PEDOT:PSS-Coated Polybenzimidazole Electroconductive Nanofibers for Biomedical Applications

Abstract

Bioelectricity drives several processes in the human body. The development of new materials that can deliver electrical stimuli is gaining increasing attention in the field of tissue engineering. In this work, novel, highly electrically conductive nanofibers made of poly [2,2'-m-(phenylene)-5,5'-bibenzimidazole] (PBI) have been manufactured by electrospinning and then coated with cross-linked poly (3,4-ethylenedioxythiophene) doped with poly (styrene sulfonic acid) (PEDOT:PSS) by spin coating or dip coating. These scaffolds have been characterized by scanning electron microscopy (SEM) imaging and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. The electrical conductivity was measured by the four-probe method at values of 28.3 S·m^-1 for spin coated fibers and 147 S·m^-1 for dip coated samples, which correspond, respectively, to an increase of about 10⁵ and 10⁶ times in relation to the electrical conductivity of PBI fibers. Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) cultured on the produced scaffolds for one week showed high viability, typical morphology and proliferative capacity, as demonstrated by calcein fluorescence staining, 4',6-diamidino-2-phenylindole (DAPI)/Phalloidin staining and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide] assay. Therefore, all fiber samples demonstrated biocompatibility. Overall, our findings highlight the great potential of PEDOT:PSS-coated PBI electrospun scaffolds for a wide variety of biomedical applications, including their use as reliable in vitro models to study pathologies and the development of strategies for the regeneration of electroactive tissues or in the design of new electrodes for in vivo electrical stimulation protocols.

Keywords: PBI; PEDOT:PSS; electroconductive; electrospinning; mesenchymal stem cells; nanofibers.

Figure 1

SEM images (top) and respective fiber diameter distributions (middle) of pristine electrospun PBI, cross-linked PEDOT:PSS-spin coated PBI and cross-linked PEDOT:PSS-dip coated PBI nanofibers. Scale bar: 7 μm. The discreet histogram values are represented on the left yy-axis and the normal probability density function each mean and standard deviation are represented on the right yy-axis. Chemical structures of poly [2,2′-m-(phenylene)-5,5′-bibenzimidazole] (PBI) and poly (3,4-ethylenedioxythiophene) doped with poly (styrene sulfonic acid) (PEDOT:PSS) are shown in the (bottom) panel.

Figure 2

ATR-FTIR spectra of the various samples analyzed. (A) Spectra normalized to peak 799 cm⁻¹ of (a) PBI electrospun fibers, and PEDOT:PSS/PBI obtained by (b) spin coating and (c) dip coating. (B) Spectra normalized to peak 2324 cm⁻¹ of PEDOT:PSS/PBI samples obtained by (b’) spin coating and (c’) dip coating, (x) PEDOT:PSS pellet and (y) PEDOT:PSS pellet with GOPS.

Figure 3

MTT assay results performed after 1 and 7 days of hBM-MSCs culture on the three types of scaffolds: pristine electrospun PBI fibers, PEDOT:PSS-spin coated PBI fibers and PEDOT:PSS-dip coated PBI fibers. Tissue culture plates were used as controls. Results are expressed as mean ± standard deviation (n = 3 independent samples).

Figure 4

Calcein fluorescence staining of hBM-MSCs cultured on pristine electrospun PBI, PEDOT:PSS-spin coated PBI fibers and PEDOT:PSS-dip coated PBI fibers at days 1 and 7. Viable cells are stained in green. Scale bar: 50 μm.

Figure 5

DAPI/Phalloidin immunofluorescence staining of hBM-MSCs cultured on pristine electrospun PBI, PEDOT:PSS-spin coated PBI fibers and PEDOT:PSS-dip coated PBI fibers for days 1 and 7. DAPI stains cell nuclei blue, while Phalloidin stains actin-rich cytoskeleton red. Scale bar: 100 μm.