The question how bioactive glasses (BGs) influence the viability and osteogenic differentiation of human osteogenic cells has already been addressed by several studies.However, a literature review revealed great differences in the type of cells used for these experiments. Primary human osteoblasts (hOBs) represent the desired standard, but possess the limitation of patient variability and time-consuming isolation protocols. Therefore, several alternative cell types have been used including primary mesenchymal stromal cells (BMSCs) and the "osteoblast-like" cell lines MG-63, Saos-2, HOS, and U2OS. The aim of our study was the identification of the cell type most suitable for tissue engineering projects involving BGs by comparative analysis of cell viability and osteogenic differentiation in response to crystallized 45S5-BG. We observed that hOBs, BMSCs, and MG-63 cells were resistant to 45S5-BG induced cytotoxicity, while the viability of Saos-2, HOS, and U2OS cells was significantly reduced. In addition, we detected alkaline phosphatase activity, except in U2OS cells, that increased upon 45S5-BG cocultivation, demonstrating the induction of osteogenic differentiation. Our data and the fact that the donor-dependent variations can be avoided when using MG-63 cells suggest that these are a promising alternative to primary cells and remain an important cell line for future BG related studies.

The ICIE16-bioactive glass (BG) (48.0 SiO2, 6.6 Na2O, 32.9 CaO, 2.5 P2O5, 10.0 K2O (wt %)) has been developed as an alternative to 45S5-BG, the original BG composition (45.0 SiO2, 24.5 Na2O, 24.5 CaO, 6.0 P2O5 (wt %)), with the intention of broadening the BG sintering window while maintaining bioactivity. Because there is a lack of reports on ICIE16-BG biological properties, the influence of ICIE16-BG on viability, proliferation, and osteogenic differentiation of human mesenchymal stromal cells (MSCs) was evaluated in direct comparison to 45S5-BG in this study. The BGs underwent heat treatment similar to that which is required in order to fabricate scaffolds by sintering, which resulted in crystallization of 45S5-BG (45S5-CBG) while ICIE16 remained amorphous. Granules based on both BGs were biocompatible, but ICIE16-BG was less harmful to cell viability, most likely due to a more pronounced pH alkalization in the 45S5-CBG group. ICIE16-BG outperformed 45S5-CBG in terms of osteogenic differentiation at the cellular level, as determined by the increased activity of alkaline phosphatase. However, granules from both BGs were comparable regarding the stimulation of expression levels of genes encoding for osseous extracellular matrix (ECM) proteins. The addition of therapeutically active ions to ICIE16-BG might further improve its ability to stimulate ECM production and should be investigated in upcoming studies.

Mesoporous bioactive glass nanoparticles (MBGNs) based on the SiO2–P2O5–CaO system have demonstrated promising properties for the local delivery of therapeutically active ions with the aim to improve their osteogenic properties. Manganese (Mn) has been identified as a candidate ion for local application in bone tissue engineering applications. It remains unknown how SiO2–P2O5–CaO‐based MBGNs influence human bone marrow‐derived mesenchymal stromal cells (BMSCs) in terms of viability, proliferation, and differentiation and how these features can be modified by the addition of Mn to the MBGNs' composition. Therefore, in this study, MBGNs (composition in mol%: 50 SiO2, 40 CaO, 10 P2O5) and its Mn‐doped derivate 5Mn‐MBGNs (composition in mol%: 50 SiO2, 35 CaO, 10 P2O5, 5 MnO) were applied to a culture of BMSCs in two different concentrations. With increasing concentration, 5Mn‐MBGNs supported osteogenic differentiation and enhanced the upregulation of genes encoding for extracellular matrix proteins but also negatively influenced cell viability and proliferation. When applied in lower concentrations, MBGNs showed not only viability‐ and growth‐enhancing effects but also significant pro‐osteogenic features—however, these positive properties deteriorated with increasing concentration. Two major conclusions can be drawn from this study: (a) supplementation with Mn enhances the osteogenic properties of MBGNs in a dose‐dependent manner and (b) MBGNs constitute an attractive vector for therapeutically active ions since it exhibits an intrinsic pro‐osteogenic potential that can be improved and/or modified by incorporation of therapeutically active ions. Future studies should focus on the evaluation of further candidate ions that are known to influence osteogenic differentiation positively.

Mesoporous bioactive glass nanoparticles (MBGNs) have demonstrated promising properties for the local delivery of therapeutically active ions with the aim to improve their osteogenic properties. Manganese (Mn), zinc (Zn), and copper (Cu) ions have already shown promising pro‐osteogenic properties. Therefore, the concentration‐dependent impact of MBGNs (composition in mol%: 70 SiO2, 30 CaO) and MBGNs containing 5 mol% of either Mn, Zn, or Cu (composition in mol%: 70 SiO2, 25 CaO, 5 MnO/ZnO/CuO) on the viability and osteogenic differentiation of human marrow‐derived mesenchymal stromal cells (BMSCs) was assessed in this study. Mn‐doped MBGNs (5Mn‐MBGNs) showed a small “therapeutic window” with a dose‐dependent negative impact on cell viability but increasing pro‐osteogenic features alongside increasing Mn concentrations. Due to a constant release of Zn, 5Zn‐MBGNs showed good cytocompatibility and upregulated the expression of genes encoding for relevant members of the osseous extracellular matrix during the later stages of cultivation. In contrast to all other groups, BMSC viability increased with increasing concentration of Cu‐doped MBGNs (5Cu‐MBGNs). Furthermore, 5Cu‐MBGNs induced an increase in alkaline phosphatase activity. In conclusion, doping with Mn, Zn, or Cu can enhance the biological properties of MBGNs in different ways for their potential use in bone regeneration approaches.

Fetal calf serum (FCS) is frequently used as a growth factor and protein source in bone-marrow-derived mesenchymal stromal cell (BMSC) culture media, although it is a xenogenic product presenting multiple disadvantages including but not limited to ethical concerns. A promising alternative for FCS is human platelet lysate (hPL), which is produced out of human platelet concentrates and happens to be a stable and reliable protein source. In this study, we investigated the influence of hPL in an expansion medium (ESM) and an osteogenic differentiation medium (ODM) on the proliferation and osteogenic differentiation capacity of human BMSC. Therefore, we assessed population doublings during cell expansion, performed alizarin red staining to evaluate the calcium content in the extracellular matrix and determined the activity of alkaline phosphatase (ALP) as osteogenic differentiation correlates. The proliferation rate of BMSC cultured in ESM supplemented with hPL exceeded the proliferation rate of BMSC cultured in the presence of FCS. Furthermore, the calcium content and ALP activity was significantly higher in samples incubated in hPL-supplemented ODM, especially in the early phases of differentiation. Our results show that hPL can replace FCS as a protein supplier in cell culture media and does not negatively affect the osteogenic differentiation capacity of BMSC.

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Mesoporous bioactive glass nanoparticles (MBGNs) have gained relevance in bone tissue engineering, especially since they can be used as vectors for therapeutically active ions like zinc (Zn) or copper (Cu). In this study, the osteogenic properties of the ionic dissolution products (IDPs) of undoped MBGNs (composition in mol%: 70 SiO2, 30 CaO) and MBGNs doped with 5 mol% of either Zn (5Zn-MBGNs) or Cu (5Cu-MBGNs; compositions in mol%: 70 SiO2, 25 CaO, 5 ZnO/CuO) on human bone marrow-derived mesenchymal stromal cells were evaluated. Extracellular matrix (ECM) formation and calcification were assessed, as well as the IDPs’ influence on viability, cellular osteogenic differentiation and the expression of genes encoding for relevant members of the ECM. The IDPs of undoped MBGNs and 5Zn-MBGNs had a comparable influence on cell viability, while it was enhanced by IDPs of 5Cu-MBGNs compared to the other MBGNs. IDPs of 5Cu-MBGNs had slightly positive effects on ECM formation and calcification. 5Zn-MBGNs provided the most favorable pro-osteogenic properties since they increased not only cellular osteogenic differentiation and ECM-related gene expression but also ECM formation and calcification significantly. Future studies should analyze other relevant properties of MBGNs, such as their impact on angiogenesis.

Novel bone substitute materials need to be evaluated in terms of their osteogenic differentiation capacity and possible unwanted cytotoxic effects in order to identify promising candidates for the therapy of bone defects. The activity of alkaline phosphatase (ALP) is frequently quantified as an osteogenic marker, while various colorimetric assays, like MTT assay, are used to monitor cell viability. In addition, the DNA or protein content of the samples needs to be quantified for normalization purposes. As this approach is time consuming and often requires the analysis of multiple samples, we aimed to simplify this process and established a protocol for the combined fluorescence-based quantification of ALP activity and cell viability within one single measurement. We demonstrate that the fluorogenic substrate 4-methylumbelliferone-phosphate (4-MUP) and the commonly used para-nitrophenylphosphate (p-NPP) produce comparable and highly correlating results. We further show that fluorescein–diacetate (FDA) can be used to quantify both cell viability and cell number without interfering with the quantification of ALP activity. The measurement of additional normalization parameters is, therefore, unnecessary. Therefore, the presented assay allows for a time-efficient, simple and reliable analysis of both ALP activity and cell viability from one sample and might facilitate experiments evaluating the osteogenic differentiation of osteoblast precursor cells.