Modified poly biomedical applications

Secondary reactions of these types are widely used to produce polyphosphazenes that are required for biomedical applications or for polymer grafting reactions. They are also used to modify the surfaces of poly(organophosphazene), as discussed in the following section. 

Rhee, W., et al. Bovine collagen modified by PEG, in J. M. Harris, Poly (ethylene glycol) Chemistry Biotechnical and Biomedical Applications, New York Plenum Press, 1992... 

From 1970, amino acids-based homo- and copolymers were studied for biomedical applications the idea was quite intuitive, because proteins are made of amino acids. However, initial studies showed that most poly(amino acids) could not be employed for biomedical applications because of immunogenicity problems and poor mechanical properties. Only a small number of poly(y-substituted glutamates) possess adequate characteristics to be interesting. In order to improve mechanical and physiological features of these materials, amino acids can be used as monomeric building blocks in polymers that do not have a backbone with the conventional structure which can be found in peptides. These materials are the so called non-peptide amino acids-based polymers or amino-acid-derived polymers with modified backbone , and can be divided into four main categories (Bourke and Kohn, 2003) ... 

Pulapura, S. and Kohn, j. (1992) XyTOsine derived polycarbonates Backbone modified, pseudo -poly(amino acids) designed for biomedical applications. Biopolymers, 32, 411-417. 

Recent research explored various chemically modified conjugates and derivatives to improve its physico-chemical and biological properties. This modification allows significant applications of chitosan in various disciplines of biomedical research. So far various fabrication methods have been employed for the development of chemically modified chitosan e.g. chitosan-poly(acrylic acid) nanoparticles and acylated chitosan nanoparticles have been recently explored to examine their modifications effect on physicochemical properties and blood compatibility [151, 152], Similarly self-aggregated NPs of cholesterol-modified 0-carboxymethyl chitosan conjugates were fabricated to improve the pharmaceutical and biomedical applications of chitosan [153], Various examples of chitosan and its chemically modified synthetic derivatives are mentioned in Table 3.2. 

Proteins are made of amino acids thus, since 1970, scientists have been evaluating these materials for biomedical applications. However, because of their immunoge-nicity responses and poor mechanical properties, only a small number of poly(y-substituted glutamates) possess interesting performances. Several efforts were made to obtain amino acid—derived polymers with modified backbone to achieve adequate physicomechanical properties. On the basis of structural configuration, these materials can be classified into different subcategories synthetic polymers with amino acid side chains, copolymers of amino acid and non—amino acid monomer, block... 

Moreover, tyrosinase-catalyzed activity is not limited only to protein substrates. Burke et al. have focused their work on the modification of biocompatible polymers such as poly(ethylene glycol) with DOPA in an effort to impart adhesive qualities to the polymers for biomedical application. Although PEG itself is not adhesive, it represents a candidate budding block for a synthetic tissue adhesive because of its high water solubility, low immunogenicity and toxicity, and availability of end groups easily modifiable with amino acids and peptides [61]. Burke et al. [12] synthesized several linear and branched PEG molecules with end groups modified by DOPA residues and have characterized their oxidation-induced... 

An obvious need exists for membranes with improved permeability and permselectivity. In addition to several earlier pieces of work contained in ref. Zg and Zh studies involving radiation-modified poly(vinyl alcohol) ordered polycarbonates " and cellulosic ion-exchange membranes have been reported. A variety of reports have appeared of the evaluation of existing polymers, such as polysulphone, in biomedical applications for which they have not previously been used, and of the synthesis of new polymers which may find use in the biomedical area. Examples include polyorganophosphazenes, biodegradable poly(ethyene oxide)-poly(ethylene terephthalate) copolymers, collagen copolymers, block copolymers of l,4-bis(acryloyl) piperazine-AW -dimethylethylene diamine and styrene, and >olymers derived fi om a miscellany of heterocyclic monomers. Information on chemically modified polymers designed for biomedical use is also contained in Chapter 16 of this Volume. 

The prototypical smart polymer is poly(N-isopropyl acrylamide) (P(NIPAM)), which exhibits an inverse temperature solubility profile in water, that is it is water-soluble below 32 °C but precipitates above 32 °C. The temperature at which this coil-to-globule phase transition occurs is known as the Lower Critical Solution Temperature (LCST), and conveniently this can be modified in P(NIPAM) by incorporation into the polymer chain of more hydrophobic or hydrophilic monomers. Owing to the fact that the LCST is close to body temperature and can readily be modified to just below or just above 37 °C through this co-monomer addition, P(NIPAM) polymers have been widely exploited in biomedical applications. The chemistries and applications of P(NIPAM) have been extensively reviewed elsewhere, [75-81] but even 15 years after one particularly well-cited review, many research groups are working with this remarkably versatile polymer [82-87]. 

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