Standard treatment for bone defects is the biological reconstruction using autologous bone—a therapeutical approach that suffers from limitations such as the restricted amount of bone available for harvesting and the necessity for an additional intervention that is potentially followed by donor-site complications. Therefore, synthetic bone substitutes have been developed in order to reduce or even replace the usage of autologous bone as grafting material. This structured review focuses on the question whether calcium phosphates (CaPs) and bioactive glasses (BGs), both established bone substitute materials, show improved properties when combined in CaP/BG composites. It therefore summarizes the most recent experimental data in order to provide a better understanding of the biological properties in general and the osteogenic properties in particular of CaP/BG composite bone substitute materials. As a result, BGs seem to be beneficial for the osteogenic differentiation of precursor cell populations in-vitro when added to CaPs. Furthermore, the presence of BG supports integration of CaP/BG composites into bone in-vivo and enhances bone formation under certain circumstances.

Bone defect treatment belongs to the most challenging fields in orthopedic surgery and requires the well-coordinated application of mesenchymal stem cells (MSC) and differentiation factors. MSC isolated from reaming material (RMSC) and iliac crest (BMSC) in combination with bone morphogenetic protein-7 (BMP-7) and insulin-like growth factor-1 (IGF-1) have been used. The short half-life of both factors limit their applications: a burst release of the factor can probably not induce sustainable differentiation. We stimulated MSC in osteogenic differentiation medium with three different concentrations of BMP-7 or IGF-1: Group A was stimulated continuously, group B for 24 h and group C remained without any stimulation. Osteogenic differentiation was measured after seven and 14 days by alizarin red staining and alkaline phosphatase (ALP) activity. Continuous stimulation led to higher levels of osteogenic differentiation than short-term stimulation. This could lead to a reconsideration of established application forms for differentiation factors, aiming to provide a more sustained release.

Patient-derived mesenchymal stromal cells (MSCs) play a key role in bone tissue engineering. Various donor-specific factors were identified causing significant variability in the biological properties of MSCs impairing quality of data and inter-study comparability. These limitations might be overcome by pooling cells of different donors. However, the effects of pooling on osteogenic differentiation, proliferation and vitality remain unknown and have, therefore, been evaluated in this study. MSCs of 10 donors were cultivated and differentiated into osteogenic lineage individually and in a pooled setting, containing MSCs of each donor in equal parts. Proliferation was evaluated in expansion (assessment of generation time) and differentiation (quantification of dsDNA content) conditions. Vitality was visualized by a fluorescence-microscopy-based live/dead assay. Osteogenic differentiation was assessed by quantification of alkaline phosphatase (ALP) activity and extracellular calcium deposition. Compared to the individual setting, generation time of pooled MSCs was shorter and proliferation was increased during differentiation with significantly lower variances. Calcium deposition was comparable, while variances were significantly higher in the individual setting. ALP activity showed high variance in both groups, but increased comparably during the incubation period. In conclusion, MSC pooling helps to compensate donor-dependent variability and does not negatively influence MSC vitality, proliferation and osteogenic differentiation.