Unlocking the Potential of Liquid Plasma Polymer Films: Characterizing Aging Effects and Their Impact on the Wrinkling Phenomenon.

Here, we present the study of the intricate dynamics between the physicochemical properties of liquid propanethiol plasma polymer films (PPFs) and the formation of wrinkles in PPF/Al bilayers. The study investigates the effect of liquid PPF aging in the air before top Al layer deposition by magnetron sputtering on the wrinkling phenomenon for 4 days. Thanks to atomic force microscopy, the wrinkle dimensions were found to decrease by approximately 55% in amplitude and 66% in wavelength, correlated with an increase in the viscosity of the PPF over the aging duration (i.e., from less than 107 to 1010 Pa·s). This behavior is not linked to alterations in cross-linking degree as evidenced by time-of-flight secondary ion mass spectrometry experiments but rather to network densification driven by the inherent molecular chain mobility due to the viscous state of the PPF. X-ray photoelectron spectroscopy measurements emphasizing the absence of oxidation of the PPF over the aging duration support this, revealing a unique aging mechanism distinct from other plasma polymer families. Overall, this study offers valuable insights into the design and application of mechanically responsive PPFs involved in bilayer systems, paving the way for advancements in nanotechnology and related fields.

Designing Nanostructured Organic-Based Material by Combining Plasma Polymerization and the Wrinkling Approach.

In this work, an innovative and versatile strategy for the fabrication of nanostructured organic thin films is established based on the wrinkling phenomenon taking place in a bilayer system constituted by a liquid plasma polymer film (PPF) and a top Al coating. By means of morphological characterization (i.e., atomic force microscopy and scanning electron microscopy), it has been demonstrated that the wrinkle dimensions (i.e., wavelength and amplitude) evolve as a function of the PPF thickness according to models established for conventional polymers. The wrinkled surfaces exhibit great stability over time as their dimension did not vary after 100 days of aging, resulting from a pinning phenomenon between the Al layer and the Si substrate, hence freezing the morphology. In a second step, the wrinkled surfaces have been employed as templates for the deposition of an additional PPF third layer, giving rise to the formation of a nanostructured organic-based surface. The chemical composition of the material can be tuned through an appropriate choice of precursor (i.e., allyl alcohol or propanethiol).

Investigating the relationship between the mechanical properties of plasma polymer-like thin films and their glass transition temperature.

This work aims at understanding the influence of the substrate temperature (Ts) on the viscoelastic properties of propanethiol plasma polymer films (PPFs). By means of state-of-the-art AFM characterization-based techniques including peak force quantitative nanomechanical mapping (PFQNM), nano dynamic mechanical analysis (nDMA) and "scratch" experiments, it has been demonstrated that the mechanical behaviour of PPFs is dramatically affected by the thermal conditions of the substrate. Indeed, the material behaves from a high viscous liquid (i.e. viscosity ∼ 106 Pa s) to a viscoelastic solid (loss modulus ∼ 1.17 GPa, storage modulus ∼ 1.61 GPa) and finally to an elastic solid (loss modulus ∼ 1.95 GPa, storage modulus ∼ 8.51 GPa) when increasing Ts from 10 to 45 °C. This behaviour is ascribed to an increase in the surface glass transition temperature of the polymeric network. The latter has been correlated with the chemical composition through the presence of unbound molecules acting as plasticizers and the cross-linking density of the layers. In a second step, this knowledge is exploited for the fabrication of a nanopattern by generating surface instabilities in the propanethiol PPF/Al bilayer system.

Kinked Silicon Nanowires: Superstructures by Metal-Assisted Chemical Etching.

We report on metal-assisted chemical etching of Si for the synthesis of mechanically stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle, and location of the kinks via successive etch-quench sequences. We analyzed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine-tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be incorporated in biological cells without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physicochemical events at the Si/Au-electrolyte interface and offers guidelines for the development of finite-element modeling of metal-assisted Si chemical etching.

Contactless Control of Local Surface Buckling in Photoaligned Gold/Liquid Crystal Polymer Bilayers.

Wrinkling is a powerful technique for the preparation of surface structures over large areas, but it is difficult to simultaneously control the direction, period, and amplitude of the wrinkles without resorting to complicated procedures. In this work, we demonstrate a wrinkling system consisting of a liquid crystal polymer network and a thin layer of gold, in which the direction of the wrinkles is controlled by the alignment of the liquid crystal molecules and the average amplitude and period are controlled by a high-intensity UV irradiation. The UV exposure represses the amplitude and period dictated by the total exposure. Using photoalignment and photomasks, we demonstrate an unprecedented control over the wrinkling parameters and were able to generate some striking optical patterns. The mechanism of the wrinkle suppression was investigated and appears to involve localized photodegradation at the polymer-gold interface, possibly due to the formation of mechanoradicals.

3D Orientational Control in Self-Assembled Thin Films with Sub-5 nm Features by Light.

While self-assembled molecular building blocks could lead to many next-generation functional organic nanomaterials, control over the thin-film morphologies to yield monolithic sub-5 nm patterns with 3D orientational control at macroscopic length scales remains a grand challenge. A series of photoresponsive hybrid oligo(dimethylsiloxane) liquid crystals that form periodic cylindrical nanostructures with periodicities between 3.8 and 5.1 nm is studied. The liquid crystals can be aligned in-plane by exposure to actinic linearly polarized light and out-of-plane by exposure to actinic unpolarized light. The photoalignment is most efficient when performed just under the clearing point of the liquid crystal, at which the cylindrical nanostructures are reoriented within minutes. These results allow the generation of highly ordered sub-5 nm patterns in thin films at macroscopic length scales, with control over the orientation in a noncontact fashion.

Probing viscoelastic response of soft material surfaces at the nanoscale.

We study the interaction between an AFM tip and a soft viscoelastic surface. Using a multifrequency method we measure the amplitude-dependence of the cantilever dynamic force quadratures, which clearly show the effect of finite relaxation time of the viscoelastic surface. A model is introduced which treats the tip and surface as a two-body dynamic problem with a nonlinear interaction depending on their separation. We find good agreement between simulations of this model and experimental data on polymer blend samples for a variety of materials and measurement conditions.

Fiber-Optic SPR Immunosensors Tailored To Target Epithelial Cells through Membrane Receptors.

We report, for the first time, the use of a surface plasmon resonance (SPR) fiber-optic immunosensor for selective cellular detection through membrane protein targeting. The sensor architecture lies on gold-coated tilted fiber Bragg gratings (Au-coated TFBGs) photoimprinted in the fiber core via a laser technique. TFBGs operate in the near-infrared wavelength range at ∼1550 nm, yielding optical and SPR sensing characteristics that are advantageous for the analyses of cellular bindings and technical compatibility with relatively low-cost telecommunication-grade measurement devices. In this work, we take consider their numerous assets to figure out their ability to selectively detect intact epithelial cells as analytes in cell suspensions in the range of 2-5 × 10(6) cells mL(-1). For this, the probe was first thermally annealed to ensure a strong adhesion of the metallic coating to the fiber surface. Its surface was then functionalized with specific monoclonal antibodies via alkanethiol self-assembled monolayers (SAMs) against extracellular domain of epidermal growth factor receptors (EGFRs) and characterized by peak force tapping atomic force microscopy. A differential diagnosis has been demonstrated between two model systems. The developed immunosensors were able to monitor, in real time, the specific attachment of single intact cells in concentrations from 3 × 10(6) cells mL(-1). Such results confirm that the developed probe fits the lab-on-fiber technology and has the potential to be used as a disposable device for in situ and real-time clinical diagnosis.

Modification of the adhesive properties of silicone-based coatings by block copolymers.

The improvement of the (bio)adhesive properties of elastomeric polydimethylsiloxane (PDMS) coatings is reported. This is achieved by a surface modification consisting of the incorporation of block copolymers containing a PDMS block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix, followed by matrix cross-linking and immersion of the obtained materials in water. Contact angle measurements (CA), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) showed the presence of the PDMAEMA block at the surface, drastic morphology changes, and improved adhesion properties after immersion in water. Finally, underwater bioadhesion tests show that mussels adhere only to block copolymer-filled coatings and after immersion in water, i.e., when the PDMAEMA blocks have been brought to the coating surface. These observations highlight the significant role of hydrophilic groups in the surface modification of silicone coatings.

Patterned silver nanoparticles embedded in a nanoporous smectic liquid crystalline polymer network.

A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic-inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

High-relaxivity and luminescent silica nanoparticles as multimodal agents for molecular imaging.

The design and synthesis of a new bimodal contrast agent for magnetic resonance imaging and optical imaging is reported. Tunable-sized silica nanoparticles were synthesized by a microemulsion-mediated pathway and used as carriers for paramagnetic and luminescent probes. The near-infrared luminescent agent was a ruthenium complex that was directly entrapped in the silica shell to provide photoluminescence enhancement and to make it highly photostable as it was protected from the surrounding environment. The paramagnetic activity came from a Gd-DTPA derivative that was grafted on the silica surface. NMRD profiles showed a strong relaxivity enhancement (increase of 432% in the r1 value at 20 MHz) when the paramagnetic complex was grafted at the nanoparticle surface, because of a reduction of its mobility. Polyethylene glycol was also grafted at the nanoparticle surface to enhance the nanoparticle residence time in the bloodstream. A thorough characterization of the material confirmed its potential as a very effective bimodal contrast agent.

Self-assembly of a barnacle cement protein into intertwined amyloid fibres and determination of their adhesive and viscoelastic properties.

The stalked barnacle Pollicipes pollicipes uses a multi-protein cement to adhere to highly varied substrates in marine environments. We investigated the morphology and adhesiveness of a component 19 kDa protein in barnacle cement gland- and seawater-like conditions, using transmission electron microscopy and state-of-the art scanning probe techniques. The protein formed amyloid fibres after 5 days in gland-like but not seawater conditions. After 7-11 days, the fibres self-assembled under gland-like conditions into large intertwined fibrils of up to 10 µm in length and 200 nm in height, with a distinctive twisting of fibrils evident after 11 days. Atomic force microscopy (AFM)-nanodynamic mechanical analysis of the protein in wet conditions determined E' (elasticity), E'' (viscosity) and tan δ values of 2.8 MPa, 1.2 MPa and 0.37, respectively, indicating that the protein is a soft and viscoelastic material, while the adhesiveness of the unassembled protein and assembled fibres, measured using peak force quantitative nanomechanical mapping, was comparable to that of the commercial adhesive Cell-Tak™. The study provides a comprehensive insight into the nanomechanical and viscoelastic properties of the barnacle cement protein and its self-assembled fibres under native-like conditions and may have application in the design of amyloid fibril-based biomaterials or bioadhesives.

Selective separation of plastic LED lamp components using electrodynamic fragmentation for material recovery.

The recycling of light-emitting diode (LED) lamps and tubes is becoming increasingly important due to their growing market share as energy-efficient lighting technology. Here we report on the use of high voltage electric-pulse fragmentation to recover elementary components such as LED chips and printed circuit boards (drivers). E27 LED lamps with plastic bulbs, which represent 48% of deposits collected by a French company, are used as a case study. More than 150 lamps were tested on a laboratory reactor for electrodynamic fragmentation. The technological process in which highly energetic electrical pulses were applied to materials immersed in water was studied in order to separate the components of the LED lamps using a minimal specific energy. The estimated energy necessary to achieve total separation assessed at 64%, without grinding pretreatment, was 5.2 ± 0.6 kWh per ton, representing a mass recycling rate of 74%. Based on the disassembled material, the commercial value of the recovered materials was thus estimated. Gold, as the most representative material, was found to represent 0.03% of the mass fraction for 83.6% of the total commercial value. The process disassembling capacity is a key issue to increase the recycling rate of current LED lamps and tubes.

Disentangling the Roles of Functional Domains in the Aggregation and Adsorption of the Multimodular Sea Star Adhesive Protein Sfp1.

Sea stars can adhere to various underwater substrata using an adhesive secretion of which Sfp1 is a major component. Sfp1 is a multimodular protein composed of four subunits (Sfp1 Alpha, Beta, Delta, and Gamma) displaying different functional domains. We recombinantly produced two fragments of Sfp1 comprising most of its functional domains: the C-terminal part of the Beta subunit (rSfp1 Beta C-term) and the Delta subunit (rSfp1 Delta). Surface plasmon resonance analyses of protein adsorption onto different model surfaces showed that rSfp1 Beta C-term exhibits a significantly higher adsorption than the fibrinogen control on hydrophobic, hydrophilic protein-resistant, and charged self-assembled monolayers, while rSfp1 Delta adsorbed more on negatively charged and on protein-resistant surfaces compared to fibrinogen. Truncated recombinant rSfp1 Beta C-term proteins were produced in order to investigate the role of the different functional domains in the adsorption of this protein. The analysis of their adsorption capacities on glass showed that two mechanisms are involved in rSfp1 Beta C-term adsorption: (1) one mediated by the EGF-like domain and involving Ca2+ and Mg2+ ions, and (2) one mediated by the sequence of Sfp1 Beta with no homology with known functional domain in databases, in the presence of Na+, Ca2+ and Mg2+ ions.

Solvent-Free Design of Biobased Non-isocyanate Polyurethanes with Ferroelectric Properties.

Increasing energy autonomy and lowering dependence on lithium-based batteries are more and more appealing to meet our current and future needs of energy-demanding applications such as data acquisition, storage, and communication. In this respect, energy harvesting solutions from ambient sources represent a relevant solution by unravelling these challenges and giving access to an unlimited source of portable/renewable energy. Despite more than five decades of intensive study, most of these energy harvesting solutions are exclusively designed from ferroelectric ceramics such as Pb(Zr,Ti)O3 and/or ferroelectric polymers such as polyvinylidene fluoride and its related copolymers, but the large implementation of these piezoelectric materials into these technologies is environmentally problematic, related with elevated toxicity and poor recyclability. In this work, we reveal that fully biobased non-isocyanate polyurethane-based materials could afford a sustainable platform to produce piezoelectric materials of high interest. Interestingly, these non-isocyanate polyurethanes (NIPUs) with ferroelectric properties could be successfully synthesized using a solvent-free reactive extrusion process on the basis of an aminolysis reaction between resorcinol bis-carbonate and different diamine extension agents. Structure-property relationships were established, indicating that the ferroelectric behavior of these NIPUs depends on the nanophase separation inside these materials. These promising results indicate a significant potential for fulfilling the requirements of basic connected sensors equipped with low-power communication technologies.

Microwave Atmospheric Plasma: A Versatile and Fast Way to Confer Antimicrobial Activity toward Direct Chitosan Immobilization onto Poly(lactic acid) Substrate.

In this study, a simple method to immobilize chitosan on a poly(lactic acid) (PLA) surface was developed in a fast manner. The immobilization was realized in two steps. First, an atmospheric plasma (MWAP) torch was used to modify the PLA surface in less than 5 min in order to create enough activated sites toward the chitosan adhesion, followed by a direct dip coating to spread and immobilize chitosan on this MWAP-modified PLA surface. The modification of the PLA surface properties was confirmed by X-ray photoelectron spectroscopy (XPS), water contact angle, and atomic force microscopy. It resulted that the activated species derived from the plasma torch, i.e., hydroxyl and carboxylic acid moieties, enabled an increase of the hydrophilicity of the PLA surface. Interestingly, this activated surface allows a good spreading of chitosan solution from dip coating and leads to a homogeneous stable coating. Our XPS results bring us the hypothesis that the stabilization of the chitosan layer is mainly induced by noncovalent interactions such as hydrogen bonding and electrostatic interactions. A first insight into the biological properties of theses surfaces was assessed in terms of the antimicrobial activity of the here-designed surfaces.

Sea star-inspired recombinant adhesive proteins self-assemble and adsorb on surfaces in aqueous environments to form cytocompatible coatings.

Sea stars adhere to various underwater substrata using an efficient protein-based adhesive secretion. The protein Sfp1 is a major component of this secretion. In the natural glue, it is cleaved into four subunits (Sfp1 Alpha, Beta, Delta and Gamma) displaying specific domains which mediate protein-protein or protein-carbohydrate interactions. In this study, we used the bacterium E. coli to produce recombinantly two fragments of Sfp1 comprising most of its functional domains: the C-terminal part of the Beta subunit (rSfp1 Beta C-term) and the Delta subunit (rSfp1 Delta). Using native polyacrylamide gel electrophoresis and size exclusion chromatography, we show that the proteins self-assemble and form oligomers and aggregates in the presence of NaCl. Moreover, they adsorb onto glass and polystyrene upon addition of Na+ and/or Ca2+ ions, forming homogeneous coatings or irregular meshworks, depending on the cation species and concentration. We show that coatings made of each of the two proteins have no cytotoxic effects on HeLa cells and even increase their proliferation. We propose that the Sfp1 recombinant protein coatings are valuable new materials with potential for cell culture or biomedical applications. STATEMENT OF SIGNIFICANCE: Biological adhesives offer impressive performance in their natural context and, therewith, the potential to inspire the development of advanced biomaterials for an increasing variety of applications in medicine or in material sciences. To date, most marine adhesive proteins that have been produced recombinantly in order to develop bio-inspired adhesives are small proteins from mussels and barnacles. Here, we produced two multi-modular proteins based on the sequence of Sfp1, a major protein from sea star adhesive secretion. These two proteins comprise most of Sfp1 functional domains which mediate protein-protein and protein-carbohydrate interactions. We characterized the two recombinant proteins with an emphasis on functional characteristics such as self-assembly, adsorption and cytocompatibility. We discuss their potential as biomaterials.

Structure and composition of the tunic in the sea pineapple Halocynthia roretzi: A complex cellulosic composite biomaterial.

Biological organisms produce high-performance composite materials, such as bone, wood and insect cuticle, which provide inspiration for the design of novel materials. Ascidians (sea squirts) produce an organic exoskeleton, known as a tunic, which has been studied quite extensively in several species. However, currently, there are still gaps in our knowledge about the detailed structure and composition of this cellulosic biocomposite. Here, we investigate the composition and hierarchical structure of the tough tunic from the species Halocynthia roretzi, through a cross-disciplinary approach combining traditional histology, immunohistochemistry, vibrational spectroscopy, X-ray diffraction, and atomic force and electron microscopies. The picture emerging is that the tunic of H. roretzi is a hierarchically-structured composite of cellulose and proteins with several compositionally and structurally distinct zones. At the surface is a thin sclerotized cuticular layer with elevated composition of protein containing halogenated amino acids and cross-linked via dityrosine linkages. The fibrous layer makes up the bulk of the tunic and is comprised primarily of helicoidally-ordered crystalline cellulose fibres with a lower protein content. The subcuticular zone directly beneath the surface contains much less organized cellulose fibres. Given current efforts to utilize biorenewable cellulose sources for the sustainable production of bio-inspired composites, these insights establish the tunic of H. roretzi as an exciting new archetype for extracting relevant design principles. STATEMENT OF SIGNIFICANCE: Tunicates are the only animals able to produce cellulose. They use this structural polysaccharide to build an exoskeleton called a tunic. Here, we investigate the composition and hierarchical structure of the tough tunic from the sea pineapple Halocynthia roretzi through a multiscale cross-disciplinary approach. The tunic of this species is a composite of cellulose and proteins with two distinct layers. At the surface is a thin sclerotized cuticular layer with a higher protein content containing halogenated amino acids and cross-linked via dityrosine linkages. The fibrous layer makes up the bulk of the tunic and is comprised of well-ordered cellulose fibres with a lower protein content. Given current efforts to utilize cellulose to produce advanced materials, the tunic of the sea pineapple provides a striking model for the design of bio-inspired cellulosic composites.

Elastic conducting polymer composites in thermoelectric modules.

The rapid growth of wearables has created a demand for lightweight, elastic and conformal energy harvesting and storage devices. The conducting polymer poly(3,4-ethylenedioxythiophene) has shown great promise for thermoelectric generators, however, the thick layers of pristine poly(3,4-ethylenedioxythiophene) required for effective energy harvesting are too hard and brittle for seamless integration into wearables. Poly(3,4-ethylenedioxythiophene)-elastomer composites have been developed to improve its mechanical properties, although so far without simultaneously achieving softness, high electrical conductivity, and stretchability. Here we report an aqueously processed poly(3,4-ethylenedioxythiophene)-polyurethane-ionic liquid composite, which combines high conductivity (>140 S cm-1) with superior stretchability (>600%), elasticity, and low Young's modulus (<7 MPa). The outstanding performance of this organic nanocomposite is the result of favorable percolation networks on the nano- and micro-scale and the plasticizing effect of the ionic liquid. The elastic thermoelectric material is implemented in the first reported intrinsically stretchable organic thermoelectric module.