Abstract
Besides osteoconductivity and a high degradation rate, mesoporous bioactive glasses (MBGs) are specific for their highly ordered channel structure and high specific surface area, making them suitable as drug and/or growth factor delivery systems. On the other hand, the mesoporous channel structure and MBG composition can have an effect on common cell evaluation assays, leading to inconclusive results. This effect is especially important when MBG is mixed in composite bioinks, together with cells. Additionally, the hydrogel component of the ink can influence the degradation of MBG, leading to different ion releases, which can additionally affect the analyses. Hence, our aim here was to show how the MBG structure and composition influence common cell viability and differentiation assays when calcium (Ca)- or magnesium (Mg)-containing glass is part of an alginate-based composite bioink. We suggested pre-labeling of cells with DiI prior to bioprinting and staining with calcein-AM to allow identification of metabolically active cells expressing signals in both green and red channels, allowing the use of fluorescence imaging for cell viability evaluations in the presence of high amounts (7 wt %) of MBGs. The release and uptake of ions during degradation of CaMBG and MgMBG were significantly changed by alginate in the composite bioinks, as confirmed by higher release and uptake from bulk glasses. Additionally, we detected a burst release of Mg2+ from composites only after 24 h of incubation. Furthermore, we demonstrated that released ions and the mesoporous channel structure affect the measurement of lactate dehydrogenase (LDH) and alkaline phosphatase activity (ALP) in bioprinted composite scaffolds. Measured LDH activity was significantly decreased in the presence of CaMBG. On the other hand, the presence of MgMBG induced increased signal measured for the ALP. Taken together, our findings show how composite bioinks containing MBGs can interfere with common analyses, obtaining misleading results.
Highlights
Bioactive glasses (BGs) are widely used for dental and orthopedic applications, thanks to their high degradation rate and capability to induce the formation of nanocrystalline calcium phosphate structures as the main inorganic component of bone matrix (Baino et al, 2018)
Earlier analyses showed the channel structure of CaMBG (Guduric et al, 2021), which was confirmed in the present study
Representative transmission electron microscope (TEM) images of both CaMBG and MgMBG are shown in the Figure 2
Summary
Bioactive glasses (BGs) are widely used for dental and orthopedic applications, thanks to their high degradation rate and capability to induce the formation of nanocrystalline calcium phosphate structures as the main inorganic component of bone matrix (Baino et al, 2018). Among a wide range of established hydrogels, the combination of ionically crosslinkable alginate (alg) and water-soluble, viscosity-enhancing methylcellulose (MC) was shown to be very useful for bioprinting (Ahlfeld et al, 2020b). In composites of algMC with MBG, the addition of up to 10 wt% of MBG, in contrast to up to 1.5 wt% described in literature (Heras et al, 2020; Zhu et al, 2020; Tavares et al, 2021), resulted in an increased viscosity that has been counteracted by reducing the MC content to 6 wt%, maintaining shape fidelity and facilitating bioprinting of embedded hMSCs (Guduric et al, 2021). It is possible to control printing properties by adjusting MBG and MC content Taken together, these properties make the system modular and adaptable to different indications
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