3-D Biomimetic Scaffolds for Bone Tissue Engineering

University Of Michigan At Ann Arbor, Ann Arbor MI

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Abstract

[unreadable] DESCRIPTION (provided by applicant): 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 bone marrow stromal cells (BMSCs) 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 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 BMSCs 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 and P ions) enhance cell function by themselves, independent of direct substrate-mediated effects. It is therefore clear that the cellular response to a biomaterial is modulated by factors other than the direct interaction with the biomaterial surface. 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 BMSCs to differentiate toward an osteoblast phenotype through substrate and solution-mediated effects, which collectively can direct cells to regenerate a mineralized matrix. This hypothesis is tested by synthesizing a series of biomimetic materials that include PLGA scaffolds with a surface that self-mineralizes into a biological apatite with a controlled composition and solubility, depending on thermodynamic conditions. The results of these studies could lead to 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 manner approach to tissue engineering. [unreadable] [unreadable] [unreadable]