Polyurethane/poly(vinyl alcohol) hydrogel coating improves the cytocompatibility of neural electrodes

Abstract

Neural electrodes, the core component of neural prostheses, are usually encapsulated in polydimethylsiloxane (PDMS). However, PDMS can generate a tissue response after implantation. Based on the physicochemical properties and excellent biocompatibility of polyurethane (PU) and poly(vinyl alcohol) (PVA) when used as coating materials, we synthesized PU/PVA hydrogel coatings and coated the surface of PDMS using plasma treatment, and the cytocompatibility to rat pheochromocytoma (PC12) cells was assessed. Protein adsorption tests indicated that the amount of protein adsorption onto the PDMS substrate was reduced by 92% after coating with the hydrogel. Moreover, the PC12 cells on the PU/PVA-coated PDMS showed higher cell density and longer and more numerous neurites than those on the uncoated PDMS. These results indicate that the PU/PVA hydrogel is cytocompatible and a promising coating material for neural electrodes to improve their biocompatibility.

Keywords: cerebral injury; cytocompatibility; hydrogel coatings; nerve growth factor; nerve regeneration; neural electrodes; neural regeneration; poly(vinyl alcohol); polydimethylsiloxane; polyurethane; protein adsorption; rat pheochromocytoma cells; synaptic differentiation.

Figure 1

Schematic diagram of the polyurethane/poly(vinyl alcohol) (PU/PVA) synthesis. (a) Polyurethane (PU) prepolymers were formed using the polymerization reaction between polyethylene glycol and isophorone diisocyanate. (b) PU/PVA formation by cross-linking reactions between PU prepolymers and poly(vinyl alcohol) (PVA).

Figure 2

Fourier transform-infrared spectra of the poly(vinyl alcohol) (PVA), polyurethane/poly(vinyl alcohol) (PU/PVA), and polyurethane (PU) films. In the PU/PVA spectrum, the -OH absorption peak at 3,330 cm⁻¹ was clearly decreased compared with that in the PVA spectrum, while the absorption peaks of C-O-C at 1,106 cm⁻¹ and N-H from carbamates at 1,541 cm⁻¹ were increased.

Figure 3

Fibrinogen adsorption on polydimethylsiloxane (PDMS), polyurethane/poly (vinyl alcohol) (PU/PVA)-coated PDMS, and polyurethane (PU)-coated PDMS films. Data are expressed as the mean ± SEM of n = 3 wells, and comparisons were made with one-way analysis of variance followed by Student-Newman-Keuls post hoc analysis. The amount of nonspecific protein adsorption was 442.67 ng/cm² on the surface of the PDMS, while fibrinogen adsorption was decreased to 36.67 ng/cm² on the PU/ PVA-coated PDMS surfaces (a reduction of ~92 %) and to 32 ng/cm² on the PU-coated PDMS surfaces. PU/PVA: PU/PVA-coated PDMS group; PU: PU-coated PDMS group.

Figure 4

Representative 4′6-diamidino-2-phenylindole (DAPI)-stained fluorescent images of the PC12 cells cultured on different materials. PC12 cells were cultured on polydimethylsiloxane (PDMS) films (A), polyurethane (PU)-coated PDMS films (B), polyurethane/poly(vinyl alcohol) (PU/PVA)-coated PDMS films (C), and tissue culture plates (TCP) (D), as a control. Scale bars: 100 μm. The PC12 cells on the PDMS films were more aggregated and at a lower density per area unit compared with those on the PU- and PU/PVA-coated PDMS films. (E) Quantitative comparison of the cell density on different materials. **P < 0.01, vs. PDMS, ##P < 0.01, vs. TCP (mean ± SEM, n = 16 wells, one-way analysis of variance followed by Student-Newman-Keuls post hoc analysis). The experiment was performed in triplicate. PU/PVA: PU/ PVA-coated PDMS films; PU: PU-coated PDMS films.

Figure 5

Representative calcein AM-stained fluorescent images of the PC12 cells cultured on different materials. The PC12 cells were cultured on polydimethylsiloxane (PDMS) films (A), polyurethane (PU)-coated PDMS films (B), polyurethane/poly(vinyl alcohol) (PU/PVA)-coated PDMS films (C), and tissue culture plates (TCP) (D) in the presence of 50 ng/mL nerve growth factor for 7 days. Scale bars: 50 μm The PC12 cells exhibited better neurite extension and formed an interconnected neurite network on the surface of the PU/PVA-coated PDMS films, but not on the uncoated PDMS films. Quantitative comparisons of the neurite number per cell (E) and neurite length per cell (F) on the different samples. *P < 0.05 and **P < 0.01, vs. PDMS; #P < 0.05 and ##P < 0.01, vs. TCP (mean ± SEM, n = 16 wells, one-way analysis of variance followed by Student-Newman-Keuls post hoc analysis). The experiment was performed in triplicate. PU/PVA: PU/PVA-coated PDMS films; PU: PU-coated PDMS films.