Biomedical polymers hydrophobicity

The conjugation of therapeutics to water-soluble biomedical polymers increases the aqueous solubility of hydrophobic drugs and reduces systemic toxicity [42, 43]. The polymer drug conjugates can preferentially accumulate in solid tumor tissues due to the hyperpermeability of tumor blood vessels or the... 

Hydrophobicity of biomedical polymers influences the biocompatibility depending on the particular application such as tissue engineering, blood contacting devices, and dental implants [35]. Polymers are dynamic structures and can switch their surface functional groups depending on the environment. For example, polymeric biomaterials need to have a hydrophilic smface for most of the applications, so that the cell-adhesive proteins present in the serum will be adsorb and promote cell adhesion and proliferation. This is achieved by snrface treatment procedures such as... 

Silicone has also a long history as a biomedical polymer and has preferably been used for special catheters and shunts which require good blood compatibility. This is because the polymer exhibits an extremely high chemical stability and hydrophobicity. Poor mechanical properties can be improved by mixing with fillers, which, howeva-, decrease the blood compatibility A commercial product, Avcothane , seems to be composed largely of polyurethane and silicone... 

Recently, many studies have focused on self-assembled biodegradable nanoparticles for biomedical and pharmaceutical applications. Nanoparticles fabricated by the self-assembly of amphiphilic block copolymers or hydrophobically modified polymers have been explored as drug carrier systems. In general, these amphiphilic copolymers consisting of hydrophilic and hydrophobic segments are capable of forming polymeric structures in aqueous solutions via hydrophobic interactions. These self-assembled nanoparticles are composed of an inner core of hydrophobic moieties and an outer shell of hydrophilic groups [35, 36]. 

M.M. Reynolds, M.C. Frost, and M.E. Meyerhoff, Nitric oxide-releasing hydrophobic polymers preparation, characterization, and potential biomedical applications. Free Radical Biol. Med. 37, 926-936... 

The past two decades have produced a revival of interest in the synthesis of polyanhydrides for biomedical applications. These materials offer a unique combination of properties that includes hydrolytically labile backbone, hydrophobic bulk, and very flexible chemistry that can be combined with other functional groups to develop polymers with novel physical and chemical properties. This combination of properties leads to erosion kinetics that is primarily surface eroding and offers the potential to stabilize macromolecular drugs and extend release profiles from days to years. The microstructural characteristics and inhomogeneities of multi-component systems offer an additional dimension of drug release kinetics that can be exploited to tailor drug release profiles. 

Despite the highly versatile application prohles of polymers with adjunct sucrose (or other sugar) residues—their major asset is enhanced hydrophUicity as compared to their hydrophobic petroleum-derived counterparts—interest appears to be restricted to biomedical uses. Currently none is produced commercially, as the generation of vinyl-sucroses and their often capricious polymerization have made their use as commodity plastics uneconomical. Another reason is their limited biodegradability only the sugar portion is biodegradable, with a polymeric carbon chain left over. Because biodegradability is a major issue today, " these polyvinylsaccharides are unlikely to become petrochemical substitution options in the near future. 

Methoxy poly(ethyleneglycol) (mPEG) was the most frequently used semitelechelic polymer for over 2 decades. It has been successfully used for the modification of various proteins, biomedical surfaces and hydrophobic anticancer drugs (for reviews see References [3,9,10]. Recently, a number of new semitelechelic (ST) polymers, such as ST-poly(A -isopropylacry-lamide) (ST-PNIPAAM) [11-15], ST-poly(4-acryloylmorpholine) (ST-PAcM) [16], ST-poly(A-vinylpyrrolidone) (ST-PVP) [17], and ST-poly[A-(2-hydroxypropyl)methacrylamide] (ST-PHPMA) [18-21] have been prepared and shown to be effective in the modification of proteins or biomedical surfaces. 

Anderson et al. [59, 75,76] have been pursuing their extensive researches on the biomedical behavior of PEUUs having various formulations modified with hydrophobic acrylate (or methacrylate) polymer or copolymer additives. The most distinguished additive was Methacrol 2138F, which is a copolymer between diisopropylaminoethyl methacrylate and decyl methacrylate [co(DIPAM/DM)] (in a 3-to-l ratio). The protein adsorption assay showed that PEUU (Biomer-type) films loaded or coated with Methacrol or poIy(DIPAM) adsorbed significantly lower amounts of human blood proteins (Fb, IgG, factor VIII, Hageman factor and Alb) than the base PEUU or PEUUs modified by other additives. It was revealed from their experiments that poly(DIPAM) as well as Methacrol exhibited a prominent suppressing effect on the protein adsorption process. 

Such materials are known as semipermeable membranes. They are essential components of nearly all living things, and the development of new materials of this type is an important component of biomedical research. The control of diffusion of molecules through a membrane can be accomplished by variations in the hydrophilicity of the polymer molecules that constitute the membrane. As in biological membranes, hydrophobic molecules are more likely to pass through the hydrophobic domains of a synthetic membrane than through the hydrophilic regions, and vice versa. 

Amino acid ester side groups are not the only units that sensitize the system to hydrolysis. The imidazolyl group has an even greater effect.197-198-219 For example, polymer 3.86, prepared by the reaction of poly(dichlorophosphazene) with imidazole, is so unstable hydrolytically that it decomposes in moist air to imidazole, phosphate, and ammonia. This is too high a sensitivity for most biomedical applications. Hence, an emphasis has been placed on the study of polymers such as 3.87 in which a hydrophobic cosubstituent group, such as aryloxy, is present to reduce the rate of erosion. 

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