Electrospun Silk Doped with Selenium Nanoparticles to Enhance Antibacterial Properties

ELECTROSPUN SILK DOPED WITH SELENIUM NANOPARTICLES TO ENHANCE ANTIBACTERIAL PROPERTIES

Stanley Chung¹, Michelle Stolzoff², Batur Ercan¹, Thomas J. Webster^1-3.

1. Chemical Engineering Department, Northeastern University, Boston, MA

2. Bioengineering Department, Northeastern University, Boston, MA

3. Center of Excellence for Advanced Materials Research, King Abdulaziz University, Saudi Arabia

Abstract                                                                        

Silk is a naturally derived biomaterial that has shown good properties for skin applications. However, unmodified silk has been shown to promote bacterial growth which is a major concern for any open wound skin application. Here, we propose for the first time, an electrospun silk scaffold doped with selenium nanoparticles to address this issue. Selenium nanoparticles have been shown to possess excellent antibacterial properties. By incorporating selenium nanoparticles into silk, we expect to retain silk's beneficial skin healing properties while increasing its antibacterial ability.

Introduction: Skin infections cause 7-10% of all hospitalizations in the United States, with the vast majority caused by bacterial infections.¹ Bacterial infections, especially antibiotic resistant microbes, are a growing threat to the hospital system.² The best protection against infection is to maintain healthy, intact skin tissue which wards off not only bacterial infection but also other environmental factors. Silk is well characterized and has been demonstrated to possess beneficial properties for skin applications.³ However, silk has poor antibacterial efficacy⁴ whereas selenium nanoparticles demonstrate good antibacterial properties⁵. By incorporating the selenium nanoparticles into electrospun silk scaffolds, we hope to improve on an otherwise ideal skin biomaterial.

Materials and Methods: Silk was extracted from Bombyx mori by the Rockwood's protocol⁶ while selenium nanoparticles were synthesized by a modified version of Tran's protocol.⁵ Briefly, the timing of the addition of the sodium selenite and glutathione and the precipitation with sodium hydroxide were controlled to yield 50 and 100 nm selenium nanoparticles. Extracted silk was resuspended in formic acid at 8-14%, w/v, and spun at flow rate of 0.75 mL/hr, distance to a collector at 10 cm, and at a voltage at 20kV. Staphylococcus aureus (ATCC-10832D-5) was cultured on the substrates with 1, 0.1, 0.01, and 0.001 mg/mL selenium nanoparticles in 0.3% tryptic soy broth (Sigma-Aldrich). After 24 hrs, 20 µL of bacterial solution was plated to determine the colony forming units (CFU)/mL. Human dermal fibroblast (HDF, ATCC-PCS-201-010) proliferation on the scaffolds was assessed by MTS assay (Promega). Experiments were conducted in triplicate. The electrospun scaffold was characterized by SEM and goniometry to determine the physical make-up of the scaffolds, with and without selenium nanoparticles. Selenium nanoparticles were characterized by DLS to determine particle size and dispersity.

Results and Discussion: Electrospun scaffolds possessed fiber diameter of 1-200 nm and pore sizes of ~2µm. Surface contact angle was 30ş, showing a hydrophilic surface. Results of this study showed approximately 1 log inhibition of S. aureus in the presence of selenium nanoparticles (Figure 1). Additionally, proliferation of human dermal fibroblast on the silk scaffold was increased when compared to growing on tissue treated polystyrene (Figure 2). The addition of selenium nanoparticles further increased the proliferation of the HDF at all time points as compared to the untreated silk and polystyrene control.

Figure 1. Bacterial density after contact with 1, 0.1, 0.01, and 0.001 mg/mL concentration of selenium nanoparticles. All selenium treated samples displayed significant difference from control. N=3, triplicates. * = P<0.02 from control, ** = P<0.005, *** = P<0.004

 Figure 2. MTS of HDF on electrospun silk scaffolds with and without selenium nanoparticles, compared to growth on tissue treated polystyrene. N=2, triplicates

Conclusions: Selenium nanoparticles inhibited S. aureus growth at all test concentrations. Electrospun silk generated fiber diameters ~200 nm and micron sized pore sizes, ideal for mammalian cellular adhesion. Indeed, HDF proliferation was increased when cultured onto the silk scaffolds.

                       

Acknowledgements: The authors thank William Fowle, Scott McNamara, and the Northeastern University Department of Chemical Engineering for facilities and funding.

References: 1) Vinh DC et al. The Lancet Inf Dis. 2005; 5(8), 501-513. 2) CDC. Antimicrobial resistance threats in the United States. 2013. 3) Roh DH. J Mat Sci Mat Med. 2006; 17 (6): 547-552. 4) Kaur J et al. Biopolymers. 2013; 101(3): 237-245. 5) Tran PA et al. I J Nanomed. 2011; 6: 1553-1558. 6. Rockwood DN, et al. Nat. Protocols. 2011; 6(10): 1612-1631.