Swelling and Mechanical Properties of Alginate Hydrogels with Respect to Promotion of Neural Growth

Abstract

Soft alginate hydrogels support robust neurite outgrowth, but their rapid disintegration in solutions of high ionic strength restricts them from long-term in vivo applications. Aiming to enhance the mechanical stability of soft alginate hydrogels, we investigated how changes in pH and ionic strength during gelation influence the swelling, stiffness, and disintegration of a three-dimensional (3D) alginate matrix and its ability to support neurite outgrowth. Hydrogels were generated from dry alginate layers through ionic crosslinks with Ca 2 + ( £ 10 mM) in solutions of low or high ionic strength and at pH 5.5 or 7.4. High-and low-viscosity alginates with different molecular compositions demonstrated pH and ionic strength-independent increases in hydrogel volume with decreases in Ca 2 + concentrations from 10 to 2 mM. Only soft hydrogels that were synthesized in the presence of 150 mM of NaCl (Ca-alginate NaCl ) displayed long-term volume stability in buffered physiological saline, whereas analogous hydrogels generated in NaCl-free conditions (Ca-alginate) collapsed. The stiffnesses of Ca-alginate NaCl hydrogels elevated from 0.01 to 19 kPa as the Ca 2 + -concentration was raised from 2 to 10 mM; however, only Ca-alginate NaCl hydrogels with an elastic modulus £ 1.5 kPa that were generated with £ 4 mM of Ca 2 + supported robust neurite outgrowth in primary neuronal cultures. In conclusion, soft Ca-alginate NaCl hydrogels combine mechanical stability in solutions of high ionic strength with the ability to support neural growth and could be useful as 3D implants for neural regeneration in vivo.

Ultrasoft Alginate Hydrogels Support Long-Term Three-Dimensional Functional Neuronal Networks

“…Similar to previous reports, 18 we found that changes in all the tested parameters correlate directly with changes in the storage modulus of the resulting hydrogels. In particular, reducing CaCl 2 from 100 to 10 mM resulted in hydrogels 10 times softer at all the alginate concentrations tested, with ultimate stiffness ranging between 10 and 1000 Pa in the presence of low CaCl 2 .…”

“…16 Despite these biological and material advantages, the use of alginate in neural tissue engineering is not widespread, as its ability to establish and maintain 3D neuronal networks is unclear. In 2D cultures on the other hand, cortical neurons cultured on the surface of soft alginate hydrogels (<1.5 kPa) develop extensive neurite networks 17,18 and the alginate itself appears to have additional cytoprotective properties. 17 While both neurons 19,20 and progenitor cells 21,22 have been encapsulated within 3D alginate hydrogels, these were relatively stiff gels and robust neuritogenesis did not occur.…”

Colorectal tumor 3Din vitromodels: advantages of biofabrication for the recapitulation of early stages of tumour development

“…We tailored the fabrication process to obtain a 3D in vitro model based on the encapsulation of HCT-116 cells in alginate beads, achieving a fine control over bead size and initial cell number. This helped us to match the mechanical and oxygen provision requirements, adjusting alginate concentration (2% w/v), fabrication parameters (voltage, flow rate, frequency), calcium chloride concentration (500 mM) and gelling time (5 min) to obtain microspheres with a diameter smaller than 600 μm (critical thickness for oxygen diffusion in hydrogels [28][29][30]) and with a final stiffness of approximately 10-15 kPa [31][32][33]. Moreover, cell number was selected avoiding high density values, typical of late stages of tumor progression, with more invasive cell behavior.…”

Alginate/graphene double-network nanocomposite hydrogel beads with low-swelling, enhanced mechanical properties, and enhanced adsorption capacity

“…Moreover, the use of hydrogels has been severely limited because conventional hydrogels inevitably "swell" under specific conditions, which leads to drastic degradation of their mechanical properties 6 . Conventional methods to stabilize alginate hydrogels include covalent crosslinking and introduction of high concentrations of crosslinking cations to ensure tight connections between polymer chains 7 . Recently, to improve mechanical properties of alginate hydrogels, the formation of novel network structures in gels, such as nanocomposite 8 and double networks 9 , has been proposed.…”