Enhancing Schwann cell migration using concentration gradients of laminin-derived peptides

Neuroregeneration following peripheral nerve injury is largely mediated by Schwann cells (SC), the principal glial cell that supports neurons in the peripheral nervous system. Axonal regeneration in vivo is limited by the extent of SC migration into the gap between the proximal and distal nerve, however, little is known regarding the principal driving forces for SC migration. Engineered microenvironments, such as molecular and protein gradients, play a role in the migration of many cell types, including cancer cells and fibroblasts. However, haptotactic strategies have not been applied widely to SC. Herein, a series of tethered laminin-derived peptides were analyzed for their influence on SC adhesion, proliferation, and alignment. Concentration gradient substrates were fabricated using a controlled vapor deposition method, followed by covalent peptide attachment via a thiol-ene reaction, and characterized by X-ray photoelectron spectroscopy (XPS) and MALDI-MS imaging. While tethered RGD peptides supported SC adhesion and proliferation, concentration gradients of RGD had little influence on biased SC directional migration. In contrast, YIGSR promoted less SC attachment than RGD, yet YIGSR peptide gradients directed migration with a strong bias to the concentration profile. With YIGSR peptide, overall speed increased with the steepness of the peptide concentration profile. YIGSR gradients had no haptotactic effect on rat dermal fibroblast migration, in contrast to fibroblast migration on RGD gradients. The response of SC to these tethered peptide gradients will guide the development of translationally relevant constructs designed to facilitate endogenous SC infiltration into defects for nerve regeneration.

Synthesis and 3D Printing of PEG-Poly(propylene fumarate) Diblock and Triblock Copolymer Hydrogels

PEG-based hydrogels are used widely in exploratory tissue engineering applications but in general lack chemical and structural diversity. Additive manufacturing offers pathways to otherwise unattainable scaffold morphologies but has been applied sparingly to cross-linked hydrogels. Herein, mono methyl ether poly(ethylene glycol) (PEG) and PEG-diol were used to initiate the ring-opening copolymerization (ROCOP) of maleic anhydride and propylene oxide to yield well defined diblock and triblock copolymers of PEG-poly(propylene maleate) (PPM) and ultimately poly(propylene fumarate) (PPF) with different molecular mass PEG macroinitiators and block length ratios. Using continuous digital light processing (cDLP) hydrogels were photochemically printed from an aqueous solution which resulted in a 10-fold increase in elongation at break compared to traditional diethyl fumarate (DEF) based printing. Furthermore, PPF-PEG-PPF triblock hydrogels were also found to be biocompatible in vitro across a number of engineered MC3T3, NIH3T3, and primary Schwann cells.