Pericellular membrane

In the past, PolyOne manufactured suspension PVC having a K number of 87, Geon 407, which has been designed for rapid absorption of plasticizer. The polymer had a highly porous structure and was lacking a pericellular membrane. Formolon S-85 has similar properties. 

Geon 471 had the ability to absorb large amounts of plasticizer. It also absorbs plasticizer much faster, which reduces dryblending time. Absorption of plasticizer is improved by the high porosity of PVC but also by virtual elimination of a pericellular membrane (skin) surrounding particles of typical suspension PVC. 

In suspension polymerization, free-radical initiation, due to decomposition of a peroxide or azo initiator, generally occurs in droplets. As PVC is insoluble in monomer, submicron-sized particles precipitate in the droplets virtually immediately. These particles migrate to the surface of the droplet and very quickly form a him at the interface called the pericellular membrane. Polymeriza-hon and precipitahon conhnue to occur in the droplet unhl the droplets are converted from solids-in-liquid to liquid-sorbed-in-solid ( 20% conversion). 

At about this point in the polymerization, the particles become unstable and agglomerate into larger aggregates. As this occurs, the pericellular membrane of individual parhcles is broken, the agglomerated parhcles are porous, and the interior structure is that of agglomerated 1 qm particles. 

As the pericellular membrane ruptures, internal void volume—empty space amidst Stage II parhcles—forms due to shrinkage. This void volume is most prevalent in high molecular weight resins. During polymerization, void volume fills with water which is later removed in the dewatering step. Plasticizer is... 

Basement membrane specific structural Pericellular in most interstitial tissues Links constituents of interstitial tissues... 

Schwannoma Verocay bodies Antoni A and B thin pericellular basement membrane S-1 00 (-I-) Leu7 type IV collagen GFAP (R) Eighth cranial nerve spinal roots PNS... 

Extracellular matrix (intercellular, pericellular matrix) is composed of a variety of polysaccharides and proteins that are spontaneously organized into ordered structures. It represents a supramolecular complex, formed by a network of molecules connected to each other [31,41]. In the human body, the extracellular matrix produces highly speciaUzed structures such as cartilage of the tendon, the basal membrane and after the secondary deposition of calcium phosphate, bones and teeth. Since these structures differ both in molecular composition and methods for organizing the main components, they comprise the various forms of the extracellular matrix [31,41]. Here we draw a generalized picture of the extracellular matrix and the functional role of hyaluronan in it. 

In 1983 Prehm [36] proposed a mechanism by which HA is synthesized on the interior side of the plasma membrane by addition of intact UDP-sugars to the reducing end of the chain and concommittant release of the UDP attached to the chain in the preceeding sugar transfer. The non-reducing end of the chain was translocated through the membrane into the pericellular space. The evidence for this mechanism was the following ... 

Tethering of hyaluronan to different cell types can occur by at least two independent mechanisms. One of these is by binding to the hyaluronan receptor, CD44, as described above for chondrocytes. A second likely mechanism is transmembrane interaction of nascent hyaluronan with hyaluronan synthase. Thus, in several cell types, hyaluronan in the process of extrusion across the plasma membrane appears to be tethered by sustained attachment to hyaluronan synthase or associated proteins on the cytoplasmic face of the plasma membrane ([29] also Chapter 21 in this volume). Some pathogenic bacteria have hyaluronan capsules that may also be tethered in this way. These capsules would represent a primitive form of pericellular matrix which acts to facilitate bacterial invasion by inhibiting phagocytosis [36] and/or by promoting adhesion to host tissues [37]. 

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