Vessel formation in biodegradable bone substitution material
Introduction: Remodeling bone tissue by insertion of resorbable bone substitution material (BSM) is a therapeutic strategy for bone defects caused by malignant diseases like multiple myeloma (MM). The migration and tube formation of vascular endothelial cells (EC) in the material is a prerequisite for successful angiogenesis as part of bone regeneration1. For the application of BSM in cancer patients it has to be considered that tumor cells may have angiogenic capacity on their own and that they are able to propagate osteolytic activity at the same time. To promote angiogenesis, growth factors (GF) like VEGF are often bound to the replacement material via heparin to induce cell migration and vessel ingrowth2. As heparin can enhance osteoclastic bone resorption by sequestering osteoprotegerin (OPG)3 we screened for alternative poly-saccharides (PS) to promote non malignant cell proliferation, GF binding and bone formation. Materials and methods: Besides heparin as an established PS we screened other PS for their angiogenic potential (tube formation assay), growth factor binding (microscale thermophoresis) and influence on proliferation of EC, fibroblasts andMMcells. All these are abilities important for angiogenesis and bone-turnover. Finally we applied co-cultures of fibroblasts and EC on collagen-based, PS coated, cylindrically BSM (3 x 5 mm) and analyzed for cellmigration and tube formation. Results: The PS investigated showed divergent results on the proliferation of selected cell types, promotion of angiogenesis and OPG binding. A promising candidate was a cellulose sulfate with special sulfatation pattern (TACS). Unlike heparin TACS did not reduce the proliferation of endothelial cells while still showing a similar angiogenic capacity. In addition TACS binds OPG to a lower extent than heparin. In 3D cultures of BSM coated with TACS vessels tend to form earlier than in control scaffolds. After 28 days in cell culture BSM were colonized to almost 90% by cells while lumen containing vessels formed in the upper parts of the scaffold (~50%) (Fig. 1). Other cellulose sulfates improved the proliferation of EC or hampered the proliferation of MM so that a combined application of these together with TACSswill be the next step. Discussion and conclusions: Co-culture of fibroblasts and HUVECs on collagen matrix leads to a vessel network in the BSM making this a promising combination of cells for preseeding. We showed that PS can improve the ability of early vessels formation, proliferation and growth factor binding. As no PS so far possesses all good attributes alone, we plan to modify the scaffolds with a combination of different PS. This way we hope to find a reliable tool to improve bone healing in multiple myeloma patients. Acknowledgments: The support by the SFB TRR79 and the DKFZ Light Microscopy Facility is gratefully acknowledged. Disclosures: The authors have nothing to disclose.