Polymer-nanohoop composition for 3D printing and methods of making and using the same

Abstract

Disclosed herein are methods for using carbon-based nanohoop compounds in combination with polymer compounds for melt electrowriting techniques. Also disclosed are compositions / combinations for use in the disclosed methods.

Description

POLYMER-NANOHOOP COMPOSITION FOR 3D PRINTING AND METHODS OFMAKING AND USING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of, and priority to, the earlier filing date of U.S. Provisional Application No. 63 / 542,182, filed October 3, 2023, which is incorporated herein by reference in its entirety.ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under CHE2102567 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD

[0003] Disclosed herein include fluorescent materials and methods for making the same. Systems and methods for using such materials for three-dimensional (3D) printing and / or manufacturing processes are also disclosed.BACKGROUND

[0004] Creating 3D-printed objects with fluorescent properties, e.g., by using electrohydrodynamic processing (EHD), etc., is significant for applications such as biotechnology, medical devices, and advanced sensors. Fluorescent 3D-printed objects can enable enhanced visualization, tracking, and detection of specific components or materials, and have the potential to revolutionize areas like personalized medicine, where custom-designed fluorescent implants or drug delivery devices could offer targeted treatments. However, achieving consistent and reliable fluorescence in 3D-printed objects can be challenging due to material compatibility, precision in printing, and controlling the fluorescence properties. Thus, there exists a need in the art for fluorescent materials that can be reliably used for 3D printing.SUMMARY

[0005] Disclosed herein is a composition comprising: a polymer; and a nanohoop having a structure according to Formula I as described herein, wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4.

[0006] Also disclosed is a system, comprising: a reservoir containing the composition according to aspects of the present disclosure; and a nozzle in fluid communication with the reservoir.

[0007] Also disclosed herein is a method for preparing a nanohoop-polymer composition, the method comprising combining a polymer with a nanohoop having a structure according to Formula I as described herein, wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4.

[0008] Also disclosed herein is a method of using the composition according to aspects of the present disclosure, the method comprising: adding the composition to an electrospinning system; heating the composition at an operating temperature that is higher than a melting point of the polymer to form a polymer melt; and extruding the polymer melt out of a nozzle of the electrospinning system.

[0009] Also disclosed herein is a method forming a composite structure, comprising: adding a first composition to a nozzle of an electrospinning system, wherein the first composition is a solution or polymer melt comprising a first polymer and a first nanohoop; adding a second composition to the nozzle of the electrospinning system, wherein the second composition is a solution or polymer melt comprising a second polymer and a second nanohoop; and wherein (i) the second composition is not mixed with the first composition in the nozzle; and (ii) the first nanohoop and the second nanohoop independently have a structure according to Formula I as disclosed herein, wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4, provided that the first nanohoop and the second nanohoop do not have the same structure.

[0010] The foregoing and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 shows an image of a “core-shell”-type composite structure printed according to aspects of the methods and systems described herein.

[0012] FIG. 2 illustrates an exemplary setup of an electrospinning system.

[0013] FIG. 3 illustrates an exemplary setup of a melt electro writing (“MEW”) system.

[0014] FIGS. 4A and 4B show (i) an exemplary synthetic scheme for [n]CPPs wherein n = 8, 9, or 10, according to aspects of the present disclosure (FIG. 4 A) and (ii) a plot of optoelectronic properties of exemplary [n]CPPs with absorbance (solid) and emission (dashed) spectra shown along with corresponding excitation maxima (Xabs), emission maxima (Xem), quantum yield (<P), and molar extinction coefficient (e) for each of the [n]CPPs according to aspects of the present disclosure (FIG. 4B).

[0015] FIGS. 5A-5F show general fluorescence of solutions and blends when using polycaprolactone (“PCL”), wherein different concentrations of cycloparaphenylene (“CPP”) in PCL were dissolved in dichloromethane (“DCM”) and shown under visible light (FIG. 5A) or ultraviolet (“UV”) excitation (FIG. 5C) with concentrations arranged logarithmically from 0.0001% by weight to 1 % by weight, left to right; FIG. 5B shows 0.01 % [n]CPP-PCL (n=8, 9, 10) dissolved in DCM under visible radiation and FIG. 5D shows results after being illuminated with UV radiation; and FIGS. 5E and 5F show solvent-removed PCL blended with 0.01 % [8], [9], and

[0010] CPP-PCL in glass syringes under visible (FIG. 5E) radiation and after being illuminated with UV radiation (FIG. 5F).

[0016] FIGS. 6A-6G show plots of thermal and viscoelastic properties of exemplary [n]CPP-PCL materials, wherein FIG. 6A shows a thermogravimetric analysis of [n]CPP-PCL compared to PCLpeiiet; FIG. 6B shows viscosity analysis of [n]CPP-PCL materials as related to shear rate at 80 °C; FIG. 6C shows viscosity analysis of [n]CPP-PCL materials as related to temperature at 1 Hz; FIG. 6D shows differential scanning calorimetry of [n]CPP-PCL materials; FIG. 6E shows melting temperature; FIG. 6F shows percent crystallinity; and FIG. 6G shows viscosity at 1 Hz and 80 °C.

[0017] FIGS. 7A-7F show results from solution electrospinning (SES) of CPP-PCL, wherein FIG. 7A shows an image of an electrospinning setup, utilizing a 14-centimeter nozzle-collector gap, a rotating six-slide collector, a syringe pump, and a high voltage supply; FIG. 7B shows analysis of the fiber diameters of the control and CPP-PCL; and FIGS. 7C-7F show exemplary SEM images of control and CPP-PCL electrospun fibers.

[0018] FIGS. 8A-8E illustrate additional aspects of SES of [n]CPP-PCL, wherein FIGS. 8A and 8B show a control and [n]CPP-PCL membranes under visible (FIG. 8A) and ultraviolet radiation (FIG. 8B); FIG. 8C shows exemplary SEM images of control and [n]CPP-PCL electrospun fibers; FIG. 8D shows ambient light image of [8]CPP-PCL MEW scaffold on

[0010] CPP-PCL solutionelectrospun substrate; and FIG. 8E shows ultraviolet radiation image of [8]CPP-PCL MEW scaffold on

[0010] CPP-PCL solution electrospun substrate.

[0019] FIGS. 9A-9F show results from melt electrowriting of CPP-PCL, including entire scaffold images under ambient (FIGS. 9A-9C) and UV radiation (FIGS. 9D-9F); FIG. 9E shows low magnification of scaffolds shows how fluorescent capabilities are retained on a fiber-specific basis; and FIG. 9F shows high magnification of scaffolds shows the capabilities of CPP-PCL in imaging fine scale properties with bulk fluorescent distribution.

[0020] FIGS. 10A-10E show results using compositions according to aspects described herein, wherein FIGS. 10A and 10B show tubular MEW scaffolds printed with control and CPP-PCL under ambient and UV light, respectively; FIGS. 10C and 10D show low magnification of multicolor scaffold utilizing control and [8], [9], and

[0010] CPP-PCL in alternating angles under ambient and UV light (wherein angles and their specific materials; 0°: control PCL, 45°: [8]CPP- PCL, 90°:

[0010] CPP-PCL, 135°: [9]CPP-PCL); and FIG. 10E shows high magnification of multicolor scaffold intersection (material directions match as described in FIGS. 10C and 10D).

[0021] FIG. 11 shows results from assessing cytotoxicity of CPP-PCL in comparison to controls. Phosphate-buffered saline (“PBS’-) and ethanol were utilized for liquid inhibition controls, while polyvinylchloride and nitrile were chosen for eluant controls.

[0022] FIG. 12 shows another plot of cytotoxicity of CPP-PCL in comparison to controls, wherein ** = / ? < 0.005; **** =p < 0.0001 ; and n = 9.

[0023] FIG. 13 shows results from leaching tests measured with ultraviolet spectroscopy.

[0024] FIG. 14 is a plot of fiber diameter of [n]CPP-PCL blends against an exemplary PCL control (PCLpeiiet) and an exemplary solvent-processed PCL control (PCLsham) according to aspects of the present disclosure.

[0025] FIGS. 15A-15D are exemplary SEM images of solution-electrospun PCL and [n]CPP-PCL blends according to aspects of the present disclosure, which show that including nanohoops in the polymer does not negatively impact the fibers printed from methods according to the present disclosure.

[0026] FIG. 16 is a plot of fiber diameter of exemplary electrospun PCL and exemplary [n]CPP- PCL blends according to aspects of the present disclosure.

[0027] FIG. 17 is a schematic diagram of an exemplary method of seeding mesenchymal stem cells (MSCs) into CPP-PCL MEW scaffolds according to aspects of the present disclosure.

[0028] FIGS. 18A and 18B show fluorescent images of fluorescein-tagged (FIG. 18A) and rhodamine-tagged (FIG. 18B) phalloidin samples according to aspects of the present disclosure.

[0029] FIGS. 19A-19H show fluorescent images of rhodamine- and fluorescein-tagged phalloidin stains conducted on PCL and [n]CPP-PCL scaffolds seeded with MSCs according to aspects of the present disclosure.

[0030] FIGS. 20A-20H illustrate sequential MEW of exemplary CPP-PCL materials according to aspects of the present disclosure, wherein FIG. 20A shows a schematic diagram of sequential MEW of CPP-PCL materials using a multi-nozzle system; FIG. 20B shows a schematic diagram of multimaterial MEW scaffold, with labeled fiber directions and materials; FIG. 20C shows a brightfield image of multi-material MEW scaffold; FIG. 20D shows a fluorescent image of multi-material MEW scaffold; FIG. 20E shows a fluorescent image of multi-material MEW junction; FIG. 20F shows a schematic of multi-material branching MEW wall; FIG. 20G shows a fluorescent image of multi-material branching MEW wall; and FIG. 20H shows a tilted fluorescent image of multimaterial MEW wall, with four distinct regions of fluorescence and non-fluorescence.DETAILED DESCRIPTIONI. General Considerations

[0031] For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, apparatus, and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed examples, alone and in various combinations and sub-combinations with one another. The methods, apparatus, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed examples require that any one or more specific advantages be present or problems be solved. The technologies from any example can be combined with the technologies described in any one or more of the other examples. In view of the many possible examples to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated examples are only preferred examples and should not be taken as limiting the scope of the disclosed technology.

[0032] Although the operations of some of the disclosed examples are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation.

[0033] As used herein, “and / or” means “and” or “or,” as well as “and” and “or.” As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the terms “coupled” and “connected” generally mean electrically, electromagnetically, and / or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language. As described herein, a range from A to B (or between A and B) encompasses both endpoints A and B.

[0034] Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth, as used in the specification or claims are to he understood as being modified by the term “about.” Accordingly, unless otherwise indicated, implicitly or explicitly, the numerical parameters set forth are approximations that can depend on the desired properties sought and / or limits of detection under standard test condi tions / methods. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited. Furthermore, not all alternatives recited herein are equivalents.

[0035] Directions and other relative references (e.g., inner, outer, upper, lower, top, bottom, etc.) may be used to facilitate discussion of the drawings and principles herein but are not intended to be limiting. For example, certain terms may be used such as “inside,” “outside,” “interior,” “exterior,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated examples. Such termsare not, however, intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, an “upper” part can become a “lower” part simply by turning the object over. Nevertheless, it is still the same part and the object remains the same.

[0036] To facilitate review of the various embodiments of the disclosure, the following explanations of specific terms are provided.

[0037] Aromatic: A cyclic, conjugated group or moiety of, unless specified otherwise, from 5 to 15 ring atoms having a single ring (e.g., phenyl) or multiple condensed rings in which at least one ring is aromatic (e.g., naphthyl, indolyl, or pyrazolopyridinyl); that is, at least one ring, and optionally multiple condensed rings, have a continuous, delocalized 7i-electron system. Typically, the number of out of plane ^-electrons corresponds to the Huckel rule (4n + 2). An aromatic group or moiety may comprise only carbon atoms in the ring, such as in an aryl group or moiety.

[0038] Aryl: An aromatic carbocyclic group comprising at least five carbon atoms to 15 carbon atoms, such as five to ten carbon atoms, having a single ring or multiple condensed rings, which condensed rings can or may not be aromatic provided that the point of attachment is through an atom of the aromatic carbocyclic group.II. Introduction

[0039] The fluorescent visualization of materials and substrates are a crucial aspect of numerous biomedical and biotechnological applications. Both SES and MEW produce membranes and scaffolds from synthetic polymers that have been utilized in several biomedical paradigms including tissue engineering, cancer research, 3D cell culture, biomaterials and sensor applications.

[0040] There is a need to incorporate further functional properties within such membranes and scaffolds, including fluorescent imaging, to allow waypoints and visualization at both low and high magnifications. Due to the requirement for sustained elevated temperatures for MEW, there are limited options for making fluorescent scaffolds with this approach. Nanohoops described herein provide ideal and unique properties for PCL membranes and scaffolds. The resulting products are resistant to photobleaching and are readily visualized with a low-cost and handheld flashlight.

[0041] In some examples, an unexpected synergistic effect of nanohoops combined with a polymer component (e.g., PCL) was observed. For example, it was observed that, upon irradiation of an ultraviolet light, nanohoops combined with the polymer can surprisingly emit a brighter fluorescent light compared to the nanohoops alone (i.e., without the polymer). Without beinglimited to a single particular theory, it currently is believed that the increased fluorescent intensity of combined nanohoops and polymer can be due to increased quantum yield relative to that observed from nanohoops alone.

[0042] As described herein, the nanohoops can be mixed within the bulk of the polymer itself, as opposed to surface tagging of the polymers. This can provide an advantage of long-term fluorescence, which will be lessened but not removed by polymer surface erosion.

[0043] As described below, the polymer can be combined with multiple fluorophores (e.g., nanohoops having different number of aromatic ring systems), thereby giving the polymer different fluorescent properties. This can provide an advantage that the resulting fibers can exhibit fluorescent at multiple wavelengths, and / or the resulting objects can have different fluorescent properties in different parts of the objects.

[0044] In summary, combining nanohoops with PCL (or other polymers) provides a simple yet potent method to orient, visualize and better understand the interactions between MEW scaffolds and tissue / cells, compatible with existing imaging systems.III. Overview of Electrohydrodynamic Processing of Fluorescent Fibers

[0045] Electrohydrodynamic (EHD) processing includes multiple manufacturing technologies, including, but not limited to, solution electrospinning (SES), melt electrospinning, electrospraying, and melt electrowriting (MEW). Products of these technologies have intensively been investigated for decades for textile, filtration, and tissue engineering (TE) applications. EHD processing is a nozzle technology and its relative simplicity has contributed to its adoption over the past two decades for research application, with SES manufactured small-diameter (typically less than 1 pm) fibers being especially investigated for biomedical applications.

[0046] SES produces non-woven meshes made from sub-micron diameter fibers using an EHD phenomenon of jet instability, often referred to as “whipping.” After a jet is initiated by surface charges overcoming the drop surface tension, a Taylor cone is formed that has a straight component to the electrified jet. As the jet surface charge density increases closer to the collector, at some threshold it undergoes an extensional event called “whipping”; a part of the jet that generates lasso rope style spirals from the electrically charged jet. SES meshes are typically non-woven and the strong electrostatic forces that draw such small diameter fibers also make it difficult to place them in a specific location.

[0047] A different, but configurationally related technology, melt electrowriting (MEW), produces well-positioned fibers but leverages a different EHD effect. When applying a high voltage to a fluid column, the charges generated can prevent Plateau-Rayleigh instabilities, allowing the flow rate of the fluid column to be reduced. With a thin, stable electrified jet achieved, the collector can be moved (or the head can be translated) to deposit small diameter fibers (e.g., typically between 1 to 50 pm) with high accuracy. Using additive manufacturing principles, this small diameter fiber from the molten jet can be repeatedly stacked. While it takes time to produce a MEW sample, the automation and continuous fabrication allows a high output for value-added applications such as tissue engineering and cancer research. MEW scaffolds can have a high porosity (e.g., a pore fraction ranging from 80% to 98%) and can be well populated with cells / tissues.

[0048] With EHD scaffolds being widely used within biomedical applications, the products of EHD manufacturing need to accommodate, and ideally enhance, existing imaging capabilities. Due to the small diameter fibers made with EHD technologies, the morphologies are regularly documented with scanning electron microscopy (SEM). When used in biomedical or biotechnology applications, however, there is a need to further identify the produced fibers / scaffolds without SEM. This is especially pertinent for distinguishing fibers and scaffolds within in vivo situations where tissues also contain small vacuoles and other ultra-structures that make histological assessment challenging.

[0049] Fluorophores either embedded or conjugated to fibers can be utilized. However, it has been conventionally challenging to use fluorophores in MEW because of the requirement that the fluorophores must sustain elevated temperatures (e.g., over multiple days) while not interfering with the processing. When performing research on cell-scaffold or tissue-scaffold interactions, fiber visualization and identification is therefore an important yet challenging aspect when understanding this relationship.

[0050] The technology aspects described herein can produce fluorescent materials that can be used for EHD processing and other 3D printing modalities and that exhibit desirable properties and performance for such applications.IV. Exemplary Features of Fluorescent Materials

[0051] As described more fully below, the disclosed fluorescent materials include cycloparaphenylenes (CPPs), also known as “nanohoops” or “[n]CPPs,” which are thermally stable and hydrophobic compounds that emit different light wavelengths depending on the cyclic radius.Contrasting with other nanocarbon-based compounds, the disclosed nanohoops can be synthesized from a bottom-up synthetic approach to yield an array of sizes, such as from n = 5-18 (wherein n = number of aromatic rings in the nanohoop). Nanohoops according to the present disclosure can have a structure according to Formula I, wherein A is an aromatic ring, such as an aryl ring (e.g., phenyl or other aryl ring system) and n is an integer representing the number of aromatic rings in the nanohoop, and, in particular aspects is selected from an integer greater than 4, such as 5 to 18, or 5 to 16, or 5 to 14, or 5 to 12, or 5 to 10, or 5 to 8, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18.Formula I

[0052] As described below, [n]CPPs can display a common absorption (340 nm) with red shifting emissions as n decreases, while remaining thermally stable to temperatures above 300 °C, such as for hoop sizes of n > 7. In some aspects, the common absorption wavelength of [n]CPPs can be advantageous for multiplexing applications using one excitation source. Moreover, in some aspects, these nanohoops have molar absorption coefficients on the order of 105M^cm1- which coupled with a high quantum yield leads to an exceptionally bright fluorescent material. Additionally, [n]CPPs are soluble in common organic solvents such as dichloromethane (DCM), tetrahydrofuran (THF), and the like, which makes them compatible for embedding in hydrophobic polymers. Thus, [n]CPPs can be a potent fluorophore when combined with a hydrophobic polymer for MEW processing which typically utilizes several days of sustained heating for a workable system.

[0053] In some examples, the amount of [n]CPPs incorporated into the polymer for any particular printing application can vary based on the fluorescence of the particular [n]CPPs, but generally the weight % of nanohoop (relative to the polymer) can range from 0.0001% to 1%. The resulting 3D- printed substrates can exhibit persistent fluorescence, indicating that the [n]CPPs can remain intact for a prolonged period (e.g., days, weeks, etc.) after printing.

[0054] In some aspects of the disclosure, the [n]CPPs are not covalently attached to the polymer, that is, the CPPs do not form covalent bonds with atoms and / or functional groups of the polymer.V. Printing Applications

[0055] The fluorescent materials described herein, such as the combination of [n]CPPs and a polymer (e.g., a combination comprising [n]CPPs and PCL), can be used in a variety of printing systems.

[0056] For example, the fluorescent materials described herein can be used in EHD processing, such as solution electrospinning, melt electrospinning, electrospraying, melt electro writing, etc.

[0057] Electrospinning involves the extrusion of a liquid solution or melt through a nozzle (also referred to as a “spinneret”). The applied electric field stretches the liquid into a thin, continuous jet or filament. As the jet travels towards a collector, solvent evaporates, solidifying the material into fine fibers. The collector can be a stationary surface or a rotating drum. Both the liquid solution used for solution electrospinning and the melt used in melt electrospinning can include the fluorescent materials described herein, along with a polymer. In some aspects, the polymer forms the liquid solution and the fluorescent material is mixed within the liquid polymer. In some aspects, the liquid solution can comprise the polymer, the fluorescent material, and a solvent.

[0058] In electrospraying, a liquid is dispensed from a nozzle or capillary, and the applied electric field forces the liquid to form a cone-shaped meniscus at the nozzle tip. When the electric field strength exceeds a critical value, this meniscus becomes unstable, resulting in the ejection of tiny droplets or charged particles. These droplets or charged particles can be collected in a container or deposited onto a surface (e.g., for coating). The fluorescent materials described herein can be incorporated in the liquid for electrospraying, along with a polymer. In some aspects, the polymer forms the liquid solution and the fluorescent material is mixed within the liquid polymer. In some aspects, the liquid solution can comprise the polymer, the fluorescent material, and a solvent.

[0059] In melt electrowriting, a polymer is heated to (or above) its melting point so that the polymer is molten and becomes a polymer melt. The molten polymer is then extruded through a nozzle or spinneret. An electric field is applied to the extruded polymer, causing it to elongate and form fibers as it cools and solidifies. The fluorescent materials described herein can be incorporated in the polymer melt, such as is described in examples below where CPP-PCL is used in MEW printing of flat and tubular scaffolds.

[0060] In some examples, the fluorescent materials described herein can be used in general melt processing independent of EHD processing (e.g., without applying an electric field to the polymer melt). One example is melt extrusion, which is a manufacturing process used in various industries,including plastics, food processing, and pharmaceuticals, to produce continuous lengths of various materials with a consistent cross-sectional shape. It involves forcing a polymer melt through a die or an orifice under controlled conditions of temperature and pressure. The fluorescent materials described herein can be incorporated in the polymer melt used in melt extrusion.

[0061] The printing is not limited to one nanohoop-containing polymer. In some examples, during the printing process, the [n]CPPs contained in the ink (e.g., polymer solution or polymer melt) can be dynamically changed. For example, in some aspects, a plurality of nanohoops is included in a composition comprising the polymer. In the plurality of nanohoops, each nanohoop can be the same or different as other nanohoops in the plurality. For example, some compositions can comprise a polymer and one or more nanohoops wherein each nanohoop is identical (e.g., each nanohoop has a structure according to Formula I wherein each ring A is the same or wherein n is the same).

[0062] In yet other aspects, the composition can comprise a polymer and a mixture of nanohoops wherein two or more of the nanohoops have different structures (e.g., each nanohoop has a structure according to Formula I and wherein one nanohoop has one or more different ring A groups than another nanohoop in the mixture; and / or wherein one nanohoop has a different n value than another nanohoop in the mixture). In such aspects, the plurality of nanohoops that is included in the composition can comprise a first nanohoop comprising an [ni]aromatic ring compound and a second nanohoop comprising an [m |aromatic ring compound, wherein m and m are two different integers, which represents that the first and second nanohoops have different hoop sizes. Solely for illustrative purposes, m of the [n aromatic ring compound can be 8 and of the | mlaromatic ring compound can be 9.

[0063] In an exemplary aspect, the ink fed to the nozzle may contain an [8]CPP in a first period and then the ink is changed to contain a [9]CPP in a second period. As a result, the fibers produced (e.g., via electrospinning or MEW) in the first period and second period may have different fluorescent properties. In some examples, by dynamically changing the [n]CPPs in the ink while controlling deposition of the resulting fibers on a substrate, the object formed by the fibers can have different fluorescent properties in different parts of the objects. For example, a 3D object can be printed with alternating layers each of different inks wherein each ink incorporates a different [n]CPP that fluoresces at a different wavelength from any [n]CPP of an ink used in a different layer. Additionally, and / or alternatively, the polymer can contain more than one [n]CPP such that a mixture of different [n]CPPs are included in the same composition, which can facilitatefluorescence at multiple different wavelengths. For example, a single composition can comprise a polymer and a mixture of an [8]CPP and a [9]CPP.

[0064] In some aspects, a printing method can be used wherein a composite structure is printed such that the composite comprises a mixture of at least two different [n]CPP compounds. In such aspects, the composite can comprise a printed fiber (or other deposited / printed structure) comprising the polymer and the two different [n]CPP compounds. Within the composite, the different [n]CPP compounds can be evenly or unevenly distributed. In some aspects, the composite can comprise a core-shell-type structure wherein a first [n]CPP compound forms a core component of the composite structure and a second [n]CPP compound forms a shell component of the composite structure surrounding the core component. An exemplary core-shell-type composite is shown in FIG. 1 (depicting a fluorescent photograph of a coaxial fiber at five different cross sections). As can be seen in FIG. 1, the composite comprises discontinuous phases of the printed compositions (e.g., a first discontinuous phase being the core and a second discontinuous phase being the shell). In some aspects, a first composition comprising the polymer and the first [n]CPP compound can be printed to provide the core and then a second composition comprising the second [n]CPP compound can be printed to cover the core, thus providing the shell. In other aspects, both a first composition comprising a polymer and a first [n]CPP compound and a second composition comprising a polymer and a second [n]CPP compound can be printed simultaneously using, for example, a coaxial nozzle. In yet some additional aspects, a first and second composition can be printed using two different nozzles, wherein one nozzle contains the first composition and the second nozzle contains the second composition. Composite structures of other geometries (e.g., multiple laminated layers, etc.) can also be printed based on the principles described herein. In aspects using a first composition and a second composition to prepare a composite structure, the first and second [n]CPP compounds have a different structure, such as different A rings and / or different integers for n, as described for Formula I.

[0065] In some aspects, the composition disclosed herein can be printed and used to image biological components, such as cells, matrix proteins, and the like. In some aspects, the composition can be printed and used to better understand interactions between a scaffold printed using the composition and a biological component, wherein imaging can be conducted using existing imaging systems. The disclosed composition enhances visibility of MEW fibers within biological systems supports multi-channel fluorescence imaging which aids in the ability to study the evolving dynamics of cell-scaffold systems for tissue engineering and regenerative medicine.VI. System

[0066] Electrospinning is a method of producing micro- and nano-polymer fibers using high voltage. Commonly used materials in electrospinning include organic polymers in the form of either solutions or melts. The polymers used for electrospinning can be organic polymers, including both natural and synthetic polymers, such as PCL, polyactic acid (PLA), polylactic-co- gly colic acid (PLGA), DNA, silk fibroin, fibrinogens, dextran, chitin, chitosan, alginate, collagen, gelatin, etc. The nanohoops or CPPs described herein can be mixed with any of the polymer described herein.

[0067] FIG. 2 depicts an example setup (not drawn to scale) of an electrospinning device, apparatus, or system 100, which can be used for both solution electrospinning and melt electrospinning. The electrospinning system 100 includes a high voltage power supply 102, a reservoir 104 which holds a liquid 120 of polymer solution or polymer melt, a nozzle 106 (also referred to as a spinneret, a needle, or a fluid dispenser) in fluid communication with reservoir 104, a pump 108 (also referred to as an “actuator”), and a collector 110. The pump 108 can be any devices configured to apply a pressure (which can be pneumatic or hydraulic) to the liquid 120 retained in the reservoir 104. For example, the reservoir 104 can be a barrel of a syringe and the pump 108 can be plunger of the syringe. Under the pressure of the pump 108, the liquid 120 in the reservoir 104 can flow into the nozzle 106, and then be extruded out of an orifice or opening 118 located at a distal tip of the nozzle 106 by the pump 108.

[0068] During electrospinning, the liquid 120 can be extruded from the nozzle 106 at a certain speed or flow rate under the control and propulsion of the pump 108. The extruded liquid 120 can initially form a pendant droplet with a spherical shape as a result of surface tension. The power supply 102 can apply a high voltage between the nozzle 106 and the collector 110. For example, the nozzle 106 can be positively charged and the collector 110 can be grounded, or vice versa. As another example, a differential voltage is applied between the nozzle 106 and the collector 110, while neither the nozzle 106 nor the collector 110 is grounded. The electrostatic repulsion of ions in the droplet under the high voltage can stretch the droplet from its initial spherical shape to a conical shape, also known as a Taylor cone 112. When the voltage exceeds a given threshold, the electric field force can overcome the surface tension of the droplet and cause a charged jet 114 to be ejected from the Taylor cone 1 12. The charged jet 114 initially extends in a straight line and then undergoes chaotic whipping motions because of bending instabilities (also known as whipping instability). As the charged jet 114 is stretched into finer diameters, it solidifies quickly, leading to the deposition and collection of solid fiber(s) 122 on a substrate 116 situated on the collector 110.The accumulation of the fiber(s) 122 on the substrate 116 can form a fiber mesh or fiber membrane / film.

[0069] In some examples, the electrospinning system 100 can include an array of nozzles, each of which can be used to extrude the liquid 120 and generate a charged jet. Such multi-nozzle configuration can be used to increase the fiber yield.

[0070] In solution electrospinning, the liquid 120 is formed, typically at room temperature, by dissolving a polymer of choice in a volatile solvent, such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), cyclohexanone, hexafluoroisopropanol (HFIP), trifluoroethanol (TFE), dichloromethane (DCM), chloroform (CHL), etc. As described herein, volatile solvents are liquids that can vaporize into a gas at the room temperature sufficiently rapidly so that fibers are formed. During the charged jetting process, polymer chain entanglements prevent the charged jet 114 from breaking into droplets (i.e., prevent electrospraying), while rapid evaporation of the solvent consolidates the charged jet into the fiber(s) 122. In some cases, residual solvent in the collected fiber(s) 122 can facilitate inter-fiber bonding that confers mechanical integrity to the resultant fiber mesh or membrane (or film).

[0071] In melt electrospinning, the liquid 120 is formed by heating a polymer of interest above its melting point so that the polymer becomes a polymer melt. Thus, unlike solution electrospinning, melt electrospinning eliminates the need for volatile solvents. During the charged jet jetting process, solidification of the polymer melt, e.g., under a cooling condition, can result in solidification of the fiber(s) 122 on the substrate 116. The degree of fiber cooling / solidification upon arrival to the collector 1 10 may control the degree of fusion between fibers 122.

[0072] FIG. 3 schematically depicts (not drawn to scale) an example device, apparatus, or system 200 configured for MEW, according to certain aspects of disclosed technology.

[0073] The system 200 includes a printhead 220 (or simply “head”). The printhead 220 can have or be coupled with a fluid dispenser 230 such as a nozzle, a needle, a spinneret, or the like. The system 200 can include a container or reservoir 240 in fluid communication with the fluid dispenser 230. The reservoir 240 is configured to hold a fluid or liquid (e.g., polymer melt) which can be ejected through the fluid dispenser. The fluid or liquid contained in the reservoir 240 can include the nanohoops or CPPs described herein.

[0074] In some examples, the reservoir 240 can be at least partially retained within the printhead 220. For example, each reservoir 240 can be received within a respective receptacle of theprinthead 220. In other examples, the reservoir 240 can be situated away from the printhead 220, and the liquid contained in the reservoir 240 can be transported to the fluid dispenser 230 through a conduit. In some examples, the fluid dispenser 230 and the corresponding reservoir 240 can be separable or integral components of an article, such as a syringe. For example, a barrel of the syringe can be the reservoir 240 and a needle of the syringe can be the fluid dispenser 230.

[0075] The system 200 can include an actuator configured to pressure or extrude the liquid out of the reservoir 240 through the fluid dispenser 230. In some examples, the actuator can be a pump 250 (e.g., a piston, a plunger, etc.). The pump 250 can be operatively connected to a pressure controller 214 configured to adjust the pressure applied by the pump 250.

[0076] From the dispenser 230, a polymer jet 202 (e.g., formed by a polymer melt) can be ejected under the pressure of the pump 250. The polymer jet 202 ejected from the dispenser 230 can be electrically charged and directed toward a substrate 280 that is situated at an operating distance from the dispenser 230, as described further below. The polymer jet 202 can be solidified on the substrate 280 to form a fiber 206.

[0077] In MEW, the flow rate of the polymer jet 202 extruded out of the dispenser 230 can be controlled, and generally much lower than the flow rate of the electrospinning, so that whipping of the charged jet is avoided. As a result, controlled deposition of the polymer melt on the substrate 280 can be achieved (e.g., polymer melt can be deposited at specific positions with precision), enabling the creation of intricate 3D structures.

[0078] In some examples, the system 200 can include a heating apparatus 260 configured to heat the liquid in the reservoir 240. Particularly, for MEW, the liquid in the reservoir 240 is a polymer melt. As described above, the polymer melt can include CPP compounds. The heating apparatus 260 can be configured to heat the polymer in the reservoir 240 at an operating temperature that is above a melting point of the polymer so that the polymer becomes the polymer melt.

[0079] In some examples, heating of the polymer in the reservoir 240 can be achieved via conductive coupling to the reservoir 240 (e.g., when the reservoir 240 and printhead 220 are made of heat conductive materials). In other examples, heating of the polymer in the reservoir 240 can be achieved by other heat transfer mechanisms, such as convection or radiation.

[0080] In some examples, the heating apparatus 260 can be operatively coupled to the printhead 220. For example, the heating apparatus 260 can surround the printhead 220 like a jacket and heat the reservoir 240 retained within the printhead 220. In cases where the reservoir 240 are situatedaway from the printhead 220, the heating apparatus 260 can also be spaced apart from the printhead 220. In such cases, the heating apparatus 260 can be configured to maintain the operating temperature within the reservoir 240 and the conduits connecting the reservoir 240 to the fluid dispenser 230 so that the polymer therein remains in the molten state.

[0081] The heating apparatus 260 can be operatively connected to a heating controller 216 configured to maintain the operating temperature, e.g., by using a proportional, integral, and derivative (PID) temperature control mechanism. In some examples, thermostats or other types of temperature sensors can be used to measure the temperature within the reservoir 240, and the heating controller 216 can be configured to control the heating to ensure the temperature within the reservoir 240 and at the fluid dispenser 230 remains as close as possible to the operating temperature.

[0082] The electrospinning system 200 further includes a power supply 270 configured to generate an electrostatic field between the fluid dispenser 230 and the substrate 280. The generated electrostatic field can have a sufficiently high voltage (also referred to as an “accelerating voltage”) to electrically charge the polymer jet 202 ejected out of the fluid dispenser 230 and direct the electrically charged polymer jet 202 to the substrate 280.

[0083] The power supply 270 can provide either direct current (DC) or alternating current (AC). For DC power, the fluid dispenser 230 can be positively charged and the substrate 280 can be grounded, or vice versa. As another example, a differential voltage is applied between the fluid dispenser 230 and the substrate 280, while neither the fluid dispenser 230 nor the substrate 280 is grounded. Both the fluid dispenser 230 and the substrate 280 can comprise conductive materials such as metals. For example, the fluid dispenser 230 can comprise stainless steel, or the like. In some examples, the power supply 270 can be operatively connected to a voltage controller 210 which is configured to program and / or adjust the accelerating voltage. In some examples, the accelerating voltage generated by the power supply 270 can range from 1 kV to 50 kV. In some examples, the electrostatic field and / or the accelerating voltage generated between the fluid dispenser 230 and the substrate 280 can be time varying.

[0084] In some examples, the operating distance between the fluid dispenser 230 and the substrate 280 can be less than 20 mm. For example, the operating distance can be between 0.05 mm and 10 mm, or between 1 mm and 5 mm.

[0085] In some examples, the substrate 280 and the printhead 220 can be configured to be movable relative to one another. In some examples, the substrate 280 can be operatively connected to a motion controller 218, which can translate the substrate 280 relative to the printhead 220. In some examples, the translational speed of the substrate 280 can range from 0 to 10,000 mm / min. In other examples, the substrate 280 can be stationary whereas the printhead 220 can be configured to translate (besides rotation movement) relative to the substrate 280.

[0086] The relative movement between the printhead 220 and the substrate 280 can be multidirectional. In one example, the substrate 280 can be translated in an X-Y plane that is perpendicular to the longitudinal axis 208 (or Z-axis) of the printhead 220. In another example, the substrate 280 can be moved along the Z-axis (e.g., moving closer to or farther away from the printhead 220). In yet additional examples, the substrate 280 can be configured to rotate in a plane (e.g., in the X-Y plane, etc.) or spin around an axis (e.g., around the X-axis, etc.).

[0087] In some examples, the substrate 280 has a planar surface. In other examples, the substrate 280 can have a curved surface (e.g., over a cylindrical mandrel, etc.) or other non-planar surfaces having multiple heights.

[0088] The direction of the polymer jets 202 is generally controlled by the electrostatic field established between the fluid dispenser 230 and the substrate 280. In the depicted example, the printhead 220 is oriented in the vertical direction and the substrate 280 is located below the printhead 220. In other examples, the printhead 220 can be oriented in other directions. For example, the longitudinal axis of the printhead 220 can be tilted so that the fluid dispenser 230 point sideways. Or the printhead 220 can be flipped upside down so that the fluid dispenser 230 point upward. The substrate 280 can be arranged accordingly (e.g., located on a side of or above the printhead 220) so long as the electrostatic field can direct the polymer jet 202 toward the substrate 280.

[0089] In some examples, the fibers 206 can be deposited on the substrate 280 to form a singlelayer membrane or form a multi-layer 3D structure or scaffold. Movement of the substrate 280 relative to the printhead 220 can be precisely controlled (e.g., by the motion controller 218) so that the resulting 3D structure or scaffold can have a desired geometry.

[0090] Although FIG. 2 shows multiple controllers (e.g., voltage controller 210, pressure controller 214, heating controller 216, and motion controller 218), it should be understood that some or all of the depicted controllers can be integrated within one unitary control module.VII. Overview of Several Embodiments

[0091] In various examples described herein, a nanohoop has a structure according to Formula IFormula I wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoop and is selected from an integer greater than 4.

[0092] In any or all of the above aspects, the techniques described herein relate to a composition comprising: a polymer; and a nanohoop having a structure according to the Formula I, and wherein the nanohoop is configured to re-emit a fluorescent light upon irradiation of the composition with an ultraviolet light.

[0093] In any or all of the above aspects, the nanohoop is not covalently attached to the polymer.

[0094] In any or all of the above aspects, the polymer includes polycaprolactone.

[0095] In any or all of the above aspects, the aromatic ring systems of the nanohoop are configured to remain intact when the composition is heated up to 300 °C.

[0096] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0097] In any or all of the above aspects, n is an integer ranging from 8 to 10.

[0098] In any or all of the above aspects, a plurality of nanohoops is included in the composition, wherein a first nanohoop includes an [m] aromatic ring compound and a second nanohoop includes an [n2]aromatic ring compound, wherein m and n2 are two different integers.

[0099] In any or all of the above aspects, a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1:100.

[0100] In any or all of the above aspects, the weight ratio is 1 : 10000.

[0101] In any or all of the above aspects, the polymer is in a liquid form.

[0102] In any or all of the above aspects, the techniques described herein relate to a composition for melt processing, the composition including: a polymer melt including a polymer that ismaintained at a temperature above a melting point of the polymer; and a nanohoop having a structure according to the Formula I, wherein the nanohoop is configured to re-emit a fluorescent light upon irradiation of the composition with an ultraviolet light.

[0103] In any or all of the above aspects, the nanohoop is not covalently attached to the polymer.

[0104] In any or all of the above aspects, the polymer includes polycaprolactone.

[0105] In any or all of the above aspects, the aromatic ring systems of the nanohoop are configured to remain intact when the polymer melt is maintained at the temperature that is above the melting point of the polymer.

[0106] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0107] In any or all of the above aspects, n is an integer ranging from 8 to 10.

[0108] In any or all of the above aspects, a plurality of nanohoops is included in the composition, wherein a first nanohoop includes an [m] aromatic ring compound and a second nanohoop includes an [n2]aromatic ring compound, wherein m and m are two different integers.

[0109] In any or all of the above aspects, a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1: 100.

[0110] In any or all of the above aspects, the weight ratio is 1 : 10000.

[0111] In any or all of the above aspects, the composition includes less than 0.5 wt.% of a solvent.

[0112] In any or all of the above aspects, the techniques described herein relate to a system including: a reservoir containing a composition according to any or all aspects of the present disclosure; and a nozzle in fluid communication with the reservoir. In some aspects, the system further comprises a power supply configured to generate an electrostatic field between the nozzle and a substrate spaced apart from the nozzle so as to draw a charged jet of the ink out of the nozzle toward the substrate and form a polymer fiber on the substrate.

[0113] In any or all of the above aspects, the nanohoop is not covalently attached to the polymer.

[0114] In any or all of the above aspects, the polymer includes polycaprolactone.

[0115] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0116] In any or all of the above aspects, the ink includes a plurality of nanohoops, wherein a first nanohoop includes an [nl] aromatic ring compound and a second nanohoop includes an [n2]aromatic ring compound, wherein nl and n2 are two different integers.

[0117] In any or all of the above aspects, a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1: 100.

[0118] In any or all of the above aspects, the ink is maintained at a temperature that is above a melting point of the polymer so that the polymer becomes a polymer melt.

[0119] In any or all of the above aspects, the ink includes a solvent.

[0120] In any or all of the above aspects, the solvent includes dichloromethane.

[0121] In any or all of the above aspects, the system further includes an actuator configured to extrude the ink out of the nozzle.

[0122] In any or all of the above aspects, the actuator comprises a pump configured to apply a pressure to the composition contained in the reservoir.

[0123] In any or all of the above aspects, the system further comprises a controller configured to move the substrate relative to the nozzle.

[0124] In any or all of the above aspects, the system further comprises a heating apparatus configured to maintain the composition at an operating temperature that is above a melting point of the polymer so that the polymer becomes a polymer melt.

[0125] In any or all of the above aspects, the techniques described herein relate to a system including: a reservoir containing an ink, wherein the ink includes a polymer and a nanohoop having a structure according to the Formula I; a nozzle configured to receive the ink from the reservoir; and an actuator configured to extrude the ink out of the nozzle, wherein the ink is maintained at an operating temperature that is above a melting point of the polymer so that the polymer becomes a polymer melt.

[0126] In any or all of the above aspects, the system further includes a power supply configured to generate an electrostatic field between the nozzle and a substrate spaced apart from the nozzle so as to draw a charged jet of the ink out of the nozzle toward the substrate and form a polymer fiber on the substrate.

[0127] In any or all of the above aspects, the system further includes a controller configured to move the substrate relative to the nozzle.

[0128] In any or all of the above aspects, the system further includes a heating apparatus configured to maintain the ink at the operating temperature.

[0129] In any or all of the above aspects, the actuator includes a pump configured to apply a pressure to the ink contained in the reservoir.

[0130] In any or all of the above aspects, the nanohoop is not covalently attached to the polymer.

[0131] In any or all of the above aspects, the polymer includes polycaprolactone.

[0132] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0133] In any or all of the above aspects, the ink includes a plurality of nanohoops, wherein a first nanohoop includes an [m] aromatic ring compound and a second nanohoop includes an [ n 21 aromatic ring compound, wherein m and are two different integers.

[0134] In any or all of the above aspects, a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1:100.

[0135] In any or all of the above aspects, the techniques described herein relate to a method for preparing an ink for electrohydrodynamic processing, the method including: forming a first solution including a polymer and a first solvent; forming a second solution including two or more nanohoops and a second solvent; and mixing the first solution with the second solution to form a mixed solution, wherein the two or more nanohoops have a structure according to the Formula I, wherein the two or more nanohoops include at least a first nanohoop including an [ni]aromatic ring compound and a second nanohoop including an | mlaromatic ring compound, wherein m and n2 are two different integers.

[0136] In any or all of the above aspects, the first solvent is the same as the second solvent.

[0137] In any or all of the above aspects, the first solvent is different from the second solvent.

[0138] In any or all of the above aspects, the method further includes removing the first solvent and the second solvent from the mixed solution to form a solvent-free mixture.

[0139] In any or all of the above aspects, the method further includes heating the solvent- free mixture above a melting point of the polymer so that the polymer becomes a polymer melt.

[0140] In any or all of the above aspects, the method further includes dissolving at least some of the solvent-free mixture in a third solvent.

[0141] In any or all of the above aspects, the third solvent includes dichloromethane and dimethylformamide.

[0142] In any or all of the above aspects, a weight ratio of the two or more nanohoops to the polymer ranges from 1: 1000000 to 1 : 100.

[0143] In any or all of the above aspects, the polymer includes polycaprolactone.

[0144] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0145] In any or all of the above aspects, the techniques described herein relate to a method for preparing a polymer melt for melt processing, the method including: forming a first solution including a polymer and a first solvent; forming a second solution including a nanohoop and a second solvent; mixing the first solution with the second solution to form a mixed solution; removing the first solvent and the second solvent from the mixed solution to form a polymer- nanohoop mixture; and heating the polymer-nanohoop mixture above a melting point of the polymer so that the polymer becomes the polymer melt, wherein the nanohoop has a structure according to the Formula I.

[0146] In any or all of the above aspects, the first solvent is the same as the second solvent.

[0147] In any or all of the above aspects, the first solvent is different from the second solvent.

[0148] In any or all of the above aspects, the first solvent, the second solvent, or both the first solvent and the second solvent include dichloromethane.

[0149] In any or all of the above aspects, the first solvent, the second solvent, or both the first solvent and the second solvent include tetrahydrofuran.

[0150] In any or all of the above aspects, removing the first solvent and the second solvent includes heating the mixed solution under a vacuum condition.

[0151] In any or all of the above aspects, the second solution includes a plurality of nanohoops, wherein a first nanohoop includes an [ni] aromatic ring compound and a second nanohoop includes an | m|aromalic ring compound, wherein m and m are two different integers.

[0152] In any or all of the above aspects, a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1: 100.

[0153] In any or all of the above aspects, the polymer includes polycaprolactone.

[0154] In any or all of the above aspects, n is an integer ranging from 5 to 18.

[0155] In any or all of the above aspects, the techniques described herein relate to a method, including: receiving an ink including a polymer and a nanohoop; extruding the ink out of a nozzle; and electrically charging the ink extruded out of the nozzle, wherein the nanohoop has a structure according to the Formula I.

[0156] In any or all of the above aspects, electrically charging the ink is configured to eject a plurality of droplets from the ink, wherein the method further includes collecting the plurality of droplets on a substrate.

[0157] In any or all of the above aspects, electrically charging the ink is configured to form a charged jet, wherein the method further includes directing the charged jet toward a substrate and collecting a fiber including the polymer and the nanohoop on the substrate.

[0158] In any or all of the above aspects, the ink further includes a solvent, wherein the fiber is formed from the charged jet after evaporation of at least some of the solvent.

[0159] In any or all of the above aspects, the ink is maintained at a temperature above a melting point of the polymer so that the polymer becomes a polymer melt, wherein the fiber is formed from the charged jet after solidification of the polymer melt on the substrate.

[0160] In any or all of the above aspects, the method further includes controlling a flow rate of the ink extruded out of the nozzle so as to avoid whipping of the charged jet, thereby allowing controlled deposition of the polymer melt on the substrate.

[0161] In any or all of the above aspects, the method further includes moving the substrate relative to the nozzle so that the fiber collected on the substrate forms a fiber layer.

[0162] In any or all of the above aspects, the method further includes controlling movement of the substrate relative to the nozzle to form a multi-layer structure on the substrate using the fiber.

[0163] In any or all of the above aspects, the method further includes dynamically changing the nanohoop in the ink by varying the number of aromatic ring systems present in the nanohoop so that fibers collected on the substrate at different times contain different nanohoop compounds.

[0164] In any or all of the above aspects, the ink includes a plurality of nanohoops, wherein a first nanohoop comprises an [n aromatic ring compound and a second nanohoop comprises an [n2]aromatic ring compound, wherein m and n2 are two different integers.

[0165] In any or all of the above aspects, the techniques described herein relate to a method including: receiving an ink including a polymer and a nanohoop; heating the ink at an operating temperature above a melting point of the polymer so that the polymer becomes a polymer melt; and extruding the ink out of a nozzle, wherein the nanohoop has a structure according to the Formula I.

[0166] In any or all of the above aspects, the ink includes a plurality of nanohoops, wherein a first nanohoop includes an [m] aromatic ring compound and a second nanohoop includes an [ ] aromatic ring compound, wherein ni and n2 are two different integers.

[0167] In any or all of the above aspects, the method further includes electrically charging the ink extruded out of the nozzle to form a charged jet and directing the charged jet toward a substrate.

[0168] In any or all of the above aspects, the method further includes collecting a fiber including the polymer and the nanohoop on the substrate, wherein the fiber is formed from the charged jet after solidification of the polymer melt on the substrate.

[0169] In any or all of the above aspects, the method further includes controlling a flow rate of the ink extruded out of the nozzle so as to avoid whipping of the charged jet, thereby allowing controlled deposition of the polymer melt on the substrate.

[0170] In any or all of the above aspects, the method further includes controlling a flow rate of the ink extruded out of the nozzle so as to cause whipping of the charged jet, thereby causing random deposition of the polymer melt on the substrate.

[0171] In any or all of the above aspects, the method further includes moving the substrate relative to the nozzle according to a programmed pattern so that the fiber collected on the substrate forms a structure with a predefined geometry.

[0172] In any or all of the above aspects, the method further includes dynamically changing the nanohoop in the ink by varying the number of aromatic ring systems present in the nanohoop so that fibers collected on the substrate at different times contain different nanohoop compounds.

[0173] In any or all of the above aspects, the structure has a first portion and a second portion, wherein the first portion includes a first fiber containing a first nanohoop including an [ni]aromatic ring compound, wherein the second portion includes a second fiber containing a second nanohoop including an [n2]aromatic ring compound, wherein m and n2 are two different integers.

[0174] In any or all of the above aspects, the first portion and the second portion are located in two different layers of the structure.

[0175] Also disclosed is a method for preparing an ink for electrohydrodynamic processing, the method comprising: forming a first solution comprising a polymer and a first solvent; forming a second solution comprising a nanohoop and a second solvent; and mixing the first solution with the second solution to form a mixed solution, wherein the nanohoop has a structure according to Formula I as described herein.

[0176] In any of the above aspects, the second solution comprises at least two nanohoops and wherein a first nanohoop is an [m] aromatic ring compound and a second nanohoop is an [n2]aromatic ring compound, wherein m and n2 are different integers.Also disclosed herein is a method for preparing a nanohoop-polymer composition according to any or all of the above aspects, the method comprising combining a polymer with a nanohoop having a structure according to Formula I described herein, wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4.

[0177] In any or all of the above aspects, the method further comprises heating the polymer at a temperature that is higher than a melting point of the polymer to form a polymer melt prior to combining the polymer with the nanohoop.

[0178] In any or all of the above aspects, the method further comprises: (i) forming a first solution comprising the polymer and a first solvent; (ii) forming a second solution comprising the nanohoop and a second solvent; or (iii) a combination of (i) an (ii).

[0179] Also disclosed herein is a method of using any or all of the above composition aspects, comprising: adding the composition to an electrospinning system; heating the composition at anoperating temperature that is higher than a melting point of the polymer to form a polymer melt; and extruding the polymer melt out of a nozzle of the electrospinning system.

[0180] In some such aspects, the method further comprises electrically charging the polymer melt extruded out of the nozzle to form a charged jet and directing the charged jet toward a substrate.

[0181] Also disclosed is a method for forming a composite structure, comprising: adding a first composition to a nozzle of an electrospinning system, wherein the first composition is a solution or polymer melt comprising a first polymer and a first nanohoop; adding a second composition to the nozzle of the electrospinning system, wherein the second composition is a solution or polymer melt comprising a second polymer and a second nanohoop; and wherein (i) the second composition is not mixed with the first composition in the nozzle; and (ii) the first nanohoop and the second nanohoop independently have a structure according to Formula I as described herein, wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4, provided that the first nanohoop and the second nanohoop do not have the same structure.

[0182] In any or all such method aspects, the nozzle is a coaxial nozzle and the composite structure comprises discontinuous phases of the first composition and the second composition.

[0183] In any or all of the above aspects, the first and second polymer are the same.VIII. ExamplesExemplary Materials and Methods

[0184] Described below are exemplary protocols describing exemplary methods of creating fluorescent materials and using the same for producing fluorescent fibers using SES and MEW. It should be understood that the described parameters and experimental setup are merely exemplary, and not limiting, for illustrating the principles of the disclosed technologies.CPP Synthesis

[0185] As illustrated in FIG. 4A, in some aspects, [n]CPPs can be synthesized from common starting materials and reagents using a bottom-up methodology. In some examples, Poly(s- caprolactone) (PCL) was purchased from Corbion (Purasorb® PC12, lot # 2007001461) while [n]CPP compounds were prepared. In some aspects, different- sized [n]CPPs were prepared from [5]CPP-

[0018] CPP (where ’n’ is the number of phenylene rings) along with functionalizedderivatives. Dichloromethane (DCM) (Fisher, ACS certified, stabilized) was used as received without further drying.

[0186] FIG. 4B shows a plot of optoelectronic properties of exemplary [n]CPPs with absorbance (solid) and emission (dashed) spectra shown along with corresponding excitation maxima (Labs), emission maxima (em), quantum yield (<D), and molar extinction coefficient (s) for each of the [n]CPPs according to aspects of the present disclosure. In some aspects, the centrosymmetric nature of the nanohoops coupled with their strained radially oriented pi-conjugated systems also enables several intriguing optoelectronic properties. These strained macrocycles have shrinking H0M0- LUMO gaps with decreasing ring size, which can be challenging to obtain using other molecules (e.g., linear pi-conjugated molecules). Consistent with this trend, in some aspects, the [n]CPPs have a red-shifting emission as the CPP ring size decreases. As introduced above, in some aspects [n]CPPs possess a common absorption at 340 nm regardless of ring size or number of rings. The common absorption wavelength can be advantageous in multiplexing applications where there is only one excitation source. Moreover, in some aspects, these nanohoops have molar absorption coefficients on the order of 10sM 'cm1,which coupled with high quantum yields (e.g., 10% for [8]CPP, 38% for [9]CPP, and 65% for

[0010] CPP) leads to exceptionally bright fluorescent material.Blending of PCL and CPPs

[0187] In some examples, PCL was added to a round bottom flask equipped with stir bar. DCM (5 mL per gram PCL) was added, and the mixture stirred for 30 minutes to ensure adequate dissolution. A stock solution of [n]CPP in DCM (1 mg / mL) was prepared and injected into the mixture at the desired concentration. The resulting mixture was stirred for 30 minutes before the stir bar was removed and the solvent was removed under vacuum for several hours. To maximize the adequate removal of solvent, [n]CPP embedded PCL samples were subjected to molten thin film (<0.5mm) spreading and placed in a vacuum oven (-0.85 Bar) at 80 °C for 7 days before use. In some examples, after the above-described solvent removal process, the final CPP-PCL mixture has less than 0.5 wt.% or less than 0.1 wt.% of the residual solvent.

[0188] In the above example, the same solvent (e.g., DCM) is used to dissolve both the polymer (e.g., PCL) and the nanohoop (e.g., [n]CPP). In other examples, different solvents can be used to dissolve the polymer and the nanohoop, respectively.

[0189] In some examples, a polymer and nanohoop compounds can be mechanically mixed together without using a solvent. Specifically, the polymer can be heated above a melting point ofthe polymer and then blended with the nanohoop compounds to form a polymer-nanohoop mixture. For example, the CPP-PCL mixture can be formed by melt blending the PCL and CPP in a heated mixing apparatus (e.g., a heated vortex mixer), which heats the PCL above its melting point and uses vortexing to thoroughly mix the PCL and CPP.Solution Electrospinning

[0190] In some examples, CPP-PCL was dissolved at 15% weight in a 60 / 40 vol% ratio of dichloromethane (DCM) and dimethylformamide (DMF) to create an electrospinning “ink.” This ink was then added to a 5 -milliliter syringe with a 27 -gauge dispensing nozzle (BSTEAN) attached and placed into a syringe pump (World Precision Instruments, AL-300, United States) and set to deliver 0.5 mL / h. The nozzle was connected to a Heinzinger LNC 20000 - 3 Negative high voltage supply. For the electrospun mesh collection, a rotating 6-slide grounded collector was placed 14 centimeters away from the nozzle, and the slides were mounted by hydrostatic force between the metal collector and the glass slides. SES was conducted for 30 minutes at 18 kV with a flow rate of 0.5 mL / h. The meshes were imaged by scanning electron microscopy (SEM) (ThermoFisher Apreo 2) and fiber diameter was analyzed through Icy. The fibers used for measurements were chosen by drawing two perpendicular lines, crossing in the center of the image, and measuring the first 10 fibers which intersect this cross, moving outward in a clockwise pattern. Statistical functions such as the mean, standard deviation, and significant differences in fiber diameter were calculated. Photobleaching tests utilized an OmniCure Series 1500 UV curing lamp with a 365 nanometer filter. Measurements of intensity utilized a Leica Thunder to measure the fluorescent output.Melt Electrowriting

[0191] In some examples, after blending PCL and CPPs, the CPP-PCL mixture was loaded into a 3 mL syringe (Nordson Continuum EFD) with a 25-gauge nozzle (Nordson EFD Precision Tip) and a pneumatic plunger. The loaded syringes were placed in an oven at 80 °C overnight prior to processing which was performed at 80 °C with 2 bars of pneumatic air pressure. A 6.0 kV electric field was established between the charged head and grounded collector, and direct writing was conducted onto glass slides with a 3-mm gap between the nozzle and the slide (i.e., the collector distance). The jet speed was determined by analyzing where the deposited fibers transitioned from a buckled to a linear state with increasing collector speed. This “critical translation speed” (CTS) was determined by varying the printing speed by 10 millimeters per minute iterations from 350 mm / min to 700 mm / min. After determining the CTS, a collector speed of 640 mm / min was used to generate all planar scaffolds and structures.

[0192] In some examples, fabrication of MEW tubes was performed on a custom-built system with a cylindrical collector. These processing parameters used the same polymer blend with overnight heating but adopted a 22-gauge nozzle in combination with a 3 mm collector distance. A metal cylinder with a diameter of 5 mm was used as the collector, while the toolpath for the scaffolds were designed with MATLAB. The other processing parameters included a 4.5 kV applied voltage to the nozzle, an air pressure of 0.5 bar, a collector translation speed of 450 mm / min, and a heater temperature of 80 °C. Optical imaging the fibers and scaffolds used a Keyence VHX-7000, which was complemented with a 365 nm flashlight to image the fiber fluorescence.Cytotoxicity Testing

[0193] In some examples, cytotoxicity tests were designed in accordance with ISO 10993-5 and ISO 10993-12. Extract tests were conducted to eliminate variance from PCL surface hydrophobicity. Sheets of the CPP-PCL and PCL control were first sterilized by soaking in 70% ethanol for 30 minutes and sheets were washed three times with sterile lx phosphate buffered saline (PBS). The samples were then submerged in serum-free media for 72 h at 37 °C utilizing the surface area-to-volume ratio of 3 cm2 / mL as described in ISO 10993-12. The eluant media was composed of Dulbecco’s Modified Eagle Media (DMEM) with 1% penicillin-streptomycin, and 10% fetal bovine serum was added before application to cells. Human adipose derived mesenchymal stem cells (hAD-MSC) were purchased from Zen Bio (Cryopreserved Adipose Derived Adult Stem Cells: Lot#ASC062118A). The cells were seeded at 4000 cells per well in a 96 well plate and cultured to 80% confluency. Primary controls included the addition of 1% or 15% phosphate buffered saline, and 1%, 5%, and 10% ethanol for positive cell inhibition. Nitrile rubber (Kimtech) and poly(vinyl chloride) (Home Depot PVC, USA) were used as secondary elution controls. Analysis used AlamarBlue as an indicator of cellular inhibition and cytotoxicity.Cell-Scaffold Visualization when using CPP-PCL

[0194] In some examples, further cell testing was done on fluorescent MEW scaffolds composed of a crosshatch design with 500 micron spacing and 5 layers. These scaffolds were punched to 5 mm diameter and sterilized with 70% ethanol for 30 minutes. Surface treatment with 0. IM sodium hydroxide was utilized to improve cell attachment by reducing hydrophobicity. hAD-MSC’ s were seeded at a density of 60,000 cells / scaffold in the same media mix utilized above (Dulbecco’s Modified Eagle Media (DMEM) with 1% penicillin-streptomycin and 10% fetal bovine serum). After 1 day, the media mix was changed to include fibroblast growth factor beta to improve cellexpansion. To analyze the development of the cellular structures, phalloidin and 4',6-diamidino-2- phenylindole (DAPI) staining was done. Brightfield imaging was done on (name of lab scope) and fluorescent imaging was done on a Leica Thunder Imager.Leaching Testing

[0195] In some examples, leaching tests were conducted utilizing the surface area-to-volume ratio established in ISO10993-12. Samples were cut into 3 cm2slabs, placed in a 1.5mL tube, then immersed in 1 mL of PBS for 7 days at 37 °C. The slabs were then removed and PBS was analyzed through ultraviolet spectroscopy (Agilent Cary 60 UV-Vis Spectrophotometer).Thermogravimetric Analysis

[0196] A TA Instruments Q500 thermogravimetric analyzer was used to investigate the thermal degradation of the materials. An aluminum pan was placed in a platinum tray and tared, then 5-10 mg of material was added to the pan. The system was set to ramp at 10°C.min-1to 600°C, with the ramp starting at room temperature. The mass loss was analyzed with Microsoft Excel, and plotted with GraphPad Prism.Viscometric Analysis

[0197] The viscosity of the materials was characterized using a TA Instruments DHR-2 rheometer. The environmental thermal system was used to heat the plates into the range needed for the experiments, with 25 mm diameter parallel plates and a 500 pm gap. For analyzing the rheological responses to changing temperatures, a shear rate of 1 s'1was used, while the temperature was changed at a ramp of 5°C.min’1, and the viscosity was measured at an interval of 1°C. To further analyze the viscosity within our chosen thermal conditions, a processing temperature of 80°C was used, and the shear rate was varied from 0.001 s’1to 10 s’1. The data was statistically analyzed and plotted in GraphPad Prism.Statistical Analysis

[0198] Analysis of the statistical significance of all quantified data used GraphPad Prism. For analyzing difference between multiple groups, analysis of the distribution and normality were followed by the respective analysis of variance (ANOVA) test. For certain examples, statistical analysis was a Kruskal Wallis one way ANOVA. For certain examples, fiber diameters were analyzed by an ordinary one-way ANOVAs. Multiple comparisons were done through Tukey’spost-hoc testing for all samples. Significance was denoted as follows: * = p < 0.05, ** = p < 0.01, *** = p < 0.001, *** = p < 0.0001. We have used the term ‘n’ to refer to sample size.Example 1: Exemplary Fluorescent Properties of Different CPPs Blends in PCL

[0199] In general, excellent fluorescent properties were achieved after blending the CPPs into PCL, and exposing them to UV radiation using a low-cost, handheld device (FIGS. 5A-5F). In some examples, a spectrum of concentrations was visualized under both excitation conditions, from 0.0001 wt.% up to 1 wt.% for [8]CPP (FIGS. 5A and 5C). It was observed that, when the ratio of[8]CPP to PCL was set to 0.01 wt.%, the resulting bulk material exhibited a strong fluorescent signal (FIGS. 5C, 5D), without fluorescence or color bias occurring under ambient visible light (FIGS. A, 5B). The fluorescent signal of the CPPs become visible under ambient light at 0.1 wt.% inclusion, with FIG. 5A showing this trend.

[0200] In some examples, this lack of fluorescence to the naked eye under ambient visible light was also observed at 0.01% weight for both [9]CPP-PCL and

[0010] CPP-PCL samples. The fluorescent capabilities of CPP’s and CPP-PCL provides a promising perspective for microscopy, as the multiple emission wavelengths can result from a singular excitation wavelength, induced by a low-cost light. Under this UV excitation, the CPP-PCL materials emit their respective fluorescence, with a blue shift occurring as the CPP’s cyclic radius increases. This leaves the [8],[9], and

[0010] CPP-PCL having fluorescent emissions in the 533 nm, 494 nm, and 466 nm wavelengths, including when the solvent is removed and only the PCL and CPPs remain as a solid blend in the glass syringes (FIGS. 5E-5F). This indicates that the fluorescence is seen in both the solid and liquid phases, which is significant in MEW and processing.Example 2: Exemplary Thermal and Viscoelastic Properties of Different CPPs Blended in PCL

[0201] Thermal analysis of exemplary PCL and [n]PCL-CPP blends was performed to assess the impact of CPP inclusion on the physical properties of the material influencing printability and mechanical properties compared to PCL alone. (FIGS. 6A-6G). PCL used in its as-provided pellet form is termed PCLpenet and a PCL control that was solvent mixed (but no fluorophore added) is termed PCLsham. DSC analysis revealed no significant difference in the melting temperature (average of 57.1 ± 0.3 °C) and no significant difference in the crystallinity (average of 57.8 ± 2.0%), as illustrated in FIGS. 6D-6F. At a concentration of 0.01 wt.%, the melting properties of the composite were dominated by the PCL phase. In some aspects, the processing steps by which theCPP was incorporated into the PCL did not impact the thermal properties of the material. No significant difference was found between the melting temperature and crystallinity of virgin, unprocessed PCL (PCLpeiiet) compared to a PCL sample that had undergone the same blending conditions without the addition of the fluorophores (PCLsham) (FIGS. 6E-6F).

[0202] Similarly, degradation measurements further validated the assertion that no significant difference in material thermal properties was observed as a result of the inclusion of CPP and processing steps (FIG. 6A). In FIG. 6A, all curves show highly repeatable degradation behavior, with negligible differences in degradation onset observed after approximately 300°C. The use of vacuum and heat evaporation was validated in successfully removing DCM from the samples, whereby no mass loss was observed around the boiling point of DCM at 39.6 °C (n=3, p=0.001), with all CPP samples measuring 99.993 ± 0.003% of initial mass (FIG. 6D).

[0203] Rheology measurements further validated the limited impact of CPP inclusion on the viscoelastic properties of the samples (FIGS. 6B-6C). Near-Newtonian behavior was observed in all samples, with some mild shear thinning observable approaching 10 s1(FIG. 6B). These results indicate that the addition of the CPP and processing steps posed no substantial difference to the materials’ viscosity over the shear range examined. For example, a marginal difference in viscosity was observed at 1 s'1between the CPP-inclusive, with viscosity of 2345 ± 82 Pa.s, compared to PCL-only samples, with viscosity of 2524 ± 48 Pa.s (n=3, p=0.01), indicating that the CPP slightly reduced the viscosity of the material at this shear rate (FIG. 6G). Similarly, in characterizing the thermoresponsive properties of the materials, the PCL samples decreased below one order-of- magnitude in viscosity, and no substantial difference in thermoresponsivity was observed with the inclusion of CPP. The marginal difference in viscosity over the shear rates tested did not significantly impact printability, and as such, the CPP composites could be fabricated with the same MEW operational parameters as PCLpenet.

[0204] Overall, in some aspects, the inclusion of CPP within the PCL instigated a negligible difference in thermal and viscoelastic properties compared to PCL alone, whereby no meaningful difference in the melting temperature, crystallinity, degradation profile or bulk viscoelastic properties was observed. These measurements suggest the utility and translatability of this new MEW material.Example 3: Exemplary SES of CPP-PCL

[0205] The CPPs investigated here, for the first time, allow simultaneous visualization of different emission wavelengths, using the same excitation source. With the CPPs dissolved into a PCL polymer solution, the electrospinning of fibers can be performed using a standard SES apparatus, and the resulting non-woven membranes can retain their fluorescent capabilities. This provides a very simple approach to non-woven production, as dissolution is straightforward and already part of the workflow for preparing SES inks.

[0206] FIGS. 7A-7F show aspects of a solution electrospinning (SES) apparatus and results of SES of CPP-PCL. Visualization of SES meshes using SEM showed that there was only a slight variation for the different CPPs, with the

[0010] CPP-PCL having a significantly (p<0.05) higher fiber diameter than the [8]CPP-PCL, [9]CPP-PCL, and control PCL. For the

[0010] CPP-PCL samples, this statistical difference can be due to a bimodal distribution of fiber diameters (i.e., both smaller and large fiber diameters), while the average remained the same compared to [8]CPP-PCL and [9]CPP- PCL solutions. This result could be attributed to either the

[0010] CPP within the material or, potentially, to the inherent variability that can occur for the SES process.

[0207] To produce fluorescent fibers for SES membranes, the technologies described herein, for the first time, make it possible to use the same excitation wavelength for a combination of fibers emitting different wavelengths. In general, the 300-400 nm fiber diameter achieved for SES and the good consistency of fiber diameter upon the addition of CPP molecules demonstrates the utility of the fluorophores with this process. Furthermore, PCL is a widely used and important polymer for SES, and the addition of the CPPs did not substantially affect the capacity to produce high quality meshes. Post-processing viewing of CPP-PCL retained the continued fluorescence under UV excitation.

[0208] FIGS. 8A-8E show additional aspects of imparting fluorescence into SES membranes using CPPs. With the [n]CPPs dissolved into a PCL polymer solution, the electrospinning of fibers was performed using the SES apparatus of FIG. 7A, and the resulting non-woven membranes fluoresced. As described above, performing MEW onto SES membrane substrates does not affect the quality of the scaffold. When MEW was performed onto

[0010] CPP-PCL SES membranes using a [8]CPP-PCL blend, the fibers and membrane could be readily contrasted with each other using the same incidence wavelength, exemplified in FIGS. 8D-8E. The MEW fibers are directly visible against the SES membrane with specific fluorescent signals.Example 4: Exemplary MEW of CPP-PCL Flat Scaffolds

[0209] As shown in FIG. 5F, the fluorescent properties of the CPP and PCL blend “inks” after solvent removal are excellent. MEW, however, imparts challenging thermal conditions on the polymer to be processed, due to the nature of the technology. The mechanism to achieve small diameters for MEW is fundamentally different to that for SES. For the latter, an EHD instability often termed “whipping” draws the fluid from the of the nozzle into a chaotic path. The electrified jet is substantially stretched during this tortuous, airborne, phase which enables both the small diameter fibers as well as assisting in the evaporation of the solvent. MEW functions in a different manner, where the diameter reduction is a result of extremely low flow rates to the nozzle, typically 2-5 pL / h. This results in the polymer in the syringe remaining heated for substantial periods of time, which can be hours and even days, when thick scaffolds are intended to be made.Furthermore, there is the added convenience in not having to replace the syringe with fresh material and continued heat exposure can be applied to the polymer for several weeks. For example, the period for MEW processing can be as long as 25 days for the same PCL as used here, during which there was no discernable change in the resulting fiber when the temperature used was 75°C. Therefore, any fluorophores to be included with the PCL should be thermally resistant without significant loss in their thermal capabilities. With a thermal degradation temperature of 300°C, the CPPs described herein are capable of providing fluorescence to MEW products.

[0210] FIGS. 9A-9F show that indeed the fluorescent capabilities of CPPs are retained after MEW processing. With a white appearance to the eye under ambient light (FIGS. 9A-9C), these scaffolds provide emissions in the corresponding wavelengths for the CPPs (FIGS. 9D-9F).

[0211] The jet speed for MEW can be determined through measuring the CTS, to determine whether the inclusion of the CPPs affects this parameter. In some examples, it was found that indeed the addition of 0. lwt% CPP did not affect the jet speed (610 mm / min for [8]CPP; 620 mm / min for [9]CPP; 620 mm / min for

[0010] CPP), nor the general printability of the material compared to pure PCL (630 mm / min) processed using the same solvent addition and removal steps. Significant differences were not measured between fiber diameters, which is described in more detail herein with reference to FIG. 3, wherein the average fiber diameter was 10.04 + 0.569 m. Without the appropriate melt compounding equipment, it was required to dissolve the CPP-PCL into DCM then subsequently remove the solvent. Performing this workflow on pure PCL may introduce residual solvent in the final material, despite extensive and prolonged removal. It likely decreases the melt viscosity and or increases charge within the PCL, increasing the CTS. In MEW,the CTS indicates the speed at which the collector must be moved to ensure that fiber buckling does not occur, and scaffolds have straight fibers.

[0212] This contrasts with unprocessed PCL (350 mm / min) which did not undergo the same processing conditions as the CPP-PCL. Since the CTS of all the processed polymer blends and PCL fell within the 610-630 mm / min range, this may require an adjustment of the collector speeds compared to the neat polymer. However, with this adjustment in collector speed, the consistency and stability further proved the usability of CPP-PCL as a MEW material. In some examples, decagonal scaffold design was composed of 40 layers of straight fibers spaced at 150 pm, where each next layer was rotated by 36° (180° / 5 directions), then were printed with [8], [9], and

[0010] CPP-PCL then imaged on various scales under ambient and UV radiation. FIGS. 9A-9F provide the overview that visualizes the fluorescent capability of CPP-PCL, ranging from the centimeter with the naked eye down to micrometer scale with an optical microscope.Example 5: Exemplary MEW of CPP-PCL Tubular Scaffolds

[0213] In some examples, several tubular MEW scaffolds were designed with different morphologies, including a 30° angular displacement between each layer to generate structures that are not typical for a “wound” tube (FIGS. 10A, 10B). Utilization of CPP-PCL proved continued retained fluorescent capabilities after melt electrowriting processing. As shown in FIG. 10B, the CPP-PCL scaffolds showed fluorescent emissions under UV excitation, which are visible on the scaffold-scale without any added optics.

[0214] In some examples, by printing with all four materials, structures with all three CPP colors and processed PCL can be printed. A scaffold was designed with 4 angles of lines, at 0°, 45°, 90°, and 135°, with the color varying by angle. This allows for orientation of the scaffold based on fluorescent imaging for improved placement and analysis capabilities. As shown in FIGS. 10C- 10E, the scaffold can be printed regularly, with ordered intersections of 500 pm in the 0° and 90° directions, and 500 pm in the 45° and 135° directions.Example 6: Exemplary Combinations of Different Colored CPP Fibers

[0215] One benefit of using CPPs beyond their thermal efficiency is the colorimetric identification of each fiber type. When viewing samples under a microscope at higher magnifications, losing orientation with respect to the sample axis and boundaries can be common, especially if the sample is infused with tissue. Different diameter MEW fibers may also be incorporated and may not be readily discernable at higher magnifications while understanding which is the top / bottom of a sample may be an aspect to determine prior to further manipulation. FIGS. 10D and 10E show how a multi-material scaffold can be fabricated with three different colored fluorescent fibers. This allows a specific orientation to be readily identified, such as the plane along the length of the tubular scaffold.Example 7: Exemplary Cytotoxicity of CPPs

[0216] As described above, CPPs can be incorporated within MEW fibers as part of scaffolds which can have utility within biomedical applications. Thus, the leaching of CPPs from the PCL scaffold or subsequent cytotoxicity would be an undesirable outcome. FIGS. 11-12 shows that the different CPPs do not demonstrate cytotoxicity in accordance with ISO 10993-5 and ISO 10993-12 methods.

[0217] As shown in FIGS. 11-12, all [n]CPP-PCL scaffold elutions displayed cytocompatible responses in the presence of mesenchymal stem cells (MSC), with relative metabolic activity recorded above the 70% threshold for all samples. MSCs were chosen for their applicability to biofabrication, as well as their sensitivity compared to other common cell types used in cytotoxicity testing, like fibroblasts. It was furthermore observed that all the [n]CPP-PCL blends yielded cell proliferation responses comparable to PCLsham. Further validation of the applied scaffold extract testing protocol was achieved through the inclusion of positive (PVC) and negative (Nitrile) material controls. Additionally, the sensitivity of the assay was confirmed by exposing it to an ethanol concentration gradient. This gradient demonstrated that concentrations of both 5% and 10% ethanol resulted in a cytotoxic read-out (less than 70% relative metabolic activity), while 1% ethanol is not enough to yield toxic effects in vitro. Overall, greater than 90% relative metabolicactivity was recorded on average across all [n]CPP-PCL variants, which indicates that this material is suitable as an in vitro or in vivo scaffold tag and imaging guide.

[0218] A potentially confounding factor in the imaging and cytotoxicity of the CPP-laden fibers is whether the fluorophore leaches out of the PCL with time. This is not likely due to the similar hydrophobicity of the fluorophore and the polymer. Leaching tests proved the stability of the blending of the fluorophores in PCL, as shown in FIG. 13, with the ultraviolet spectroscopy of the leached PBS proving a minimal leaching. Compared with the processing controls, it is shown that no significant amount of the CPPs leach from the polymer. However, some residual solvent is seen leaching into the solution, with the processing control having a similar peak at 203 -nanometers. This matches the peak locations seen if DCM is run under the same conditions.Example 8: Exemplary Fiber Diameter of MEW-Processed [n]CPP-PCL Blends

[0219] FIG. 14 illustrates measurement of printing properties of [n]CPP-PCL blends against an untouched PCL control (PCLpeiiet) and a solvent-processed PCL control (PCLsham). Fiber diameter was imaged at the same speed across all materials, and no statistically significant differences were observed. Statistical analysis used an ordinary one-way ANOVA followed by Dunnett’s multiple comparisons test.Example 9: SEM imaging of Solution-Electrospun [n]CPP-PCL

[0220] FIGS. 15A-15D are exemplary SEM images of solution-electrospun PCL and [n]CPP-PCL blends according to aspects of the present disclosure. Materials were dissolved at 15 wt% in a 3:2 ratio of DCM / DMF. Next, they were pipetted into 3 mL syringes fitted with 27-gauge needles, which were then loaded into a syringe pump set to 0.5 mL / hr. A collector distance of 14 cm was used, and the needle tips were charged to 18 kV.Example 10: Exemplary Fiber Diameter of Electrospun PCL and [n]CPP-PCL Blends

[0221] FIG. 16 illustrates electrospun fiber diameter analysis for PCL and [n]CPP-PCL Blends. Statistical analysis used an ordinary one-way ANOVA followed by Dunnett’s multiple comparisons test. * = p<0.05; n=9. In some aspects, a significant increase in fiber diameter was observed for

[0010] CPP-PCL relative to PCL.Example 11: Fluorescent Staining of Seeded Cells on [n]CPP-PCL Scaffolds

[0222] To investigate the usability of the CPP-PCL materials within a bioengineering context, seeding of MSCs onto CPP-PCL MEW scaffolds showed the relation of fluorescence between the materials and common fluorophores. In some aspects, the seeding was conducted onto scaffolds with the intention of investigating whether DAPI, rhodamine and fluorescein stains would be visible against the CPP-PCL materials.

[0223] FIG. 17 shows a seeding workflow for MEW scaffolds. Cells were seeded after sterilization and NaOH etching, at 60,000 cells per scaffold. The cells were seeded onto the scaffolds by first suspending them at a concentration of 5m cells / mL, then pipetting 12 pL of cell suspension onto dry scaffolds. Every 2nd hour, 5 L of media was added to the scaffolds, until hour 6, wherein the scaffolds were immersed in excess media. No secondary structures were used to hold the scaffolds in place, and the seeding processes ensured that the scaffolds did not retain surface tension and float on top of the media. After approaching confluency at 6 days of culture, the scaffolds were fixed then stained with fluorescein or rhodamine-tagged phalloidin.

[0224] With the [n]CPP-PCL blends emitting fluorescent light in common wavelengths, experimentation with the emission filters on the microscope were conducted. FIG. 18A shows selective channels of fluorescein-tagged phalloidin samples. FIG. 18B shows selective channels of rhodamine-tagged phalloidin samples.

[0225] With the [n]CPP-PCL blends emitting fluorescent light in common wavelengths, experimentation with the emission filters on the microscope was conducted. Initial images using the filters that closest matched the emission peak of the respective [n]CPP-PCL blends had an issue with the excitation of DAPI. Therefore, by shifting the filters to the next commonly used wavelength for each material, specificity could be achieved for the scaffolds alone.

[0226] The [n]CPP-PCL materials common excitation range of 300-400 nm greatly increases their usability within fluorescent imaging. There is some overlap of the [n]CPPs fluorescence within the DAPI channel, as the [n]CPP’s have broad fluorescent emissions with a similar excitation as DAPI. This is visible within the scaffold columns in FIGS. 18A-18B, as the scaffold is visible as well as cell nuclei. This is most strongly visible with

[0010] CPP-PCL, as the nuclei are clearly visible against the scaffold. Overlap is reduced for [8]CPP-PCL and [9]CPP-PCL in the DAPI channel, but still exists.

[0227] As shown in FIGS. 19A-19H, human adipose stem cells attach to all MEW scaffold formulations and demonstrate typical growth behavior to that of a square-shaped porous scaffold. Specifically, cells adhere along the fibers and trigger the deposition of cytoskeleton, resulting in rounded comers and the formation of a distinct central opening.

[0228] In some aspects, the fluorescent materials are visible together with traditional fluorescent DNA and filamentous actin probes using cytochemical techniques. Through the use of preexisting filter and laser assemblies, the [n]CPP-PCL materials were easily visible against the stains. The contrast of [8]CPP-PCL and [9]CPP-PCL from DAPI, rhodamine, and fluorescein is notable, as the emission and excitation spectra of these materials has minimal overlap with these common fluorophores. However, [9]CPP-PCL has strong specificity in its individual channel, but still is visible in the DAPI channel. Overall, the fluorescence of these materials does not overpower the DAPI signal and can facilitate analysis of cell-scaffold interactions. The strong fluorescent signal of all materials across common emission wavelengths, while still remaining specific to the scaffolds indicates high usability as in vitro and in vivo imaging tags. Overall, the exemplary [n]CPP-PCL blends showcase fluorescent properties that can be customized to image various biological samples.Example 12: Multi-Material MEW using [n]CPP-PCL Blends

[0229] In some aspects, differently colored fluorophores can aid in performing fundamental multimaterial MEW research, generating proof-of-concept designs. By printing with all four materials, a composite scaffold with all three CPP colors and a control PCL can be achieved. FIGS. 20A-20H show four different MEW jets printed in a sequential and cyclic manner (FIG. 20A), achieving semi- woven fiber intersections across a scaffold. This demonstrates multi-material MEW fiber printing control beyond a series of walls printed sequentially, but not interlocked. While in this example, all the fibers are made from PCL, the [n]CPP allows testing of multi-nozzle MEW concepts and generation of G-code libraries while the technical issues surrounding processingdifferent polymers, with differing melting points and thermal degradation profiles, are developed in parallel.

[0230] Another benefit of using [n]CPPs beyond their thermal stability is colorimetric orientation and waymarking for MEW scaffolds. When viewing samples under a microscope at higher magnifications, losing orientation with respect to the sample axis and boundaries is common, especially when the sample is embedded within tissue. FIGS. 20B-20E shows a scaffold designed with lines at 4 angles: 0°, 45°, 90°, and 135°, with the material, and therefore the color, varying by angle. This capability helps investigate cell-scaffold interactions within a single scaffold. For example, fibers of different diameters or even polymer composition could be fluorescently tagged, which otherwise would be hard to distinguish under fluorescent imaging setting.

[0231] FIGS. 20F-20H demonstrate how four differently colored fiber walls can be printed upon each other, branching out into separate fibers. Within this fiber wall, discrete fluorescent and non- fluorescent regions are shown in FIG. 20G, that match our intended program. In addition to visualizing fiber-cell interactions, fluorescent MEW fibers and SES membranes can be used for fundamental processing and design research. In some aspects, multi-material processing can be aided by validation of manufacture with fluorescent fibers. The fluorescent properties of [n]CPPs can be used in other forms beyond what is presented here, including other biofabrication processing approaches where PCL can be used.

[0232] In view of the many possible embodiments to which the principles of the disclosed technologies may be applied, it should be recognized that the illustrated embodiments are only certain examples of the disclosed technologies and should not be taken as limiting the scope of the disclosed technologies. Rather, the scope of the claimed subject matter is defined by the following claims and their equivalents.

Claims

We claim:

1. A composition comprising: a polymer; and a nanohoop having a structure according to Formula IFormula I wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoop and is an integer greater than 4, and wherein the nanohoop is configured to re-emit a fluorescent light upon irradiation of the composition with an ultraviolet light.

2. The composition of claim 1 , wherein the nanohoop is not covalently attached to the polymer.

3. The composition of claim 1, wherein the polymer comprises polycaprolactone.

4. The composition of claim 1 , wherein aromatic ring systems of the nanohoop are configured to remain intact when the composition is heated at a temperature of up to 300 °C.

5. The composition of claim 1, wherein n is an integer ranging from 5 to 18.

6. The composition of claim 5, wherein n is an integer ranging from 8 to 10.

7. The composition of claim 1, wherein a plurality of nanohoops is included and wherein a first nanohoop of the plurality comprises an [ni]aromatic ring compound and a second nanohoop of the plurality comprises an | rr laromatic ring compound, wherein m and n are different integers.

8. The composition of claim 1, wherein a weight ratio of the nanohoop to the polymer ranges from 1 :1000000 to 1 :100.

9. The composition of claim 8, wherein the weight ratio is 1 : 10000.

10. The composition of claim 1 wherein the polymer is in a liquid form.

11. A system, comprising: a reservoir containing the composition according to claim 1 ; and a nozzle in fluid communication with the reservoir.

12. The system of claim 1 1 , further comprising a power supply configured to generate an electrostatic field between the nozzle and a substrate spaced apart from the nozzle so as to draw a charged jet of the composition out of the nozzle and directing the composition toward the substrate and form a polymer fiber on the substrate.

13. The system of claim 11, further comprising a controller configured to move the substrate relative to the nozzle.

14. The system of claim 11, further comprising an actuator configured to extrude the composition out of the nozzle.

15. The system of claim 14, wherein the actuator comprises a pump configured to apply a pressure to the composition contained in the reservoir.

16. The system of claim 11 , further comprising a heating apparatus configured to maintain the composition at an operating temperature that is above a melting point of the polymer so that the polymer becomes a polymer melt.

17. The system of claim 1 1, wherein the composition comprises a plurality of nanohoops, wherein a first nanohoop of the plurality comprises an [ni]aromatic ring compound and a second nanohoop of the plurality comprises an | m laromatic ring compound, wherein m and n2 are two different integers.

18. A method for preparing a nanohoop-polymer composition, the method comprising combining a polymer with a nanohoop having a structure according to Formula IFormula I wherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4.

19. The method of claim 18, further comprising heating the polymer at a temperature that is higher than a melting point of the polymer to form a polymer melt prior to combining the polymer with the nanohoop.

20. The method of claim 18, further comprising:(i) forming a first solution comprising the polymer and a first solvent;(ii) forming a second solution comprising the nanohoop and a second solvent; or(iii) a combination of (i) and (ii).

21. A method of using the composition of claim 1, comprising: adding the composition to an electrospinning system; heating the composition at an operating temperature that is higher than a melting point of the polymer to form a polymer melt; and extruding the polymer melt out of a nozzle of the electrospinning system.

22. The method of claim 21 , further comprising electrically charging the polymer melt extruded out of the nozzle to form a charged jet and directing the charged jet toward a substrate.

23. A method for forming a composite structure, comprising: adding a first composition to a nozzle of an electrospinning system, wherein the first composition is a solution or polymer melt comprising a first polymer and a first nanohoop; adding a second composition to the nozzle of the electrospinning system, wherein the second composition is a solution or polymer melt comprising a second polymer and a second nanohoop; and wherein (i) the second composition is not mixed with the first composition in the nozzle; and (ii) the first nanohoop and the second nanohoop independently have a structure according to Formula IFormula Iwherein ring A is an aromatic ring system and n is an integer representing the number of the aromatic ring systems present in the nanohoops and is selected from an integer greater than 4, provided that the first nanohoop and the second nanohoop do not have the same structure.

24. The method of claim 23, wherein the nozzle is a coaxial nozzle and the composite structure comprises discontinuous phases of the first composition and the second composition.

25. The method of claim 23, wherein the first and second polymer are the same.

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