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The discovery of bicontinuous interfacially jammed emulsion gels (bijels) in 2007 motivated the development of processing techniques to harness their unique morphological attributes in applications such as electrochemical energy storage and conversion, catalysis, and regenerative biomaterials. These techniques are primarily based on selective polymerization of one phase, and subsequent chemical processing of the resultant scaffold into porous, micro-architectured materials. A significant limitation of these protocols is the need to transport polymer precursors into one of the fluid phases after bijel formation, a time-consuming step that can also impose disruptive gravitational and interfacial stresses, sometimes causing a complete breakdown of the bijel backbone. Here, we introduce a class of intrinsically polymerizable bijels (IPBs) comprising partially miscible mixtures of solvent and poly(ethylene glycol) precursor, which can be directly transformed into bijel-templated materials (BTMs), completely bypassing the precursor transport step and relaxing the associated limitations of previous protocols. To achieve selective polymerization, we incorporated into the mixture a common fluorescent dye, sodium fluorescein, which had strong affinity for the monomer-poor phase. Spectrophotometry experiments demonstrated a local photon quenching effect due to the fluorescent dye, which in turn curtailed activation of the photoinitiator and thus prevented polymerization in the monomer-poor phase. We establish the generality of our approach by using different monomers and monomer blends, and demonstrate how this modularity enables tuning of the mechanical properties of BTMs, measured by flexural testing. Our protocol establishes a scalable and efficient platform for producing BTMs, paving the way for their protential applications in emerging technologies.

We introduce laser cavitation rheology (LCR) as a minimally-invasive optical method to characterize mechanical properties within the interior of biological and synthetic aqueous soft materials at high strain-rates. We utilized time-resolved photography to measure cavitation bubble dynamics generated by the delivery of focused 500 ps duration laser radiation at λ = 532 nm within fibrin hydrogels at pulse energies of Ep = 12, 18 µJ and within polyethylene glycol (600) diacrylate (PEG (600) DA) hydrogels at Ep = 2, 5, 12 µJ. Elastic moduli and failure strains of fibrin and PEG (600) DA hydrogels were calculated from these measurements by determining parameter values which provide the best fit of the measured data to a theoretical model of cavitation bubble dynamics in a Neo-Hookean viscoelastic medium subject to material failure. We demonstrate the use of this method to retrieve the local, interior elastic modulus of these hydrogels and both the radial and circumferential failure strains.

Hypothesis The presence of colloidal particles on fluid interfaces can have a significant impact on the rheology of solid-stabilized high internal phase emulsions (HIPEs). Experiments Using dynamic oscillatory rheometry and confocal microscopy, we investigate a broad array of solid-stabilized HIPEs formulated along four different compositional trajectories in their ternary state diagram, using particles of three different sizes and two different surface chemistries. Findings We unveil three important consequences of the use of particles, in lieu of surfactants, on the rheology of HIPEs. First, particle excluded volume interactions take a pronounced role in the transition to solid-like rheology due to crowding. An effective dispersed phase volume fraction, taking into account the particle three-phase contact angle, must be defined to account for the dependence of the mixture’s rheology on its composition. Second, weak, chemistry-dependent attractive colloidal interactions through the continuous phase result in a finite elastic modulus at low effective dispersed phase volume fractions. Third, we observe a secondary rise in the mixture’s elastic modulus at increasingly high dispersed-to-continuous-phase volumetric ratios. We postulate these interactions stem from attractive lateral capillary interactions between the particles, due to thinning of the continuous fluid film between faceted droplets.

Mitigation of the foreign body response (FBR) and successful tissue integration are essential to ensuring the longevity of implanted devices and biomaterials. The use of porous materials and coatings has been shown to have an impact, as the textured surfaces can mediate macrophage interactions with the implant and influence the FBR, and the pores can provide space for vascularization and tissue integration. In this study, we use a new class of implantable porous biomaterials templated from bicontinuous interfacially jammed emulsion gels (bijels), which offer a fully percolating, non-constricting porous network with a uniform pore diameter on the order of tens of micrometers, and surfaces with consistent curvature. We demonstrate that these unique morphological features, inherent to bijel-templated materials (BTMs), can enhance tissue integration and vascularization, and reduce the FBR. Cylindrical polyethylene glycol diacrylate (PEGDA) BTMs, along with PEGDA particle-templated materials (PTMs), and non-templated materials (NTMs), were implanted into the subcutaneous space of athymic nude mice. After 28 days, implants were retrieved and analyzed via histological techniques. Within BTMs, blood vessels of increased size and depth, changes in collagen deposition, and increased presence of pro-healing macrophages were observed compared to that of PTM and NTM implants. Bijel templating offers a new route to biomaterials that can improve the function and longevity of implantable devices. Statement of Significance All implanted biomaterials are subject to the foreign body response (FBR) which can have a detrimental effect on their efficacy. Altering the surface chemistry can decrease the FBR by limiting the amount of proteins adsorbed to the implant. This effect can be enhanced by including pores in the biomaterial to allow new tissue growth as the implant becomes integrated in the body. Here, we introduce a new class of self-assembled biomaterials comprising a fully penetrating, non-constricting pore phase with hyperbolic (saddle) surfaces for enhanced tissue integration. These unique morphological characteristics result in dense blood vessel formation and favorable tissue response properties demonstrated in a four-week implantation study.

Three-dimensional porous architectures of graphene are desirable for energy storage, catalysis, and sensing applications. Yet it has proven challenging to devise scalable methods capable of producing co-continuous architectures and well-defined, uniform pore and ligament sizes at length scales relevant to applications. This is further complicated by processing temperatures necessary for high quality graphene. Here, bicontinuous interfacially jammed emulsion gels (bijels) are formed and processed into sacrificial porous Ni scaffolds for chemical vapor deposition to produce freestanding three-dimensional turbostratic graphene (bi-3DG) monoliths with high specific surface area. Scanning electron microscopy (SEM) images show that the bi-3DG monoliths inherit the unique microstructural characteristics of their bijel parents. Processing of the Ni templates strongly influences the resultant bi-3DG structures, enabling the formation of stacked graphene flakes or fewer-layer continuous films. Despite the multilayer nature, Raman spectra exhibit no discernable defect peak and large relative intensity for the Raman 2D mode, which is a characteristic of turbostratic graphene. Moire patterns, observed in scanning tunneling microscopy images, further confirm the presence of turbostratic graphene. Nanoindentation of macroscopic pillars reveals a Young's modulus of 30 MPa, one of the highest recorded for sp2 carbon in a porous structure. Overall, this work highlights the utility of a scalable self-assembly method towards porous high quality graphene constructs with tunable, uniform, and co-continuous microstructure.

Numerous processing techniques aim to impart interconnected, porous structures within regenerative medicine materials to support cell delivery and direct tissue growth. Many of these techniques lack predictable control of scaffold architecture, and rapid prototyping methods are often limited by time-consuming, layer-by-layer fabrication of micro-features. Bicontinuous interfacially jammed emulsion gels (bijels) offer a robust, self-assembly-based platform for synthesizing a new class of morphologically unique cell delivery biomaterials. Bijels form via kinetic arrest of temperature-driven spinodal decomposition in partially miscible binary liquid systems. These non-equilibrium soft materials are comprised of co-continuous, fully percolating, non-constricting liquid domains separated by a nanoparticle monolayer. Through the selective introduction of biocompatible precursors, hydrogel scaffolds displaying the morphological characteristics of the parent bijel can be formed. We report using bijel templating to generate structurally unique, fibrin-loaded polyethylene glycol hydrogel composites. Demonstration of composite bijel-templated hydrogels (CBiTHs) as a new cell delivery system was carried out in vitro using fluorescence-based tracking of cells delivered to previously acellular fibrin gels. Imaging analysis confirmed repeatable delivery of normal human dermal fibroblasts to acellular fibrin gels.

Collagen is the most abundant protein in extracellular matrices and is commonly used as a tissue engineering scaffold. However, collagen and other biopolymers from native sources can exhibit limitations when tuning mechanical and biological properties. Cysteines do not naturally occur within the triple-helical region of any native collagen. We utilized a novel modular synthesis strategy to fabricate variants of recombinant human collagen that contained 2, 4, or 8 non-native cysteines at precisely defined locations within each biopolymer. This bottom-up approach introduced capabilities using sulfhydryl chemistry to form hydrogels and immobilize bioactive factors. Collagen variants retained their triple-helical structure and supported cellular adhesion. Hydrogels were characterized using rheology, and the storage moduli were comparable to fibrillar collagen gels at similar concentrations. Furthermore, the introduced cysteines functioned as anchoring sites, with TGF-β1-conjugated collagens promoting myofibroblast differentiation. This approach demonstrates the feasibility to produce custom-designed collagens with chemical functionality not available from native sources.

We utilize a custom-built shear cell mounted on a confocal microscope to directly visualize and quantify the microdynamic mechanisms that mediate the rheology of a nearly jammed colloidal suspension under constant-stress deformation, with and without attractive interparticle interactions. The application of external stresses systematically increases particle mobility, as well as the ease by which the colloids can escape from topological cages formed by their nearest neighbors. We quantify the characteristic size and timescale of microstructural rearrangements within the suspension and show that these relaxation events become less spatiotemporally heterogeneous as the applied stress is increased. When interparticle attraction is introduced, the colloids tend to move more congruently under low stresses and the characteristic size of dynamically cooperative clusters increases. However, particle displacements become decorrelated under large external loads, with an abrupt transition occurring at the yield stress. In contrast, the repulsive system shows a more gradual transition from creep deformation to flow, with a nonmonotonic dependence of the particle displacement correlation function on the applied stress. Our results contribute to a better understanding of the jamming phase diagram in disordered colloidal materials, and the connection between the microstructure and nonlinear rheology of colloidal gels and glasses.

© 2016 The Royal Society of Chemistry. Emerging demands for national security, transportation, distributed power, and portable systems call for energy storage and conversion technologies that can simultaneously deliver large power and energy densities. To this end, here we report three-dimensional Ni/Ni(OH)2composite electrodes derived from a new class of multi-phase soft materials with uniform, co-continuous, and tunable internal microdomains. These remarkable morphological attributes combined with our facile chemical processing techniques allow the electrode's salient morphological parameters to be independently tuned for rapid ion transport and a large volumetric energy storage capacity. Through microstructural design and optimization, our composite electrodes can simultaneously deliver energy densities equal to that of batteries and power densities equivalent to or greater than that of the best supercapacitors, bridging the gap between these modern technologies. Our synthesis procedure is robust and can be extended to a myriad of other chemistries for next generation energy storage materials.

The internal dynamics of fractal cluster gels of colloidal boehmite rods with aspect ratios r = 3.9 , 8.6, and 30.1, and colloidal polystyrene spheres ( r = 1 ) are reported. Increasing r decreases the minimum colloid volume fraction for gelation. The behavior of the dynamic structure factor of rod gels is consistent with the internal dynamics of a constrained Brownian fractal object. Colloidal boehmite gels display an abrupt transition from floppy to brittle dynamics at ϕ ∼ 10 −4 . Moreover, the fractal cluster size of rod gels is not the determinant of the relaxation time of density fluctuations as it is in spherical particle gels. Instead, the relative behavior of the magnitude and time scale of the constrained fluctuations suggests that the fractal rod network is viscously coupled only on local, rather than cluster, scales. We hypothesize that noncentral forces between the anisometric particles are responsible for this anomalous behavior.

The transient structural evolution of polystyrene colloidal gels with fractal structure is quantified during start-up of steady shear flow by time-resolved small-angle light scattering and rheometry. Three distinct regimes are identified in the velocity-gradient plane: structural orientation, network breakup, and cluster densification. Structural anisotropy in the first regime is a universal function of applied strain. Flow cessation in this regime shows a lack of structural relaxation for Pe⪡1, where Pe is the Peclet number. In the second regime, the anisotropy attains a maximum value before monotonically decreasing. The volume fraction dependence of the critical strain for maximum anisotropy follows the scaling: 1+0.6γc,r∼ϕ(1−x)(3−D). Here x and D are the backbone and cluster fractal dimensions, respectively. This scaling agrees with the simple model of a gel network that ruptures after the cluster backbone is extended affinely to its full length. Rheological measurements demonstrate that the maximum an...