Optimization of an Electrospinning Mechanism to Apply Protein-Treated Fibers to Surgical Sutures

Katherine Magee, Dr. Jorge Rodriguez, and CI Team Members

Introduction

To improve the effectiveness of sutures and healing from procedures, medicines and proteins are  being spun onto the surface of sutures giving rise to specific bio-responses in the body. Since this type of electrospinning is a new method and there is not a standardized method of applying the fibers to the suture, there is a need for an optimized mechanism for the fiber application for research sample composure. This mechanism development will determine the ideal rotational velocity of fiber spinning, as well as the best fiber brush size for the wrapping of the suture. Scanning electron microscopy (SEM) is used to analyze the angles and number of fibers twisted around a section of surgical suture. The development of this device provides a standardized method of electrospinning treated fibers to sutures, allowing for consistent samples of these wrapped sutures for use in future research exploring the possibilities presented by specialized surgical sutures.

Figure 1. This image shows the box complete with humidity control,  a charged syringe extruder, and a grounded fiber collection apparatus.  The collection apparatus rotates while the syringe expels the polymer, capturing nanofibers.

Materials and Methods

A polymer solution is prepared with 15 weight:volume percent (wt/v%) poly (lactic-co-glycolic acid) (PLGA) (50:50, 50 kDa; 50:50, 100 kDa) and 1 wt/v% poly(ethylene oxide) (PEO) (1,000 kDa) in N,N-Dimethylacetamide (DMAc) and heated at 60℃. The heated polymer solution is then extruded through a syringe with a flowrate of 0.5 mL/hr and electrospun using +7 kV and -1.2 kV. The electrospun nanofibers are collected on a rotating collector for 30 minutes in the clockwise direction and then 30 minutes in the counterclockwise direction. The fibers are then twisted over an existing 4-0 Vicryl commercial suture using a patent-pending collection mechanism. Fibers are twisted at varying speeds and imaged using a Hitachi TM3000 scanning electron microscope for analysis.

Figure 2. Flow chart depicting order of current and future testing for optimization of the device and samples produced by its use.

Results

Figure 3. Diameters of sutures measured with SEM images.  This data was used to determine averages for each rpm and location on the suture.

Suture Diameters

Analyzing the SEM Images taken on a Hitachi TM3000 Microscope, the diameters of each coated suture could be determined using the scale at the bottom of the scan.  On average, the ends of the sutures, no matter the speed, were closer to original suture size than the middles of the sutures (Figure 3).  Also, the average end diameter did not vary much between speeds, but the average middle diameter did (Figure 3).

Figure 4. Above are the images of the sutures coated with nanofibers .  The ends of the coated sutures depicted were samples spun at 206 rpm(A), 436 rpm(B), 664 rpm(C), and 898(D).  The middles of the same coated sutures were spun at 206 rpm(E), 436 rpm(F), 664 rpm(G), and 898 rpm(H).  Each of these SEM images were taken using a Hitachi TM3000 Scanning Electron Microscope at a magnification power of 80x.

SEM Image Analysis

The images below are examples of the SEM scans taken of each sample with the varying rpms and suture location the image was taken of.  Like the diameters in Figure 3, there are few differences seen in the wrapping of the fibers around the sutures at the ends of the samples (Figure 4 A-D).  However, looking at the middles of the wrapped sutures (Figure 4 E-H), the highest (5H) and lowest (5E) rpm values have the most tightly wound fibers.  Between the different sample sets, the middle would occasionally unwind from the suture, but this phenomenon was never observed for the ends of sutures.  This could possibly be due to the the high angle between the fiber brush and the suture during fiber application at the ends of the sutures.  This could lead to the higher angle of alignment, which may be related to the prevention of unwinding of fibers from the suture’s surface.

Figure 5. Above are SEM Images of the coated sutures at 150x magnification.  These images are the end of the sutures spun at 206 rpm(A) and 898 rpm(B), as well as the middle of the sutures spun at 206 rpm(C) and 898 rpm(D).

Fiber Alignment Analysis

In Figure 5 above, the SEM images taken of each sample at a magnification of 150x were analyzed to determine the angles at which the nanofibers wrap around the sutures. As seen above, the angle of the wrap is higher in both of the end samples (5A, 5B) compared to both of the middle samples (5C, 5D).  Both of the lower rpm samples (5A, 5C) also depict having higher angles of the wrapping of the fibers compared to their higher rpm counterparts (5B, 5D).  This higher angle of the fibers in the wrap compared to the central axis of the suture is a visual indicator for a more tightly coated suture.

Future Work

  • Moving forward, there are many more parts of the mechanism that can be optimized for suture coating.  Examples of these parameters are: optimal distance between fiber brushes, fiber brush materials, and fiber brush size. Tensile strength tests as well as SEM imaging will be preformed to quantify optimal parameters.

    Once the suture coating method has been optimized for basic PLGA:PEO nanofibers, a drug loading vector will be added to the polymer solution and a hydrophobic therapeutic agent will be loaded in the core of the nanofiber. Certain proteins such as Heparin will also be electrostically bound to the electrospun fibers. Various drug loading and release studies will be preformed to optimize the drug-eluding properties of the suture.

Conclusions

  • Highest and lowest rpm values had most consistent ideal results
  • Ends of sutures had higher angles of fiber alignment compared to the middles
  • Diameters varied the most between the middle sections of sutures based on rpms