Client Citation Analysis
Static water contact angle was measured by static sessile drop on three samples — the uncoated control catheter and the two bare coating architectures, PEI+GO and PEI/GO. Table 1 contains no peptide-loaded sample, so no contact angle exists for any of the four AMP-loaded coatings the paper's antibacterial results concern.
Section 2.5, Characterization Techniques: "Wettability of coated UC samples was assessed via static sessile drop (10 µL, n = 5) using a Droplet Lab system (Brampton, ON, Canada)." That is the paper's only mention of the instrument. No product or model name is given, no software version, and no drop-fitting method (polynomial or Young–Laplace) is stated.
The contact-angle data were used to compare the control, PEI+GO and PEI/GO surfaces and to show that the coating processes increased hydrophilicity together with surface roughness. The paper's own summary of this result is one sentence: "both samples exhibited increased surface roughness and hydrophilicity as a result of the coating processes (Table 1)." The data are not used again anywhere in the Results, Discussion or Conclusions. These surface-property results sat alongside FTIR, Raman, microscopy, molecular dynamics, and antibacterial assays in the architecture-dependent comparison.
Wettability was assessed by static sessile drop using 10 µL droplets with n = 5. The paper states no measurement temperature, no humidity, no equilibration or image-capture timing, and does not say whether the ± 1.0° in Table 1 is a standard deviation or a standard error. No advancing/receding angles or hysteresis were measured, and no drop-fitting model is named.
It measured static water contact angle on three bare surfaces — uncoated control, PEI+GO and PEI/GO — producing Figure 3B and one column of Table 1, 1 of the paper's 5 figures. It was not the primary measurement instrument; the paper's principal outcomes were produced by NAMD 2.13 molecular dynamics simulations and agar diffusion assays. No contact angle was measured on any peptide-loaded coating, and the instrument did not measure peptide release.
Static water contact angles were determined for control, PEI+GO and PEI/GO catheter samples, yielding values of 98.3 ± 1.0°, 76.4 ± 1.0° and 75.5 ± 1.0° respectively — all three measured on bare coatings before antimicrobial peptide loading. The two coated architectures differ by 0.9°, inside the reported uncertainty; the coating step is what the measurement resolves, not the choice between architectures.
Zeta potential, surface roughness, FTIR, Raman spectroscopy, optical microscopy, VP-SEM and FEG-SEM characterised the coatings. The paper's two principal outputs are not supporting measurements: 50 ns NAMD 2.13 molecular dynamics simulations of the GO–AMP and PEI–AMP complexes (Figure 5A,B) and agar diffusion antibacterial assays against E. coli and E. faecalis (Figure 5C) together produce the mechanistic conclusion the paper's title announces.
Droplet Lab system (Brampton, ON, Canada)
Zetasizer Advance (Malvern; Worcestershire, UK)
PCE-RT 2300 tester (PCE Instruments; Southampton, UK)
FTIR: 4600, Jasco (Tokyo, Japan)
Dual Hound, Unchained Labs (Pleasanton, CA, USA)
Eclipse E200, Nikon (Tokyo, Japan)
SU-3500, Hitachi (Tokyo, Japan)
JSM-7800, Jeol (Tokyo, Japan)
Autoflex Speed, Bruker (Billerica, MA, USA)
NAMD 2.13 — 50 ns production runs at 300 K, 1 fs step, 12 Å cutoff, PME, TIP3P solvation; CHARMM36 / CGenFF / SwissParam force fields
Orca (B3LYP/DEF2-TZVPP), GO sheet built in VMD and Chemcraft
Harrick Plasma (Ithaca, NY, USA) — 15 min, < 0.2 mmHg, 18 W
Liberty Blue microwave-assisted synthesizer, CEM (Kamp-Lintfort, Germany)
OriginLab v.2022b — ANOVA with Tukey post hoc
The Droplet Lab instrument appears once in the characterization workflow, in Section 2.5: "Wettability of coated UC samples was assessed via static sessile drop (10 µL, n = 5) using a Droplet Lab system (Brampton, ON, Canada)." The paper names no model and no software version. The resulting water contact angles are reported for the control, PEI+GO and PEI/GO samples — the three bare surfaces, measured before either antimicrobial peptide was loaded.
In the study's comparison of coating architectures, the wettability results showed that both GO-based coatings shifted the catheter surface toward higher hydrophilicity — from 98.3 ± 1.0° to 76.4 ± 1.0° and 75.5 ± 1.0°. What they did not do was separate the two architectures from each other: those two values differ by 0.9°, inside the reported uncertainty, for coatings that differ by 570 nm in thickness and by the paper's widest antibacterial margin. The layered and embedded structures were separated by morphology, thickness, simulated interaction energetics and antibacterial response, and the paper's explanation of peptide release invokes none of them through wettability.
The control catheter showed a water contact angle of 98.3 ± 1.0°, while PEI+GO and PEI/GO measured 76.4 ± 1.0° and 75.5 ± 1.0° respectively. The authors' own summary: "both samples exhibited increased surface roughness and hydrophilicity as a result of the coating processes."
Microscopy described PEI+GO as porous and cracked, whereas PEI/GO appeared smoother. Cross-sectional SEM gave an average thickness of 320 ± 33 nm for PEI+GO and 890 ± 115 nm for PEI/GO — the paper notes the embedded coating is "nearly three times thicker".
Potential-energy profiles stabilized from about 8 ns onward, and the most negative energies corresponded to the PEI complexes with E14LKK and fLFB. The paper's inference: "these complexes remain more stable over time, and therefore, the peptides will be released less into the PEI matrix than GO." These are NAMD 2.13 simulation outputs over 50 ns, not measurements.
The GO–fLFB complex maintained the highest potential energy and showed the greatest RMSD fluctuations among the four modeled complexes — all four had mean RMSD above 3 Å. The authors conclude: "fLFB will be released more readily in this matrix." Both quantities are simulation outputs; the paper notes the simulations modelled the GO–AMP and PEI–AMP complexes individually, "rather than the full coating architectures".
Against both E. coli and E. faecalis, the PEI+GO–fLFB coating produced the largest inhibition zones (agar diffusion, Mueller–Hinton, 0.5 McFarland, 35 °C for 24 h, n = 3). The paper attributes this to "(i) the weaker interaction between GO and fLFB, which facilitates peptide release... and (ii) the coating architecture", and records that PEI/GO–E14LKK was the weakest of all samples tested. The authors caveat the method itself: "antimicrobial peptides (AMPs) generally exhibit limited diffusivity in agar-based systems."
The study's conclusion is that coating configuration and GO–AMP interaction strength together dictated antimicrobial performance on urinary catheters; in the tested set, PEI+GO outperformed PEI/GO. The paper's own wording: "These findings underscore the importance of both coating architecture and AMPs–GO interaction strength in dictating antimicrobial performance."
PEI+GO measured 76.4 ± 1.0° and PEI/GO 75.5 ± 1.0° — a 0.9° gap inside the stated uncertainty, with no statistical test reported between them. Over the same two coatings, cross-sectional SEM found 320 ± 33 nm versus 890 ± 115 nm, Raman found I(D)/I(G) of 1.83 versus 2.09, and the agar assays separated PEI+GO–fLFB (largest inhibition zones) from PEI/GO–E14LKK (weakest of every sample tested). Wettability resolves the coating step; it does not resolve the architecture, and the paper never claims it does — its explanation of the difference is "the weaker interaction between GO and fLFB, which facilitates peptide release" and "screening of GO's functional groups" in the embedded structure.
The paper contains no UV-vis, HPLC or any other time-resolved measurement of peptide release. Its abstract describes the agar assays as "a comparative indicator of peptide release from surface-bound coatings", and the release mechanism is reconstructed from simulated potential energy and RMSD together with inhibition-zone size. The authors are explicit that this is mechanistic groundwork: "Rather than targeting immediate clinical translation, this work provides mechanistic insight into how GO–polymer architecture modulates antimicrobial peptide availability."
Figure 1. This schematic lays out the plasma pretreatment (15 min, 18 W), the PEI+GO and PEI/GO coating routes, and the thermal curing (120 °C, 1 h) and AMP loading steps used in the overall study design. The authors flag it as non-literal: "The scheme is illustrative; chemical changes are idealized," and "All assays used cylindrical catheter sections (0.5 cm); the rectangular shape in Figure 1 is a schematic reference only."
Figure 3B and Table 1 present the wettability and roughness comparison for the control, PEI+GO and PEI/GO samples. The contact angles come from the Droplet Lab sessile-drop system; the R(RMS) roughness values in the same panel (0.16, 0.25 and 0.28 ± 0.03 µm) come from a PCE-RT 2300 tester measured per ISO 4287. This is the only panel in the paper containing Droplet Lab data.
Cross-sectional SEM in Figure 4 shows the layered PEI+GO structure (320 ± 33 nm, folded and corrugated) and the embedded PEI/GO structure (890 ± 115 nm, smoother and more homogeneous). This is where the two architectures visibly diverge — a 570 nm thickness difference that the contact-angle measurement in Figure 3B does not register, since the two coatings' angles differ by 0.9°.
Figure 5 combines molecular dynamics outputs (5A: the four complexes; 5B(1): 50 ns potential-energy profiles; 5B(2): RMSD) with antibacterial data (5C: inhibition zones vs E. coli and E. faecalis, mean ± SD, n = 3, ANOVA with Tukey) to interpret why the PEI+GO–fLFB system showed the strongest activity. The simulations modelled GO–AMP and PEI–AMP complexes individually rather than the assembled coatings; the authors list extending them "to encompass the complete coating architectures" as future work.
For this urinary-catheter coating study, the Droplet Lab contact-angle data establish the surface-state shift that follows GO-based coating deposition: the uncoated silicone control sat at 98.3 ± 1.0°, both coated surfaces at roughly 76°. Wettability is the paper's direct readout for whether a coating is present and has changed the interface. It is not a readout for which architecture was used — PEI+GO and PEI/GO returned 76.4 ± 1.0° and 75.5 ± 1.0°, and the paper draws no distinction between them on this basis.
Those wettability results matter because they confirm, cheaply and quickly, that the coating deposited and altered the surface — the check that has to pass before any of the downstream work means anything. The explanation of peptide availability itself rests elsewhere: the authors attribute the PEI+GO–fLFB result to "the weaker interaction between GO and fLFB, which facilitates peptide release", supported by simulated potential-energy and RMSD profiles, and to the embedded architecture "screening of GO's functional groups". Contact angle is not part of that causal chain, and the paper never places it there.
What this study does not establish, in the authors' own terms: it is not a clinical result — "this study does not aim to deliver a clinically validated catheter coating". Peptide release was never measured directly; agar inhibition zones stand in for it, and the authors note that "antimicrobial peptides (AMPs) generally exhibit limited diffusivity in agar-based systems". The simulations modelled isolated GO–AMP and PEI–AMP complexes, "rather than the full coating architectures". Coating durability was probed only by Raman after 7 days in PBS at 37 °C, with no mechanical or flow challenge. The authors' own next steps are "complementary antibiofilm assays" and expanded simulations covering the complete architectures.
In this paper, sessile-drop contact angle clearly separated the uncoated catheter from both GO-coated surfaces, making it a straightforward readout of coating-induced surface change.
PEI+GO and PEI/GO had very similar contact angles, yet they differed strongly in morphology and thickness, which became important in the later release and antibacterial interpretation.
The authors did not rely on wettability by itself; they interpreted it alongside roughness, FTIR, Raman, and SEM to characterize the coated surfaces.
The study ran three layers of evidence — surface characterization, peptide-interaction simulations and antibacterial assays — but they do different jobs. Characterization establishes that the two architectures were built as intended; the simulations and assays explain the performance difference between them. Use surface measurements to verify the sample is what you think it is, then expect the mechanism to come from elsewhere.
Every contact angle in this paper was measured on a bare coating. All four functional systems — PEI+GO–E14LKK, PEI+GO–fLFB, PEI/GO–E14LKK, PEI/GO–fLFB — carry an adsorbed peptide layer applied at 0.5 mg/mL for 1 h, and none was measured. Peptide adsorption is exactly the kind of change that shifts wettability, so if you are correlating surface state with release behaviour, measure after loading as well as before. It is a cheap addition to a protocol and it closes the gap between what was characterised and what was tested.