Application of Linear and Branched Poly(Ethylene Glycol)‐Poly(Lactide) Block Copolymers for the Preparation of Films and Solution Electrospun Meshes

Poly(ethylene glycol)‐poly(lactide) (PEG‐PLA) block copolymers are processed to solvent cast films and solution electrospun meshes. The effect of polymer composition, architecture, and number of anchoring points for the plasticizer on swelling, degradation, and mechanical properties of these films and meshes is investigated as potential barrier device for the prevention of peritoneal adhesions. As a result, adequate properties are achieved for the massive films with a longer retention of the plasticizer PEG for star‐shaped block copolymers than for the linear triblock copolymers and consequently more endurable mechanical properties during degradation. For electrospun meshes fabricated using the same polymers, similar trends are observed, but with an earlier start of fragmentation and lower tensile strengths. To overcome the poor mechanical strengths and an occurring shrinkage during incubation, which may impair the coverage of the wound, further adaptions of the meshes and the fabrication process are necessary.

     

Visible Light Activation of Boronic Esters Enables Efficient Photoredox C(sp2)–C(sp3) Cross‐Couplings in Flow

We report herein a new method for the photoredox activation of boronic esters. Using these reagents, an efficient and high‐throughput continuous flow process was developed to perform a dual iridium‐ and nickel‐catalyzed C(sp²)–C(sp³) coupling by circumventing solubility issues associated with potassium trifluoroborate salts. Formation of an adduct with a pyridine‐derived Lewis base was found to be essential for the photoredox activation of the boronic esters. Based on these results we were able to develop a further simplified visible light mediated C(sp²)–C(sp³) coupling method using boronic esters and cyano heteroarenes under flow conditions.     

Conformation orientation of syndiotactic polypropylene induced by deformation at different temperatures

Two syndiotactic polypropylene (sPP) sample films (S0 and S90) with different initial structures were prepared in this paper by isothermal crystallization from the melt at 0 and 90 degrees C, respectively. The polymorphic transitions of the two samples induced by deformation at different temperatures (20, 40, and 60 degrees C) were investigated by rheo-optical FTIR spectroscopy. The results indicated that stretching leads to the transition from the helical to trans-planar conformation and improves the orientation of both helical and trans-planar conformations for the sPP films. With increasing stretching temperature, the conformational transitions for the two sPP samples are all suppressed, and the orientation behavior of the two samples appears completely different. The orientation degree of S0 decreases with increasing stretching temperature, while that of S90 increases. These results suggest that the stretching temperature and initial structure have great influence on the conformation transition and orientation behavior of the sPP sample. On the basis of the experimental results, the schematic illustration of the conformation transition and orientation behavior of sPP during stretching has been proposed.     

Water-stable biphasic nanocolloids with potential use as anisotropic imaging probes

Electrified co-jetting of two aqueous polymer solutions followed by a thermal cross-linking step was used to create water-stable biphasic nanocolloids. For this purpose, aqueous solution mixtures of poly(acrylamide-co-acrylic acid) and poly(acrylic acid) were employed as jetting solutions. When the biphasic nanocolloids created by side-by-side electrified co-jetting were thermally treated, a cross-linking reaction occurred between amide groups and carboxylic groups to form stable imide groups. Infrared spectroscopy was employed to monitor the reaction. The quality and the integrity of the resulting biphasic nanocolloids were confirmed by confocal laser scanning microscopy, flow cytometry analysis, and dynamic light scattering. Selective encapsulation of two biomolecules in each phase of the biphasic colloids was maintained even after thermal reaction and suspension in aqueous environment. Well-dispersed spherical colloids with stable dye loadings in each hemisphere were kept intact without aggregation or dissolution for several weeks. Finally, biphasic nanocolloids were selectively surface-modified with a biotin-dextran resulting in water-stable particles to ensure binding of proteins only to a single hemisphere.     

Ring-opening and ring-closing reactions of a shikimic acid-derived substrate leading to diverse small molecules

An epoxide derived from (-)-shikimic acid was attached to a solid support and used to synthesize over 5000 diverse small molecules. Key transformations include a Lewis acid-catalyzed epoxide opening with amines and an intramolecular Heck reaction with aryl iodides. Compounds derived from this pathway were printed onto small-molecule microarrays and screened for binding to proteins. Compounds that bound to Aurora A kinase were characterized using surface plasmon resonance.     

Surface instabilities of thin liquid film flow on a rotating disk

 Steady flow of a liquid jet from a nozzle onto the centre of a rotating disk is studied with a streak line method to determine the superficial velocity of the spreading liquid film. Good agreement is found with an asymptotic analysis of the unperturbed flow field. Experimentally, the liquid surface is always perturbed by surface waves which appear as regular spirals, steady in the laboratory system in the low Reynolds number range. It could be shown that wave formation is very sensitive to entrance conditions. Therefore, it is assumed that wave generation is an entrance effect which acts as periodic forcing on the forming liquid film. Wave velocities outside the entrance region are measured and proved to be in good agreement with the prediction of a linear stability theory, as long as the flow rate and entrance perturbations are small. At higher flow rates or stronger disturbances, the radial development of the wave velocities takes on the characteristics predicted by nonlinear stability theories and is in qualitative agreement with experiments performed on an inclined plane. Received: 15 January 1998/Accepted: 8 June 1998     

Micropatterned Fiber Scaffolds for Spatially Controlled Cell Adhesion

Because the local microstructure plays a pivotal role for many biological functions, a wide range of methods have been developed to design precisely engineered substrates for both fundamental biological studies and biotechnological applications. However, these techniques have been by‐and‐large limited to flat surfaces. Herein, we use electrohydrodynamic co‐spinning to prepare biodegradable three‐dimensional fiber scaffolds with precisely engineered, micrometre‐scale patterns, wherein each fiber is comprised of two distinguishable compartments. When bicompartmental fiber scaffolds are modified via spatially controlled peptide immobilization, highly selective cell guidance at spatial resolutions (<10 µm), so far exclusively reserved for flat substrates, is achieved. Microstructured fiber scaffolds may have utility for a range of biotechnological applications including tissue engineering or cell‐based assays.

     

Comparison of LFQ and IPTL for Protein Identification and Relative Quantification

(1) Background: Mass spectrometry-based quantitative proteome profiling is most commonly performed by label-free quantification (LFQ), stable isotopic labeling with amino acids in cell culture (SILAC), and reporter ion-based isobaric labeling methods (TMT and iTRAQ). Isobaric peptide termini labeling (IPTL) was described as an alternative to these methods and is based on crosswise labeling of both peptide termini and MS2 quantification. High quantification accuracy was assumed for IPTL because multiple quantification points are obtained per identified MS2 spectrum. A direct comparison of IPTL with other quantification methods has not been performed yet because IPTL commonly requires digestion with endoproteinase Lys-C. (2) Methods: To enable tryptic digestion of IPTL samples, a novel labeling for IPTL was developed that combines metabolic labeling (Arg-0/Lys-0 and Arg-d4/Lys-d4, respectively) with crosswise N-terminal dimethylation (d4 and d0, respectively). (3) Results: The comparison of IPTL with LFQ revealed significantly more protein identifications for LFQ above homology ion scores but not above identity ion scores. (4) Conclusions: The quantification accuracy was superior for LFQ despite the many quantification points obtained with IPTL.