The biocompatible, viscoelastic properties of poly(vinyl alcohol) (PVA) in combination with the antimicrobial and antioxidant natural polyphenolic, tannic acid (TA), and the natural flavonoid and antioxidant curcumin (Cur), were used in the preparation of PVA:TA and PVA:TA:Cur cryogel composites using cryotropic gelation to combine the individually beneficial properties. The effect of TA content on the antioxidant and antimicrobial activities of PVA:TA cryogel composites and the antioxidant activities of PVA:TA:Cur cryogel composites was determined using Trolox equivalent antioxidant capacity (TEAC) and total phenol content (TPC) assays, and were compared. The PVA:TA:Cur cryogel composite showed the highest antioxidant activity, with a TEAC value of 2.10 ± 0.24 and a TPC value of 293 ± 12.00. The antibacterial capacity of the PVA:TA and PVA:TA:Cur 1:1:0.1 cryogel composites was examined against two different species of bacteria, E. coli and S. aureus. It was found that the minimum inhibition concentration (MIC) value of the PVA:TA:Cur 1:1:0.1 cryogel composites varied between 5 and 10 mg/mL based on the type of microorganism, and the minimum bactericidal concentration (MBC) value was 20 mg/mL irrespective of the type of microorganism. Furthermore, the hemocompatibility of the PVA:TA cryogel composites was evaluated by examining their hemolytic and coagulation behaviors. PVA:TA 1:1 cryogels with a value of 95.7% revealed the highest blood clotting index value amongst all of the synthesized cryogels, signifying the potential for blood contacting applications. The release of TA and Cur from the cryogel composites was quantified at different pH conditions, i.e., 1.0, 7.4, and 9.0, and additionally in ethanol (EtOH) and an ethanol–water (EtOH:Wat) mixture. The solution released from the PVA:TA cryogels in PBS was tested for inhibition capability against α-glucosidase (E.C. 3.2.1.20). Concentration-dependent enzyme inhibition was observed, and 70 µL of 83 µg/mL PVA:TA (1:1) cryogel in PBS inhibited α-glucosidase enzyme solution of 0.03 unit/mL in 70 µL by 81.75 ± 0.96%.

Linear polyethyleneimine (L-PEI) was obtained from the acidic hydrolysis of poly(2-ethyl-2-oxazoline) and employed in the synthesis of physically crosslinked L-PEI hydrogel, PC-L-PEI^H, chemically crosslinked L-PEI hydrogel, CC-L-PEI^H, and cryogels, CC-L-PEI^C. The preparation of L-PEI-based hydrogel networks was carried out in two ways: 1) by cooling the L-PEI solution from 90 °C to room temperature, and 2) by crosslinking L-PEI chains with a crosslinker, glycerol diglycidyl ether = 20 °C for CC-L-PEI^C. Furthermore, a polyphenolic compound, tannic acid (TA), with superior antibacterial, antioxidant, and anti-inflammatory properties as an active biomedical functional agent, was encapsulated during the synthesis process within L-PEI-based hydrogels and cryogels, at 10% and 25% (w/w) based on the L-PEI amount. A linear and higher TA release was observed from physically crosslinked PEI-based hydrogels containing 10% and 25% TA-containing PC-L-PEI/TA^H within 6 h, with 9.5 ± 05 mg/g and 60.2 ± 3.8 mg/g cumulative released amounts, respectively. A higher antioxidant activity was observed for 25% TA containing PC-L-PEI/TA^H with 53.6 ± 5.3 µg/mL total phenol content and 0.48 ± 0.01 µmole Trolox equivalent/g. The minimum bactericidal concentration (MBC) of PC-L-PEI^H and CC-L-PEI^C networks against both E. coli (ATCC 8739) and Gram-positive B. subtilis (ATCC 6633) bacteria was determined at 5 mg/mL, whereas the MBC value of 10 mg/mL for CC-L-PEI^H networks against the same bacteria was achieved.

Carbon nanotubes (CNTs) due to their outstanding mechanical, thermal, chemical, and optical properties were utilized as a base material and were coated with polydopamine (PDA) (PDA@CNT) via the simple self-polymerization of dopamine (DA). Then, PDA@CNT coatings of up to five layers were examined for potential biomedical applications. The success of multiple coating of CNTs with PDA was confirmed via increased weight loss values with the increased number of PDA coatings of CNTs at 500 °C by thermogravimetric analysis. The surface area of bare CNTs was measured as 263.9 m²/g and decreased to 197.0 m²/g after a 5th coating with PDA. Furthermore, the antioxidant activities of CNT and PDA@CNTs were determined via total flavonoid content (TFC), total phenol content (TPC), and Fe(III)-reducing antioxidant power (FRAP) tests, revealing the increased antioxidant ability of PDA@CNTs with the increasing numbers of PDA coatings. Moreover, a higher inhibition percentage of the activity of the alpha-glucosidase enzyme with 95.1 ± 2.9% inhibition at 6 mg/mL PDA-1st@CNTs concentration was found. The CNT and PDA@CNTs exhibited blood compatibility, less than a 2.5% hemolysis ratio, and more than 85% blood clotting indexes. The minimum inhibition concentration (MIC) of PDA-5th@CNTs against E. coli and S. aureus bacteria was determined as 10 mg/mL.

Fluorescent graphitic carbon nitride (g-C₃N₄) doped with various heteroatoms, such as B, P, and S, named ^Bg-C₃N₄, ^Pg-C₃N₄, and ^Sg-C₃N₄, were synthesized with variable band-gap values as diagnostic materials. Furthermore, they were embedded within hyaluronic acid (HA) microgels as g-C₃N₄@HA microgel composites. The g-C₃N₄@HA microgels had a 0.5–20 μm size range that is suitable for intravenous administration. Bare g-C₃N₄ showed excellent fluorescence ability with 360 nm excitation wavelength and 410–460 emission wavelengths for possible cell imaging application of g-C₃N₄@HA microgel composites as diagnostic agents. The g-C₃N₄@HA-based microgels were non-hemolytic, and no clotting effects on blood cells or cell toxicity on fibroblasts were observed at 1000 μg/mL concentration. In addition, approximately 70% cell viability for SKMEL-30 melanoma cells was seen with ^Sg-C₃N₄ and its HA microgel composites. The prepared g-C₃N₄@HA and ^Sg-C₃N₄@HA microgels were used in cell imaging because of their excellent penetration capability for healthy fibroblasts. Furthermore, g-C₃N₄-based materials did not interact with malignant cells, but their HA microgel composites had significant penetration capability linked to the binding function of HA with the cancerous cells. Flow cytometry analysis revealed that g-C₃N₄ and g-C₃N₄@HA microgel composites did not interfere with the viability of healthy fibroblast cells and provided fluorescence imaging without any staining while significantly decreasing the viability of cancerous cells. Overall, heteroatom-doped g-C₃N₄@HA microgel composites, especially ^Sg-C₃N₄@HA microgels, can be safely used as multifunctional theragnostic agents for both diagnostic as well as target and treatment purposes in cancer therapy because of their fluorescent nature.

In this study, a super porous polymeric network prepared from a natural polymer, carboxymethyl cellulose (CMC), was used as a scaffold in the preparation of conductive polymers such as poly(Aniline) (PANi), poly(Pyrrole) (PPy), and poly(Thiophene) (PTh). CMC–conductive polymer composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) techniques, and conductivity measurements. The highest conductivity was observed as 4.36 × 10⁻⁴ ± 4.63 × 10⁻⁵ S·cm⁻¹ for CMC–PANi cryogel composite. The changes in conductivity of prepared CMC cryogel and its corresponding PAN, PPy, and PTh composites were tested against HCl and NH₃ vapor. The changes in conductivity values of CMC cryogel upon HCl and NH₃ vapor treatment were found to increase 1.5- and 2-fold, respectively, whereas CMC–PANi composites showed a 143-fold increase in conductivity upon HCl and a 12-fold decrease in conductivity upon NH₃ treatment, suggesting the use of natural polymer–conductive polymer composites as sensor for these gases.

Graphitic carbon nitride (g-C₃N₄) is an intriguing nanomaterial that exhibits photoconductive fluorescence properties under UV–visible light. Dopamine (DA) coating of g-C₃N₄ prepared from melamine was accomplished via self-polymerization of DA as polydopamine (PDA). The g-C₃N₄ was coated with PDA 1, 3, and 5 times repeatedly as (PDA@g-C₃N₄) in tris buffer at pH 8.5. As the number of PDA coatings was increased on g-C₃N₄, the peak intensity at 1512 cm⁻¹ for N–H bending increased. In addition, the increased weight loss values of PDA@g-C₃N₄ structures at 600 °C from TGA thermograms confirmed that the coating was accomplished. The band gap of g-C₃N₄, 2.72 eV, was reduced to 0.87 eV after five coatings with PDA. A pristine g-C₃N₄ was found to have an isoelectric point (IEP) of 4.0, whereas the isoelectric points of 1PDA@g-C₃N₄ and 3PDA@g-C₃N₄ are close to each other at 3.94 and 3.91, respectively. On the other hand, the IEP of 5PDA@g-C₃N₄ was determined at pH 5.75 assuming complete coating with g-C₃N₄. The biocompatibility of g-C₃N₄ and PDA@g-C₃N₄ against L929 fibroblast cell lines revealed that all PDA@g-C₃N₄ coatings were found to be biocompatible up to a 1000 mg/mL concentration, establishing that PDA coatings did not adversely affect the biocompatibility of the composite materials. In addition, PDA@g-C₃N₄ was screened for antioxidant potential via total phenol content (TPC) and total flavonoid content assays and it was found that PDA@g-C₃N₄ has recognizable TPC values and increased linearly with an increased number of PDA coatings. Furthermore, blood compatibility of pristine g-C₃N₄ is enhanced considerably upon PDA coating, affirmed by hemolysis and the blood clotting index%. Additionally, α-glucosidase inhibitory properties of PDA@g-C₃N₄ structures revealed that 67.6 + 9.8% of this enzyme was evenly inhibited by 3PDA@g-C₃N₄ structure.