Iliya Rashkov

Electrospun Non-Woven Nanofibrous Hybrid Mats Based on Chitosan and PLA for Wound-Dressing Applications

Continuous defect-free nanofibers containing chitosan (Ch) or quaternized chitosan (QCh) were successfully prepared by one-step electrospinning of Ch or QCh solutions mixed with poly[(L-lactide)-co-(D,L-lactide)] in common solvent. XPS revealed the surface chemical composition of the bicomponent electrospun mats. Crosslinked Ch- and QCh-containing nanofibers exhibited higher kill rates against bacteria S. aureus and E. coli than the corresponding solvent-cast films. SEM observations showed that hybrid mats were very effective in suppressing the adhesion of pathogenic bacteria S. aureus. The hybrid nanofibers are promising for wound-healing applications.

Preparation of chitosan-containing nanofibres by electrospinning of chitosan/poly(ethylene oxide) blend solutions

Abstract The first successful preparation of chitosan-containing nanofibres was achieved by electrospinning of chitosan/poly(ethylene oxide) (PEO) blend aqueous solutions. The diameters of the nanofibres were in the range 40 - 290 nm and decreased with increasing chitosan content and decreasing total concentration. An increase of the applied field strength leads to an increase of the diameter of the nanofibres and to a broadening of the size distribution. The possibility to prepare nanofibres containing a model drug - potassium 5-nitro-8-quinolinolate (K5N8Q), a broad-spectrum antimicrobial and antimycotic agent - was shown. The incorporation of K5N8Q in the nanofibres resulted in a decrease of the nanofibre diameters and the appearance of bead-shaped defects. Non-woven mats from the drugloaded nanofibres with composition chitosan : PEO = 1:1 (w/w) and 1% K5N8Q showed antibacterial and antimycotic activity against E. coli, S. aureus and C.albicans.

Electrospun Antibacterial Chitosan-Based Fibers

Chitosan is non-toxic, biocompatible, and biodegradable polysaccharide from renewable resources, known to have inherent antibacterial activity, which is mainly due to its polycationic nature. The combining of all assets of chitosan and its derivatives with the unique properties of electrospun nanofibrous materials is a powerful strategy to prepare new materials that can find variety of biomedical applications. In this article the most recent studies on different approaches for preparation of antibacterial fibrous materials from chitosan and its derivatives such as electrospinning, coating, and electrospinning-electrospraying, loading of drugs or bioactive nanoparticles are summarized.

Perspectives On: Criteria for Complex Evaluation of the Morphology and Alignment of Electrospun Polymer Nanofibers

Electrospinning is a promising method for producing polymer materials composed of micro- and nanosized fibers. This method allows the preparation of random and aligned fibers of different morphologies, such as cylindrical or ribbon-shapes, defect-free or with defects, and with or without pores or porous. The increasing number of studies on electrospinning requires a set of criteria for more complex evaluation of the fiber morphology and the topology of these polymer materials to be established. The main characteristics necessary for a complex evaluation of the morphology of electrospun micro- and nanofibers have been systematized in this paper. Examples of characterization of the morphology and of the alignment of various micro- and nanofibers are given.

Electrospun Nanofibrous Mats Containing Quaternized Chitosan and Polylactide with In Vitro Antitumor Activity against HeLa Cells

Nanofibrous materials containing the antitumor drug doxorubicin hydrochloride (DOX) were easily prepared using a one-step method by electrospinning of DOX/poly(L-lactide-co-D,L-lactide) (coPLA) and DOX/quaternized chitosan (QCh)/coPLA solutions. The pristine and DOX-containing mats were characterized by ATR-FTIR and X-ray photoelectron spectroscopy (XPS). The release rate of DOX from the prepared fibers increased with the increase in DOX content. The DOX release process was diffusion-controlled. MTT cell viability studies revealed that incorporation of DOX and QCh in the nanofibrous mats led to a significant reduction in the HeLa cells viability. It was found, that the antitumor efficacy of the DOX-containing mats at 6 h was higher than that of the free DOX. SEM, TEM, and fluorescence microscopic observations confirmed that the antitumor effect of QCh-based and DOX-containing fibrous mats was mainly due to induction of apoptosis in the HeLa cells.

Polylactide Stereocomplex-Based Electrospun Materials Possessing Surface with Antibacterial and Hemostatic Properties

Novel fibrous materials of stereocomplex between high-molecular-weight poly(d- or l-)lactide (HMPDLA or HMPLLA) and diblock copolymers consisting of poly(l- or d-)lactide and poly(N,N-dimethylamino-2-ethyl methacrylate) blocks, respectively (PLLA-block-PDMAEMA or PDLA-block-PDMAEMA), were prepared by solution electrospinning. Fibers with mean diameters ranging from 1400 to 1700 nm were obtained. The stereocomplex formation was evidenced by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. Annealing at 100 degrees C for 8 h resulted in the appearance of crystalline peaks at 2theta values of 12, 21, and 24 degrees for PLA stereocomplex. X-ray photoelectron spectroscopy (XPS) analyses revealed the gradient composition of the fibers with a surface enriched in tertiary amino groups from PDMAEMA blocks. The availability of tertiary amino groups imparts hemostatic and antibacterial properties to the stereocomplex fibrous materials, as indicated by the performed tests on blood cells and on pathogenic microorganisms.

Hydrolytic degradation of poly(oxyethylene)–poly-(ε-caprolactone) multiblock copolymers

The degradation of poly(oxyethylene)–poly(e-caprolactone) (POE–PCL) multiblock copolymers was investigated at 37°C in a 0.13M, pH 7.4 phosphate buffer selected to mimic in vivo conditions. The copolymers were obtained by coupling polycaprolactone diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. Various techniques, such as weighing, size exclusion chromatography, infrared, 1H nuclear magnetic resonance, differential scanning calorimetry, and X-ray diffractometry, were used to monitor changes in total mass, water absorption, molar mass, thermal properties, degree of crystallinity, and composition. The results showed that introduction of POE sequences considerably increased the hydrophilicity of the copolymers as compared with PCL homopolymers. Nevertheless, the degradability of PCL sequences was not enhanced due to the phase separation between the two components. Significant morphological changes were also observed during the degradation.

Drug-loaded electrospun materials in wound-dressing applications and in local cancer treatment

Introduction: During the last decade, the use of electrospinning for the fabrication of nanofibrous materials loaded with antibacterial agents or anticancer drugs for biomedical applications such as dressing materials for wound treatment and for local cancer treatment has evoked considerable interest. Different drugs can be easily incorporated in electrospun materials and their release profile can be controlled through changes in the fibers morphology, porosity and composition. The large specific surface area of the electrospun materials, the possibility for gradual release and site-specific local delivery of the active compounds lead to cytotoxicity decrease and enhancement of the therapeutic effect of the drugs. Areas covered: The most recent studies on drug-loaded electrospun mats as materials for wound dressing or local cancer treatment are briefly summarized. Expert opinion: The possibility for local drug delivery in cancer therapy using electrospun materials allows avoiding the oral or systemic drug application, thus leading to decrease in some deleterious side effects. The recent achievements in the comprehension of the electrospinning, in control over the surface chemical composition of the electrospun materials, and in diversifying the applied approaches and techniques, propound larger prospects for creating new materials for wound dressing and local cancer treatment.

Amphiphilic poly(D- or L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) block copolymers: controlled synthesis, characterization, and stereocomplex formation.

Novel well-defined amphiphilic poly(D-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PDLA-b-PDMAEMA) and poly(L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PLLA-b-PDMAEMA) copolymers were obtained. The synthesis strategy consisted of a three-step procedure: (i) controlled ring-opening polymerization (ROP) of (D- or L-)lactide initiated by Al(O(i)Pr)(3), followed by (ii) quantitative conversion of the polylactide (PLA) hydroxyl end-groups with bromoisobutyryl bromide and (iii) atom transfer radical polymerization (ATRP) of DMAEMA. The PLA block molecular weight was kept below 5000 g/mol. The macromolecular parameters of the (co)polymers were determined by (1)H NMR spectroscopy and size exclusion chromatography (SEC). The stereocomplexes of PDLA-b-PDMAEMA/PLLA-b-PDMAEMA diblock copolymers were prepared via solvent casting. The stereocomplex formation was evidenced by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The obtained stereocomplexes had melting temperature of about 65 degrees C above that of the individual copolymers and exhibited diffraction patterns assigned to the stereocomplex crystallites. In addition, for the first time it was shown that the replacement of one of the PLA partners with high molecular weight PLLA or PDLA did not hamper the stereocomplex formation. The presence of PDMAEMA blocks proved to impart hydrophilicity of the synthesized copolymers and related stereocomplexes, as determined by static water contact angle measurements.

Preparation of Polyelectrolyte-Containing Nanofibers by Electrospinning in the Presence of a Non-Ionogenic Water-Soluble Polymer

The first successful preparation of nanofibers of a polyampholyte (N-carboxyethylchitosan) by electrospinning was achieved by adding a non-ionogenic water-soluble polymer to the spinning solution. Using this approach, other polyelectrolytes, poly(2-acryloylamido-2-methylpropanesulphonic acid) (PAMPS), and copolymers of 2-acryloylamido-2-methylpropane-sulphonic acid (AMPS) and acrylic acid [P(AMPS-co-AA)] were also electrospun into nanofibers. The non-ionogenic water-soluble polymers were polyacrylamide (PAAm) and poly(vinyl alcohol) (PVA). The average diameters of the electrospun nanofibers were in the range 50-260nm. The average diameter of the nanofibers significantly decreased with increasing polyelectrolyte content. The electrospun nanofibers were crosslinked by heat treatment at 100, 120 or 150°C for the N-carboxyethylchitosan/PAAm pair and at 90°C in the case of P(AMPS-co-AA)/PVA. The presence of an ionizable low-molecular-weight compound (7-iodo-8-hydroxyquinoline-5-sulphonic acid, SQ) led to a more than two-fold decrease in the diameter of the nanofibers and to the appearance of defects. The SQ-containing nanofibers showed antimicrobial activity against pathogenic microorganisms.