Nikoleta Stoyanova

Dr. Nikoleta Stoyanova

orcid

Research Focus & Metrics

Academic Career Length

7Years (2020-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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11 March 2020 in Antioxidants
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Journal Article
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NSNikoleta Stoyanova
Nikoleta Stoyanova
Maria SpasovaMaria Spasova
Maria Spasova
NMNevena Manolova
Nevena Manolova
IRIliya Rashkov
Iliya Rashkov
AGAni Georgieva
Ani Georgieva
RTReneta Toshkova
Reneta Toshkova
The aim of present study was to obtain novel fibrous materials based on cellulose derivative and polyethylene glycol loaded with natural biologically active compound quercetin by electrospinning. Several methods including scanning electron microscopy (SEM), IR spectroscopy, X-ray diffraction analysis (XRD), water contact angle measurements, differential scanning calorimetry (DSC), and UV-VIS spectroscopy were utilized to characterize the obtained materials. The incorporation of polyethylene glycol in the fibrous material resulted in increased hydrophilicity and burst release of quercetin from the fibers. Quercetin-containing fibrous mats exhibited high antioxidant activity as estimated by DPPH free radical scavenging method. In vitro tests with HeLa tumor cells and SH-4 melanoma skin cells were performed in order to determine the cytotoxicity of the novel materials. It was found that the fibrous CA/PEG/QUE materials exhibited high cytotoxic effect against both cell lines. Therefore, the novel polymeric materials containing quercetin are promising candidates for biomedical and pharmaceutical applications.

21 February 2023 in Polymers
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NSNikoleta Stoyanova
Nikoleta Stoyanova
Maria SpasovaMaria Spasova
Maria Spasova
NMNevena Manolova
Nevena Manolova
IRIliya Rashkov
Iliya Rashkov
MKMariana Kamenova-Nacheva
Mariana Kamenova-Nacheva
MTMaya Tavlinova-Kirilova
Maya Tavlinova-Kirilova
In the present study, the plant extract Melissa officinalis (M. officinalis) was successfully loaded in polymer fibrous materials on the basis of a biodegradable polyester–poly(L-lactide) (PLA) and biocompatible polyether–polyethylene glycol (PEG) by applying the electrospinning method. The optimal process conditions for the preparation of hybrid fibrous materials were found. The extract concentration was varied—0, 5 or 10 wt% in respect of the polymer weight, in order to study its influence on the morphology and the physico-chemical properties of the obtained electrospun materials. All the prepared fibrous mats were composed of defect-free fibers. The mean fiber diameters of the PLA, PLA/M. officinalis (5 wt%) and PLA/M. officinalis (10 wt%) were 1370 ± 220 nm, 1398 ± 233 nm and 1506 ± 242 nm, respectively. The incorporation of the M. officinalis into the fibers resulted in slight increase of the fiber diameters and in increase of the water contact angle values to 133°. The presence of the polyether in the fabricated fibrous material assisted the wetting of the materials imparting them with hydrophilicity (the value of the water contact angle become 0°). Extract-containing fibrous materials displayed strong antioxidant activity as determined by the 2,2-diphenyl-1-picryl-hydrazyl-hydrate free radical method. The DPPH solution color changed to yellow and the absorbance of the DPPH radical dropped by 88.7% and 91% after being in contact with PLA/M. officinalis and PLA/PEG/M. officinalis mats, respectively. These features revealed the M. officinalis—containing fibrous biomaterials promising candidates for pharmaceutical, cosmetic and biomedical use.

21 October 2023 in Membranes
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NSNikoleta Stoyanova
Nikoleta Stoyanova
NNNasko Nachev
Nasko Nachev
Maria SpasovaMaria Spasova
Maria Spasova
Since antiquity, humans have known about plants as a medicinal cure. Recently, plant extracts are attracting more attention as a result of their natural origin and wide range of desirable features. Nanotechnology’s progress and innovations enable the production of novel materials with enhanced properties for a broad range of applications. Electrospinning is a cutting-edge, flexible and economical technique that allows the creation of continuous nano- and microfibrous membranes with tunable structure, characteristics and functionalities. Electrospun fibrous materials are used in drug delivery, tissue engineering, wound healing, cosmetics, food packaging, agriculture and other fields due to their useful properties such as a large surface area to volume ratio and high porosity with small pore size. By encapsulating plant extracts in a suitable polymer matrix, electrospinning can increase the medicinal potential of these extracts, thus improving their bioavailability and maintaining the required concentration of bioactive compounds at the target site. Moreover, the created hybrid fibrous materials could possess antimicrobial, antifungal, antitumor, anti-inflammatory and antioxidant properties that make the obtained structures attractive for biomedical and pharmaceutical applications. This review summarizes the known approaches that have been applied to fabricate fibrous materials loaded with diverse plant extracts by electrospinning. Some potential applications of the extract-containing micro- and nanofibers such as wound dressings, drug delivery systems, scaffolds for tissue engineering and active food packaging systems are discussed.

8 December 2022 in Polymers
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Journal Article
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NSNikoleta Stoyanova
Nikoleta Stoyanova
Maria SpasovaMaria Spasova
Maria Spasova
NMNevena Manolova
Nevena Manolova
IRIliya Rashkov
Iliya Rashkov
AGAni Georgieva
Ani Georgieva
RTReneta Toshkova
Reneta Toshkova
Innovative fibrous materials from cellulose derivative, cellulose acetate (CA) and water-soluble polyether, polyethylene glycol (PEG) loaded with natural biologically active compounds (BAC), quercetin (QUE) and rutin (RUT), have been successfully fabricated by blend electrospinning and dual electrospinning. Scanning electron microscopy revealed that the mean fiber diameters of all the obtained fibers were in the nanometer range. QUE and RUT incorporated in the fibrous mats were in the amorphous state, as evidenced by the performed differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. The presence of the polyether in the developed fibrous material assisted the in vitro release of the biologically active compounds by improving the hydrophilicity and wettability of the mats. Rutin-containing fibrous materials manifest the highest antioxidative activity, as determined by the 2,2-diphenyl-1-picryl-hydrazyl-hydrate free radical method. The cytotoxicity of the fabricated novel materials was evaluated using a tumor cell line and normal mouse fibroblast cells. The mats containing QUE and QUE/RUT independent of the applied spinning method show a higher cytotoxic effect against cancer cells and 3 to 4.5 times lower cytotoxicity to a noncancer cell line. These features make the quercetin- and rutin-containing fibrous materials promising candidates for pharmaceutical, cosmetic, and biomedical use.

19 April 2025 in Gels
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VKVladimir Krastev
Vladimir Krastev
NSNikoleta Stoyanova
Nikoleta Stoyanova
IVIliyana Valcheva
Iliyana Valcheva
DDDonka Draganova
Donka Draganova
Maria SpasovaMaria Spasova
Maria Spasova
Olya StoilovaOlya Stoilova
Olya Stoilova
Chitosan gel beads represent a promising biopolymer-based delivery system for encapsulating Bacillus subtilis, an effective biocontrol agent in sustainable agriculture. This study investigates the influence of chitosan molecular weight on bead structure, water retention, and swelling behavior, as well as its impact on the viability and antifungal activity of encapsulated B. subtilis. The results demonstrate that chitosan provides a protective microenvironment, enhancing microbial viability, promoting colonization, and ensuring controlled release for prolonged plant protection. Moreover, encapsulation within chitosan gel beads preserved bacterial viability during long-term storage for up to 90 and 180 days. Additionally, the biodegradable and antimicrobial properties of chitosan contribute to pathogen suppression while supporting the plant growth-promoting activities of B. subtilis. The encapsulated bioagent exhibited strong antifungal activity against Fusarium avenaceum and Rhizoctonia solani, highlighting the effectiveness of this eco-friendly approach as an alternative to chemical pesticides. These findings underscore the potential of chitosan-based formulations to enhance the efficacy of bioinoculants, offering a sustainable solution for modern crop management.

27 April 2025 in Pharmaceutics
Verified
Journal Article
Open access
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NSNikoleta Stoyanova
Nikoleta Stoyanova
NNNasko Nachev
Nasko Nachev
AGAni Georgieva
Ani Georgieva
RTReneta Toshkova
Reneta Toshkova
Maria SpasovaMaria Spasova
Maria Spasova
Background: The plant extract of quercetin possesses valuable pharmacological properties. However, its high instability, poor water solubility, and low cell bioavailability has limited its medical applications. An innovative approach used to overcome these limitations is the QUE incorporation in suitable polymer carriers. Methods: In the present study, fibrous materials based on PLA or PLA/PEG loaded with the flavonoid quercetin (QUE) were obtained by the electrospinning technique. Diverse morphological, spectroscopic, physico-mechanical, and spectrophotometric methods were used to characterize the prepared electrospun mats. Results: The addition of hydrophilic PEG to the polymer matrix improved its wettability and assisted the more rapid release of QUE from the PLA/PEG fibrous mat than from the PLA one. The obtained fibrous mats possess good mechanical properties. Moreover, QUE-loaded electrospun mats exhibited high anticancer activity against HeLa cervical cancer cells, but lower toxicity to normal cells. Conclusions: The obtained perspective results revealed the potential of the obtained QUE-loaded materials to find applications for wound healing and cancer treatment.