Multiphoton Lithography of Organic Semiconductor Devices for 3D Printing of Flexible Electronic Circuits, Biosensors, and Bioelectronics.

In recent years, 3D printing of electronics have received growing attention due to their potential applications in emerging fields such as nanoelectronics and nanophotonics. Multiphoton lithography (MPL) is considered the state-of-the-art amongst the microfabrication techniques with true 3D fabrication capability owing to its excellent level of spatial and temporal control. Here, a homogenous and transparent photosensitive resin doped with an organic semiconductor material (OS), which is compatible with MPL process, is introduced to fabricate a variety of 3D OS composite microstructures (OSCMs) and microelectronic devices. Inclusion of 0.5 wt% OS in the resin enhances the electrical conductivity of the composite polymer about 10 orders of magnitude and compared to other MPL-based methods, the resultant OSCMs offer high specific electrical conductivity. As a model protein, laminin is incorporated into these OSCMs without a significant loss of activity. The OSCMs are biocompatible and support cell adhesion and growth. Glucose-oxidase-encapsulated OSCMs offer a highly sensitive glucose sensing platform with nearly tenfold higher sensitivity compared to previous glucose biosensors. In addition, this biosensor exhibits excellent specificity and high reproducibility. Overall, these results demonstrate the great potential of these novel MPL-fabricated OSCM devices for a wide range of applications from flexible bioelectronics/biosensors, to nanoelectronics and organ-on-a-chip devices.

Femtosecond Laser 3D-printing of Conductive Microelectronics for Potential Biomedical Applications.

Development of soft and conductive micro devices represents a demanding research topic in various biomedical applications, particularly organic bioelectronics. Among various fabrication methods, two-photon polymerization (2PP) using a wide range of photocurable inks is a promising 3D printing technique for construction of structures in submicron resolution. Herein, we introduce a novel conductive photosensitive resin by using poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and poly(ethylene glycol) diacrylate), and fabricate 3D conductive polymeric microstructures via 2PP. In the developed resin, presence of PEDOT:PSS significantly enhances the electrical conductivity of microstructures (~ 10 orders of magnitude).Clinical Relevance- Conductive microdevices based on the PEDOT:PSS-doped resin open new avenues in a broad range of biomedical research areas including neural interfaces, biosensors, and bioelectronics.

Electrospinning of Highly Aligned Fibers for Drug Delivery Applications.

Electrospinning is a straightforward, cost-effective, and versatile technique for fabrication of polymeric micro/nanofibers with tunable structural properties. Controlling the size, shape, and spatial orientation of the electrospun fibers is crucial for utilization in drug delivery and tissue engineering applications. In this study, for the first time, we systematically investigate the effect of processing parameters, including voltage, syringe needle gauge, angular velocity of rotating wheel, syringe-collector distance, and flow rate on the size and alignment of electrospun PLGA fibers. Optimizing these parameters enabled us to produce highly aligned and monodisperse PLGA fibers (spatial orientation> 99% and coefficient of variation< 0.5). To assess the effect of fiber alignment on the release of encapsulated drugs from these fibers, we incorporated dexamethasone, an anti-inflammatory drug, within highly-aligned and randomly-oriented fibers with comparable diameters (~0.87 µm) and compared their release profiles. In-vitro release studies revealed that the aligned fibers had less burst release (~10.8% in 24 hr) and more sustained release (~8.8% average rate of change for 24 days) compared to the random fibers. Finally, the degradation modes of the aligned and random fibers after 25 days incubation were characterized and compared. The findings of this study can be applied for the development of 3D degradable aligned fibers for controlled drug release and tissue engineering applications.

Aligned Conducting Polymer Nanotubes for Neural Prostheses.

The long-term performance of neural microelectrodes relies on biocompatibility and sensitivity of the electrode-tissue interface. Current neural electrodes are limited by poor electrical performance including high initial impedance and low charge storage capacity. In addition, they are mechanically hard which causes cellular reactive response to the implanted electrode. In this report, we have demonstrated a new templating method for fabrication of highly aligned conducting polymer nanotube. The structure of nanotubes can be precisely modulated by varying the time of electropolymerization. The electrical performance of poly(pyrrole) (PPY) and poly(3,4-ethylenedioxythiophine) (PEDOT) nanotubes including impedance and charge storage capacity were studied and compared as the surface morphology and structure of nanotube varied during the fabrication process. PEDOT nanotubes were found to have lower impedance than PPY nanotubes. By contrast, PPY nanotubes were shown to have higher charge storage capacity. These finding suggest that aligned conducting polymer nanotubes may enhance the long-term performance of neural microelectrodes.

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.

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.