Structure of PEP-PEO block copolymer micelles: Exploiting the complementarity of small-angle X-ray scattering and static light scattering

The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP–PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8–49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core–shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.</jats:p

Aggregative adherence fimbriae form compact structures as seen by SAXS

Bacterial colonization is mediated by fimbriae, which are thin hair-like appendages dispersed from the bacterial surface. The aggregative adherence fimbriae from enteroaggregative E. coli are secreted through the outer membrane and consist of polymerized minor and major pilin subunits. Currently, the understanding of the structural morphology and the role of the minor pilin subunit in the polymerized fimbriae are limited. In this study we use small-angle X-ray scattering to reveal the structural morphology of purified fimbriae in solution. We show that the aggregative fimbriae are compact arrangements of subunit proteins Agg5A + Agg3B which are assembled pairwise on a flexible string rather than extended in relatively straight filaments. Absence of the minor subunit leads to less compact fimbriae, but did not affect the length. The study provides novel insights into the structural morphology and assembly of the aggregative adherence fimbriae. Our study suggests that the minor subunit is not located at the tip of the fimbriae as previously speculated but has a higher importance for the assembled fimbriae by affecting the global structure.</p

Aquaporin-Based Biomimetic Polymeric Membranes: Approaches and Challenges

In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes

Selecting analytical tools for characterization of polymersomes in aqueous solution

Selecting the appropriate analytical methods for characterizing the assembly and morphology of polymer-based vesicles, or polymersomes are required to reach their full potential in biotechnology. This work presents and compares 17 different techniques for their ability to adequately report size, lamellarity, elastic properties, bilayer surface charge, thickness and polarity of polybutadiene-polyethylene oxide (PB-PEO) based polymersomes. The techniques used in this study are broadly divided into scattering techniques, visualization methods, physical and electromagnetical manipulation and sorting/purification. Of the analytical methods tested, Cryo-transmission electron microscopy and atomic force microscopy (AFM) turned out to be advantageous for polymersomes with smaller diameter than 200 nm, whereas confocal microscopy is ideal for diameters >400 nm. Polymersomes in the intermediate diameter range can be characterized using freeze fracture Cryo-scanning electron microscopy (FF-Cryo-SEM) and nanoparticle tracking analysis (NTA). Small angle X-ray scattering (SAXS) provides reliable data on bilayer thickness and internal structure, Cryo-TEM on multilamellarity. Taken together, these tools are valuable for characterizing polymersomes per se but the comparative overview is also intended to serve as a starting point for selecting methods for characterizing polymersomes with encapsulated compounds or polymersomes with incorporated biomolecules (e.g. membrane proteins)

Incidence of central post-stroke pain

Central post-stroke pain (CPSP) is a neuropathic pain syndrome characterized by constant or intermittent pain in a body part occurring after stroke and associated with sensory abnormalities in the painful body part. This study describes CPSP prospectively during the first year after stroke and characterizes the cerebrovascular lesions and neurological signs associated with the CPSP syndrome. Two hundred and sixty-seven consecutively admitted patients younger than 81 years were examined in the first week, at 1, 6 and 12 months after stroke. Sensibility to touch (cotton wool), temperature (20 degrees C and 40 degrees C), and pinprick was studied using the contralateral face and extremity as control. A CT scan was done 8 (median) days (range: 1-34 days) after stroke. Two hundred and seven (78%) patients surviving at least 6 months who were able to communicate reliably formed the basis of the study. Abnormal sensory signs were found at least once in 87 (42%) patients. CPSP was found in 16 (8%) patients of whom all but 1 patient also had evoked dysesthesia or allodynia. Further 1 patient had persistent evoked dysesthesia but denied pain. CPSP was not related to sex or age. In patients with single acute cerebral lesions there were no relation between size or location of the lesions and the presence of CPSP. The pain was light in 6 (3%) patients and moderate to severe in 10 (5%) patients. The pain quality was usually lacerating or aching. Fifteen (94%) patients had decreased temperature, touch and pain sensibility and 9 (56%) reported allodynia to cold stimulation and another 9 (56%) patients reported this to touch.(ABSTRACT TRUNCATED AT 250 WORDS)</p