Recent trends in the application of protein electrospun fibers for loading food bioactive compounds.

Electrospun fibers (EFs) have emerged as promising one-dimensional materials for a myriad of research/commercial applications due to their outstanding structural and physicochemical features. Polymers of either synthetic or natural precursors are applied to design EFs as carriers for bioactive compounds. For engineering food systems, it is crucial to exploit polymers characterized by non-toxicity, non-immunogenicity, biocompatibility, slow/controllable biodegradability, and structural integrity. The unique attributes of protein-based biomaterials endow a wide diversity of desirable features to EFs for meeting the requirements of advanced food/biomedical applications. In this review paper, after an overview on electrospinning, different protein materials (plant- and animal-based) as biodegradable/biocompatible building blocks for designing EFs will be highlighted. The potential application of protein-based EFs in loading bioactive compounds with the intention to inspire interests in both academia and industry will be summarized. This review concludes with a discussion of prevailing challenges in using protein EFs for the bioactive vehicle development.

Metal nanoparticles and carbohydrate polymers team up to improve biomedical outcomes.

The convergence of carbohydrate polymers and metal nanoparticles (MNPs) holds great promise for biomedical applications. Researchers aim to exploit the capability of carbohydrate matrices to modulate the physicochemical properties of MNPs, promote their therapeutic efficiency, improve targeted drug delivery, and enhance their biocompatibility. Therefore, understanding various attributes of both carbohydrates and MNPs is the key to harnessing them for biomedical applications. The many distinct types of carbohydrate-MNP systems confer unique capabilities for drug delivery, wound healing, tissue engineering, cancer treatment, and even food packaging. Here, we introduce distinct physicochemical/biological properties of carbohydrates and MNPs, and discuss their potentials and shortcomings (alone and in combination) for biomedical applications. We then offer an overview on carbohydrate-MNP systems and how they can be utilized to improve biomedical outcomes. Last but not least, future perspectives toward the application of such systems are highlighted.

Dialdehyde carbohydrates - Advanced functional materials for biomedical applications.

Dialdehyde carbohydrates (DCs) have found applications in a wide range of biomedical field due to their great versatility, biocompatibility/biodegradability, biological properties, and controllable chemical/physical characteristics. The presence of dialdehyde groups in carbohydrate structure allows cross-linking of DCs to form versatile architectures serving as interesting matrices for biomedical applications (e.g., drug delivery, tissue engineering, and regenerative medicine). Recently, DCs have noticeably contributed to the development of diverse physical forms of advanced functional biomaterials i.e., bulk architectures (hydrogels, films/coatings, or scaffolds) and nano/-micro formulations. We underline here the current scientific knowledge on DCs, and demonstrate their potential and newly developed biomedical applications. Specifically, an update on the synthesis approach and functional/bioactive attributes is provided, and the selected in vitro/in vivo studies are reviewed comprehensively as examples of the latest progress in the field. Moreover, safety concerns, challenges, and perspectives towards the application of DCs are deliberated.

Encapsulation of antioxidant beta-carotene by cyclodextrin complex electrospun nanofibers: Solubilization and stabilization of beta-carotene by cyclodextrins.

Carotenoids act as effective antioxidant defense systems in humans as they scavenge molecular oxygen and peroxyl radicals. However, their poor water solubility and being susceptible to degradation driven by light and oxygen hinder their bioactivity, therefore, they should be stabilized by host matrices against oxidation. Here, ß-carotene was encapsulated in electrospun cyclodextrin (CD) nanofibers to increase its water-solubility and photostability to enhance its antioxidant bioactivity. ß-carotene/CD complex aqueous solutions were electrospun into nanofibers. The bead-free morphology of the ß-carotene/CD nanofibers was confirmed by SEM. The formation of ß-carotene/CD complexes was explored through computational modeling and experimentally by FTIR, XRD and solubility tests. The antioxidant activity of the fibers exposed to UV irradiation was demonstrated via a free radical scavenger assay, where ß-carotene/CD nanofibers revealed protection against UV radiation. Overall, this work reports the water-borne electrospinning of antioxidant ß-carotene/CD inclusion complex nanofibers, which stabilize the encapsulated ß-carotene against UV-mediated oxidation.

Rapid Sublingual Delivery of Piroxicam from Electrospun Cyclodextrin Inclusion Complex Nanofibers.

Piroxicam (Px) is a nonsteroidal anti-inflammatory drug (NSAID) used for the treatment of osteoarthritis and rheumatoid arthritis. It is administered orally; however, its poor water solubility causes low loading to the nonconventional drug delivery systems (DDSs), such as electrospun fibers. Furthermore, the rapid dissolution of DDS and fast release of the embedded drugs are crucial for oral delivery of drugs to patients who are unconscious or suffering from dysphagia. In this regard, this study reports the development of rapidly dissolving cyclodextrin (CD)-based inclusion complex (IC) nanofibers by waterborne electrospinning for fast oral delivery of Px. Scanning electron microscopy analysis revealed the formation of bead-free fibers with a mean diameter range of 170-500 nm at various concentrations of Px; increasing the Px loading decreased the fiber diameter. The formation of IC was demonstrated by X-ray diffraction (XRD) analysis by the disappearance of crystalline peaks of Px. Likewise, differential scanning calorimetry (DSC) analysis showed the disappearance of the melting peak of the embedded Px due to IC formation. Both Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) confirmed the presence of Px within the fibers. 1H NMR experiments demonstrated Px preservation in the fibers after six months. Px-loaded nanofibers were employed for sublingual drug delivery. To mimic the environment of the mouth, the nanofibers were treated with artificial saliva, which revealed the instant dissolution of the nanofibers. Furthermore, dissolution experiments were performed on the tissues wetted with artificial saliva, where the dissolution of the fibers could be extended to a few seconds, demonstrating the suitability of the materials for sublingual oral drug delivery. Overall, this paper, for the first time, reports the rapid oral delivery of Px from polymer-free CD fibers produced by waterborne electrospinning without the requirement of any carrier polymer and toxic solvent.

Advances in the development of cyclodextrin-based nanogels/microgels for biomedical applications: Drug delivery and beyond.

Nanogels/microgels are swollen cross-linked polymer networks with tunable physicochemical properties and are commonly employed for the effective delivery of hydrophilic drugs. By structural engineering, they can be adapted for the delivery of hydrophobic drugs. Likewise, the use of cyclodextrins (CDs) as pharmaceutical excipients in nanogels drastically boosts the loading capacity of lipophilic drugs while enhancing their stability, bioavailability, and permeability owing to their capability of hosting drugs in their somewhat lipophilic cavity. Here, the synthesis and biomedical applications of CD-based nanogels/microgels were compiled with regard to the CD's role in nanogel synthesis. Even though most applications focused on using CD molecules as functional motifs to carry drugs and construct nanogels for biomedical applications, others used CDs in engineering nanogels to benefit from their supramolecular complexation ability. The applications of CD-based nanogels for drug-mediated cancer/tumor therapy were also discussed. Finally, the review points to the challenges/horizons to boost their biomedical applications.

Removal of polycyclic aromatic hydrocarbons (PAHs) from water through degradable polycaprolactone electrospun membrane.

Polycyclic aromatic hydrocarbons (PAHs) are common and persistent environmental pollutants produced during the incomplete combustion of fuels. They are known for their carcinogenic and mutagenic properties. Thus, their removal from water bodies is highly crucial and has become a critical issue globally. As a solution, here an electrospun polycaprolactone (PCL) membrane with a mean fiber diameter of 2.74 ± 1.3 µm was produced by electrospinning. Water contact angle (WCA) analysis confirmed the hydrophobic nature of the PCL membrane with a WCA of 124°, which remained stable over time. Differential scanning calorimetry analysis (DSC) revealed the semicrystalline nature of the membrane with the respective melting temperature (Tm) of 61.5 °C and crystallization temperature (Tc) of 29.6 °C. X-ray diffraction (XRD) analysis demonstrated that the crystalline structure of the PCL membrane could be preserved after electrospinning. Scanning electron microscopy analysis revealed that the membrane could be stretched without any rupture. The PCL membrane was used to scavenge PAHs (i.e. phenanthrene and anthracene) from water; the membrane could reach equilibrium capacity in a few hours, demonstrating the rapid removal of PAHs from water. The adsorption capacities for anthracene and phenanthrene were found to be 173 ± 17 and 560 ± 51 µg/g, respectively. The adsorption data fitted well with the pseudo-first-order kinetics model for both PAH molecules. The sorption could be attributed to hydrophobic adsorption, which allowed using the PCL membrane repeatedly with ethanol exposure to get rid of the adsorbed PAHs from the membrane's surface. The partial degradation of the fibrous membrane in water was observed due to their hydrolysis-induced bulk erosion. However, the degradation was slow for the membrane kept in the air for 3 months. Overall, the PCL membrane with inherent biocompatibility, biodegradability, and good PAH sorption performance is a promising material for water depollution from toxic PAH compounds.

Nanofibrous membranes comprising intrinsically microporous polyimides with embedded metal-organic frameworks for capturing volatile organic compounds.

Here, we report the fabrication of nanofibrous air-filtration membranes of intrinsically microporous polyimide with metal-organic frameworks (MOFs). The membranes successfully captured VOCs from air. Two polyimides with surface areas up to 500 m2 g-1 were synthesized, and the impact of the porosity on the sorption kinetics and capacity of the nanofibers were investigated. Two Zr-based MOFs, namely pristine UiO-66 (1071 m2 g-1) and defective UiO-66 (1582 m2 g-1), were embedded into the nanofibers to produce nanocomposite materials. The nanofibers could remove polar formaldehyde and non-polar toluene, xylene, and mesitylene from air. The highest sorption capacity with 214 mg g-1 was observed for xylene, followed by mesitylene (201 mg g-1), toluene (142 mg g-1), and formaldehyde (124 mg g-1). The incorporation of MOFs drastically improved the sorption performance of the fibers produced from low-surface-area polyimide. Time-dependent sorption tests revealed the rapid sequestration of air pollutants owing to the intrinsic porosity of the polyimides and the MOF fillers. The porosity allowed the rapid diffusion of pollutants into the inner fiber matrix. The molecular level interactions between VOCs and polymer/MOFs were clarified by molecular modeling studies. The practicality of material fabrication and the applicability of the material were assessed through the modification of industrial N95 dust masks. To the best of our knowledge, this is the first successful demonstration of the synergistic combination of intrinsically microporous polyimides and MOFs in the form of electrospun nanofibrous membranes and their application for VOC removal.

Fast-dissolving antibacterial nanofibers of cyclodextrin/antibiotic inclusion complexes for oral drug delivery.

HYPOTHESIS: The widespread use of antibacterial electrospun nanofibers is mostly restricted due to their low loading capacity to carry antibiotics and the need to use toxic organic solvents to boost the antibiotic loading capacity. Nanofibers based on natural excipients, such as cyclodextrin (CD)-based nanofibers, can carry larger amounts of antibiotics while achieving better stability via inclusion complexation. EXPERIMENTS: Nanofibers were produced by electrospinning and analyzed by electron microscopy to investigate the morphology of fibers. The formation of inclusion-complexation was analyzed by 1H NMR, FTIR, and XRD. Thermal analysis of the fibers was done using TGA. Ab initio modeling studies were done to calculate the complexation energies of antibiotics with CD. A disk-diffusion assay was used to test the antibacterial activity of the fibers. FINDINGS: Bead-free antibacterial nanofibers with mean diameters between 340 and 550 nm were produced. The formation of inclusion complexes (IC) between the CD and the antibiotics was confirmed by FTIR and 1H NMR, which was further verified by the disappearance of the crystalline peaks of antibiotics as determined by XRD analysis. Thermal analysis of the nanofibers revealed that the formulations showed good antibiotic encapsulation (45-90%). Ab initio simulations revealed that gentamicin had the highest complexation energy, followed by kanamycin, chloramphenicol, and ampicillin. The antibacterial nanofibers rapidly dissolved in water and artificial saliva, successfully releasing the CD antibiotic complexes. The nanofibers showed high antibacterial activity against Gram-negative Escherichia coli.

Antioxidant, antibacterial and antifungal electrospun nanofibers for food packaging applications.

Food packaging is a multidisciplinary area that encompasses food science and engineering, microbiology, as well as chemistry, and ignited tremendous interest in maintaining the freshness and quality of foods and their raw materials from oxidation and microbial spoilage. With the advances in the packaging industry, they could be engineered as easy-to-open, resealable, active, as well as intelligent with the incorporation of sensory elements while offering desired barrier properties against oxygen and water vapor. In this regard, the use of the electrospinning approach allows producing nanofibrous packaging materials with large surface-to-volume ratios and enables the higher loading of active agents into packaging materials. Electrospun packaging materials have been produced from various polymers (i.e., synthetic and natural) and their (nano)composites, and were mainly exploited for the encapsulation of active agents for their use as active food packaging materials. The electrospinning process was also used for the deposition of electrospun fibers on films to enhance their performance (e.g., as reinforcement material, or to enhance barrier properties). They could be even engineered to provide nutraceuticals to food, or antioxidant, antimicrobial or antifungal protection to the packaged food. In this article, first, introductory descriptions of food packaging, barrier properties, and electrospinning are given. Afterward, active and intelligent food packaging materials are briefly discussed, and the use of electrospinning for the fabrication of active food packaging materials is elaborated. Particular interest has been given to the polymer-type used in the production of electrospun fibers and active properties of the resultant packaging materials (e.g., antioxidant, antibacterial, antifungal). Finally, this review paper concludes with a summary and future outlook towards the development of electrospun food packaging materials.

Efficient Removal of Polycyclic Aromatic Hydrocarbons and Heavy Metals from Water by Electrospun Nanofibrous Polycyclodextrin Membranes.

Here, a highly efficient membrane based on electrospun polycyclodextrin (poly-CD) nanofibers was prepared and exploited for the scavenging of various polycyclic aromatic hydrocarbons (PAHs) and heavy metals from water. The poly-CD nanofibers were produced by the electrospinning of CD molecules in the presence of a cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid), followed by heat treatment to obtain an insoluble poly-CD nanofibrous membrane. The membrane was used for the removal of several PAH compounds (i.e., acenaphthene, fluorene, fluoranthene, phenanthrene, and pyrene) and heavy metals (i.e., Pb2+, Ni2+, Mn2+, Cd2+, Zn2+, and Cu2+) from water over time. Experiments were made on the batch sorption of PAHs and heavy metals from contaminated water to explore the binding affinity of PAHs and heavy metals to the poly-CD membrane. The equilibrium sorption capacity (q e) of the poly-CD nanofibrous membrane was found to be 0.43 ± 0.045 mg/g for PAHs and 4.54 ± 0.063 mg/g for heavy metals, and the sorption kinetics fitted well with the pseudo-second-order model for both types of pollutants. The membrane could be recycled after treatment with acetonitrile or a 2% nitric acid solution and reused up to four times with similar performance. Further, dead-end filtration experiments showed that the PAH removal efficiencies were as high as 92.6 ± 1.6 and 89.9 ± 4.8% in 40 s for the solutions of 400 and 600 µg/L PAHs, respectively. On the other hand, the removal efficiencies for heavy metals during the filtration were 94.3 ± 5.3 and 72.4 ± 23.4% for 10 and 50 mg/L solutions, respectively, suggesting rapid and efficient filtration of heavy metals and PAHs by the nanofibrous poly-CD membrane.

RNA-mediated, green synthesis of palladium nanodendrites for catalytic reduction of nitroarenes.

Palladium (Pd)-catalyzed reactions mostly show structure sensitivity: i.e., the selectivity and activity of the reactions are highly dependent on the arrangement of Pd atoms. In this regard, branched Pd nanoparticles show enhanced catalytic performance owing to the presence of low coordinated Pd atoms. In this paper, a novel solution-phase synthesis of flower-like Pd nanodendrites using ribonucleic acid (RNA) as a capping agent and ascorbic acid as a reducing agent was described. On the other hand, the co-use of polyvinylpyrrolidone (PVP) and potassium bromide (KBr) instead of RNA at the same synthesis conditions led to cuboid nanoparticles, while the sole use of ascorbic acid resulted in faceted nanoparticles. The formation of nanodendritic morphology was attributed to the RNA-assisted growth through particle attachment. This scenario was supported by TEM analysis that demonstrated the aggregation of small particles to form larger nanoparticles at the onset of the reaction. The shape and size of the nanoparticles could be readily tuned by the RNA content used. XPS confirmed the formation of metallic Pd nanoparticles. The presence of crystalline planes of {1 1 1}, {2 0 0}, {2 2 0}, {3 1 1} and {2 2 2} was demonstrated by XRD and SAED analyses. The Pd nanodendrites were used for the reduction of p-nitrophenol (PNP) and 2,4,6-trinitrotoluene (TNT), and reduction rate constants (k) were calculated as 1.078 min-1 (normalized rate constant, knor = 59.66 mmol-1 s-1) for PNP and 0.3181 min-1 (knor = 17.6 mmol-1 s-1) for TNT with the corresponding turnover frequencies (TOFs) as 16.06 and 40.80 h-1, respectively.

One-step green synthesis of antibacterial silver nanoparticles embedded in electrospun cyclodextrin nanofibers.

Antibacterial electrospun nanofibers based on cyclodextrin (CD) and silver nanoparticles (Ag-NPs) were produced by solution electrospinning from aqueous and DMF solutions using different Ag contents. CD molecules acted as the reducing agent and catalyzed the formation of Ag-NPs. The nanofibers with smaller diameters were observed for the fibers generated from DMF solutions than those produced from aqueous solutions. TEM and STEM analyses revealed the Ag-NPs (∼2-5 nm depending on solvent-type and Ag loading) in nanofibers, while FTIR and surface enhanced Raman scattering (SERS) analyses showed the apparent frequency shift of OH stretching band and the enhancement of Raman bands of CD molecules with the incorporation of the Ag-NPs. The polycrystalline structure of the Ag-NPs was shown by XRD and SAED analyses over {111}, {200}, {220} and {311} planes. The nanofibers showed significant inhibition against the growth of Escherichia coli and Staphylococcus aureus owing to the antibacterial activity of the Ag-NPs.

Nanocomposite Bioinks Based on Agarose and 2D Nanosilicates with Tunable Flow Properties and Bioactivity for 3D Bioprinting.

Three-dimensional (3D) bioprinting enables the controlled fabrication of complex constructs for tissue engineering applications and has been actively explored in recent years. However, its progress has been limited by the existing difficulties in the development of bioinks with suitable biocompatibility and mechanical properties and at the same time adaptability to the process. Herein, we describe the engineering of a nanocomposite agarose bioink with tailored properties using 2D nanosilicate additives. The suitability of agarose for 3D bioprinting has been debated due to its bioinert nature and compatibility with extrusion-based bioprinting. Nanosilicates were used to tailor the flow behavior of agarose solutions, and detailed rheological characterization of different bioink formulations was performed to elucidate the effect of nanosilicates on the flow behavior and gelation of agarose bioinks. The proper selection of nanosilicate concentration resulted in extrusion 3D printed structures with high shape fidelity and structural integrity. Moreover, the influence of addition of nanosilicates on the bioactivity of agarose was studied, and nanocomposite bioinks showed significant improvement in metabolic activity of encapsulated cells. The bioactivity of the nanocomposite bioinks was also evaluated through a cell spreading assay; the charged surfaces of nanosilicates resulted in full spreading and elongation of fibroblasts, and the extent of change in morphology of cells was found to be directly correlated with the nanosilicate concentration. Our findings suggested that engineered agarose-nanosilicate bioinks can be exploited as a new generation of hydrogel bioinks for extrusion 3D bioprinting with tunable flow properties and bioactivity.

Atomic layer deposition of palladium nanoparticles on a functional electrospun poly-cyclodextrin nanoweb as a flexible and reusable heterogeneous nanocatalyst for the reduction of nitroaromatic compounds.

We here show a rational approach for the fabrication of a flexible, insoluble catalytic electrospun nanoweb of cross-linked cyclodextrin (CD) for the reduction of nitroaromatics. CD nanofibers were produced by electrospinning an aqueous HP-ß-CD solution containing a multifunctional cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid, BTCA) and were subsequently cross-linked by heat treatment, which led to an insoluble electrospun poly-CD nanoweb. The poly-CD nanoweb was decorated with Pd nanoparticles (Pd-NPs) by atomic layer deposition (ALD) technique over 20 cycles to give rise to a catalytic electrospun nanoweb (i.e., Pd@poly-CD). The formation of the Pd-NPs on the poly-CD nanofiber surface was clearly evidenced by TEM and STEM imaging, which displayed the homogeneously distributed Pd-NPs with a mean size of 4.34 nm. ICP-MS analysis revealed that the Pd content on the Pd@poly-CD nanoweb was 0.039 mg per mg of nanoweb. The catalytic performance of the Pd@poly-CD nanoweb was tested for the reduction of a nitroaromatic compound (i.e., 4-nitrophenol (4-NP)), and high catalytic performance of the Pd@poly-CD nanoweb was observed with a corresponding TOF value of 0.0316 min-1. XPS was used to explore the oxidation state of Pd atoms before and after the catalytic reduction of 4-NP, and no significant change was observed after catalytic reactions. In brief, the Pd@poly-CD nanoweb having handy, flexible, structural stability and reusability can be effectively used in environmental applications as a heterogeneous nanocatalyst for the reduction of toxic nitroaromatics.

Electrospinning of Cyclodextrin Functional Nanofibers for Drug Delivery Applications.

Electrospun nanofibers have sparked tremendous attention in drug delivery since they can offer high specific surface area, tailored release of drugs, controlled surface chemistry for preferred protein adsorption, and tunable porosity. Several functional motifs were incorporated into electrospun nanofibers to greatly expand their drug loading capacity or to provide the sustained release of the embedded drug molecules. In this regard, cyclodextrins (CyD) are considered as ideal drug carrier molecules as they are natural, edible, and biocompatible compounds with a truncated cone-shape with a relatively hydrophobic cavity interior for complexation with hydrophobic drugs and a hydrophilic exterior to increase the water-solubility of drugs. Further, the formation of CyD-drug inclusion complexes can protect drug molecules from physiological degradation, or elimination and thus increases the stability and bioavailability of drugs, of which the release takes place with time, accompanied by fiber degradation. In this review, we summarize studies related to CyD-functional electrospun nanofibers for drug delivery applications. The review begins with an introductory description of electrospinning; the structure, properties, and toxicology of CyD; and CyD-drug complexation. Thereafter, the release of various drug molecules from CyD-functional electrospun nanofibers is provided in subsequent sections. The review concludes with a summary and outlook on material strategies.

Nanosilicate embedded agarose hydrogels with improved bioactivity.

This paper reports the synthesis of nanocomposite agarose hydrogels with improved bioactivity with the incorporation of anisotropic 2D nanosilicates (Laponite) to promote cell binding, growth and proliferation. Rheological measurements showed that the incorporation of nanosilicates slightly increased the gelation temperature (Tgel). The use of higher nanosilicate content at the constant agarose concentration improved the mechanical properties of the gels. Due to the non-swelling nature of agarose, the addition of nanosilicates did not result in any remarkable change in the swelling properties of the agarose gels, while collapsed agarose nanofibers were observed with the incorporation of nanosilicates. EDX analysis confirmed the presence of the embedded nanosilicates in the gel matrix. The existence of physical interactions between nanosilicate and agarose was demonstrated by FTIR over the shifting of SiO stretching band to a lower frequency. The encapsulated NIH/3T3 fibroblast cells showed enhanced proliferation and spreading in the presence of nanosilicates.

Cyclodextrin-assisted synthesis of tailored mesoporous silica nanoparticles.

Mesoporous silica nanoparticles (MSNs) have sparked considerable interest in drug/gene delivery, catalysis, adsorption, separation, sensing, antireflection coatings and bioimaging because of their tunable structural properties. The shape, size and pore structure of MSNs are greatly influenced by the type of additives used, e.g., solvent and pore-templating agent. Here, we studied the influence of cyclodextrin (CD) molecules on the formation of MSNs. The nanoparticles over 100 nm in diameter were synthesized by surfactant-templated, hydrolysis-polycondensation reactions in the presence of pristine CD (ß-CD) or hydroxypropyl-functionalized CDs (HP-γ-CD and HP-ß-CD). Depending on the formulation conditions, differently shaped MSNs, such as bean-like, spherical, ellipsoid, aggregate and faceted were generated. The morphology and size of MSNs varied with the CD-type used. Generally, spherical particles were obtained with ß-CD, while a faceted morphology was observed for the particles synthesized using HP-CDs. The particle size could be tuned by adjusting the amount of CD used; increasing the CD concentration led to larger particles. MSNs synthesized in the presence of ß-CD displayed a smaller particle size than those produced with HP-functional CDs. FTIR, TGA and solid-state 13C NMR demonstrated the adsorption of CDs on the particle surfaces. The proposed concept allows for the synthesis of silica nanoparticles with control over particle shape and size by adjusting the concentration of additives in a simple, one-pot reaction system for a wide range of applications.

Influence of Hydrogen-Bonding Additives on Electrospinning of Cyclodextrin Nanofibers.

The electrospinning of highly concentrated solutions of cyclodextrin (CD) leads to bead-free nanofibers without the need of a polymeric carrier. The occurrence of numerous hydrogen bonds among CD molecules is the main driving force for their electrospinning, and hence, additives with hydrogen-bonding potential can disturb the aggregation of CD molecules and affect their electrospinning. In this study, we systematically investigated the influence of five different hydrogen-bonding additives, i.e., methylamine (MA), ethylenediamine (ED), urea, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), on the solution behavior of hydroxypropyl-ß-CD (HP-ß-CD) by rheology, conductivity, and NMR analyses, and the morphology of the electrospun HP-ß-CD nanofibers by scanning electron microscopy. The 1H NMR chemical shifts of the HP-ß-CD protons in D2O were observed with the incorporation of hydrogen-bonding molecules due to the occurrence of intermolecular associations between HP-ß-CD and additives. Dynamic light scattering measurements revealed a clear decrease in the aggregate size with the introduction of additives. Unlike other additives, which showed a general decreasing trend in viscosity with increasing additive content, the addition of MA led to a significant increase in the viscosity with increasing concentration and gave rise to HP-ß-CD nanofibers at lower concentrations. The addition of low concentrations of ED, urea, TFE, and HFIP led to thinner nanofibers due to the lower viscosity of the respective solutions. Increasing additive content deteriorated the electrospinnability of HP-ß-CD solutions, resulting in beaded fibers. A systematic relationship was found between the solution viscosity and morphology of the respective electrospun fibers. Overall, this study, for the first time, reports the influence of hydrogen bonding on the polymer-free electrospinning of CD molecules and shows a correlation between solution properties and morphology of their electrospun nanofibers.

Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon.

The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.