Characterisation of polyamide 11/copper antimicrobial composites for medical device applications

Mechanical performance of negative-stiffness multistable bi-material composites

Architected latticed structural systems, known as metamaterials or metastructures, have recently garnered significant attention due to their superior performance under various loading conditions. This class includes metamaterials exhibiting multistability, characterized by negative stiffness, which enables energy entrapment during transitions between equilibrium states, making them suitable for applications such as lightweight protective systems. In this study, in three folds, we investigate the mechanical performance of a negative stiffness honeycomb metamaterial (NSHM) with unit cells composed of curved double beams. First, the quasi-static compressive response is numerically examined using the finite element method, revealing that this response is independent of the number of cells. Next, we analyze the transient dynamic response of both mono-material NSHMs and bi-material composites, where the stiffeners are replaced by brittle polystyrene, under localized striker and uniform plate impacts. Finally, we present an analytical model for the total potential energy, with solutions obtained through an optimization technique, and validate these results against the numerical simulations. Through these analyses, we study the effects of several parameters influencing multistability. Our findings demonstrate that the bistability ratio significantly impacts the overall response of the honeycomb, and the desired negative stiffness can be achieved with high bistability ratios. Additionally, the contact force peaks resulting from striker impact are found to be independent of the number of constituent elements. The optimized geometry of the lattice is determined through a trade-off between porosity and stiffness, achieved by thicker cell walls.

Effect of Powder Bed Fusion Laser Sintering on Dimensional Accuracy and Tensile Properties of Reused Polyamide 11

Polyamide 11 (PA11) is a plant-based nylon made from castor beans. Powder bed fusion laser sintering (PBF-LS) is an additive manufacturing process used for PA11 which allows for the reuse of the unsintered powder. The unsintered powder is mixed with virgin powders at different refresh rates, a process which has been studied extensively for most semi-crystalline polyamides. However, there is lack of information on the effect of using 100% reused PA11 powder and the effect of the number of times it is reused on its own, during powder bed fusion laser sintering. This paper investigates the effect of reusing PA11 powder in PBF-LS and the effect of the number of times it is reused on the dimensional accuracy, density and thermal and tensile properties. From the 100% virgin powder to the third reuse of the powder, there is a decrease in powder wastage, crystallinity and tensile strength. These are associated with the polymerisation and cross-linking process of polymer chains, upon exposure to high temperatures. This results in a higher molecular weight and, hence, a higher density. From the fourth reuse to the tenth reuse, the opposite is observed, which is associated with an increase in high-viscosity unmolten particles, resulting in defects in the PBF-LS parts.

Antimicrobial Activity of a Titanium Dioxide Additivated Thermoset

The transmission of pathogens via surfaces poses a major health problem, particularly in hospital environments. Antimicrobial surfaces can interrupt the path of spread, while photocatalytically active titanium dioxide (TiO2) nanoparticles have emerged as an additive for creating antimicrobial materials. Irradiation of such particles with ultraviolet (UV) light leads to the formation of reactive oxygen species that can inactivate bacteria. The aim of this research was to incorporate TiO2 nanoparticles into a cellulose-reinforced melamine-formaldehyde resin (MF) to obtain a photocatalytic antimicrobial thermoset, to be used, for example, for device enclosures or tableware. To this end, composites of MF with 5, 10, 15, and 20 wt% TiO2 were produced by ultrasonication and hot pressing. The incorporation of TiO2 resulted in a small decrease in tensile strength and little to no decrease in Shore D hardness, but a statistically significant decrease in the water contact angle. After 48 h of UV irradiation, a statistically significant decrease in tensile strength for samples with 0 and 10 wt% TiO2 was measured but with no statistically significant differences in Shore D hardness, although a statistically significant increase in surface hydrophilicity was measured. Accelerated methylene blue (MB) degradation was measured during a further 2.5 h of UV irradiation and MB concentrations of 12% or less could be achieved. Samples containing 0, 10, and 20 wt% TiO2 were investigated for long-term UV stability and antimicrobial activity. Fourier-transform infrared spectroscopy revealed no changes in the chemical structure of the polymer, due to the incorporation of TiO2, but changes were detected after 500 h of irradiation, indicating material degradation. Specimens pre-irradiated with UV for 48 h showed a total reduction in Escherichia coli when exposed to UV irradiation.

The Composites of Polyamide 12 and Metal Oxides with High Antimicrobial Activity

The lack of resistance of plastic objects to various pathogens and their increasing activity in our daily life have made researchers develop polymeric materials with biocidal properties. Hence, this paper describes the thermoplastic composites of Polyamide 12 mixed with 1-5 wt % of the nanoparticles of zinc, copper, and titanium oxides prepared by a twin-screw extrusion process and injection moulding. A satisfactory biocidal activity of polyamide 12 nanocomposites was obtained thanks to homogenously dispersed metal oxides in the polymer matrix and the wettability of the metal oxides by PA12. At 4 wt % of the metal oxides, the contact angles were the lowest and it resulted in obtaining the highest reduction rate of the Escherichia coli (87%), Candida albicans (53%), and Herpes simplex 1 (90%). The interactions of the nanocomposites with the fibroblasts show early apoptosis (11.85-27.79%), late apoptosis (0.81-5.04%), and necrosis (0.18-0.31%), which confirms the lack of toxicity of used metal oxides. Moreover, the used oxides affect slightly the thermal and rheological properties of PA12, which was determined by oscillatory rheology, thermogravimetric analysis, and differential scanning calorimetry.

Levels of leachable elements from long-term use of enFlow fluid warmer

Objective:

In the delivery of intravenous fluids, in-line warming devices frequently transfer heat using a metal heating plate, which if uncoated can risk elution. This bench study examined extractable elements detected following long-term use of the parylene-coated enFlow^® Disposable IV/Blood Warmer.

Methods:

We tested 16 clinically relevant challenge fluids typical of the surgical setting, including commercially available single donor blood and blood products as well as intravenous saline and electrolyte solutions. After 72 h of warming at 40°C (104°F) via the enFlow, analytical chemistry identified and quantified the most clinically significant extractable elements (arsenic, barium, cadmium, copper, and lead) to estimate chemical exposure. We also measured the extracted concentrations of these five elements following simulated use of the device with three solutions (Sterofundin ISO, Plasma-Lyte 148, and whole blood) that were pumped through the warmed device at two different flow rates (0.2 and 5.5 mL min⁻¹).

Results:

Across all scenarios of acute and long-term exposures for different populations, the enFlow demonstrated low toxicological risks as measured by the calculation of tolerable exposure for extracted arsenic, barium, cadmium, copper, and lead.

Conclusion:

The results suggest biological safety for the use of parylene-coated enFlow with a variety of intravenous solutions and in different therapeutic scenarios.

Polymeric Materials with Antibacterial Activity: A Review

Infections caused by bacteria are one of the main causes of mortality in hospitals all over the world. Bacteria can grow on many different surfaces and when this occurs, and bacteria colonize a surface, biofilms are formed. In this context, one of the main concerns is biofilm formation on medical devices such as urinary catheters, cardiac valves, pacemakers or prothesis. The development of bacteria also occurs on materials used for food packaging, wearable electronics or the textile industry. In all these applications polymeric materials are usually present. Research and development of polymer-based antibacterial materials is crucial to avoid the proliferation of bacteria. In this paper, we present a review about polymeric materials with antibacterial materials. The main strategies to produce materials with antibacterial properties are presented, for instance, the incorporation of inorganic particles, micro or nanostructuration of the surfaces and antifouling strategies are considered. The antibacterial mechanism exerted in each case is discussed. Methods of materials preparation are examined, presenting the main advantages or disadvantages of each one based on their potential uses. Finally, a review of the main characterization techniques and methods used to study polymer based antibacterial materials is carried out, including the use of single force cell spectroscopy, contact angle measurements and surface roughness to evaluate the role of the physicochemical properties and the micro or nanostructure in antibacterial behavior of the materials.

Recent advances in functionalized nanomaterials for the diagnosis and treatment of bacterial infections

The growing problem of resistant infections due to antibiotic misuse is a worldwide concern that poses a grave threat to healthcare systems. Thus, it is necessary to discover new strategies to combat infectious diseases. In this review, we provide a selective overview of recent advances in the use of nanocomposites as alternatives to antibiotics in antimicrobial treatments. Metals and metal oxide nanoparticles (NPs) have been associated with inorganic and organic supports to improve their antibacterial activity and stability as well as other properties. For successful antibiotic treatment, it is critical to achieve a high drug concentration at the infection site. In recent years, the development of stimuli-responsive systems has allowed the vectorization of antibiotics to the site of infection. These nanomaterials can be triggered by various mechanisms (such as changes in pH, light, magnetic fields, and the presence of bacterial enzymes); additionally, they can improve antibacterial efficacy and reduce side effects and microbial resistance. To this end, various types of modified polymers, lipids, and inorganic components (such as metals, silica, and graphene) have been developed. Applications of these nanocomposites in diverse fields ranging from food packaging, environment, and biomedical antimicrobial treatments to diagnosis and theranosis are discussed.

The Covalent Tethering of Poly(ethylene glycol) to Nylon 6 Surface via N,N'-Disuccinimidyl Carbonate Conjugation: A New Approach in the Fight against Pathogenic Bacteria

Different forms of unmodified and modified Poly(ethylene glycols) (PEGs) are widely used as antifouling and antibacterial agents for biomedical industries and Nylon 6 is one of the polymers used for biomedical textiles. Our recent study focused on an efficient approach to PEG immobilization on a reduced Nylon 6 surface via N,N'-disuccinimidyl carbonate (DSC) conjugation. The conversion of amide functional groups to secondary amines on the Nylon 6 polymer surface was achieved by the reducing agent borane-tetrahydrofuran (BH3-THF) complex, before binding the PEG. Various techniques, including water contact angle and free surface energy measurements, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy, were used to confirm the desired surface immobilization. Our findings indicated that PEG may be efficiently tethered to the Nylon 6 surface via DSC, having an enormous future potential for antifouling biomedical materials. The bacterial adhesion performances against S. aureus and P. aeruginosa were examined. In vitro cytocompatibility was successfully tested on pure, reduced, and PEG immobilized samples.

Preparation, structural characterization, thermal properties and antifungal activity of alginate-CuO bionanocomposite

In this study, the antifungal activity rate of alginate-CuO bionanocomposite was assessed against Aspergillus niger using colony forming units (CFU) and disc diffusion methods. Employing the Taguchi method, nine experiments were designed for the synthesis of alginate-CuO nanocomposite with the highest antifungal activity. The nanocomposite synthesized under the conditions of experiment 5 (4 mg/mL CuO nanoparticles and 1 mg/mL alginate biopolymer with stirring time of 90 min) showed the greatest inhibition rate on fungal growth (83.17%). In the optimum conditions for the synthesis of alginate-CuO nanocomposite with the highest antifungal activity the second level of CuO NPs (14.14%), alginate biopolymer (8.16%) and stirring time (5.63%) showed the best improvement performance on inhibiting the fungal growth. The results of ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) confirmed the formation of alginate-CuO nanocomposite. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicated that the thermal stability of alginate biopolymer and CuO nanoparticles were improved by the formation of the nanocomposite. Due to the favorable properties of alginate-CuO nanocomposite, its antifungal feature can be used in various biomedical fields.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

Antibiofilm Activity of Polyamide 11 Modified with Thermally Stable Polymeric Biocide Polyhexamethylene Guanidine 2-Naphtalenesulfonate

The choice of efficient antimicrobial additives for polyamide resins is very difficult because of their high processing temperatures of up to 300 °C. In this study, a new, thermally stable polymeric biocide, polyhexamethylene guanidine 2-naphtalenesulfonate (PHMG-NS), was synthesised. According to thermogravimetric analysis, PHMG-NS has a thermal degradation point of 357 °C, confirming its potential use in joint melt processing with polyamide resins. Polyamide 11 (PA-11) films containing 5, 7 and 10 wt% of PHMG-NS were prepared by compression molding and subsequently characterised by FTIR spectroscopy. The surface properties were evaluated both by contact angle, and contactless induction. The incorporation of 10 wt% of PHMG-NS into PA-11 films was found to increase the positive surface charge density by almost two orders of magnitude. PA-11/PHMG-NS composites were found to have a thermal decomposition point at about 400 °C. Mechanical testing showed no change of the tensile strength of polyamide films containing PHMG-NS up to 7 wt%. Antibiofilm activity against the opportunistic bacteria Staphylococcus aureus and Escherichia coli was demonstrated for films containing 7 or 10 wt% of PHMG-NS, through a local biocide effect possibly based on an influence on the bacterial eDNA. The biocide hardly leached from the PA-11 matrix into water, at a rate of less than 1% from its total content for 21 days.

Comparative activity of silver-based antimicrobial composites for urinary catheters

Biomedical polymers are an integral component in a wide range of medical devices because of their many desirable properties. However, extensive use of polymer materials in medical devices has been associated with an increasing incidence of patient infections. Efforts to address this issue have included incorporating antimicrobial additives to develop novel antimicrobial polymeric materials. Silver, with its high toxicity towards bacteria, oligodynamic effect and good thermal stability, has been employed as an additive for polymeric medical devices. In the present study, commercially available elemental (Biogate) and ionic (Ultrafresh 16) silver additives were incorporated into a Polyamide 11 (PA 11) matrix using a compression press. These polymer composites were evaluated for their antimicrobial and ion-release properties. Elemental silver composites were shown to retain their antimicrobial properties for extended periods and actively released silver ions for 84 days; whereas ionic silver composites lost their ion-release activity and, therefore, their antibacterial activity after 56 days. Bacterial log reduction units of 3.87 for ionic silver and 2.41 for elemental silver were identified within 24 h, when tested in accordance with the ISO 22196 test standard; this indicates that ionic silver is more efficient for short-term applications than elemental silver.