Study on cellulose nanofibrils/copolymacrolactone based nano-composites with hydrophobic behaviour, self-healing ability and antioxidant activity

The multiple uses of cellulose nanofibrils (CNFs) originate from their availability from renewable resources, and are due to their physico-chemical properties, biodegradability and biocompatibility. At the same time, reducing sensitivity to humidity, increasing interfacial adhesion and hydrophobic modification of the CNF surface to diversify applications and improve operation, are current targets pursued. This study focuses on the preparation of a novel gel structure using cellulose nanofibrils (CNFs) and poly(ethylene brassylate-co-squaric acid) (PEBSA50/50), a bio-based copolymacrolactone. The primary goal is to achieve the gel with reduced sensitivity to humidity and enhanced hydrophobic behaviour. The new system was characterized in comparison to its constituent components using various techniques, such as Fourier transform infrared spectroscopy, thermal analysis, X-ray diffraction, and NIR - chemical imaging. Rheological tests demonstrated the formation of the CNF_PEBSA50/50 gel as a result of physical interactions between the two polymeric partners and revealed self-healing abilities for the prepared gels. Determination of the contact angle, surface free energy, as well as dynamic measurements of the vapour sorption of the CNF_PEBSA50/50 system, confirmed the achievement of the study's aim. Furthermore, the CNF_PEBSA50/50 network was utilized to encapsulate citric acid, resulting in the creation of a new bioactive composite with both antioxidant and antimicrobial activity.

Riboflavin mediated UV crosslinking of chitosan-gelatin cryogels for loading of hydrophobic bioactive compounds

Chitosan-gelatin cryogels with good loading capacity of hydrophobic compounds were successfully obtained by UV-induced crosslinking. Using riboflavin as photoinitiator was a suitable alternative to classical carbodiimide crosslinking in obtaining carrier matrices for bioactive hydrophobic compounds. Chitosan had a double role, acting both as a base polymer for the hydrogel network and as co-initiator in riboflavin photo-crosslinking. This co-initiator role of chitosan is due to its electron donor capacity, being well known as a Lewis base type macromolecule. The rheological behaviour of the chitosan-gelatin hydrogel precursor solutions was greatly influenced by riboflavin addition as well as by UV irradiation. As a consequence, the temperature of the sol-gel transition during cooling decreased to 25.5 °C. Compared with classical carbodiimide crosslinking, UV irradiation lead to gels with increased network stability, enhanced elastic behaviour, higher structural strength and almost total stress recovery yield (99 %), the latter indicating self-healing capacity. The cryogels manifested pH responsive swelling, this being highest at close to neutral pH of 7.4. Although hydrophilic in nature, the chitosan-gelatin cryogels crosslinked under the combined effect of riboflavin and UV exposure possess the necessary chemical functionality and morphology that allowed successful embedding of hydrophobic clove essential oil. This was loaded by immersion or fumigation and imparted antioxidant activity to the polymeric matrix.

Hybrid green bionanocomposites based on chitosan/starch/gelatin and metallic nanoparticles for biological applications

Multicomponent composites based on natural biopolymers: chitosan, starch and gelatin in two different ratios (0.5:1:1 and 1:1:1) were in situ crosslinked by intermolecular interactions and used as matrices for zinc oxide and magnetite fillers. The bionanocomposite films have been evaluated by spectral and microscopy methods: Fourier-Transform Infrared spectrometry (FT-IR), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) confirming the electrostatic and hydrogen bonding interactions between the components of the polymeric matrices and the inorganic fillers and the crosslinking process. AFM and SEM images showed a compact, non-porous and homogenous morphology of the hybrid films, proving a good miscibility of the blends. At lower concentrations of embedded filler, the composites were less hardened and more ductile due to the interaction with the polymeric matrix. Increased amounts of inorganic NPs led to the reduced mechanical properties of the prepared materials and increased thermal stability. The bionanocomposites revealed a similar behavior of the dielectric constant with frequency and increased values at higher temperatures. The wettability of the films' surface and the values of the water sorption capacity revealed a slight hydrophilicity of the bionanocomposites as compared with the initial matrices. The biocompatibility, evaluated by means of the surface free energy components and the interfacial tension with blood, and the hemolysis analysis demonstrated that the bionanocomposites possess a low risk of thrombosis, being promising materials for in vivo biomedical applications.

Bioactive Composite Cryogels Based on Poly (Vinyl Alcohol) and a Polymacrolactone as Tissue Engineering Scaffolds: In Vitro and In Vivo Studies

In light of the increasing resistance of pathogenic microorganisms to the action of antibiotics, essential oils extracted from plants with therapeutic activity provide a significant alternative to obtaining dressings for the treatment of skin wounds. The encapsulation of essential oils in an amphiphilic gel network allows better dispersion and preservation of hydrophobic bioactive substances while promoting their prolonged release. In this study, we focused on the development of a poly (vinyl alcohol) (PVA)/poly (ethylene brassylate-co-squaric acid) (PEBSA) platform embedded with thymol (Thy), and α-tocopherol (α-Tcp) as a co-drug structure with prospective use for the treatment and healing of skin wounds. The new complex bioactive system was prepared through repeated freeze-thaw processes. The influence of the composition on surface topography, hydrophilic/hydrophobic character, and in vitro interaction with simulated body fluids was evidenced. BALB/3T3 fibroblast cell culture demonstrated the cryogel scaffolds' cytocompatibility. Tests on Wistar rats confirmed their biocompatibility, integration with host tissue, and the absence of inflammatory processes. The bioactive compound significantly enhanced the healing process of full-thickness excision wounds in a rat model. Further investigations on in vivo infection models would assess the potential of the PVA/PEBSA platform with dual bioactive activity for clinical antimicrobial and wound healing therapy.

Mucoadhesive and Antimicrobial Allantoin/β Cyclodextrins-Loaded Carbopol Gels as Scaffolds for Regenerative Medicine

Allantoin and its β-cyclodextrin and hydroxypropyl-β-cyclodextrin inclusion complexes 1:1 have been used to prepare carbopol-based mucoadhesive gels. The gelation process occurred by adjustment with glycerol 10% in the presence of triethanolamine. The structural features induced by the presence of allantoin and the corresponding β-cyclodextrins inclusion complexes have been first investigated by infrared spectroscopy highlighting strong interactions within the gels network and ideal crosslinks for the self-healing behavior. The hydrophilicity of the gels was investigated by the determination of the surface tension parameters and the free energy of hydration. The interfacial free energy values indicated prolonged biocompatibility with blood. The gels-water molecule interactions in terms of sorption, permeability, and diffusion coefficients were evaluated by dynamic vapor sorption analysis. The self-assembly process through intermolecular H-bonding, the high hydrophilicity, the mechanical performance, the hydrolytic stability in simulated biological media, the biocompatibility with normal human dermal fibroblast (NHDF) cells, the mucoadhesivity and antimicrobial activity on selected microorganism species (S. Aureus and C. albicans) of the allantoin-based gels recommend them as promising scaffold alternatives in regenerative medicine.

Synthesis of Bioactive Materials by In Situ One-Step Direct Loading of Syzygium aromaticum Essential Oil into Chitosan-Based Hydrogels

Hydrogel conjugates based on chitosan and an essential oil were synthetized by an ultrasound-assisted emulsification approach. Rheology studies revealed a gel-type structure with pronounced compactness and flexibility while SEM showed the formation of a two-level ordered network with highly interconnected pores. The swelling studies indicated a pH-dependent behavior with a significant overshooting effect. The synergistic effects of the components in clove essential oil led to a strong antioxidant character and an enhanced antimicrobial activity of the conjugate hydrogels. The bioactivity was maintained for 6 months, despite a slight decrease in the antimicrobial effect. Hydrogel conjugates were found to be very stable even after two months immersed in acidic solutions that would otherwise dissolve the chitosan matrix. Ultrasound emulsification was proved as an efficient one-step loading method of hydrophobic clove essential oil into hydrophilic chitosan matrix. It was found that clove oil and its components have a double role. Besides providing bioactivity, they also behave as gelation-inducing agents, acting as an alternative to the classical chemical cross-linkers to ensure the good physical and chemical stabilization of chitosan.

Stabilization Techniques of Essential Oils by Incorporation into Biodegradable Polymeric Materials for Food Packaging

Human health, food spoilage, and plastic waste, which are three great topical concerns, intersect in the field of food packaging. This has created a trend to replace synthetic food preservatives with natural ones, to produce bio-functional food packaging, and to shift towards biodegradable polymeric materials. Among the natural bioactive agents, essential oils are gaining more and more attention in food packaging applications due to their various benefits and fewer side-effects. However, their volatility, hydrophobicity, and strong odor and taste limit the direct use in food-related applications. Fixation into polymeric matrices represents a suitable strategy to promote the benefits and reduce the drawbacks. Emulsification and electrospinning are largely used techniques for protection and stabilization of essential oils. These methods offer various advantages in active food packaging, such as controlled release, ensuring long-term performance, decreased amounts of active agents that gain enhanced functionality through increased available surface area in contact with food, and versatility in packaging design. This review focuses on creating correlations between the use of essential oils as natural additives, stabilization methods, and biodegradable polymeric matrices or substrates in developing bioactive food packaging materials. Documentation was performed via the Scopus, ScienceDirect, and PubMed databases, selecting the publications after the year 2018. Particular attention was given to the publications that tested materials on food/food pathogens to evaluate their performances in retarding spoilage. Research gaps were also identified on the topic, materials being tested mainly at short time after preparation without considering the long-term storage that usually occurs in actual practice between production and use, and insufficient research related to upscaling.

Bioactive Electrospun Fibers of Poly(ε-Caprolactone) Incorporating α-Tocopherol for Food Packaging Applications

Antioxidant activity is an important feature for food contact materials such as packaging, aiming to preserve freshness and retard food spoilage. Common bioactive agents are highly susceptible to various forms of degradation; therefore, protection is required to maintain functionality and bioavailability. Poly(ε-caprolactone) (PCL), a biodegradable GRAS labeled polymer, was used in this study for encapsulation of α-tocopherol antioxidant, a major component of vitamin E, in the form of electrospun fibers. Rheological properties of the fiber forming solutions, which determine the electrospinning behavior, were correlated with the properties of electrospun fibers, e.g., morphology and surface properties. Interactions through hydrogen bonds were evidenced between the two components. These have strong effect on structuration of macromolecular chains, especially at low α-tocopherol amounts, decreasing viscosity and elastic modulus. Intra-molecular interactions in PCL strengthen at high α-tocopherol amounts due to decreased solvation, allowing good structural recovery after cease of mechanical stress. Morphologically homogeneous electrospun fibers were obtained, with ~6 μm average diameter. The obtained fibers were highly hydrophobic, with fast release in 95% ethanol as alternative simulant for fatty foods. This induced good in vitro antioxidant activity and significant in vivo reduction of microbial growth on cheese, as determined by respirometry. Therefore, the electrospun fibers from PCL entrapping α-tocopherol as bioactive agent showed potential use in food packaging materials.

Towards a Bioactive Food Packaging: Poly(Lactic Acid) Surface Functionalized by Chitosan Coating Embedding Clove and Argan Oils

Here we introduce a new method aiming the immobilization of bioactive principles onto polymeric substrates, combining a surface activation and emulsion entrapment approach. Natural products with antimicrobial/antioxidant properties (essential oil from Syzygium aromaticum-clove and vegetal oil from Argania spinosa L-argan) were stabilized in emulsions with chitosan, a natural biodegradable polymer that has antimicrobial activity. The emulsions were laid on poly(lactic acid) (PLA), a synthetic biodegradable plastic from renewable resources, which was previously activated by plasma treatment. Bioactive materials were obtained, with low permeability for oxygen, high radical scavenging activity and strong inhibition of growth for Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli bacteria. Clove oil was better dispersed in a more stable emulsion (no separation after six months) compared with argan oil. This leads to a compact and finely structured coating, with better overall properties. While both clove and argan oils are highly hydrophobic, the coatings showed increased hydrophilicity, especially for argan, due to preferential interactions with different functional groups in chitosan. The PLA films coated with oil-loaded chitosan showed promising results in retarding the food spoilage of meat, and especially cheese. Argan, and in particular, clove oil offered good UV protection, suitable for sterilization purposes. Therefore, using the emulsion stabilization of bioactive principles and immobilization onto plasma activated polymeric surfaces we obtained a bioactive material that combines the physical properties and the biodegradability of PLA with the antibacterial activity of chitosan and the antioxidant function of vegetal oils. This prevents microbial growth and food oxidation and could open new perspectives in the field of food packaging materials.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

New trends in biomedical applications of the hybrid polymeric hydrogels, obtained by combining natural polymers with synthetic ones, have been reviewed. Homopolysaccharides, heteropolysaccharides, as well as polypeptides, proteins and nucleic acids, are presented from the point of view of their ability to form hydrogels with synthetic polymers, the preparation procedures for polymeric organic hybrid hydrogels, general physico-chemical properties and main biomedical applications (i.e., tissue engineering, wound dressing, drug delivery, etc.).

Structural and sorption properties of bio-nanocomposite films based on κ-carrageenan and cellulose nanocrystals

There is an increased interest on changing the synthetic based materials to biodegradable ones, especially with natural polymers, polysaccharides or proteins. In this research we prepared bio-nanocomposite formulations with different component concentrations and investigated their structural features, with focus on the interactions, sorption properties, and how the combination between them influences these properties. By infrared spectroscopy, principal component analysis (PCA) and two-dimensional correlation spectroscopy (2DCOS) was identified that in the blending process are involved the -SO₄ and C(4)-O-S groups of β-d-galactose, CO groups, (O=S=O) of carrageenan and -OH and CO groups from CNCs. The water uptake and water sorption properties decrease with increasing the CNCs content in the formulations from about 15% for κ to 10% for κC15 and from about 128% for κ to 115% for κC15, respectively. The increase of the CNCs content induced an increase of the water contact angle from 47° for κ to 90° for κC15, indicating once again the involvement of the free hydroxyl groups in the hydrogen bonded interactions.

Chitosan-Based Bionanocomposite Films Prepared by Emulsion Technique for Food Preservation

Biopolymer nanocomposite films were prepared by casting film-forming emulsions based on chitosan/Tween 80/rosehip seed oil and dispersed montmorillonite nanoclay C30B. The effect of composition on structural, morphological characteristics and, mechanical, barrier, antimicrobial and antioxidant properties was studied. The presence of rosehip seed oil in chitosan films led to the formation of flexible films with improved mechanical, gas and water vapour barrier properties and antioxidant activity. The in vitro antibacterial tests against Escherichia coli, Salmonella typhymurium, and Bacillus cereus showed that the chitosan/rosehip seed oil/montmorillonite nanoclay composites effectively inhibited all the three microorganisms.

Evaluation of the Rosemary Extract Effect on the Properties of Polylactic Acid-Based Materials

New multifunctional materials containing additives derived from natural resources as powdered rosemary ethanolic extract were obtained by melt mixing and processed in good conditions without degradation and loss of additives. Incorporation of powdered rosemary ethanolic extract (R) into poly(lactic acid) (PLA) improved elongation at break, rheological properties, antibacterial and antioxidant activities, in addition to the biocompatibility. The good accordance between results of the chemiluminescence method and radical scavenging activity determination by chemical method evidenced the increased thermoxidative stability of the PLA biocomposites with respect to neat PLA, with R acting as an antioxidant. PLA/R biocomposites also showed low permeability to gases and migration rates of the bioactive compounds and could be considered as high-performance materials for food packaging. In vitro biocompatibility based on the determination of surface properties demonstrated a good hydrophilicity, better spreading and division of fibroblasts, and increased platelet cohesion. The implantation of PLA/R pellets, was proven to possess a good in vivo biocompatibility, and resulted in similar changes in blood parameters and biochemical responses with the control group, suggesting that these PLA-based materials demonstrate very desirable properties as potential biomaterials, useful in human medicine for tissue engineering, wound management, orthopedic devices, scaffolds, drug delivery systems, etc. Therefore, PLA/R-based materials show promising properties for applications both in food packaging and as bioactive biomaterials.

Complex poly(lactic acid)-based biomaterial for urinary catheters: II. Biocompatibility

The present paper is focused on the surface and bulk characterization of poly(lactic acid) (PLA)-based composites that contain hydrolyzed collagen as a biological polymer, silver nanoparticles and vitamin E and epoxidized soybean oil as a plasticizer. The bionanocomposites were obtained by melt processing and evaluated for structural and surface characteristics, biocompatibility, functional properties such as antimicrobial and antioxidant activity and hydrolytic degradation behavior. It has been established that the optimal composition to impart functional properties to the PLA matrix is a formulation containing 15% epoxidized soybean oil, 15% hydrolyzed collagen, 5% Pluronic, 5% vitamin E and 0·3% silver nanoparticles. This bionanocomposite inhibits the growth of both Gram-positive bacteria, Escherichia coli and Salmonella typhimurium, and Gram-negative bacteria, Listeria monocytogenes, and reaches 100% radical-scavenging activity. The PLA-based biomaterials obtained in this study are stable in biological media in the short and medium terms and therefore are recommended as multifunctional biomaterials for the manufacture of medical devices, such as urinary catheters.

Complex poly(lactic acid)-based biomaterial for urinary catheters: I. Influence of AgNP on properties

The present study focused on the development of biocompatible antimicrobial/antioxidant biodegradable bionanocomposite renewable resources based on poly(lactic acid) (PLA) plasticised with epoxidised soybean oil. To the main PLA matrix hydrolysed collagen (HC) (to enhance biocompatibility), vitamin E (as antioxidant agent) and silver (Ag) nanoparticles (NPs) (for imparting antimicrobial properties for medical applications and also for active packaging) were incorporated. The blends were produced by using the classical technological flow of melt processing. The presence of the additives in the PLA matrix improved the processability and flexibility and slightly decreased the thermal properties. The specific interactions of silver NPs with the other components of nanocomposites, mainly with HC protein and vitamin E (by ionic and other types of secondary bonds), led to a better HC and vitamin E dispersion in the samples with a higher silver content (1·5%), which further caused the enhancement of the mechanical properties for high silver NP concentration. Therefore, the silver NPs were successfully embedded into the polymer matrix. The aim of this research was to improve the flexibility, biocompatibility and functionality of PLA and to obtain bionanocomposites destined for medical applications such as catheters. This first part of research deals with mechanical and thermal characterisation correlated with morphological features.

Lactoferrin-Immobilized Surfaces onto Functionalized PLA Assisted by the Gamma-Rays and Nitrogen Plasma to Create Materials with Multifunctional Properties

Both cold nitrogen radiofrequency plasma and gamma irradiation have been applied to activate and functionalize the polylactic acid (PLA) surface and the subsequent lactoferrin immobilization. Modified films were comparatively characterized with respect to the procedure of activation and also with unmodified sample by water contact angle measurements, mass loss, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), and chemiluminescence measurements. All modified samples exhibit enhanced surface properties mainly those concerning biocompatibility, antimicrobial, and antioxidant properties, and furthermore, they are biodegradable and environmentally friendly. Lactoferrin deposited layer by covalent coupling using carbodiimide chemistry showed a good stability. It was found that the lactoferrin-modified PLA materials present significantly increased oxidative stability. Gamma-irradiated samples and lactoferrin-functionalized samples show higher antioxidant, antimicrobial, and cell proliferation activity than plasma-activated and lactoferrin-functionalized ones. The multifunctional materials thus obtained could find application as biomaterials or as bioactive packaging films.

Plasma-activated fibrinogen coatings onto poly(vinylidene fluoride) surface for improving biocompatibility with tissues

CO2, N2, and N2/H2 radiofrequency plasma exposure was used for functionalization of poly(vinylidene fluoride) surface aiming the fibrinogen immobilization. Fibrinogen was immobilized onto poly(vinylidene fluoride) surface using both simple plasma activation and covalent coupling. The modified surfaces have been characterized by X-ray photoelectron spectroscopy, attenuated total reflectance–Fourier transform infrared spectroscopy, near infrared–chemical imaging, atomic force microscopy, and wettability measurements, and the obtained materials were tested as supports for fibroblast cell cultures. The plasma type and the immobilization procedure have influenced the fibrinogen attachment onto the poly(vinylidene fluoride) surface, which was achieved mainly through amide bonds when using coupling agents. Covalent immobilization of fibrinogen onto poly(vinylidene fluoride) surface leads to a more stable protein-modified polymer surface. Non-cytotoxic plasma-based coating technology has the ability to covalently immobilize bioactive molecules for surface modification of some biomaterials that mainly could be achieved by the immobilization of proteins such as fibrinogen that triggers desirable cellular responses. The fibrinogen-modified poly(vinylidene fluoride) materials showed increased cell viability of fibroblasts. Cell viability was enhanced by plasma-activated fibrinogen coatings onto poly(vinylidene fluoride) surface, this being more significant if coating was linked further by a coupling reaction. Hence, they could be good candidates for biomedical applications.