Direct Measurement of Mass Transport in Actuation of Conducting Polymers Nanotubes.

Nanostructured Conducting polymer (CP) actuators are promising materials for biomedical applications such as drug release systems. However, understanding the actuation behavior at the nano-scale has not yet been explored. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) nanotubes doped with a large counter ion (i.e. poly(styrene sodium sulfonate) (PSS)) were fabricated using electrochemical deposition of PEDOT and PPy around poly(L-lactide) (PLLA) nanofiber templates, followed by template removal in chloroform. The actuation and mass transport behavior of PPy and PEDOT nanotubes were investigated and compared. The nanotubes were subjected to a redox process using cyclic voltammetry in 0.1M NaPSS electrolyte solution as the potential swept between -0.8 V and +0.4 V for 20 cycles at 10, 50, 100, and 200 mV/s scan rates. The mass transport behavior of these nanotubes was characterized via electrochemical quartz crystal microbalance (EQCM) technique. The EQCM results showed that PEDOT nanotubes had a higher mass exchange capability than their PPy counterparts, especially at higher scan rates. Also, it was revealed that PPy nanotubes were more sensitive to the scan rate than the PEDOT nanotubes, and the maximum mass exchange capability of the PPy nanotubes was noticeably reduced by increasing the scan rate.

Conducting polymer microcontainers for biomedical applications.

Advancement in the development of metallic-based implantable micro-scale bioelectronics has been limited by low signal to noise ratios and low charge injection at electrode-tissue interfaces. Further, implantable electrodes lose their long-term functionality because of unfavorable reactive tissue responses. Thus, substantial incentive exists to produce bioelectronics capable of delivering therapeutic compounds while improving electrical performance. Here, we have produced hollow poly(pyrrole) microcontainers (MCs) using poly(lactic-co-glycolic) acid (PLGA) as degradable templates. We demonstrate that the effective surface area of the electrode increases significantly as deposition charge density is increased, resulting in a 91% decrease in impedance and an 85% increase in charge storage capacity versus uncoated gold electrodes. We also developed an equivalent circuit model to quantify the effect of conducting polymer film growth on impedance. These MC-modified electrodes offer the potential to improve the electrical properties of implantable bioelectronics, as well as provide potential controlled release avenues for drug delivery applications.

Tunable nanostructured conducting polymers for neural interface applications.

Advancement in the development of traditional metallic-based implantable electrodes for neural interfacing has reached a plateau in recent years in terms of their ability to provide safe, long-term, and high resolution stimulation and/or recording. The reduction of electrode size enables higher selectivity through increased electrodes per implant device; however, it also results in lower sensitivity at electrode-tissue interfaces. This limitation can be addressed through the utilization of conducting polymer (CP) coatings, which increase the effective surface area. In this work, we investigate the surface roughness of two common conducting polymers; poly(pyrrole) (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) in the form of films deposited using both potentiostatic (PSTAT) and galvanostatic (GSTAT) methods. We found that the surface roughness of both CP films can be increased by over 90% through control of both deposition time and applied electrical deposition (current for GSTAT and voltage for PSTAT). The impedance of PPy-modified electrodes was found to decrease by up to 88%. This study shows that the surface roughness of CPs can be modulated to control electrical properties of neural electrodes and may improve the cellular response of neurons.

Conducting Polymer Microcups for Organic Bioelectronics and Drug Delivery Applications.

An ideal neural device enables long-term, sensitive, and selective communication with the nervous system. To accomplish this task, the material interface should mimic the biophysical and the biochemical properties of neural tissue. By contrast, microfabricated neural probes utilize hard metallic conductors, which hinder their long-term performance because these materials are not intrinsically similar to soft neural tissue. This study reports a method for the fabrication of monodisperse conducting polymer microcups. It is demonstrated that the physical surface properties of conducting polymer microcups can be precisely modulated to control electrical properties and drug-loading/release characteristics.

Graphical analysis of mammalian cell adhesion in vitro.

Short-term (<2h) cell adhesion kinetics of 3 different mammalian cell types: MDCK (epithelioid), MC3T3-E1 (osteoblastic), and MDA-MB-231 (cancerous) on 7 different substratum surface chemistries spanning the experimentally-observable range of water wettability (surface energy) are graphically analyzed to qualitatively elucidate commonalities and differences among cell/surface/suspending media combinations. We find that short-term mammalian cell attachment/adhesion in vitro correlates with substratum surface energy as measured by water adhesion tension, τ≡γlvcosθ, where γlv is water liquid-vapor interfacial energy (72.8 mJ/m2) and cosθ is the cosine of the advancing contact angle subtended by a water droplet on the substratum surface. No definitive functional relationships among cell-adhesion kinetic parameters and τ were observed as in previous work, but previously-observed general trends were reproduced, especially including a sharp transition in the magnitude of kinetic parameters from relatively low-to-high near τ=0mJ/m2, although the exact adhesion tension at which this transition occurs is difficult to accurately estimate from the current data set. We note, however, that the transition is within the hydrophobic range based on the τ=30mJ/m2 surface-energetic dividing line that has been proposed to differentiate "hydrophobic" surfaces from "hydrophilic". Thus, a rather sharp hydrophobic/hydrophilic contrast is observed for cell adhesion for disparate cell/surface combinations.

Mammalian cell-adhesion kinetics measured by suspension depletion.

Mammalian cell-adhesion kinetics is measured by counting the number of cells lost from suspension due to adhesion to planar or particulate substrata as a function of time rather than by the counting of adherent cells that is widely applied in the literature. A simple statistical model shows that this "suspension-depletion" method is most accurate at low cell counts in the critical early stage of cell adhesion that is diagnostic of forces in close proximity between cell and substratum responsible for cell adhesion. Furthermore, suspension depletion avoids experimental artifacts associated with substratum rinsing and the removal of cells from the substratum using enzymatic and/or mechanical methods. Experimental method is demonstrated for three different cell types (MDCK, epithelioid; MC3T3-E1, pre-osteoblast; MDA-MB-231, human breast tumor) adhering to seven different substrata incrementally sampling the observable water-wettability range in Petri-dish format, as well as MDCK adhesion to particulate carriers in stirred suspension. Suspension depletion is ideal for biocompatibility and fouling studies where quantification of "low-and-slow" cell adhesion is important. In particular, it is shown that a typical method of counting adherent cells does not correctly measure adhesion kinetics to hydrophobic surfaces that are generally resistant to mammalian cell adhesion.