Biomaterial hydrophobicity

Preparation of polyfethylene oxide) (PEO) and poly(arylene ether) based hydrophilic-hydrophobic block copolymer is of special interest because PEO has been proven to be particularly reliable and versatile for the surface modification of biomaterials. The first poly(ediylene oxide)-/ /oc/c-polysulfonc (PEO-fc-PSF) copolymers were reported by Aksenov et al.217 They employed diisocyanate chemistry to link hydroxy-terminated sulfone oligomers and polyfethylene... 

Aryloxyphosphazene polymers, such as compound 1 or its mixed-substituent analogs, are also hydrophobic (contact angles in the region of 100°). These too show promise as inert biomaterials on the basis of preliminary in vivo tissue compatibility tests (13). 

Hydrophobically modified HA derivatives,91 obtained through the partial esterification of the HA carboxyl groups with methylprednisolone (45% in HYCp45 and 60% in HYCp60),92 have been deeply studied 93 A key point prior to any in vivo study of the biomaterial is the assessment of the so-called "stealth character" of the species itself. Such characteristic corresponds to be invisible towards the immune system, so that colloids are not recognized as foreign objects by body fluid components, as plasma proteins fibrinogen, BSA and lipidic components.94,95... 

Okano, T., Yamada, N., Okuhara, M., Sakai, H., and Sakurai, Y. Mechanism of cell detachment from temperature-modulated, hydrophilic-hydrophobic polymer surfaces, Biomaterials, 1995, 16, 297-303. 

Cloud point extraction from biological and clinical samples. The most frequent use of CPE is for the separation and purification of biological analytes, principally proteins. In this way, the cloud point technique has been used as an effective tool to isolate and purify proteins when combined with chromatographic separations. Most of the applications deal with the separation of hydrophobic from hydrophilic proteins, with the hydrophobic proteins having more affinity for the surfactant-rich phase, and the hydrophilic proteins remaining in the dilute aqueous phase. The separation of biomaterials and clinical analytes by CPE has been described [105,106,113]. 

Hydrophilicity and hydrophobicity are the most fundamental properties to be controlled for materials whenever they are utilized in biomedical devices. Protein-adsorption behavior on several biomaterials of different hydrophilicity was discussed by comparing available data with two modellings (Ikada and Peppas) for the protein-adsorption process. The adsorptive behavior of poly(HEMA) carrying polyamine functional groups was also discussed. It is well-known that protein adsorption is the first event when any of the body fluids encounters an artificial material. 

Heller, J., Ng, S.Y., Fritzinger, B.K., and Roskos, K.V. (1990) Controlled drug release from bioerodible hydrophobic ointments. Biomaterials, 11, 235-237. 

Elastomers of this type are usually cross-linked during fabrication, and often contain fillers such as carbon black or iron oxide to reduce the compliance of the elastomer (i.e. to provide a greater resistance to deformation). Such materials are depicted in Figure 3.1. They are used in technology because of their flexibility and elasticity at low temperatures (-60 °C), their resistance to hydrocarbon solvents, oils, and hydraulic fluids, and their fire resistance.145 For these reasons, they are utilized in aerospace and advanced automotive applications. Some interest exists in their development as inert biomaterials, mainly because of their surface hydrophobicity and consequent biocompatibility. 

Mowery KA, Schoenfisch MH, Saavedra JE, Keefer LK, Meyerhoff ME. Preparation and characterization of hydrophobic polymeric films that are thromboresistant via nitric oxide release. Biomaterials 2000, 21, 9-21. 

The self-assembly and inhibition of protein adsorption by thiolated dextran monolayers at hydrophobic metal surfaces. In Ratner BD, Castner DG (eds) Surface modification of polymeric biomaterials. Plenum, New York, p 117... 

Xing BG, Yu CW, Chow KH et al. (2002) Hydrophobic interaction and hydrogen bonding cooperatively confer a vancomycin hydrogel a potential candidate for biomaterials. J Am Chem Soc 124 14846-14847... 

The protein elastin presents another opportunity to create amyloid-like fibrils from natural proteins for the purpose of developing biomaterials. Elastin is found in tissue where it imparts elastic recoil, and fibrils formed from this protein may demonstrate some of the elastic properties of the constituent elastic proteins (Bochicchio et al., 2007). Elastin typically contains the sequence poly(ZaaGlyGlyYaaGly) (where Zaa, Yaa = Val or Leu) (Tamburro et al., 2005), and short stretches of the protein retain the ability to form structures similar to the original protein. Simple proline to glycine mutations in the hydrophobic domains of elastin can induce the formation of amyloid-like fibrils (Miao et al., 2003), suggesting that fibrillar materials can be easily generated from these sequences. 

Fig. 8. Schematic representation of protein-mediated cell adhesion on biomaterial surfaces. Biomaterial surface properties (such as hydrophilicity/hydrophobicity, topography, energy, and charge) affect subsequent interactions of adsorbed proteins these interactions include but are not limited to adsorbed protein type, concentration, and conformation. Changes in protein-surface interactions may alter accessibility of adhesive domains (such as the peptide sequence arginine-glycine-aspartic acid) to cells (such as osteoblasts, fibroblasts, or endothelial cells) and thus modulate cellular adhesion. (Adapted and redrawn from Schakenraad, 1996.)...

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