Sapropel Exploration and Characterisation for the Development of Sodium Carboxymethylcellulose-Based Bioactive Hydrogels: Formulation and Functional Evaluation. Summary of the Doctoral Thesis

Sapropel, an organic-rich freshwater sediment, has long been used in traditional medicine and cosmetics, however its therapeutic potential remains underexplored by modern science. Nevertheless, the use of sapropel in these traditional ways presents some practical challenges, like requirement for specialised facilities and large quantities of fresh sapropel sediments. Sapropel application, particularly in the form of mud baths, necessitates dedicated spaces equipped for the storage, preparation, application, and removal of the mud. This Doctoral Thesis investigates sapropel as a source of bioactive compounds and its integration into sodium carboxymethylcellulose (Na-CMC) hydrogels for potential biomedical and cosmetic applications. The study begins with a comprehensive analysis of sapropel’s origin, structure, and biologically active constituents, particularly humic and fulvic acids. A critical review of extraction methodologies was conducted, comparing solid–liquid, ultrasound-assisted, and supercritical fluid extraction techniques. Emphasis was placed on establishing quality criteria for sapropel extracts suitable for medical use, addressing the current lack of standardised protocols. Sapropel samples from Latvian freshwater lakes were systematically collected, layer-wise characterised, and processed to obtain extracts. These were analysed for total organic carbon, humic and fulvic acid content, polyphenol levels, antioxidant status, trace elements, and microbiological indicators. Selected extracts demonstrated significant antioxidant activity and promoted cell regeneration in vitro, particularly in fibroblast and keratinocyte models; however cytotoxic effects were observed at prolonged, high concentrations. In the final phase, the functional incorporation of sapropel extracts into Na-CMC-based hydrogels was achieved. Eight formulations were developed and evaluated for physicochemical properties, stability, pH, and viscosity under various conditions. Hydrogels containing sapropel extract exhibited favourable stability, a biocompatible pH range, and maintained organoleptic qualities, making them suitable as a platform for topical application. This research supports the potential of sapropel as a valuable natural resource for developing bioactive formulations. The results contribute to the scientific foundation for its evidence-based use in dermal therapeutics and cosmetics, and open avenues for further product development based on local natural resources. The Doctoral Thesis was developed at Institute of Occupational Safety and Environmental Health, Laboratory of Hygiene and Occupational Diseases and Faculty of Pharmacy, Rīga Stradiņš University, Latvia. Defence of the Doctoral Thesis will take place at the public session of the Promotion Council of Basic Medicine on 22 January 2026 at 14.00 in the Room 204, 21 Konsula Street, Rīgas Stradiņš University. This Doctoral Thesis was developed with the funding from the project “Analysis of characteristics of medical sapropel and its usage for medical purposes and elaboration of industrial extraction methods” was financed by European Regional Development Fund, project No 1.1.1.1/16/A/165 and with financing from the European Social Fund and Latvian state budget within the project No 8.2.2.0/20/I/004 “Support for involving doctoral students in scientific research and studies” at Rīga Stradiņš University. 3.1. Basic Medicine; Sub-Sector – Technology of Drug Form. Keywords: Sapropel; hydrogel; antioxidants; fulvic acid; humic acid; sapropel extract; sodium carboxymethylcellulose (Na-CMC); pharmaceuticals; natural compounds; polyacids.