Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response.

For almost a century, the iridescence of tropical Morpho butterfly scales has been known to originate from 3D vertical ridge structures of stacked periodic layers of cuticle separated by air gaps. Here we describe a biological pattern of surface functionality that we have found in these photonic structures. This pattern is a gradient of surface polarity of the ridge structures that runs from their polar tops to their less-polar bottoms. This finding shows a biological pattern design that could stimulate numerous technological applications ranging from photonic security tags to self-cleaning surfaces, gas separators, protective clothing, sensors, and many others. As an important first step, this biomaterial property and our knowledge of its basis has allowed us to unveil a general mechanism of selective vapor response observed in the photonic Morpho nanostructures. This mechanism of selective vapor response brings a multivariable perspective for sensing, where selectivity is achieved within a single chemically graded nanostructured sensing unit, rather than from an array of separate sensors.

Tropoelastin improves adhesion and migration of intra-articular injected infrapatellar fat pad MSCs and reduces osteoarthritis progression.

Intra-articular injection of mesenchymal stem cells (MSCs) is a promising strategy for osteoarthritis (OA) treatment. However, more and more studies reveal that the injected MSCs have poor adhesion, migration, and survival in the joint cavity. A recent study shows that tropoelastin (TE) regulates adhesion, proliferation and phenotypic maintenance of MSCs as a soluble additive, indicating that TE could promote MSCs-homing in regenerative medicine. In this study, we used TE as injection medium, and compared it with classic media in MSCs intra-articular injection such as normal saline (NS), hyaluronic acid (HA), and platelet-rich plasma (PRP). We found that TE could effectively improve adhesion, migration, chondrogenic differentiation of infrapatellar fat pad MSCs (IPFP-MSCs) and enhance matrix synthesis of osteoarthritic chondrocytes (OACs) in indirect-coculture system. Moreover, TE could significantly enhance IPFP-MSCs adhesion via activation of integrin ß1, ERK1/2 and vinculin (VCL) in vitro. In addition, intra-articular injection of TE-IPFP MSCs suspension resulted in a short-term increase in survival rate of IPFP-MSCs and better histology scores of rat joint tissues. Inhibition of integrin ß1 or ERK1/2 attenuated the protective effect of TE-IPFP MSCs suspension in vivo. In conclusion, TE promotes performance of IPFP-MSCs and protects knee cartilage from damage in OA through enhancement of cell adhesion and activation of integrin ß1/ERK/VCL pathway. Our findings may provide new insights in MSCs intra-articular injection for OA treatment.

Etanercept embedded silk fibroin/pullulan hydrogel enhance cartilage repair in bone marrow stimulation.

Background: Bone marrow stimulation (BMS) is the most used operative treatment in repairing cartilage defect clinically, but always results in fibrocartilage formation, which is easily worn out and needs second therapy. In this study, we prepared an Etanercept (Ept) embedded silk fibroin/pullulan hydrogel to enhance the therapeutic efficacy of BMS. Methods: Ept was dissolved in silk fibroin (SF)-tyramine substituted carboxymethylated pullulan (PL) solution and enzyme crosslinked to obtain the Ept contained SF/PL hydrogel. The synergistical effect of SF/PL hydrogel and Ept was verified by rabbit osteochondral defect model. The mechanism of Ept in promoting articular cartilage repair was studied on human osteoarthritic chondrocytes (hOACs) and human bone marrow mesenchymal stromal cells (hBMSCs) in vitro, respectively. Results: At 4 and 8 weeks after implanting the hydrogel into the osteochondral defect of rabbit, histological analysis revealed that the regenerated tissue in Ept + group had higher cellular density with better texture, and the newly formed hyaline cartilage tissue was seamlessly integrated with adjacent native tissue in the Ept + group. In cellular experiments, Ept treatment significantly promoted both gene and protein expression of type II collagen in hOACs, while decreased the protein levels of metalloproteinase (MMP)-13 and a disintegrin and metalloprotease with thrombospondin motifs 5 (ADAMTS5); alcian blue staining, type II collagen and aggrecan stainings showed that addition of Ept significantly reversed the chondrogenesis inhibition effect of tumor necrosis factor alpha (TNF-α) on hBMSCs. Conclusion: BMS could be augmented by Ept embedded hydrogel, potentially by regulating the catabolic and anabolic dynamics in adjacent chondrocytes and enhancement of BMSCs chondrogenesis.

Observation of Solute Transport between Articular Cartilage and Subchondral Bone in Live Mice.

OBJECTIVE: To establish a method for investigating the permeability of calcified cartilage zone (CCZ) and to observe solute transport between articular cartilage (AC) and subchondral bone (SB) through intact CCZ in vivo. DESIGN: We developed a novel fixing device combined with un-decalcified fluorescence observation method to address the permeability of CCZ in live mice. Twenty-four Balb/c female mice aged 1 to 8 months were used to observe the development of CCZ. Eighty-four Balb/c female mice (aged 1 or 6 months) with mature or immature CCZ of distal femur were used to investigate the permeability of intact CCZ in vivo. Diffusivity of rhodamine B (476 Da) and tetramethyl-rhodamine isothicyanate-dextran (TRITC-Dextran, 20 kDa) was tested from AC to SB in 0 minutes, 1 minute, 15 minutes, 30 minutes, 1 hour, and 2 hours. None diffused knee joints (0 minutes) served as blank control, while in vitro immersion of distal femurs in rhodamine B or TRITC-Dextran for 72 hours served as positive control. RESULTS: CCZ was well developed in 6-month mice. Both tracers penetrated immature CCZ down to SB in less than 1 hour in live mice, while the diffusion of both tracers decreased rapidly at tidemark in all testing time points. CONCLUSION: Current study provided direct evidence of blocking effect of CCZ in solute transportation during short diffusion period in live animal, indicating the important role of CCZ in joint development and microenvironment maintenance.

Microconvex Dot-Featured Silk Fibroin Films for Promoting Human Umbilical Vein Endothelial Cell Angiogenesis via Enhancing the Expression of bFGF and VEGF.

Insufficient vascularization of grafts often leads to delayed tissue ingrowth and impaired tissue function in tissue engineering. The surface topography of grafts plays critical roles in angiogenesis. In the present study, we prepared silk fibroin (SF)-based microtopography films with the number of convex dots ranging from 37 to 4835/mm2. The convex dot-featured topography surfaces were characterized by scanning electron microscopy, a Profilm3D optical profilometer, atomic force microscopy, and a contact angle goniometer. The effect of microtopographic films on the proliferation, adhesion, and expression of angiogenic factors of human umbilical vein endothelial cells (HUVECs) was investigated. Our results demonstrated that the SF film surface with 2899 convex dots/mm2 significantly enhanced adhesion, viability, and levels of vascular endothelial growth factors and basic fibroblast growth factors of HUVECs and significantly downregulated the level of α-SMA in human aortic smooth muscle cells, indicating that the microtopographic films could promote angiogenesis. Furthermore, in vitro results showed that HUVEC proliferation was positively correlated with yes-associated protein (YAP) activation, suggesting that the enhanced angiogenesis was mediated via the YAP pathway. Finally, mice subcutaneous embedding model results indicated that the SF film surface with 2899 convex dots/mm2 could significantly enhance angiogenesis in vivo. Altogether, our results showed that the SF film surface with 2899 convex dots/mm2 promoted the angiogenesis of HUVECs and offered a novel angiogenesis-promoting strategy of implant surface design for tissue engineering.

Towards outperforming conventional sensor arrays with fabricated individual photonic vapour sensors inspired by Morpho butterflies.

Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.

Battery-free radio frequency identification (RFID) sensors for food quality and safety.

Market demands for new sensors for food quality and safety stimulate the development of new sensing technologies that can provide an unobtrusive sensor form, battery-free operation, and minimal sensor cost. Intelligent labeling of food products to indicate and report their freshness and other conditions is one important possible application of such new sensors. This study applied passive (battery-free) radio frequency identification (RFID) sensors for the highly sensitive and selective detection of food freshness and bacterial growth. In these sensors, the electric field generated in the RFID sensor antenna extends from the plane of the RFID sensor and is affected by the ambient environment, providing the opportunity for sensing. This environment may be in the form of a food sample within the electric field of the sensing region or a sensing film deposited onto the sensor antenna. Examples of applications include monitoring of milk freshness, fish freshness, and bacterial growth in a solution. Unlike other food freshness monitoring approaches that require a thin film battery for operation of an RFID sensor and fabrication of custom-made sensors, the passive RFID sensing approach developed here combines the advantages of both battery-free and cost-effective sensor design and offers response selectivity that is impossible to achieve with other individual sensors.

Synthesis and characterization of amphiphilic phenylene ethynylene oligomers and their Langmuir-Blodgett films.

We report the synthesis of a series of amphiphilic molecular building blocks that can be self-assembled at the air-water interface to form two- and three-dimensional nanostructures with tunable optoelectronic properties. Compression of these molecular building blocks using the Langmuir-Blodgett method gives rise to monolayer and multilayer thin films with different packing densities and electronic properties that are tunable due to varying pi-pi (hydrophobic) interactions. Depending on the noncovalent interaction between chromophores, we observe a transition toward denser packing with increasing number of phenylene ethynylene repeat units. Additionally, we use quantum-chemical simulations to help determine the excited-state electronic structure, intermolecular interactions, and packing trends. Our results demonstrate that the interplay between dipole-dipole and pi-pi interactions dominates the formation of thin films with various packing densities and determines the associated optical properties.

Synthesis and characterization of monolayers and Langmuir-Blodgett films of an amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline conjugate.

A novel amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline (A16) tricomponent conjugate, C60>(A16-EG43), possessing a well-defined number of repeating aniline donor units and a hydrophilic ethylene glycol oligomer chain was synthesized. The compound is composed of a covalently bound donor-acceptor chromophore structure. Molecular self-assembly of C60>(A16-EG43) at the air-water interface formed a densely packed Langmuir monolayer with all highly hydrophobic fullerene cages located above the liquid interface. The monolayer can then be transferred onto a glass substrate via Langmuir-Blodgett (LB) deposition. LB multilayered thin films formed by multiple deposition of the monolayer yielded broadened optical absorption peaks extending beyond 600 nm into the 950 nm region, suggesting strong intermolecular interactions among the C60 cages and the A16 moieties. An X-ray reflectometry study clearly reveals that the Langmuir film at the air-water interface consists of a C60 top layer and a bottom layer containing hexcadecaaniline and oligo(ethylene glycol) with gradually decreasing electron density over a distance of approximately 130 A above bulk water. The pressure isotherm shows that the packing density of the C60>(A16-EG43) monolayer, corresponding to a molecular area of approximately 95 A2/molecule, is similar to that of the surface area of the C60 monolayer. This result suggests that C60 packing plays a dominant role in guiding the formation of the monolayer structure. Further photoexcitation of hexadecaaniline moieties of aligned (C60>)-A16 layers by a flash light source induces cross linking between adjacent A16 segments forming an interlinked A16 array. Our results have demonstrated a unique fabrication method for preparing the aligned donor-acceptor array using strong intermolecular interactions between fullerenes as the molecular orientation guiding force in the Langmuir-Blodgett technique.

Synthesis and characterization of amphiphilic fullerenes and their Langmuir-Blodgett films.

We report here the synthesis and characterization of three amphiphilic fullerene derivatives and their Langmuir-Blodgett thin films. Two of the C(60) amphiphiles are mono-derivatives with a long alkyl chain terminated with either -COOH (2) or NH(2) (3) as the hydrophilic headgroup, and the third one (5) is designed to bear the same NH(2) group as 3 but with 10 additional hydrophobic alkyl chains grafted on the C(60) sphere (Scheme 1). These amphiphiles form stable, ordered monolayers at the air-water interface. The molecular packing at the air-water interface and the mean area per molecule are determined by pressure isotherms at room temperature. Hysteresis of pressure isotherms of side chain C(60) (5) shows complete reversibility upon compression and decompression, which suggests that side chains on the C(60) sphere inhibit formation of aggregates at the air-water interface. Comparative studies of all three amphiphiles allow us to better determine the interaction between C(60)'s and their self-assembly kinetics at the air-water interface. Monolayers of monoderivatized amphiphiles (2 and 3) were transferred successfully onto quartz substrates as Z-type multilayered Langmuir-Blodgett films, and monolayers of 5 were transferred as Y-type films. Detailed characterization of the multilayer films (Z-type deposition) prepared from amine-terminated C(60) (3) using X-ray and neutron reflectometry reveals staggering of C(60) spheres and a head-to-head (Y-type) structure presumably due to flipping and reattaching of C(60) amphiphiles to the previous underlying C(60) layer.