Biomedical Engineering Reference
In-Depth Information
2.2.2.1.2 Bacteria. Lvov and coworkers report that bacterial spores are
encapsulated in organized nanofilms using layer-by-layer assembly in
order to assess the biomaterial as a suitable core and determined the
physiological effects of the coating. The shells are constructed on Bacillus
subtilis spores using biocompatible polymers polyglutamic acid, polylysine,
albumin, lysozyme, gelatin A, protamine sulfate, and chondroitin sulfate.
The assembly process was monitored by measuring the electrical surface
potential, z-potential, of the particles at each stage of assembly. CLSM and
scanning electron microscopy (SEM) confirmed the formation of uniform
coatings on the spores. The ultrathin coating surface charge and thickness
could be selectively tuned by using appropriate polymers and the number
of bilayers assembled. The coated spores are viable, but the kinetics and
extent of germination are changed compared with control spores in all in-
stances.
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These experiments give the insight to design various bioinspired
systems inspired by Nature. For example, the spores can be made dormant
for one certain period using the LbL encapsulation approach and can re-
turn to being active when needed.
Another method for encapsulation of living micro-organisms is by using
the preparation of hollow polymer microspheres based on the pre-
precipitation of porous calcium carbonate cores with an average size of
5 mm. The microspheres filled with individual living E. coli cells are prepared
by LbL deposition of different polyelectrolytes and proteins on the porous
calcium carbonate cores leading to the formation of matrix-like complexes of
the compounds followed by calcium carbonate core dissolution using EDTA.
Both the influence of the encapsulation process as well as of the used
polyelectrolytes on the survival rate of the cells are determined by CLSM and
microtiter plate fluorescence tests. Around 40% of the cells are alive after the
encapsulation process. Cultivation tests indicate that the lag phase of cells
treated with polyelectrolytes increases and the encapsulated E. coli cells are
able to produce green fluorescent protein inside the microcapsules, which
proves the viabilities are kept well after LbL deposition.
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The encapsulation of probiotic Lactobacillus acidophilus (L. acidophilus)
through LbL self-assembly of polyelectrolytes chitosan (CHI) and carboxy-
methyl cellulose (CMC) has been investigated by Raichur and coworkers to
enhance its survival in adverse conditions encountered in the GI tract. The
survival of encapsulated cells in simulated gastric and intestinal fluids is
significant when compared to nonencapsulated cells. On sequential exposure
to simulated gastric and intestinal fluids for 120 min, almost complete death
of free cells is observed. However, for cells coated with three nanolayers of
PEs (CHI/CMC/CHI), about 33 log% of the cells (6 log cfu/500mg) survived
under the same conditions. The enhanced survival rate of encapsulated
L. acidophilus can be attributed to the impermeability of polyelectrolyte
nanolayers to large enzyme molecules like pepsin and pancreatin that cause
proteolysis and to the stability of the polyelectrolyte nanolayers in gastric and
intestinal pH. The PE coating also serves to reduce viability losses during
freezing and freeze-drying. About 73 and 92 log% of uncoated and coated cells
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