Antibacterial brush polypeptide coatings with anionic backbones.

Preventing initial colonization of bacteria on biomaterial surfaces is crucial to address the medical device-associated infection issues. Antimicrobial peptide (AMP) or cationic polymer modified surfaces have shown promising potentials to inhibit the initial colonization of bacteria by contact killing. However, their development has been impeded because of bacterial adhesion and high cytotoxicity. Herein, we report a series of brush polypeptide coatings with anionic backbones and cationic AMP mimetic side-chains that displayed superior bactericidal activity, antibacterial adhesion property, and biocompatibility. The cationic side-chain density played an important role in the bioactivities of the brush polypeptide modified surfaces. Brush polypeptide coating with low side-chain density exhibited improved bactericidal activity and antibacterial adhesion property, ascribing to the cooperative effects of adjacent side-chains and backbones/side-chains, respectively. It also showed negligible hemolysis/cytotoxicity in vitro and potent anti-infection property (≥99.9% bactericidal efficacy) in vivo. Brush polymers with anionic backbones and cationic side-chains can be used as a promising design motif to potentiate both antibacterial property and biocompatibility of coatings for combating device-associated infections. STATEMENT OF SIGNIFICANCE: Device-associated infections (DAIs) have led to increased medical cost, pain, and even mortality of patients. Antimicrobial peptide and cationic polymer coatings provide an important strategy to combat DAIs by preventing initial colonization of bacteria on biomaterial surfaces. Nevertheless, they have suffered bacterial adhesion and cytotoxicity issues. Herein, we developed a brush polypeptide coating with anionic backbones and cationic side-chains. The brush polypeptide coating showed superior bactericidal and antibacterial adhesion properties outperforming conventional antibacterial coatings based on antimicrobial peptide (i.e., melittin), lysozyme (i.e., lysostaphin), cationic polymer, anionic polymer, and the blends of cationic/anionic polymers. It also showed good biocompatibility and potent anti-infection property, making it a promising candidate to combat the DAIs.

Impact of Charge Composition and Distribution on the Antibacterial Properties of Polypeptide Coatings.

Inspired by the charge composition and distribution of proteins and peptides, we designed and prepared a series of brush polypeptides with positive and negative charges separately distributed in the side chains and the backbones. The brush polypeptides can self- or co-deposit on various substrates forming ultrathin and stable coatings. They showed potent bactericidal activity and antibiofilm property, outperforming conventional linear polypeptide coatings with randomly distributed positive and negative charges. Keeping the balance of positive/negative charges and increasing the numbers of positive/negative charges can further improve the antibacterial property of brush polypeptide coatings without sacrificing their biocompatibility.

Imidazolium-Based Polypeptide Coating with a Synergistic Antibacterial Effect and a Biofilm-Responsive Property.

Surface modification with cationic polymer coatings represented an important strategy to address the medical device-related infection issues. However, limited antibacterial activities and high cytotoxicity have hampered their development. Herein, we report a facile method to enhance the surface antibacterial activity by construction of an imidazolium-based polypeptide with fosfomycin counteranions (i.e., S4-PIL-FS). The polypeptide coating displayed a synergistic antibacterial effect from the combination of membrane disruption and inhibition of initial cell wall synthesis, leading to higher in vitro and in vivo surface antibacterial activities than cationic polypeptide or fosfomycin sodium alone. S4-PIL-FS also showed a decrease in the hemolytic ratio and cytotoxicity toward different mammalian cells. Moreover, we observed an interesting biofilm-responsive property of S4-PIL-FS originating from the esterase-induced cleavages of side-chain ester bonds that enabled an antibiofilm property of the cationic polypeptide coating.

Single-Chain Nanoparticle-Based Coatings with Improved Bactericidal Activity and Antifouling Properties.

Dual-function antibacterial surfaces have exhibited promising potential in addressing implant-associated infections. However, both bactericidal and antifouling properties need to be further improved prior to practical uses. Herein, we report the preparation and properties of a linear block copolymer coating (LP-KF) and a single-chain nanoparticle coating (NP-KF) with poly(ethylene glycol) (PEG) and cationic polypeptide segments. NP-KF with cyclic PEG segments and densely charged polypeptide segments was expected to display improved bactericidal and antifouling properties. LP-KF was prepared by the combination of ring-opening polymerization of N-carboxyanhydride (NCA) monomers and subsequent deprotection. NP-KF was prepared by intramolecular cross-linking of LP-KF in diluted solutions. Both LP-KF- and NP-KF-coated PDMS surfaces were prepared by dipping with polydopamine-coated surfaces. They showed superior in vitro bactericidal activity against both Staphylococcus aureus and Escherichia coli with >99.9% killing efficacy, excellent protein adsorption resistance, antibacterial adhesion, and low cytotoxicity. The NP-KF coating showed higher bactericidal activity and antifouling properties than its linear counterpart. It also showed significant anti-infective property and histocompatibility in vivo, which makes it a good candidate for implants and biomedical device applications.

A sulfonate-based polypeptide toward infection-resistant coatings.

Multifunctional coatings have gained significant attention for their promising potential to address the issue of medical device-related infections. However, they usually have multiple components in one layer which decreases the density of functional groups on surfaces and hence reduces the biological properties. Herein, we report a mono-component and sulfonate-based anionic polypeptide coating with on-demand antibacterial activity, antifouling property, and biocompatibility. The anionic polypeptide was prepared by ring-opening polymerization of L-cysteine-based N-carboxyanhydride (NCA) with allyl groups and a subsequent thiol-ene reaction to incorporate the sulfonate pendants. It adopted a 17.1-19.5% ß-sheet conformation and self-assembled into a spherical nanoparticle. The polypeptide coating showed excellent in vitro antibacterial activity against both Gram-positive (i.e., S. aureus) and Gram-negative bacteria (i.e., E. coli) with >99% killing efficacy after acidic solution treatment and prominent antifouling property and biocompatibility after weak base treatment. An in vivo study revealed that the sulfonate-based polypeptide-coated polydimethylsiloxane (PDMS) exhibited good anti-infection property and histocompatibility.

Facile Synthesis of Imidazolium-Based Block Copolypeptides with Excellent Antimicrobial Activity.

Antimicrobial polypeptides are promising mimics of antimicrobial peptides (AMPs) with low risks of antimicrobial resistance (AMR). Polypeptides with facile and efficient production, high antimicrobial activity, and low toxicity toward mammalian cells are highly desirable for practical applications. Herein, triblock copolypeptides with chloro groups (PPGn-PCPBLGm) and different main-chain lengths were synthesized via an ultrafast ring-opening polymerization (ROP) using a macroinitiator, namely poly(propylene glycol) bis(2-aminopropyl ether), and purified or nonpurified monomer (i.e., CPBLG-NCA). PPGn-PCPBLGm with 90 amino acid residues can be readily prepared within 300 s. Imidazolium-based block copolypeptides (PPGn-PILm) were facilely prepared via nucleophilic substitution of PPGn-PCPBLGm with NaN3 and subsequent "click" chemistry. α-Helical PPGn-PILm can self-assemble into nanostructured and cationic micelles which displayed highly potent antimicrobial activity and low hemolysis. The top-performing material, namely PPG34-PIL70, showed low minimum inhibitory concentration (MIC) against both Gram-positive S. aureus and Gram-negative E. coli (25 µg mL-1). It also displayed low toxicity against mouse embryonic fibroblast (NIH 3T3) and human embryonic kidney (293T) cells at 2× MIC.

Transition of Conformation and Solubility in ß-Sheet-Structured Poly(l-cysteine)s with Methylthio or Sulfonium Pendants.

Poly(l-cysteine)s with methylthio pendants (PMTLCs) were synthesized by ring-opening polymerization of a new l-cysteine-based N-carboxyanhydride. The thioether bonds of PMTLC can be readily oxidized by H2O2 yielding water-soluble PMTLCOX. The methylthio groups can undergo an alkylation reaction using methyl iodide and a subsequent ion-exchange reaction yielding sulfonium-based polypeptides (PPLC-DMS-X, where X = I, BF4). PPLC-DMS-X showed upper critical solution temperature-type thermo- and oxidation-responsive properties in aqueous solutions. Both PMTLC and PPLC-DMS-X showed oxidation-induced ß-sheet to α-helix transitions. The absorbance of PPLC-DMS-I and methyl orange aqueous solution displayed a significant linear correlation with temperature, which makes the sulfonium-based polypeptides good candidates in the field of temperature sensors.

Efficient synthesis and excellent antimicrobial activity of star-shaped cationic polypeptides with improved biocompatibility.

Antimicrobial peptides (AMPs) have been considered as a promising new tool to combat the antimicrobial resistance (AMR) crisis. However, the high toxicity and high cost of AMPs hampered their further development. Herein, a series of star poly(L-lysine) (PLL) homo- and copolymers with excellent antimicrobial activity and improved biocompatibility were prepared by the combination of ultra-fast ring opening polymerization (ROP) and side-chain modification. The amine-terminated polyamidoamine dendrimer (Gx-PAMAM) mediated ROP of Nε-tert-butyloxycarbonyl-L-lysine N-carboxyanhydride (Boc-L-Lys-NCA) and γ-benzyl-L-glutamic acid-based N-carboxyanhydride (PBLG-NCA) was able to prepare star PLL homo- and copolymers with 400 residues within 50 min. While the star PLL homopolymers exhibited low minimum inhibitory concentration (MIC = 50-200 µg mL-1) against both Gram-positive and Gram-negative bacteria (i.e., S. aureus and E. coli), they showed high toxicity against various mammalian cell lines. The star PLL copolymers with low contents of hydrophobic and hydroxyl groups showed enhanced antimicrobial activity (MIC = 25-50 µg mL-1) and improved mammalian cell viability. Both SEM and CLSM results indicated the antimicrobial mechanism of membrane disruption.