Selestina Gorgieva

Homogeneous and heterogeneous methods for laccase-mediated functionalization of chitosan by tannic acid and quercetin

Homogeneous and heterogeneous methods for functionalization of chitosan with quercetin or tannic acid using laccase from Trametes versicolor is presented, yielding a bio-based product with synergistic antioxidant and antimicrobial properties. HPLC-SEC analysis and cyclic voltammetry kinetic studies showed that laccase catalyzes the oxidation of quercetin to electrophilic o-quinones, which undergo to an oligomer/polymer-forming structures. On the other hand, tannic acid was converted into gallic acid, its dimers, partially gallic acid esterified glucose and glucose, when exposed to laccases. ATR-FTIR spectroscopy provided evidence that quercetin o-quinones undergo coupling reactions with amino groups of chitosan via Schiff-base and Michael addition mechanisms under heterogeneous method, while oxidized tannic acid cross-linked with chitosan by hydrogen and electrostatic interactions under both methods. All polyphenols functionalized chitosans showed greatly improved ABTS(+) cation radicals scavenging capacity, compared with the untreated chitosan, while antimicrobial activities significantly depended on the mode of functionalization and type of microorganism.

Collagen- vs. Gelatine-Based Biomaterials and Their Biocompatibility: Review and Perspectives

Selection of a starting material, which will somehow mimic a naturally-existing one, is one of the most important points and crucial elements in biomaterials development. Material biomimetism is one of those approaches, where restoration of an organ’s function is assumed to be obtained if the tissues themselves are imitated (Barrere et al., 2008). However, some of the biopolymers as e.g collagen can be selected from within a group of biomimetic materials, since they already exist, and have particular functions in the human body. Collagen is one of the key structural proteins found in the extracellular matrices of many connective tissues in mammals, making up about 25% to 35% of the whole-body protein content (Friess, 2000; Muyonga et al., 2004). Collagen is mostly found in fibrous tissues such as tendons, ligaments and skin (about one half of total body collagen), and is also abundant in corneas, cartilages, bones, blood vessels, the gut, and intervertebral discs (Brinckmann et al., 2005). It constitutes 1% to 2% of muscle tissue, and accounts for 6% of strong, tendinous muscle-weight. Collagen is synthesized by fibroblasts, which originate from pluripotential adventitial cells or reticulum cells. Up to date 29 collagen types have been identified and described. Over 90% of the collagen in the body is of type I and is found in bones, skins, tendons, vascular, ligatures, and organs. However, in the human formation of scar tissue, as a result of age or injury, there is an alteration in the abundance of types I and III collagen, as well as their proportion to one another (Cheng et al., 2011). Collagen is readily isolated and purified in large quantities, it has well-documented structural, physical, chemical and immunological properties, is biodegradable, biocompatible, non-cytotoxic, with an ability to support cellular growth, and can be processed into a variety of forms including cross-linked films, steps, sheets, beads, meshes, fibres, and sponges (Sinha & Trehan, 2003). Hence, collagen has already found considerable usage in clinical medicine over the past few years, such as injectable collagen for the augmentation of tissue defects, haemostasis, burn and wound dressings, hernia repair, bioprostetic heart valves, vascular grafts, a drug –delivery system, ocular surfaces, and nerve regeneration (Lee et al., 2001). However, certain properties of collagen have adversely influenced some of its usage: poor dimensional stability due to swelling in vivo; poor in vivo mechanical strength and low elasticity, the possibility of an antigenic response (Lynn et

Chitosan hydrogels enriched with polyphenols: Antibacterial activity, cell adhesion and growth and mineralization.

Injectable hydrogels for bone regeneration consisting of chitosan, sodium beta-glycerophosphate (Na-β-GP) and alkaline phosphatase (ALP) were enriched with the polyphenols phloroglucinol (PG) and gallic acid (GA) and characterized physicochemically and biologically with respect to properties relevant for applications in bone regeneration, namely gelation kinetics, mineralizability, antioxidant properties, antibacterial activity, cytocompatibility and ability to support adhesion and growth of human osteoblast-like MG63 cells. Enrichment with PG and GA had no negative effect on gelation kinetics and mineralizability. PG and GA both enhanced antioxidant activity of unmineralized hydrogels. Mineralization reduced antioxidant activity of hydrogels containing GA. Hydrogels containing GA, PG and without polyphenols reduced colony forming ability of Escherichia coli after 1h, 3h and 6h incubation and slowed E. coli growth in liquid culture for 150min. Hydrogels containing GA were cytotoxic and supported cell growth more poorly than polyphenol-free hydrogels. PG had no negative effect on cell adhesion and growth.

Mechanically strong, flexible and thermally stable graphene oxide/nanocellulosic films with enhanced dielectric properties

Flexible and eco-friendly films, with enhanced dielectric properties and the potential for energy storage applications, have been fabricated from ammonia-functionalized graphene oxide (NGO) nanoplatelets and wood-based cellulose nanofibrils (CNF) vs. (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pre-oxidized (carboxylated) CNFs (TCNF) by the solvent casting method. Various CNF-NGO (CNG) and TCNF-NGO (TCNG) composite films prepared with 0.5–3 wt% of NGO were analysed structurally by FTIR and XRD spectroscopy, and evaluated optically by UV-Vis spectroscopy. The morphological analysis using SEM showed good dispersibility of the NGO sheets in the randomly-distributed CNF, and the dense and parallel-oriented TCNF cellulose nanofibrils. Such a synergistic effect of both components contributed to ultra-strong and ultra-stiff composite films with good mechanical and thermal stability, although they were more brittle with a smoother surface and lower transmittance for the TCNF based films, due to the stronger physico–chemical interactions with NGO. The dielectric performance was verified with a higher (3 wt%) NGO loading capacity, which resulted in a dielectric constant of ∼46 vs. ∼52, and conductivity of ∼2.07 × 10−4 S m−1 vs. 3.46 × 10−4 S m−1 for CNG vs. TCNG films, respectively, at a frequency of 1 MHz, showing greater enhancement than other reported studies. Cyclic voltammetry and electrochemical impedance studies reveal the energy storage ability and electrochemical performance of the composite films, under kinetic- and diffusion-controlled processes for the CNG, and under a kinetic-controlled process for the TCNG films.

Evaluation of surface/interface-related physicochemical and microstructural properties of gelatin 3D scaffolds, and their influence on fibroblast growth and morphology.

This article present new insights in complex relation between surface- and interface-related physicochemical properties and microstructuring of three-dimensional (3D) gelatin scaffolds, being fabricated by simultaneous temperature-controlled freeze-thawing cycle and in situ cross-linking using variable conditions (pH) and molarity of carbodiimide reagents, on the seeding and growth of fibroblast cells with subsequent tracking of their spreading and morphology. Rarely populated cells with rounded morphology and small elongations are observed on negative charge-rich scaffold surface with a lower cross-linking degree (CD), and consequently higher molecular mobility and availability of cell-recognition sequences, in comparison with the prominently elongated and densely populated cells on a positively charged scaffolds surface with higher CD and low mobility. Surface microstructure effect was demonstrated by cell vacuolization and their pure intercommunication being present on scaffolds bottom side with smaller pores (25 ± 19 µm) and pore wall thickness (9 ± 5 µm), over the air-exposed side with twice bigger pores (56 ± 38 µm) and pore wall thicknesses (12 ± 6 µm). Strong correlations of CD (r(2) = 0.96) and local molecular mobility (r(2)  = -0.44) with pH and reagents molarity, as well as microstructure features being related to temperature gradient, imply on possibility to modulate scaffolds properties in a direction to guide cell viability and most likely its genotype development.

Molecular mobility of scaffolds’ biopolymers influences cell growth

Understanding biocompatibility of materials and scaffolds is one of the main challenges in the field of tissue engineering and regeneration. The complex nature of cell-biomaterial interaction requires extensive preclinical functionality testing by studying specific cell responses to different biomaterial properties, from morphology and mechanics to surface characteristics at the molecular level. Despite constant improvements, a more general picture of biocompatibility is still lacking and tailormade scaffolds are not yet available. The scope of our study was thus the investigation of the correlation of fibroblast cell growth on different gelatin scaffolds with their morphological, mechanical as well as surface molecular properties. The latter were thoroughly investigated via polymer molecular mobility studied by site-directed spin labeling and electron paramagnetic resonance spectroscopy (EPR) for the first time. Anisotropy of the rotational motion of the gelatin side chain mobility was identified as the most correlated quantity with cell growth in the first days after adhesion, while weaker correlations were found with scaffold viscoelasticity and no correlations with scaffold morphology. Namely, the scaffolds with highly mobile or unrestricted polymers identified with the cell growth being five times less efficient (N(cells) = 60 ± 25 mm(-2)) as compared to cell growth on the scaffolds with considerable part of polymers with the restricted rotational motion (N(cells) = 290 ± 25 mm(-2)). This suggests that molecular mobility of scaffold components could play an important role in cell response to medical devices, reflecting a new aspect of the biocompatibility concept.

Polydispersity and assembling phenomena of native and reactive dye-labelled nanocellulose

The assembling (self-association vs. aggregation or agglomeration) of highly polydispersed nanocelluloses (NCs) is a well-known but difficult to identify phenomena. In this research complementary analytical tools were applied for tracking and assessing this phenomena under different conditions (base vs. buffer) using both native and dye-labelled cellulose nanofibrils (CNFs) and cellulose nanocrystals. For this purpose, dichlorotriazine-type reactive blue 4 (RB4) dye was covalently (through alkyl-aryl ether bond) and regioselectively (to C6–OH groups) attached to the NC, being identified by ATR-FTIR and 13C CP/MAS solid-state NMR spectroscopies, and quantified by UV–Vis spectroscopy. The introduced RB4’s anthraquinone (i.e. hydrophobic) moieties evoked aggregation of those CNFs being quantified from the shifting and broadening of size-distribution profiles within differential light scattering analysis and their ζ-potential reduction. In addition, their high polydispersity profiles was assessed by qualitatively supported differential centrifugal sedimentation, nanoparticle tracking analysis, and transmission electron microscopy. A desorption of chemically non-bonded, yet highly substantive (i.e. partially or fully hydrolysed), dye from both types of NCs was also identified by capillary electrophoresis, which simultaneously excluded the non-labelled fractions, thus obtaining free dye-absent NC dispersions. Finally, labelling extent-triggered separation within the RB4-labelled CNFs was identified by applying the micellar capillary electrophoresis, thus confirming the conformational changes affecting NCs’ hydrodynamic (size) profiles.

Textile-based biomaterials for surgical applications

Abstract Medical textiles (MedTech), as the cross-point of (bio)polymer chemistry, textile technology, and medical science, represent the most emerging technical textile area, evidencing innovations far beyond the “classical.” In that frame, a state of the art is presented for implantable MedTech products as the most demanding (by functionality and safety) among health care and hygiene materials, extracorporeal devices, and nonimplantable materials. Innovative processing and finishing technologies in combination with (bio)polymers and high standards applied for medium-to-high risk medical devices for soft and hard tissue regeneration, cardiovascular implants, or sutures are overviwed. Particular accent is given on authors’ research topics, that is, hernia repair composites, vascular grafts, and orthopedic implants with emphasis on their acceptance from biomedical aspects: cells’ adherence/growth, cytotoxicity, biocompatibility with the host, hemocompatibility, and biodegradation kinetic. Finally, recent regulations within directives are presented, covering the quality, safety, and reliability of medical devices. The adaption of textile manufacturing/finishing processes for development of smart and personalized textile implants are foreseen as future MedTech perspective.

Antibacterial activity and cytotoxycity of gelatine-conjugated lysine-based peptides

The effect of the coupling approach (chemical by using carbodiimide chemistry, and enzymatic by using transglutaminase) of a hydrophilic ɛ-poly-L-lysine (ɛPL) and a structurally-hydrophobic oligo-acyl-lysyl (OAK) to a gelatine (GEL) macromolecule, and their antibacterial activity against Gram-negative E. coli and Gram-positive S. aureus bacteria, as well as cytotoxicity to human osteoblast cells was studied as potential macromolecules for biomedical applications. Different spectroscopic (ultraviolet-visible, infrared, fluorescence, and electron paramagnetic resonance) and separation (size-exclusion chromatography and capillary zone electrophoresis) techniques, as well as zeta-potential analysis were performed to confirm the ɛPL/OAK covalent coupling and to determine their amount and orientation of the immobilization. The highest and kinetically the fastest reduction of bacteria (≥77% against E. coli vs. ≥82% against S. aureus) was achieved with GEL functionalized with ɛPL/OAK by the chemical grafting-to approach being correlated with conformationally the highly-flexible ˝brush-like˝ orientation linkage of peptides, enable its targeted and rapid interactions with bacteria membrane. The up to 400-fold lower yield of OAKs being immobilized may be related also to its cationic charge and hydrophobic alkyl chain moieties, compared to more hydrophilic ɛPL easily causing random polymerization and self-conjugation. The ɛPL/OAK-functionalized GEL did not induce citotoxicity to osteoblasts, even at ∼25-fold higher concentration than bacterial minimum inhibitory (MIC) concentration of ɛPL/OAK.