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Enzymatic functionalization of cellulosic fi bres for textiles 279

et al., 2005). As such, this chemical cycling represents a proof-of-concept for
dynamically altering cellulose surface chemistry.

Biomolecule capture
The capture of biological molecules represents a special kind of surface
activation, with numerous applications in separations, diagnostics, and bio-
medicine. Cellulose surfaces, including bacterial cellulose hydrogels, display

low non-specific protein adsorption and high biocompatibility (Brumer
et al., 2004; Helenius et al., 2006; Klemm et al., 2001; Miyamoto et al., 1989;
Wan et al., 2006). Although desirable in certain applications, this biological
‘non-stickiness’ is a limitation in the use of cellulose to capture biological
molecules or as a scaffold for tissue engineering. Here also the XET/XG

system provides a solution. As a first example, adsorption of a XG bearing
the small organic ligand biotin (XG–biotin) to Whatman No. 1 has yielded

filters that are able to bind the protein streptavidin conjugated to the
reporter enzyme alkaline phosphatase. Sensitive detection via conversion
of a phosphatase substrate indicated that the XG–biotin-activated fi lters
bound significant amounts of the protein conjugate, whereas control fi lters

showed no detectable background binding (Brumer et al., 2004).
We have recently extended this methodology to improve the adhesion of
endothelial cells to artificial blood vessels composed of bacterial cellulose

(Bodin et al., 2007a). Here, the adsorption of a XG–pentapeptide conjugate,
XG–GRGDS, improves the ability of bacterial cellulose to function as a
tissue scaffold and facilitates cell proliferation by interaction with integrin
receptor proteins on endothelial cell surfaces. Importantly, adsorption of
XG–FITC to the bacterial cellulose hydrogel, which is 95–99% water, indi-
cates that the gentle aqueous binding conditions employed do not alter the
morphology and, thus, the material properties of the substrate (Bodin et al.,
2007a).
Although the use of XG conjugates to anchor or capture biological mol-
ecules on cellulosic fibres is only in its infancy, one can readily envision a

range of biomolecular probe–target systems of practical importance (Table
11.1).

Extension to polymers: multivalent effects
A potential limitation of the XET/XG-based method of cellulose modifi ca-
tion is that in all of the examples described thus far, a single functional
group is appended per XG chain. Given that a minimum XG-R chain length
is required for binding, this ultimately limits the functional group density
on the cellulosic material. Consequently, we have developed XG–initiator
conjugates for the grafting of polymers from cellulose surfaces. This

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