Increasing capillary diameter and the incorporation of gelatin enhance axon outgrowth in alginate-based anisotropic hydrogels

Abstract

Substantial recovery of function following peripheral and central nervous system (CNS) injury critically depends on longitudinally directed axon regeneration across the injury site, which requires a mech. guidance providing scaffold. We have previously shown that anisotropic alginate-based hydrogels with a defined capillary diam. (25 μm), which form via a self-organizing process driven by unidirectional diffusion of divalent cations into sodium alginate sols, promoted longitudinally oriented elongation of CNS axons in vitro and in vivo. In the present study the influence of various capillary diams. and the incorporation of gelatin to promote directed axon outgrowth and Schwann cell migration were assessed in a dorsal root ganglion outgrowth assay in vitro. Superimposing an alginate sol with Cu2+, Sr2+, or Zn2+ ion contg. solns. allowed the creation of hydrogels with capillaries 18, 25 and 55 μm in diam., resp. Axon outgrowth and Schwann cell migration were analyzed in terms of axon length/d. and Schwann cell d. within the capillary structures. Axon ingrowth into capillary hydrogels, which was always accompanied by Schwann cells, was enhanced with increasing capillary diam. The incorporation of gelatin did not influence overall axon d., but promoted the length of axon outgrowth within the hydrogels. The longitudinal orientation of axons decreased in wider capillaries, which suggests that medium-sized capillaries are the optimal substrate to elicit substantial axon growth and longitudinal orientation after axon injury.