(722d) Biomimetic Polymer Scaffolds for Neural Stem Cell Adhesion & Differentiation

Neurodegenerative diseases and neurotraumatic injuries result
in an irreplaceable cell loss and concomitant deficit in motor and sensory
functions.  An ideal strategy for repair will
allow for cell survival, migration, and integration of exogenous cells with
host tissue. Biomaterials provide a potential strategy to elicit these
responses by presentation of specific cues to control cellular behavior. 
While much of current biomaterials research has focused on optimizing the
mechanical and soluble cues required to direct neural cell behavior, adhesive
cues and, more importantly, cell-cell interactions may also play a role.  In this study, we investigated the
role of differential presentation of fragments of L1, a transmembrane,
homophilic binding, neural cell adhesion molecule, as a biointerfacial strategy
to direct neuronal cell retention and differentiation of neural stem cells on
implantable scaffolds, while inhibiting the adhesion of non-neuronal
phenotypes, such as astrocytes and fibroblasts.  This approach is
hypothesized to not only promote the survival and outgrowth phenomena of
neuronally developed cells, but also guide the development of neural stem cells
as L1 has been implicated in the normal development of the central nervous
system.

Two-dimensional films of poly(desaminotyrosyl tyrosine ethyl
ester carbonate) (poly(DTE carbonate) polymers were used as the
biomaterial model for L1 functionalization as these polymers are highly
biocompatible and can be tuned to alter protein adsorption,
hydration/biomechanical properties, and degradation behaviors.  Various
configurations of L1 presentation were compared in terms of relative
concentrations, orientations, and multivalency of L1 display, including passive
adsorption on cationic, poly-D-lysine-treated substrates or L1-Fc fused
fragment presentation from protein A-coated polymer substrates.  Protein
A-based presentation of L1-Fc was hypothesized to result in the outward display
of L1 while resulting in a clustered ligand presentation of L1 and increase
ligand efficacy, as well as enhance cell binding affinity and L1-mediated
intracellular signaling.

We report that the configuration of L1 presentation marked
affected neural cell behavior on the biofunctionalized polymer
substrates.  When presented through an in vivo-like
configuration on protein A, L1 significantly increased neurite outgrowth of
spinal cord neurons compared to the traditional presentation of passive
adsorption on poly-D-lysine as early as 24 hours.  After 72 hours, while
both conditions supported the formation of neural networks, protein A-presented
L1 resulted in a denser population of extended neurites.  Next, the role
of L1 on active differentiation of human neural stem cells was examined.  Neural
stem cells derived from H9 human embryonic stem cells were used for these
studies.  Protein A presented-L1 yielded quantitative enhancement in levels of
neuronal differentiation and outgrowth of human neural stem cells in comparison
to PDL-presented L1 after 7 days in culture.  This approach is being
integrated within three-dimensional scaffolds for the design of neural stem
cell-transplantable constructs for the management of spinal cord injury.