Despite advanced sterilization and aseptic techniques, infections associated with medical implants have not been eradicated. Most present coatings cannot simultaneously fulfil the requirements of antibacterial and antifungal activity as well as biocompatibility and reusability. Here, we report an antimicrobial hydrogel based on dimethyldecylammonium chitosan (with high quaternization)-graft-poly(ethylene glycol) methacrylate (DMDC-Q-g-EM) and poly(ethylene glycol) diacrylate, which has excellent antimicrobial efficacy against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Fusarium solani. The proposed mechanism of the antimicrobial activity of the polycationic hydrogel is by attraction of sections of anionic microbial membrane into the internal nanopores of the hydrogel, like an 'anion sponge', leading to microbial membrane disruption and then microbe death. We have also demonstrated a thin uniform adherent coating of the hydrogel by simple ultraviolet immobilization. An animal study shows that DMDC-Q-g-EM hydrogel coating is biocompatible with rabbit conjunctiva and has no toxicity to the epithelial cells or the underlying stroma.

Facilely synthesized cationic peptidopolysaccharides, which have a bacterial peptidoglycan‐mimetic structure, show outstanding broad‐spectrum activities against clinically significant bacteria and fungi and low mammalian cytotoxicity. Their structural affinity with microbial cell‐wall constituents promotes penetration to reach the cytoplasmic membrane resulting in excellent antimicrobial activity and high selectivity.

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Antibacterial polypeptides as ancient immune defense systems are effective against bacteria. Here we report a novel kind of “armed” carrier: an antibacterial polypeptide-grafted chitosan-based nanocapsule with an excellent antibacterial efficacy against both Gram-positive and Gram-negative bacteria. This nanocapsule also has excellent blood compatibility and low cytotoxicity. Patients after tumor surgery may benefit from this “armed” carrier because it is highly anti-inflammation and is able to deliver anticancer and antiepileptic drugs simultaneously.

Antimicrobial peptides (AMPs), particularly those effective against methicillin-resistant Staphylococcus aureus ( S. aureus ) and antibiotic-resistant Pseudomonas aeruginosa ( P. aeruginosa ), are important alternatives to antibiotics. Typical peptide synthesis methods involving solid-phase sequential synthesis are slow and costly, which are obstacles to their more widespread application. In this paper, we synthesize peptides via ring-opening polymerization of alpha-amino acid N-carboxyanhydrides (NCA) using a transition metal initiator. This method offers high potential for inexpensive synthesis of substantial quantities of AMPs. Lysine (K) was chosen as the hydrophilic amino acid and alanine (A), phenylalanine (F), and leucine (L) as the hydrophobic amino acids. We synthesized five series of AMPs (i.e., P(KA), P(KL), P(KF), P(KAL), and P(KFL)), varied the hydrophobic amino acid content from 0 to 100%, and determined minimal inhibitory concentrations (MICs) against clinically important Gram-negative and Gram-positive bacteria and fungi (i.e., Escherichia coli ( E. coli ), P. aeruginosa , Serratia marcescens ( S. marcescens ), and Candida albicans ( C. albicans ). We found that P(K(10)F(7.5)L(7.5)) and P(K(10)F(15)) show the broadest activity against all five pathogens and have the lowest MICs against these pathogens. For P(K(10)F(7.5)L(7.5)), the MICs against E. coli , P. aeruginosa , S. marcescens , S. aureus , and C. albicans are 31 microg/mL, 31 microg/mL, 250 microg/mL, 31 microg/mL, and 62.5 microg/mL, while for P(K(10)F(15)) the respective MICs are 31 microg/mL, 31 microg/mL, 250 microg/mL, 31 microg/mL, and 125 microg/mL. These are lower than the MICs of many naturally occurring AMPs. The membrane depolarization and SEM assays confirm that the mechanism of microbe killing by P(K(10)F(7.5)L(7.5)) copeptide includes membrane disruption, which is likely to inhibit rapid induction of AMP-resistance in pathogens.

Food corruption and spoilage caused by food-borne pathogens and microorganisms is a serious problem. As a result, the demand for antibacterial drugs in food packaging is growing. In this review, biodegradable and non-biodegradable materials for food packaging are discussed based on their properties. Most importantly, antibacterial agents are essential to inhibit the growth of bacteria in food. To keep food fresh and prolong the shelf life, different kinds of antibacterial agents were used. The composition and application of natural antibacterial agents and synthetic antibacterial agents are discussed. Compared with natural antibacterial agents, synthetic antibacterial agents have the advantages of low cost and high activity, but their toxicity is usually higher than that of natural antibacterial agents. Finally, future development of antimicrobial food packaging is proposed. It is an urgent problem for researchers to design and synthesize antibacterial drugs with high efficiency and low toxicity.

Cancer patients after chemotherapy may also suffer bacterial attack due to badly decreased immunity. Although with high bacterial efficacy, conventional antibiotics are prone to inducement of drug resistance and may be not suitable for some cancer patients. In contrast, antibacterial peptides are highly effective in inhibiting bacteria without inducing resistance in pathogens. Presented in this article is a novel kind of highly effective antibacterial peptide-based biocompatible and biodegradable block copolymer vesicle. The copolymer is poly(ε-caprolactone)-block-poly[phenylalanine-stat-lysine-stat-(lysine-folic acid)] [PCL19-b-poly[Phe12-stat-Lys9-stat-(Lys-FA)6]], which can self-assemble into vesicles in aqueous solution. The biocompatible and biodegradable PCL forms the vesicle membrane, whereas the poly[Phe12-stat-Lys9-stat-(Lys-FA)6] block constitutes the vesicle coronas. Compared to the individual polymer chains, the vesicles showed enhanced antibacterial activities against both Gram-positive and Gram-negative bacteria (16 μg mL(-1)) due to the locally concentrated antibacterial poly[Phe12-stat-Lys9-stat-(Lys-FA)6] coronas, which may avoid the inducement of antibiotic-resistant bacteria and side effects of multidrug interactions. Furthermore, folic acid is introduced into the vesicle coronas for potential further applications such as cancer-targeted drug delivery. Moreover, the amino groups can be further functionalized when necessary. This low cytotoxic, biocompatible, biodegradable, and antibacterial vesicle (without antibiotic resistance) may benefit patients after tumor surgery because it is highly anti-inflammatory, and it is possible to deliver the anticancer drug to tumor cells simultaneously.

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