Hyaluronan hydrophilicity

In aqueous solutions, at a physiological pH, HA is represented by negatively charged hyaluronate macromolecules (pK = 3.21) [15] with extended conformations. In a polyanionic form, hyaluronan functional groups make the biopolymer so hydrophilic that it binds 1000 times more water than is predicted from its molar mass. The heterogeneity and hydrophilicity of HA facilitate its interaction with a variety of tissue constituents inside and outside the cells. In the extracellular space, HA controls the retention of water, ionic and molecular diffusion and provides a 3D-structural meshwork [16]. 

Several hydrophilic coatings were applied to PUs to increase surface hydrophilicity, including poly(ethylene glycol) (PEG), hyaluronan, dermatan sulfate, and heparin. 

Other hydrophilic coalings have been proposed to reduce bacterial adhesion onto Morra et al. studied in vitro the adhesion of S. epidermidis onto bare PU catheters and PU catheters coated with hyaluronan. A significant reduction in bacterial adhesion was found by using the soft, hydrated surface of the modified PU. ° Highly sulfonated hyaluronan as PU coating resulted in the inhibition of S. epidermidis adhesion with respect to the unmodified PU. ... 

PHBHHx Hyaluronan coating Improved hydrophilicity, low fibroblast L929 cellular growth 1.6x10 (4x10 ) cells per ml. Could be employed in biomaterial selection and design. 77... 

The studies by means of NMR and circular dichroism methods [29] made it possible to identify the presence of relatively rigid and more flexible structures alternating within a single hyaluronan chain with a balance between these structures. Extremely high viscosity of hyaluronan solutions was due, on the one hand to its structure and, on the other hand, was conditioned by specific and non-specific intermolecular interactions of macromolecules [29]. It all points to the fact that not only hydrophilic but also hydrophobic interactions play a significant role in stabilization of hyaluronan structure associated with the specific macromolecular structure. 

The immune system is connected with HA [91-94], Hyaluronan is included into drugs used for the complex treatment of immunodeficient conditions associated with viral diseases. At the molecular level, the mechanism of action of the biopolymer is connected with the blocking of several molecular inflammation factors [93]. On the one hand hyaluronan activates inferonogenesis but on the other it increases action of the interferon inductor (e.g. double-stranded RNA) [91,92]. Interferon is produced mainly by the activated monocytes and T-cells of the immune system. The interleukins-2 and -5 (IL-2, IK-5) play a major role in the activation of T-cells that, in turn, activate synthesis of hyaluronan by endothelial capillary cells. Then hyaluronan stimulates synthesis of CD44 receptors, which is the key event for the activation of the lymphocytes and monocytes [93]. HA is used alone or in combination with interferon to slow down the development of the infection by the virus herpes simplex by application on the infected epithelium [61]. The obvious antimicrobial action of HA can be achieved by its cross-linking with hydrophilic polymers, which are capable of accelerated penetration through cell membranes or intercellular gaps [61]. 

In a departure from historical approaches to introducing fillers in UHMWPE, researchers from Colorado State University have developed a novel UHMWPE-hyaluronan microcomposite [50, 51]. This microcomposite is detailed in Chapter 18. Hyaluronan is a natural lubricant in articular cartilage. By incorporating this biomolecule into UHMWPE, researchers theorized that wear could be reduced. Because hyaluronan is hydrophilic and UHMWPE is hydrophobic, fabrication of an UHMWPE-hyaluronan microcomposite is by no means a straightforward proposition and is accomplished via a complex and elegant multistep procedure. The process, which is described in greater detail in Chapter 18, begins with the production of a porous UHMWPE substrate, which constitutes the matrix of the microcomposite. The hyaluronan is complexed with quaternary ammonium cations (CTA-I-) and silylated [52]. A solution of silyl hyaluronan-CTA is then diffused into the open celled porous UHMWPE matrix, chemically crosslinked in situ, and then hydrolyzed... 

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