Controlled swelling of biomaterial devices for improved antifouling polymer coatings

Nonspecific interactions between cells and implantable elastomers often leads to failure modes for devices such as catheters, cosmetic and reconstructive implants, and sensors. To reduce these interactions, device surfaces can be coated with hydrophilic polymers, where greater polymer density enhances antifouling properties. Although graft-from coating techniques result in higher density polymer films and lower fouling in controlled settings, simpler graft-to methods show similar results on complex implanted devices, despite limited density. To address the need for improved graft-to methods, we developed Graft then shrink (GtS) where elastomeric materials are temporarily swollen during polymer grafting. Herein, we demonstrate a graft-to based method for poly(oligo(ethylene glycol) methyl ether methacrylate) (pOEGMA) on swollen silicone, GtS, that enhances grafted polymer content and fouling resistance. Total grafted polymer content of pOEGMA on toluene swollen silicone increased over ~ 13 × compared to non-swollen controls, dependent on the degree of silicone swelling. Increases in total grafted polymer within the top 200 µm of the material led to bacterial and mammalian cell adhesion reductions of 75% and 91% respectively, compared to Shrink then Graft (StG) antifouling polymer coated controls. GtS allows for the simple 3D coating of swellable elastomers (e.g., silicone medical devices) with improved antifouling pOEGMA coatings.

To explore the influence of GHCl on pCB-COOH, we conducted gel permeation chromatography (GPC) studies in buffers containing GHCl.GPC analysis of pCB-COOH in varying GHCl buffer strengths between 1 and 100 mм (pH 6.5) showed decreasing apparent Mws and hydrodynamic radii with increasing buffer concentration, while PEG standards eluted at nearly identical times, with no change in apparent Mw, in all three GHCl buffer strengths tested (Figure S5).Differences in grafting efficiency may be the result of improved polymer packing at 10 mм over 1 mм and improved thiol accessibility and reactivity at 10 mм over 100 mм due to the more extended polymer conformation at 10 mм.Guanidine has previously shown effects on amphiphilic block copolymer grafting density 42 , and has also been shown to control the collapsed and uncollapsed state of elastin like peptides in solution through interactions with amide bonds 39 , which are also present in pCB-COOH.Therefore, GHCl is most likely influencing the hydrodynamic radius of pCB-COOH, indicating that buffer conditions beyond solubility can also influence grafting density for zwitterionic polymers.

Figure S2 .
Figure S2.Maleimide content of elastomers after polymer grafting.(A) Surface fluorescence of SMCC modified elastomers after reaction with a thiol-fluorescein tracer.(B) Maleimide content of elastomers before and after polymer grafting.Means ± SD, n = 3.

Figure
Figure S3.pCB-TBu ester deprotection in pH 1.3 HCl.(A) Relative tert-butyl group signal by NMR after exposure to HCl at pH 1.3 for between 2 and 6 hours at room temperature and 50°C.(B) Calculated percent of ester deprotection based on relative signal from NMR of pCB-TBu.(C) Solution fluorescence intensity of pCB-TBu and pCB-COOH fluorescein methacrylate copolymers.Mean ± SD, n = 3.

Figure S4 .
Figure S4.Grafting salt choice and concentration modifies grafted pCB-COOH content.(A) Absorbance of elastomers at 502 nm modified with fluorescent pCB-COOHf copolymers (mean ± SD, n = 3).Concentrations refer to MES or GHCl, polymer concentration was 2 mg mL -1 for all cases.(B, C) Photographs of grafting solution after polymer grafting procedure and 10:1 Graft then shrink elastomers grafted with fluorescent pCB-COOHf copolymers in various buffers.(D) Surface fluorescence of 10:1 PDMS elastomers modified with fluorescent pCB-COOH in MES and GHCl grafting buffers between 1 and 1000 mM.(E) Grafting solution fluorescence of 10:1 PDMS elastomers modified with fluorescent pCB in MES and GHCl grafting buffers between 1 and 1000 mм.

Figure S5 .
Figure S5.Apparent molecular weight of pCB changes with GHCl concentration.(A) GPC of PEG standards and pCB-co-fluorescein methacrylate in three GHCl buffer concentrations.(B) Plotted apparent molecular weight of pCB as calculated by GPC calibrated with PEG standards in PBS.

Figure S7 .
Figure S7.Macrophage adhesion to PDMS modified with non-antifouling polymers.(A) Cell adhesion of Raw 264.7 macrophages on 10:1 and 30:1 PDMS modified with 2mer and 4mer pOEGMA (mean ± SD, n = 3).(C) Ratio of cells adhered between Graft then shrink and Shrink then graft materials modified with 2mer and 4mer pOEGMA.

Figure S9 .
Figure S9.Water contact angle measurements of polymer modified PDMS.(A) Representative images of 3 µL droplets of MilliQ water on PDMS samples.(B) Average water contact angle of PDMS samples.Mean ± SD, n = 4.

Figure S10 .
Figure S10.Contact angle measurements with cell maintenance media of 8mer pOEGMA PDMS.Average water contact angle on PDMS samples of 3 µL droplets of 10% FBS supplemented cell media.Mean ± SD, n = 4.

Figure S11 .
Figure S11.Water contact angle measurements of pCB-co-APMA grafted PDMS that is crosslinked with EDC immediately following grafting and dynamic water contact angle measurements of 8mer 100 kDa pOEGMA.(A) Schematic showing when EDC crosslinking was performed in the grafting and swelling process.(B) Average water contact angle on PDMS grafted with pCB-co-APMA, samples of 3 µL droplets of water.(C) Average advancing and receding water contact angles on 8mer pOEGMA coated PDMS samples, with ~ 5 uL droplets.Mean ± SD, n = 3.

Figure
Figure S12.H NMR spectroscopy of CB-TBu monomer.

Figure S13 .
Figure S13.NMR spectroscopic characterization of pCB-TBu synthesis from pDMAPMA.(A) Quantification of monomer percent modification by NMR.(B) Reaction scheme of pCB-TBu preparation.(C-E) H NMR of precursor pDMAPMA, protected pCB-TBu and deprotected pCB-COOH.(F) Structures and assignments of H NMR.

Figure S14 .
Figure S14.Terminal thiol presence verification by Ellman assay.Blank subtracted absorbance measurements at 412 nm of thiol terminal 2mer pOEGMA solutions following incubation for 15 minutes at room temperature with Ellman's reagent (means ± SD, n = 3).