Amanda R. Murphy

Progress Toward Development of All-Printed RFID Tags: Materials, Processes, and Devices

Printed electronics provides a promising potential pathway toward the realization of ultralow-cost RFID tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials, processes, and devices for the realization of ultralow-cost printed RFID tags. Using printed nanoparticle patterns that are subsequently sintered at plastic-compatible temperatures, low-resistance interconnects and passive components have been realized. Simultaneously, printed transistors with mobilities >10/sup -1/ cm/sup 2//V-s have been realized using novel pentacene and oligothiophene precursors for pMOS and ZnO nanoparticles for nMOS. AC performance of these devices is adequate for 135-kHz RFID, though significant work remains to be done to achieve 13.56-MHz operation.

Modification of silk fibroin using diazonium coupling chemistry and the effects on hMSC proliferation and differentiation

A simple chemical modification method using diazonium coupling chemistry was developed to tailor the structure and hydrophilicity of silk fibroin protein. The extent of modification using several aniline derivatives was characterized using UV-vis and 1H NMR spectroscopies, and the resulting protein structure was analyzed with ATR-FTIR spectroscopy. Introduction of hydrophobic functional groups facilitated rapid conversion of the protein from a random coil to a beta-sheet structure, while addition of hydrophilic groups inhibited this process. hMSCs were grown on these modified silks to assess the biocompatibility of these materials. The hydrophilicity of the silk derivatives was found to affect the growth rate and morphology, but hMSCs were able to attach, proliferate and differentiate into an osteogenic lineage on all of the silk derivatives.

Printable polythiophene gas sensor array for low-cost electronic noses

A route for generating arrays of printable polythiophene-based gas sensor materials suitable for low-cost manufacturing is demonstrated. Materials with complementary sensor responses are synthesized by incorporating functional groups into the molecule, either along the polymer backbone or as end-capping groups. Using these materials as printable sensor inks, a functional, integrated gas sensor array chip is fabricated using additive deposition techniques. The sensor array shows sensitivity to a range of volatile organic compounds down to concentrations of 10ppm. A three-terminal thin film transistor structure is used, allowing the extraction of multiple parameters that help to elucidate the mechanisms responsible for sensor response and the role of the functional groups in this response.

The use of sulfonated silk fibroin derivatives to control binding, delivery and potency of FGF-2 in tissue regeneration.

The development of biomaterials that mimic the physiological binding of growth factors to the extracellular matrix (ECM) is an appealing strategy for advanced growth factor delivery systems. In vivo, fibroblast growth factor 2 (FGF-2) binds to the sulfated glycosaminoglycan heparan sulfate, which is a major component of the ECM. Therefore, we tested whether silk fibroin (SF) decorated with a sulfonated moiety could mimic the natural ECM environment and lead to advanced delivery of this heparin-binding growth factor. Using a diazonium coupling reaction, modified SF derivatives containing approximately 20, 40, 55 and 70 sulfonic acid groups per SF molecule were obtained. Films of the SF derivative decorated with 70 sulfonic acid groups per SF molecule resulted in a 2-fold increase in FGF-2 binding as compared to native SF. More than 99% of bound FGF-2 could be retained on all SF derivatives. However, protection of FGF-2 potency was only achieved with at least 40 sulfonic acid groups per SF molecule, as observed by reduced metabolic activity and enhanced levels of phosphorylated extracellular signal-regulated kinases (pERK1/2) in cultured human mesenchymal stem cells (hMSCs). This study introduces a first step towards the development of an ECM-mimicking biomaterial for sustained, non-covalent binding, controlled delivery and preserved potency of biomolecules.

Enhancing the interface in silk-polypyrrole composites through chemical modification of silk fibroin.

To produce conductive, biocompatible, and mechanically robust materials for use in bioelectrical applications, we have developed a new strategy to selectively incorporate poly(pyrrole) (Ppy) into constructs made from silk fibroin. Here, we demonstrate that covalent attachment of negatively charged, hydrophilic sulfonic acid groups to the silk protein can selectively promote pyrrole absorption and polymerization within the modified films to form a conductive, interpenetrating network of Ppy and silk that is incapable of delamination. To further increase the conductivity and long-term stability of the Ppy network, a variety of small molecule sulfonic acid dopants were utilized and the properties of these silk-conducting polymer composites were monitored over time. The composites were evaluated using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), optical microscopy, energy-dispersive X-ray (EDX) spectroscopy, cyclic voltammetry, a 4-point resistivity probe and mechanical testing. In addition, the performance was evaluated following exposure to several biologically relevant enzymes. Using this strategy, we were able to produce mechanically robust polymer electrodes with stable electrochemical performance and sheet resistivities on the order of 1 × 10(2) Ω/sq (conductivity ∼1 S/cm).

Curcumin-functionalized silk materials for enhancing adipogenic differentiation of bone marrow-derived human mesenchymal stem cells

Curcumin, a natural phenolic compound derived from the plant Curcuma longa, was physically entrapped and stabilized in silk hydrogel films, and its influence on human bone marrow-derived mesenchymal stem cells (hBMSC) was assessed related to adipogenic differentiation. The presence of curcumin significantly reduced the silk gelation time and changed the porous morphology of gel matrix, but did not change the formation of the silk beta-sheet structure. Based on spectrofluorimetric analysis, curcumin most likely interacted with hydrophobic residues in silk, interacting with the beta-sheet domains formed in the hydrogels. The antioxidant activity of silk film-associated curcumin remained functional over at least one month in both the dry and hydrated state. Negligible curcumin was released from silk hydrogel films over 48 h incubation in aqueous solution. For hBMSC cultured on silk films containing more than 0.25 mg ml(-1) curcumin, cell proliferation was inhibited, while adipogenesis was significantly promoted based on transcripts as well as Oil Red O staining. When hBMSC were cultured in media containing free curcumin, both proliferation and adipogenesis of hBMSC were inhibited when curcumin concentrations exceeded 5 μM, which is more than 1000 times higher than the level of curcumin released from the films in aqueous solution. Thus, silk film-associated curcumin exhibited different effects on hBMSC proliferation and differentiation compared with curcumin in solution.

Inkjetted crystalline single monolayer oligothiophene OTFTs

Crystalline monolayer films of a novel organic semiconducting material were deposited as the active layer for organic thin-film transistors (OTFTs) via inkjet printing. Devices exhibited field-effect mobilities up to 0.07 cm/sup 2//V/spl middot/s and on/off ratios >10/sup 8/, surpassing values measured for devices cast with thicker films of the same material. The printed monolayer devices exhibited superior subthreshold characteristics with less hysteresis, and defect and trap densities are improved over thicker film analogs. These results show that solution deposition techniques such as inkjet printing can result in the monolayer crystalline thin films that are requisite for near-ideal electrostatics in OTFTs.

Versatile Method for Producing 2D and 3D Conductive Biomaterial Composites Using Sequential Chemical and Electrochemical Polymerization.

Flexible and conductive biocompatible materials are attractive candidates for a wide range of biomedical applications including implantable electrodes, tissue engineering, and controlled drug delivery. Here, we demonstrate that chemical and electrochemical polymerization techniques can be combined to create highly versatile silk-conducting polymer (silk-CP) composites with enhanced conductivity and electrochemical stability. Interpenetrating silk-CP composites were first generated via in situ deposition of polypyrrole during chemical polymerization of pyrrole. These composites were sufficiently conductive to serve as working electrodes for electropolymerization, which allowed an additional layer of CP to be deposited on the surface. This sequential method was applied to both 2D films and 3D sponge-like silk scaffolds, producing conductive materials with biomimetic architectures. Overall, this two-step technique expanded the range of available polymers and dopants suitable for the synthesis of mechanically robust, biocompatible, and highly conductive silk-based materials.

Sustained Delivery of Chemokine CXCL12 from Chemically Modified Silk Hydrogels

A delivery platform was developed using silk-based hydrogels, and sustained delivery of the cationic chemokine CXCL12 at therapeutically relevant doses is demonstrated. Hydrogels were prepared from plain silk and silk that had been chemically modified with sulfonic acid groups. CXCL12 was mixed with the silk solution prior to gelation, resulting in 100% encapsulation efficiency, and both hydrated and lyophilized gels were compared. By attaching a fluorescein tag to CXCL12 using a site-specific sortase-mediated enzymatic ligation, release was easily quantified in a high-throughput manner using fluorescence spectroscopy. CXCL12 continually eluted from both plain and acid-modified silk hydrogels for more than 5 weeks at concentrations ranging from 10 to 160 ng per day, depending on the gel preparation method. Notably, acid-modified silk hydrogels displayed minimal burst release yet had higher long-term release rates compared to those of plain silk hydrogels. Similar release profiles were observed over a range of loading capacities, allowing dosage to be easily varied.

Single-monolayer inkjetted oligothiophene organic TFTs exhibiting high performance and low leakage

Through the use of a novel oligothiophene precursor, we have demonstrated organic TFTs exhibiting relatively high mobility while simultaneously retaining ultra-low leakage and excellent on-off ratios. The unique tendency of this material to self-assemble into a crystalline morphology allows non-uniform printed droplets to reorganize into high-quality monolayers. The resulting structure provides excellent electrostatic characteristics, ideal for low power analog applications.