Production of a rhamnolipid biosurfactant by cells of Pseudomonas aeruginosa
strain BN10 immobilized into PEO and PAAm cryogels was investigated under
semicontinuous shake flask conditions and compared to biosurfactant secretion by
free cells [33]. The yield of rhamnolipids in the immobilized system exceeded that
of the free bacterial cells, distinguishing an effective bioprocess. The polymer
matrices possessed chemical and biological stability and very good physicomechanical characteristics, which are prerequisites for a high life span of these
materials for the production of rhamnolipids.
The temperature-responsive properties of poly(glycidol-co-ethyl glycidyl carbamate) cryogels were exploited for the growth of fibroblast cells on their surface
[19]. It was shown that the nonionic hydrophilic surface hinders interactions with
cells. When the environmental temperature is above T VPT of the cryogel, the
support became hydrophobic, allowing cell attachment and proliferation.
Supermacroporous PNIPAAm cryogels containing urease were prepared via the
UV irradiation technique, with hydrogen peroxide as initiator [34]. Taking the
advantage of cryostructuration phenomenon during the cryogenic treatment, most
enzyme molecules were embedded into the cryogel walls. Although the enzyme
was physically entrapped, the system exhibited remarkable resistance against
leakage due to the dense polymer network formed in the cryogel walls. The
immobilized urease can catalyze the hydrolysis of urea over a broad temperature
range in both batch and flow regimes. The interconnected macropores assist
unhindered diffusion of the substrate and reaction products through the gel, thus
paving the way for consecutive re-use at a constant activity, in contrast to the
conventional PNIPAAm hydrogel (Fig. 19). The relatively high flow rate through
the cryogel matrix and the good activity of urease make it possible to directly
remove urea from the feed solution in a continuous flow regime. Hence, this
material might be attractive for treatment of contaminated water, blood detoxication, the dialysate regeneration system of artificial kidneys, removal of urea from
beverages, etc.
Encapsulation of a high amount of enzyme, comparable to the weight of cryogel
matrix, is only possible when the enzyme solution fills the large volume pores of a
pre-made cryogel. In this case, the performance of the system depends strongly on
the enzyme retention. It was demonstrated that the fabrication of an outer PEO layer
onto a PHEMA cryogel containing urease in the pores (Fig. 20) is an effective
strategy for preventing leakage of enzyme into the medium [35]. Moreover, one
could expect that the urease molecules, simply located in the confined space of the
macropores, are not restricted and behave like the free enzyme molecules. Due to
the high sensitivity of urease, such a system is able to detect very low contamination
of metal ions in water and, therefore, can find application as a biosensor.
One important issue in modern medicine is linked to the controlled release of
active substances. It is assumed that a drug delivery system can supply a constant
dose of the active substance over a period of several hours or days, depending on the
particular disease. Thus, it has an advantage over the conventional system, characterized by a spontaneous release of the active substance immediately after administration (known as the “burst” effect) [36]. The potential of polymer cryogels for
218
P.D. Petrov and C.B. Tsvetanov
strain BN10 immobilized into PEO and PAAm cryogels was investigated under
semicontinuous shake flask conditions and compared to biosurfactant secretion by
free cells [33]. The yield of rhamnolipids in the immobilized system exceeded that
of the free bacterial cells, distinguishing an effective bioprocess. The polymer
matrices possessed chemical and biological stability and very good physicomechanical characteristics, which are prerequisites for a high life span of these
materials for the production of rhamnolipids.
The temperature-responsive properties of poly(glycidol-co-ethyl glycidyl carbamate) cryogels were exploited for the growth of fibroblast cells on their surface
[19]. It was shown that the nonionic hydrophilic surface hinders interactions with
cells. When the environmental temperature is above T VPT of the cryogel, the
support became hydrophobic, allowing cell attachment and proliferation.
Supermacroporous PNIPAAm cryogels containing urease were prepared via the
UV irradiation technique, with hydrogen peroxide as initiator [34]. Taking the
advantage of cryostructuration phenomenon during the cryogenic treatment, most
enzyme molecules were embedded into the cryogel walls. Although the enzyme
was physically entrapped, the system exhibited remarkable resistance against
leakage due to the dense polymer network formed in the cryogel walls. The
immobilized urease can catalyze the hydrolysis of urea over a broad temperature
range in both batch and flow regimes. The interconnected macropores assist
unhindered diffusion of the substrate and reaction products through the gel, thus
paving the way for consecutive re-use at a constant activity, in contrast to the
conventional PNIPAAm hydrogel (Fig. 19). The relatively high flow rate through
the cryogel matrix and the good activity of urease make it possible to directly
remove urea from the feed solution in a continuous flow regime. Hence, this
material might be attractive for treatment of contaminated water, blood detoxication, the dialysate regeneration system of artificial kidneys, removal of urea from
beverages, etc.
Encapsulation of a high amount of enzyme, comparable to the weight of cryogel
matrix, is only possible when the enzyme solution fills the large volume pores of a
pre-made cryogel. In this case, the performance of the system depends strongly on
the enzyme retention. It was demonstrated that the fabrication of an outer PEO layer
onto a PHEMA cryogel containing urease in the pores (Fig. 20) is an effective
strategy for preventing leakage of enzyme into the medium [35]. Moreover, one
could expect that the urease molecules, simply located in the confined space of the
macropores, are not restricted and behave like the free enzyme molecules. Due to
the high sensitivity of urease, such a system is able to detect very low contamination
of metal ions in water and, therefore, can find application as a biosensor.
One important issue in modern medicine is linked to the controlled release of
active substances. It is assumed that a drug delivery system can supply a constant
dose of the active substance over a period of several hours or days, depending on the
particular disease. Thus, it has an advantage over the conventional system, characterized by a spontaneous release of the active substance immediately after administration (known as the “burst” effect) [36]. The potential of polymer cryogels for
218
P.D. Petrov and C.B. Tsvetanov