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INTRODUCTION: Bioactive materials for the repair and regeneration of human bone tissue, as well as for the restoration of teeth, are the focus of numerous studies in the field of biomaterials. Orthopaedic surgeons anticipate that bioactive materials have the potential to facilitate the formation of new apatite-like crystals upon contact with body fluids, promoting the development of new bone tissue under in vivo conditions. On the other hand, dentists expect that bioactive materials have the potential for remineralization of partially demineralized enamel and dentin. In the preceding years, the Bioceramic Materials Group, founded within the Department of Inorganic Chemical Technology at the Faculty of Technology and Metallurgy, University of Belgrade (FTM-UB), conducted extensive research on the advancement of bioactive and biocompatible materials with adequate mechanical properties, designed for application in dentistry, orthopaedics, maxillofacial surgery, and also bone tissue engineering (BTE). EXPERIMENTAL: Different forms of bioactive materials were processed starting from nanostructured mesoporous calcium hydroxyapatite (HAp), synthesized by controlled precipitation and hydrothermal method, and mesoporous bioactive glasses (BAG), synthesized by sol-gel method, doped with various cations and anions. Calcium phosphate dental inserts and potential solo implants in maxillofacial region were obtained by isostatic pressing of HAp nano-powders, followed by sintering by different techniques. Calcination of multi-ion-doped calcium-deficient HAp powders enabled a phase transformation into α-tricalcium phosphate (α-TCp), known for its binding properties. Doped α-TCp, combined with polymeric materials and Ag and BN nanoparticles possessing antimicrobial properties, was the basis for the development of innovative bioactive dental cements. Three types of bioactive scaffolds were developed: bioceramic scaffolds obtained by the replica technique based on multi-ion doped HAp, β-TCP and BAG, additionally coated with polymers; polymer-based scaffolds created by combining various hydrogels with the BAG, β-TCP, and HAP as nano-fillers; metallic scaffolds modified through the deposition of biodegradable polymers, doped BAG, β-TCP, and HAP nanoparticles. RESULTS AND DISCUSSION: Calcium phosphate dental inserts exhibited fracture toughness within the range of human dentin, as well as a strong bond with dental composites and adhesives, thereby ensuring the restoration of teeth with satisfactory mechanical properties. The dental cements demonstrated high bioactivity, biocompatibility, along with appropriate rheological, mechanical, and antimicrobial properties. Bioactive ceramic scaffolds for application in BTE with optimal macro-porosity and suitable biocompatibility were successfully fabricated, and biodegradable polymeric coatings significantly enhanced their mechanical properties. Macroporous hydrogels based on poly(methacrylic acid)/gelatine interpenetrating network exhibiting appropriate swelling behavior, while their mechanical properties were improved by the incorporation of bioactive nano-fillers. The greater antimicrobial properties and bioactivity of 3Dprinted titanium scaffolds were achieved by the formation of multi-layered bioceramic coating composed of nanoparticles of doped HAp and ZnO. CONCLUSIONS: Owing to the achieved mechanical and biological properties, the obtained bioactive materials show significant potential for application in dentistry, biomedicine, and bone tissue engineering. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Hydrogels, characterized by their three-dimensional hydrophilic polymer networks capable of retaining substantial amounts of water or biological fluids, hold significant promise for biomedical and pharmaceutical applications. While numerous polymers have been explored for hydrogel development, those derived from natural sources possess inherent advantages due to their abundance, affordability, biocompatibility, and biodegradability. Gelatin, a widely used natural polymer in biomedicine, stands out for its cost-effectiveness, compatibility with biological systems, and degradability. Hydroxypropyl methylcellulose (HPMC), a cellulose derivative, exhibits hydrophilicity, biodegradability, and biocompatibility. However, natural polymer-based hydrogels often exhibit low mechanical strength and solubility in physiological conditions, necessitating innovative cross-linking strategies to enhance their functionality. Citric acid (CA) emerges as a promising crosslinking agent owing to its affordability and non-toxic nature. EXPERIMENTAL: HPMC-G hydrogels were synthesized by dissolving gelatin (0.05 g) and HPMC (0.1 g) with specified amounts of CA and sodium hypophosphite in 1 ml of distilled water in a reaction vessel. The mixture was homogenized, poured into a Teflon mold, and frozen at -20°C for 24 hours. After lyophilization, the hydrogels underwent crosslinking at 160°C for 7 minutes. By varying the CA content from 0% to 40% (w/w) while maintaining constant temperature and time, the optimal CA/HPMC ratio was determined. Subsequently, various heat treatments (140–180°C, 3-12 minutes) were applied to explore the optimal curing conditions. RESULTS AND DISCUSSION: The investigation elucidates how the CA/HPMC ratio and curing conditions impact the physicochemical and mechanical properties of HPMC-G hydrogels. Swelling tests and compressive mechanical property evaluations reveal that the incorporation of citric acid, along with increases in curing temperature and time, enhances compressive modulus and degradation stability while reducing equilibrium swelling. Scanning electron microscopy analysis reveals a highly porous microstructure in the resulting hydrogels, while differential scanning calorimetry curves indicate the formation of strong interactions between gelatin and HPMC. CONCLUSIONS: The utilization of these materials not only contributes to environmental conservation efforts but also drives the advancement of eco-friendly technology, aligning with the principles of the circular economy. Moreover, it offers promising avenues for innovative solutions in potential biomedical applications. [ABSTRACT FROM AUTHOR]

Composite hydrogels capable of controlled drug delivery via ion exchange are an interesting group of materials for the construction of implantable drug reservoirs for electrically charged drugs. In this study, we synthesized composite poly(DL-lactide- co -glycolide)/poly(acrylic acid) (PLGA-PAA) hydrogels by sequential application of UV or gamma irradiation and traditional phase inversion. Physicochemical properties of the composite PLGA-PAA hydrogels were investigated using Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). We examined the ion exchange capacity (IEC) and swelling behavior of these materials to determine their potential as drug reservoirs. Composite PLGA-PAA hydrogel synthesized using UV irradiation (UV-PLGA-PAA) exhibited a porous microstructure with submicron-sized hydrogel-rich aggregates and homogeneous chemical composition. Swelling behavior and IEC of this material were highly reproducible. Composite PLGA-PAA hydrogels synthesized using gamma irradiation (G-PLGA-PAAs) had a less uniform microstructure with larger pores and micron-sized hydrogel-rich aggregates while exhibiting rather inhomogeneous chemical composition. These materials showed superior swelling properties, but a more variable IEC, compared to the material fabricated using UV irradiation. Results of DSC analysis showed a dose-dependent decrease in glass transition temperature for G-PLGA-PAAs indicating the effects of PLGA chain scission. Our findings indicate that gamma irradiation is a possible alternative to UV irradiation in the synthesis of composite PLGA-PAA hydrogels which can modify or control important material properties. However, the synthesis protocol using gamma irradiation should be further optimized to improve the IEC reproducibility. In our future research, we will investigate the in vitro release of charged drugs from synthesized composite PLGA-PAA hydrogels under physiological conditions. • Synthesis of composite poly(DL-lactide- co -glycolide)/poly(acrylic acid) hydrogels. • Comparison of UV and gamma irradiation effects on composite hydrogel properties. • Gamma irradiation improves the swelling performance of composite hydrogels. • Gamma irradiation increases the size of microgel particles in composite hydrogels. [ABSTRACT FROM AUTHOR]