Advances in peptide/polymer antimicrobial assemblies

Antimicrobial peptides (AMPs) have been extensively exploited as promising drugs to cope with antibiotic-resistant bacteria in clinical treatment. Peptide/polymer assembly provides a particularly important contribution to this topic and has emerged as a new paradigm for the development of nano-antimicrobial systems with previously unattainable outcomes. In this review article, we systematically summarize the recent advances in antimicrobial peptide/polymer assemblies. We describe a brief background and several classified systems based on peptide/polymer assemblies. We discuss the molecular design and the general rules behind the assembled nanostructures and bioactivities. The key role of polymers in improving the antimicrobial activity, stability, cytotoxicity, and bioavailability of peptides is emphasized based on the reported systems. The resulting peptide/polymer assemblies with stimuli-responsiveness, value-added properties and potential applications are demonstrated. The outlook of the antimicrobial peptide/polymer assemblies is also presented from the viewpoint of bio-applications.

Uniform, Length-Tunable Antibacterial 1D Diblock Copolymer Nanofibers

The rapid increase in antibiotic resistant strains of bacteria has led to an urgent need to develop new methods of treating bacterial infections. Antibacterial polymeric nanoparticles are of interest for...

Synthesis of substituted N-(2'-nitrophenyl)pyrrolidine-2-carboxamides towards the design of proline-rich antimicrobial peptide mimics to eliminate bacterial resistance to antibiotics

The treatment of diseases is under threat due to the increasing resistance of disease-causing bacteria to antibiotics. Likewise, free radical-induced oxidative stress has been implicated in several human disease conditions, such as cancer, stroke and diabetes. In the search for amino acid analogues with antibacterial and antioxidant properties as possible mimics of antimicrobial peptides, substituted N-(2'-nitrophenyl)pyrrolidine-2-carboxamides 4a-4k and N-(2'-nitrophenyl)piperidine-2-carboxamides 4l-4n have been synthesized via a two-step, one-pot amidation of the corresponding acids, using thionyl chloride with different amines in dichloromethane. The carboxamides were characterized by infrared and nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. Carboxamides 4a-4n were assayed against five Gram-positive and five Gram-negative bacterial strains using the broth micro-dilution procedure and compared to standard antibiotic drugs (streptomycin and nalidixic acid). 4b showed the highest antibacterial activity with a minimum inhibitory concentration (MIC) value of 15.6 µg/mL against Staphylococcus aureus. Pertinently, 4b and 4k are promising candidates for narrow-spectrum (Gram-positive) and broad-spectrum antibiotics, respectively. The antioxidant properties of the carboxamides were also evaluated using the 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation. 4a and 4k recorded the lowest IC₅₀ values of 1.22 × 10^-3 mg/mL (with DPPH) and 1.45 × 10^-4 mg/mL (with ABTS), respectively. Notably, 4k recorded about 2.5 times better antioxidant capacity than the positive controls - ascorbic acid and butylated hydroxyanisole. These results bode well for N-aryl carboxamides as good mimics and substitutes for antimicrobial peptides towards mitigating bacterial resistance to antibiotics as well as ameliorating oxidative stress-related diseases.

Synthesis and properties of a temperature-sensitive hydrogel based on physical crosslinking via stereocomplexation of PLLA-PDLA

A synthetic route to amphiphilic conetwork (APCN) gels was developed and involved (1) a ring-opening polymerization (ROP) synthesis of the macromonomer HEMA-PLLA/PDLA, and (2) a radical polymerization of a stereocomplex of the synthesized macromonomers with P(MEO₂MA-co-OEGMA) to form the APCN gels. The structure of the gel was successfully verified using X-ray diffraction. Thermal analysis and differential scanning calorimetry data showed that the thermal behaviors of the gels were greatly improved compared with that of polylactic acid (PLA). The mechanical properties of the gels were measured by using a dynamic viscometer, and the results indicated a greater mechanical strength before swelling than afterwards, and an increasing strength of the gels with increasing amount of PLA stereocomplex. Gels placed in different aqueous phases at different temperatures showed different swelling ratio (SR) values. Specifically, the SR gradually decreased as the temperature was increased, indicating a temperature sensitivity of the gels. In addition, the gels placed in the aqueous and organic phases presented as hydrogels and hydrophobic gels, respectively, and their SR values were relatively low. These results indicated the amphiphilic nature of the gel, and indicated great application prospects for the gel in biomedicine.

A synthetic route to amphiphilic conetwork (APCN) gels was developed and involved (1) ring-opening polymerization synthesis of the macromonomer, and (2) radical polymerization of stereocomplex of the synthesized macromonomers with MEO₂MA, OEGMA to form the APCN gels.

Chondroitin sulfate immobilized PCL nanofibers enhance chondrogenic differentiation of mesenchymal stem cells

Cold Atmospheric Plasma (CAP) is used as a promising method in surface modification for immobilization of chondroitin sulfate functional biomacromolecules on PCL nanofibrous substrates for cartilage tissue engineering. The GAG-grafted scaffolds are able to successfully support the attachment and proliferation of mesenchymal stem cells (MSCs). The seeded scaffolds show the chondro-differentiation of MSCs during a 21-days cell culture in a non-differential medium. Expression of SOX9, Collagen10 and Collagen2 proved the chondro-inductive effect of GAG-grafted scaffolds. Besides, no external chondro-genic differential agent was used in the differentiation of MSCs to chondrocyte. The cells passed the last phase of chondrogenesis after 14 days of incubation. Thus, the GAG-fabricated fibrous scaffolds using CAP are potential candidates for cartilage tissue engineering.

Polymeric Antimicrobial Food Packaging and Its Applications

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.

Polypeptides Micelles Composed of Methoxy-Poly(Ethylene Glycol)-Poly(l-Glutamic Acid)-Poly(l-Phenylalanine) Triblock Polymer for Sustained Drug Delivery

Methoxy-poly(ethylene glycol)-poly(l-glutamic acid)-poly(l-phenylalanine) triblock polymers with different architecture were synthesized as drug carrier to obtain sustained and controlled release by tuning the composition. These triblock polymers were prepared by ring opening polymerization and poly(ethylene glycol) was used as an initiator. Polymerization was confirmed by ¹H NMR, FT-IR and gel penetration chromatography. The polymers can self-assemble to form micelles in aqueous medium and their critical micelle concentrations values were examined. The micelles were spherical shape with size of 50–100 nm and especially can arranged in a regular manner. Sorafenib was selected as the model drug and the drug loading performance was dependent on the composition of the block copolymer. In vitro drug release indicated that the polymers can realize controlled and sustained drug release. Furthermore, in vitro cytotoxicity assay showed that the polymers were biocompatible and the drug-loaded micelles can increase toxicity towards tumor cells. Confocal fluorescence microscopy assays illustrated that the micelles can be uptaken quickly and release drug persistently to inhibit tumor cell growth.

β-Carotene: a natural osteogen to fabricate osteoinductive electrospun scaffolds

β-Carotene (βC) as a natural osteogenic material was incorporated in PCL electrospun mats to fabricate scaffolds for bone tissue engineering. These scaffolds successfully supported the attachment and proliferation of mesenchymal stem cells (MSCs). Seeded scaffolds were calcinated during 21 days of cell culture in a non-differential medium, which showed the osteodifferentiation of MSCs. Expression of RUNX2, SOX9, and osteonectin proved the osteoinductive effect of incorporated β-carotene on the differentiation of MSCs to osteoblasts without using any external osteogenic differential agent. However, the cells did not pass the early phase of osteogenesis and were still osteochondro-progenitor after 21 days of incubation. Thus, the fabricated fibrous scaffolds are potential candidates for direct bone tissue engineering.

Electrospun PCL scaffolds containing β-carotene as a natural osteogenic material can differentiate MSCs to osteoblasts without using external differential agents.