SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Elastomer

194

We demonstrate a new optical approach to generate high-frequency (>15 MHz) and high-amplitude focused ultrasound, which can be used for non-invasive ultrasound therapy. A nano-composite film of carbon nanotubes (CNTs) and elastomeric polymer is formed on concave lenses, and used as an efficient optoacoustic source due to the high optical absorption of the CNTs and rapid heat transfer to the polymer upon excitation by pulsed laser irradiation. The CNT-coated lenses can generate unprecedented optoacoustic pressures of >50 MPa in peak positive on a tight focal spot of 75 μm in lateral and 400 μm in axial widths. This pressure amplitude is remarkably high in this frequency regime, producing pronounced shock effects and non-thermal pulsed cavitation at the focal zone. We demonstrate that the optoacoustic lens can be used for micro-scale ultrasonic fragmentation of solid materials and a single-cell surgery in terms of removing the cells from substrates and neighboring cells.

Concepts: Photographic lens, Sonar, Electromagnetic radiation, Elastomer, Optics, Ultrasound, Sound, Pressure

146

Understanding high-velocity microparticle impact is essential for many fields, from space exploration to medicine and biology. Investigations of microscale impact have hitherto been limited to post-mortem analysis of impacted specimens, which does not provide direct information on the impact dynamics. Here we report real-time multi-frame imaging studies of the impact of 7 μm diameter glass spheres traveling at 700-900 m/s on elastomer polymers. With a poly(urethane urea) (PUU) sample, we observe a hyperelastic impact phenomenon not seen on the macroscale: a microsphere undergoes a full conformal penetration into the specimen followed by a rebound which leaves the specimen unscathed. The results challenge the established interpretation of the behaviour of elastomers under high-velocity impact.

Concepts: Medicine, Ethylene-vinyl acetate, Specimen, Elastomer, Polymer, Biology, Space exploration, Sample

33

Fabricated adhesives are demonstrated to support high loads while maintaining easy release on a variety of “real world” surfaces. These adhesives consist of simple elastomers and fabrics without nano or micron scale features, yet they surpass the adhesive force capacity of live Tokay geckos and can be scaled to large sizes.

Concepts: Universe, Polyurethane, 2002 albums, Elastomer, Gecko, Tokay gecko, Adhesion, Adhesive

30

Materials often exhibit a trade-off between stiffness and extensibility; for example, strengthening elastomers by increasing their cross-link density leads to embrittlement and decreased toughness. Inspired by cuticles of marine mussel byssi, we circumvent this inherent trade-off by incorporating sacrificial, reversible iron-catechol cross-links into a dry, loosely cross-linked epoxy network. The iron-containing network exhibits two to three orders of magnitude increases in stiffness, tensile strength, and tensile toughness compared to its iron-free precursor while gaining recoverable hysteretic energy dissipation and maintaining its original extensibility. Compared to previous realizations of this chemistry in hydrogels, the dry nature of the network enables larger property enhancement owing to the cooperative effects of both the increased cross-link density given by the reversible iron-catecholate complexes and the chain-restricting ionomeric nanodomains that they form.

Concepts: Cross-linked polyethylene, Tensile strength, Polymer chemistry, Thermoplastic, Elastomer, Materials science, Cross-link

29

Chain alignment can significantly influence the macroscopic properties of a polymeric material, but no general and versatile methodology has yet been reported to obtain highly ordered crystalline packing of polymer chains, with high stability. Here, we disclose a strategy that relies on ‘ordered crosslinks’ to produce polymeric materials that exhibit a crystalline arrangement. Divinyl crosslinkers (2,5-divinyl-terephthalate) were first embedded, as substitutional ligands, into the structure of a porous coordination polymer (PCP), [Cu(terephthalate)triethylenediamine0.5]n. A representative vinyl monomer, styrene, was subsequently polymerized inside the channels of the host PCP. The polystyrene chains that form within the PCP channels also crosslink with the divinyl species. This bridges together the polymer chains of adjacent channels and ensures that, on selective removal of the PCP, the polymer chains remain aligned. Indeed, the resulting material exhibits long-range order and is stable to thermal and solvent treatments, as demonstrated by X-ray powder diffraction and transmission electron microscopy.

Concepts: Diffraction, Elastomer, Synthetic rubber, Monomer, Polystyrene, Cross-link, Polymer chemistry, Polymer

28

Although biodegradable polymers have found extensive applications in medical areas, there are limited reports that show elastomeric behavior. In this work, a biodegradable, elastomeric polymer is demonstrated from a four-armed star copolymer. With a fixed middle core composition, comprising caprolactone (CL) and L-lactide (LA), an elastomer is obtained by increasing the polylactide (PLA) end block lengths to obtain sufficient end block crystallinity. This increase suppressed the middle core’s crystallinity yet ensured cocrystallization of the PLA ends of individual star copolymer chains to form a three-dimensional network via physical crosslinking. Cyclic and creep test of the star copolymers showed that at least 75% of recovery was achieved. Degradation study of the copolymer showed that degradation first occurred in the caprolactone-co-lactide (CLLA) core, followed by degradation in the PLA ends. Chain scission in the middle core resulted in immediate formation of CL crystals within the core and increased crystallinity over time, in both CLLA core and PLA ends. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:3436-3445, 2012.

Concepts: Cross-link, Materials science, Copolymer, Thermoplastic, Polybutadiene, Polymer chemistry, Elastomer, Polymer

27

Low density shape memory polymer foams hold significant interest in the biomaterials community for their potential use in minimally invasive embolic biomedical applications. The unique shape memory behavior of these foams allows them to be compressed to a miniaturized form, which can be delivered to an anatomical site via a transcatheter process, and thereafter actuated to embolize the desired area. Previous work in this field has described the use of a highly covalently crosslinked polymer structure for maintaining excellent mechanical and shape memory properties at the application-specific ultra low densities. This work is aimed at further expanding the utility of these biomaterials, as implantable low density shape memory polymer foams, by introducing controlled biodegradability. A highly covalently crosslinked network structure was maintained by use of low molecular weight, symmetrical and polyfunctional hydroxyl monomers such as Polycaprolactone triol (PCL-t, Mn 900 g), N,N,N0,N0-Tetrakis (hydroxypropyl) ethylenediamine (HPED), and Tris (2-hydroxyethyl) amine (TEA). Control over the degradation rate of the materials was achieved by changing the concentration of the degradable PCL-t monomer, and by varying the material hydrophobicity. These porous SMP materials exhibit a uniform cell morphology and excellent shape recovery, along with controllable actuation temperature and degradation rate. We believe that they form a new class of low density biodegradable SMP scaffolds that can potentially be used as “smart” non-permanent implants in multiple minimally invasive biomedical applications.

Concepts: Materials science, Branching, Minimally invasive, Polymerization, Elastomer, Monomer, Polymer, Polymer chemistry

27

The production of hot embossed plastic microfluidic devices is demonstrated in 1-2 h by exploiting vinyl adhesive stickers as masks for electroplating nickel molds. The sticker masks are cut directly from a CAD design using a cutting plotter and transferred to steel wafers for nickel electroplating. The resulting nickel molds are used to hot emboss a variety of plastic substrates, including cyclo-olefin copolymer and THV fluorinated thermoplastic elastomer. Completed devices are formed by bonding a blank sheet to the embossed layer using a solvent-assisted lamination method. For example, a microfluidic valve array or automaton and a droplet generator were fabricated with less than 100 μm x-y plane feature resolution, to within 9% of the target height, and with 90 ± 11% height uniformity over 5 cm. This approach for mold fabrication, embossing, and bonding reduces fabrication time and cost for research applications by avoiding photoresists, lithography masks, and the cleanroom.

Concepts: Polyvinyl chloride, Metal, Hydrogen, Oxygen, Elastomer, Thermoplastic elastomer, Thermoplastic, Polymer

27

Polymeric hydrogels typically release their drug payload rapidly due to their high water content and the diffusivity for drug molecules. This study proposes a multimaterial system to sustain the release by covering the hydrogel with a poly(alkyl-2-cyanoacrylate) [PACA]-based film, which should be formed by an in situ polymerization on the hydrogel surface initiated upon contact with water. A series of PACA-hydrogel hybrid systems with increasing PACA side chain hydrophobicity was prepared using physically crosslinked alginate films and hydrophilic diclofenac sodium as model hydrogel/drug system. Successful synthesis of PACA at the hydrogel surface was confirmed and the PACA layer was identified to be most homogeneous for poly(n-butyl-2-cyanoacrylate) on both the micro- and nanolevel. At the same time, the diclofenac release from the hybrid systems was substantially sustained from ~ 1 d for unmodified hydrogels up to >14 d depending on the type of PACA employed as diffusion barrier. Overall, in situ polymerized PACA films on hydrogels may be widely applicable to various hydrogel matrices, different matrix sizes as well as more complex shaped hydrogel carriers.

Concepts: Polyethylene, Elastomer, Polymerization, Monomer, Water, Branching, Polymer, Polymer chemistry

26

A common and prevailing complication for patients with abdominal surgery is the peritoneal adhesion that follows during the post-operative recovery period. Biodegradable polymers have been suggested as a barrier to prevent the peritoneal adhesion. In this work, as a preventive method, PVA/Gelatin hydrogel-based membrane was investigated with various combinations of PVA and gelatin (50/50, 30/70/, and 10/90). Membranes were made by casting method using hot PVA-gelatin solution and the gelatin was cross-linked by exposing UV irradiation for 5 days to render stability of the produced sheathed form in the physiological environment. Physical crosslinking was chosen to avoid the problems of potential cytotoxic effect of chemical crosslinking. Their materials characterization and mechanical properties were evaluated by SEM surface characterization, hydrophilicity, biodegradation rate, and so forth. Cytocompatibility was observed by in vitro experiments with cell proliferation using confocal laser scanning microscopy and the MTT assay by L-929 mouse fibroblast cells. The fabricated PVA/Gel membranes were implanted between artificially defected cecum and peritoneal wall in rats and were sacrificed after 1 and 2 weeks post-operative to compare their tissue adhesion extents with that of control group where the defected surface was not separated by PVA/Gel membrane. The PVA/Gel membrane (10/90) significantly reduced the adhesion extent and showed to be a potential candidate for the anti-adhesion application. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

Concepts: Elastomer, Collagen, Cross-linked polyethylene, MTT assay, Fibroblast, Polymer chemistry, Cross-link, Cytotoxicity