Polyphosphazene-based

A different approach to polyphosphazene-based drug delivery systems deals with hydrolytically unstable phosphazene substrates, able to degrade in a controlled way under physiological conditions in human body. A list of these bio-erodible substrates is reported in Table 21. 

Cross-linked, sulfonic-acid-substituted, polyphosphazene-based PEMs have primarily been examined for potential use in DMFC applications due to their low MeOH crossover with reported values 2.5 times lower than that of Nafion. These materials have also been shown to display good thermomechanical and chemical stability (in a Fenton test). Sulfonamide-substituted polyphosphazenes have exhibited very high power densities that are comparable with Nation and may be suitable for use in PEMFC applications. ... 

Guo, Q., Pintauro, P. N., Tang, H. and O Cormor, S. 1999. Sulfonated and cross-linked polyphosphazene-based proton-exchange membranes. Journal of Membrane Science 154 175-181. 

Chalkova, E., Zhou, X., Ambler, C., Hofmann, M. A., Weston, J. A., Allcock, H. R. and Lvov, S. N. 2002. Sulfonimide polyphosphazene-based H2/O2 fuel cells. Electrochemical and Solid-State letters 5 A221-A222. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

TABLE 1. Physical Properties of Polyphosphazene-Based Energetic Polymers... 

Guo, Q. et al., Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes, J. Membr. Sci., 154, 175, 1999. 

Caliceti, P. Lora, S. Marsilio, E. Veronese, F.M. Preparation and characterization of polyphosphazene-based controlled release systems for naproxen. Farmaco 1995, 50 (12), 867-874. 

At the present time, only a few side-chain liquid crystal polyphosphazenes have been synthesized and investigated. Opportunities exist to prepare a wide variety of side-chain liquid crystalline polyphosphazenes, based on the polymerization-substitution process outlined in Figure 2. Alternative approaches, such as side chain modification of polyphosphazenes prepared by the thermal decomposition of N-silylphosphoranimines (19), may provide even further options for preparing liquid crystal polyphosphazenes. 

Diffusion coefficients for methanol (concentration range 1.0-5.0 M) in ion-exchange membranes of UV-crosslinked sulfonated poly(bis-3-methoxyphenoxyphosphazene) (134) have been reported to be much smaller than those in Nafion perfluorosulfonic ion-exchange membranes. Application of polyphosphazene-based membranes in methanol-based fuel cells has been reported. ... 

Other interesting systems such as polysilacetylenes [69], polyphosphinoboranes, and polyphosphazene-based materials [70] are currently being investigated. 

A. Conforti, et al.. Anti-inflammatory activity of polyphosphazene-based naproxen slow-release systems, 1. Pharm. Pharmacol. 48 (5) (1996) 468-473. 

FIGURE 21.15 Polyphosphazene-based 3D matrices for tissue engineering, (a) Sintered polyphosphazene scaffolds, (b) SEM image of polyphosphazene microsphere scaffolds. 

Q. Guo, P.N. PiNTAURO, H. Tang, S. O Connor, Sulfonated and crosslinked polyphosphazene-based proton-ex-change membranes. Journal of Membrane Science 154 (1999) 175. 

Scheme 1. Polymethacrylates, polyacrylates, polysiloxanes and polyphosphazene based on 4-MHMS and 4 -MHMS constitutional isomeric mesogenic groups.

Figure 3.16 Schematic depiction of the preparation of graft polyphosphazene-based polymersomes. The systems can be loaded with hydrophobic DOX, as well as its more hydrophilic HCl salt. The DOX.HCl-loaded polymersome (PEP-5-DH) was able to suppress MCF-7 xenograft tumours in nude mice with a comparable efficacy to that of the free drug. Reproduced with permission from J. Xu, Q. Zhao, Y. Jin and L. Qiu, Nanomedicine Nanotechnology, Biology and Medicine, 2014,10, 2, 349. 2014,...

The success of PCPP in clinical trials bodes well for other polyphosphazene-based nanomedicines, as does the multitude of data from in vitro and animal studies presented. These promising results, coupled with recent advances in synthetic approaches (see Chapter 1), should mean it is possible to provide well characterised reproducible materials required for a successful transition to the clinic. 

TE scaffolds made from polymers are available in different formats as already mentioned in Section 4.1. Polymeric scaffolds can be based on fibres, foams, membranes and 3D bulk materials, using simple linear polymers or crosslinking these, ending up with elastomeric or even thermoplastic structures. In general, the usage of polyphosphazenes should also allow the realisation of similar concepts. Nevertheless, in the literature only a relatively small number of examples are given for the fabrication of polyphosphazene-based scaffolds for TE [2-27]. 

The mass loss of the polyphosphazene-based scaffolds is a general phenomenon and, of course, explainable by the desired final degradability or erosion of the polymers in the absence or presence, respectively, of cells. However, during cultivation of the tissues, it is important to understand how, and how fast, the degradation or erosion takes place. For this purpose, Nykanen and co-workers investigated the change of the fibre dimensions of an electrospun polyphosphazene coupled with proline groups poly[f /s(L-proline... 

Akgol Y, Hofmann C, Karatas Y, Cramer C, Wiemhofer HD, Schonhoff M (2007) Conductivity spectra of polyphosphazene-based polyelectrolyte multilayers. J Phys Chtan B 111 8532-8539... 

Argun AA, Ashcraft JN, Herring MK, Lee DKY, Allcock HR, Hammmid PT (2010) Iwater transport in polyphosphazene-based multilayers. Chem Mafia- 22 226-232... 

Razavi R, Khan Z, Haenerle C B and Beam D, Clinical applications of polyphosphazene-based resilient denture liner , J. Prosthodontics, 1993, 2,224-7. 

Membranes with promising properties have been prepared from polyphosp-hazenes in combination with sulfonimide (polyphosphazene-based sulfonimide Chalkova et al., 2002) or with polyacrylonitrile (blended polyphosp-hazene/polyacrylonitrile Carter et al., 2002). Low methanol crossover was also seen with membranes prepared from poly(vinyl alcohol) that contained mordenite (a zeolite variety Libby et al., 2001). Various aspects of the work on composite membranes prepared from different polymers have been discussed in detail in a review by Savadogo (2004). 

Studies of methanol permeation through proton-conducting polyphosphazene membranes show that polyphosphazene-based proton-exchange membranes have low methanol permeability and good proton conductivity [15], These membranes have been tested in the DMFCs and have shown good performance. 

The direct methanol fuel-cell performance of three polyphosphazene-based membrane systems is presented below. The first system deals with blends of PVDF with either sulfonated poly[(3-methylphenoxy)(4-ethylphenoxy)phos-phazene] (SP3MP4EPP) or sulfonated poly[(4-ethylphenoxy)(phenoxy)phos-phazene] (SP4EPPP), where the membranes were prepared by solution casting mixtures with subsequent crosslinking using electron-beam irradiation (60 MRad). The second membrane system was based on UV-photocrossHnked... 

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