4.1.5. LentiKatsÒ
By repeated freeze–thawing polyvinyl alcohol (PVAL) normally
forms hydrogels, so-called cryogels (Lozinsky et al., 1986) which are incompatible for most living cells (Jekel et al., 1998a). However, a variation where the gelation of a PVAL-hydrogel occurs at room temperature was developed. Mixing PVAL with living cells and glycerol and then extruding it onto a surface will produce lens- shaped droplets that are then air-dried to a certain water content (LentiKatsÒ) (Jekel et al., 1998a, 1998b) (Fig. 3F). The resulting particles are then rehydrated to yield a hydrogel stable at room temperature with superior diffusion characteristics. Due to its thin lens-shape internal diffusional limitations are minimized com- pared to beads resulting in better diffusion of substrates and prod- ucts into and out of the gel matrix. In contrast to biopolymer hydrogels LentiKatsÒ also show a low biological degradability and a high mechanical stability.