Full Length ArticleSurface conjugation of poly (dimethyl siloxane) with itaconic acid-based materials for antibacterial effects
Graphical abstract
Introduction
Poly (dimethyl siloxane) (PDMS) is widely used as a biomaterial because it is non-toxic, inert, optically transparent, non-flammable, permeable to gasses, and has excellent mechanical properties [[1], [2], [3]]. Although PDMS has many advantages, the PDMS surface is known to cause bacterial adhesion and protein absorption issues due to its high hydrophobicity [4,5]. Generally, antibacterial agents have been used to prevent bacterial film formation on PDMS surfaces [6,7]. However, the emergence of antibiotic-resistant bacteria is becoming an increasingly serious health problem with the ineffectiveness of antibacterial drugs [8].
Recently, there have been other studies on treating the surface of PDMS [[9], [10], [11]]. Also, Komaromy et al. investigated the effect of changing the physical properties by increasing the hydrophilicity by UV radiation; the PDMS surfaces showed a promising repellent effect against both live and dead Escherichia coli and Staphylococcus aureus cells [12]. Although these methods proved to be effective, challenges remain, including the reduced biocompatibility found after chemical treatment, hydrophobicity recovery, and physical damage to the PDMS surface [13,14]. Thus, the design and modification of PDMS surfaces using biomaterials that inhibit bacterial growth has been investigated to improve current medical devices [15]. Wu et al. demonstrated a method for producing chlorogenic acid (CA)-modified PDMS substrates to increase the antimicrobial properties and improve the viability of the target cells [16]. More recently, Xu et al. reported the prevention of bovine serum albumin (BSA) adsorption and reduction of bacterial adhesion with (mucin/poly (ethyleneimine)) n-functionalized PDMS films [17]. Hou et al. grafted poly(ethylene oxide) onto thermoplastic (carboxylated cardopoly(aryl ether ketone), PEK-COOH) membrane surfaces via the carbodiimide/N-hydroxysuccinimide EDC/NHS methodology to modify the membrane hydrophilicity, and excellent renewable antimicrobial and antifouling activities were found [18]. Wang et al. synthesized a novel poly (methacrylisobutyl polyhedral oligomeric silsesquioxane-co-2-(dimethylamino)-ethyl methacrylate) (p (MA POSS-co-DMAEMA)) coating by using a reversible addition–fragmentation chain-transfer (RAFT) polymerization method to improve the antibacterial and anti-adhesive properties of PDMS membranes. After being quaternized by treatment with 1-bromoheptane, the resulting p (MA POSS-co-DMAEMA+) brushes showed a remarkable bactericidal activity against S. aureus owing to the p (DMAEMA+) component [19].
Itaconic acid (IA) is a naturally occurring non-amino and non-toxic organic acid that shows a good antimicrobial activity [[20], [21], [22]]. Recently, Sood et al. reported the synthesis of an IA-conjugated carboxymethyl cellulose-cl-poly (lactic acid-co-itaconic acid) hydrogel via a facile graft copolymerization using N-N1-methylene-bis-acrylamide (MBA) and potassium persulfate as the crosslinker and initiator. The prepared hydrogel showed excellent antimicrobial activities against S. aureus and E. coli [23]. Krezovic et al. reported a series of semi-interpenetrating polymer networks (semi-IPNs) of 2-hydroxyethyl acrylate and IA hydrogels, in the presence of poly (N-vinylpyrrolidone) via free radical copolymerization. The synthesized hydrogels showed the best antibacterial activity against Pseudomonas aeruginosa. From this study, it is apparent that the IA content and time of exposure greatly influence the antibacterial potential [24]. Therefore, in this study, we chemically and physically conjugated IA and poly (itaconic acid) (PIA) to the surface of PDMS to investigate their antibacterial properties. Herein, we have prepared substrates including IA- and PIA-conjugated PDMS, IA- and PIA-blended PDMS, and conjugated and blended IA- and PIA-PDMS using both a chemical conjugation and physical blending method to enhance the bactericidal efficacy.
Section snippets
Materials
The PDMS elastomer (Sylgard® 184 silicone elastomer kit) was purchased from Dow Corning, USA. Itaconic acid (IA, analytical grade, assay ≥99%, MW: 130.10 g/mol, density: 1.573 g/mL at 25 °C (lit.)), choline chloride (ChCl, assay ≥ 99%, MW: 139.62 g/mol), ammonium persulfate (APS, assay ≥ 98%, MW: 228.20 g/mol), N-hydroxysuccinimide (NHS, assay ≥ 98%, MW: 115.09 g/mol), (3-aminopropyl)triethoxysilane (APTES, assay ≥ 99%, MW: 221.37 g/mol, density: 0.946 g/mL at 25 °C(lit.)), and bovine serum
1H NMR spectra of IA and PIA (D2O, 600 MHz)
The 1H NMR spectra of IA and PIA are shown in the Fig. S5. In contrast to the spectrum of IA, two absorptions of approximately equal intensities were observed for PIA at 2.30 and 2.65 ppm, which can be assigned to the backbone and sidechain methylene groups, respectively. Therefore, we can confirm that PIA has successfully been synthesized. A similar result was reported previously [[25], [26], [27]].
ATR-FTIR spectra of IA and PIA
The pure IA monomer and lyophilized PIA polymer were characterized by their functional groups
Conclusions
In the present study, PDMS surfaces were conjugated separately with different concentrations of itaconic acid (IA) and poly (itaconic acid) (PIA). Free radical polymerization was used to successfully synthesize the PIA. The characterization with SEM, XPS, FT-IR, and contact angle confirmed the presence of IA and PIA in all groups. It was found that IA and PIA led to decrease of bacterial adhesion. Especially, the highest bacterial anti-adhesion effect was observed for the high-concentration
Acknowledgments
This work was supported by the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (HI15C1744), and the Technology Innovation Program (10050526, Development of disposable diaper based on biomass-oriented biodegradable super-absorbent polymers), funded by the Ministry of Trade, Industry & Energy (MI, Korea).
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These authors contributed equally to this work.