Abstract
Along with biocompatibility, bioinductivity and appropriate biodegradation, mechanical properties are also of crucial importance for tissue engineering scaffolds. Hydrogels, such as gellan gum (GG), are usually soft materials, which may benefit from the incorporation of inorganic particles, e.g. bioactive glass, not only due to the acquired bioactivity, but also due to improved mechanical properties. They exhibit complex viscoelastic properties, which can be evaluated in various ways. In this work, to reliably evaluate the effect of the bioactive glass (BAG) addition on viscoelastic properties of the composite hydrogel, we employed and compared the three most commonly used techniques, analyzing their advantages and limitations: monotonic uniaxial unconfined compression, small amplitude oscillatory shear (SAOS) rheology and dynamic mechanical analysis (DMA). Creep and small amplitude dynamic strain-controlled tests in DMA are suggested as the best ways for the characterization of mechanical properties of hydrogel composites, whereas the SAOS rheology is more useful for studying the hydrogel’s processing kinetics, as it does not induce volumetric changes even at very high strains. Overall, the results confirmed a beneficial effect of BAG (nano)particles on the elastic modulus of the GG–BAG composite hydrogel. The Young’s modulus of 6.6 ± 0.8 kPa for the GG hydrogel increased by two orders of magnitude after the addition of 2 wt.% BAG particles (500–800 kPa).
Highlights
Medical applications of hydrogels as scaffold materials were extended for various tissue engineering applications [1,2,3]
Creep and small amplitude dynamic strain-controlled tests in dynamic mechanical analysis (DMA) are suggested as the best ways for the characterization of mechanical properties of hydrogel composites, whereas the small amplitude oscillatory shear (SAOS) rheology is more useful for studying the hydrogel’s processing kinetics, as it does not induce volumetric changes even at very high strains
The macroscopic appearance of the hydrogel-based composite H1, containing 2 wt. % of bioactive glass (BAG) nanoparticle hydrogel is presented in figure 1(a), while the figures 1(b) and (c) illustrate the microstructure of the freeze-dried sample at two magnifications
Summary
Medical applications of hydrogels as scaffold materials were extended for various tissue engineering applications [1,2,3]. For bone tissue engineering scaffolds, it is known that hydroxyapatite (HA) and bioactive glass (BAG) have an ability to promote osteogenesis [4], but they are rather brittle and with limited strain compliance. It has been suggested that the stiffness of the scaffold (substrate) and stresses generated from the cell–substrate strains substantially affect a cell’s fate, especially for stem cell differentiation [7, 8]. Even for ‘hard’ tissues, like bone [11], viscoelastic properties are significant, especially at low strain rates and within the physiological frequency ranges. To know how well the scaffold material resembles the tissue being regenerated, their time and/or frequency dependent mechanical properties have to be evaluated in sufficient detail
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