Biomedical Engineering Reference
In-Depth Information
O
O
CH
3
O
O
OH
O
HO
OH
HO
R
m
O
CH
3
O
O
O
O
O
O
O
O
O
O
O
R
¢
O
O
R
*
*
O
n
1.15
POE
IV
synthesis.
R
N
P
*
*
R
n
1.16
Structure of polyphosphazene.
control on properties and degradation rate by varying the diol, the latent acid
diol, and the proportion between these two. For low latent acid concentration
there is an induction period, which is the result of the hydrophobic nature
of the material, because an adequate amount of water must diffuse into the
matrix in order to start hydrolysis. The induction period can be decreased
by increasing matrix hydrophilicity, the amount of latent acid diol and by
using lower molecular weight materials. This induction period can be very
useful if the aim is a delayed drug release.
nowadays, POe iV are the most promising poly(ortho esters); they were
tested for treatment of postsurgical pain (with short-term delivery of analgesic
agents), release of peptides and proteins, and postoperative treatment of
cancer (with drug delivery systems containing antineoplastic agents in order
to destroy tumor cells that were not removed during surgery) (Heller
et al.
,
2000, Heller and Barr, 2004).
1.5 Polyphosphazenes
Polyphosphazenes are a particular class of inorganic polymers, which do
not have carbon atoms in their backbone. Their structure exhibits alternate
sequences of nitrogen and phosphorus atoms, with two side groups of various
nature (organic, inorganic, organometallic … ) (Mark
et al.
, 1992). The
bonding structure along the chain shows an alternate sequence of single and
double bonds (Fig. 1.16).
synthesis of polyphosphazenes dates back to 1895 when H. n. stokes
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