Mechanical properties and tuning of three-dimensional polymeric photonic crystals

Applied Physics LettersMechanical properties of photopolymerized photonic crystal PhC structures having woodpile and spiral three-dimensional architectures were examined using flat-punch indentation. The structures were found to exhibit a foamlike response with a bend-dominated elastic deformation regime observed at strain levels up to 10%. Numerical simulations of optical properties of these PhC structures demonstrate the possibility of achieving a substantial and reversible spectral tuning of the photonic stop gap wavelength by applying a mechanical load to the PhC

Mechanisms of Structure Formation in Ice-Templated Materials Experimental Observations

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The mechanical performance of natural materials

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Crosslinking Poly(allylamine) Fibers Electrospun from Basic and Acidic Solutions

Mechanically robust, non-toxic polymer fiber mats are promising materials for a range of biomedical applications; however, further research into enhancing polymer selection is needed. In this study, poly(allylamine) (PAH), an amine-containing polyelectrolyte, was successfully electrospun from aqueous solutions into continuous, cylindrical fibers with a mean diameter of 150 ± 41 nm. A one-step crosslinking method using glutaraldehyde provides insight into the chemical and morphological changes that result from altering the molar ratio of amine to aldehyde groups, whereas a two-step crosslinking method yielded chemically and mechanically robust mats. These results indicate PAH fibrous mats synthesized from aqueous solutions could potentially be applied in biomedical applications

Shear Lag Sutures: Improved Suture Repair through the Use of Adhesives

Conventional surgical suture is mechanically limited by the ability of the suture to transfer load to tissue at suture anchor points. Sutures coated with adhesives can improve mechanical load transfer beyond the range of performance of existing suture methods, thereby strengthening orthopaedic repairs and decreasing the risk of failure. The mechanical properties of suitable adhesives were identified using a shear lag model. Examination of the design space for an optimal adhesive demonstrated requirements for strong adhesion and low stiffness to maximize strength. As a proof of concept, cyanoacrylate-coated sutures were used to perform a clinically relevant flexor digitorum profundus tendon repair in cadaver tissue. Even with this non-ideal adhesive, the maximum load resisted by repaired cadaveric canine flexor tendon increased by ∼ 17.0% compared to standard repairs without adhesive. To rapidly assess adhesive binding to tendon, we additionally developed a lap shear test method using bovine deep digital flexor tendons as the adherends. Further study is needed to develop a strongly adherent, compliant adhesive within the optimal design space described by the model

Heterogeneous Ice Nucleation Studied with Single-Layer Graphene

Control of heterogeneous ice nucleation (HIN) is critical for applications that range from iceophobic surfaces to ice-templated materials. HIN on 2D materials is a particular interesting topic that still lacks extensive experimental investigations. Here, we focus on the HIN on single-layer graphene (SLG) transferred onto different substrates, including silicon, silica, and thermal oxide on silicon. Complemented by other samples without SLG, we obtain a large range of wetting contact angles (WCAs) from 2° to 95°. All pristine SLG samples exhibit a large contact angle of ∼95°, which is close to the theoretical value of 96° for free-standing SLG, irrespective of the substrate and even in the presence of nanoscale wrinkles on SLG, which are due to the transfer process, indicating that the topographical features have little impact on the wetting behavior. Interestingly, SLG displays changes in hydrophobicity upon repeated water droplet freezing–melting–drying cycles due to a shift in Fermi level and/or enhanced water–substrate polar molecular interactions, likely induced by residual adsorption of H2O molecules. We found that a 0.04 eV decrease in SLG Fermi level reduces the SLG/water interface energy by ∼6 mJ/m2, thereby making SLG less hydrophobic. Counterintuitively, the reduction in SLG/water interface energy and the enhanced hydrophilicity after repeated freezing–melting–evaporation cycles actually decreases the freezing temperature by ∼3–4 °C, thereby slightly retarding rather than enhancing HIN. We also found that the water droplet freezing temperature differed by only ∼1 °C on different substrates with WCAs from 2° to 95°, an intriguing and yet reasonable result that confirms that wettability alone is not a good indicator of HIN capability. The HIN rate is rather determined by the difference between substrate/water and substrate/ice interface energies, which was found to stay almost constant for substrates weakly interacting with water/ice via van der Waals or hydrogen bonds, irrespective of hydrophilicity