Construction and characterization of biomimetic cell membranes on the surface of electrospun conductive nanofiber mats

Cell membranes are utilized by every organism for separation and protection of their contents from external environment. For higher organisms, biological membranes are used for compartmentalization and organelle formation. Understanding the structure and function of the cell membrane is crucial for manipulation of cellular trafficking, signaling pathways, drug delivery/targeting systems and biosensor applications. Biomimetic cell membranes are developed for these purposes with various strategies. One of these strategies is utilization of lipid bilayer membranes. Since the 45-50 % of the cell membrane is composed of lipid structures, lipid bilayer membranes are well suited candidates for their studies. Despite the development of variety of biosensors by immobilization of globular proteins, biosensors based on membrane proteins containing large hydrophobic parts have not been easily produced. When these proteins are incorporated into biomimetic membranes, both their structural integrity and the functionality would be preserved. The objective of this work was to construct a lipid bilayer on a conductive nanofiber mat. Constructed structure was aimed to be used as a model biosensing platform. Polycaprolactone (PCL) nanofiber mats were produced by electrospinning process. These mats were then coated with polypyrrole (PPy) by in situ polymerization method using various monomer concentrations and polymerization durations. Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) and Raman Spectroscopy were used for the analysis of bare PCL and PPy coated PCL structures. Broad N-H bond peak at 3500-2700 cm-1 and N-H in plane deformation peak at 1100 cm-1 were attributed to the PPy structure and it was concluded that polymerization was successfully performed. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) techniques were used for the morphological characterization of nanofibers. Smooth Polycaprolactone fibers with 251.81 nm diameter were obtained by electrospinning. When in situ polymerization performed at low concentration of pyrrole monomer, nanofibers with cauliflower-like structures (453.20 nm) were produced. With the increased Py concentration, PPy layer seemed to cover both the PCL nanofiber surfaces and the pores in between. The thickness and coverage of PPy was increased with the increasing Py monomer concentration and the duration of polymerization process. PCL/PPy electrodes were coated with phosphatidyl choline (PC) liposomes (PCL/PPy/PC) by vesicle fusion method in Phosphate Buffered Saline (PBS). PC liposome covered PCL/PPy mats were observed with SEM micrographs. Electrochemical Impedance Spectroscopy (EIS) and Equivalent Circuit Modelling (ECM) methods were utilized for the determination of electrochemical properties of electrodes. Impedance measurements were carried out between 0.01 Hz and 100 kHz. The charge transfer resistance (Rct) of PCL was highest. Rct of PPy significantly reduced. With increased concentration of PPy, Rct was further reduced. Coverage with PC resulted in an increase in resistance and provides an insulating layer on surface of the electrodes. Total coverage of the electrode surface rather than coverage of only nanofiber surface with PC resulted in better electrochemical properties. The constructed system was aimed to be used for different applications such as integration of membrane proteins and/or detection of different compounds which interact with cell membranes. This system can be further improved by using binary mixture of PC and phosphatidyl serine (PS) lipid for vesicle production.