Thermoresponsive Copolypeptide Hydrogel Vehicles for Central Nervous System Cell Delivery

Abstract

Biomaterial vehicles have the potential to facilitate cell transplantation in the central nervous system (CNS). We have previously shown that highly tunable ionic diblock copolypeptide hydrogels (DCH) can provide sustained release of hydrophilic and hydrophobic molecules in the CNS. Here, we show that recently developed non-ionic and thermoresponsive DCH called DCHT exhibit excellent cytocompatibility. Neural stem cell (NSC) suspensions in DCHT were easily injected as liquids at room temperature. DCHT with a viscosity tuned to prevent cell sedimentation and clumping significantly increased the survival of NSC passed through injection cannulae. At body temperature, DCHT self-assembled into hydrogels with a stiffness tuned to that of CNS tissue. After injection in vivo, DCHT significantly increased by three-fold the survival of NSC grafted into healthy CNS. In injured CNS, NSC injected as suspensions in DCHT distributed well in non-neural lesion cores, integrated with healthy neural cells at lesion perimeters and supported regrowing host nerve fibers. Our findings show that non-ionic DCHT have numerous advantageous properties that make them useful tools for in vivo delivery of cells and molecules in the CNS for experimental investigations and potential therapeutic strategies.

Astrocyte scar formation aids central nervous system axon regeneration

“…Although our observations with stimulated AST axon regeneration needs extension to other axonal systems, our findings are consistent with evidence that (i) astrocytes can support growth of different CNS axons in vivo during development 42,43 or after mature CNS injury 19,44 , (ii) genetic activation of axonal growth programs by mature neurons leads to axon regeneration across CNS lesions only when scar-forming astrocyte bridges are present 2,45 , and (iii) grafts of progenitor-derived astrocytes support axon regeneration through non-neural SCI lesion cores 46,47 .…”

“…These observations provide direct evidence that the requirements for achieving axon regeneration across severe CNS lesions, where transected axons lack intrinsic and extrinsic conditions for long distance regrowth, are fundamentally different from requirements to achieve local neurite outgrowth in perilesion intact but reactive grey matter, where conditions compatible with axon terminal growth and remodeling are present and where blocking inhibitory regulators such as CSPGs and others produced by astrocytes and other cells may be sufficient to promote axon sprouting that might also improve function 9,15,24,29,41,49 . Our findings have important implications for CNS repair strategies by demonstrating that rather than being hostile to axon growth, newly generated immature scar-forming astrocytes derived after SCI from endogenous progenitors 18,42,45 , and potentially from grafted progenitors 46,47 , aid axon regeneration and may represent exploitable bridges for regrowing axons across severe CNS lesions.…”

Conformation-Directed Formation of Self-Healing Diblock Copolypeptide Hydrogels via Polyion Complexation

“…To showcase their potential utility, we encapsulated primary neural stem progenitor cells (NSPCs) 33 in an (M O A) 155 E/K 60 hydrogel (Figure 5). The NSPCs were encapsulated by mixing a suspension of cells in media with an equal volume of (M O A) 155 E 60 solution in media, which was then combined with an equal volume of (M O A) 155 K 60 solution in media to rapidly form the cell-containing hydrogel.…”

Cell biology of spinal cord injury and repair

“…Mature injured CNS axons regrow along astrocytes after CNS injury when stimulated by appropriate growth factors (57) or by genetic activation (58). Grafts of progenitor-derived astrocytes support axon regeneration though SCI lesion cores (59)(60)(61). Targeted disruption of astrocyte scar formation attenuates stimulated axon regeneration after SCI (19).…”

“…Without glia, neuronal elements are unlikely to persist. Neuroglial cell grafts that can support host axon regrowth include Schwann cells (89,161,163) and astroglia (59)(60)(61). Coaxing of axons to regrow past grafts into spared host tissue and form connections can be facilitated by chemoattractive growth factors (88).…”