*2.1. Synthesis of Silver Nanoparticles and Coating of Polyetheretherketone (PEEK) Films*

Polyetheretherketone (PEEK) films were coated with 1 and 2 layers of silver nanoparticles (AgNP), reducing ammoniacal silver complexes with glucose in aqueous medium at room temperature. AgNO3 (99.9%) was purchased from Sigma-Aldrich (Saint Louis, MO, USA), NaOH (99%), Ammonia (25%) and D-Glucose (99%) was obtained from Merck (Darmstadt, Germany). The PEEK film used was Sigma-Aldrich with a thickness of 0.006 mm. The PEEK film was washed with sulfochromic solution (concentrated sulfuric acid with potassium dichromate 90%/10%), for 5 min to remove contaminants in the polymer and to facilitate the coating with silver nanoparticles. For the synthesis of silver nanoparticles, Tollens reagent was used [21,22]. Stoichiometric amounts of silver nitrate in different concentrations were available in a glass reactor previously washed with sulfochromic solution. Subsequently a NaOH dissolution (0.5 mol/L) was added to the above solutions producing silver monoxide, as shown in Equation (1) [23,24].

$$2\text{AgNO}\_3\text{ (aq)} + 2\text{NaOH}\_{\text{(aq)}} \rightarrow \text{Ag}\_2\text{O}\_{(s)} + 2\text{NaNO}\_{3(aq)} + \text{H}\_2\text{O}\_{(aq)}\tag{1}$$

The precipitated silver monoxide was completely dissolved with ammonia (2 mol/L), producing the Tollens reagent (Equation (2)) [25].

$$\mathrm{Ag\_2O\_{(s)}} + 4\mathrm{NH\_{3(aq)}} + 2\mathrm{NaNO\_3} + \mathrm{H\_2O\_{(aq)}} \to 2\mathrm{Ag(NH\_3)\_2NO\_{3(aq)}} + 2\mathrm{NaOH\_{(aq)}}\tag{2}$$

The silver nanoparticles (Ag0) were obtained by chemical reduction of the silver diamine complex with D-glucose (1 mol/L) as a reducing agent, forming gluconic acid [26]. Equation (3) summarizes the previous reaction. At this stage, the PEEK films were immersed in the solution containing the AgNPs in three different concentrations (0.04, 0.08 and 0.12 mol/L). The immersion was done for 5 min at room temperature and under agitation at 250 rpm; this favored the random sequential adsorption of the silver particles on the polymer surface, thus obtaining the PEEK/Ag0.04, PEEK/Ag0.08 and PEEK/Ag0.12 systems with both single and two layers [27,28]. It must be clarified that the two-layer systems were obtained by repeating the aforementioned procedure for a single-layer film.

$$2[\text{Ag(NH}\_3\text{)}\_2]^+\_{\text{(aq)}} + \text{RCHO}\_{\text{(aq)}} + 2\text{OH}^- \rightarrow 2\text{Ag}\_{(s)} + \text{RCOOH}\_{\text{(aq)}} + 4\text{NH}\_{3(aq)} + \text{H}\_2\text{O}\_{(aq)}\tag{3}$$

The PEEK films coated with one and two-layer silver nanoparticles were dried at 100 ◦C for 2 h to remove remaining water solvent. In this way, the synthesis route using the Tollens reagent and reducing monosaccharides such as glucose contributes to the progress in the deposition of metal nanostructures in polymeric films by chemical methods.

#### *2.2. Characterization of PEEK Films Coated with AgNPs*

X-ray diffraction (XRD) measurements of all the coated films were made on a PANalytical X'Pert PRO MPD diffractometer (Bogotá, Colombia), equipped with an Ultra-Fast X´celerator detector and a Bragg–Brentano configuration, using the Cu Kα radiation (λ = 1.5418 Å) between 20◦ and 90◦. The measurements were developed with an acceleration voltage of 40 kV and a current of 20 mA. The average size of the crystalline domains was determined with the Debye–Scherrer equation using the highest intensity peak in the diffraction pattern of each sample [29]. The infrared (IR) spectra were obtained in the Thermo Scientific Nicolet iS50 spectrometer, by the technique of total attenuated reflection (ATR). The IR spectra were processed with a resolution of 4 cm−<sup>1</sup> in the average IR (4000–400 cm<sup>−</sup>1). The samples were placed directly on the cell and pressed to carry out the analysis. The spectra were collected and manipulated with the OmnicR software (version 6.1).

Transmission electron microscopy (TEM) images were obtained from a Tecnai F20 Super Twin TMP (Medellín, Colombia) of a Field Electron and Ion (FEI) microscope, equipped with a system Ion Milling PIPS II Model 695 GATAN (Medellín, Colombia) and Ultramicrotome EM UC7 LEICA (Medellín, Colombia). The thermal analysis was developed in a Seteram Thermobalance equipment. For the analysis, 5 mg of each sample was weighed and placed in an alumina crucible. The sample was subjected to a heating rate from 25 to 700 ◦C, under an atmosphere of N2 with a flow of 20 mL/min.

The morphology of the AgNPs on the PEEK films were analyzed by scanning electron microscopy (SEM) without coating in a JSM-6490 JEOL microscope (Tokyo, Japan), with an acceleration voltage of 15 KV, using secondary electron scattering under high vacuum conditions. Energy-dispersive X-ray spectroscopy (EDS) microanalysis was performed on an Inca Energy 250 EDS System LK-IE250 from Oxford, England, UK, equipped with a silicon detector for light elements and resolution of 138 eV. The surface analysis of PEEK films coated with silver was performed in an atomic force microscope (AFM) Asylum Research, model MFP-3D-BIO. The AFM images were analyzed with the Gwyddion software (version 2.49).

#### *2.3. Antibacterial Activity*

The antibacterial activity of the films of PEEK with a coating of AgNPs was studied by the disc diffusion method, for which 100 μL of bacterial suspensions in nutrient broth (this medium contains, in g/L: meat extract, 1.0; yeast extract, 2.0; peptone, 5.0 and sodium chloride, 5.0) of *Escherichia coli*, *Serratia marcescens* and *Bacillus licheniformis* with optical density of 0.01 (OD 600) were spread homogeneously on the nutrient agar plate (meat extract B, 3.0 g/L; peptone, 5.0 g/L and agar, 15.0 g/L) [30]. PEEK discs of 6 mm diameter and 0.006 mm thickness with a coating of AgNPs in different concentrations were used. The samples were placed on the agar plate and were kept in the

incubator at 37 ◦C for 24 h [16]. Each antibacterial test was evaluated in triplicate. The ImageJ software was employed to measure the diameter of the zone of inhibition of the AgNPs deposited on the PEEK under bacterial activity.

#### **3. Results and Discussion**
