Coated membrane

Abstract: The binding of various biologically significant macromolecules to specific cell surface receptors is followed by their internalization, a process called receptor-mediated endocytosis1,2. In most cases, it has been shown that receptor-bound ligands cluster in characteristic, bristle-coated indentations of the cell surface known as coated pits1–3. In addition to coated pits, cultured cells have a population of smaller, non-coated membrane invaginations4–6, which may have a role in endocytosis2,7. However, no receptor-bound biologically active ligand has been shown to enter cells via these non-coated invaginations. The studies implicating coated pits in receptor-mediated endocytosis concern essentially ligands that bind to receptors thought to be glycoproteins. We have therefore investigated by electron microscopy the endocytosis of cholera toxin and tetanus toxin, ligands which bind to membrane glycolipids, in particular to either GM1 monosialoganglioside8–11 or di- and trisialogangliosides12–15 respectively. We show here that in cultured liver cells, non-coated membrane microinvaginations are preferentially involved in both the initial binding and subsequent internalization of colloidal gold-labelled cholera and tetanus toxin.

Abstract: Aim—To describe the early formation of drusen and their relation to normal aging changes at the macula and to the development of age related maculopathy (ARM). Method—Histopathological features of 353 eyes without histological evidence of ARM are described and correlated with the clinical appearance. In addition, 45 of these eyes were examined by transmission electron microscopy. Results—Drusen were detected histopathologically in 177 (50%) eyes but were seen clinically in only 34% of these. Drusen were mainly small hard drusen with an occasional soft distinct drusen: no soft indistinct drusen were seen. Only those drusen deposits larger than 25‐30 µm in diameter were detectable clinically. Preclinical drusen in eyes with only an occasional drusen were seen on electron microscopy as entrapment sites of coated membrane bound bodies which formed adjacent to the inner collagenous zone of Bruch’s membrane. In contrast, preclinical drusen deposits in eyes with many drusen were seen as accumulations of amorphous material which appeared hyalinised by light microscopy. A distinct feature were rows of dense hyalinised microdrusen (1‐2 µm in diameter), over which larger globular hyalinised drusen formed. Conclusion—Histological and ultrastructural examination can recognise and distinguish the earliest drusen formed as a result of normal aging from those associated with ARM. In eyes without diVuse deposits, histologically all drusen were of the hard hyalinised variety or their derivatives; no soft drusen composed of membranous debris were found. These findings support and explain those of other authors who do not consider the presence of a few small hard drusen to be a risk factor for the development of ARM. (Br J Ophthalmol 1999;83:358‐368)

Abstract: We report a facile method for the antimicrobial modification of a thin-film composite polyamide reverse osmosis (RO) membrane. The membrane surface was first coated with polydopamine (PDA), whose reducing catechol groups subsequently immobilized silver ions in situ to form uniformly dispersed silver nanoparticles (AgNPs) inside the coating layer. Agglomeration of AgNPs was not observed despite a high silver loading of 13.3 ± 0.3 μg/cm(2) (corresponding to a surface coverage of 18.5% by the nanoparticles). Both diffusion inhibition zone tests and colony formation unit tests showed clear antimicrobial effects of the silver loaded membranes on model bacteria Bacillus subtilis and Escherichia coli. Furthermore, the silver immobilized membrane had significantly enhanced salt rejection compared to the control PDA coated membrane, which is attributed to the preferential formation of AgNPs at defect sides within the PDA layer. This self-healing mechanism can be used to prepare antimicrobial RO membranes with improved salt rejection without scarifying the membrane permeability, which provides a new dimension for membrane surface modification.