XiaoMeng Sui

Tough Nanocomposites: The Role of Carbon Nanotube Type

Unusually large deformation is observed in poly(methyl metacrylate) (PMMA) electrospun fibers under tension when multiwall or single-wall carbon nanotubes (MWCNTs and SWCNTs) are included as a second phase in the fibers. These distortions are virtually absent in pure PMMA fibers and stem from markedly different energy dissipation mechanisms and necking modes arising from the dissimilar nanotube morphologies. Thus, both nanotubes types are effective tougheners of PMMA fibers, with an advantage for MWCNTs over SWCNTs.

Effect of carbon nanotube surface modification on dispersion and structural properties of electrospun fibers

Covalent surface modification of multiwall carbon nanotubes leads to enhanced nanotube dispersion in the polymer. Despite this, the mechanical properties of electrospun fibers made of polymethylmethacrylate containing surface modified nanotubes generally fall below those of fibers with pristine nanotubes, sometimes below those of pure polymer fibers. We show that covalent functionalization produces defects in the graphene structure, leading to mechanical weakening of the nanotube and, therefore, of the nanocomposite.

Structural origins of morphing in plant tissues

Plant tissues are able to generate complex movements via shape modifications. These effects are tightly related to distinctive multi-scale composite architectures of the plant material, and can therefore largely be interpreted by composite mechanics principles. Here, we propose a generic framework for the analysis and prediction of the shape morphing of intricate biological composite materials, arising from changes in humidity. We have examined in depth the hierarchical structures of three types of seed pods for which we propose a theoretical scheme that is able to accurately simulate the relevant shape deformations. The validity and generality of this approach are confirmed by means of laboratory scale synthetic models with similar architectures leading to equivalent morphing patterns. Such synthetic configurations could pave the way to future morphing architectures of advanced materials and structures.

Free-Standing Nanocrystalline Materials Assembled from Small Molecules

We demonstrate a solution-based fabrication of centimeter-size free-standing films assembled from organic nanocrystals based on common organic dyes (perylene diimides, PDIs). These nanostructured films exhibit good mechanical stability, and thermal robustness superior to most plastics, retaining the crystalline microstructure and macroscopic shape upon heating up to 250-300 °C. The films show nonlinear optical response and can be used as ultrafiltration membranes. The macroscopic functional materials based on small molecules can be alternative or complementary to materials based on macromolecules.

Bioinspired Flexible and Tough Layered Peptide Crystals

One major challenge of functional material fabrication is combining flexibility, strength, and toughness. In several biological and artificial systems, these desired mechanical properties are achieved by hierarchical architectures and various forms of anisotropy, as found in bones and nacre. Here, it is reported that crystals of N-capped diphenylalanine, one of the most studied self-assembling systems in nanotechnology, exhibit well-ordered packing and diffraction of sub-Å resolution, yet display an exceptionally flexible nature. To explore this flexibility, the mechanical properties of individual crystals are evaluated, assisted by density functional theory calculations. High-resolution scanning electron microscopy reveals that the crystals are composed of layered self-assembled structures. The observed combination of strength, toughness, and flexibility can therefore be explained in terms of weak interactions between rigid layers. These crystals represent a novel class of self-assembled layered materials, which can be utilized for various technological applications, where a combination of usually contradictory mechanical properties is desired.

Long-Term Biomechanical and Histologic Results of WST-D/NIR Corneal Stiffening in Rabbits, Up to 8 Months Follow-up

Purpose To determine the long-term safety and efficacy of WST-D/near-infrared (NIR) corneal stiffening. Methods One eye of 23 New Zealand White rabbits was de-epithelialized mechanically followed by topical application of 2.5 mg/mL WST11, combined with dextran-500 (WST-D) for 20 minutes. Subsequently, samples were irradiated with a NIR (755 nm) laser at 10 mW/cm2 for 30 minutes. Untreated fellow eyes served as controls. One week (n = 4), 1 month (n = 6), 4 months (n = 9), or 8 months (n = 4) after treatment rabbits were euthanized. Corneal strips were cut in superior-inferior direction for extensiometry testing (1, 4, and 8 months), and histologic sections were prepared for evaluation of keratocyte distribution (1 week and 8 months). Results Elastic modulus after treatment was significantly higher than in paired controls (16.0 ± 2.3 MPa versus 9.6 ± 3.6 MPa [P = 0.008], 18.1 ± 4.5 MPa versus 12.6 ± 2.3 MPa [P = 0.003], and 18.6 ± 3.6 MPa versus 14.2 ± 3.6 MPa [P = 0.010], at 1, 4, and 8 months, respectively). A significant decrease in keratocyte count at the anterior stroma was observed directly after treatment (1.5 ± 1.7 vs. 19.0 ± 4.1 [P = 0.002]). At 8 months keratocyte repopulation appeared completed, with similar distribution in treated and untreated corneas (15.9 ± 1.1 vs. 14.5 ± 2.5 [P = 0.562]). Corneal thickness was comparable between treated and untreated corneas at all time points. Conclusions WST-D/NIR treatment resulted in significant and persistent long-term increase in corneal stiffness. Initial keratocyte apoptosis in the anterior stroma is followed by repopulation to normal level at 8 months after treatment. The safe nature of NIR light allows treatment of corneas of any thickness without endangering corneal endothelium or deeper ocular structures, potentially benefiting patients deemed unsuitable for riboflavin/UV-A cross-linking.

Corneal Stiffening by a Bacteriochlorophyll Derivative With Dextran and Near-Infrared Light : Effect of Shortening Irradiation Time up to 1 Minute

Purpose: The aim of this study is to determine the effect of variation of the exposure time of near-infrared irradiation on corneal stiffening after a bacteriochlorophyll derivative (WST11) with dextran (WST-D) application. Methods: One hundred four paired eyes of 3-month-old New Zealand White rabbits were included in this study. Fifty-two eyes (ex vivo n = 34, in vivo n = 18) were mechanically deepithelialized, treated topically with WST-D, and irradiated at 10 mW/cm2 using a diode laser at 755 nm for 1, 5, or 30 minutes. Untreated fellow eyes served as controls. Corneoscleral rings were removed immediately after treatment (ex vivo), or 1 month after treatment (in vivo). Corneal strips were cut and underwent biomechanical stress–strain measurements. Results: Ex vivo, the mean tangent elastic modulus was significantly higher in the treatment groups than in the control groups for 1, 5, and 30 minutes of irradiation, respectively, 6.06 MPa, 95% confidence interval (CI, 4.5–7.6) versus 14.02 MPa, 95% CI (10.2–17.8), n = 11, 4.8 MPa, 95% CI (3.9–5.7) versus 15.03 MPa, 95% CI (12–18.1), n = 11, and 7.8 MPa, 95% CI (5.6–10.02) versus 16.2 MPa, 95% CI (13.6–18.9), n = 11; P < 0.001 for all comparisons. In vivo, the mean elastic moduli in the treatment groups were significantly higher for 5 and 30 minutes of irradiation but not for 1 minute of irradiation, respectively, 11.4 MPa, 95% CI (8.5–14.2), versus 17.1 MPa, 95% CI (14.5–19.7), n = 5; P < 0.001, and 9.4 MPa, 95% CI (5.1–13.8) versus 16 MPa, 95% CI (13.1–19), n = 5; P < 0.01, and 11.3 MPa, 95% CI (6–16.6) versus 12.2 MPa, 95% CI (7.5–16.8), n = 5; P = 0.7. Conclusions: WST-D/near-infrared treatment using shortened irradiation time (1 minute ex vivo and 5 minutes in vivo) results in significant corneal stiffening, and this might provide an alternative to the currently applied riboflavin/ultraviolet A cross-linking.