Zeolites are microporous tectosilicates of natural or synthetic origin, which have been extensively used in various technological applications, e.g. as catalysts and as molecular sieves, for separating and sorting various molecules, for water and air purification, including removal of radioactive contaminants, for harvesting waste heat and solar heat energy, for adsorption refrigeration, as detergents, etc. These applications of zeolites were typically related with their porous character, their high adsorption capacity, and their ion exchange properties. This review is focused on potential or already practically implemented applications of zeolites in biotechnology and medicine. Zeolites are promising for environment protection, detoxication of animal and human organisms, improvement of the nutrition status and immunity of farm animals, separation of various biomolecules and cells, construction of biosensors and detection of biomarkers of various diseases, controlled drug and gene delivery, radical scavenging, and particularly tissue engineering and biomaterial coating. As components of scaffolds for bone tissue engineering, zeolites can deliver oxygen to cells, can stimulate osteogenic cell differentiation, and can inhibit bone resorption. Zeolites can also act as oxygen reservoirs, and can improve cell performance in vascular and skin tissue engineering and wound healing. When deposited on metallic materials for bone implantation, zeolite films showed anticorrosion effects, and improved the osseointegration of these implants. In our studies, silicalite-1 films deposited on silicon or stainless steel substrates improved the adhesion, growth, viability and osteogenic differentiation of human osteoblast-like Saos-2 cells. Zeolites have been clinically used as components of haemostatics, e.g. in the Advanced Clotting Sponge, as gastroprotective drugs, e.g. Absorbatox® 2.4D, or as antioxidative agents (Klinobind®). Some zeolites are highly cytotoxic and carcinogenic, e.g. erionite. However, in other zeolites, the antiproliferative and pro-apoptotic effects can be used for tumor therapy.

The role of adsorption in the single and binary permeation of CH4 and CO2 through a silicalite-1 membrane has been investigated. Adsorption on the zeolite is favorable for CO2, resulting in selectivity for CO2 in the permeation. The generalized Maxwell−Stefan (GMS) equations, in combination with the ideal adsorbed solution theory (IAST), were used to model their binary permeation. It is found that the use of accurate adsorption data is of utmost importance for extracting transport properties from the single-component permeation as well as for modeling multicomponent permeation. The GMS model qualitatively and quantitatively predicts the temperature-dependent properties of the mixture permeation, while it slightly deviates from the experimental observation on the pressure dependence of the mixture selectivity. This deviation is ascribed to intercrystalline or surface barriers for the larger molecule CH4 in the membrane as well as to the overprediction of the CO2 loading in the zeolite by the IAST.

This study presents new photofunctional materials producing singlet oxygen, 1O2, and investigates the interdependence between their structural and photophysical properties. These materials consist of Mg−Al layered double hydroxides (LDH) with intercalated photosensitizers, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) or Pd(II)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (PdTPPC). Powder X-ray diffraction and X-ray photoelectron spectroscopies were employed to characterize the host structure and confirm intercalation of porphyrins into the interlayer space. Because the kinetic parameters of the sensitizer triplet states predetermine the formation of 1O2, the excited-state kinetics of intercalated porphyrins were investigated by means of time-resolved diffuse reflectance. Comparison of the decay rates in the presence and absence of oxygen confirms that the triplet states of PdTPPC and TPPS in LDHs are quenched by oxygen. Photoproduction of 1O2 was monitored by time-resolved measurement of its luminescence at 1270 nm. It was established that PdTPPC-doped LDHs are very effective producers of 1O2, regardless of whether the porphyrin molecules are intercalated or adsorbed on the surface. The measured lifetimes of 1O2 lie in the 6−64 μs range, which means that the 1O2 molecules generated in the interior of LDHs can diffuse out of the matrix and react with a contiguous substrate. Dehydration of the LHD matrices enhances its singlet oxygen quenching capacity and inhibits the production of the long-lived 1O2 molecules, a process that can be reverted by exposing the material to atmospheric humidity. Consequently, we envisage LDHs with intercalated PdTPPC as efficient 1O2 sources whose oxidative activity can be modulated by successive dehydration−rehydration cycles.

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