Toward spinal cord injury repair strategies: peptide surface modification of expanded poly(tetrafluoroethylene) fibers for guided neurite outgrowth in vitro.

Expanded poly(tetrafluoroethylene) fibers were surface modified using an ultraviolet-activated mercury/ammonia reaction to yield amine-functional groups for the coupling of laminin-derived cell adhesive peptides CYIGSR, CDPGYIGSR, CIKVAV, and CQAASIKVAV. Surface elemental composition, determined by X-ray photoelectron spectroscopy, and radiolabeling data indicated that the amount of peptide introduced was approximately equivalent regardless of peptide type, yet mixed peptide surfaces had approximately 60% YIGSR and 40% IKVAV. The peptide-modified surfaces were compared in terms of the response of dorsal root ganglia with neurite length and number of cells attached to each fiber measured. All peptide-functionalized surfaces had a greater cellular response than the aminated ePTFE and ePTFE controls. Surfaces modified with extended peptide sequences CDPGYIGSR and CQAASIKVAV demonstrated a greater cellular response than those modified with the shorter peptide sequences CYIGSR and CIKVAV, respectively, likely because the extended peptides more closely mimic the three-dimensional conformation that the peptides maintain in laminin. Differences in neurite extension were evident among the peptide-functionalized surfaces, with the longest neurites observed on surfaces modified with both CQAASIKVAV and CDPGYIGSR. The "guidance capacity" of the fibers as a function of fiber diameter was investigated in terms of length and directionality of neurite outgrowth. As fiber diameter decreased (from 100+ to 10 microm), the neurites tended to grow to a greater degree down the length of the fiber. The thinnest fibers (with diameters <20 microm) extended shorter neurites than the fibers with a wider diameter. Combining neurite length with guidance indicated that of the fiber diameters investigated, the optimal fiber diameter for neurite guidance was between 30 and 50 microm.