Expanded polytetrafluoroethylene (ePTFE) was chemically modified to retard the growth of Staphylococcus aureus bacteria. This was accomplished by microwave plasma reactions in the presence of maleic anhydride (MA) to create acid functional groups on ePTFE surfaces, followed by esterification reactions with 200 and 600 molecular weight linear polyethylene glycol (PEG). Such surfaces were utilized for further reactions with penicillin (PEN) through etherification reactions to create anti-microbial surfaces. These reactions resulted in surface morphological changes, and spectroscopic analysis using attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR) revealed the formation of ester linkages resulting from reactions between PEN and PEG functionalities. Antibacterial activities were evaluated by a series of experiments where PEN-modified ePTFE specimens were immersed in a liquid aureus culture, and the bacteria growth was quantified by measuring % absorbance of the suspension at 600 nm wavelength. The lowest absorbance was observed for the solution containing PEN-PEG-MA-ePTFE specimens, thus showing highly effective anti-bacterial activity toward gram-positive Staphylococcus aureus bacteria. To our best knowledge, this is the first study that shows PEN-ePTFE surface modifications that are effective against gram-positive aureus bacteria.

Recent studies identified and established a platform of polymer surface modifications allowing the attachment of penicillin (PEN) to expanded poly(tetrafluoroethylene) (ePTFE) surfaces. The effectiveness of this approach was accomplished by creating surfaces with chemically attached PEN that prevent the proliferation of microbes. In this study, quantitative assessments of PEN effectiveness attached to ePTFE were conducted. Using variable-angle attenuated total reflectance (ATR-FTIR) spectroscopy, the volume concentration changes of PEN were determined as a function of depth from the ePTFE surface. At depths ranging from 0.2 to 1.2 mum from the surface, PEN concentration levels decrease from 8.85 to 3.33 mug/m3. Assessments of concentration levels of the colony forming units (CFUs) of Staphylococcus aureus bacteria as a function of contact time with the penicillin-polyethylene glycol spacer separated by maleic anhydride ePTFE (PEN-PEG-MA-ePTFE) surfaces showed profound effectiveness of PEN in preventing microbial proliferation. Hydrolytic stability of PEN-PEG-MA-ePTFE surfaces revealed that even with a 32% loss of PEN due to the cleavage of the ester linkages between PEN and PEG spacer, antimicrobial activity is still maintained.

The broad spectrum antibiotic, ampicillin (AM), was reacted to expanded poly (tetrafluoroethylene) (ePTFE) surfaces and resulted in the formation of antimicrobial surfaces effective against gram-positive, Staphylococcus aureus, Bacillus thuringiensis, and Enterococcus faecalis, and gram-negative, Escherichia coli, Pseudomonas putida, and Salmonella enterica bacteria. These ePTFE surface modifications were accomplished by utilization of microwave maleic anhydride (MA) plasma reactions leading to the formation of acid groups, followed by amidation reactions of heterofunctional NH 2/COOH-terminated polyethylene glycol (PEG). The final step, the attachment of AM to the PEG spacer, was achieved by amidation reactions between COOH-terminated PEG and NH 2 groups of AM. This approach protects the COOH-AM functionality and diminishes the possibility of hydrolysis of the antimicrobial active portion of AM. These studies also show that approximately 90% of AM molecules are still covalently attached to PEG-MA-ePTFE surfaces after exposure to the bacteria solutions. Even after a 24 h period, the AM volume concentration changes only from 2.25 to 2.04 microg/m3, and depending upon the bacteria type, the bacteria suspensions containing AM-PEG-MA-ePTFE specimens retain 85-99% of their initial optical density.

Surface reactions were performed on polypropylene (PP) surfaces to retard the simultaneous growth of Staphylococcus aureus (S. aureus) and Pseudomonas putida (P. putida) bacteria. Microwave plasma reactions in the presence of maleic anhydride (MA) resulted in the formation of acid groups on the surface of PP. Such surfaces were further modified by conducting two parallel reactions: (1) poly(ethylene glycol) (PEG) was attached to COOH groups of the PP surface, followed by penicillin V (PEN) reactions to target S. aureus destruction and (2) diglycidyl PEG was attached, followed by gentamicin (GEN) reactions, to create antimicrobial surfaces targeted at P. putida . Simultaneous gram "+" and gram "-" resistance was obtained by varying the PEN/GEN ratios on such modified PP surfaces, thus providing the controllable degree of gram "+" and gram "-" antimicrobial strength. While spectroscopic analyses revealed chemical attachments of PEN and GEN, the effectiveness against proliferation of S. aureus (Gram +) and P. putida (Gram -) bacteria was determined using liquid culture tests. These studies show for the first time the formation of tunable antimicrobial polypropylene surfaces with controllable strength.

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