(570g) Modifying Synthetic Membranes: A Personal View

Since our discovery nearly 30 years ago that poly(aryl sulfone) surfaces form radicals on exposure to light (UV) radiation, we have together with collaborators at RPI and MIT developed a vigorous membrane surface modification program that continues to be active today. The seminal reasons are that (a) modifying previously cast commercial synthetic membranes such as poly(ether sulfone), polyimide (PI), poly(vinylidene fluoride) (PVDF) and regenerated cellulose (RC) are widely available, (b) PI and PES are too apolar for effective use in the health, biotechnology, food and beverage industries, and (c) modifying commercially available membranes with desirable properties is less expensive and simpler than developing and processing new polymer materials as membranes. It is widely known that industrial membrane companies modify base PES and PVDF membranes to form composite membranes so as to render their surfaces polar with cross-linked hydroxyalkyl acrylate and RC^{1, 2}

The Belfort group first utilized surface irradiation methods, like photooxidation and atmospheric plasma of PES for ultrafiltration, to hydrophilize the surfaces and reduce protein and organic fouling^3-5. We developed the first truly high throughput platform to screen, select and synthesize winners from a 66-member monomer library for a series of different feeds (i.e., proteins, bacteria, mammalian cells)^6-9. We then used solution methods such as activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP)^{10, 11} and single electron transfer- living radical polymerization (SET-LRP)¹² that rely on copper (Cu(1) and Cu(0) to catalyze the free radical polymerization. To better understand both processes, we implemented and solved their respective reaction schemes using MATLAB and fit the models to literature data and determined the rate constants and other parameters^{10, 13}. Significant findings from our work were as follows: (a) The use of our high throughput platform to seek chemistries with desired behavior for a particular application in a very short period. GE Global used the platform to develop a DNA detection product in 2 months. (b) The discovery of surface chemistries such as specific polyethylene glycols and zwitterions that exhibit low protein fouling using our high throughput platform. (c) The discovery of amines and the natural molecule NSP1 (FG residue-rich sequence)¹⁴ from the nucleopore complex that exhibit reduced protein fouling. (d) Demonstrating that ARGET-ATRP and SET-LRP are able to produce a new class of membranes based on grafting bottle brushes that have high surface areas and can be chemically and physically designed a priori for a particular application. New focus is on replacing distillation with organic nanofiltration¹², selectively purifying mRNA for vaccines, and purifying IgG using adsorptive bottle brushes.

Acknowledgement: To collaborators Chip Kilduff, Bob Langer and Dan Anderson and to my lab manager of 15.5 years, Mirco Sorci, and all the wonderful graduate students who worked on surface modifications.

References

1. Tuccelli, R.; Karnakis, A. T. Cellulosic ultrafiltration membranes. 1994.
2. Steuck, M. J. Porous membrane having hydrophilic surface and process. 1986.
3. Crivello, J. H. Y., H. and Belfort, G. Low Fouling Ultrafiltration and Microfiltration Aryl Polysulfone. 1995.
4. Pieracci, J.; Crivello, J. V.; Belfort, G., Photochemical modification of 10kDa polyethersulfone ultrafiltration membranes for reduction of biofouling. Journal of Membrane Science 1999, 156 (2), 223-240.
5. Yamagishi, H.; Crivello, J. V.; Belfort, G., Evaluation of photochemically modified poly (arylsulfone) ultrafiltration membranes. Journal of Membrane Science 1995, 105 (3), 249-259.
6. Zhou, M., Liu, H., Venkiteshwaran, A., Kilduff, J. C., Anderson, D. G., Langer, R. Belfort G. , High throughput discovery of new fouling-resistant surfaces. Journal of Materials Chemistry 2011, 21, 11.
7. Zhou, M.; Liu, H.; Kilduff, J. E.; Langer, R.; Anderson, D. G.; Belfort, G., High-throughput membrane surface modification to control NOM fouling. Environmental science & technology 2009, 43 (10), 3865-71.
8. Zhou, M.; Liu, M.; Venkiteshwaran, A.; Kilduff, J.; Anderson, D. G.; Langer, R.; Belfort, G., High throughput discovery of new fouling-resistant surfaces,. J. Materials. Chem 2011, 21, 12.
9. Zhou, M. Y.; Liu, H. W.; Kilduff, J. E.; Langer, R.; Anderson, D. G.; Belfort, G., High-Throughput Membrane Surface Modification to Control NOM Fouling. Environmental Science & Technology 2009, 43 (10), 3865-3871.
10. Keating, J. J.; Lee, A.; Belfort, G., Predictive Tool for Design and Analysis of ARGET ATRP Grafting Reactions. Macromolecules 2017, 50 (20), 7930-7939.
11. Keating, J. J. I.; Sorci, M.; Kocsis, I.; Setaro, A.; Barboiu, M.; Underhill, P.; Belfort, G., Atmospheric Pressure Plasma - ARGET ATRP Modification of Poly(ether sulfone) Membranes: A Combination Attack. J. Membr. Sci. 2017, 546, 6.
12. Ramesh, P.; Xu, W., L.; Sorci, M.; Trant, C.; Lee, S.; Kilduff, J.; Yu, M.; Belfort, G., Organic solvent filtration by brush membranes: Permeability, selectivity and fouling correlate with degree of SET-LRP grafting. J. Membr. Sci. 2020, 618, 118699.
13. Gunter, K.; Sorci, M.; Belfort, G., Predictive Tool for Design and Analysis of SET-LRP Polymer Grafting Reactions. ACS Applied Polymer Materials, 2020, 2 (11), 4924=4935.
14. Hayama, R.; Sorci, M.; Keating Iv, J. J.; Hecht, L. M.; Plawsky, J. L.; Belfort, G.; Chait, B. T.; Rout, M. P., Interactions of nuclear transport factors and surface-conjugated FG nucleoporins: Insights and limitations. PLoS One 2019, 14 (6), e0217897.