Optically and mechanically active nanoscale media

Abstract

The present invention relates to a method for incorporating dye and/or nanoparticles into polymer films and into electrospun polymeric nanofibers, and, more specifically, to a method for electrospinning a molecularly homogenous solution of dye (and/or nanoparticles) and polymer dissolved in a mutual solvent leading to uniform distribution of dye across the cross-section of each constituent fiber and to resulting nanofibers with the dye/nanoparticles incorporated therein.

Claims

1. A near infrared fluorescent marker for a target medical device, comprising: a fiber mat including a plurality of fibers formed from a shape memory polymer and a near infrared dye that is homogenously distributed within the plurality of fibers of said shape memory polymer; wherein the shape memory polymer is programmed to shrink from a temporary shape to a permanent shape in response to a stimulus so that said fiber mat will shrink around a portion of the target medical device; and wherein said near infrared dye within the plurality of fibers of fiber mat will emit fluorescence between 750 nm and 950 nm when subject to near infrared excitation after the fiber mat has been shrunk around the portion of the target medical device.

2. The marker of claim 1, wherein said polymer and said dye are present in a ratio of 0.00625 milligrams to 1.25 milligrams of dye per 2.0 grams of polymer.

3. The marker of claim 1, wherein said shape memory polymer has a transition temperature below 50 degrees Celsius.

4. The marker of claim 3, wherein said shape memory polymer is poly(vinyl acetate).

5. The marker of claim 4, wherein said dye is indocyanine green.

6. The marker of claim 4, wherein said dye has an excitation wavelength and an emission wavelength in the near infrared spectrum.

7. A method of visualizing a medical device positioned in a patient, comprising the steps of: providing a near infrared marker comprising a fiber mat including a plurality of fibers formed from a shape memory polymer and a near infrared dye that is molecularly homogenously distributed within the plurality of fibers of said shape memory polymer, wherein the shape memory polymer is programmed to shrink from a temporary shape to a permanent shape in response to a stimulus so that said fiber mat will shrink around a portion of a target medical device and wherein said near infrared dye will emit fluorescence between 750 nm and 950 nm when subject to near infrared excitation after the fiber mat has been shrunk around the portion of the target medical device; positioning the near infrared marker around a portion of said target medical device; stimulating the shape memory polymer of the near infrared marker so that the fiber mat shrinks from the temporary shape to the permanent shape; positioning said target medical device and said near infrared marker within said patient; exciting said near infrared marker with near infrared light so that the near infrared marker fluoresces between 750 nm and 950 nm; capturing any near infrared emissions from said near infrared marker and from a predetermined area of said patient proximate to said near infrared marker; and displaying said near infrared emissions from said near infrared marker and said proximate area.

8. The method of claim 7, wherein the temporary shape of said near infrared marker is configured into a tube.

9. The method of claim 8, wherein the step of positioning the near infrared marker around a portion of said target medical device comprises the step of positioning said target medical device in said tube and the step of stimulating the near infrared marker comprises the step of applying heat until said tube constricts around said target medical device.

10. The method of claim 7, wherein said near infrared marker is configured into a strip.

11. The method of claim 7, wherein said near infrared marker is configured into an end cap.

12. The method of claim 9, wherein said shape memory polymer comprises poly(vinyl acetate).

13. The method of claim 10, wherein said dye comprises indocyanine green.

14. The marker of claim 1, wherein said near infrared dye of said electrospun fibrous web has a highest near infrared (NIR) emission intensity at a concentration of 0.0125 milligrams of said dye per 2.0 grams of said polymer.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

(2) FIG. 1A is a schematic representation of an electrospinning device used in accordance with an embodiment of the present invention.

(3) FIG. 1B is an SEM image of an electrospun fiber mat having an average fiber diameter of 0.61 m.

(4) FIG. 2A is a schematic representation illustrating a procedure of incorporating ICG dye into a polymer solution according to an embodiment of the present invention.

(5) FIG. 2B is a photographic representation of ICG concentrations of (a) 0 mg/ml, (b) 0.00625 mg/ml, (c) 0.0125 mg/ml, (d) 0.025 mg/ml, (e) 0.05 mg/ml, and (f) 0.125 mg/ml along with the NIR images of the same vials under a NIRF imaging system at the gain of 1 and exposure time of 150 ms.

(6) FIG. 3 is a series of images showing (I) photographs of PVAc fiber mat, (II) NIRF images of fiber mat, (III) photographs of PVAc film, (IV) NIRF images of PVAc film, each with ICG concentrations of: (a) 0 mg/ml, (b) 0.00625 mg/ml, (c) 0.0125 mg/ml, (d) 0.025 mg/ml, (e) 0.05 mg/ml, and (f) 0.125 mg/ml. The gain and exposure time were 1 and 140 ms respectively. The scale bars each represent 5 mm.

(7) FIG. 4 is a graphical representation of spectrofluorometry of (a) PVAc fiber mat with different ICG concentration, and (b) PVAc films with ICG concentration of: (i) 0 mg/ml, (ii) 0.00625, (iii) 0.0125, (iv) 0.025, (v) 0.05, and (vi) 0.125.

(8) FIG. 5 is a graphical representation of a comparison of PVAc fiber mat and PVAc film with different ICG concentration by using (a) Spectrofluorometry, and (b) NIR imaging, according to an embodiment of the present invention. The mean gray values were computed by using ImageJ program. PVAc fiber mat showed higher intensity and mean gray values compared to the PVAc film. The highest intensity by spectrofluorometry and the highest mean gray value by NIR imaging were observed for samples with 0.0125 mg/ml ICG concentration.

(9) FIG. 6 is a schematic and photographic representation showing a small strip that was cut from the electrospun fiber mat and then wrapped around a pediatric catheter tube (i). The strip was shrunk on to the tube by applying (ii) 25 C. water or (iii) 50 C. heat. (b) Small rings were cut from a halo tube of electrospun fiber mat ((i) and (ii)) and recovered by applying (iii) 25 C. water and (iv) 50 C. heat.

(10) FIG. 7 is a series of images of: (a) and (b) photographs of an electrospun tube and small strip cut from electrospun fiber mat of PVAc/ICG with the ICG concentration of 0.0125 mg/ml wrapped around a pediatric catheter tube; (c) and (d) NIRF images of same devices taken with the gain of 1 and exposure time of 140 ms. The scale bar represents 10 mm.

(11) FIG. 8 is a graph of absorbance measurements using a plate reader at 790 nm for (a) polymer solutions before electropsinning and (b) after electrospinning by dissolving the fiber mats in methanol and DMF to yield the same polymer concentration.

(12) FIG. 9 is a series of NIR images of a tube coated with NIR fluorescence polymer as placed (a) subcutaneous, (b) intraperitoneal, and (c) behind the bowel in a mouse.

(13) FIG. 10 is a series of NIRF images of a tube coated with NIRF polymer as placed outside and then inside a mouse.

DETAILED DESCRIPTION OF THE INVENTION

(14) As discussed and shown herein and in the accompanying figures, a molecularly homogeneous solution of dye and polymer dissolved in a mutual solvent has been electrospun, which lead to uniform distribution of dye across the cross-section of each constituent fiber. Unexpectedly, the fluorescence intensity of dye incorporated into nanofibers is dramatically higher than when incorporated in films of the same host polymer. This effect increase in intensity is important to the successful utilization of NIR-emmitting materials in the imaging for medical devices and for other applications. Further, it was observed unexpectedly that the materials shrink dramatically upon heating. Combining the two effects allows for medical device labeling for surgical imaging with benign light rather than x-ray imaging shrink-wrap NIR bands for catheters and light-activated, subcutaneous sutures, and antimicrobial materials, for example. There are no limitations in incorporating thermally unstable dyes in this technique since the process is preferably conducted at room temperature.

(15) Advantages of the invention are illustrated by the Examples set forth herein. However, the particular conditions and details are to be interpreted to apply broadly in the art and should not be construed to unduly restrict or limit the invention in any way.

EXAMPLE

(16) This Example describes the preparation of a polymer solution for electrospinning, electrospinning a solution of polymer and ICG dye of varying concentrations, and the utilization of spectrofluormetry and NIR imaging to compare resulting polymer fiber mats and casted polymer films containing different concentrations of ICG dye in accordance with an embodiment of the present invention.

(17) In a first step, the polymer solution for electrospinning can be prepared by dissolving any thermoplastic polymer in its respective solvent. Herein, poly(vinyl acetate) (PVAc) (MW=260,000 g/mole) and different concentrations of ICG were dissolved in a solution containing 80% methanol and 20% N,N-dimethylformamide (DMF) to generate a 20 wt % polymer solution as seen in FIG. 2. The electrospinning solution was then loaded into a glass syringe and electrospun using known methods to fabricate nanofibers containing the ICG dye. In this technique, uniform dye incorporation is achieved compared to incorporation of the dye via diffusion. Other shape memory polymers may be used provided that they are shrinkable as spun, i.e., they are ready to be shrunk upon electrospinning, in response to heat and/or a solvent, and will retain their fibrous nature when shrunk so that the fibrous matrix is preserved and not melted. For example, in addition to PVAc, the polymer may comprise poly(-caprolactone).

(18) FIG. 1A shows a schematic representation of an electrospinning device 10 used for this Example. For electrospinning, a polymer solution 12 is placed in a glass syringe 14 bearing a metal needle which is connected to a high voltage power supply 16. A collector 18 is grounded and rotates at the speed of 300 rpm. The electrospinning is then performed at a voltage of 8-12 kV, with 7 cm distance between the needle tip 20 and collector 18. The flow rate of the polymer solution, e.g., 1 mL per hour, is maintained by a syringe pump 22. Under the influence of the electric field, electrostatic charges build up on the surface of the liquid droplets and form a charged jet 24. Then charged jet 24 is stretched to form continuous fibers on metal collector 18. The solvent evaporates before charged jet 24 has reached collector 18. As a result, fibers are formed and collected on the surface of the metal collector 18. As seen in FIG. 1B, the electrospinning process may be used for form an electrospun fiber mat having an average fiber diameter of about 0.61 m.

(19) Spectrofluorometry and NIR imaging were utilized to compare polymer fiber mats and casted polymer films containing different concentration of ICG dye. FIG. 3 shows NIR imaging results of PVAc fiber mat with different ICG concentration and casted PVAc films with different ICG concentrations. Spectrofluorometry of PVAc fiber mat with different ICG concentration and casted PVAc films with different ICG concentration are shown in FIG. 4.

(20) FIG. 5 shows graphs of comparison of PVAc fiber mat and PVAc film with different ICG concentration by using spectrofluorometry and NIR imaging as a function of concentration, noting that the mean gray values indicating intensity were computed by using ImageJ program. Unexpectedly, PVAc fiber mats showed significantly higher intensity, whether measured by spectrofluorometry or by NIR imaging, when compared to the PVAc film. Moreover, the existence of an optimum dye concentration was evident from the trends, the highest NIR emission intensities being observed for samples with 0.0125 mg/ml ICG concentration. It is understood that higher concentrations that this optimum value lead to excessive light absorption, limiting the depth to which the excitation light can penetrate the materials.

(21) It was observed in separate experiments that PVAc fibrous webs prepared by electrospinning with the method indicated, with or without dye, exhibited significant shrinkage when heated above about 50 C. or when immersed in water, the former being faster. This surprising finding was interpreted as evidence that electrospun PVAc features frozen-in molecular orientation along the fiber axes. This molecular orientation is apparently relaxed upon heating to a temperature above Tg (glass transition temperature) or upon lowering Tg to near-room-temperature by water-plasticization.

(22) The idea was conceived that the combination of high-intensity NIR emission and heat or water-triggered shrinkage can be combined to enable facile NIR labeling of medical devices to be imaged with NIR equipment. One application of this combination of properties is the NIR labeling of catheters via shrink-wrapping, as shown in FIG. 6, for the purpose of NIR imaging. For example, a small strip of a fiber mat 30 that has been elongated into a temporary shape is cut and then wrapped around the end of a catheter 32. Upon the application of heat, such as to 50 degrees Celsius, the fiber mat strip 30 will shrink to its permanent shame memory configuration and tighten around catheter 32 as seen in FIG. 6(a)(iii). The fiber mat may also be formed into a tube or even an end cap that can be positioned over the end of a post or other member of a medical device.

(23) The NIR excitation and emission of ICG dye embedded in the polymer of strip 30 allows for tracking the device by using an NIR imaging system, which is non-invasive compared to other imaging techniques such as X-ray and MRI. As seen in FIG. 7, excitation of strip 30 with the appropriate infrared wavelength results in near infrared emissions that are easy to capture using a near infrared filter and camera.

(24) Referring to FIG. 8, testing of near infrared emissions prior to and after electrospinning establishes that the ICG is responsible for post-electrospinning fluorescence.

(25) As seen in FIG. 9, positioning of a near infrared marker comprising a NIR fluorescence polymer according to the present invention allows for visualization of the catheter when it is inserted into a patient (in this case a mouse). The marked catheter is visible when placed subcutaneously, intraperitoneally, and even behind the bowel. As further seen in FIG. 10, a tube coated with an NIRF polymer according to the present invention is readily visualized when the marked tube is placed outside and then inside a mouse.

(26) Another application of the present invention is light-activated shape memory PVAc fiber mat containing ICG that will shrink in response to light activation for easy positioning on a medical device. For example, light-activated shape change through photo-thermal heating of the materials with relatively high intensity NIR-excitation is possible. Using higher intensity incident NIR light than is used for imaging, the materials are expected to heat up and once the temperature exceeds Tg they will shrink, bend, twist, or contract, depending on configuration. A surgical application envisioned for such a light-activated SMP is internal suturing, where the suture itself can be located by NIR imaging and then activated (partially or completely) from outside the body by using NIR irradiation. This will tighten the loosened sutures without the need for an open incision. Periodic and continued contraction of subcutaneous sutures may be useful for plastic surgery.

(27) Other potential applications of the PVAc fiber mat with incorporated ICG include antimicrobial medical devices, packaging, drug delivery, and temperature sensors.

(28) Although the present invention has been described in connection with a preferred embodiment, it should be understood that modifications, alterations, and additions can be made to the invention without departing from the scope of the invention as defined by the claims.