Viscoelastic properties of mineralized alginate hydrogel beads

Abstract

Alginate hydrogels have applications in biomedicine, ranging from delivery of cells and growth factors to wound management aids. However, they are mechanically soft and have shown little potential for the use in bone tissue engineering. Here, the viscoelastic properties of alginate hydrogel beads mineralized with calcium phosphate, both by a counter-diffusion (CD) and an enzymatic approach, are characterized by a micro-manipulation technique and mathematical modeling. Fabricated hydrogel materials have low mineral content (below 3 % of the total hydrogel mass, which corresponds to mineral content of up to 60 % of the dry mass) and low dry mass content (<5 %). For all samples compression and hold (relaxation after compression) data was collected and analyzed. The apparent Young's modulus of the mineralized beads was estimated by the Hertz model (compression data) and was shown to increase up to threefold upon mineralization. The enzymatically mineralized beads showed higher apparent Young's modulus compared to the ones mineralized by CD, even though the mineral content of the former was lower. Full compression-relaxation force-time profiles were analyzed using viscoelastic model. From this analysis, infinite and instantaneous Young's moduli were determined. Similarly, enzymatic mineralized beads, showed higher instantaneous and infinite Young's modulus, even if the degree of mineralization is lower then that achieved for CD method. This leads to the conclusion that both the degree of mineralization and the spatial distribution of mineral are important for the mechanical performance of the composite beads, which is in analogy to highly structured mineralized tissues found in many organisms.

Alginate-Based Biomaterials for Regenerative Medicine Applications

“…The diameter of the alginate gel-microspheres lies between 200 µm and 500 µm, and the cells are distributed homogeneously inside the gel-microspheres [78,79,80,81,82]. For growth factor encapsulation, transforming growth factor-beta (TGF- β ) is firstly combined with alginate solution to achieve a uniform solution, and then cross-linked with Ca 2+ in CaCl 2 solution to form gel-microspheres.…”

“…For growth factor encapsulation, transforming growth factor-beta (TGF- β ) is firstly combined with alginate solution to achieve a uniform solution, and then cross-linked with Ca 2+ in CaCl 2 solution to form gel-microspheres. Monodispersed alginate droplets can be generated to form uniform gel-spheres with consistent pore sizes by using a microfluidic device [80,81,82,83]. Besides, the uniform alginate gel-spheres can cumulate to highly organized 3D gel-sphere scaffolds with interconnecting porous structures [84].…”

Matrices (re)loaded: Durability, viability, and fermentative capacity of yeast encapsulated in beads of different composition during long‐term fed‐batch culture

“…a measure of the ability of a material to withstand changes in length when under lengthwise tension or compression, and viscosity, a parameter that integrates resistance to force and relaxation under a constant force 72,73. Specifically, for each bead type, Young's modulus and viscosity were measured at eight timepoints by applying 0.3 N of force, then maintaining that position for 50 s. Young's modulus and viscosity were calculated from the resulting data (Figure 1a-d), and these data were compared across bead types.Overall, similar trends were observed in both parameters.…”

3D brown adipogenesis to create “Brown-Fat-in-Microstrands”

“…Mouse ESCs have also been encapsulated in alginate-poly-L-lysine microcapsules and have been exposed to a differentiation scheme leading to functional hepatocytes [98]. Although the mouse ESCs have the ability to grow within the microbeads and microcapsules, the diameter is typically just outside of the 200-µm diffusion limit, and thus, oxygen and nutrients will not be transported to the center of the cell aggregates uniformly [99–103]. Therefore, it is beneficial to fabricate long microstrands with diameters less than 200 µm, to overcome the diffusion limit and prevent necrotic regions in the center of cell aggregates [104] while still allowing for abundant cell growth.…”