Cytocompatibility and Toxicity of Functional Coatings Engineered at Cell Surfaces - Cell Surface Engineering: Fabrication of Functional Nanoshells - page 104

envelope of bacterial and fungal (yeast) cells is comprised of the inner
plasma membrane and an outer cell wall that protects the cell and maintains
its shape. The bacterial cell wall is composed of layers of peptidoglycan, a
complex of proteins and oligosaccharides, and is quite thin for some bac-
teria, e.g.,inEscherichia coli, while others possess a thicker cell wall. 38 The
rigid cell wall of plant cells is composed of cellulose and other polymers. In
Saccharomyces cerevisiae (yeast), the plasma lipid bilayer is about 7 nm thick
and contains proteins of various functions. The space between the plasma
membrane and the cell wall (periplasm) in yeast is a thin layer of 35-45 Å
containing mostly mannoproteins. The wall of a yeast cell is 100 to 200 nm
thick and contains polysaccharides (80-90%) and a small percentage of
chitin providing strength to the cell wall and forming a network of
microfibrils 39,40
Eukaryotic (e.g., mammalian) cells are surrounded by a plasma membrane
without a reinforcing cell wall. Also, for surface modification of pancreatic
islets, it is important to know that the islet is a multicellular cluster of
secretory endocrine cells, i.e. insulin-producing b-cells, glucagon-containing
a-cells, somatostatin-containing d-cells, and the pancreatic polypeptide-
producing cells. Although different types of mammalian islets contain
similar types of cells, the islet architectures are different. For instance, in-
sulin-producing b-cells of rodent islets form an inner core of the islet with
other secretory cells on the periphery, while in human islets b-cells are
interspersed with other cells more on the islet periphery. 41,42
Because of these structural and morphological differences between vari-
ous types of cells, there might be a different tolerance of the cells towards
various cell surface modifications resulting in either cytocompatibility or
cytotoxicity of the treatments. Because of the higher vulnerability of mam-
malian cells, harsh conditions, such as pH variations, salt concentrations,
presence of specific ions, and abnormal temperature, a range of materials
and/or processes available for encapsulation of individual mammalian cells
under specific conditions might be limited.

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6.2.2 Cytotoxicity of Polymers
Polymers can induce cell death via various routes including plasma mem-
brane permeabilization, 43 formation of harmful polymer degradation
products including reactive oxygen species, 44 and permeabilization of a
nuclear membrane. 45,46 The cytotoxicity of positively charged polyelec-
trolytes for mammalian cells was demonstrated in many reports. 47-50 The
viability of MELN cells derived from MCF-7 human breast cancer cells
transfected with an estrogen-regulated luciferase gene decreased to less than
40% when exposed to poly(L-lysine) (PLL) and protamine sulfate and to less
than 10% in the case of poly(allylamine hydrochloride) (PAH), poly(pho-
sphoric acid), and poly(ethylene imine) (PEI). The lowest polycation cyto-
toxicity, yet that decreased cell viability by 30%, was achieved in the

presence of poly(diallyldimethyl ammonium chloride) (PDDA) with MELN

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