Y28 - Surface-engineerable Piezoelectric PVDF Films​ for Next Generation Tissue Engineering

Introduction: : We present an engineered piezoelectric polymer for enhanced cell adhesion. The beta phase of poly (vinylidene fluoride), known as PVDF, generates an additive dipole moment due to the trans-planar structure of the fluorine atoms within the film, which may impact the cell adhesion when contacted (Figure 1). We sought to engineer the surface of PVDF films in a way that the beta phase can be realized regionally through patternable poling. We hypothesize that patternable beta-phase configuration within the poled film can enhance surface charge density, resulting in control over cell adhesion.

We test this effect on the cell adhesion of neuroblastoma (SH-SY5Y) and Fibroblast (NIHT3T) cell lines to the surface of the film. Through a simple poling process, the smooth surface PVDF can exhibit altered cell attachment and growth between poled and unpoled regions. Specifically, beta-phase regions tend to see higher cell attachment and growth, while alpha-phase regions observe the opposite trend. The proposed surface - engineered piezoelectric polymer (PVDF) enables highly controllable and patternable cell adhesion and proliferation by inducing cell manipulation due to electrical charge on surfaces controlled through patterned poling. When four different variants of the surface-engineered PVDF films (unpoled, poled, line poled, and angle poled) were tested in static culture conditions, mature cell adhesion occurred following the poled regions (Figure 3).

Materials and

Methods: : The PVDF solution was prepared by adding 1 g of PVDF powder to 8 mL of Acetone while stirring at 600 RPM at 85 °C for 10 min before adding 4 mL of Dimethyl sulfoxide and mixing for 45 min. A pre-cut silicon wafer (4 x 4 cm2) was used as a substrate to spin coat 2 mL of PVDF solution in a two-step process of 500RPM for 5 seconds followed by 5000RPM for 15 seconds. The PVDF was then soft baked for 2 hours at 85 degrees Celsius.

The electrical poling of the PVDF was achieved by applying a voltage of 333kV/mm, while heating to 40 °C for 20min. For the design poled (e.g., line and angled) samples, a square cross-section copper wire with a width of 0.5mm was used to define the poling regions. The wire was positioned such that it served as the sole electrical contact during the poling process.

The PVDF was trimmed to fit 24-well plates for in vitro assays. The films were sterilized using 70% ethanol supplemented with penicillin and streptomycin for 10 min per cycle, repeated over three consecutive cycles. This was followed by three cycles of DPBS washes and air drying. After sterilization and washing, neuroblast (SH-SY5Y) and Fibroblast (NIHT3T) cells were seeded on the films directly at a density of 1 x 10^5 cells per well. The films were imaged every day over the following 7 days. For cell adhesion analysis, F-actin was used along with DAPI staining on day 7.

Results, Conclusions, and Discussions:: Surface morphology across all groups was comparable, and the average thickness of the fabricated PVDF films was approximately 6 µm (Figure 2). Microscopic images captured on day 1 revealed that beta-phase activated PVDF film effectively guided cell adhesion and proliferation, whereas nonpolarized counterparts exhibited minimal attachment. Notably, patterned poling directed cellular alignment along the polarized pathways, highlighting its potential for controlled tissue formation. This trend was found to have higher concentrations of cell attachment and proliferation on poled regions than unpoled regions over the 7-day testing period. F-actin/nuclei staining on day 7 further confirmed healthy cell adhesion in polarized PVDF films, with minimal adhesion observed on nonpolarized surfaces (Figure 3). These findings demonstrate that patterned poling on piezoelectric PVDF films enables directed tissue growth, facilitating precise cellular alignment and scaffold integration for functional tissue engineering, such as in tissue-engineered bio-prosthetic heart valves.

Acknowledgements and/or References (Optional):: The authors would like to thank Dr. Meisam Asgari for his help in the physical characterization of the PVDF films.