Cytocompatibility and Toxicity of Functional Coatings Engineered at Cell Surfaces - Cell Surface Engineering: Fabrication of Functional Nanoshells - page 103

DPA) released by the spores exposed to a solution of nutrients to germin-
ate. 27 During germination, the growth and metabolism of dormant bacterial
spores is triggered by nutrients such as amino acids, sugars, etc. The changes
in the inner membrane of the germinating spores upon interaction of the
membrane receptors with certain nutrients lead to DPA release from the
spores, and, eventually to a fully functioning viable cell. 28 The DPA release
from germinating nanocoated Bacillus subtilis was monitored by measuring
fluorescence from complexes of released DPA with terbium ions after the
germination was induced in the presence of 1.1 mM L-alanine at 37 1C. 27
The induction of a colorimetric signal from fluorescent species within the
metabolically active cells as a reporter of functional capability of cells un-
affected by cell modification was also utilized for Acinetobacter baylai bac-
terial cells 29 and Chlorella pyrenoidosa green algae cells 30 entrapped into
shells of magnetic particles of iron oxide. In the latter case, photosynthetic
activity of the green algae cells after encasing with 15-nm iron oxide nano-
particles modified with PAH (M w 15 000 g mol 1 ) was tested. The fluo-
rescence from Chlorophyll B was recorded as the reporter of functionally
unaffected algae cells. 30
To evaluate functional capacity of insulin-producing b-cells within the
modified pancreatic islets, the glucose-stimulated insulin release in static
incubation or in a cell perifusion system is usually carried out for noncoated
and coated pancreatic islets as a function of time in response to variations in
glucose concentration. The glucose concentration of

d n 8 y 4 n g | 8

B 3 mM refers to a low

glucose (basal glucose) level, while 16 mM glucose concentration is used as

a high glucose level. The stimulation of b-cells in pancreatic islets with a high
glucose concentration should result in a larger amount of released insulin. As
a result, a stimulation index of the islets, defined as the ratio of the released
insulin at high glucose level to that at basal level, can be calculated and
utilized as a measure of functional capacity of the pancreatic cell clusters.

B

.

6.2 Cytocompatibility of Functionalizing Species
Here, we will discuss possible cytotoxic effects of synthetic and natural
polymers, metal and metal-oxide nanoparticles and carbon-based materials
on different types of cells under modification. There exists a seeming dis-
crepancy in toxicity data in the reports on encapsulating cells with various
functional species. For example, very often, functional species used for
functionalization of yeasts and bacterial cells that are found to be cyto-
compatible demonstrate acute toxicity when applied for engineering of
mammalian cells. The differences of cyto-architecture in various cell types
might be critical in understanding the reported variability of toxicity.

6.2.1 Architectural Differences of Cells
Among individual living cells that have been used for cell functionalization
are fungi, 31,32 bacteria, 17,27 and mammalian cells. 18,26,33-37

The cellular