeletal organization, osteogenic differentiation) and in-vivo function (volume fraction of regenerated bone) of osteoprogenitor cells was reproducibly enhanced, compared to polymer controls, by controlling the nucleation and growth of a layer of bone-like mineral onto an organic template. By altering mineral composition, we were able to synthesize a series of mineral surfaces which exhibited controllable solubility, and preliminary data suggests that the dissolution products of the biomimetic layer (i.e. Ca ions) enhance cell function by themselves, independent of direct substrate-mediated effects. Collectively, these data demonstrate the ability to controllably self-assemble nanoscale mineral analogues, providing material-based control over cell function, and that the response of cells to biomaterial perturbations is the superposition of surface and solution-mediated (inorganic soluble factor) pathways. Taken together, these results form the basis for the global hypothesis to be tested in this competing renewal: the extracellular microenvironment provided by a biomaterial controls the ability of progenitor cells to proliferate and differentiate toward an osteoblast phenotype through solution as well as substrate-mediated effects, which collectively can direct cells to regenerate a mineralized matrix. It is further hypothesized that less soluble materials (surface-mediated effects) promote progenitor cell proliferation, whereas more soluble materials (solution-mediated effects) promote cell differentiation. These hypotheses are tested by synthesizing a series of biomimetic materials that includes polymer scaffolds with surfaces that self-mineralize into a biological apatite of controlled composition and solubility, depending on thermodynamic conditions, and assessing the in-vitro and in-vivo response of human progenitor cells to these biomimetic variants. The results of these studies could lead to the development of biomaterials that better control bone formation by progenitor cells. If the response of cells to a biomaterial is the superposition of surface and soluble factor-mediated pathways, this could represent a new paradigm in understanding cell/biomaterial interactions, and also lead to the development of therapeutic strategies based on a direct presentation of soluble inorganic factors, in a less invasive approach to tissue engineering.
Reconstruction of orofacial skeletal defects represents a major clinical challenge, with over 1 million surgical procedures performed each year. New strategies of regenerating bone are needed because of limitations with existing techniques. Cells expanded from human bone marrow aspirates are capable of forming new bone in-vivo. However, the degree of new bone formation is unpredictable, and dependent upon factors in the cellular microenvironment, including the supporting biomaterial. In this proposal, we will demonstrate that a biomaterial can control cell function and bone regeneration by both its surface properties of the material and soluble ionic species released from the material. Results of these studies could lead to the development of biomaterials that better control bone formation by progenitor cells. If the response of cells to a biomaterial is the superposition of surface and soluble factor-mediated pathways, this could represent a new paradigm in understanding cell/ biomaterial interactions, and also lead to the development of therapeutic strategies based on a direct presentation of soluble inorganic factors, in a less invasive approach to tissue engineering. Moreover, the balance between surface and soluble factor effects could also explain the superior biological performance of nanostructured materials.
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