Chemistry Reference
In-Depth Information
6.3.1
Intraocular Lenses and Hard Contact Lenses
The most embarrassing problem related to GPHCL (gas-permeable hard contact
lens) for clinical eye doctors is the clouding of its surface during wearing (such as
shown in Fig.
6.14
) owing to its lack of biocompatibility for tears.
We have developed dextran-MMA copolymers for IOL (intraocular lens) and
HCL (hard contact lens) having a hydrophilic-hydrophobic microseparated-domain
[
7
-
9
].
Matrix polymerization was first reported by Kargin et al. [
35
] and matrix polymeri-
zation between cationic matrix and unsaturated acid has been reported in the case of
poly(ethylene imine)/acrylic acid [
36
-
38
]. We have newly prepared a transparent
dextran matrix copolymer that is composed of both a PEC between cationic dextran
and unsaturated acids and vinyl compounds. It is expected to have a regular hydrophi-
lic-hydrophobic microseparated domain. The PEC used as a matrix is expected to be a
material having biocompatibility and the ability to transport O
2
[
39
]. We also think that
this matrix copolymer can have good biocompatibility because it not only has a
hydrophilic-hydrophobic microseparated domain structure (from the hydrophilic
PEC and the hydrophobic vinyl compound), but also an electric charge distribution
of localized polyions. For a biomembrane such as a cell membrane, Singer and
Nicolson proposed the “fluid mosaic model”, which is composed of a lipid binary
molecule membrane having a hydrophilic-hydrophobic microseparated domain,
containing proteins and polysaccharides chains on the surface of the protein [
40
]as
showninFig.
6.15
.
As mentioned above, the matrix copolymer can be considered as a model
substance for the component of this biomembrane.
For antibody reaction by the immune system, the recognition of antibody is
made by the polysaccharide chains on the surface of the protein. From this view-
point, a matrix copolymer using a biocompatible polysaccharide such as the dextran
used for plasma expanders (e.g., Dextran 70) is not expected to produce an antibody
response in vivo.
6.3.2 Preparation of DMC
DMC has been prepared to be bulk-polymerized by reacting the basic type of
DEAE [(2-diethyl-aminoethyl)-dextran] dissolved in a methacrylic acid (MA)
with methyl methacrylate (MMA) using azobisisobutyronitrile (AIBN) as initiator.
Chemicals
. DEAE-dextran having 5 % of nitrogen content, obtained by Shotten-
Baumann reaction between dextran 500(
M
w
500,000) and 2-diethyl-aminoethyl-
chloride in an alkali solution, was used after purification by acetone-NaCl-water
sedimentation. MA and MMA were purified from first grade reagents by distillation
under a reduced pressure.
