Table 2.

Selected Examples of Neural Scaffolds with Synthetic Polymers for Cell Delivery

Synthetic Polymers	Structure	Cell Type	Injury Model	Outcomes	Advantages and Disadvantages
Silicone (Murakami et al., 2003)	Conduit with collagen gel	NSC	Rat 15mm sciatic nerve gap	Histology: NSC embedded conduit resulted in significantly higher number of myelinated fibers and larger fiber diameter. Inflammatory response was not reported. Behavior: Nerve action potentials from NSC-conduit showed similar delay time and lower amplitude compared to un-operated control.	Pros: One of the earlier uses of NSCs in peripheral nerve injury and showed myelination occurs. Cons: Silicone tube likely requires removal in clinical settings.
PGA (Komiyama et al., 2004)	Nerve-like 3D scaffold with pluronic F127 gel	SC	Rat 10mm sciatic nerve gap	Histology: SC-scaffold showed higher number of axons than silicone tube and was not statistically different from autograft. Axonal diameter was similar to silicone tube and lower than autograph. Behavior: SC-scaffold showed similar SFI as autograft group, whereas silicone conduit did not improve functional recovery.	Pros: Bioresorbable, consistent physical and mechanical properties. Enable high SC seeding density. SCs are allowed to deposit ECM and change the scaffold prior to implantation. Cons: Degraded product can be acidic to the host tissue. Degraded shortly after implantation and may not provide sufficient time for regeneration.
PLLA (Evans et al., 2002)	Conduit with collagen matrix	SC	Rat 12mm sciatic nerve gap	Histology: SC-conduit with lower density of SCs showed the highest nerve fiber density in the distal stump of injured nerve; however, it was still significantly lower than isograft. Behavior: SFI demonstrated no difference among all groups, including silicone conduit, over 4 months.	Pros: Bioresorbable, consistent physical and mechanical properties. Cons: Long degradation time of PLLA makes it an undesirable scaffold material for long term implantation.
PDLLA (Hsu et al., 2009)	Conduit with aligned micro- pattern	NSC	Rat 10mm sciatic nerve gap	Histology: NSC-conduit showed similar mean area of a xons, number of myelinated a xons, and number of blood vessels as autograft. NSC on micro-patterned scaffold have higher NGF and BDNF gene expression. Behavior: SFI of NSC-conduit was significantly higher than all other groups including autograft.	Pros: Bioresorbable, consistent physical and mechanical properties. Micropatterned inner lumen promotes NSC alignment. Cons: Low permeability of the conduit wall makes host tissue integration difficult.
PLGA (Liu et al., 2017)	Conduit with salidroside (SDS)	SC	Rat 12mm sciatic nerve gap	Histology: SC with aligned orientation was observed. Neurofilament was positive in both PLGA and PLGA+SDS group. No quantitative information was reported. No inflammation was observed. Behavior: SFI values suggest PLGA-SDS have the best functional recovery compared to SDS alone, PLGA alone, and direct suture control. Nerve conduction velocity was also the highest with PLGA-SDS group.	Pros: Remained structurally intact throughout the study. Cons: Lack of cell adhesion molecules may affect SC viability.
PLGA (Teng et al., 2002)	Bi-layer scaffold with different pore size and structure	NSC	Rat thoracic lateral hemisection SCI	Histology: Reduction in tissue loss from secondary injury and glial scar. Corticospinal tract ingrowth was observed. Behavior: NSC+scaffold had significantly higher BBB score for both ipsilateral and contralateral hindlimb functions, than cell alone or lesion control. Upward inclined plane test showed no difference between groups but downward incline indicated NSC+scaffold group showed improvement in function.	Pros: Bi-layer scaffold that emulate both the gray and white matter. The outer portion effectively reduced scar tissue infiltrat ion while the inner portion maintained NSC survival. Cons: The structure of the scaffold is fixed such that host tissue may need to be further removed to accommodate the scaffold.