Electroactive poly(sulfobetaine-3,4-ethylenedioxythiophene) (PSBEDOT) with controllable antifouling and antimicrobial properties† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc03887a

A multifunctional zwitterionic PSBEDOT material, which can switch between antifouling and antimicrobial states by controlling the potential of the surface, is synthesized.


Chemicals and general instrumentation
Electro-polymerization and other electrochemical characterizations were performed on a Solartron Modulab XM ECS test system or a Gamry Reference 600 potentiostat. XPS spectra were obtained from a PHI VersaProbe II Scanning XPS Microprobe. All NMR experiments were performed at 303.2 K unless stated otherwise and on Varian Mercury 300 MHz spectrometers.

Synthetic procedures
Chloromethyl-EDOT was first synthesized following a method published previously. 1 Figure S4. 13 C spectrum of SBEDOT

Electropolymerization was performed on a Solartron Modulab XM ECS test system or a Gamry
Reference 600 potentiostat equipped with a three-electrode electrochemical set-up, using a Pt electrode as the counter electrode and an Hg/HgCl 2 electrode (sat. KCl) as the reference electrode. One of the great advantages of this SBEDOT monomer is it could be directly polymerized in aqueous solution, which significantly facilitates its future applications in vivo.
SBEDOT was polymerized on either ITO coated PET films or Gold coated SPR sensor chips

X-Ray photoelectron spectroscopy (XPS) study
XPS was also used to examine the composition profile of electropolymerized PSBEDOT film, using a PHI VersaProbe II Scanning XPS Microprobe. All data processing were performed using the software provided with the instrument. The PSBEDOT samples were run for both the survey and the high resolution spectra. The survey spectra of PEDOT sample was used for comparison.
All data processing were performed using the software provided with the instrument. Peak areas, line shapes, and intensities of C 1s, O 1s, N 1s and S 2p high resolution spectra were monitored.
As shown in Figure S6, The atomic ratios were in agreement with molecular compositions. From the S 2p high resolution spectra of PSBEDOT, two types of S were observed with equivalent peak intensity, indicating its elemental and chemical composition was exactly the same as expected. Figure S6. The XPS profiles of PSBEDOT coating. Survey spectrum (left), high-resolution spectrum of S 2p (right).

Electrochemical characterization of PSBEDOT
Electrochemical impedance spectroscopy (EIS) and Cyclic Voltammetry (CV) were performed in PBS using a Gamry Reference 600 potentiostat in PBS buffer. Stability measurement of PSBEDOT film was carried out with CV (-0.3 V to 0.6 V). Although PSBEDOT was hydrophilic, it showed excellent stability in aqueous solution, even after applying a potential sweep for over 500 cycles ( Figure S7). The PSBEDOT films for measurements were coated on gold coated SPR sensor chips. For EIS, the frequencies were spaced from 10 kHz to 1 Hz with a S7 low amplitude voltage (~10 mV). Before EIS experiment, samples were equilibrated in PBS buffer for 10 minutes. Potentiodynamic study of PSBEDOT film was recorded with CV, from -0.8 V to 1.0 V, at different scan rates of 10, 20, 50, 100, 200 mv/s. Figure S7. Cyclic voltammograms of PSBEDOT film at different scan rate.

BAEC and NIH-3T3 cell adhesion study
Bovine aorta endothelial cell (BAEC) and NIH3T3 were purchased from American Type Culture Collection (Manassas, MD, USA). Cell attachment study was carried out following a similar procedure to that used in a previous work. PSBEDOT and PEDOT was electro-deposited on ITO coated PET substrates, then equilibrated in DI-water for 24 hours and transferred to sterilized PBS. All samples were exposed under UV for half an hour before the cell adhesion experiment.
BAECs and NIH3T3 were separately seeded on different substrates at 10 5 cells/mL with DMEM medium consisting of DMEM, 10% fetal bovine serum (FBS), and 1% penicillin-streptomycin and kept in an incubator with 5% CO 2 at 37 o C for 24 hours. After the incubation, medium was S8 removed from the wells. After very gently rinsed with sterilized PBS, it was changed to the staining solution that prepared in sterilized PBS as follows. Fluorescein diacetate was dissolved at a concentration of 10 mg mL -1 in acetone, then 50 μL of the solution was diluted in 10 mL sterilized PBS and used for staining the cells. After incubated for 5 min with the staining solution, surface cell coverage and cell morphology was visualized and imaged with an Olympus IX81 fluorescence microscope (Olympus, Japan) equipped with a FITC filter at 4× or 10× magnification.

Protein adsorption study -SPR
A custom-built four-channel SPR sensor was used to measure protein adsorption on PSBEDOT surface. Firstly, PBS solution at a 50 μL min -1 flow rate was used to obtain a baseline signal. 100% human blood plasma and 30% diluted human blood serum were then injected into different channels for 10 minutes followed by a PBS wash to remove any loosely bound proteins. The amount of adsorbed proteins was calculated as the change in wavelength before and after protein injection.

Bacterial adhesion, antimicrobial and releasing study
The method for evaluating the antibacterial efficiency of polymer surfaces was modified from a previously published method 2 . E. coli K12 was first cultured in separate pure cultures overnight at 37 o C on Luria-Bertani (LB) agar plates. One colony was used to inoculate 5 mL of LB medium (20 g/L). These initial cultures were incubated at 37 o C with shaking at 200 rpm for 12 hours. This culture was then used to inoculate a second culture in 25 mL of LB medium.
When the second suspended culture reached an optical density of 0.8 at 600 nm, bacteria were collected by centrifugation at 8,000 x g for 10 min at 4 o C. Cell pellets were washed three times S10 with sterile PBS (pH 7.4) and subsequently suspended in PBS to get a final concentration of 10 9 cells/mL.

Bacterial attachment study
Before the bacterial attachment study, PSBEDOT coated Au substrates was equilibrated under 0.6 V and 0 V in PBS for 20 minutes to obtain surface at the oxidized state and reduced state respectively. A 0.1 mL suspension of E. coli at a concentration of10 9 cells/mL was pipetted onto each PSBEDOT coated Au substrate and then covered with a glass cover slip. The sample was incubated at room temperature for 1 hour. The cover slide was removed and the sample was