Metamaterial-like aerogels for broadband vibration mitigation.

We report a mechanical metamaterial-like behavior as a function of the micro/nanostructure of otherwise chemically identical aliphatic polyurea aerogels. Transmissibility varies dramatically with frequency in these aerogels. Broadband vibration mitigation is provided at low frequencies (500-1000 Hz) through self-assembly of locally resonant metastructures wherein polyurea microspheres are embedded in a polyurea web-like network. A micromechanical constitutive model based on a discrete element method is established to explain the vibration mitigation mechanism. Simulations confirm the metamaterial-like behavior with a negative dynamic material stiffness for the micro-metastructured aerogels in a much wider frequency range than the majority of previously reported locally resonant metamaterials.

Multi-scale progressive failure mechanism and mechanical properties of nanofibrous polyurea aerogels.

The nonlinear mechanical properties, deformation and failure mechanisms of polyurea aerogels (PUAs) were investigated using a multi-scale approach that combines nanoindentation, analytical and computational modeling. The atomistic structure of primary particles of PUAs and their mechanical interactions were investigated with molecular dynamics simulations. From nanoindentation we identified four deformation and failure modes: free ligament buckling, cell ligament bending, stable cell collapsing, and ligament crush induced strain hardening. The corresponding structural evolution during indentation and strain hardening were analyzed and modeled. The material scaling properties were found to be dependent on both the relative density and the secondary particle size of PUAs. Using a porosity-dependent material constitutive model, a linear relationship was found between the strain hardening index and secondary particle size instead the conventional power-law relationship. Finally, the structural efficiency of PUAs with respect to the capability for energy absorption is evaluated as a function of structural parameters and base polymeric material properties.

PARP Targeted Alpha-Particle Therapy Enhances Response to PD-1 Immune-Checkpoint Blockade in a Syngeneic Mouse Model of Glioblastoma.

We have previously demonstrated potent antitumor effects of PARP targeted alpha-therapy with astatine-211-MM4 ([211At]MM4) in neuroblastoma preclinical models, although differential sensitivity suggests it is unlikely to be curative as a single-agent in all tumor types. Alpha-particle induced DNA damage can elicit an immune response that results in T-cell activation against tumor cells; however, tumor cells can evade immune surveillance through expression of programmed death ligand 1 (PD-L1). Therefore, we investigated the effects of α particle therapy in combination with immune-checkpoint blockade using astatine-211-MM4 and anti-programmed death receptor 1 (anti-PD-1) immunotherapy in a syngeneic mouse model of glioblastoma. We characterized the sensitivity of four human glioblastoma cell lines to [211At]MM4 in vitro. To evaluate [211At]MM4 treatment effects on hematological tissues, complete blood counts were performed after a single dose at 12, 24, or 36 MBq/kg. In vivo efficacy was evaluated in a syngeneic mouse model of glioblastoma using GL26 glioblastoma cells in CB57BL/6J mice treated with either 36 MBq/kg [211At]MM4, anti-PD-1 antibody, or a combination of the two. Following a single dose of [211At]MM4, lymphocytes are significantly decreased compared to control at both 72 h and 1 week following treatment followed by recovery of counts by 2 weeks. However, neutrophils showed an increase with all dose levels of [211At]MM4 exhibiting higher levels than control. The average best tumor responses for combination, anti-PD-1, and [211At]MM4 were 100%, 83.6%, and 58.2% decrease in tumor volume, respectively. Average progression free intervals for combination, anti-PD-1, [211At]MM4, and control groups was 65, 36.4, 23.2, and 3 days, respectively. The percentages of disease-free mice at the end of the study for combination and anti-PD-1 were 100% and 60%, while [211At]MM4 and control groups were both 0%. In summary, combination therapy was more effective than either single agent in all response categories analyzed, highlighting the potential for PARP targeted alpha-therapy to enhance PD-1 immune-checkpoint blockade.

K-Index: A Descriptor, Predictor, and Correlator of Complex Nanomorphology to Other Material Properties.

Morphology is a qualitative property of nanostructured matter and is articulated by visual inspection of micrographs. For deterministic procedures that relate nanomorphology to synthetic conditions, it is necessary to express nano- and microstructures numerically. Selecting polyurea aerogels as a model system with demonstrated potential for rich nanomorphology and guided by a statistical design-of-experiments model, we prepared a large array of materials (208) with identical chemical composition but quite different nanostructures. By reflecting on SEM imaging, it was realized that our first preverbal impression about a nanostructure is related to its openness and texture; the former is quantified by porosity ( Π), and the latter is oftentimes related to hydrophobicity, which, in turn, is quantified by the contact angle (θ) of water droplets resting on the material. Herewith, the θ-to-Π ratio is referred to as the K-index, and it was noticed that all polyurea samples of this study could be put in eight K-index groups with separate nanomorphologies ranging from caterpillar-like assemblies of nanoparticles, to thin nanofibers, to cocoon-like structures, to large bald microspheres. A first validation of the K-index as a morphology descriptor was based on compressing samples to different strains: it was observed that as the porosity decreases, the water-contact angle decreases proportionally, and thereby the K-index remains constant. The predictive power of the K-index was demonstrated with 20 polyurea aerogels prepared in 8 binary solvent systems. Subsequently, several material properties were correlated to nanomorphology through the K-index and that, in turn, provided insight about the root cause of the diversity of the nanostructure in polyurea aerogels. Finally, using response surface methodology, K-indexes and other material properties of practical interest were correlated to the monomer, water, and catalyst concentrations as well as the three Hansen solubility parameters of the sol. That enabled the synthesis of materials with up to six prescribed properties at a time, including nanomorphology, bulk density, BET surface area, elastic modulus, ultimate compressive strength, and thermal conductivity.

Selective CO2 Sequestration with Monolithic Bimodal Micro/Macroporous Carbon Aerogels Derived from Stepwise Pyrolytic Decomposition of Polyamide-Polyimide-Polyurea Random Copolymers.

Polymeric aerogels (PA-xx) were synthesized via room-temperature reaction of an aromatic triisocyanate (tris(4-isocyanatophenyl) methane) with pyromellitic acid. Using solid-state CPMAS 13C and 15N NMR, it was found that the skeletal framework of PA-xx was a statistical copolymer of polyamide, polyurea, polyimide, and of the primary condensation product of the two reactants, a carbamic-anhydride adduct. Stepwise pyrolytic decomposition of those components yielded carbon aerogels with both open and closed microporosity. The open micropore surface area increased from <15 m2 g-1 in PA-xx to 340 m2 g-1 in the carbons. Next, reactive etching at 1,000 °C with CO2 opened access to the closed pores and the micropore area increased by almost 4× to 1150 m2 g-1 (out of 1750 m2 g-1 of a total BET surface area). At 0 °C, etched carbon aerogels demonstrated a good balance of adsorption capacity for CO2 (up to 4.9 mmol g-1), and selectivity toward other gases (via Henry's law). The selectivity for CO2 versus H2 (up to 928:1) is suitable for precombustion fuel purification. Relevant to postcombustion CO2 capture and sequestration (CCS), the selectivity for CO2 versus N2 was in the 17:1 to 31:1 range. In addition to typical factors involved in gas sorption (kinetic diameters, quadrupole moments and polarizabilities of the adsorbates), it is also suggested that CO2 is preferentially engaged by surface pyridinic and pyridonic N on carbon (identified with XPS) in an energy-neutral surface reaction. Relatively high uptake of CH4 (2.16 mmol g-1 at 0 °C/1 bar) was attributed to its low polarizability, and that finding paves the way for further studies on adsorption of higher (i.e., more polarizable) hydrocarbons. Overall, high CO2 selectivities, in combination with attractive CO2 adsorption capacities, low monomer cost, and the innate physicochemical stability of carbon render the materials of this study reasonable candidates for further practical consideration.