BIOMIMETIC MATERIALS FOR ENGINEERING OF NEURAL TISSUES: CONTROL OF CELL ADHESION AND GUIDING NEURAL CELL OUTGROWTH WITH PEPTIDE-CONJUGATED POLYMER STRUCTURES - Biologically-Responsive Hybrid Biomaterials - page 337

Yet in spinal cord, the vertebral column withstands cyclical mechanical loads
and the amount of collagenous material within the cord is comparatively low. In
brain, the local tissue arrangement can be extremely complex, but a global
organization is lacking. The cellular vs. connective tissue proportion further
influences observed mechanical properties. Not surprisingly, CNS tissue has a
different set of biomechanical characteristics compared to peripheral nerve.

A B

Fig. 2. (A) Hydrogel based therapy is well suited for CNS repair. In this schematic, solubilized
polymer (with or without cells) is injected into the lesion and cross-linked in situ . The polymerized
polymer conforms to the defect and directly interfaces with surrounding tissue. (B) For PNS gap
defects, nerve guidance conduits (NGCs) are used to bridge the proximal and distal segments. The
NGC is designed to enclose the injury site and provide the necessary guidance cues to accelerate
and direct regeneration through the lesion.

While the diversity of neuronal networks underpins functional adaptations,
certain challenges also arise in terms of repair. For example, disparities between
the CNS and PNS anatomy predispose particular injuries. Localized crush
injuries are prevalent in the spinal cord, while in the PNS, stretch and lacerations
occur with higher frequency. Within brain, traumatic brain injury (TBI) or
disease states may cause patterns of damage that are either focal or diffuse. These
dissimilar injury modalities, coupled with the structural variations (and
mechanical properties) within the nervous system can define intra-operative
decision making and the therapeutic regime. Severe damage to the spinal cord or
brain resulting in significant tissue loss may warrant in situ polymerization with
hydrogels (Figure 2). In contrast, transection of peripheral nerve is generally
repaired via pre-fabricated implants that bridge the proximal and distal segments.
Thus, medical therapies intended for the CNS or PNS will need to consider the
native mechanical, structural and cellular characteristics.