(574c) Electrospun Silk Doped with Selenium Nanoparticles to Enhance Antibacterial Properties

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.⁵Briefly, 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 30º, 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.