Biologically modified ceramics (biocers) are understood as a class of nanocomposites which combine biocomponents with ceramic-like matrices. Biocers containing biocomponents can be prepared as a bulk material or as coatings by sol-gel and freeze-cast techniques from inorganic nanosols or by special CVD methods. By avoiding critical preparation conditions (high temperature, organic solvents) which would lead to denaturation, even bacteria, fungi, and yeast cells can be incorporated while maintaining their viability ('living ceramics'). In this article the preparation and structure of such biocers and their applicative potential for biocatalytic, biosorptive and structure-forming processes will be discussed.

Biological ceramic composites (biocers) made according to aqueous sol-gel protocol were used as selective metal binding filters. The biological component of the biocers Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile. Vegetative cells and spores of this strain are known to bind selectively U, Cu, Al, Cd, and Pb in large amounts. Sol-gel ceramics were prepared by dispersing vegetative cells, spores, and stabilized surfacelayer proteins (S-layer) in aqueous silica nanosols, gelling, and drying. The biosorption of uranium and copper by the three kinds of biocers and by their single components was investigated with dependence on time, concentration, and preparation conditions. Biocers with cells possess the highest binding capacity compared to matrixes with spores and an S-layer. Freeze-drying of prepared biocers or adding water-soluble compounds as sorbitol lead to higher porosity and faster metal binding. Uranium was bound mainly to the biological component but also to the SiO 2 network. In contrast, copper was only bound by the cells, spores, or S-layer. Bound uranium and copper were completely removed by washing with aqueous citric acid.

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Thin layers and patterned dot arrays of sodium alginate containing living microalgal cells were deposited onto glass carriers which were subsequently gelled using amino-functionalized silica sol to obtain reinforced alginate hydrogels. The resulting alginate/silica hybrid materials showed improved stability in salt-containing solutions compared to alginate gels gelled by traditional methods using Ca 2+ -ions. Cell arrays were patterned by printing nanolitre-scale drops of sodium alginate/cell suspension using a noncontact micro-dosage system which allows the printing of solutions of high viscosity. Cultures of the green microalga Chlorella vulgaris were immobilized within the newly developed alginate/silica hydrogels in order to demonstrate the potential of the hybrid matrix for the design of cell-based detection systems. The herbicide atrazine as well as copper ions have been used as model toxicants.Short-term toxicity tests (exposure time: 1 h) have been carried out using atrazine and changes in chlorophyll a (Chl a) fluorescence were measured by imaging pulse amplitude modulated-fluorometry (Imaging-PAM). C. vulgaris cells immobilized within alginate/silica hydrogels demonstrated a highly reproducible response pattern and compared well to freely suspended cells. Activity and response sensitivity of immobilized cells to atrazine was largely maintained for up to 8 weeks, especially when stored under cool conditions in the dark. Furthermore, immobilized cells could be repeatingly used for short-term toxicity tests as atrazine produces a reversible inhibition of photosynthesis.

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Biofilters with long lifetime and high storage stability are very important for bioremediation processes to ensure the readiness at the occurrence of sudden contaminations. By using the freeze-gelation technique, living cells can be immobilized within a mechanically and chemically stable ceramic-like matrix. Due to a freeze-drying step, the embedded microorganisms are converted into a preserved form. In that way, they can be stored under dry conditions, which comply better with storage, transport, and handling requirements. Thus, in contrast to other immobilization techniques, there is no need for storage in liquid or under humid atmosphere. The biological activity, mechanical strength, and the structure of the biologically active ceramic-like composites (biocers) produced by freeze gelation have been investigated by using the phenol-degrading bacteria Rhodococcus ruber as model organism. Samples of freeze-gelation biocers have been investigated after defined storage periods, demonstrating nearly unchanged mechanical strength of the immobilization matrix as well as good storage stability of the activity of the immobilized cells over several months of storage at 4 °C. Repeated-batch tests demonstrated further that the freeze-gelation biocers can be repeatedly used over a period of more than 12 months without losing its bioactivity. Thus, these results show that freeze-gelation biocers have high potential of being scaled up from laboratory test systems to applications in real environment because of their long bioactivity as well as mechanical stability.

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Living bacteria (Rhodococcus ruber) and yeast (Saccharomyces cerevisiae) cells can be embedded within magnesium phosphate cement (MPC). The cements are prepared by the admixture of microorganisms to a water‐based slurry system of Mg3(PO4)2 powder and ammonium phosphate solution whereas the setting of the slurry occurs within few minutes. To test the biocatalytic activity of the embedded microorganisms the phenol degradation by R. ruber and the glucose conversion by S. cerevisiae are described. Embedded cells survived within the cements and remain active. However, the glucose or phenol consumption rate was clearly reduced after immobilization within the compact macroporous concrete matrix. By using leachable pore forming additives or by admixture of cellulose fibers the macroporous structure of the MPC can be improved. The bioactive composite material exhibits good mechanical and chemical stability. It can be used as new stable biocatalysts, e.g., for applications in bioremediation and biotechnology.