T ptd 200

The tribological performance of lubricants is another crucial factor affecting the oil properties. Five milliliters of the obtained suspensions (from Section “Oil-based suspensions”) were dispersed and degassed using an ultrasonic homogenizer UP400S (Hielscher, Germany) for 15 min in a cooling bath. The tribological properties of the suspensions and base oil were analyzed using an MCR tribometer (T-PTD 200) with a ball-on-three-pin setup (Anton Paar, Austria)^{5 (link)}. A new set of balls and pins was used for each sample; 100Cr6 steel pins and balls were purchased from Anton Paar. The engine can produce the most emissions during the first few minutes after starting due to the required rich air–fuel mixture in cold engines and the inefficient catalytic converter under cold conditions. Due to the changing weather throughout the year, the measurements were performed at − 10, 0, 25, 75, and 100 °C. The measurements for each suspension were repeated three times.

In order to mimic the in vivo composition of viscosupplemented SF for the assay, the considered commercial hydrogel products were combined in equal proportion to freshly harvested equine SF. The lubrication capacities of the obtained samples were determined in rotational tribology using an MCR 302 rotational rheometer (Anton Paar, Graz, Austria) equipped with a T-PTD 200 ball-on-three-plates tribology cell. The instrument was equipped with a SoLi glass ball of 12.7 mm in diameter. The tribology cell was equipped with three plates made from the load-bearing surface of bovine articular cartilage, crafted to replace the original steel or polydimethylsiloxane (PDMS) plates of the manufacturer. All measurements were performed on volumes of 700 µL for the ex vivo samples and for the control groups (i.e., undiluted fresh equine SF). Measurements were performed at 37 °C using a normal force of 3 N, resulting in a maximum contact pressure of 290 kPa. The friction factor/coefficient μ, representing the interaction between both sliding surfaces, was measured at 0.1, 1, and 10 mm·s⁻¹ sliding velocities. The entire assay was eventually repeated using PDMS plates instead of the bovine articular cartilage plates, using undiluted commercial products.

Tribology measures were performed using a rotational rheometer (Modular Compact Rheometer MCR302, Anton Paar GmbH, Graz, Austria) equipped with the tribological measuring cell T-PTD 200.
To best simulate in vivo conditions, a biological substrate (pig femur) was used.
The formulation under test (0.5 g) was loaded on the cartilage placed on a steel disc and a probe, containing a cylinder of bone plus cartilage, was lowered to contact the sample, exerting a force equal to 1 Newton. To minimize sample evaporation, measures were effected at 20 °C. Thermosetting was assured by a Peltier heating plane.
The lubrication properties of the optimized HA + PC formulation was compared with those of the optimized HA formulation. Physiologic solution was also subjected to tribology measures as control.