Thermoresponsive and Conductive Chitosan-Polyurethane Biocompatible Thin Films with Potential Coating Application

Abstract

Conductive thin films have great potential for application in the biomedical field. Herein, we designed thermoresponsive and conductive thin films with hydrophilicity, strain sensing, and biocompatibility. The crosslinked dense thin films were synthesized and prepared through a Schiff base reaction and ionic interaction from dialdehyde polyurethane, N-carboxyethyl chitosan, and double-bonded chitosan grafted polypyrrole. The thin films were air-dried under room temperature. These thin films showed hydrophilicity and conductivity (above 2.50 mS/cm) as well as responsiveness to the deformation. The tensile break strength (9.72 MPa to 15.07 MPa) and tensile elongation (5.76% to 12.77%) of conductive thin films were enhanced by heating them from 25 °C to 50 °C. In addition, neural stem cells cultured on the conductive thin films showed cell clustering, proliferation, and differentiation. The application of the materials as a conductive surface coating was verified by different coating strategies. The conductive thin films are potential candidates for surface modification and biocompatible polymer coating.

Keywords: biocompatibility; chitosan; conductive thin film; polymer coating; polyurethane; thermoresponsive.

Figure 1

A schematic representation of the preparation process of the DAPU/CEC/DCP (DCD) thin films and their potential as biocompatible conductive polymer coating. DAPU: dialdehyde polyurethane; CEC: N-carboxyethyl chitosan; DCP: double-bonded chitosan modified polypyrrole.

Figure 2

Scanning electron microscope (SEM) images of the control film and the DCDF film (DCDF2) in top-surface and cross-sectional views.

Figure 3

Water contact angles for the surface of the control group and different DCDFs as a function of time. The data points were an average of five test results. Control group: thin films without DCP. * p < 0.05 and **** p < 0.0001 between the indicated groups.

Figure 4

Thermal properties of the control group and DCDFs by (A) thermogravimetric analysis and (B) differential scanning calorimetry. Control group: thin films without DCP.

Figure 5

Tensile properties of DCDFs and the control group evaluated by DMA and a tensile tester under 25 °C or 50 °C. (A–D) Tensile stress-strain curves of (A) the control group, (B) DCDF1, (C) DCDF2, and (D) DCDF3. Changes of (E) tensile break strength and (F) tensile elongation of all films. * p < 0.05, ** p < 0.01, and *** p < 0.001 between the indicated groups.

Figure 6

Sensing functions of DCDFs under 0.5 V of applied voltage. Changes of the thin film conductivity versus repeated loading weight of 50 g, repeated twisting of 180°, and repeated bending of 90°. Data were obtained from DCDF2.

Figure 7

The morphology of neural stem cells (NSCs) seeded on DCDFs examined using time-lapse recording after pre-incubation for 3 h. NSCs were seeded in 12-well plates (4 × 10⁵ NSCs per well) coated with DCDFs or the control group. The NSCs on DCDFs had obvious aggregation behavior after 4 h, indicated by red circles. Data were obtained from DCDF2. Control group: thin films without DCP.

Figure 8

The proliferation of neural stem cells (NSCs) on DCDFs in a period of 4 days compared with the control group (cells on the thin film without DCP). The data were obtained using the CCK-8 assay. The viability of NSCs was deducted from that of the blank group (the same thin films without cells), normalized to the value at day 0, and expressed as the percentage of cell viability (%). * p < 0.05, ** p < 0.01, and *** p < 0.001 between the indicated groups.

Figure 9

The differentiation of NSCs on DCDFs. The gene expressions of neural-related genes, including (A) Nestin, (B) GFAP, (C) β-tubulin, and (D) MAP2, were analyzed by RT-PCR at 4 days. The expression levels are represented by the relative ratios of gene expression normalized to that of GAPDH. * p < 0.05 between the indicated groups. Control group: thin films without DCP.