Utilization of star-shaped polymer architecture in the creation of high-density polymer brush coatings for the prevention of platelet and bacteria adhesion

Abstract

We demonstrate utilization of star-shaped polymers as high-density polymer brush coatings and their effectiveness to inhibit the adhesion of platelets and bacteria. Star polymers consisting of poly(2-hydroxyethyl methacrylate) (PHEMA) and/or poly(methyl methacrylate) (PMMA), were synthesized using living radical polymerization with a ruthenium catalyst. The polymer coatings were prepared by simple drop casting of the polymer solution onto poly(ethylene terephthalate) (PET) surfaces and then dried. Among the star polymers prepared in this study, the PHEMA star polymer (star-PHEMA) and the PHEMA/PMMA (mol. ratio of 71/29) heteroarm star polymer (star-H71M29) coatings showed the highest percentage of inhibition against platelet adhesion (78-88% relative to noncoated PET surface) and Escherichia coli (94-97%). These coatings also showed anti-adhesion activity against platelets after incubation in Dulbecco's phosphate buffered saline or surfactant solution for 7 days. In addition, the PMMA component of the star polymers increased the scratch resistance of the coating. These results indicate that the star-polymer architecture provides high polymer chain density on PET surfaces to prevent adhesion of platelets and bacteria, as well as coating stability and physical durability to prevent exposure of bare PET surfaces. The star polymers provide a simple and effective approach to preparing anti-adhesion polymer coatings on biomedical materials against the adhesion of platelets and bacteria.

Fig. 1

Polymer brush structures on surfaces by (A) graft polymers vs. (B) star polymers.

Fig. 2

(A) SEC curves of the star-H47M53 polymer at 0 and 52 h after the cross-linking reaction. As the star polymers formed, a new peak appeared in the higher molecular weight (MW) region (MW ~ 10⁵), and only a trace amount of precursor polymers (MW ~ 10⁴) was observed. After purification by precipitation and TMS-deprotection, the unreacted precursor polymers were removed. (B) ¹H NMR spectra of the heteroarm star PTMSOEMA/PMMA (before deprotection) and star-H47M53 polymers (after deprotection). The peak of the TMS of PTMSOEMA at 0.2 ppm disappeared after HCl treatment, indicating the complete removal of TMS groups to give hydroxyl groups.

Fig. 3

Polymer-coated surfaces. (A) Preparation of polymer coatings by drop casting. The polymer solution in a methanol or methanol/acetone mixture was dropped onto a PET surface and dried under reduced pressure overnight. (B) Pictures of polymer coatings. An unmodified PET film is transparent; the star-PHEMA and star-PMMA coatings appear to be heterogeneous. (C) SEM images of polymer-coated surfaces, and (D) AFM topographic images. See Supplementary Information for surface images of other polymers.

Fig. 4

Scratch resistance test. (A) SEM of star-PHEMA and star-H71M29 coatings at the different scratch loads. (B) Scratch widths on star-PHEMA and star-H71M29 coating surfaces after loading (mean ± standard deviation, n = 3). ***p < 0.001.

Fig. 5

Surface characterization after scratch testing. AFM images of edge of scratch on (A) star-PHEMA- and (B) star-H71M29-coated surfaces.

Fig. 6

Platelet adhesion to polymer-coated surfaces. (A) SEM images of adherent platelets on the polymer-coated surfaces. The platelets on the star-PHEMA and star-PMMA polymers are highlighted by circles for clarification. Image magnification: × 400 (top) and × 1,500 (bottom). Images of samples are shown in Fig. S3, S4 in the supplementary information. (B) The number of adherent platelets on polymer coatings. The number of platelets was determined from the SEM images (mean ± standard deviation, n = 3). ***p < 0.0001, **p < 0.001, *p < 0.005 vs. PET.

Fig. 7

Bacterial adhesion to polymer-coated surfaces. (A) SEM images of adherent E. coli (ATCC 25922) on polymer-coated surfaces. Image magnification× 400 (top) and × 2,500 (bottom). Images of samples are shown in Fig. S5, S6 in the supplementary information. (B) Bacterial adhesion and growth in solution (mean ± standard deviation, n = 3). Adhesion of E. coli on to polymer-coated surface was quantified using luminescence assay. The growth of E. coli was determined by OD590 (•) after 20 h, 37 °C incubation. ***p < 0.0001 vs. PET.

Fig. 8

Stability test of polymer-coated surface by platelet adhesion to the coatings after incuba ion in PBS for 12 h, and PBS or 0.5 wt% Triton X-100 solution with gentle shaking for 7 days. ***p < 0.0001, **p< 0.001, *p < 0.005 vs. PET.

Scheme

Synthesis of PHEMA/PMMA heteroarm star polymers by Ru(II)-catalyzed living radical polymerization.