Cooperative Catechol-Functionalized Polypept(o)ide Brushes and Ag Nanoparticles for Combination of Protein Resistance and Antimicrobial Activity on Metal Oxide Surfaces

Phytic Acid-Promoted Deposition of Gold Nanoparticles with Grafted Cationic Polymer Brushes for the Construction of Synergistic Contact-Killing and Photothermal Bactericidal Coatings

Medical implants are constantly facing the risk of bacterial infections, especially infections caused by multidrug resistant bacteria. To mitigate this problem, gold nanoparticles with alkyl bromide moieties (Au NPs-Br) on the surfaces were prepared. Xenon light irradiation triggered the plasmon effect of Au NPs-Br to induce free radical graft polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA), leading to the formation of poly(DMAEMA) brush-grafted Au NPs (Au NPs-g-PDM). The Au NPs-g-PDM nanocomposites were conjugated with phytic acid (PA) via electrostatic interaction and van der Waals interaction. The as-formed aggregates were deposited on the titanium (Ti) substrates to form the PA/Au NPs-g-PDM (PAP) hybrid coatings through surface adherence of PA and the gravitational effect. Synergistic bactericidal effects of contact-killing caused by the cationic PDM brushes, and local heating generated by the Au NPs under near-infrared irradiation, conferred strong antibacterial effects on the PAP-deposited Ti (Ti-PAP) substrates. The synergistic bactericidal effects reduced the threshold temperature required for the photothermal sterilization, which in turn minimized the secondary damage to the implant site. The Ti-PAP substrates exhibited 97.34% and 99.97% antibacterial and antiadhesive efficacy, respectively, against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), compared to the control under in vitro antimicrobial assays. Furthermore, the as-constructed Ti-PAP surface exhibited a 99.42% reduction in the inoculated S. aureus under in vivo assays. In addition, the PAP coatings exhibited good biocompatibility in the hemolysis and cytotoxicity assays as well as in the subcutaneous implantation of rats.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

The Bioanalytical and Biomedical Applications of Polymer Modified Substrates

Polymers with different structures and morphology have been extensively used to construct functionalized surfaces for a wide range of applications because the physicochemical properties of polymers can be finely adjusted by their molecular weights, polydispersity and configurations, as well as the chemical structures and natures of monomers. In particular, the specific functions of polymers can be easily achieved at post-synthesis by the attachment of different kinds of active molecules such as recognition ligand, peptides, aptamers and antibodies. In this review, the recent advances in the bioanalytical and biomedical applications of polymer modified substrates were summarized with subsections on functionalization using branched polymers, polymer brushes and polymer hydrogels. The review focuses on their applications as biosensors with excellent analytical performance and/or as nonfouling surfaces with efficient antibacterial activity. Finally, we discuss the perspectives and future directions of polymer modified substrates in the development of biodevices for the diagnosis, treatment and prevention of diseases.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Tuning the PEG surface density of the PEG-PGA enveloped Octaarginine-peptide Nanocomplexes

One of the main limitations of protein drugs is their restricted capacity to cross biological barriers. We have previously reported nanostructured complexes of insulin and modified octaarginine (C12-r8), enveloped by a polyethyleneglycol-polyglutamic acid (PEG-PGA) protective shell, and showed their capacity to overcome different barriers associated to the oral modality of administration. The objective of this work was to produce the said nanocomplexes with structurally diverse PEG-PGA shells, i.e. with different chain lengths and PEG substitution degrees, and comparatively analyze their PEG surface density and subsequent impact on their interaction with mucus glycoproteins and Caco-2 cells. The new PEG-PGA enveloped C12-r8-insulin nanocomplexes (ENCPs) exhibited a narrow size distribution (average size of 210-239 nm), a neutral surface charge and a 100% insulin association efficiency (final insulin loading of 16.5-29.6% w/w). Proton nuclear magnetic resonance (¹H NMR) analysis indicated the possibility to modulate the PEG density on the ENCPs from 6.7 to 44.5 PEG chains per 100 nm². This increase in the ENCPs PEG surface density resulted in their reduced interaction with mucins in vitro, while their interaction with Caco-2 cells in vitro remained unaltered. Overall, these data indicate the capacity to tune the surface characteristics of the ENCPS in order to maximize the capacity of these nanocarriers to overcome barriers associated to mucosal surfaces.

Evasion of the accelerated blood clearance phenomenon by polysarcosine coating of liposomes

Using polyethylene glycol (PEG) to functionalize liposomes improves their stealth properties and stability in blood. However, PEG is known to induce the accelerated blood clearance (ABC) phenomenon, which occurs for multiple doses owing to anti-PEG IgM being produced after the initial injection. In this study, as an alternative to PEG, polysarcosine (PSar) was selected owing to its low antigenicity and its highly dense chains with controllable lengths, similar to PEG. Furthermore, we directly evaluate the potential of PSar for avoiding the ABC phenomenon by comparing PSar with PEG on the same liposome platform, which has similar physicochemical properties such as hydrophobic region, membrane fluidity, and size. PEG- and PSar-liposomes were prepared and characterized for comparison. PSar-liposomes showed similar physicochemical properties to PEG-liposomes in terms of size control, zeta potential, membrane polarity, and fluidity; however, ELISA results showed noticeably lower levels and faster production speeds of both IgM and IgG for PSar-liposomes than for PEG-liposomes. In addition, a pharmacokinetics experiment with multiple injections showed that PSar-PE coating of liposomes may help to circumvent the ABC phenomenon.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Fabrication of Robust Antibacterial Coatings Based on an Organic-Inorganic Hybrid System

Antibacterial coatings have drawn much attention because of their high potential applications in medicine. However, the weak mechanical property, poor biosafety, and biocompatibility of most established antibacterial coatings restrict their applications. In this study, robust antibacterial coatings were fabricated via a simple organic-inorganic hybrid method. The polymer component provides an excellent antibacterial property to the coatings, and the hybrid silica sol improves the hardness of coatings. After cross-linking, network-structured coatings were formed. The coating surfaces exhibited high transmittance, excellent mechanical property, and good antibacterial effect against Escherichia coli (Gram-negative) and Streptococcus mutans (Gram-positive). Additionally, the robust coatings were noncytotoxic with satisfactory biocompatibility. Such results provide a theoretical basis for their applications in the biomedical field.

Antifouling and Antibacterial Properties Constructed by Quaternary Ammonium and Benzyl Ester Derived from Lysine Methacrylamide

Hemocompatibility and antibacterial property are essential for blood contact devices and medical intervention materials. In this study, positively charged quaternary ammonium (QAC) and hydrophobic benzyl group (OBzl) were introduced onto hydrophilic lysine methacrylamide (LysAAm) to obtain two monomers LysAAm-QAC and LysAAm-OBzl, respectively. The structure characterizations of LysAAm-QAC and LysAAm-OBzl were determined by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry. LysAAm-QAC and LysAAm-OBzl were cografted onto a silicon wafer with different feeding ratios to construct antifouling and antibacterial properties. The results of fibrinogen adsorption and platelet adhesion proved that the modified sample with the feeding ratio of 3:7 had superior antifouling property. Furthermore, an antimicrobial test with both 2 and 24 h indicated that the modified sample with the feeding ratio of 3:7 had antibacterial ability. The antifouling property was provided by the high surface coverage of LysAAm-QAC and LysAAm-OBzl (91.49%) and the hydrophilic main structure LysAAm on LysAAm-QAC and LysAAm-OBzl (water contact angle was 43.6°). The antibacterial property was improved with the proportion of LysAAm-OBzl (43.6-58.5%) because the increasing hydrophobic OBzl enhanced the ability to insert into the membrane of bacteria and raise the bactericidal efficiency. In application, LysAAm-QAC and LysAAm-OBzl with the feeding ratio of 3:7 were grafted onto the surface of poly(styrene-b-(ethylene-co-butylene)-b-styrene), and a bifunctional surface with antifouling and antibacterial properties was fabricated, which had promising applications in blood contact devices and medical intervention materials.

"Command" surfaces with thermo-switchable antibacterial activity

In the presented work "smart" antibacterial surfaces based on silver nanoparticles (AgNPs) embedded in temperature-responsive poly(di(ethylene glycol)methyl ether methacrylate) - (POEGMA188) as well as poly(4-vinylpyridine) - (P4VP) coatings attached to a glass surface were successfully prepared. The composition, thickness, morphology and wettability of the resulting coatings were analyzed using ToF-SIMS, XPS, EDX, ellipsometry, AFM, SEM and CA measurements, respectively. Temperature-switched killing of the bacteria was tested against Escherichia coli ATCC 25922 (representative of Gram-negative bacteria) and Staphylococcus aureus ATCC 25923 (representative of Gram-positive bacteria) at 4 and 37 °C. In general at 4 °C no significant difference was observed between the amounts of bacteria accounted on the grafted brush coatings and within the control sample. In contrast, at 37 °C almost no bacteria were visible for temperature-responsive coating with AgNPs, whereas the growth of bacteria remains not disturbed for "pure" coating, indicating strong temperature-dependent antibacterial properties of AgNPs integrated into brushes.

Recent advances in antibacterial applications of metal nanoparticles (MNPs) and metal nanocomposites (MNCs) against multidrug-resistant (MDR) bacteria

Introduction: In recent years, multidrug resistance (MDR) in bacteria has drastically increased and has posed a great threat to the human health. This problem has generated an urgent need to search alternatives for the treatment of MDR bacteria. It has been proved that metal nanoparticles (MNPs) and metal nanocomposites (MNCs) possess remarkable antimicrobial potential, and hence can be used in alternative therapy. Areas covered: This review is aimed to discuss recent reports on antibacterial activities of MNPs and MNCs against MDR bacteria. Expert opinion: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Serratia marcescens, Streptococcus pneumoniae, and Staphylococcus epidermidis are important pathogenic bacteria which have shown MDR against a wide range of conventional antibiotics. In this context, effects of MNPs and MNCs on these pathogens have demonstrated considerable efficacy. Several mechanisms concerning activity of MNPs and MNCs against pathogenic bacteria which are mainly dependent on type of their precursors and treated bacterium have been investigated. In addition, many studies have been made on antibacterial activities of these nanomaterials with similar and different results.

Coordinative Binding of Polymers to Metal-Organic Framework Nanoparticles for Control of Interactions at the Biointerface

Metal-organic framework nanoparticles (MOF NPs) are of growing interest in diagnostic and therapeutic applications, and due to their hybrid nature, they display enhanced properties compared to more established nanomaterials. The effective application of MOF NPs, however, is often hampered by limited control of their surface chemistry and understanding of their interactions at the biointerface. Using a surface coating approach, we found that coordinative polymer binding to Zr- fum NPs is a convenient way for peripheral surface functionalization. Different polymers with biomedical relevance were assessed for the ability to bind to the MOF surface. Carboxylic acid and amine containing polymers turned out to be potent surface coatings and a modulator replacement reaction was identified as the underlying mechanism. The strong binding of polycarboxylates was then used to shield the MOF surface with a double amphiphilic polyglutamate-polysarcosine block copolymer, which resulted in an exceptional high colloidal stability of the nanoparticles. The effect of polymer coating on interactions at the biointerface was tested with regard to cellular association and protein binding, which has, to the best of our knowledge, never been discussed in literature for functionalized MOF NPs. We conclude that the applied approach enables a high degree of chemical surface confinement, which could be used as a universal strategy for MOF NP functionalization. In this way, the physicochemical properties of MOF NPs could be tuned, which allows for control over their behavior in biological systems.

Improved radiosynthesis and preliminary in vivo evaluation of the 11C-labeled tetrazine [11C]AE-1 for pretargeted PET imaging

Pretargeted nuclear imaging based on the ligation between tetrazines and nano-sized targeting agents functionalized with trans-cyclooctene (TCO) has recently been shown to improve both imaging contrast and dosimetry in nuclear imaging of nanomedicines. Herein, we describe the improved radiosynthesis of a ¹¹C-labeled tetrazine ([¹¹C]AE-1) and its preliminary evaluation in both mice and pigs. Pretargeted imaging in mice was carried out using both a new TCO-functionalized polyglutamic acid and a previously reported TCO-functionalized bisphosphonate system as targeting agents. Unfortunately, pretargeted imaging was not successful using these targeting agents in pair with [¹¹C]AE-1. However, brain imaging in pig indicated that the tracer crossed the blood-brain-barrier. Hence, we suggest that this tetrazine scaffold could be used as a starting point for the development of pretargeted brain imaging, which has so far been a challenging task.

Development of Multimodal Antibacterial Surfaces Using Porous Amine-Reactive Films Incorporating Lubricant and Silver Nanoparticles

Anti-biofouling has been improved by passive or active ways. Passive antifouling strategies aim to prevent the initial adsorption of foulants, while active strategies aim to eliminate proliferative fouling by destruction of the chemical structure and inactivation of the cells. However, neither passive antifouling strategies nor active antifouling strategies can solely resist biofouling due to their inherent limitations. Herein, we successfully developed multimodal antibacterial surfaces for waterborne and airborne bacteria with the benefit of a combination of antiadhesion (passive) and bactericidal (active) properties of the surfaces. We elaborated multifunctionalizable porous amine-reactive (PAR) polymer films from poly(pentafluorophenyl acrylate) (PPFPA). Pentafluorophenyl ester groups in the PAR films facilitate creation of multiple functionalities through a simple postmodification under mild condition, based on their high reactivity toward various primary amines. We introduced amine-containing poly(dimethylsiloxane) (amine-PDMS) and dopamine into the PAR films, resulting in infusion of antifouling silicone oil lubricants and formation of bactericidal silver nanoparticles (AgNPs), respectively. As a result, the PAR film-based lubricant-infused AgNPs-incorporated surfaces demonstrate outstanding antibacterial effects toward both waterborne and airborne Escherichia coli, suggesting a new door for development of an effective multimodal anti-biofouling surface.

Controllable synthesis of mussel-inspired catechol-formaldehyde resin microspheres and their silver-based nanohybrids for catalytic and antibacterial applications

Size-controlled CFR microspheres and their silver-based nanohybrids were constructed and the nanohybrids display high catalytic reduction activity and antibacterial properties.

Antibacterial Polymeric Films Fabricated by [2+2] Cycloaddition-Retroelectrocyclization and Ag+ Ion Coordination

The [2+2] cycloaddition-retroelectrocyclization (CA-RE) between N,N-dialkylaniline-substituted alkynes and 7,7,8,8-tetracyanoquinodimethane (TCNQ) is employed to fabricate functional cross-linked polymer films containing the intramolecular charge-transfer (CT) chromophores at the cross-linking points. Polystyrene bearing N,N-dialkylaniline-substituted alkynes (P1) and TCNQ polyester (P2) are mixed in tetrahydrofuran (THF), then this solution is spray-coated onto an indium tin oxide or glass plate. Heating to 100 °C initiates the [2+2] CA-RE reaction, resulting in the formation of cross-linked polymer films. The reaction progress and completion are evaluated by monitoring the CT absorption band and cyano vibration peaks. The resulting cross-linked polymer films show reversible cathodic electrochromism between the neutral and anion radical states. In addition, they also display the visual detection behavior of protic acids and Lewis acids, such as Ag⁺ ions. Accordingly, the Ag⁺ ion-loaded polymer films are prepared, and their antibacterial activities are studied. As more Ag⁺ ions are loaded, the CT band more bathochromically shifts and more potent antibacterial activities are obtained. Therefore, the antibacterial activity of the polymer films can be visually recognized by the film colors. Furthermore, the loaded Ag⁺ ions can be released from the polymer films by application of an electrochemical potential.

Poly-sarcosine and Poly(Ethylene-Glycol) Interactions with Proteins Investigated Using Molecular Dynamics Simulations

Nanoparticles coated with hydrophilic polymers often show a reduction in unspecific interactions with the biological environment, which improves their biocompatibility. The molecular determinants of this reduction are not very well understood yet, and their knowledge may help improving nanoparticle design. Here we address, using molecular dynamics simulations, the interactions of human serum albumin, the most abundant serum protein, with two promising hydrophilic polymers used for the coating of therapeutic nanoparticles, poly(ethylene-glycol) and poly-sarcosine. By simulating the protein immersed in a polymer-water mixture, we show that the two polymers have a very similar affinity for the protein surface, both in terms of the amount of polymer adsorbed and also in terms of the type of amino acids mainly involved in the interactions. We further analyze the kinetics of adsorption and how it affects the polymer conformations. Minor differences between the polymers are observed in the thickness of the adsorption layer, that are related to the different degree of flexibility of the two molecules. In comparison poly-alanine, an isomer of poly-sarcosine known to self-aggregate and induce protein aggregation, shows a significantly larger affinity for the protein surface than PEG and PSar, which we show to be related not to a different patterns of interactions with the protein surface, but to the different way the polymer interacts with water.

Efficient Shielding of Polyplexes Using Heterotelechelic Polysarcosines

Shielding agents are commonly used to shield polyelectrolyte complexes, e.g., polyplexes, from agglomeration and precipitation in complex media like blood, and thus enhance their in vivo circulation times. Since up to now primarily poly(ethylene glycol) (PEG) has been investigated to shield non-viral carriers for systemic delivery, we report on the use of polysarcosine (pSar) as a potential alternative for steric stabilization. A redox-sensitive, cationizable lipo-oligomer structure (containing two cholanic acids attached via a bioreducible disulfide linker to an oligoaminoamide backbone in T-shape configuration) was equipped with azide-functionality by solid phase supported synthesis. After mixing with small interfering RNA (siRNA), lipopolyplexes formed spontaneously and were further surface-functionalized with polysarcosines. Polysarcosine was synthesized by living controlled ring-opening polymerization using an azide-reactive dibenzo-aza-cyclooctyne-amine as an initiator. The shielding ability of the resulting formulations was investigated with biophysical assays and by near-infrared fluorescence bioimaging in mice. The modification of ~100 nm lipopolyplexes was only slightly increased upon functionalization. Cellular uptake into cells was strongly reduced by the pSar shielding. Moreover, polysarcosine-shielded polyplexes showed enhanced blood circulation times in bioimaging studies compared to unshielded polyplexes and similar to PEG-shielded polyplexes. Therefore, polysarcosine is a promising alternative for the shielding of non-viral, lipo-cationic polyplexes.