Development of electrically conductive oligo(polyethylene glycol) fumarate-polypyrrole hydrogels for nerve regeneration

Abstract

Electrically conductive hydrogel composites consisting of oligo(polyethylene glycol) fumarate (OPF) and polypyrrole (PPy) were developed for applications in nerve regeneration. OPF-PPy scaffolds were synthesized using three different anions: naphthalene-2-sulfonic acid sodium salt (NSA), dodecylbenzenesulfonic acid sodium salt (DBSA), and dioctyl sulfosuccinate sodium salt (DOSS). Scaffolds were characterized by ATR-FTIR, XPS, AFM, dynamic mechanical analysis, electrical resistivity measurements, and swelling experiments. OPF-PPy scaffolds were shown to consist of up to 25 mol % polypyrrole with a compressive modulus ranging from 265 to 323 kPa and a sheet resistance ranging from 6 to 30 × 10(3) Ohms/square. In vitro studies using PC12 cells showed OPF-PPy materials had no cytotoxicity and PC12 cells showed distinctly better cell attachment and an increase in the percent of neurite bearing cells on OPF-PPy materials compared to OPF. The neurite lengths of PC12 cells were significantly higher on OPF-PPyNSA and OPF-PPyDBSA. These results show that electrically conductive OPF-PPy hydrogels are promising candidates for future applications in nerve regeneration.

Figure 1

Chemical structure of oligo(polyethylene glycol) fumarate, polypyrrole, and anions dodecylbenzenesulfonic acid sodium salt (DBSA), naphthalene-2-sulfonic acid sodium salt (NSA), and dioctyl sulfosuccinate sodium salt (DOSS) used in the synthesis of OPF-PPy hydrogels.

Figure 2

ATR-FTIR of OPF and OPF-PPy materials. Overlapping spectra show the distinct addition of skeletal C-C stretches from polypyrrole at 1550 cm⁻¹ and a broad band from 720–900 associated with C-H stretches from pyrrole and S-O stretches from NSA.

Figure 3

XPS regional scans for C, O, N, and S of OPF-PPy_NSA. Regional scan of N show the peak at 402 eV that corresponds to N⁺ species that is the conductive species of polypyrrole.

Figure 4

Compressive modulus of OPF and OPF-PPy composite materials synthesized with NSA, DBSA or DOSS anions. Results are reported as means ± standard deviations, sample size (n=3). *(p<0.05) statistically significant differences of OPF-PPy materials compared to OPF. No statistically significant differences were observed between different OPF-PPy materials.

Figure 5

AFM images and corresponding surface profiles of A) OPF B) OPF-PPy_DBSA, C) OPF-PPy_NSA, D) OPF-PPy_DOSS.

Figure 6

MTS assay evaluating toxicity of potentially leachable materials from OPF-PPy hydrogels. Percent viability was normalized to the tissue culture plate control and values are represented as means ± standard deviations.

Figure 7

MTS assay of PC12 indicating cell attachment and proliferation over 7 days. Data are presented as means ± standard deviations. *(p < 0.05) significantly higher compared to OPF at the same time point. ^#(p< 0.05) significantly higher compared to the tissue culture plate (TCP) at the same time point.

Figure 8

Fluorescence micrographs of PC12 cells at a magnification of 10x or 40x cultured for 1, 3, and 7 days on OPF, OPF-PPy_NSA, OPF-PPy_DBSA, or OPF-PPy_DOSS. All scale bars represent 50 um.

Figure 9

Neurite extension from PC12 cells after 24h quantified as a) percent of neurite bearing cells from the total number of cells. b) average neurite number of neurite bearing cells is shown. c) The distribution of neurite lengths for the OPF and OPF-PPy materials. *(p<0.05) Significant difference compared to OPF. ^#(p<0.05) Significant difference comparing OPF-PPy_NSA and OPF-PPy_DBSA materials.