Page 85 - Advances in Textile Biotechnology

64 Advances in textile biotechnology

Polymer-NH 2

Biotinylation

+ Avidin

+ Biotinylated enzymes

3.2 Immobilization of biotinylated enzymes.

Fischelghodsian et al., 1988, Hsieh et al., 1981, Kim et al., 1994, Kost et al.,
1989, Pothakamury and BarbosaCanovas, 1995, Risch and Reineccius, 1995,
Vingerhoeds et al., 1994). There are three primary mechanisms by which
active agents can be released from this kind of delivery system: diffusion,
swelling followed by diffusion and degradation. Many controlled-release
systems are designed to create a sustained release by diffusion or swelling
(Bagshawe et al., 1988, Cox, 1993, Merlin, 1991, Risch and Reineccius, 1995,
Vingerhoeds et al., 1993). Diffusion occurs when a drug or other active agent
passes from the polymer matrix into the external environment through the
polymer that forms the controlled-release device. The only structure effec-
tively limiting the release of the drug is the polymer layer surrounding the
reservoir.
Since this polymer coating is essentially uniform and of a non-changing
thickness, the diffusion rate of the active agent can be kept fairly stable
throughout the lifetime of the delivery system. The diffusion can occur on
a macroscopic scale, as through pores in the polymer matrix, or on a molec-
ular level, by passing between polymer chains. The diffusion controlled
systems, which require hydrophilic polymers such as hydroxyethylcellulose
and sodium carboxymethylcellulose, allow a sustained release of drugs, but
do not permit a rigorous control because the release rate is not constant.
Although the polymeric membranes or matrices do not change during
the release process, uptake of solvent leads to polymer expansion and thus

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