Abstract
Bioactive glasses, such as 45S5 Bioglass (BG), have been shown to promote bone ingrowth both in vitro and in vivo. The goal of this study was to analyze the effect of a high dose of BG (20%) in Direct Ink Writing (DIW)-produced controlled-geometry PCL-BG composite scaffolds in both their mechanical and biological performance.
Porous cubes of 5 × 5 × 5 mm, 50% porosity and pore size and strut diameter of 400 µm were fabricated in a 3D-Bioplotter (EnvisionTec) to investigate their biological performance (n = 3). Additionally, cylindrical specimens (10 mm diameter; 15 mm height) with same internal structure were fabricated for mechanical testing (n = 6). The cylindrical specimens were tested by compression in a universal testing machine (ZwickRoell) with a 10 kN load cell. The tests were performed at 1.00 mm/min with extensometers in both sides. For biological characterization, scaffolds were sterilized in 70% ethanol overnight and pre-incubated with DMEM for 1 hour at room temperature. 1×105 human gingival mesenchymal stem cells (hGMSCs) in 50 µl DMEM were seeded on the scaffolds using agarose molds to improve cell adhesion, and cultured in standard cell-culture conditions for 3, 7 and 14 days. To measure cell proliferation, the reagent CellTiter 96® AQueous One Solution Cell Proliferation Assay (MTS, Promega) was added to the cell-seeded scaffolds at each time point, using non-seeded scaffolds as blank controls. The OD (490 nm) was measured in a BioTek 800 TS plate reader.
Both the apparent elastic modulus and yield stress were significantly lower in the scaffolds with 20% BG than their PCL control counterparts (p < 0.0001 for elastic modulus and p < 0.005 for yield stress, t-test). Cell proliferation in the scaffolds by MTS was variable, with the 20% BG scaffolds showing a significantly higher signal after seven days in culture (p < 0.05 by t-test), but a significantly lower signal after 14 days in culture (p < 0.05 by t-test).
In conclusion, scaffolds with 20% BG showed a lower mechanical performance than their PCL counterparts in terms of both their apparent elastic modulus and yield stress. Additionally, scaffolds with 20% BG showed variable cell proliferation rates in terms of their metabolic activity over a two-week period. The decrease in proliferation rate after week 2 after an initial increase at the end of week 1 could be due to cytotoxic effects of the BG at this high dose (20%) after long term exposure. These results suggest that a dosage of 20% BG may not necessarily improve the mechanical and biological performance of scaffolds, so future experiments are required in order to characterize the optimum BG dosage in PCL scaffolds for tissue engineering applications.
