Application of Targeted Molecular and Material Property Optimization to Bacterial Attachment-Resistant (Meth)acrylate Polymers

Abstract

Developing medical devices that resist bacterial attachment and subsequent biofilm formation is highly desirable. In this paper, we report the optimization of the molecular structure and thus material properties of a range of (meth)acrylate copolymers which contain monomers reported to deliver bacterial resistance to surfaces. This optimization allows such monomers to be employed within novel coatings to reduce bacterial attachment to silicone urinary catheters. We show that the flexibility of copolymers can be tuned to match that of the silicone catheter substrate, by copolymerizing these polymers with a lower Tg monomer such that it passes the flexing fatigue tests as coatings upon catheters, that the homopolymers failed. Furthermore, the Tg values of the copolymers are shown to be readily estimated by the Fox equation. The bacterial resistance performance of these copolymers were typically found to be better than the neat silicone or a commercial silver containing hydrogel surface, when the monomer feed contained only 25 v% of the "hit" monomer. The method of initiation (either photo or thermal) was shown not to affect the bacterial resistance of the copolymers. Optimized synthesis conditions to ensure that the correct copolymer composition and to prevent the onset of gelation are detailed.

Figure 1

Structures of monomers used in the synthesis of the copolymers

Figure 2

Comparison of the observed T_gs with those calculated by the Fox equation. The y=x line is drawn, R² = 0.95.

Figure 3

Bacterial coverage of three different strains after 72 h culture where PA = P. aeruginosa, PAO1 (blue/first bar), SA = S. aureus 8325-4, (red/second bar), UPEC = uropathogenic E. coli 536 (green/third bar). Average bacterial attachment across the three different strains (purple/fourth bar). No homopolymer DEGMA data is presented in this figure because this material did not form a viable stable film for subsequent material testing under the experimental conditions used. DEGMA materials only proved sufficiently stable when copolymerized.

Figure 4

The level of DEGMA present on the surface of the EGDPEA/DEGMA copolymers. Secondary ion C₂H₅O⁺ was chosen as an indicative DEGMA daughter ion, whilst secondary ion C₄H₅⁺ was chosen as an indicative EGDPEA daughter ion.

Figure 5

SEM images of polymer-coated silicone catheters after fatigue tests. Polymers were dip coated onto silicone catheters. (A) silicone without coating; (B) EGDPEA; (C) EGDPEA/DEGMA(75/25)