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.
The electrospinning of high-performance polyimides (PI) has recently sparked great interest. In this study, we explore the effect of the electrospinning parameters — namely polymer concentration, ...voltage, tip-to-collector distance and flow rate — and salt addition on the diameter, morphology, and spinnability of electrospun PI nanofibers. Three different polyimides of intrinsic microporosity (PIM-PIs) with high Brunauer–Emmett–Teller (BET) ranging from 270 to 506 m2 g−1, and two microporous polyimides, were synthesized through the polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and aromatic diamines. The addition of tetraethylammonium bromide (TEAB) salt considerably increased the conductivity of all the PI solutions, significantly improved spinability, and resulted in thinner fibers. We also used molecular dynamic simulations to investigate the macromolecular mechanism of improved spinnability and fiber morphology in the presence of an ammonium salt. The small droplets detached from the parent droplet, followed by the rapid evaporation of the ions through the hydration effect, which facilitated the electrospinning. The resulting uniform nanofibers have great potential in environmental applications due to the presence of microporosity and hydrophobic pendant trifluoromethyl groups, which enhance the sorption performance of the fibers for hydrophobic species.
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•Five different microporous polyimides having pendant trifluoromethyl groups were synthesized through polycondensation.•Uniform nanofibers were produced at low polymer concentrations due to improved spinnability in the presence of a salt.•Higher salt content drastically increased the solution conductivity and led to thinner electrospun fibers.•A higher flow rate increased fiber diameter due to the higher mass flow.•Molecular dynamics simulations demonstrated faster solvent evaporation in the presence of salt.
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•A comprehensive review of functional electrospun nanofibers for food packaging.•Nanofibers with antioxidant, antibacterial and antifungal functionalities via ...electrospinning.•Bioactive agents are encapsulated in electrospun nanofibers for active food packaging.
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.
Hydrophobic cyclodextrin (CD) nanofibers were produced by the electrospinning of peracetylated
β
-CD without requiring any polymer as a carrier matrix. Native
β
-CD was peracetylated through the ...reaction with acetic anhydride, and the conversion of all hydroxyl groups into acetyl was confirmed by NMR, XPS, and TGA analyses. The peracetyl modification drastically boosted the thermal stability of the
β
-CD molecules. The electrospinning of the peracetylated
β
-CD from its highly concentrated solutions (180% (w/v)) in DMF led to bead-free nanofibers, while electrospinning at the concentrations of 140 and 160% (w/v) CDs resulted in beads and beaded nanofibers, respectively. The electrospinning process parameters such as applied voltage, flow rate, and tip-to-collector distances were systematically altered to produce a uniform nanofiber structure. The flow rate had the most drastic effect on the diameter and morphology of the resultant nanofibers: A threefold rise in the fiber diameter was observed with increasing the flow rate from 0.1 to 2 mL h
−1
. Similarly, higher electrical field increased the fiber diameter due to higher mass flow, while boosting the tip-to-collector distance did not reveal any significant change on the fiber diameter. The stability of the peracetylated
β
-CD nanofibers was observed in water for 24 h without any significant morphological change; however, the dissolution of the nanofiber mat was observed with a long-time exposure to water. We demonstrated production of hydrophobic uniform CD nanofibers without using any carrier polymer.
Horseradish peroxidase (HRP) can be used for the enzymatic cross‐linking of thiol‐functionalized polymers under mild conditions to form hydrogels and nanogels without the need for added H2O2. Cells ...can be embedded in the hydrogels and proteins can be entrapped and released from the nanogels. These gels are fully degradable under mild and cytocompatible reductive conditions.
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-β-CD (HP-β-CD) by rheology, conductivity, and NMR analyses, and the morphology of the electrospun HP-β-CD nanofibers by scanning electron microscopy. The 1H NMR chemical shifts of the HP-β-CD protons in D2O were observed with the incorporation of hydrogen-bonding molecules due to the occurrence of intermolecular associations between HP-β-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-β-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-β-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.
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.
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.
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•The first use of a macromer cross-linker for DNA gelation.•The first use of isocyanates for DNA cross-linking.•The cross-linking of DNA molecules without a catalyst.•The elasticity ...of DNA gels has been greatly increased by the DNA renaturation.
Denatured DNA molecules were used as building blocks to fabricate thermoresponsive hydrogels by cross-linking DNA strands with an isocyanate (NCO) end-capped star-shaped poly(EO-stat-PO) cross-linker. The NCO groups reacted with the amine groups of DNA’s bases through urea links while base pairing between the matching strands of DNA led to the self-assembly of DNA into a three-dimensional hydrogel network. Analysis of the ultrastructure by scanning force microscopy (SFM) revealed the temperature-mediated transition from the rod-to-coil structure as a result of the destabilization of double-stranded DNA (dsDNA) to form a single-stranded DNA (ssDNA), which eventually resulted in a DNA network due to base pairing, along with hairpin loops due to mismatches between nucleotides. Dynamic oscillatory and large deformation creep tests, as well as stress relaxation tests, revealed the formation of robust cross-linked gels: A ten-fold rise in the elastic modulus was observed for the covalent DNA gel compared to the physical gel at the identical DNA concentration. The thermoresponsiveness of the hydrogels was confirmed by a heating–cooling cycle while the non-porous internal morphology of the hydrogel was demonstrated through scanning electron microscopic analysis. Overall, this is the first study showing the fabrication of covalent DNA hydrogels using an NCO-end-capped hydrophilic prepolymer. Such gels have a high potential to be exploited in many fields to benefit from the structural properties of DNA molecules.
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