Nanofiber/Microsphere Hybrid Matrices In Vivo for Bone Regenerative Engineering: A Preliminary Report

The demand for bone grafts has led to advances in regenerative engineering, a field at the intersection of advanced biomaterials, stem cell science, physics, developmental biology, and clinical translation. In this work, the authors evaluated a hybrid nanofiber/microsphere matrix both in vitro and in vivo for its ability to promote bone regeneration. Quantitative measures of cellular characteristics in vitro showed a higher fraction of marrow stromal cells with collagen promoter activity on hybrid matrices compared to control matrices (41 vs. 24%, p=0.02). Control and hybrid matrices were then implanted for 6weeks in calvarial defects of mice, and the animals received a single injection of calcein 1day prior to sacrifice to visualize bone formation. Cryohistology of the undecalfied implants were evaluated for markers of bone mineralization, which revealed the evidence of higher levels of bone tissue formation in hybrid matrices compared to controls. These data provide support that nanofiber-permeated, sintered, composite microsphere matrices may be a particularly useful matrix for the regenerative engineering of bone.Lay SummaryOne idea to regenerate bone is to mimic the structure, composition, and feature size of natural human bone in a synthetic matrix to guide human stem cells. In this work, the authors combine an advanced material matrix with special genetically engineered stem cells to investigate if the special composition of the matrix can help improve existing matrices to support the regeneration of human bone. These results show that while the new matrices support a smaller population of cells, those cells are more likely to show evidence of growing into cells that may create bone.Future WorkFuture studies will include the implantation of transgenic, cell-seeded matrices of one fluorescent reporter mouse implanted in a host mouse that contains a separate fluorophore with a similar promoter. These studies will allow determination of the source of bone formation in these models: from host or from implant.