(818g) Nano BaSO4 : A Novel Means to Create Antimicrobial Radiopaque Thermoplastics

Abstract:

Hospital acquired infections remain a major costly problem. This study seeks to understand how incorporating nano-barium sulfate into pellethane composites affect the physical properties and antimicrobial nature of the resulting polymers. The results of this study showed that the incorporation of nano-barium sulfate into pellethane polymers yielded polymers which had enhanced antimicrobial properties, yet had similar hydrodynamic properties and were still radiopaque.

Introduction: Hospital acquired infections remain a costly problem. Each year there are approximately 2 million hospital acquired infections, 90,000 of which are fatal ¹. Catheter-related bloodstream infections alone represent a potential burden on the healthcare system of at least $35billion ². The main challenge is to prevent bacteria growth early before biofilm production takes place, since once the bacterial biofilm matrix forms, bacterial infections can become profoundly more resistant to the host defenses as well as antibiotic treatments ³. Barium sulfate (BaSO₄) is a common agent used to make medical tubing radiopaque; however, in addition to this, BaSO₄ polymeric formulations have been shown to exhibit antimicrobial activity⁴. Additional studies have shown that the use of nano structures on surfaces can lead to surfaces that are antimicrobial or resistant to bacterial proliferation ⁵. The goal of this study was to investigate if nano-BaSO₄ pellethane composites are able to effectively act  as surfaces which prevent initial bacterial adhesion and proliferation, while still remaining radiopaque.

Materials and Methods: Foster Biomedical Polymers and Compounds (Putnam, CT, USA) extruded pellethane tapes with various weight percentages of BaSO₄ powder and nano- BaSO₄. Seven different sample groups  made with varying weight percentages of BaSO₄ (0% BaSO₄, 20% nano-BaSO₄, 30% nano- BaSO₄, 40% nano- BaSO₄, 20% BaSO₄, 30% BaSO₄, and 40% BaSO₄). Tapes were then cut into disks that fit into 12-well plates (approximately 22mm in diameter). These disks were then sterilized with EtOH and UV light treatment prior to use.

Contact angle measurements were made on a Krüss Easy Drop contact angle instrument (Krüss, Germany) connected to an image analysis program (Drop Shape Analysis (Version 1.8)). The Krüss Easy Drop apparatus was used to measure the contact angles that resulted when a 10μL drop of either H₂O, glycerol, or ethylene glycol was placed on the surface of a sample disk ⁶.

Polymer samples were labeled and radiograph images were taken using a infinity XMA HF-30AP, set to Manual technique mode with an exposure time of 0.016 seconds and MAS@6.1 and 70KV. Images were taken of each sample individually and s-values, numeric value of exposure received by the receptors in the digital system, were recorded ⁷. For analysis the s-value for the 0% BaSO4 sample was used as a base and subtracted from all the other values to normalize the results.

Stock solutions of Staphylococcus aureus (S. aureus) (ATCC# 25923) and Pseudomonas aeruginosa (Schroeter) Migula (P. aeruginosa) (ATCC# 27853) were diluted and frozen. Bacteria from stock solutions were streaked out for isolation on agar plates. Bacteria was cultured in sterile tryptic soy broth (TSB) (Sigma Aldrich) then diluted to a density of 1×10⁷ bacteria/mL (as estimated by the McFarland scale which corresponded to an optical density of 0.52 at 562 nm then further diluted at a ratio of 1:100) ⁸. The sterile polymer disks were placed in separately labeled wells of a sterile 12 well tissue culture plate. They were then covered in 1ml of the bacteria in. The plates were sealed with parafilm and then incubated at 37°C while shaking at 200rpm for 1.5 hours. Next, 10μL samples of each solution were obtained and diluted  in fresh TSB. Finally, colony counts were taken to determine the number of colony forming bacteria units in each well.

 Results and Discussion: Contact angle trials yielded no significant differences. Radiopacity trials indicated that the nano-BaSO₄ samples were still radiopaque. Figure 1 displays the growth curve of S.  aureus at room temperature (line) paired with bacterial growth on polymer samples (bars) The bacteria results indicated a significant decrease in bacteria proliferation at certain concentrations of nano BaSO₄. In the case of S. aureus, significant decreases were observed when 20% and 40% nano BaSO₄ polymers were used. In the case of P. aeruginosa, significant decreases verse control were observed when 0% BaSO₄ as well as 30% and 40% nano BaSO₄ polymers were used. Additionally the 40% nano BaSO₄ led to a significant decrease in P. aeruginosa compared to the 40% BaSO₄ polymer (results not shown). The results of these trials indicated that adding nano-BaSO₄ to the extrusion process of pellethane was able to change the surface dynamics and microbial surface interactions of the resulting polymer sample. From the results, it appears that the nano 20% and the nano 40% polymer blends yielded a marked reduction in S. aureus proliferation, while the 30% and 40% blends showed mark decreases in P. aeruginosa proliferation. These results indicated that longer antimicrobial trials should be conducted to investigate the potency and longevity of the antimicrobial effects seen.

Conclusion: These trials indicated that although the nano-BaSO₄ did not change not change the hydrodynamic nature of the samples there was a significant change in bacteria function when nano-BaSO₄ was present in the polymer. The result was a reduction in bacterial proliferation. Further trails need to be completed to better understand the mechanisms of the trends observed in the present study as well as determine bacteria growth on samples over prolonged periods of time.

Acknowledgements: The authors would like to thank Adriana Noemí Santiago, and Gozde Durmus for aid in performing trials. Special thanks to Foster Biomedical Polymers and Compounds for providing samples.

References:

1.      Burke JP. Infection Control — A Problem for Patient Safety. New England Journal of Medicine. 2003;348(7):651-656.

2.      Fears R, van der Meer JWM, ter Meulen V. The Changing Burden of Infectious Disease in Europe. Science translational medicine. Oct 2011;3(103).

3.      Hall-Stoodley L, Costerton JW, Stoodley P. Bacterial biofilms: From the natural environment to infectious diseases. Nat. Rev. Microbiol. Feb 2004;2(2):95-108.

4.      LaBrec BC. Brown University Biomedical Research Sponsored By Foster Corporation. In: Webster T, ed. Email Comunication between Foster and Brown university. ed2011.

5.      Taylor E, Webster TJ. Reducing infections through nanotechnology and nanoparticles. Int. J. Nanomed. 2011;6:1463-1473.

6.      Puckett SD, Lee PP, Ciombor DM, Aaron RK, Webster TJ. Nanotextured titanium surfaces for enhancing skin growth on transcutaneous osseointegrated devices. Acta Biomaterialia.6(6):2352-2362.

7.      Sprawls P. S-Values - Digital Radiology. 2012; http://www.acrrt.com/index.php/11-articles/29-s-values-digital-radiology. Accessed 11-7-12, 2012.

8.      Puckett SD, Taylor E, Raimondo T, Webster TJ. The relationship between the nanostructure of titanium surfaces and bacterial attachment. Biomaterials. 2010;31(4):706-713.