Nowadays, there is a widespread usage of sodium periodate as an oxidant for synthesizing gelatin–tannin hydrogels. The impact of iodine compounds could have a harmful effect on human health. The study focuses on the proposal of alternative oxidizing systems for tannin oxidation. Gelatin–tannin hydrogels were obtained based on the usage of H2O2/DMSO/KMnO4/KIO4 oxidants and characterized with sorption, thermal (TGA, DTG, DSC), mechanical, FTIR and other methods. The sorption experiments were carried out in a phosphate buffer (pH = 5.8/7.4/9) and distilled water and were investigated with Fick’s law and pseudosecond order equation. The pH dependence of materials in acid media indicates the possibility of further usage as stimuli-responsive systems for drug delivery. Thermal transitions demonstrate the variation of structure with melting (306 ÷ 319 °C) and glass transition temperatures (261 ÷ 301 °C). The activation energy of water evaporation was calculated by isoconversional methods (Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa) ranging from 4 ÷ 18 to 14 ÷ 38 kJ/mole and model-fitting (Coats–Redfern, Kennedy–Clark) methods at 24.7 ÷ 45.3 kJ/mole, indicating the smooth growth of values with extent of conversion. The network parameters of the hydrogels were established by modified Flory–Rehner and rubber elasticity theories, which demonstrated differences in values (5.96 ÷ 21.27·10−3 mol/cm3), suggesting the limitations of theories. The sorption capacity, tensile strength and permeability for water/oxygen indicate that these materials may find their application in field of biomaterials.

Hydrogels became an essential class among all biomaterials. Specialized biomaterials are highly appreciated in the field of biomedical applications. One of problem in wound management is a local deficiency of microelements related to extensive wound lesions. The significant absence of an elemental iron in human body leads to serious consequences and prolongation of treatment. The synthesis of gelatin-tannin hydrogels with ion delivery function is proposed in this study. The ability to release ions in low acidity solution is a sphere of great interest. pH downing in wound cavity usually concerns with contamination of some bacterial cultures. pH-controlled delivery of iron in buffer solutions (рН=5.5/6.4/7.4) was considered for these hydrogels. The kinetic of iron release was determined by visible spectroscopy. Theoretical models were applied to describe process of ion delivery. The structure of materials was examined by IR-spectroscopy and demonstrated incorporation of ferrous ascorbate in hydrogel matrix. Thermal analysis was used to pointed the key differences in thermal behavior by isoconversional methods (Flynn-Wall-Ozawa/Kissinger-Akahira-Sunose). Mechanical characteristics of materials were studied. The effect of iron ascorbate on polymer network parameters was discussed. Current study showed a possibility of obtaining gelatin-tannin hydrogels for pH-dependent iron delivery. That provides future perspectives to expand the set of releasing microelements for biomedical applications.

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The purpose of this work is to describe and summarize main design principles of sealing joints for cable penetrators of deepwater vehicles. The study was performed on typical sealed areas of watertight cable penetrators, like soldered joint between copper sheath of a heat resistant cable with mineral isolation (KMZh) and cable penetrator body; polymeric termination of cable ends; sealing joint of metal penetrator body in pressure hull with circular elastomeric gaskets. The case study in this paper is a metal casing attached to KMZh cable by a heat-resistant silverized brazing alloy. The quality of soldering joints was estimated metallographically, i.e. by means of optical microscopy and electronic raster spectroscopy. Watertightness of KMZh cable is ensured by reactoplast-based polymers that must be not only adequate to their operational conditions but also comply with fire safety regulations for ships. Watertightness of penetrator interface with pressure hull is achieved by means of elastomeric gaskets. The study investigated main sealing joints of penetrators, as well as the mechanisms achieving watertightness of each given joint. Analysis in ANSYS software package yielded the optimal thermal scenario of casing warm-up offering the best quality of both soldering process and adhesion to the KMZh cable. The calculation was also performed for the minimum length of brazed joint of constant width so as to ensure strength and watertightness at different external pressures. Calculation results were performed by hydraulic tests of penetrator samples. The study also identified the peculiarities of polymeric sealant selection. A promising approach for cable termination manufacturing would be to use heat-resistant materials featuring shape memory effect.

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