Hydrogel polyphosphazenes

Allcock HR, Kwon S, Riding GH, Fitzpatrick RJ, and Bennett JL. Hydrophilic polyphosphazenes as hydrogels Ration cross-linking and hydrogel characteristics of poly [bis(methoxyethoxyethoxy)phos-phazene. Biomaterials, 1988, 9, 509. 

Polyphosphazenes can be considered as biomaterials in several different ways, depending on the type of utilization one can predict for these substrates. In this regard, we will consider three different topics concerning water-soluble POPs and their hydrogels, bioerodible POPs for drug delivery systems and for tissue engineering, and the surface implications of POP films. 

Additional polyphosphazene hydrogels deal with polymers in which gluco-syl side groups are co-substituted with trifluoroethoxy, phenoxy, methylamino or methoxyethoxyethoxy moieties [646]. 

Finally, a new water-soluble polyphosphazene was recently synthesized that has the structure shown in 36 (46). This polymer has two attributes as a biomedical macromolecule. First, the pendent carboxylic acid groups are potential sites for condensation reactions with amines, alcohols, phenols, or other carboxylic acid units to generate amide, ester, or anhydride links to polypeptides or bioactive small molecules. Second, polymer forms ionic crosslinks when brought into contact with di- or trivalent cations such as Ca or Ai3+. The crosslinking process converts the water-soluble polymer to a hydrogel, a process that can be reversed when the system... 

It has been demonstrated that a variety of different polyphosphazenes can be developed as biomaterials, membranes or hydrogels, bioactive polymers, and bioerodible polymers. As with most new areas of polymer chemistry and biomaterials science, molecular design forms the basis of most new advances, but the rate-controlling step is the testing and evaluation of the materials in both in vitro and in vivo environments. This is particularly true for polyphosphazenes where the availability of research quantities only has limited the... 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

The versatility of water-soluble polyphosphazenes is in the variations in the structures that can be prepared. Structures with a low glass-transition temperature backbone can be modified with a variety of versatile side units. These may find use in solid polymeric ionic conductors, as a means to entrap and immobilize enzymes with retention of enzymic activity, and in biological functions as hydrogels with the capability of exhibiting biocompatibility and... 

As discussed in an earlier section, the chemistry exists to convert hydrophobic polyphosphazenes to materials with hydrophilic surfaces. Hydrogels of MEEP (3.79) have been radiation grafted to the surfaces of hydrophobic polymers to generate highly hydrophilic interfaces, and these systems have the advantage that the interior of the polymer retains its hydrophobicity and other properties, and only the surface layers are changed.187,188... 

The principal polyphosphazenes that have been used in hydrogels are those with linear or branched ethyleneoxy side chains, aryloxy groups with carboxylic acid substituents, or mixed-substituent polymers that bear hydrophilic methylamino side groups plus a hydrophobic cosubstituent such as phenoxy or trifluoroethoxy. Cross-linking is usually accomplished by gamma-ray irradiation or, in the case of the carboxylic acid functional species, by treatment with a di- or tri-valent cation. Here, we will consider another example based on MEEP (3.79), a polymer that is well suited to the clean method of radiation cross-linking. 

Hydrogels and amphiphilic membranes Poly(carbophosphazenes) and poly(thiophosphazenes) New condensation syntheses NLO and high refractive index polymers Microencapsulation of mammalian cells (PCPP) Polyphosphazene polymer blends and IPN s Borazine derivatives Poly(phosphazophosphazenes)... 

Title Thermosensitive Poly(Organophosphazenes), Preparation Method Thereof and Injectable Thermosensitive Polyphosphazene Hydrogels Using the Same... 

Recent developments in the polyphosphazene chemistry have been re-viewed. The role of polyphosphazenes as biodegradable polymers as hydrogels for tissue engineering and as induced helical polymers has been discussed. Preparation and application of poly(thionyl phosphazenes) are discussed in two review chapters. ... 

A number of general reviews on polyphosphazenes have appeared. Specific reviews on polyphosphazenes deal with radiation graft polymerization, anionic polymerization, hydrogel microspheres,controlled biodegradability,coatings, and membrane separation. 

Alexeev VL, Das S, Finegold DN, Asher SA (2004) Photonic crystal glucose-sensing material for noninvasive monitoring of glucose in tear fluid. Clin Chem 50(12) 2353-2360 Allcock HR, Phelps MVB, Barrett EW, Pishko MV, Koh WG (2006) Ultraviolet photolithographic development of polyphosphazene hydrogel microstructures for potential use in microarray biosensors. Chem Mater 18(3) 609-613... 

This basic structure provides for considerable flexibility in the design of biomaterials, as described in a recent review [27]. By selection of the side groups on the polymer chain, both hydrophobic and hydrophilic polymers can be produced. Hydrophobic polyphosphazenes may be useful as the basis of implantable biomaterials, such as heart valves. The hydrophilic polymers can be used to produce materials with a hydrophilic surface or, when the polymer is so hydrophilic that it dissolves in water, cross-linked to produce hydrogels or solid implants. In addition, a variety of bioactive compounds can be linked to polyphosphazene molecules allowing the creation of bioactive water-soluble macromolecules or polymer surfaces with biological activity. 

Thermosensitive, injectable polyphosphazene hydrogels have atfiacted research interest in recent years. An injectable and thermosensitive poly(organophosphazene)-Arg-Gly-Asp (RGD) eonjngate to enhance functionality was synthesized by covalently binding... 

As already reflected by the number of review papers, the interest in biomedical applications of polyphosphazenes continues to grow. The biodegradable polymer NP(NHC6H4C02H-4)i.8(NHC6H4C02H-4)o.2 n has been prepared and fully characterized. The carboxylato groups can react with Ca -ions to form crosslinks and to convert the water-soluble polymer to a hydrogel. Controlled drug release experiments have been carried out for chitosan en-... 

Park, M.R., Chun, CJ., Ahn, S.W., Ki, M.H., Cho, C.S., Song, S.C., 2010. Sustained dehvery of human growth hormone using a polyelectrolyte complex-loaded thennosensitive polyphosphazene hydrogel. Journal of Controlled Release 147 (3), 359—367. 

Andrianov, A. K., Cohen, S., Visscher, K. B., Payne, L. G., Allcock, H. R., and Langer, R., 1993, Controlled release using ionotropic polyphosphazene hydrogels, J. Controlled Release 27 69-77. 

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