Freely Suspended Cellular “Backpacks” Lead to Cell Aggregate Self-Assembly

Cellular “backpacks” are a new type of anisotropic, nanoscale thickness microparticle that may be attached to the surface of living cells creating a “bio-hybrid” material. Previous work has shown that these backpacks do not impair cell viability or native functions such as migration in a B and T cell line, respectively. In the current work, we show that backpacks, when added to a cell suspension, assemble cells into aggregates of reproducible size. We investigate the efficiency of backpack−cell binding using flow cytometry and laser diffraction, examine the influence of backpack diameter on aggregate size, and show that even when cell−backpack complexes are forced through small pores, backpacks are not removed from the surfaces of cells.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-08-19762)National Science Foundation (U.S.) (Graduate Research Fellowship)United States. Dept. of DefenseUnited States. Air Force Office of Scientific ResearchHoward Hughes Medical Institute (Investigator)United States. Dept. of Defense (National Defense Science and Engineering Graduate Fellowship 32 CFR 168a

Role of organo-modifier and metal impurities of commercial nanoclays in the photo-and thermo-oxidation of polyamide 11 nanocomposites

The photo-oxidative degradation processes of bio-based PA11 nanocomposites containing montmorillonite (MMT) and the organo-modified Cloisite®30B were investigated to discriminate the influence of organo-modified components on the polymer durability. Indeed, despite the extensive studies reported, there are still ambiguous points to be clarified from the chemical point of view. To this aim, UV-aged materials were analyzed by Size Exclusion Chromatography (SEC), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). This enabled determining changes in both chemical structure and Molar Masses (MMs) induced by light, heat and oxygen exposure. The addition of organo-modified nanoclays strongly affected the PA11 light durability, triggering the macromolecular chains scission due to the typical αH, Norrish I and II mechanisms. However, the main contribution in boosting the photo-oxidative degradation is induced by iron impurities contained into the clays. Conversely, thermo-oxidation process performed at 215 °C was unambiguously affected by the presence of the organo-modifiers, whose presence determined an enhancement of crosslinking reactions

Cross-linking of starch with 1,2,3,4-diepoxybutane or 1,2,7,8-diepoxyoctane

Water-soluble and native potato starches were modified with 1, 2, 3, 4-diepoxybutane (DEB) or 1, 2, 7, 8-diepoxyoctane (DEO). Optimal reaction conditions and the effectiveness of the cross-linkers were determined on the basis of yields of water-soluble and insoluble material. The presence of the introduced groups was confirmed by NMR spectroscopy in solution as well as in solid state. According to multi-angle laser light-scattering method, the weight average molecular masses of the water-soluble fractions prepared from water-soluble starch were larger (M-w = 471 kDa using DEB; M-w = 931 kDa with DEO) in comparison with the starting material (Mw = 291 kDa). Due to high molecular mass only new anomeric signals were observed by H-1 NMR in solution. Maximal yields of insoluble parts were 18 or 50% for DEB or DEO. On native starch the yields of insoluble products decreased with increasing concentration of cross-linker and NaOH in comparison to unmodified material. Solubilized components were dialyzed and we suppose that starch was degraded under these conditions. This material is not suitable for the modification when the goal is to increase the yield of insoluble part. With water-soluble starch the initial first order rate constants of cross-linking with E, DEB and DEO were determined with rheometer. From the relation of complex shear modulus and time by linear regression method at 20-70 degreesC, first-order rate constants of the same order of magnitude were calculated. The corresponding activation energies of the process are decreasing in the order: E (131 kJ/mol) > DEO (105 kJ/mol) > DEB (55 kJ/mol). We consider these results in agreement with the differences in the structure of the cross-linkers and the mechanism of cross-linking. Both crosslinkers gave spherical particles when cross-linked by the water-in-oil emulsion method with dimensions 60-610 (10% less than or equal to 192; 50% less than or equal to 294; 90% less than or equal to 425) mum, when cross-linked with DEB or 250-730 (10% less than or equal to 278; 50% less than or equal to 392; 90% less than or equal to 548) mum, when DEO was used. (C) 2003 Elsevier Ltd. All rights reserved

Cross-linking of starch with 1,2,3,4-diepoxybutane or 1,2,7,8-diepoxyoctane

Water-soluble and native potato starches were modified with 1, 2, 3, 4-diepoxybutane (DEB) or 1, 2, 7, 8-diepoxyoctane (DEO). Optimal reaction conditions and the effectiveness of the cross-linkers were determined on the basis of yields of water-soluble and insoluble material. The presence of the introduced groups was confirmed by NMR spectroscopy in solution as well as in solid state. According to multi-angle laser light-scattering method, the weight average molecular masses of the water-soluble fractions prepared from water-soluble starch were larger (M-w = 471 kDa using DEB; M-w = 931 kDa with DEO) in comparison with the starting material (Mw = 291 kDa). Due to high molecular mass only new anomeric signals were observed by H-1 NMR in solution. Maximal yields of insoluble parts were 18 or 50% for DEB or DEO. On native starch the yields of insoluble products decreased with increasing concentration of cross-linker and NaOH in comparison to unmodified material. Solubilized components were dialyzed and we suppose that starch was degraded under these conditions. This material is not suitable for the modification when the goal is to increase the yield of insoluble part. With water-soluble starch the initial first order rate constants of cross-linking with E, DEB and DEO were determined with rheometer. From the relation of complex shear modulus and time by linear regression method at 20-70 degreesC, first-order rate constants of the same order of magnitude were calculated. The corresponding activation energies of the process are decreasing in the order: E (131 kJ/mol) > DEO (105 kJ/mol) > DEB (55 kJ/mol). We consider these results in agreement with the differences in the structure of the cross-linkers and the mechanism of cross-linking. Both crosslinkers gave spherical particles when cross-linked by the water-in-oil emulsion method with dimensions 60-610 (10% less than or equal to 192; 50% less than or equal to 294; 90% less than or equal to 425) mum, when cross-linked with DEB or 250-730 (10% less than or equal to 278; 50% less than or equal to 392; 90% less than or equal to 548) mum, when DEO was used. (C) 2003 Elsevier Ltd. All rights reserved

Synthesis, characterisation and solution behaviour of thermo- and pH-responsive polymers bearing L-leucine residues in the side chains

Polymers capable of responding to both temperature and pH changes were synthesised by radical copolymerisation of N-isopropylacrylamide (NIPAAm) and N-methacryloyl-l-leucine (MALEU) in different NIPAAm/MALEU molar ratios (15:1, 10:1, 2:1 and 1:1). The polymers were characterised by Size Exclusion Chromatography, acid–base titrations, FT-IR and 1H-NMR analyses. Their solution behaviour was studied in 0.1 M NaCl and in citrate buffers (pH 4.0, 4.5, 5.0 and 6.0). At pH 4.0 and 4.5 the cloud point temperature (TCP) of copolymers was depressed proportionally to their MALEU content. In contrast, at pH 5.0 and 6.0 the phase transition temperature increased linearly. The behaviour of the copolymers with NIPAAm/MALEU ratios 15:1 and 10:1 was investigated also between pH 3 and 11 in 0.1 M NaCl. In both cases a sharp increase in TCP was observed around pH 4–5. The TCP vs. pH curve was linearised and the acidity constants were determined by the linearisation procedure. Furthermore, it was possible to demonstrate that the phase transition temperature increases linearly with the ionic content of the polymers