Injectable polypeptide hydrogels via methionine modification for neural stem cell delivery

Abstract

Injectable hydrogels with tunable physiochemical and biological properties are potential tools for improving neural stem/progenitor cell (NSPC) transplantation to treat central nervous system (CNS) injury and disease. Here, we developed injectable diblock copolypeptide hydrogels (DCH) for NSPC transplantation that contain hydrophilic segments of modified l-methionine (Met). Multiple Met-based DCH were fabricated by post-polymerization modification of Met to various functional derivatives, and incorporation of different amino acid comonomers into hydrophilic segments. Met-based DCH assembled into self-healing hydrogels with concentration and composition dependent mechanical properties. Mechanical properties of non-ionic Met-sulfoxide formulations (DCH) were stable across diverse aqueous media while cationic formulations showed salt ion dependent stiffness reduction. Murine NSPC survival in DCH was equivalent to that of standard culture conditions, and sulfoxide functionality imparted cell non-fouling character. Within serum rich environments in vitro, DCH was superior at preserving NSPC stemness and multipotency compared to cell adhesive materials. NSPC in DCH injected into uninjured forebrain remained local and, after 4 weeks, exhibited an immature astroglial phenotype that integrated with host neural tissue and acted as cellular substrates that supported growth of host-derived axons. These findings demonstrate that Met-based DCH are suitable vehicles for further study of NSPC transplantation in CNS injury and disease models.

Foreign body responses in central nervous system mimic natural wound responses and alter biomaterial functions

“…1a). Lysine-based DCHK and methioninesulfoxide based DCHMO are both well tolerated in vivo [8,25], but exhibit noticeably different FBRs. For comparison, mild or severe CNS wound responses were induced by injection of innocuous phosphate buffered saline (PBS), or N5-(1-iminoethyl)-l-ornithine (L-NIO) solution that creates a small focal ischemic stroke [27].…”

“…We next characterized FBRs to various cationic, anionic and nonionic hydrogels. We manufactured DCH that presented different polar side chains to interface with host cells but maintained consistent poly(L-leucine) hydrophobic blocks [8,24,25] ( Supplementary Fig. 3a,b).…”

“…We compared these DCH with various commercially available formulations commonly used in CNS applications: methylcellulose (MC) [31], a hyaluronic acid/methylcellulose blend (HAMC) [32], and a chitosan/βglycerophosphate (CHIT) system [33]. Hydrogels with comparable mechanical properties (see [8,25,34] and Supplementary Fig.3c) were injected into mouse forebrain (Fig. 1b), and cellular FBR profiles were first characterized with immunohistochemistry for CD13, GFAP and NeuN ( Fig.…”

“…Biomaterials with specialized properties have been incorporated in implantable neuroprostheses that are used clinically for recording neuronal activity and stimulating neural circuits in the CNS [2,3]. In addition, injectable biomaterial hydrogels are used extensively as experimental tools to provide local delivery of growth factors for example to attract injured and regenerating axons to grow across CNS lesions [4,5] as well as to afford molecular and physical support to co-suspended neural progenitor cells (NPC) to improve survival and modulate differentiation upon grafting into the CNS [6][7][8].…”

“…As a platform to determine the effects of specific molecular features on biomaterial-evoked FBRs, we used synthetic, diblock copolypeptide hydrogels (DCH), which can be readily modified to present interfaces with different representative physiochemical properties to host cells whilst retaining consistent polymer chain lengths and mechanical properties [8,24,25]. These shear-thinning, physical hydrogels can be administered to focal CNS regions in a minimally invasive manner by infusion through narrow cannulae ensuring that minimal tissue damage is induced by the implantation of the biomaterial that could otherwise confound the CNS FBR evaluation of the host-biomaterial interface [24][25][26].…”