On the other hand, it was found that HEC cryogels degrade slower than conventional HEC hydrogels of similar GF yield.
An appropriate strategy for increasing the GF yield and enhancing the mechanical strength of cryogels based on cellulose derivatives is to incorporate
suitable crosslinking agents into the polymer network [11]. For instance, the
storage modulus of HPMC cryogel prepared in the presence of 3 mass%
N,N
0 -methylenebisacrylamide (BisAAm) is an order of magnitude higher than
that of HPMC cryogel obtained without crosslinking agent. More interesting, the
formation of a polymer co-network between HEC and another polymer such as
chitosan (CS) leads to a material with significantly increased storage modulus and
Fig. 6 Gel fraction yield of
HEC cryogels prepared with
different photoinitiators.
Cryogels were prepared at a
freezing temperature of
À20
C, initial polymer
concentration 1 mass%,
polymer molar mass
1,300,000 g/mol, 2 mass%
initiator, irradiation time
2 min
Fig. 5 Gel fraction yield of
HEC cryogels obtained at
various negative
temperatures. Cryogels
were prepared at initial
polymer concentration
1 mass%, polymer molar
mass 1,300,000 g/mol,
2 mass% BBTMAC,
irradiation time 2 min.
Reprinted from [12] with
permission from Elsevier
206
P.D. Petrov and C.B. Tsvetanov