In Vitro Antibacterial Activity of Silver Nanoparticles Conjugated with Amikacin and Combined with Hyperthermia against Drug-Resistant and Biofilm-Producing Strains.

In view of the current increase and spread of antimicrobial resistance (AMR), there is an urgent need to find new strategies to combat it. This study had two aims. First, we synthesized highly monodispersed silver nanoparticles (AgNPs) of approximately 17 nm, and we functionalized them with mercaptopoly(ethylene glycol) carboxylic acid (mPEG-COOH) and amikacin (AK). Second, we evaluated the antibacterial activity of this treatment (AgNPs_mPEG_AK) alone and in combination with hyperthermia against planktonic and biofilm-growing strains. AgNPs, AgNPs_mPEG, and AgNPs_mPEG_AK were characterized using a suite of spectroscopy and microscopy methods. Susceptibility to these treatments and AK was determined after 24 h and over time against 12 clinical multidrug-resistant (MDR)/extensively drug-resistant (XDR) isolates of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The efficacy of the treatments alone and in combination with hyperthermia (1, 2, and 3 pulses at 41°C to 42°C for 15 min) was tested against the same planktonic strains using quantitative culture and against one P. aeruginosa strain growing on silicone disks using confocal laser scanning microscopy. The susceptibility studies showed that AgNPs_mPEG_AK was 10-fold more effective than AK alone, and bactericidal efficacy after 4, 8, 24, or 48 h was observed against 100% of the tested strains. The combination of AgNPs_mPEG_AK and hyperthermia eradicated 75% of the planktonic strains and exhibited significant reductions in biofilm formation by P. aeruginosa in comparison with the other treatments tested, except for AgNPs_mPEG_AK without hyperthermia. In conclusion, the combination of AgNPs_mPEG_AK and hyperthermia may be a promising therapy against MDR/XDR and biofilm-producing strains. IMPORTANCE Antimicrobial resistance (AMR) is one of the greatest public health challenges, accounting for 1.27 million deaths worldwide in 2019. Biofilms, a complex microbial community, directly contribute to increased AMR. Therefore, new strategies are urgently required to combat infections caused by AMR and biofilm-producing strains. Silver nanoparticles (AgNPs) exhibit antimicrobial activity and can be functionalized with antibiotics. Although AgNPs are very promising, their effectiveness in complex biological environments still falls below the concentrations at which AgNPs are stable in terms of aggregation. Thus, improving the antibacterial effectiveness of AgNPs by functionalizing them with antibiotics may be a significant change to consolidate AgNPs as an alternative to antibiotics. It has been reported that hyperthermia has a large effect on the growth of planktonic and biofilm-producing strains. Therefore, we propose a new strategy based on AgNPs functionalized with amikacin and combined with hyperthermia (41°C to 42°C) to treat AMR and biofilm-related infections.

Plasma-induced nanostructured metallic silver surfaces: study of bacteriophobic effect to avoid bacterial adhesion on medical devices.

Biofilm formation in medical devices represents one of the major problems for the healthcare system, especially those that occur on implantable silicone-based devices. To provide a general solution to avoid biofilm formation in the first stages of development, this work studied how nanostructured metallic silver coatings hinder bacteria-surface interaction by preventing bacteria adhesion. The three studied silver nanostructures ("Sharp blades", "Thick blades" and "Leaves") combined superhydrophobic behavior with a physical impediment of the coating nanostructure that produced a bacteriophobic effect avoiding the adhesion mechanism of different bacterial strains. These silver nanostructures are immobilized on stretchable substrates through a polymeric thin film of plasma-polymerized penta-fluorophenyl methacrylate. The control over the nanostructures and therefore its bacteriophobic-bactericidal effect depends on the plasma polymerization conditions of the polymer. The characterization of this bacteriophobic effect through FE-SEM microscopy, live/dead cell staining, and direct bacterial adhesion counts, provided a complete mapping of how bacteria interact with the surface in each scenario. Results revealed that the bacterial adhesion was reduced by up to six orders of magnitude in comparison with uncoated surfaces thereby constituting an effective strategy to avoid the formation of biofilm on medical materials.

Analytical Parameters of a Novel Glucose Biosensor Based on Grafted PFM as a Covalent Immobilization Technique.

Bioanalytical methods, in particular electrochemical biosensors, are increasingly used in different industrial sectors due to their simplicity, low cost, and fast response. However, to be able to reliably use this type of device, it is necessary to undertake in-depth evaluation of their fundamental analytical parameters. In this work, analytical parameters of an amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) were evaluated. GOx was immobilized using plasma-grafted pentafluorophenyl methacrylate (pgPFM) as an anchor onto a tailored HEMA-co-EGDA hydrogel that coats a titanium dioxide nanotubes array (TiO2NTAs). Finally, chitosan was used to protect the enzyme molecules. The biosensor offered outstanding analytical parameters: repeatability (RSD = 1.7%), reproducibility (RSD = 1.3%), accuracy (deviation = 4.8%), and robustness (RSD = 2.4%). In addition, the Ti/TiO2NTAs/ppHEMA-co-EGDA/pgPFM/GOx/Chitosan biosensor showed good long-term stability; after 20 days, it retained 89% of its initial sensitivity. Finally, glucose concentrations of different food samples were measured and compared using an official standard method (HPLC). Deviation was lower than 10% in all measured samples. Therefore, the developed biosensor can be considered to be a reliable analytical tool for quantification measurements.

Specially Designed Polyaniline/Polypyrrole Ink for a Fully Printed Highly Sensitive pH Microsensor.

pH sensing for healthcare applications requires sensors with mechanically stable materials of high sensitivity and high reproducibility combined with low-cost fabrication technologies. This work proposes a fully printed pH sensor based on a specially formulated conducting polymer deposited on a microelectrode in a flexible substrate. A formulation, which combined polyaniline (PANI) and polypyrrole (PPy) with integrated polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), was specially prepared to be printed by inkjet printing (IJP). The sensor has good sensitivity in the physiological region (pH 7-7.5) key for the healthcare biosensor. This mixture printed over a commercial gold ink, which has a singular chemical functionalization with phthalocyanine (Pc), increased the sensor sensitivity, showing an excellent reproducibility with a linear super-Nernstian response (81.2 ± 0.5 mV/pH unit) in a wide pH range (pH 3-10). This new ink together with the IJP low-cost technique opens new opportunities for pH sensing in the healthcare field with a single device, which is disposable, highly sensitive, and stable in the whole pH range.

Study of the Human Albumin Role in the Formation of a Bacterial Biofilm on Urinary Devices Using QCM-D.

Catheter-associated urinary tract infections (CAUTIs) are the most common health care-associated infections due to rapid bacterial colonization+ and biofilm formation in urinary catheters. This behavior has been extensively documented in medical devices. However, there is a few literature works on CAUTI providing a model that allows the exhaustive study of biofilm formation in a urinary environment. The development of an effective model would be helpful to identify the factors that promote the biofilm formation and identify strategies to avoid it. In this work, we have developed a model to test biofilm formation on urinary medical device surfaces by simulating environmental and physical conditions using a quartz crystal microbalance with dissipation (QCM-D) module with an uropathogenic strain. Moreover, we used the developed model to study the role of human albumin present in artificial urine at high concentrations because of renal failure or heart-diseases in patients. Despite model limitations using artificial urine, these tests show that human albumin can be considered as a promoter of biofilm formation on hydrophobic surfaces, being a possible risk factor to developing a CAUTI.

Allylamine PECVD Modification of PDMS as Simple Method to Obtain Conductive Flexible Polypyrrole Thin Films.

In this paper, we report a one-step method to obtain conductive polypyrrole thin films on flexible substrates. To do this, substrates were modified through allylamine plasma grafting to create a high amount of reactive amine groups on PDMS surface. These groups are used during polypyrrole particle synthesis as anchoring points to immobilize the polymeric chains on the substrate during polymerization. Surface morphology of polypyrrole thin films are modified, tailoring the polyelectrolyte used in the polypyrrole synthesis obtaining different shapes of nanoparticles that conform to the film. Depending on the polyelectrolyte molecular weight, the shape of polypyrrole particles go from globular (500 nm diameter) to a more constructed and elongated shape. The films obtained with this methodology reflected great stability under simple bending as well as good conductivity values (between 2.2 ± 0.7 S/m to 5.6 ± 0.2 S/cm).

Extended 2,2'-Bipyrroles: New Monomers for Conjugated Polymers with Tailored Processability.

The synthesis of 2,2'-bipyrroles substituted at positions 5,5' with pyrrolyl, N-methyl-pyrrolyl and thienyl groups and their application in the preparation of conducting polymers is reported herein. The preparation of these monomers consisted of two synthetic steps from a functionalized 2,2'-bipyrrole: Bromination of the corresponding 2,2'-bipyrrole followed by Suzuki or Stille couplings. These monomers display low oxidation potential compared to pyrrole because of the extended length of their conjugation pathway. The resulting monomers can be polymerized through oxidative/electropolymerization. Electrical conductivity and electrochromic properties of the electrodeposited polymeric films were evaluated using 4-point probe measurements and cyclic voltammetry to evaluate their applicability in electronics.

Stretchable conductive polypyrrole films modified with dopaminated hyaluronic acid.

In this paper, we report the modification of polypirrole (PPy) with dopaminated hyaluronic acid (HADA). This design improves PPy adhesion onto stretchable materials such as poly(dimethylsiloxane) (PDMS) allowing the formation of conducting films on this kind of very flexible, hydrophobic materials. The results revealed that described PPy modification allows to obtain stable PPy:HADA nano-suspension able to cast films directly on PDMS. The comparison of PPy:HADA films with conventional PPy and other modified PPy shows that the modification improved the strength of the films under tension stress and their water resistance. Moreover, the modification proposed does not affect significantly the conductivity of the PPy films. The resulting properties of the material make it especially suitable for bio-integrated device applications, where a biocompatible material with stable electrical behaviour under deformation and water media is needed.