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Introduction
Introduction
Silk fibroin has great potential for biomedical applications (i.e. sutures, implants, scaffolding for tissue engineering, etc. 1-3) since it is mechanically strong, biodegradable, and biocompatible 1
However, silk fibroin is relatively hydrophobic in its natural state, which can cause issues with cell adhesion and protein adsorption in vivo 4,5
Nitrogen plasma and water vapor plasma modifications have both been shown to increase the hydrophilicity of various polymers 6-9
Hydrophobic recovery has been documented in plasma-modified polymers; this process is when the surface reverts back to its original state upon aging 7,8 → hydrophobic recovery of silk fibroin has not been explored
Research questions: how does hydrophobic recovery effect plasma treated silk films and how does this differ with different precursors?
Experimental Design
Experimental Design
Silk fibroin films were prepared by a degumming process followed by a casting process onto glass slides 10
The samples were then nitrogen plasma treated or water vapor plasma treated using previously optimized treatment conditions and aged to evaluate hydrophobic recovery
Plasma Reactor Set-up
Plasma Reactor Set-up
This figure shows the home built reactor set-up that was used for our experiment. The glass slide is represented in the reactor with the silk films cast onto it. The slides were always kept 10.4 cm from the inlet valve. The precursor gases are also shown.
Precursor Parameters
Precursor Parameters
Parameters were selected using previously optimized conditions.
Measuring Hydrophobicity
Measuring Hydrophobicity
Fitting methods: Ellipse for untreated controls/circle for treated samples
Water contact angle goniometer: KRUSS DSA1005
Image Credit: Alyssa Morelli
The image shows the water contact angle (WCA) goniometer used. This machine distributes one drop onto the surface and measures the WCA, this angle represents hydrophobicity.
Results
Results
Each data point represents one drop. The y-axis is water contact angle (WCA), which correlates to hydrophobicity (a higher WCA represents a more relatively hydrophobic sample, while a lower WCA represents a more relatively hydrophilic sample.
This table shows the average water contact angle (WCA) including the standard deviation as error.
Discussion
Discussion
Nitrogen plasma-modified films exhibited ~50% decrease in hydrophobicity upon initial treatment
Water vapor plasma-modified films exhibited ~60-70% decrease in hydrophobicity upon initial treatment
The water vapor plasma-modification showed more variation in water contact angle when compared to the nitrogen plasma-modification, indicating that the water vapor plasma treatment is less homogeneous than the nitrogen plasma treatment
Neither plasma-modified samples showed significant hydrophobic recovery over the 42 day aging process, indicating that these processes are relatively stable
This is not what has been seen with other plasma-modified polymers 7,8
Future Work
Future Work
The hydrophobic recovery of the silk fibroin films could be investigated using different plasma precursors
Research should be conducted to examine the secondary structure of the films, i.e. Fourier transform infrared spectroscopy (FTIR) analysis
Research could be replicated using free-standing films to investigate the effects of bulk matrix mobility varying by casting process
References
References
Vepari C.; Kaplan D.L. Silk as a biomaterial, Progress in Polymer Science, 2007, 32 (8-9), 991-1007. https://doi.org/10.1016/j.progpolymsci.2007.05.013.
Jeong L.; YeoI.S; KimH.N.; Yoon Y.I.; Jang D.H.; Jung S.Y.; Min B.M.; Park W.H. Plasma-treated silk fibroin nanofibers for skin regeneration, International Journal of Biological Macromolecules, 2009, 44 (3), 222-228. https://doi.org/10.1016/j.ijbiomac.2008.12.008.
Cai K.; Yao K.; Lin S.; Yang Z.; Li X.; Xie H.; Qing T.; Gao L. Poly(D,L-lactic acid) surfaces modified by silk fibroin: effects on the culture of osteoblast in vitro. Biomaterials. 2002, 23 (4), 1153-60. doi: 10.1016/s0142-9612(01)00230-7.
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Anselme K. Osteoblast adhesion on biomaterials, Biomaterials, 2000, 21 (7), 667-681. https://doi.org/10.1016/S0142-9612(99)00242-2.
Amornsudthiwat P.; Mongkolnavin R.; Kanokpanont S.; Panpranot J.; Wong C.S.; Damrongsakkul S. Improvement of early cell adhesion on Thai silk fibroin surface by low energy plasma, Colloids and Surfaces B: Biointerfaces, 2013, 111, 579-586. https://doi.org/10.1016/j.colsurfb.2013.07.009
Sanchis R.M.; Calvo, O.; Sánchez, L.; García, D.; Balart, R. Enhancement of wettability in low density polyethylene films using low pressure glow discharge N2 plasma. J. Polym. Sci. B Polym. Phys., 2007, 45, 2390-2399. https://doi.org/10.1002/polb.21246
Sanchis R.M.; Calvo O.; Fenollar O.; Garcia D.; Balart R. Characterization of the surface changes and the aging effects of low-pressure nitrogen plasma treatment in a polyurethane film, Polymer Testing, 2008, 27 (1), 75-83. https://doi.org/10.1016/j.polymertesting.2007.09.002
Tompkins B.D.; Dennison J.M.; Fisher E.R. H2O plasma modification of track-etched polymer membranes for increased wettability and improved performance. Journal of Membrane Science. 2013, 428, 576-588. https://doi.org/10.1016/j.memsci.2012.10.037
Rockwood D.N.; Preda R.C.; Yücel T.; Wang X.; Lovett M.L.; Kaplan D.L. Materials fabrication from Bombyx mori silk fibroin. Nat Protoc. 2011, 6 (10),1612-31. https://doi.org/10.1038/nprot.2011.379
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