Polyphosphazenes degradation products

For the hydrolytic degradation of polyphosphazenes several mechanisms have been proposed (Allcock et al, 1977-1994 Goedemoed et al., 1988). Ffowever, analysis of the degradation products revealed that the main hydrolysis pathway involves release of the amino acid ester side group, followed by hydrolysis of the ester with formation of the amino acid and the alcohol (Crommen et al, 1992) (Fiigpre 12). 

Figure 2.10 The relative pH of the degradation products is shown by the amount of sodium hydroxide required to neutralise the acid released during the degradation of the PLGA-polyphosphazene blends and its parent polymers PLGA and the poly(organo) phosphazene-PPHOS-EG50. Reproduced with permission from A.M.A. Ambrosio, H.R. Allcock, D.S. Katti and C.T. Laurencin, Biomaterials, 2002, 23, 7, 1667. 2002, Elsevier [62]...

In several publications, a number of variations of polyphosphazenes in terms of different side groups have been demonstrated to be applicable for TE. The desired scaffolds can be fabricated in different appropriate formats such as 2D objects, e.g., films and membranes, or in the form of 3D matrices. A few examples of cell types are described in the literature, which have been used for TE on polyphosphazene scaffolds, like osteoblasts, EC or Schwann cells. Most of the polyphosphazenes appear to be quite compatible with the cells they are intended to support in terms of adhesion and proliferation, they can be degradable and with careful design, the degradation products tend to be toxicologically harmless. It can be expected that some future implanted bones, blood vessels or even nerves will have been made based on tailored, highly advanced polyphosphazenes. 

Biodegradability and biocompatibility of polyphosphazenes were studied as well as their degradation behavior in vitro and in vivo. It was reported that their degradation products are also biocompatible. Some reviews are devoted to using polyphosphazenes as hydrogel-forming materials. " ... 

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