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Biomaterials such as cotton and silk are abundant natural resources that have demonstrated material properties equal or superior to many synthetic polymers. Using ionic liquids (ILs) and the Natural Fiber Welding (NFW) process, these biomaterials can be chemically and physically enhanced. Here we present our progress on using imidazolium-based polymerizable ionic liquids (Poly-ILs) in the NFW process to prepare polyionic biocomposites. A variety of Poly-ILs with different cation and anion structures were synthesized and subsequently characterized using 1H and 13C NMR. Each Poly-IL was evaluated for its ability to (i) polymerize and (ii) solubilize a biopolymer (cellulose) matrix, revealing anion structural motifs that either limit or enhance a Poly-IL’s ability to polymerize and weld. Optimized parameters yielded polyionic biocomposite materials whose physicochemical properties were evaluated using ATR, SEM and EIS. Figure 1

We investigated a chemically modified rhodamine B dye as a sensor of local water content in dye-modified epoxy resins, where these measurements were combined with dielectric measurements to estimate the dye-water association ratio in the material. In particular, the water-sensitive fluorogenic dye was covalently attached to the epoxy resin backbone. This dye becomes fluorescent only upon photoactivation by ultraviolet light and its protonation in the presence of water. High-resolution noncontact microwave cavity dielectric measurements on these materials indicate a decrease of the dielectric permittivity upon photoactivation. We utilize this effect to determine the average extent of hydration of the activated dye molecules. Our results suggest that fluorogenic dyes are promising for the quantification of the local water content in polymer materials, such as the technologically important problem of interfacial water in epoxy materials.

Polymer nanocomposites containing self-assembled cellulose nanocrystals (CNCs) are ideal for advanced applications requiring both strength and toughness as the helicoidal structure of the CNCs deflects crack propagation and the polymer matrix dissipates impact energy. However, any adsorbed water layer surrounding the CNCs may compromise the interfacial adhesion between the polymer matrix and the CNCs, thus impacting stress transfer at that interface. Therefore, it is critical to study the role of water at the interface in connecting the polymer dynamics and the resulting mechanical performance of the nanocomposite. Here, we explore the effect of polymer confinement and water content on polymer dynamics in CNC nanocomposites by covalently attaching a fluorogenic water-sensitive dye to poly(diethylene glycol methyl ether methacrylate) (PMEO

This study experimentally substantiates that the micromechanical compatibility between cell and substrate is essential for cells to achieve energetically favorable mechanotransduction that directs phenotypic transitions. The argument for this compatibility is based on a thermodynamic model that suggests that the response of cells to their substrate mechanical environment is a consequence of the interchange between forms of energy governing the cell-substrate interaction. Experimental validation for the model has been carried out by investigating the osteogenic differentiation of dental follicle stem cells (DFSCs) seeded on electrospun fibrous scaffolds. Electrospinning of blends containing polycaprolactone (PCL) and silk fibroin (SF) with varying composition of cellulose nanocrystals (CNCs) resulted in three-dimensional (3D) fibrous scaffolds with bimodal distribution of fiber diameter, which provides both macroscopically stiff and microscopically compliant scaffolds for cells without affecting the surface chemical functionality of scaffolds. Atomic force microscopy (AFM) with a colloidal probe and single-cell force spectroscopy were used to characterize cell stiffness and scaffold stiffness on the cellular level, as well as cell-scaffold adhesive interaction (chemical functionality). This study has successfully varied scaffold mechanical properties without affecting their surface chemistry. In vitro tests indicate that the micromechanical compatibility between cells and scaffolds has been significantly correlated with mechanosensitive gene expression markers and osteogenic differentiation markers of DFSCs. The agreement between experimental observations and the thermodynamic model affirms that the cellular response to the mechanical environment, though biological in nature, follows the laws of the energy interchange to achieve its self-regulating behavior. More importantly, this study provides systematic evidence, through extensive and rigorous experimental studies, for the first time that rationalizes that micromechanical compatibility is indeed important to the efficacy of regenerative medicine.

Scratches in polymer coatings and barrier layers negatively impact optical properties (haze, light transmission, etc.), initiate routes of degradation or corrosion (moisture permeability), and nucleate delamination of the coating. Detecting scratches in coatings on advanced materials systems is an important component of structural health monitoring but can be difficult if the defects are too small to be detected by the naked eye. The primary focus of the present work is to investigate scratch damage using fluorescence lifetime imaging microscopy (FLIM) and mechanical activation of a mechanophore (MP)-containing transparent epoxy coating. The approach utilizes a Berkovich tip to scratch MP-epoxy coatings under a linearly increasing normal load. The goal is to utilize the fluorescent behavior of activated MPs to enable the detection of microscale scratches and molecular scale changes in polymeric systems. Taking advantage of the amine functionality present in a polyetheramine/bisphenol A epoxy network, a modified rhodamine dye is covalently bonded into a transparent, thermoset polymer network. Following instrumented scratch application, subsequent fluorescence imaging of the scratched MP-epoxy reveals the extent of fluorescence activation induced by the mechanical deformation. In this work, the rhodamine-based mechanophore is used to identify both ductile and fracture-dominated processes during the scratch application. The fluorescence intensity increases linearly with the applied normal load and is sensitive to fracture dominated processes. Fluorescence lifetime and hyperspectral imaging of damage zones provide additional insight into the local (nanoscopic) environment and molecular structure of the MP around the fracture process zone, respectively. The mechanophore/scratch deformation approach allows a fluorescence microscope to probe local yielding and fracture events in a powerful way that enhances the optical characterization of damage zones formed by standard scratch test methods and leads to novel defect detection strategies.

In this case report, we focus on Muenke syndrome (MS), a disease caused by the p.Pro250Arg variant in fibroblast growth factor receptor 3 (FGFR3) and characterized by uni- or bilateral coronal suture synostosis, macrocephaly without craniosynostosis, dysmorphic craniofacial features, and dental malocclusion. The clinical findings of MS are further complicated by variable expression of phenotypic traits and incomplete penetrance. As such, unraveling the mechanisms behind MS will require a comprehensive and systematic way of phenotyping patients to precisely identify the impact of the mutation variant on craniofacial development. To establish this framework, we quantitatively delineated the craniofacial phenotype of an individual with MS and compared this to his unaffected parents using three-dimensional cephalometric analysis of cone beam computed tomography scans and geometric morphometric analysis, in addition to an extensive clinical evaluation. Secondly, given the utility of human induced pluripotent stem cells (hiPSCs) as a patient-specific investigative tool, we also generated the first hiPSCs derived from a family trio, the proband and his unaffected parents as controls, with detailed characterization of all cell lines. This report provides a starting point for evaluating the mechanistic underpinning of the craniofacial development in MS with the goal of linking specific clinical manifestations to molecular insights gained from hiPSC-based disease modeling.

An optimal methodology for locating and tracking cellulose nanofibers (CNFs) in vitro and in vivo is crucial to evaluate the environmental health and safety properties of these nanomaterials. Here, we report the use of a new boron-dipyrromethene (BODIPY) reactive fluorescent probe, meso-DichlorotriazineEthyl BODIPY (mDTEB), tailor-made for labeling CNFs used in simulated or in vivo ingestion exposure studies. Time-correlated single photon counting (TCSPC) fluorescence lifetime imaging microscopy (FLIM) was used to confirm covalent attachment and purity of mDTEB-labeled CNFs. The photoluminescence properties of mDTEB-labeled CNFs, characterized using fluorescence spectroscopy, include excellent stability over a wide pH range (pH2 to pH10) and high quantum yield, which provides detection at low (μM) concentrations. FLIM analysis also showed that lignin-like impurities present on the CNF reduce the fluorescence of the mDTEB-labeled CNF, via quenching. Therefore, the chemical composition and the methods of CNF production affect subsequent studies. An in vitro triculture, small intestinal, epithelial model was used to assess the toxicity of ingested mDTEB-labeled CNFs. Zebrafish (Danio rerio) were used to assess in vivo environmental toxicity studies. No cytotoxicity was observed for CNFs, or mDTEB-labeled CNFs, either in the triculture cells or in the zebrafish embryos.

Cellulose nanocrystals (CNCs) have great potential as sustainable reinforcing materials for polymers, but there are a number of obstacles to commercialization that must first be overcome. High levels of water absorption, low thermal stabilities, poor miscibility with nonpolar polymers, and irreversible aggregation of the dried CNCs are among the greatest challenges to producing cellulose nanocrystal–polymer nanocomposites. A simple, scalable technique to modify sulfated cellulose nanocrystals (Na-CNCs) has been developed to address all of these issues. By using an ion exchange process to replace Na+ with imidazolium or phosphonium cations, the surface energy is altered, the thermal stability is increased, and the miscibility of dried CNCs with a nonpolar polymer (epoxy and polystyrene) is enhanced. Characterization of the resulting ion exchanged CNCs (IE-CNCs) using potentiometry, inverse gas chromatography, dynamic vapor sorption, and laser scanning confocal microscopy reveals that the IE-CNCs have lower...

Carbon nanotube (CNT) nanocomposites are enticing materials that enable engineers to tailor structural and electrical properties for applications in the automotive and aerospace industries. CNT mass fraction and the matrix cure temperature are two ways to tune the direct and alternating current electrical properties of these nanocomposites; yet, how mass fraction and cure temperature affect electrical properties remains unclear. In many cases, nanofillers such as carbon nanotubes appear in concentrated domains within the nanocomposite. Recent insights into nanoparticle-rich domain formation and its influence on electrical properties raise questions about which processing variables might optimally tune a material's functionality. Utilizing recently developed, nondestructive measurement techniques such as scanning lithium ion microscopy and microwave cavity perturbation spectroscopy, new insights are presented into the role of mass fraction and cure temperature in multiwall carbon nanotube – bisphenol A diglycidyl ether epoxy composites. Here, it is found that both mass fraction and cure temperature affect the electrical properties. Specifically, beyond the electrical percolation threshold, the DC conductivity is an order of magnitude higher for composites prepared at elevated cure temperatures for a given CNT mass fraction. Direct observations of the microdomain morphology do not show substantial differences due to cure temperature. These findings suggest pathways to generate designer nanocomposites for advanced electrically-active applications.

Ionic liquids, and the novel cations and anions which they are comprised of, have been used to modify the properties of many classes of materials. This includes their use as co-solvents and co-catalysts in simple chemical reactions. However, ionic liquid cations and anions have also been used to improve the properties and processing of nanomaterials as well. This paper will present recent efforts utilizing ionic liquid cations to dramatically improve the properties of cellulose nanocrystals (CNCs) such as water sensitivity, thermal stability, dispersibility, and polymer-miscibility. This is accomplished via a classic continuous, industrial process using ion-exchange resin. Novel measurement methods, used to characterize the impact of these cations on the CNC properties such as dynamic vapor desorption (DVS), optical imaging and inverse gas chromatography (iGC), will also be presented.

Due to the large volume fraction of nanoscale-reinforcement in cellulose-rich CNC-polymer nanocomposites and the extensive surface area, nearly all the soft/polymeric phase is interfacial (interphase polymer) and therefore, under nanoconfinement. It is well-established that the dynamic properties of any interphase polymer are determined by the structure of the polymer and strength of the interactions with the hard phase, and can deviate significantly from that of the neat polymer. With optimal interfacial interactions, this leads to significantly enhanced performance in many natural composites, such as those found in crustacean and insects shells, and bone. Yet, the role of interfacial interactions, polymer structure, and nano-confinement in helicoidal cellulose nano crystal nanocomposites remains incompletely understood. Here, we use fluorescently labelled helicoidal cellulose nanocomposites and fluorescent lifetime imaging microscopy (FLIM) to study the nature of the effect of polymer structure (cross linked, blend) on the confinement effect in alkyl ammonium modified sulfate-CNC. nanocomposites. Figure 1

Fiber fracture is a major contributor for the initiation of failure in fiber-reinforced polymer composites. The purpose of this study was to identify where damage occurs when a fiber fractures in a composite. Because this dynamic event occurs in less than 100 1ns, obtaining experimental evidence has been prohibitively difficult. Here, we report a novel method using a model composite, comprised of a spirolactam-based mechanophore-functionalized epoxy resin with a single embedded glass fiber. The ductile epoxy matrix is loaded under tension, which transfers load through interfacial shearing to the embedded brittle fiber, causing the fiber to break into segments. Fluorescence lifetime imaging microscopy (FLIM) is used to visualize regions of mechanophore activation and quantify changes in the dye's local environment such as relaxations on the nanosecond timescale. FLIM of these single fiber fragmentation test (SFFT) samples reveals localized damage zones in the epoxy matrix, not only at the point of fiber fragmentation, but also at distances remote from the fracture site that extend radially into the matrix up to two fiber diameters. The average mechanophore lifetime in the bulk epoxy is (1.5 ± 0.5) ns and in the damage regions is (0.75 ± 0.15) ns. This new data reveals the existence of polymer matrix yielding, which occurs during the fiber fracture event, and agrees with a dynamic model that predicts yielding behavior in the matrix during fracture. These results suggest that the damage from fiber fracture is more extensive than previously recognized. This new approach can be used to elucidate damage in other mechanical tests. The subsequent insights into composite damage mechanisms promises to dramatically accelerate the development of tough, durable, and damage tolerant composites.

We demonstrate a multimodal superresolution microscopy technique based on a phase masked excitation beam in combination with spatially filtered detection. The theoretical foundation for calculating the focus from a non-paraxial beam with an arbitrary azimuthally symmetric phase mask is presented for linear and two-photon excitation processes as well as the theoretical resolution limitations. Experimentally this technique is demonstrated using two-photon luminescence from 80 nm gold particle as well as two-photon fluorescence lifetime imaging of fluorescent polystyrene beads. Finally to illustrate the versatility of this technique we acquire two-photon fluorescence lifetime, two-photon luminescence, and second harmonic images of a mixture of fluorescent molecules and 80 nm gold particles with

Polymer composite materials are found throughout the world both natural and artificial in origin. In the vast majority of applications in these arenas, composites serve as structural support or reinforcement. Demand for lightweight tough composites is growing in multiple application spaces such as aerospace, biomaterials, and infrastructure with physical properties as diverse as the applications. The unifying component in all composites is the presence of the interphase. Many measurement techniques and measurement tools have been developed for the study of this crucial region in composite materials. Many of these methods are great for the measurement and study of bulk properties or model systems. However, development of tools that permit the direct observation of interactions at the interphase during applied stress are needed. Here we employ fluorescence lifetime imaging and hyperspectral imaging to observe activation of a fluorogenic dye at the composite interface as a result of applied stress. The advantages of this system include commercial availability of the dye precursor, and simple one-pot functionalization. The attachment of the dye at the interface is easily monitored through emission wavelength shifts or fluorescence lifetime. Interfacial mechano-responsive dyes have potential for both fundamental studies as well as industrial use as a structural health monitoring tool.

This Article reports on the synthesis of a series of well-defined, tertiary-amine-containing ABA triblock copolymers, composed of a poly(ethylene oxide) (PEO) central block and thermo- and pH-sensitive outer blocks, and the study of the effect of different tertiary amines on thermally induced sol-gel transition temperatures (T(sol-gel)) of their 10 wt % aqueous solutions. The doubly responsive ABA triblock copolymers were prepared from a difunctional PEO macroinitiator by atom transfer radical polymerization of methoxydi(ethylene glycol) methacrylate and ethoxydi(ethylene glycol) methacrylate at a feed molar ratio of 30:70 with ∼5 mol % of either N,N-diethylaminoethyl methacrylate (DEAEMA), N,N-diisopropylaminoethyl methacrylate, or N,N-di(n-butyl)aminoethyl methacrylate. The chain lengths of thermosensitive outer blocks and the molar contents of tertiary amines were very similar for all copolymers. Using rheological measurements, we determined the pH dependences of T(sol-gel) of 10 wt % aqueous solutions of these copolymers in a phosphate buffer. The T(sol-gel) versus pH curves of all polymers exhibited a sigmoidal shape. The T(sol-gel) increased with decreasing pH; the changes were small on both high and low pH sides. At a specific pH, the T(sol-gel) decreased with increasing the hydrophobicity of the tertiary amine, and upon decreasing pH the onset pH value for the T(sol-gel) to begin to increase noticeably was lower for the more hydrophobic tertiary amine-containing copolymer. In addition, we studied the effect of different tertiary amines on the release behavior of FITC-dextran from 10 wt % micellar gels in an acidic medium at 37 and 27 °C. The release profiles for three studied hydrogels at 37 °C were essentially the same, suggesting that the release was dominated by the diffusion of FITC-dextran. At 27 °C, the release was significantly faster for the DEAEMA-containing copolymer, indicating that both diffusion and gel dissolution contributed to the release at this temperature.

To better assess risks associated with nano-enabled products including multiwalled carbon nanotubes (MWCNT) within polymer matrices, it is important to understand how MWCNT are dispersed throughout the composite. The current study presents a method which employs imaging X-ray photoelectron spectroscopy (XPS) to chemically detect spatially segregated MWCNT rich regions at an epoxy composites surface by exploiting differential charging. MWCNT do not charge due to high conductivity and have previously been shown to energetically separate from their insulating surroundings when characterized by XPS. XPS in imaging mode revealed that these conductive regions were spatially separated due to micrometer-scale MWCNT aggregation and poor dispersion during the formation of the composite. Three MWCNT concentrations were studied; (1, 4 and 5) % by mass MWCNT within an epoxy matrix. Images acquired in periodic energy intervals were processed using custom algorithms designed to efficiently extract spectra from regions of interest. As a result, chemical and electrical information on aggregate and non-aggregate portions of the composite was extracted. Raman imaging and scanning electron microscopy were employed as orthogonal techniques for validating this XPS-based methodology. Results demonstrate that XPS imaging of differentially charging MWCNT composite samples is an effective means for assessing dispersion quality.

We report on the synthesis of thermo- and enzyme-responsive hydrophilic ABA triblock copolymers, poly(ethoxydi(ethylene glycol) acrylate-co-4-((dihydroxyphosphoryl)oxy)butyl acrylate)-b-poly(ethylene oxide)-b-poly(ethoxydi(ethylene glycol) acrylate-co-4-((dihydroxyphosphoryl)oxy)butyl acrylate) (P(DEGEA-co-OPBA)-b-PEO-b-P(DEGEA-co-OPBA)), and the enzyme-induced formation of thermoreversible micellar gels from their moderately concentrated aqueous solutions at 37 °C. PDEGEA is a thermosensitive water-soluble polymer with a lower critical solution temperature (LCST) at 9 °C in water. The block copolymers were prepared by atom transfer radical polymerization of DEGEA and 4-((di-tert-butoxyphosphoryl)oxy)butyl acrylate and subsequent removal of tert-butyl groups. To seek optimal conditions for enzymatic gelation of aqueous solutions of triblock copolymers, a study of dephosphorylation of a random copolymer P(DEGEA-co-OPBA) by acid phosphatase in water at 37 °C was carried out. The time for the solution to tur...

This article reports on the synthesis of a hydrophilic diblock copolymer composed of two distinct thermosensitive polymers with one block containing a small amount of carboxylic acid groups, poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate) (P(TEGMA-co-AA)-b-PDEGEA), and the study of thermo-induced sol−gel−sol transitions of its moderately concentrated aqueous solutions at various pH values. The diblock copolymer was obtained by the removal of tert-butyl groups of P(TEGMA-co-tert-butyl acrylate)-b-PDEGEA, which was synthesized by reversible addition−fragmentation chain transfer polymerization. PTEGMA and PDEGEA are thermosensitive polymers with lower critical solution temperatures (LCSTs) of 58 and 9 °C, respectively, in water. The incorporation of a small amount of carboxylic acid groups into PTEGMA allowed the LCST of the P(TEGMA-co-AA) block to be tuned by changing the solution pH. We found that a 20 wt % aqueous solution of P(TEGMA-co-AA)-b-PDEGEA wi...

Hybrid agarose hydrogels embedded with pH-responsive diblock copolymers micelles were developed to achieve functional hydrogels capable of stimulus-triggered drug release. Specifically, a well-defined poly(ethylene oxide) (PEO)-based diblock copolymer, PEO-b-poly(2-(N,N-diisopropylamino)ethyl methacrylate) (PEO(113)-b-PDPAEMA(31), where the subscripts represent the degrees of polymerization of two blocks), was synthesized by atom transfer radical polymerization. PDPAEMA is a pH-responsive polymer with a pKa value of 6.3. The PEO(113)-b-PDPAEMA(31) micelles were formed by a solvent-switching method, and their pH-dependent dissociation behavior was investigated by dynamic light scattering and fluorescence spectroscopy. Both studies indicated that the micelles were completely disassembled at pH = 6.40. The biocompatibility of PEO(113)-b-PDPAEMA(31) micelles was demonstrated by in vitro primary cortical neural culture. Hybrid agarose hydrogels were made by cooling 1.0 wt % agarose solutions that contained various amounts of PEO(113)-b-PDPAEMA(31) micelles at either 2 or 4 °C. Rheological measurements showed that the mechanical properties of gels were not significantly adversely affected by the incorporation of diblock copolymer micelles with a concentration as high as 5.0 mg/g. Using Nile Red as a model hydrophobic drug, its incorporation into the core of diblock copolymer micelles was demonstrated. Characterized by fluorescent spectroscopy, the release of Nile Red from the hybrid hydrogel was shown to be controllable by pH due to the responsiveness of the block copolymer micelles. Based on the prominent use of agarose gels as scaffolds for cell transplantation for neural repair, the hybrid hydrogels embedded with stimuli-responsive block copolymer micelles could allow the controlled delivery of hydrophobic neuroprotective agents to improve survival of transplanted cells in tune with signals from the surrounding pathological environment.

This article presents a systematic study of the effect of pH on the rheological properties of aqueous micellar gels formed from 10.0 wt % aqueous solutions of a thermo- and pH-sensitive ABA triblock copolymer, poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethylene oxide)-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid) (P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA)). The block copolymer was synthesized by atom transfer radical polymerization of DEGEA and tert-butyl acrylate with a molar ratio of 100:5 from a difunctional PEO macroinitiator and subsequent removal of tert-butyl groups using trifluoroacetic acid. PDEGEA is a thermosensitive water-soluble polymer with a cloud point of 9 °C in water. The thermo-induced sol-gel transition temperature (T(sol-gel)) of the 10.0 wt % aqueous solution of P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA) can be continuously and reversibly tuned over a wide temperature range by varying the solution pH. The sol-gel transition became broader with the increase of pH, which stemmed from the weaker and broader LCST transition of P(DEGEA-co-AA) blocks at higher pH values. The maximum value of dynamic storage modulus, obtained from heating ramp, and the plateau storage moduli (G(N)), evaluated from frequency sweeps at three normalized temperatures (T/T(sol-gel) = 1.025, 1.032, and 1.039), decreased with the increase of pH from 3.00 to 5.40 with the sharpest drop observed at pH = ∼4.7. The decrease in G(N) reflects the reduction of the number of bridging polymer chains and simultaneously the increase of the numbers of loops and dangling polymer chains. The ionization of carboxylic acid groups at higher pH values introduced charges onto the thermosensitive blocks and made the polymer chains more hydrophilic, facilitating the formation of loops and dangling chains in the gels. The increase in the number of dangling polymer chains with the increase of pH was supported by fluorescence spectroscopy studies, which showed that the critical micelle concentration of P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA) at a temperature corresponding to T(sol-gel) was higher at a higher pH. The results reported in this article showed that both T(sol-gel) and gel strength can be tuned by varying the solution pH, providing greater design flexibility for potential applications.

We report in this article the synthesis of a series of thermo- and light-sensitive hydrophilic ABA linear triblock copolymers, poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate)-b-poly(ethylene oxide)-b-poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate) (P(TEGEA-co-NBA)-b-PEO-b-P(TEGEA-co-NBA)), with various NBA molar contents and the study of sol–gel transitions of their aqueous solutions. The copolymers were prepared by ATRP from a difunctional PEO macroinitiator; the polydispersity indexes of all polymers were