Leila F. Deravi

The structure–function relationships of a natural nanoscale photonic device in cuttlefish chromatophores

Cuttlefish, Sepia officinalis, possess neurally controlled, pigmented chromatophore organs that allow rapid changes in skin patterning and coloration in response to visual cues. This process of adaptive coloration is enabled by the 500% change in chromatophore surface area during actuation. We report two adaptations that help to explain how colour intensity is maintained in a fully expanded chromatophore when the pigment granules are distributed maximally: (i) pigment layers as thin as three granules that maintain optical effectiveness and (ii) the presence of high-refractive-index proteins—reflectin and crystallin—in granules. The latter discovery, combined with our finding that isolated chromatophore pigment granules fluoresce between 650 and 720 nm, refutes the prevailing hypothesis that cephalopod chromatophores are exclusively pigmentary organs composed solely of ommochromes. Perturbations to granular architecture alter optical properties, illustrating a role for nanostructure in the agile, optical responses of chromatophores. Our results suggest that cephalopod chromatophore pigment granules are more complex than homogeneous clusters of chromogenic pigments. They are luminescent protein nanostructures that facilitate the rapid and sophisticated changes exhibited in dermal pigmentation.

Differential Contributions of Conformation Extension and Domain Unfolding to Properties of Fibronectin Nanotextiles

Fibronectin (FN) textiles are built as nanometer-thick fabrics. When uniaxially loaded, these fabrics exhibit a distinct threshold between elastic and plastic deformation with increasing stretch. Fabric mechanics are modeled using an eight-chain network and two-state model, revealing that elastic properties of FN depend on conformational extension of the protein and that plastic deformation depends on domain unfolding. Our results suggest how the molecular architecture of a molecule can be exploited for designer mechanical properties of a bulk material.

Self-Organizing Large-Scale Extracellular-Matrix Protein Networks

S. Ahn, Prof. K. Shin Department of Chemistry and Institute of Biological Interfaces Sogang University Seoul 121-742 , Republic of Korea E-mail: kwshin@sogang.ac.kr Dr. L. F. Deravi, Dr. S.-J. Park, B. E. Dabiri, Prof. K. K. Parker Disease Biophysics Group Harvard School of Engineering and Applied Sciences Cambridge , MA 02138 , USA E-mail: kkparker@seas.harvard.edu Prof. J.-S. Kim Department of Polymer Science and Engineering and BK21 Education Center of Mould Technology for Advanced Materials and Parts Chosun University Gwangju 501-759 , Republic of Korea

A Printed Superoxide Dismutase Coated Electrode for the Study of Macrophage Oxidative Burst

The miniaturization of electrochemical sensors allows for the minimally invasive and cost effective examination of cellular responses at a high efficacy rate. In this work, an ink-jet printed superoxide dismutase electrode was designed, characterized, and utilized as a novel microfluidic device to examine the metabolic response of a 2D layer of macrophage cells. Since superoxide production is one of the first indicators of oxidative burst, macrophage cells were exposed within the microfluidic device to phorbol myristate acetate (PMA), a known promoter of oxidative burst, and the production of superoxide was measured. A 46 ± 19% increase in current was measured over a 30 min time period demonstrating successful detection of sustained macrophage oxidative burst, which corresponds to an increase in the superoxide production rate by 9 ± 3 attomoles/cell/s. Linear sweep voltammetry was utilized to show the selectivity of this sensor for superoxide over hydrogen peroxide. This novel controllable microfluidic system can be used to study the impact of multiple effectors from a large number of bacteria or other invaders along a 2D layer of macrophages, providing an in vitro platform for improved electrochemical studies of metabolic responses.

Output analysis of materials inkjet printer

Piezoelectric inkjet printing was used to deposit single spot microarrays onto Au-coated quartz crystals or SiN3 substrates in air. Composite solutions of nanospheres, carbon nanotubes, and colloidal silver were printed, and their properties were quantitated. The average weight of one spot of each deposited material was determined directly using a quartz crystal microbalance. The calculated weight was used in conjunction with density to estimate the average volume of a single spot of each deposited material. It was shown that inkjet printing reproducibly formed sub-15pl spots, suggesting this deposition method to be highly reproducible for rapid, small-scale fabrication of microarrays.

Color Richness in Cephalopod Chromatophores Originating from High Refractive Index Biomolecules.

Cephalopods are arguably one of the most photonically sophisticated marine animals, as they can rapidly adapt their dermal color and texture to their surroundings using both structural and pigmentary coloration. Their chromatophore organs facilitate this process, but the molecular mechanism potentiating color change is not well understood. We hypothesize that the pigments, which are localized within nanostructured granules in the chromatophore, enhance the scattering of light within the dermal tissue. To test this, we extracted the phenoxazone-based pigments from the chromatophore and extrapolated their complex refractive index (RI) from experimentally determined real and approximated imaginary portions of the RI. Mie theory was used to calculate the absorbance and scattering cross sections (cm2/particle) across a broad diameter range at λ = 589 nm. We observed that the pigments were more likely to scatter attenuated light than absorb it and that these characteristics may contribute to the color richness of cephalopods.

Contributions of Phenoxazone-Based Pigments to the Structure and Function of Nanostructured Granules in Squid Chromatophores.

Understanding the structure-function relationships of pigment-based nanostructures can provide insight into the molecular mechanisms behind biological signaling, camouflage, or communication experienced in many species. In squid Doryteuthis pealeii, combinations of phenoxazone-based pigments are identified as the source of visible color within the nanostructured granules that populate dermal chromatophore organs. In the absence of the pigments, granules experience a reduction in diameter with the loss of visible color, suggesting important structural and functional features. Energy gaps are estimated from electronic absorption spectra, revealing highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energies that are dependent upon the varying carboxylated states of the pigment. These results implicate a hierarchical mechanism for the bulk coloration in cephalopods originating from the molecular components confined within in the nanostructured granules of chromatophore organs.

Design and fabrication of bio-hybrid materials using inkjet printing

The integration of biomolecules such as proteins, carbohydrates, or enzymes into functional materials, whether through physical or chemical coupling, remains a critical processing step in the fabrication of engineered biosensors or tissue scaffolds, where anisotropy and composition can directly impact material function and host integration. A means to achieve these features is through the selective patterning of biomolecules, which is used to recruit and direct cell growth in vitro. The authors describe the design of protein-based materials using inkjet printing and discuss how fluid physical properties of the formulated inks influence pattern formation and material performance. When interfaced with carbon nanotubes, the biohybrid films retain their chemical signature but with enhanced structural stability and electrical conductivity over time. These structures also support the adhesion and proliferation of human dermal fibroblasts. Together, these properties demonstrate the utility of printed biohybrid f...

A Method for Extracting Pigments from Squid Doryteuthis pealeii

Cephalopods can undergo rapid and adaptive changes in dermal coloration for sensing, communication, defense, and reproduction purposes. These capabilities are supported in part by the areal expansion and retraction of pigmented organs known as chromatophores. While it is known that the chromatophores contain a tethered network of pigmented granules, their structure-function properties have not been fully detailed. We describe a method for isolating the nanostructured granules in squid Doryteuthis pealeii chromatophores and demonstrate how their associated pigments can be extracted in acidic solvents. To accomplish this, the chromatophore containing dermal layer is first manually isolated using a superficial dissection, and the pigment granules are removed using sonication, centrifugation, and washing cycles. Pigments confined within the purified granules are then extracted via acidic methanol solutions, leaving nanostructures with smaller diameters that are void of visible color. This extraction procedure produces a 58% yield of soluble pigments isolated from granules. Using this method, the composition of the chromatophore pigments can be determined and used to provide insight into the mechanism of adaptive coloration in cephalopods.

Fabrication of Millimeter‐Long Carbon Tubular Nanostructures Using the Self‐Rolling Process Inherent in Elastic Protein Layers

Millimeter-long conducting fibers can be fabricated from carbon nanomaterials via a simple method involving the release of a prestrained protein layer. This study shows how a self-rolling process initiated by polymerization of a micropatterned layer of fibronectin (FN) results in the production of carbon nanomaterial-based microtubular fibers. The process begins with deposition of carbon nanotube (CNT) or graphene oxide (GO) particles on the FN layer. Before polymerization, particles are discrete and nonconducting, but after polymerization the carbon materials become entangled to form an interconnected conducting network clad by FN. Selective removal of FN using high-temperature combustion yields freestanding CNT or reduced GO microtubular fibers. The properties of these fibers are characterized using atomic force microscopy and Raman spectroscopy. The data suggest that this method may provide a ready route to rapid design and fabrication of aligned biohybrid nanomaterials potentially useful for future electronic applications.