Spreading of Cell Aggregates on Zwitterion-Modified Chitosan Films

The
sulfobetaine (SB) moiety, which comprises a quaternary ammonium
group linked to a negatively charged sulfonate ester, is known to
impart nonfouling properties to interfaces coated with polysulfobetaines
or grafted with SB-polymeric brushes. Increasingly, evidence emerges
that the SB group is, overall, a better antifouling group than the
phosphoryl­choline (PC) moiety extensively used in the past.
We report here the synthesis of a series of SB-modified chitosans
(CH-SB) carrying between 20 and 40 mol % SB per monosaccharide unit.
Chitosan (CH) itself is a naturally derived copolymer of glucosamine
and N-acetyl-glucosamine linked with a β-1,4
bond. Analysis by quartz crystal microbalance with dissipation (QCM-D)
indicates that CH-SB films (thickness ∼ 20 nm) resist adsorption
of bovine serum albumin (BSA) with increasing efficiency as the SB
content of the polymer augments (surface coverage ∼ 15 μg
cm–2 for films of CH with 40 mol % SB). The cell
adhesivity of CH-SB films coated on glass was assessed by determining
the spreading dynamics of CT26 cell aggregates. When placed on chitosan
films, known to be cell-adhesive, the CT26 cell aggregates spread
by forming a cell monolayer around them. The spreading of CT26 cell
aggregates on zwitterion-modified chitosans films is thwarted remarkably.
In the cases of CH-SB30 and CH-SB40 films, only a few isolated cells
escape from the aggregates. The extent of aggregate spreading, quantified
based on the theory of liquid wetting, provides a simple in
vitro assay of the nonfouling properties of substrates toward
specific cell lines. This assay can be adopted to test and compare
the fouling characteristics of substrates very different from the
chemical viewpoint.