Novel Tissue-Engineered Multimodular Hyaluronic Acid-Polylactic Acid Conduits for the Regeneration of Sciatic Nerve Defect

Abstract

The gold standard for the treatment of peripheral nerve injuries, the autograft, presents several drawbacks, and engineered constructs are currently suitable only for short gaps or small diameter nerves. Here, we study a novel tissue-engineered multimodular nerve guidance conduit for the treatment of large nerve damages based in a polylactic acid (PLA) microfibrillar structure inserted inside several co-linear hyaluronic acid (HA) conduits. The highly aligned PLA microfibers provide a topographical cue that guides axonal growth, and the HA conduits play the role of an epineurium and retain the pre-seeded auxiliary cells. The multimodular design increases the flexibility of the device. Its performance for the regeneration of a critical-size (15 mm) rabbit sciatic nerve defect was studied and, after six months, very good nerve regeneration was observed. The multimodular approach contributed to a better vascularization through the micrometrical gaps between HA conduits, and the pre-seeded Schwann cells increased axonal growth. Six months after surgery, a cross-sectional available area occupied by myelinated nerve fibers above 65% at the central and distal portions was obtained when the multimodular device with pre-seeded Schwann cells was employed. The results validate the multi-module approach for the regeneration of large nerve defects and open new possibilities for surgical solutions in this field.

Multimodular Bio-Inspired Organized Structures Guiding Long-Distance Axonal Regeneration

“…In previous studies [ 31 , 32 , 34 , 35 ], we verified that SC seeded and cultured within HA conduits formed a ‘SC sheath’, a cell cylinder templated by the inner surface of the conduit’s lumen. These SC also grow on PLA fibers when these are placed inside the conduit’s lumen.…”

“…Biohybrid approaches for neural tissue engineering seem to have better results in terms of functional recovery in comparison with purely material-based constructs [ 40 ]. SC have demonstrated to enhance axonal growth in vitro [ 41 ] and to regenerate nerves in combination with implants [ 35 , 42 ], and even in the CNS they proved to support the recovery of spinal cord function [ 43 ]. The regeneration of tract-like axon structures demands bridging sometimes long distances directing axon growth in an ordered way.…”

“…The synthesis of HA sodium salt from Streptococcus equi (HA; 1.5–1.8 MDa; Sigma-Aldrich, Madrid, Spain) conduits was carried out as previously described [ 31 , 32 , 33 , 34 , 35 ]. Briefly, poly-ε-caprolactone (PCL; Mw = 40 kDa; PolySciences, Madrid, Spain) fibers of 400 µm were extruded in Hater Minilab, and a polytetrafluoroethylene thin block with grooves 1.5 mm wide with a single PCL fiber of 400 µm diameter was used as a mould for the conduits.…”

“…In our previous studies [ 31 , 32 , 33 , 34 , 35 ], we found that SC seeded into hyaluronic acid (HA) conduits with poly-L-lactide acid (PLA) microfibers in their lumina were able to proliferate and self-organize into a continuous cylindrical cell sheath in the lumen of the conduits. Additionally, SC grew on the PLA fibers, spanning the whole distance of a biohybrid construct 6 mm in length.…”

“…We compare the multimodular conduit with a unimodular conduit with the same length to study the cells viability and distribution, and the axonal extension of neurons coming from the DRG explant. In a separate study [ 35 ], we adapted the present multimodular concept for an in vivo experimental model of sciatic nerve regeneration in rabbits, which we discuss in connection with the present findings below.…”