Progress 10/01/03 to 09/30/07
Outputs
OUTPUTS: A simple two-step method (SiCl4 plasma functionalization and polyethylene glycol - PEG - immobilization) to graft PEG molecules onto polyamide (PA) and polyester (PET) surfaces has been developed using plasma techniques. Both PA and PET grafted with PEG inhibited the biofilm formation by L. monocytogenes. The chain length of PEG might play a significant role in the antifouling effectiveness of PEG; the influence of molecular weight of PEG on the grafting efficacy and bacterial adhesion has been studied. Bacterial-adhesion tests demonstrated that the bacterial adhesion on PET surfaces was decreased with the increase of the molecular weight of PEG molecules. The shelf-life of PEG-grafted PET surfaces over various storage periods was investigated. It was shown that PEG-grafted surfaces still significantly reduce biofilm formation even after a 2 month storage period under room-condition environment.
PARTICIPANTS: Participants are: F.S.Denes, Amy Wong, Baiyan Dog (Grad student), Dr. Sorin Manolache (Assistant Scientist)and Eileen Somers.
TARGET AUDIENCES: Efforts made will have significant, beneficial impact on the development of advanced, efficient anti-fouling surfaces with applications in food--processing and biomedical areas.
Impacts
Among all the reported methods for immobilization of polyethylene glycol (PEG) on various material surfaces, covalent grafting provides the most stable PEG layers. We have reported a simple two-step method to graft PEG molecules onto polyamide (PA) and polyester (PET) surfaces using plasma techniques. In this method, the surfaces were functionalized using SiCl4 plasma to introduce active Si-Cl functionalities and subsequently PEG molecules were grafted to the surfaces by immersing the plasma-treated samples into PEG solutions. ESCA data showed the presence of a high surface area C-O peak in the C1s high resolution spectrum as a result of grafting the PEG molecules. We demonstrated that both PA and PET grafted with PEG600 inhibited the biofilm formation by L. monocytogenes by 1.4 Log (P< 0.05). It was assumed that the chain length of PEG plays a significant role in the antifouling effectiveness of PEG. Accordingly, the influence of molecular weight of PEG on the
grafting efficiency and bacterial adhesion has been studied. The antifouling ability of the grafted PEG in the presence of Salmonella was investigated. The molecular weights of PEG used in these experiments were 200, 400, 600, 2000, and 4600 respectively. ESCA data clearly indicated that with the increase of molecular weight (up to 2000), the C-O binding energy peak surface area has increased. Bacterial-adhesion tests demonstrated that among PEG 400, 600 and 2000, the bacterial adhesion on PET surfaces was decreased with the increase of the molecular weight of PEG molecules. PEG2000-grafted surfaces were the most effective, which inhibited the bacterial attachment by about 3 Log and biofilm formation by about 2 Log. The stability of PEG2000-grafted PET surfaces over storage periods of 0, 1 and 2 months was evaluated. It was shown that PEG2000-grafted surfaces still significantly reduce biofilm formation in the presence of Salmonella even after a 2 month storage period under
room-condition environment. This is the first extensive study, to our knowledge, that emphasizes the influence of molecular weight of PEG on bacterial adhesion. It is noteworthy that our bacterial adhesion results are at least comparable if not better than similar data reported in the literature. Results of these investigations will allow the development of non-equilibrium SiCl4- and SiH2Cl2-plasma technologies for the generation of inorganic and organic material surfaces (e.g. polymers) with antifouling properties that will significantly limit protein- and bacterial-adherence, and the formation of biofilm. Applications of these plasma-modified materials will find their applications in food-packaging environments and in the development of various advanced medical implants for temporary or permanent utilization. The design and development of catheters, artificial organs or artificial organ parts with antifouling characteristic, will probably benefit most from the results of these
investigations.
Publications
- Dong, B.; Manolache, S.; Somers, E. B.; Wong, A. C. L.; Denes, F. S. (2005). Generation of antifouling layers on stainless steel surfaces by plasma-enhanced crosslinking of polyethylene glycol, Journal of Applied Polymer Science, 97(2): 485-497.
- Dong, B.; Jiang, H.; Manolache, S.; Wong, A. C. L.; Denes, F. S. (2007). Plasma-mediated grafting of polyethylene glycol on polyamide and polyester surfaces and evaluation of antifouling ability of modified substrates, Langmuir, 23(13): 7306-7313.
- Dong, B.; Manolache, S.; Wong, A. C. L.; Denes, F. S. 2007. Plasma-enhanced covalent grafting of various molecular weights polyethylene glycol on polyester surfaces, (in preparation).
- Dong, B. (2007) Generation of Antifouling Layers from Polyethylene Glycol by Cold Plasma Technique on Stainless Steel and Polymer Surfaces, PhD Thesis, Advisors: Denes, F. S.; Wong, A. C. L. University of Wisconsin.
|
Progress 01/01/06 to 12/31/06
Outputs
The objective of the 2006 investigations was to graft efficiently PEG molecules onto plasma-functionalized polymer surfaces that are commonly used in food processing industry as packaging materials and as components of food-processing tools such as polyesters (PET) and polyamides (PA) to create stable antifouling layers. A low pressure, non-equilibrium plasma-enhanced surface functionalization of PET and PA was developed followed by the attachment of the PEG molecules in a post-discharge process. Very reactive Si-Clx functionalities were implanted onto the polymer surfaces in a SiCl4 -plasma environment that promoted in the next step the covalent linkage of the PEG molecules under an argon blanket from the selected and degassed liquid phase PEG. The reaction of the PEG molecules with the plasma-functionalized surfaces was performed at various time periods (2, 5, and 20 hours) and at 60C. Survey and high resolution X-ray photoelectron spectroscopy measurements
indicated the presence of a relative C/O surface atomic ratio that is comparable to the C/O ratio of PEG, and the existence of a dominant surface area C-O binding energy peak. These finding clearly demonstrate that the PEG molecules were successfully attached to the PET and PA surfaces. Chemical derivatization performed on SiCl4-plasma exposed and PEG-grafted surfaces indicated the presence of OH functionalities that substantiates the conclusion that the grafting process has been accomplished. The longer the grafting reaction time and higher the MW of PEG higher the C-O binding energy peak surface area (higher C-O concentration). PEG-600 and 20 hours were selected as the optimal conditions for the generation of PEG layers and for the evaluation of antifouling behavior of the modified polymers. Residual gas analysis (RGA) of the SiCl4 vapor phase reaction environment in the absence and presence of plasma, and absence of SiCl4 in-flow, revealed that the silicon tetrachloride molecular
ion is absent in the RGA-spectrum and that the intensity of SiCl+ was increased as a result of plasma-induced fragmentation in the discharge. Plasma-enhanced dechlorination of SiCl4 and the formation of SiClx species are suggested as potential plasma-driven reaction mechanisms. The antifouling behavior of PEG-600-grafted PET and PA was evaluated by monitoring biofilm formation by L. nonocytogenes. A decrease of 96% was found on both PA-PEG and PET-PEG surfaces. Water contact angle data and atomic force microscopy indicated that more PEG molecules are grafted to the PA surfaces in comparison to the PET, however, a similar degree of inhibition of biofilm formation was associated with both substrates. Surface saturation with PEG molecules of the substrates might be responsible for this behavior. Due to the successful and efficient grafting of PEG using the SiCl4-plasma approach, the more elaborate H2O/O2 plasma conditions for the implantation of OH surface functionalities, followed by
reaction with with glutaric anhydride to generate -COOH group and oxallyl chloride for the convertion of -COOH groups into-COCl functionalities will not be followed up.
Impacts
Results of these investigations will allow the development of non-equilibrium SiCl4- and SiH2Cl2-plasma technologies for the generation of inorganic and organic material surfaces (e.g. polymers) with antifouling properties that will significantly limit protein- and bacterial-adherence, and the formation of biofilm formation. Applications of these plasma-modified materials will find their applications in food-packaging environments and in the development of various advanced medical implants for temporary or permanent utilization. The design and development of catheters, artificial organs or artificial organ parts with antifouling characteristic, will probably benefit most from the results of these investigations.
Publications
- No publications reported this period
|
Progress 01/01/05 to 12/31/05
Outputs
Bacterial attachment and biofilm formation is a concern in both food processing industries and medical device industries, due to its detrimental economic and health consequences. The main objective of our project is to generate stable antifouling layers on the surfaces of materials commonly used in food processing and medical environments. Polyethylene glycol (PEG) was selected as the primary precursor for the generation of anti-fouling layers since previous studies indicate that this polymer and its analogs are the most promising structures for reducing protein and cell adsorption, even if the protein- and microbial-repellent mechanisms are still not fully understood. We have successfully crosslinked PEG-pre-coated stainless steel surfaces using non-equilibrium, low pressure, plasma technique and demonstrated that the PEG-coated and crosslinked stainless steel surfaces can reduce Listeria monocytogenes attachment and biofilm formation by one log. Polymers are also
common materials encountered in food processing and medical environments, including silicone rubber (SR), polyester, polypropylene and polyamide. Some of these polymers are chemically inert and also are characterized by very low glass transition temperatures (GTs), such as silicon rubber and polypropylene. Attachment to these polymer surfaces of PEG molecules is more difficult. As a consequence, a novel, three step surface-modification approach of SR substrates was developed. First the SR is decorated with OH and C-O-C functionalities using a H2O/O2 plasma environment for increasing its wettability (high surface energy), and generating a hard brittle surface layer, followed in the second step, by a swelling procedure of the modified SR substrate in a PEG in benzene solution. This step will result in the entrapment and strong retention of PEG molecules during the solvent removal. The thoroughly washed PEG-containing substrates are exposed during the last step to an argon-plasma
environment for the generation of a stable crosslinked PEG layer. Survey and high resolution ESCA evaluations and SEM images demonstrated the presence on the SR surfaces of PEG structures and the swelling-induced surface topographies (cracks). It was also shown that the wettability of the modified-SR surfaces has been significantly improved. However, the bacterial tests conducted by Listeria monocytogenes attachment and biofilm formation showed no decrease on the PEG-modified SR compared with the unmodified SR. This is not surprising, because the transfer of bacteria to unmodified SR surfaces is very limited. Plasma-enhanced modification and subsequent PEG coating of two other polymers including, polyester and polyamide are also under current investigation. Grafting of PEG will be performed by oxidizing the substrates under H2O/O2 plasma conditions for the implantation of OH functionalities, followed by reaction with with glutaric anhydride to generate -COOH groups. In the next step
oxallyl chloride will be employed to convert -COOH groups into -COCl functionalities. These groups will react with the -OH groups of the PEG molecules and lead to their covalent attachment to the plasma-modified surfaces.
Impacts
Results of these investigations will allow the development of non-equilibrium plasma technologies for the generation on inorganic and organic material surfaces (e.g. polymers) with antifouling properties that will significantly limit protein- and bacterial-adherence, and the formation of biofilm formation. Applications of these plasma-modified materials will find their applications in food-packaging environments and in the development of various advanced medical implants for temporary or permanent utilization. The design and development of catheters, artificial organs or artificial organ parts with antifouling characteristic, will probably benefit most from the results of these investigations. Space-flight application might also take advantage of the results of this plasma-aided research.
Publications
- B. Dong, S. Manolache, E. B. Somers, A. C. L. Wong and F. S. Denes, Generation of Antifouling Layers on Stainless Steel Surfaces by Plasma-Enhanced Crosslinking of Polyethylene Glycol, Journal of Applied Polymer Science 97(2), 485-497 (2005).
|
Progress 01/01/04 to 12/31/04
Outputs
Bacteria can attach to all kinds of surfaces and form biofilms which are more resistant to normal cleaning procedures and antibiotics than their planktonic cells. Biofilms formation could lead to economic and health problems in many environments, including food processing industries and medical device industries. Surface modification of materials, including physical adsorption and entrapment, covalent grafting or graft polymerization, and crosslinking, is one of the major approaches for minimizing or preventing biofilm formation. It has been shown that surfaces modified with hydrophilic polymers (polyethylene glycol - PEG - being most promising) can reduce protein and cell adsorption. Nonetheless, relatively less work has been done on the PEG-modification of stainless steel, which is a common material used in food processing and medical industries. An alternative strategy to deposit PEG onto stainless steel surfaces by cold plasma mediated crosslinking of predeposited
PEG layers was developed. Chips of stainless steel type 304 (#4 and #8 finish, and additionally polished #4) were cleaned, plasma oxidized to enhance the wettability, PEG (400 and 2000 molecular weight) spin coated from ethanol solutions, and argon-plasma treated to crosslink the thin PEG layer. A series of plasma conditions (power, treatment time) were tested to get an optimal crosslinking condition. Finally, the PEG-modified samples were rinsed by deionized water to remove the linear PEG and vacuum dried for further analysis. ESCA and ATR-FTIR data provided proofs that the PEG was successfully crosslinked on all the stainless steel surfaces used. The ESCA spectra demonstrated the presence of dominant C-C-O peak after PEG modification. The appearance of C-C-C peak on PEG-modified surfaces was an indication of the crosslinked structure of PEG. The iron signal was undetectable on all PEG-modified surfaces, suggesting that the surfaces had been fully covered by a PEG deposition beyond
the probe depth of ESCA. SEM and AFM images demonstrated the presence of a newly deposited polymer layer, which covered some of the manufacturing grooves and showed significantly smoother topographies. The PEG-modified surfaces had relative increased hydrophilicity. The antifouling ability of the PEG-modified surfaces was carried out using L. monocytogenes attachment and biofilm formation. About 0.8 - 1.2 log decreases were observed on the attachment, and the decrease on biofilm formation was about 0.8 - 0.9 log, and no decrease was found on the oxidized stainless steel. Further experiments were required for the modification of silicone rubber, which is also a common material in food processing and medical industries. Two different approaches will be taken into consideration: silicone rubber surfaces will be treated by plasma technique to increase the wettability with PEG, and PEG will be spin coated and crosslinked by plasma; silicone rubber samples will be swelled in PEG-dissolved
solvent and the surface layer will be crosslinked by plasma to stabilize the trapped PEG.
Impacts
Results from these investigations will allow the development of non-equilibrium plasma technologies for the generation on inorganic and organic solid material surfaces (e.g. polymers) of antifouling thin layers that will significantly limit protein- and bacterial-adherence, and the formation of biofilms as a consequence. Applications of these plasma-modified materials will find use in food-packaging environments and in the development of advanced various medical implants for temporary or permanent utilization. The design and development of catheters, artificial organs or artificial organ parts with antifouling characteristic, will probably benefit most from the results of these investigations. Space-flight application might also take advantage of the results of this plasma-aided research.
Publications
- No publications reported this period
|
|