© 2015 Mayo Foundation for Medical Education and Research

Erik Wennberg1, Brandon J. Tefft, Ph.D1,2, Susheil Uthamaraj2, Dan Dragomir-Daescu, Ph.D2,3,Gurpreet S. Sandhu M.D., Ph.D1

1Division of Cardiovascular Diseases, 2Division of Engineering, and 3Mayo Clinic School of MedicineMayo Clinic, Rochester, MN

• The electrospun PU scaffolds from both methods do not show results of the target pore size of 50-100 µm. Figures E and H when compared to figures C and G show that nanofiber quality increases when a size of NaCl larger than 63 µm is salt leached out. Overall, larger salt size tended to increase pore size. The method 1 of applying 0.50g NaCl showed larger pore sizes than applying 0.25g NaCl. This may be due to the larger amount of NaCl available to stick to the scaffold between each spinning. Method 1 using 0.50g NaCl was comparable to method 2. These methods may have failed to produce the target pore size due to method 1 using too small NaCl granules and method 2 not having NaCl granules make it to the collector plate.

• In the future, researchers may incorporate larger NaCl granules (>100 µm) or electrospin vertically so the NaCl granules use gravity to make it to collector.

Discussion

• Our current methods created micron- scale pores, but did not reach our target goal of 50-100 µm to introduced cells for infiltration. Future alterations should produce larger pores able to succeed this goal.

Conclusions

1. Wang, Kai, Meifeng Zhu, Ting Li, Wenting Zheng, Li Li, Mian Xu, Qiang Zhao, Deling Kong, and Lianyong Wang. "Improvement of Cell Infiltration in Electrospun Polycaprolactone Scaffolds for the Construction of Vascular Grafts." Biomedical Nanotechnology 10 (2014): 1588-598. NCBI. Web. 10 July 2015.

2. Sanaz Khademolqorani, Ali Zeinal Hamadani, and Hossein Tavanai, “Response Surface Modelling of Electrosprayed Polyacrylonitrile Nanoparticle Size,” Journal of Nanoparticles, vol. 2014, Article ID 146218, 7 pages, 2014. doi:10.1155/2014/146218

3. B. Wulkersdorfer, K. K. Kao, V. G. Agopian, et al., “Bimodal Porous Scaffolds by Sequential Electrospinning of Poly(glycolic acid) with Sucrose Particles,” International Journal of Polymer Science, vol. 2010, Article ID 436178, 9 pages, 2010. doi:10.1155/2010/436178

References

Many vascular grafts are electrospun from synthetic or natural substances into a nanofiber scaffold. However, a major limitation of electrospinning is the lack large pore sizes. Large pore sizes allow interstitial cells to pass through. Small pore size can result in generating the graft prone to intimal hyperplasia and thrombosis. Researchers have tried many different approaches to create large pores, such as using sacrificial poly(ethylene oxide) fibers with polycaprolactone1, electrospraying polyacrylonitrile2 and the use of other poragens such as sucrose particles3. However, these methods have all been accomplished with a biodegradable polymer.

Background

• Find an effective method of introducing sodium chloride to electrospun PU nanofibers

• To create a porous PU scaffold that allows interstitial cell infiltration and integration with the surrounding tissue

Objectives

Control

• Fig. A: Electrospun PU nanofibers control show pore sizes of 1-2 µm with dense fibers under 1µm.

Method 1: 0.25g NaCl applied to scaffolds

• Fig. B: Non- salt leached fibers show NaCl granules ~300-750 µm. Nanofibers just under 1 µm thick.

• Fig. F: High quality, dense nanofibers with smaller pore sizes

• Fig. D: Nanofiber pore size 1-3 µm. Nanofiber thickness below 1 µm.

• Fig. E: Nanofibers shows blobs of polyurethane in some areas of the scaffold.

Results

• To create micropores (50-100 µm) in a non-biodegradable polyurethane scaffold

• Seed interstitial cells in vitro on a porous scaffold and assess migration into the scaffold

Study Aim

Methods

SEM Images

Electrospun Polyurethane Graft Porosity for Cellular Infiltration: Current Methods and Future Directions

HypothesisThe addition of sodium chloride to an electrospun non-biodegradable polyurethane (PU) vascular graft will create large micropores in an electrospun scaffold, allowing interstitial cells to migrate through.

SEM Images: A) Control nanofibers. B) Method 1: 38-75µm NaCl+ nanofibers. C) Method 1: 0.50g of 63-75 µm NaCl salt leached nanofibers. D) Method 1: 0.25g of >75 µm NaCl salt leached nanofibers. E) Method 1: 0.25g of 53-63 µm NaCl salt leached nanofibers. F) Method 1: 0.25g of 63-75 µm NaCl salt leached nanofibers. G) Method 1: 0.50g of 63-75 µm NaCl salt leached nanofibers. H) Method 1: 0.5g 53-63 µm salt leached nanofibers. I) Method 2: PU+NaCl salt leached solution nanofibers. J) Method 2: PU+ NaCl non- salt leached solution nanofibers.

AcknowledgementsA thank you to the Mayo Clinic undergraduate research employment program, the summer undergraduate research fellowship program and the European Regional Development Fund – FNUSA-ICRC (no. CZ.1.05/ 1.1.00/ 02.0123).

Method 1 Method 2

Method 1: 0.50g NaCl applied to scaffolds

• Fig. C: Few larger nanofibers. Some white debris on a few fibers. Nanofiber thickness ranges from below 1- 2 µm.

• Fig G: Nanofibers look dense, small pore sizes.

• Fig. H: Nanofibers shows blobs of polyurethane in some areas and the nanofibers overall were dense.

Method 2: 15%PU + 4g NaCl solution

• Fig. I: Pore sizes 1-3 µm. Few very small fiber pieces on some of the larger fibers. Regular fibers under 1 µm thick.

• Fig. J: Fibers do not appear present. Few pores in the scaffold of 1-5 µm varying sizes.

Results

A

B F

D

E

C G

H

I

J