Elastic Fluorescent Protein-Based Down-Converting Optical Films for Flexible Display.

Protein-based material design provides great advantages to developing smart biomaterials with tunable structures and desired functions. They have been widely used in many biomedical applications including tissue engineering and drug delivery. However, protein-based materials are not yet widely used in optoelectronic materials despite their excellent optical and tunable mechanical properties. Here, we synthesized engineered fluorescent proteins (FPs) fused with elastic protein for the development of optoelectrical down-converting optical filters for flexible display materials. We synthesized sequence-specific FPs to tune blue, green, yellow, and red colors and fused them with elastic protein to tune mechanical properties. We fabricated flexible self-supporting film materials and characterized mechanical properties and down-converting optical properties. We also fabricated a hybrid light-emitting diode (LED) to down convert blue to desired green, red, and white colors. Furthermore, we constructed a flexible white LED using organic LED as a flexible substrate. Our modular synthesis approach of tunable bio-optoelectrical material approaches will be useful to design future biocompatible and flexible display materials and technologies.

Catechol-Functionalized Elastin-like Polypeptides as Tissue Adhesives.

Adhesives can potentially be used to achieve fast and efficient wound closure; however, current products show poor bonding on wet surfaces, undergo swelling, and lack adequate biocompatibility. We designed a hydrogel adhesive with recombinant elastin-like polypeptides (ELPs), which are flexible proteins that can be customized for biomedical needs. The adhesive proteins are synthesized by chemically modifying the ELPs with dopamine, which contain adhesive catechol moieties. The resulting catechol-functional ELPs or Cat-ELPs can form flexible hydrogels that show stable swelling in aqueous conditions at 37 °C. We demonstrate their flexibility and viscoelastic properties through rheology. We also show the advantage of using customizable recombinant proteins to improve the material biological properties by demonstrating improved fibroblast binding on Cat-ELP by adding ELP with "RGD" peptides. We further confirmed in vivo biocompatibility and biodegradation of Cat-ELP hydrogels by implanting them in mice and monitoring for 10 weeks. Finally, we tested the bonding strength of the adhesives on porcine skin through tensile pull-off and lap-shear testing, in which we found strengths of 37 and 39 kPa, respectively. We demonstrated the tensile bonding strength by suspending a 2 kg mass on a one square inch (6.5 cm2) skin sample. As our adhesives are developed further, our strategy combining recombinant protein engineering and chemical modification will help yield an ideal bioadhesive for wound closure.

Elastin-Based Thermoresponsive Shape-Memory Hydrogels.

A shape-memory hydrogel is a programmable hydrogel material that can store specific shapes and execute functions in response to stimuli. In this report, we developed shape-memory hydrogels by creating double-network polymeric structures using a physically cross-linking elastin-like polypeptide (ELP) and a chemically cross-linking polyacrylamide (PAM). We synthesized the hydrogel matrix by polymerizing the acrylamide mixed in an ELP solution. We exploited the lower critical solution temperature transition of the ELP to enable the hydrogel to hold a new desired shape at an elevated temperature of 55 °C. The original shape of the hydrogel can then be recovered by lowering the temperature to 20 °C. The shape-memory hydrogels we developed exhibit ultrafast functionality and high repeatability. Taking advantage of the temperature-induced shape-memory capability, we also demonstrate practical functions such as gripping an object and connecting two tubes. Our materials with effective temperature-driven shape-memory functionality will be useful for developing novel materials for biomedical applications in the future.

Vertical Self-Assembly of Polarized Phage Nanostructure for Energy Harvesting.

Controlling the shape, geometry, density, and orientation of nanomaterials is critical to fabricate functional devices. However, there is limited control over the morphological and directional characteristics of presynthesized nanomaterials, which makes them unsuitable for developing devices for practical applications. Here, we address this challenge by demonstrating vertically aligned and polarized piezoelectric nanostructures from presynthesized biological piezoelectric nanofibers, M13 phage, with control over the orientation, polarization direction, microstructure morphology, and density using genetic engineering and template-assisted self-assembly process. The resulting vertically ordered structures exhibit strong unidirectional polarization with three times higher piezoelectric constant values than that of in-plane aligned structures, supported by second harmonic generation and piezoelectric force microscopy measurements. The resulting vertically self-assembled phage-based piezoelectric energy harvester (PEH) produces up to 2.8 V of potential, 120 nA of current, and 236 nW of power upon 17 N of force. In addition, five phage-based PEH integrated devices produce an output voltage of 12 V and an output current of 300 nA, simply by pressing with a finger. The resulting device can operate light-emitting diode backlights on a liquid crystal display. Our approach will be useful for assembling many other presynthesized nanomaterials into high-performance devices for various applications.

Diphenylalanine Peptide Nanotube Energy Harvesters.

Piezoelectric materials are excellent generators of clean energy, as they can harvest the ubiquitous vibrational and mechanical forces. We developed large-scale unidirectionally polarized, aligned diphenylalanine (FF) nanotubes and fabricated peptide-based piezoelectric energy harvesters. We first used the meniscus-driven self-assembly process to fabricate horizontally aligned FF nanotubes. The FF nanotubes exhibit piezoelectric properties as well as unidirectional polarization. In addition, the asymmetric shapes of the self-assembled FF nanotubes enable them to effectively translate external axial forces into shear deformation to generate electrical energy. The fabricated peptide-based piezoelectric energy harvesters can generate voltage, current, and power of up to 2.8 V, 37.4 nA, and 8.2 nW, respectively, with 42 N of force, and can power multiple liquid-crystal display panels. These peptide-based energy-harvesting materials will provide a compatible energy source for biomedical applications in the future.

Improvement of physical properties of calcium phosphate cement by elastin-like polypeptide supplementation.

Calcium phosphate cements (CPCs) are synthetic bioactive cements widely used as hard tissue substitutes. Critical limitations of use include their poor mechanical properties and poor anti-washout behaviour. To address those limitations, we combined CPC with genetically engineered elastin-like polypeptides (ELPs). We investigated the effect of the ELPs on the physical properties and biocompatibility of CPC by testing ELP/CPC composites with various liquid/powder ratios. Our results show that the addition of ELPs improved the mechanical properties of the CPC, including the microhardness, compressive strength, and washout resistance. The biocompatibility of ELP/CPC composites was also comparable to that of the CPC alone. However, supplementing CPC with ELPs functionalized with octaglutamate as a hydroxyapatite binding peptide increased the setting time of the cement. With further design and modification of our biomolecules and composites, our research will lead to products with diverse applications in biology and medicine.

Phage-Based Structural Color Sensors and Their Pattern Recognition Sensing System.

The mammalian olfactory system provides great inspiration for the design of intelligent sensors. To this end, we have developed a bioinspired phage nanostructure-based color sensor array and a smartphone-based sensing network system. Using a M13 bacteriophage (phage) as a basic building block, we created structural color matrices that are composed of liquid-crystalline bundled nanofibers from self-assembled phages. The phages were engineered to express cross-responsive receptors on their major coat protein (pVIII), leading to rapid, detectable color changes upon exposure to various target chemicals, resulting in chemical- and concentration-dependent color fingerprints. Using these sensors, we have successfully detected 5-90% relative humidity with 0.2% sensitivity. In addition, after modification with aromatic receptors, we were able to distinguish between various structurally similar toxic chemicals including benzene, toluene, xylene, and aniline. Furthermore, we have developed a method of interpreting and disseminating results from these sensors using smartphones to establish a wireless system. Our phage-based sensor system has the potential to be very useful in improving national security and monitoring the environment and human health.

Self-Healing Elastin-Bioglass Hydrogels.

Tailorable hydrogels that are mechanically robust, injectable, and self-healable, are useful for many biomedical applications including tissue repair and drug delivery. Here we use biological and chemical engineering approaches to develop a novel in situ forming organic/inorganic composite hydrogel with dynamic aldimine cross-links using elastin-like polypeptides (ELP) and bioglass (BG). The resulting ELP/BG biocomposites exhibit tunable gelling behavior and mechanical characteristics in a composition and concentration dependent manner. We also demonstrate self-healing in the ELP/BG hydrogels by successfully reattaching severed pieces as well as through rheology. In addition, we show the strength of genetic engineering to easily customize ELP by fusing cell-stimulating "RGD" peptide motifs. We showed that the resulting composite materials are cytocompatible as they support the cellular growth and attachment. Our robust in situ forming ELP/BG composite hydrogels will be useful as injectable scaffolds for delivering cell and drug molecules to promote soft tissue regeneration in the future.

Elastin-Based Rubber-Like Hydrogels.

We developed rubber-like elastomeric materials using a natural elastin derived sequence and genetic engineering to create precisely defined elastin-like polypeptides. The coiled elastin-like polypeptide chains, which behave like entropic springs, were cross-linked using an end-to-end tethering scheme to synthesize simple hydrogels with excellent extensibility and reversibility. Our hydrogels extend to strains as high as 1500% and remain highly resilient with elastic recovery as high as 94% even at 600% strain, significantly exceeding any other protein-based hydrogel. These materials are valuable as elastomeric hydrogels for designing extremely robust scaffolds useful for tissue engineering.

Biomimetic sensor design.

Detection of desired target chemicals in a sensitive and selective manner is critically important to protect human health, environment and national security. Nature has been a great source of inspiration for the design of sensitive and selective sensors. In this mini-review, we overview the recent developments in bio-inspired sensor development. There are four major components of sensor design: design of receptors for specific targets; coating materials to integrate receptors to transducing machinery; sensitive transducing of signals; and decision making based on the sensing results. We discuss the biomimetic methods to discover specific receptors followed by a discussion about bio-inspired nanocoating material design. We then review the recent developments in phage-based bioinspired transducing systems followed by a discussion of biomimetic pattern recognition-based decision making systems. Our review will be helpful to understand recent approaches to reverse-engineer natural systems to design specific and sensitive sensors.

Protein-based functional nanomaterial design for bioengineering applications.

In this review article, we describe recent progress in the field of protein-based bionanomaterial design with focus on the four well-characterized proteins: mammalian elastin and collagen, and insect-derived silk and resilin. These proteins are important structural components and understanding their physical and biochemical properties has allowed us to not only replicate them but also create novel smart materials. The 'smart' properties of a material include its ability to self-assemble, respond to stimuli, and/or promote cell interactions. Such properties can be attributed to unique structural modules from elastin, collagen, silk, and resilin as well as functional modules identified from other proteins directly or using display techniques such as phage display. Thus, the goal of this article is to not only emphasize the types of protein-based peptide modules and their uses but also encourage and inspire the reader to create new toolsets of smart polypeptides to overcome their challenges.

Graphene-based materials functionalized with elastin-like polypeptides.

Graphene-based materials commonly require functionalization for biological applications in order to control their physical/colloidal properties and to introduce additional capabilities, such as stimuli-responsiveness and affinity to specific biomolecules. Here, we functionalized CVD-grown graphene and graphene oxide with a genetically engineered elastin-like polypeptide fused to a graphene binding peptide and then showed that the resulting hybrid materials exhibit thermo- and photoresponsive behaviors. Furthermore, we demonstrate that our genetic engineering strategy allows for the facile introduction of bioactivity to reduced graphene oxide. The stimuli-responsiveness and genetic tunability of our graphene-protein nanocomposites are attractive for addressing future biomedical applications.

Light-controlled graphene-elastin composite hydrogel actuators.

Hydrogels actuators (HAs) that can reversibly respond to stimuli have applications in diverse fields. However, faster response rates and improved control over actuation timing and location are required to fulfill their potential. To address these criteria, we synthesized near-infrared light-driven HAs by interfacing genetically engineered elastin-like polypeptides with reduced-graphene oxide sheets. The resulting nanocomposites exhibited rapid and tunable motions controlled by light position, intensity, and path, including finger-like flexing and crawling. This work demonstrates the ability of rationally designed proteins to be combined with synthetic nanoparticles for the creation of macroscale functional materials.