Client Citation Analysis
Primary surface measurement reported
Static water contact angle was measured by static sessile drop on three samples — the uncoated control catheter and the two coating architectures as listed in Table 1, PEI+GO and PEI/GO. Table 1 contains no peptide-loaded sample, so the paper reports no contact angle for any of the four AMP-loaded coatings the paper's antibacterial results concern.
How the paper credits the instrument
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)." This is the paper's only mention of the instrument, which it identifies by manufacturer and location.
How the contact-angle data were used in the study
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 rest of the Discussion and the Conclusions focus on morphology, thickness, simulations and antibacterial results. These surface-property results sat alongside FTIR, Raman, microscopy, molecular dynamics, and antibacterial assays in the architecture-dependent comparison.
Replication / reliability statement
Wettability was assessed by static sessile drop using 10 µL droplets with n = 5, and Table 1 reports each angle as ± 1.0°. The methods section does not describe further measurement conditions, and the study reports static angles only.
What the Droplet Lab instrument did and did not do
It measured static water contact angle on the three samples in Table 1 (uncoated control, PEI+GO and PEI/GO), producing the contact angle values in Figure 3B and one column of Table 1. The roughness values in the same panel came from a separate PCE-RT 2300 tester. 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 is reported for any peptide-loaded coating, and the instrument did not measure peptide release.
Primary surface / interfacial measurement
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 — none of the three is a peptide-loaded sample. 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.
Supporting measurements
Zeta potential (of the GO, PEI and PEI/GO solutions), surface roughness, FTIR, Raman spectroscopy, optical microscopy, VP-SEM and FEG-SEM (for GO sheet dimensions) characterised the coating materials and 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.
Wettability / water contact angle
Droplet Lab system (Brampton, ON, Canada)
Zeta potential
Zetasizer Advance (Malvern; Worcestershire, UK)
Surface roughness
PCE-RT 2300 tester (PCE Instruments; Southampton, UK)
Raman spectroscopy
Dual Hound, Unchained Labs (Pleasanton, CA, USA)
Optical microscopy
Eclipse E200, Nikon (Tokyo, Japan)
VP-SEM
SU-3500, Hitachi (Tokyo, Japan)
FEG-SEM
JSM-7800, Jeol (Tokyo, Japan)
MALDI-ToF MS
Autoflex Speed, Bruker (Billerica, MA, USA)
Molecular dynamics engine
NAMD 2.13 — 50 ns production runs at 300 K, 1 fs step, 12 Å cutoff, PME, TIP3P solvation; CHARMM36 / CGenFF / SwissParam force fields
DFT geometry optimisation
Orca (B3LYP/DEF2-TZVPP), GO sheet built in VMD and Chemcraft
Plasma surface activation
Harrick Plasma (Ithaca, NY, USA) — 15 min, < 0.2 mmHg, 18 W
Peptide synthesis
Liberty Blue microwave-assisted synthesizer, CEM (Kamp-Lintfort, Germany)
Statistics
OriginLab v.2022b — ANOVA with Tukey post hoc
FTIR
4600, Jasco (Tokyo, Japan)
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 — none of them a peptide-loaded sample.
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. The layered and embedded structures were separated by morphology, thickness, simulated interaction energetics and antibacterial response, and the paper's explanation of peptide release does not invoke wettability.
If you check how a coating shifts water contact angle on catheter surfaces, we can show you the same sessile drop workflow on your samples.
Coating lowered water contact angle
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."
Architecture changed surface morphology and thickness
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".
PEI–peptide complexes were more stable in simulation
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.
GO–fLFB showed the highest mobility
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".
Layered PEI+GO–fLFB produced the strongest antibacterial response
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."
Architecture and interaction strength were interpreted together
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."
Contact angle did not distinguish the two architectures
PEI+GO measured 76.4 ± 1.0° and PEI/GO 75.5 ± 1.0° — a 0.9° gap inside the stated uncertainty. 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 does not use it to — 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.
Release was assessed through antibacterial activity and simulation
The study assesses peptide release indirectly rather than with a time-resolved release measurement. Its abstract describes the agar assays as "a comparative indicator of peptide release from surface-bound coatings", and the release mechanism is interpreted 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 — coating process schematic
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."
What it shows
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.
What it shows
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°.
What it shows
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 one of several readouts in the paper, alongside roughness, FTIR, Raman and microscopy, showing that the coating processes 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, together with roughness, FTIR, Raman and microscopy, they show that the coating processes altered the surface. 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.
The scope of this study, in the authors' own terms: it is not a clinical result — "the present study does not aim to deliver a clinically validated catheter coating". The authors use agar inhibition zones as a comparative indicator of peptide release and 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 stability was assessed by Raman after 7 days in PBS at 37 °C. The authors' own next steps are "complementary antibiofilm assays" and expanded simulations covering the complete architectures.
Use wettability as a coating check
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.
Expect morphology to matter beyond angle alone
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.
Pair contact angle with structural measurements
The authors did not rely on wettability by itself; they interpreted it alongside roughness, FTIR, Raman, and SEM to characterize the coated surfaces.
Connect surface data to functional outputs
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.
Measure the surface in the state you are testing
Every contact angle reported in this paper is for the control or an unloaded 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 has a reported contact angle. Peptide adsorption can change wettability, so if you are correlating surface state with release behaviour, consider measuring after loading as well as before.
It measured static water contact angle by sessile drop (10 µL, n = 5) on three samples: the uncoated catheter control and the PEI+GO and PEI/GO coatings. The paper identifies the instrument as "a Droplet Lab system" and reports the values in Table 1 and Figure 3B; no contact angle is reported for the peptide-loaded coatings.
The uncoated control measured 98.3 ± 1.0°, PEI+GO 76.4 ± 1.0° and PEI/GO 75.5 ± 1.0°. The authors report that both coating processes increased hydrophilicity and surface roughness, with roughness measured separately on a PCE-RT 2300 tester.
The paper does not use it that way: the two coated surfaces gave similar angles, and the authors explain the antibacterial differences through coating morphology and thickness, molecular dynamics simulations and agar diffusion assays. Advancing and receding angles, surface energy and contact angle after peptide loading were outside the scope of this study.
