Osteoclast lineage cell differentiation on poly(L-lactide-co-caprolactone)/β-tricalcium phosphate/bioactive glass composite

Abstract

Bone is a dynamic tissue, continuously renewing itself through a process called bone remodelling. This involves seamless collaboration of multinuclear osteoclasts resorbing old or damaged bone and osteoblasts forming new bone tissue, allowing scar-free healing. However, bone grafts are necessary to treat defects beyond the bone’s natural healing capacity. Bone is the second most transplanted tissue globally with clinical demand increasing due to an aging population. Autologous bone grafts are the gold standard for treating bone defects, but novel synthetic bone grafts are making their way into operation rooms.

Bone tissue engineering is a multidisciplinary field focused on promoting effective bone healing using biomaterials, cells, and growth factors. Ideal biomaterials should support cell attachment and proliferation, promote the differentiation of immature cells into bone cells, degrade through biochemical and cell-mediated manner, and facilitate adequate vascularization. In vitro assessment is crucial for early biomaterial development. Synthetic biomaterials used in orthopedics include metals, bioceramics, and polymers. Since no material alone mimics the natural bone tissue, composites are developed and the search for the optimal biomaterial for scaffold fabrication continues. Human stem cells, such as bone marrow stromal cells or human peripheral blood monocytes, can differentiate into the bone cell lineage and are actively used in biomaterial research. The critical role of osteoblasts in bone healing is well-established, which is why this study concentrates on responses of osteoclasts and their precursor cells.

In this study, a poly(L-lactide-co-ɛ-caprolactone)/β-tricalcium phosphate/bioactive glass composite was investigated. Two material structures of this composite were created: a sheet-like, heat-compressed structure and a supercritical carbon dioxide foamed, porous structure (referred to as un-foamed and foamed biomaterial, respectively). Mouse MC3T3 cells and human bone marrow-derived mesenchymal stromal cells were used as osteoblast precursor cells. Cell attachment on the material surface was observed in these cultures. Mouse MC3T3 cells were also cultured for cell viability assessment. Mouse RAW cells, human peripheral blood and bone marrow derived monocytes were used as osteoclast precursor cells to study osteoclastogenesis. Another part of the study focused on optimizing osteoclastogenesis from healthy human peripheral blood monocytes using different growth factors.

All cell types attached to the composite structures with adhesion structures visible on the biomaterials. The foamed biomaterial was challenging to view due to its three-dimensional structure. Multinuclear osteoclasts were not observed on the biomaterials, indicating that the biomaterial lacks the capability of inducing differentiation of progenitor cells. Resorption pit staining resulted unspecific staining of the biomaterials and no resorption pits were observed. The biomaterials showed similar cell viability results compared to bone, confirming their biocompatibility. Multinuclear cells were not observed in cell cultures when osteoclastogenesis was attempted to optimize. Osteoclastogenesis from healthy donors’ monocytes could not be induced with the growth factor cocktails used in this study.