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66 Advances in textile biotechnology

pH release Enzymes Drug release

Micro- Micro-
capsule
capsule
Magnetic release
Moisture

3.3 Release of an active agent triggered by different external
conditions.

sources, synthetic hydrogels incorporating defined biological moieties that
can be degraded enzymatically are also under intensive investigation. One
way to fabricate this type of hydrogel is to incorporate peptide substrates
for enzymatic hydrogel formation and degradation (Hu and Messersmith,
2003, Lutolf et al., 2003a, 2003b).

3.3.2 Covalent attachment of enzyme substrates

Beside encapsulation, covalent attachment of the active agent to the carrier
system is often used (Albrecht et al., 1997, Dosio et al., 1997, Fiume et al.,
1986, Franssen, 1993, Molema and Meijer, 1994, Narayani and Rao, 1996,
Pirrung and Huang, 1996, Trouet et al., 1982). For binding the active agents,
carriers with high affinity and selectivity like biotin-, lipid-, phosphate-, and

sulfate-binding proteins, as well as bacterial periplasmic proteins, lectins,
serum albumins, immunoglobulins, and inactivated enzymes are of great
interest. Several systems are used for the specific targeting (homing) of the

entrapped agents (Poznansky and Juliano, 1984, Tomlinson, 1987, Felgner,
2009, Vingerhoeds et al., 1994, Hirabayashi et al., 1996), whereas most
systems are designed to control the kinetics of release of the active agent
in a site- and time-dependent manner (Albin et al., 1987, Amidon, 1997,
Bagshawe et al., 1988, Brannon-Peppas, 1995, Brownlee and Cerami, 1979,
Cox, 1993, Fischelghodsian et al., 1988, Hsieh et al., 1981, Jain, 1989, Jeong
et al., 1985, Merlin, 1991, Pothakamury and BarbosaCanovas, 1995, Risch
and Reineccius, 1995, Vingerhoeds et al., 1993, 1994). The application of
carrier components that selectively and reversibly bind the active agent

with high affinity offers additional possibilities to stabilize the agent and
improve the control of its release (Cohen et al., 1977, 1979, Hattori et al.,
1995, Mitchell, 1986, Schaeffer and Brooks, 1992).
A possible application for such release systems is chemotherapy, because
of the severe side effects caused by the toxicity of traditional cytostatic agents

towards normal tissues. Therefore, the site-specific activation of non-toxic
prodrugs in tumours has been proposed in order to enhance their selectivity
for the killing of cancer cells. Those prodrugs comprise trigger, linker and

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