Hr 2 rheometer

The macro-indentation experiments were performed on hydrogels (1.20 mL) poured into a 12-well plate after six days of aging at 37 °C in a humid atmosphere. The experiment was done in duplicate. The indentation test was performed with a duralumin cylinder connected at one end to the stress-controlled rheometer (HR-2 rheometer from TA Instruments) and presented a circular flat surface on the other end (diameter 10 mm). The speed of descent was set to 0.1 mm/s until a 200 µm gap (≈ 92% of strain) was reached. The normal force sensor of the rheometer was used as a force gauge to determine the stress-strain relation during the sample indentation. The maximum normal stress (σmax) and compressive strain (εmax) could be read when the hydrogel cracked under compression, leading to a fall in the σ = f(ε) curve due to the rupture (Figure S12). In the first moments of the deformation (under 5% of deformation), the linear low-strain regime provided a way to define an apparent elastic modulus (E * = δσ/δε) and, after calculation, the Young’s modulus E and then the storage modulus by calculation from E. Finally, the mesh size could be calculated (see Supplementary Materials Figure S12, Equations (1)–(3)).

Dynamic shear moduli were measured on a TA Instruments HR-2 rheometer with an 8 mm parallel plate geometry. Hydrogel macromer solution (same formulation as in section “Hydrogel formation”) was placed on a quartz plate and exposed to 10 mW/cm², 365 nm light in situ. A time sweep recorded the increase in the storage and loss moduli (G′ and G″, respectively) during the gelation process at 1 Hz and 1% strain. After gelation, a frequency sweep was performed from 0.01 to 100 Hz (Fig. S2) to confirm these measurements were in the linear viscoelastic range; all subsequent modulus measurements were then acquired at 1 Hz and 1% strain.

The viscoelastic response of biofilms (~1 ml) was determined under oscillatory shear strain (Discovery HR-2 rheometer, TA instruments) using a circular flat plate tool (40 mm diameter). Temperature (±0.1°C) was controlled with a Peltier element assisted by an external water thermostat. Shear measurements were performed at a 1 mm gap between the peltier element and the plate tool. To avoid any solvent evaporation during the experiment, both the sample and the plate tool were covered with a Solvent Trap (TA instruments). A sinusoidal strain γ of amplitude γ₀ was applied to the biofilm at a frequency of ω: γ(t) = γ₀sin(ωt). The shear stress was monitored as σ(t) = G*γ(t), where G* is the shear viscoelastic modulus G* = G' + iG'', where G' is the storage modulus and G'' is the loss modulus. The shear viscosity was calculated as η = G''/ω.

The rheological properties were carried out on a HR‐2 rheometer (TA Instruments) equipped with a temperature controller. The test was performed in an 8 mm parallel‐plate geometry using 100 µL DNA/DOPA hydrogel. Temperature rheological test was carried out from 25 to 75 °C at a rate of 2 °C min⁻¹ at fixed frequency (1 Hz) and strain (1%). Time scanning was performed with a fixed strain (1%) and a fixed frequency (1 Hz) at 25 °C for 3 min. Strain scanning was conducted from 0.1% to 1000% with a fixed frequency (1 Hz) at 25 °C.

P-BMB was synthesized and characterized as previously described (Shah et al., 2011 (link)). The higher polarity of biodegradable oils compared to conventional mineral oils increases their affinity for the surface and may also have implications for the transport properties of the IL. Two representative biodegradable oils were selected for the tests. Oil soluble polyalkylene glycol (OPAG), UCON OSP46 (Dow Chemicals inherently biodegradable; more than 35 % during 28 days), and a monoester (ME), Estisol 240 (Estichem, readily biodegradable; more than 60% during 28 days), were used in the lubrication tests. The exact chemical structure of OPAG is undisclosed which underlines some of the challenges of performing relevant tribological research from a chemical perspective. Estisol 240 is a C8-C6 monoester, hexyl-octanoate with a structure shown in Figure 1 and has a non-polarity index of 32. To ensure homogeneous blends, the blends were ultrasonicated for at least 60 min at 50°C. Table S1 shows viscosities of IL, oils and the blends of oils with IL. Viscosities were measured with a HR-2 rheometer, TA Instruments.