Publications by authors named "Melik C Demirel"

34 Publications

Hydration-Induced Structural Transitions in Biomimetic Tandem Repeat Proteins.

J Phys Chem B 2021 03 17;125(8):2134-2145. Epub 2021 Feb 17.

Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, 81377 Munich, Germany.

A major challenge in developing biomimetic, high-performance, and sustainable products is the accurate replication of the biological materials' striking properties, such as high strength, self-repair, and stimuli-responsiveness. The rationalization of such features on the microscopic scale, together with the rational design of synthetic materials, is currently hindered by our limited understanding of the sequence-structure-property relationship. Here, employing state-of-the-art nuclear magnetic resonance (NMR) spectroscopy, we link the atomistic structural and dynamic properties of an artificial bioinspired tandem repeat protein TR(1,11) to its stunning macroscopic properties including high elasticity, self-healing capabilities, and record-holding proton conductivity among biological materials. We show that the hydration-induced structural rearrangement of the amorphous Gly-rich soft segment and the ordered Ala-rich hard segment is the key to the material's outstanding physical properties. We found that in the hydrated state both the Ala-rich ordered and Gly-rich disordered parts contribute to the formation of the nanoconfined β-sheets, thereby enhancing the strength and toughness of the material. This restructuring is accompanied by fast proline ring puckering and backbone - isomerization at the water-protein interface, which in turn enhances the elasticity and the thermal conductivity of the hydrated films. Our in-depth characterization provides a solid ground for the development of next-generation materials with improved properties.
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http://dx.doi.org/10.1021/acs.jpcb.0c11505DOI Listing
March 2021

Biosynthetic self-healing materials for soft machines.

Nat Mater 2020 11 27;19(11):1230-1235. Epub 2020 Jul 27.

Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Stuttgart, Germany.

Self-healing materials are indispensable for soft actuators and robots that operate in dynamic and real-world environments, as these machines are vulnerable to mechanical damage. However, current self-healing materials have shortcomings that limit their practical application, such as low healing strength (below a megapascal) and long healing times (hours). Here, we introduce high-strength synthetic proteins that self-heal micro- and macro-scale mechanical damage within a second by local heating. These materials are optimized systematically to improve their hydrogen-bonded nanostructure and network morphology, with programmable healing properties (2-23 MPa strength after 1 s of healing) that surpass by several orders of magnitude those of other natural and synthetic soft materials. Such healing performance creates new opportunities for bioinspired materials design, and addresses current limitations in self-healing materials for soft robotics and personal protective equipment.
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http://dx.doi.org/10.1038/s41563-020-0736-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7610468PMC
November 2020

Self-Assembly of Topologically Networked Protein-TiCT MXene Composites.

ACS Nano 2020 06 28;14(6):6956-6967. Epub 2020 May 28.

Center for Research on Advanced Fiber Technologies (CRAFT), Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, United States.

Hierarchical organization plays an important role in the stunning physical properties of natural and synthetic composites. Limits on the physical properties of such composites are generally defined by percolation theory and can be systematically altered using the volumetric filler fraction of the inorganic/organic phase. In natural composites, organic materials such as proteins that interact with inorganic filler materials can further alter the hierarchical order and organization of the composite topological interactions, expanding the limits of the physical properties defined by percolation theory. However, existing polymer systems do not offer a topological parameter that can systematically modulate the assembly characteristics of composites. Here, we present a composite based on proteins and titanium carbide (TiCT) MXene that manifests a topological network that regulates the organization, and hence physical properties, of these biomimetic composites. We designed, recombinantly expressed, and purified synthetic proteins consisting of polypeptides with repeating amino acid sequences (tandem repeats) that have the ability to self-assemble into topologically networked biomaterials. We demonstrated that the interlayer distance between MXene sheets can be controlled systematically by the number of tandem repeat units. We varied the filler fraction and number of tandem repeat units to regulate the in-plane and out-of-plane electrical conductivities of these composites. Once TiCT MXene sheets are separated enough to facilitate formation of cross-links in our proteins with the number of tandem repeat units reaching 11, the linear characteristics of the composites switched into nonlinear curves with a distinct hysteresis for out-of-plane electron transport, while the in-plane characteristics remained linear. This highlights the impact of synthetic protein templates, which can be designed to modulate electronic transport in composites both isotropically and anisotropically.
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http://dx.doi.org/10.1021/acsnano.0c01431DOI Listing
June 2020

Squid-Inspired Tandem Repeat Proteins: Functional Fibers and Films.

Front Chem 2019 21;7:69. Epub 2019 Feb 21.

Center for Research on Advanced Fiber Technologies, Materials Research Institute, Pennsylvania State University, University Park, PA, United States.

Production of repetitive polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions have been an interest for the last couple of decades. Their molecular structure provides a rich architecture that can micro-phase-separate to form periodic nanostructures (e.g., lamellar and cylindrical repeating phases) with enhanced physicochemical properties via directed or natural evolution that often exceed those of conventional synthetic polymers. Here, we review programmable design, structure, and properties of functional fibers and films from squid-inspired tandem repeat proteins, with applications in soft photonics and advanced textiles among others.
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http://dx.doi.org/10.3389/fchem.2019.00069DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6393770PMC
February 2019

Squid Ring Teeth-coated Mesh Improves Abdominal Wall Repair.

Plast Reconstr Surg Glob Open 2018 Aug 7;6(8):e1881. Epub 2018 Aug 7.

Department of Surgery, Penn State University College of Medicine, Hershey, Pa.

Background: Hernia repair is a common surgical procedure with polypropylene (PP) mesh being the standard material for correction because of its durability. However, complications such as seroma and pain are common, and repair failures still approach 15% secondary to poor tissue integration. In an effort to enhance mesh integration, we evaluated the applicability of a squid ring teeth (SRT) protein coating for soft-tissue repair in an abdominal wall defect model. SRT is a biologically derived high-strength protein with strong mechanical properties. We assessed tissue integration, strength, and biocompatibility of a SRT-coated PP mesh in a first-time pilot animal study.

Methods: PP mesh was coated with SRT (SRT-PP) and tested for mechanical strength against uncoated PP mesh. Cell proliferation and adhesion studies were performed in vitro using a 3T3 cell line. Rats underwent either PP (n = 3) or SRT-PP (n = 6) bridge mesh implantation in an anterior abdominal wall defect model. Repair was assessed clinically and radiographically, with integration evaluated by histology and mechanical testing at 60 days.

Results: Cell proliferation was enhanced on SRT-PP mesh. This was corroborated in vivo by abdominal wall histology, dramatically diminished craniocaudal mesh contraction, improved strength testing, and higher tissue failure strain. There was no increase in seroma or visceral adhesion formation. No foreign body reactions were noted on liver histology.

Conclusions: SRT applied as a coating appears to augment mesh-tissue integration and improve abdominal wall stability following bridged repair. Further studies in larger animals will determine its applicability for hernia repair in patients.
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http://dx.doi.org/10.1097/GOX.0000000000001881DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6143318PMC
August 2018

Tunable thermal transport and reversible thermal conductivity switching in topologically networked bio-inspired materials.

Nat Nanotechnol 2018 10 13;13(10):959-964. Epub 2018 Aug 13.

Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, USA.

The dynamic control of thermal transport properties in solids must contend with the fact that phonons are inherently broadband. Thus, efforts to create reversible thermal conductivity switches have resulted in only modest on/off ratios, since only a relatively narrow portion of the phononic spectrum is impacted. Here, we report on the ability to modulate the thermal conductivity of topologically networked materials by nearly a factor of four following hydration, through manipulation of the displacement amplitude of atomic vibrations. By varying the network topology, or crosslinked structure, of squid ring teeth-based bio-polymers through tandem-repetition of DNA sequences, we show that this thermal switching ratio can be directly programmed. This on/off ratio in thermal conductivity switching is over a factor of three larger than the current state-of-the-art thermal switch, offering the possibility of engineering thermally conductive biological materials with dynamic responsivity to heat.
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http://dx.doi.org/10.1038/s41565-018-0227-7DOI Listing
October 2018

Mechanical Properties of Tandem-Repeat Proteins Are Governed by Network Defects.

ACS Biomater Sci Eng 2018 Mar 15;4(3):884-891. Epub 2018 Feb 15.

Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.

Topological defects in highly repetitive structural proteins strongly affect their mechanical properties. However, there are no universal rules for structure-property prediction in structural proteins due to high diversity in their repetitive modules. Here, we studied the mechanical properties of tandem-repeat proteins inspired by squid ring teeth proteins using rheology and tensile experiments as well as spectroscopic and X-ray techniques. We also developed a network model based on entropic elasticity to predict structure-property relationships for these proteins. We demonstrated that shear modulus, elastic modulus, and toughness scale inversely with the number of repeats in these proteins. Through optimization of structural repeats, we obtained highly efficient protein network topologies with 42 MJ/m ultimate toughness that are capable of withstanding deformations up to 350% when hydrated. Investigation of topological network defects in structural proteins will improve the prediction of mechanical properties for designing novel protein-based materials.
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http://dx.doi.org/10.1021/acsbiomaterials.7b00830DOI Listing
March 2018

3D Printing of PDMS Improves Its Mechanical and Cell Adhesion Properties.

ACS Biomater Sci Eng 2018 Feb 8;4(2):682-693. Epub 2018 Jan 8.

Mechanical Engineering Department, Ceyhan Engineering Faculty, Cukurova University, Adana 01950, Turkey.

Despite extensive use of polydimethylsiloxane (PDMS) in medical applications, such as lab-on-a-chip or tissue/organ-on-a-chip devices, point-of-care devices, and biological machines, the manufacturing of PDMS devices is limited to soft-lithography and its derivatives, which prohibits the fabrication of geometrically complex shapes. With the recent advances in three-dimensional (3D) printing, use of PDMS for fabrication of such complex shapes has gained considerable interest. This research presents a detailed investigation on printability of PDMS elastomers over three concentrations for mechanical and cell adhesion studies. The results demonstrate that 3D printing of PDMS improved the mechanical properties of fabricated samples up to three fold compared to that of cast ones because of the decreased porosity of bubble entrapment. Most importantly, 3D printing facilitates the adhesion of breast cancer cells, whereas cast samples do not allow cellular adhesion without the use of additional coatings such as extracellular matrix proteins. Cells are able to adhere and grow in the grooves along the printed filaments demonstrating that 3D printed devices can be engineered with superior cell adhesion qualities compared to traditionally manufactured PDMS devices.
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http://dx.doi.org/10.1021/acsbiomaterials.7b00646DOI Listing
February 2018

Ultrafast laser-probing spectroscopy for studying molecular structure of protein aggregates.

Analyst 2017 May;142(9):1434-1441

CRAFT Center, Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA. and Engineering Science and Mechanics Department, Pennsylvania State University, University Park, PA 16802, USA and Huck Institutes of Life Sciences, Pennsylvania State University, University Park, PA 16802, USA.

We report the development of a new technique to screen protein aggregation based on laser-probing spectroscopy with sub-picosecond resolution. Protein aggregation is an important topic for materials science, fundamental biology as well as clinical studies in neurodegenerative diseases and translation studies in biomaterials engineering. However, techniques to study protein aggregation and assembly are limited to infrared spectroscopy, fluorescent assays, immunostaining, or functional assays among others. Here, we report a new technique to characterize protein structure-property relationship based on ultrafast laser-probing spectroscopy. First, we show theoretically that the temperature dependence of the refractive index of a protein is correlated to its crystallinity. Then, we performed time-domain thermo-transmission experiments on purified semi-crystalline proteins, both native and recombinant (i.e., silk and squid ring teeth), and also on intact E. coli cells bearing overexpressed recombinant protein. Our results demonstrate, for the first time, relative quantification of crystallinity in real time for protein aggregates. Our approach can potentially be used for screening an ultra-large number of proteins in vivo. Using this technique, we could answer many fundamental questions in structural protein research, such as the underlying sequence-structure relationship for protein assembly and aggregation.
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http://dx.doi.org/10.1039/c6an02570fDOI Listing
May 2017

Self-Healing Textile: Enzyme Encapsulated Layer-by-Layer Structural Proteins.

ACS Appl Mater Interfaces 2016 Aug 26;8(31):20371-8. Epub 2016 Jul 26.

U.S. Naval Research Laboratory, Code 6910, 4555 Overlook Avenue, S.W., Washington, D.C. 20375, United States.

Self-healing materials, which enable an autonomous repair response to damage, are highly desirable for the long-term reliability of woven or nonwoven textiles. Polyelectrolyte layer-by-layer (LbL) films are of considerable interest as self-healing coatings due to the mobility of the components comprising the film. In this work mechanically stable self-healing films were fabricated through construction of a polyelectrolyte LbL film containing squid ring teeth (SRT) proteins. SRTs are structural proteins with unique self-healing properties and high elastic modulus in both dry and wet conditions (>2 GPa) due to their semicrystalline architecture. We demonstrate LbL construction of multilayers containing native and recombinant SRT proteins capable of self-healing defects. Additionally, we show these films are capable of utilizing functional biomolecules by incorporating an enzyme into the SRT multilayer. Urease was chosen as a model enzyme of interest to test its activity via fluorescence assay. Successful construction of the SRT films demonstrates the use of mechanically stable self-healing coatings, which can incorporate biomolecules for more complex protective functionalities for advanced functional fabrics.
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http://dx.doi.org/10.1021/acsami.6b05232DOI Listing
August 2016

Molecular tandem repeat strategy for elucidating mechanical properties of high-strength proteins.

Proc Natl Acad Sci U S A 2016 Jun 24;113(23):6478-83. Epub 2016 May 24.

Materials Research Institute, Pennsylvania State University, University Park, PA 16802; Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802; The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802;

Many globular and structural proteins have repetitions in their sequences or structures. However, a clear relationship between these repeats and their contribution to the mechanical properties remains elusive. We propose a new approach for the design and production of synthetic polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions. Our designed sequences are based on a structural protein produced in squid suction cups that has a segmented copolymer structure with amorphous and crystalline domains. We produced segmented polypeptides with varying repeat number, while keeping the lengths and compositions of the amorphous and crystalline regions fixed. We showed that mechanical properties of these synthetic proteins could be tuned by modulating their molecular weights. Specifically, the toughness and extensibility of synthetic polypeptides increase as a function of the number of tandem repeats. This result suggests that the repetitions in native squid proteins could have a genetic advantage for increased toughness and flexibility.
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http://dx.doi.org/10.1073/pnas.1521645113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988609PMC
June 2016

Remote calorimetric detection of urea via flow injection analysis.

Analyst 2015 Dec;140(23):8033-40

Department of Biomedical Engineering, The Pennsylvania State University, University Park, PA, USA and Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, USA.

The design and development of a calorimetric biosensing system enabling relatively high throughput sample analysis are reported. The calorimetric biosensor system consists of a thin (∼20 μm) micromachined Y-cut quartz crystal resonator (QCR) as a temperature sensor placed in close proximity to a fluidic chamber packed with an immobilized enzyme. Layer by layer enzyme immobilization of urease is demonstrated and its activity as a function of the number of layers, pH, and time has been evaluated. This configuration enables a sensing system where a transducer element is physically separated from the analyte solution of interest and is thereby free from fouling effects typically associated with biochemical reactions occuring on the sensor surface. The performance of this biosensing system is demonstrated by detection of 1-200 mM urea in phosphate buffer via a flow injection analysis (FIA) technique. Miniaturized fluidic systems were used to provide continuous flow through a reaction column. Under this configuration the biosensor has an ultimate resolution of less than 1 mM urea and showed a linear response between 0-50 mM. This work demonstrates a sensing modality in which the sensor itself is not fouled or contaminated by the solution of interest and the enzyme immobilized Kapton® fluidic reaction column can be used as a disposable cartridge. Such a system enables reuse and reliability for long term sampling measurements. Based on this concept a biosensing system is envisioned which can perform rapid measurements to detect biomarkers such as glucose, creatinine, cholesterol, urea and lactate in urine and blood continuously over extended periods of time.
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http://dx.doi.org/10.1039/c5an01306bDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5549664PMC
December 2015

Segmented molecular design of self-healing proteinaceous materials.

Sci Rep 2015 Sep 1;5:13482. Epub 2015 Sep 1.

Pennsylvania State University, Department of Engineering Science and Mechanics, University Park, PA, 16802, USA.

Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure-property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.
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http://dx.doi.org/10.1038/srep13482DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4555047PMC
September 2015

A Fluidic Device with Polymeric Textured Ratchets.

Polymer (Guildf) 2015 Feb;58:30-35

Materials Research Institute and Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania 16802, USA.

Nanotextured surfaces are widely used throughout nature for adhesion, wetting, and transport. Chemistry, geometry, and morphology are important factors for creating tunable textured surfaces, in which directionality of droplets can be controlled. Here, we fabricated nano textured polymeric surfaces, and studied the effect of tilting on the mobility of frequency modulated water droplet transported on asymmetric nano-PPX tracks. Plastically-deformed tracks guided water droplets for sorting, gating, and merging them as a function on their volume. Polymeric ratchets open up new avenues for the fields of digital fluidics and flexible device fabrication.
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http://dx.doi.org/10.1016/j.polymer.2014.12.031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310011PMC
February 2015

Recent advances in nanoscale bioinspired materials.

Macromol Biosci 2015 Mar 4;15(3):300-11. Epub 2014 Dec 4.

Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, 16802, USA; Huck Institutes of Life Sciences, Pennsylvania State University, University Park, Pennsylvania, 16802, USA; College of Engineering, Pennsylvania State University, University Park, Pennsylvania, 16802, USA.

Natural materials have been a fundamental part of human life since the dawn of civilization. However, due to exploitation of natural resources and cost issues, synthetic materials replaced bio-derived materials in the last century. Recent advances in bio- and nano-technologies pave the way for developing eco-friendly materials that could be produced easily from renewable resources at reduced cost and in a broad array of useful applications. This feature article highlights structural and functional characteristics of bio-derived materials, which will expedite the design fabrication and synthesis of eco-friendly and recyclable advanced nano-materials and devices.
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http://dx.doi.org/10.1002/mabi.201400324DOI Listing
March 2015

Effects of surface asymmetry on neuronal growth.

PLoS One 2014 3;9(9):e106709. Epub 2014 Sep 3.

Department of Physics and Astronomy and Center for Nanoscopic Physics, Tufts University, Medford, Massachusetts, United States of America.

Detailed knowledge of how the surface physical properties, such as mechanics, topography and texture influence axonal outgrowth and guidance is essential for understanding the processes that control neuron development, the formation of functional neuronal connections and nerve regeneration. Here we synthesize asymmetric surfaces with well-controlled topography and texture and perform a systematic experimental and theoretical investigation of axonal outgrowth on these substrates. We demonstrate unidirectional axonal bias imparted by the surface ratchet-based topography and quantify the topographical guidance cues that control neuronal growth. We describe the growth cone dynamics using a general stochastic model (Fokker-Planck formalism) and use this model to extract two key dynamical parameters: diffusion (cell motility) coefficient and asymmetric drift coefficient. The drift coefficient is identified with the torque caused by the asymmetric ratchet topography. We relate the observed directional bias in axonal outgrowth to cellular contact guidance behavior, which results in an increase in the cell-surface coupling with increased surface anisotropy. We also demonstrate that the disruption of cytoskeletal dynamics through application of Taxol (stabilizer of microtubules) and Blebbistatin (inhibitor of myosin II activity) greatly reduces the directional bias imparted by these asymmetric surfaces. These results provide new insight into the role played by topographical cues in neuronal growth and could lead to new methods for stimulating neuronal regeneration and the engineering of artificial neuronal tissue.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0106709PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4153665PMC
November 2015

Accelerating the design of biomimetic materials by integrating RNA-seq with proteomics and materials science.

Nat Biotechnol 2013 Oct 8;31(10):908-15. Epub 2013 Sep 8.

1] School of Materials Science and Engineering, Nanyang Technological University, Singapore. [2].

Efforts to engineer new materials inspired by biological structures are hampered by the lack of genomic data from many model organisms studied in biomimetic research. Here we show that biomimetic engineering can be accelerated by integrating high-throughput RNA-seq with proteomics and advanced materials characterization. This approach can be applied to a broad range of systems, as we illustrate by investigating diverse high-performance biological materials involved in embryo protection, adhesion and predation. In one example, we rapidly engineer recombinant squid sucker ring teeth proteins into a range of structural and functional materials, including nanopatterned surfaces and photo-cross-linked films that exceed the mechanical properties of most natural and synthetic polymers. Integrating RNA-seq with proteomics and materials science facilitates the molecular characterization of natural materials and the effective translation of their molecular designs into a wide range of bio-inspired materials.
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http://dx.doi.org/10.1038/nbt.2671DOI Listing
October 2013

Bioinspired Directional Surfaces for Adhesion, Wetting and Transport.

Adv Funct Mater 2012 Jun 13;22(11):2223-2234. Epub 2012 Mar 13.

Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802 USA.

In Nature, directional surfaces on insect cuticle, animal fur, bird feathers, and plant leaves are comprised of dual micro-nanoscale features that tune roughness and surface energy. This feature article summarizes experimental and theoretical approaches for the design, synthesis and characterization of new bioinspired surfaces demonstrating unidirectional surface properties. The experimental approaches focus on bottom-up and top-down synthesis methods of unidirectional micro- and nanoscale films to explore and characterize their anomalous features. The theoretical component of the review focuses on computational tools to predict the physicochemical properties of unidirectional surfaces.
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http://dx.doi.org/10.1002/adfm.201103017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601762PMC
June 2012

Emerging technologies for assembly of microscale hydrogels.

Adv Healthc Mater 2012 Mar;1(2):149-158

Bio-Acoustic MEMS in Medicine (BAMM) Laboratory Center for Bioengineering Brigham and Women's Hospital Harvard Medical School Boston, MA 02115, USA.

Assembly of cell encapsulating building blocks (i.e., microscale hydrogels) has significant applications in areas including regenerative medicine, tissue engineering, and cell-based in vitro assays for pharmaceutical research and drug discovery. Inspired by the repeating functional units observed in native tissues and biological systems (e.g., the lobule in liver, the nephron in kidney), assembly technologies aim to generate complex tissue structures by organizing microscale building blocks. Novel assembly technologies enable fabrication of engineered tissue constructs with controlled properties including tunable microarchitectural and predefined compositional features. Recent advances in micro- and nano-scale technologies have enabled engineering of microgel based three dimensional (3D) constructs. There is a need for high-throughput and scalable methods to assemble microscale units with a complex 3D micro-architecture. Emerging assembly methods include novel technologies based on microfluidics, acoustic and magnetic fields, nanotextured surfaces, and surface tension. In this review, we survey emerging microscale hydrogel assembly methods offering rapid, scalable microgel assembly in 3D, and provide future perspectives and discuss potential applications.
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http://dx.doi.org/10.1002/adhm.201200011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3774531PMC
March 2012

Neuronal alignment on asymmetric textured surfaces.

Appl Phys Lett 2012 Oct 2;101(14):143701. Epub 2012 Oct 2.

Department of Physics and Astronomy and Center for Nanoscopic Physics, Tufts University, Medford, Massachusetts 02155, USA.

Axonal growth and the formation of synaptic connections are key steps in the development of the nervous system. Here, we present experimental and theoretical results on axonal growth and interconnectivity in order to elucidate some of the basic rules that neuronal cells use for functional connections with one another. We demonstrate that a unidirectional nanotextured surface can bias axonal growth. We perform a systematic investigation of neuronal processes on asymmetric surfaces and quantify the role that biomechanical surface cues play in neuronal growth. These results represent an important step towards engineering directed axonal growth for neuro-regeneration studies.
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http://dx.doi.org/10.1063/1.4755837DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3477179PMC
October 2012

Ultrasensitive detection of a protein by optical trapping in a photonic-plasmonic microcavity.

J Biophotonics 2012 Aug 18;5(8-9):629-38. Epub 2012 Jun 18.

Materials Research Institute, 212 EES Bldg, Pennsylvania State University, University Park, Pennsylvania 16802, USA.

Microcavity and whispering gallery mode (WGM) biosensors derive their sensitivity from monitoring frequency shifts induced by protein binding at sites of highly confined field intensities, where field strengths can be further amplified by excitation of plasmon resonances in nanoparticle layers. Here, we propose a mechanism based on optical trapping of a protein at the site of plasmonic field enhancements for achieving ultra sensitive detection in only microliter-scale sample volumes, and in real-time. We demonstrate femto-Molar sensitivity corresponding to a few 1000 s of macromolecules. Simulations based on Mie theory agree well with the optical trapping concept at plasmonic 'hotspots' locations.
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http://dx.doi.org/10.1002/jbio.201200040DOI Listing
August 2012

Stimuli responsive release of metalic nanoparticles on semiconductor substrates.

Langmuir 2012 Apr 28;28(14):5975-80. Epub 2012 Mar 28.

Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

Optically active metal nanoparticles have been of recent and broad interest for applications to biomarker detection because of their ability to enable high sensitivity enhancements in various optical detection techniques. Here, we report stimuli responsive release of metallic nanoparticles on a semiconductor thin film array structure based on pH change. The metallic nanoparticles are obtained by a simple redox procedure on the semiconductor surface. This approach allows controlling nanoparticle surface coatings in situ for biomolecule conjugation, such as DNA probes on nanoparticles, and rapid stimuli responsive release of these nanoparticles upon pH change.
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http://dx.doi.org/10.1021/la3002256DOI Listing
April 2012

Fibroblast adhesion on unidirectional polymeric nanofilms.

Biointerphases 2011 Dec;6(4):158-63

Applied Physical Chemistry, University of Heidelberg, Germany.

Nanotextured polymeric surfaces with inclined rods reveal highly anisotropic properties concerning wetting and adhesion. In this work, we report on the interaction of fibroblast cells with these highly anisotropic materials. The authors quantified removal of adherent cells from such surfaces by a laminar flow. The critical shear force needed for cell removal from the surface depends on the inclination direction. Based on electron microscopy cross sections we deduce that interactions of cellular filopodia extending into the nanotextured surface are causing the direction depending removal.
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http://dx.doi.org/10.1116/1.3646093DOI Listing
December 2011

Transport of a soft cargo on a nanoscale ratchet.

Appl Phys Lett 2011 Aug 12;99(6):63703-637033. Epub 2011 Aug 12.

Surface ratchets can guide droplet transport for microfluidic systems. Here, we demonstrated the actuation of microgels encapsulated in droplets using a unidirectional nanotextured surface, which moves droplets with low vibration amplitudes by a ratcheting mechanism. The nanofilm carries droplets along the ratchets with minimal drop shape deformation to move the encapsulated soft cargo, i.e., microscale hydrogels. The tilted nanorods of the nanofilm produce unidirectional wetting, thereby enabling droplet motion in a single direction. Maximum droplet translation speed on the nanofilm was determined to be 3.5 mm∕s, which offers a pathway towards high throughput microgel assembly applications to build complex constructs.
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http://dx.doi.org/10.1063/1.3625430DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3166334PMC
August 2011

Responsive microgrooves for the formation of harvestable tissue constructs.

Langmuir 2011 May 30;27(9):5671-9. Epub 2011 Mar 30.

Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.

Given its biocompatibility, elasticity, and gas permeability, poly(dimethylsiloxane) (PDMS) is widely used to fabricate microgrooves and microfluidic devices for three-dimensional (3D) cell culture studies. However, conformal coating of complex PDMS devices prepared by standard microfabrication techniques with desired chemical functionality is challenging. This study describes the conformal coating of PDMS microgrooves with poly(N-isopropylacrylamide) (PNIPAAm) by using initiated chemical vapor deposition (iCVD). These microgrooves guided the formation of tissue constructs from NIH-3T3 fibroblasts that could be retrieved by the temperature-dependent swelling property and hydrophilicity change of the PNIPAAm. The thickness of swollen PNIPAAm films at 24 °C was approximately 3 times greater than at 37 °C. Furthermore, PNIPAAm-coated microgroove surfaces exhibit increased hydrophilicity at 24 °C (contact angle θ = 30° ± 2) compared to 37 °C (θ = 50° ± 1). Thus PNIPAAm film on the microgrooves exhibits responsive swelling with higher hydrophilicity at room temperature, which could be used to retrieve tissue constructs. The resulting tissue constructs were the same size as the grooves and could be used as modules in tissue fabrication. Given its ability to form and retrieve cell aggregates and its integration with standard microfabrication, PNIPAAm-coated PDMS templates may become useful for 3D cell culture applications in tissue engineering and drug discovery.
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http://dx.doi.org/10.1021/la200183xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3098811PMC
May 2011

An engineered anisotropic nanofilm with unidirectional wetting properties.

Nat Mater 2010 Dec 10;9(12):1023-8. Epub 2010 Oct 10.

Department of Engineering Science and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.

Anisotropic textured surfaces allow water striders to walk on water, butterflies to shed water from their wings and plants to trap insects and pollen. Capturing these natural features in biomimetic surfaces is an active area of research. Here, we report an engineered nanofilm, composed of an array of poly(p-xylylene) nanorods, which demonstrates anisotropic wetting behaviour by means of a pin-release droplet ratchet mechanism. Droplet retention forces in the pin and release directions differ by up to 80 μN, which is over ten times greater than the values reported for other engineered anisotropic surfaces. The nanofilm provides a microscale smooth surface on which to transport microlitre droplets, and is also relatively easy to synthesize by a bottom-up vapour-phase technique. An accompanying comprehensive model successfully describes the film's anisotropic wetting behaviour as a function of measurable film morphology parameters.
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http://dx.doi.org/10.1038/nmat2864DOI Listing
December 2010

Quantitative analysis of creatinine in urine by metalized nanostructured parylene.

J Biomed Opt 2010 Mar-Apr;15(2):027004

Pennsylvania State University, Department of Engineering Science, University Park, Pennsylvania 16802, USA.

A highly accurate, real-time multisensor agent monitor for biomarker detection is required for early detection of kidney diseases. Urine creatinine level can provide useful information on the status of the kidney. We prepare nanostructured surface-enhanced Raman spectroscopy (SERS) substrates without template or lithography, which provides controllable, well-organized nanostructures on the surface, for the quantitative analysis of creatinine concentration in urine. We present our work on sensitivity of the SERS substrate to urine samples collected from diabetic patients and healthy persons. We report the preparation of a new type of SERS substrate, which provides fast (<10 s), highly sensitive (creatinine concentration <0.5 microg/mL) and reproducible (<5% variation) detection of urine. Our method to analyze the creatinine level in urine is in good agreement with the enzymatic method.
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http://dx.doi.org/10.1117/1.3369002DOI Listing
September 2010

Noncovalent mechanism for the conformal metallization of nanostructured parylene films.

Langmuir 2010 Mar;26(6):4382-91

Materials Research Institute and Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania 16802, USA.

We describe a rapid, reliable method of preparing nanoporous Ni or Co films using nanostructured poly(chloro-p-xylylene) (nanoPPX) films as templates. The nanoPPX films are vapor deposited onto Si substrates using oblique angle polymerization (OAP), resulting in the formation of an obliquely aligned PPX nanorod array on the substrate. The nanoPPX films are then subjected to noncovalent functionalization using an aromatic ligand (i.e., pyridine) by means of treatment with either an aqueous solution of the ligand or ligand vapor. The results of quartz crystal microbalance and X-ray diffraction studies support a model in which pyridine adsorption is facilitated by the formation of pi-pi interactions with aromatic moieties in the amorphous surface regions of nanoPPX. The physisorbed pyridine in the nanoPPX film can subsequently bind a catalytic Pd(II)-based colloidal seed layer. Continuous, conformal Ni or Co films, characterized by FIB/SEM and AFM, are grown on the Pd(II)-laden nanoPPX films using electroless metallization. Analogous metallization of a conventionally deposited planar PPX film results in noncontinuous or patchy metal deposits. Such behavior is attributed to the sluggish adsorption of pyridine in the planar PPX film, resulting in an approximately 22-fold decrease in the quantity of pyridine adsorbed compared to that in a nanoPPX film. Consequently, the level of Pd(II) bound by pyridine on a planar PPX film is insufficient to catalyze continuous metallization. Results of a statistical two-level factorial design indicate that the morphology of the metal layer formed on a nanoPPX film is profoundly influenced by the ligand adsorption condition (i.e., aqueous ligand vs ligand vapor treatment) and is correlated to the catalytic activity of Co films for the production of hydrogen from sodium borohydride decomposition.
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http://dx.doi.org/10.1021/la9034529DOI Listing
March 2010

Control of protein adsorption onto core-shell tubular and vesicular structures of diphenylalanine/parylene.

Langmuir 2010 Feb;26(3):1460-3

Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.

The self-assembly of peptides, specifically dipeptides, offers numerous advantages for biological applications. We describe an easy, versatile method of fabricating different types of zwitterionic Phe-Phe dipeptide structures (i.e., tubes and vesicles) through solvent-mediated assembly. The stability of the dipeptide structures is increased by thin polymer coatings of poly(chloro-p-xylylene), a PPX film. We also investigated protein adsorption onto PPX-coated peptide tubes and vesicles by varying the thickness of the polymer film.
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http://dx.doi.org/10.1021/la903571yDOI Listing
February 2010

Molecular dynamics simulations of DiI-C18(3) in a DPPC lipid bilayer.

Phys Chem Chem Phys 2008 Jun 7;10(24):3548-60. Epub 2008 May 7.

Department of Bioengineering, The Pennsylvania State University, 228 Hallowell Building, University Park, PA 16802, USA.

We performed a 40 ns simulation of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI-C18(3)) in a 1,2-dipalmitoyl-sn-glycero-3-phosphatidyl choline (DPPC) bilayer in order to facilitate interpretation of lipid dynamics and membrane structure from fluorescence lifetime, anisotropy, and fluorescence correlations spectroscopy (FCS). Incorporation of DiI of 1.6 to 3.2 mol% induced negligible changes in area per lipid but detectable increases in bilayer thickness, each of which are indicators of membrane structural perturbation. The DiI chromophore angle was 77 +/- 17 degrees with respect to the bilayer normal, consistent with rotational diffusion inferred from polarization studies. The DiI headgroup was located 0.63 nm below the lipid head group-water interface, a novel result in contrast to some popular cartoon representations of DiI but consistent with DiI's increase in quantum yield when incorporated into lipid bilayers. Importantly, the fast component of rotational anisotropy matched published experimental results demonstrating that sufficient free volume exists at the sub-interfacial region to support fast rotations. Simulations with non-charged DiI head groups exhibited DiI flip-flop, demonstrating that the positively-charged chromophore stabilizes the orientation and location of DiI in a single monolayer. DiI induced detectable changes in interfacial properties of water ordering, electrostatic potential, and changes in P-N vector orientation of DPPC lipids. The diffusion coefficient of DiI (9.7 +/- 0.02 x 10(-8) cm2 s(-1)) was similar to the diffusion of DPPC molecules (10.7 +/- 0.04 x 10(-8) cm2 s(-1)), supporting the conclusion that DiI dynamics reflect lipid dynamics. These results provide the first atomistic level insight into DiI dynamics, results essential in elucidating lipid dynamics through single molecule fluorescence studies.
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http://dx.doi.org/10.1039/b716979eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3251217PMC
June 2008