Biomedical Engineering Reference
In-Depth Information
The activity of enzyme systems, their versatility and lability allow this group of living
organisms to use different polymers of both natural and synthetic origin as a food source [3].
On the other hand, ecological significance of biostability is dual: first, protection of
materials from the negative action of microorganisms (resource saving) and, second,
improvement of the quality of the human habitat since many fungi. Being active
biodegradants, are opportunistic pathogenic organisms capable of causing serious diseases of
a man [4]. That is why special attention has been paid lately to fabrication of polymer
compositions based on natural (chitin, chitosan, starch, and cellulose) and synthetic polymers.
The advantage of these materials is associated with their regular stability to the action of
microorganisms that allows producing both biostable and, on the contrary, biodegradable
compositions.
For the properties of such hybrid polymer compositions to be purposefully controlled, it
is necessary to study the effect of the components on their physical-chemical properties. In
this connection, we have studied variations in the physical-chemical properties of the block-
copolymer of crab chitosan (CHS) with methyl actlate (MA) under the action of
micromycetes (
Aspergillus terreus ВКМ F-1025, Thom, 1918
).
The obtained data were compared with the characteristics of CHS, polymethyl acrylate
(PMA), as well as the mixture extracted from the solution of the corresponding
homopolymers. The physical-chemical properties of the above compositions were studied
using the method of differential thermal analysis (DTA) in the range of 190-350
о
С.
2.
M
ATERIALS AND
M
ETHODS
The investigations were carried out using chitosan ( -D-1,4-N-glucosamine,
(C
6
H
11
0
4
N)
n
) extracted from crab shells manufactured by “Shanghai AZ import & export Co.,
Ltd” (China). Its molecular mass was 1
●
10
5
, the degree of deacetylation (DD) was 78%, the
molar mass of the repeat CHS unit was 161 g/mol. DD was determined using potentiometric
titration in the HCl solution (0.1 N) with NaOH (0.1 N) serving as a titrant [5], while the
viscosity average molar mass was measured using a viscosimetric method at 21
о
С in the
mixture of СН
3
СООН (0.33 N) and NaCl (0.33 N) with the Ubbelohde viscosimeter. The
calculations were performed with the formula [ ] =
kM
, where
k
= 3.41 10
3
,
= 1.02 [6].
The diluted solutions of CHS in the acetic acid (AA) of the purum grade, State Standard
(GOST 61-75) were used. The concentration of the ground substance was 99.5%, ρ
20
=1.049
g/cm
3
.
Before using, the methyl acrylate (CH
2
=CH-C(O)-O-CH
3
) was dried with СаН
2
and
distilled in the setup with the complete condensation attachment collecting the fraction with
t
boil
=80.2
о
C and ρ
25
=0.950 g/cm
3
.
The oxidation-reduction system based on hydrogen peroxide (ρ(25% solution)=1.4
g/cm
3
) and ascorbic acid served as an initiator of solution block-copolymerization of MA
with CHS. The concentration of the AA in water was 6 mass%, while the concentration of
CHS in it was 3 mass%. Block-copolymerization was performed for 24 h at 18-23
о
С. The
films based on the CHS/MA block-copolymer were prepared by pouring of reaction mixtures
on a lavsan substrate [8].
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