## Materials and Methods  
The \"Ticona GUR 2122\" UHMWPE powder (Celanese Corporation, Irving, TX, USA; Figure 1a) was used for sample fabrication. Natural wollastonite fibers were also added as a filler (diameter of 10 \(\upmu\)m, aspect ratio of 5:1; produced by GEOKOM CJSC, Kaluga region, Russia; Figure 1b). The following silane-containing coupling agents were used:  
* \"KH-550\" (NH\({}_{2}\)CH\({}_{2}\)CH\({}_{2}\)CH\({}_{2}\)Si(OC\({}_{2}\)H\({}_{5}\))\({}_{3}\), DFRPT Co., Ltd., Guangdong, China). * \"Penta-1006\" (polyorganosiloxane, (CH\({}_{3}\))\({}_{3}\)SiO((CH\({}_{3}\))2 SiO)\({}_{n}\)-Si(CH\({}_{3}\))\({}_{3}\)), PENTA-91 Company LLC, Moscow, Russia). * \"OTS\" (Trimethoxy(octadecyl)silane, CH\({}_{3}\)(CH\({}_{2}\))17 Si(OCH\({}_{3}\))\({}_{3}\)), Nanjing Chemical Reagent Co., Ltd., Nanjing, China). Wollastonite fibers were treated with a water-ethanol (pH = 4.5-5.5) solution of the \"KH-550\" by continuous stirring at room temperature for 30 min. The \"KH-550\" weight fraction was 1% Treatment with the \"Penta-1006\" and \"OTS\" silane-containing coupling agents was according to the same procedure as the \"KH-550\" one. UHMWPE and wollastonite fibers were mixed and prepared much like the techniques described in [42]. Figure 1: SEM-micrographs of the powder: (**a**) GUR 2122 and (**b**) wollastonite. For uniaxial static tensile testing, \"dog-bone\" shaped specimens, with a gauge-dimension of \(3.18\times 9.53\times 3.2\) mm\({}^{3}\), were cut from the samples using a milling machine. The tests were carried out using an \"Instron 5582\" (Instron, Norwood, MA, USA) universal electro-mechanical testing machine at room temperature. The mechanical properties were examined according to ASTM D638 (Standard Test Method For Tensile Properties Of Plastics). The tensile tests of \"dog-bone\" specimens (Type V) were carried out using an \"INSTRON 5582\" electro-mechanical testing machine. Four samples were studied with the following dimensions: thickness (T) of \(3.2\times 0.4\) mm; narrow section width (W) of \(3.18\times 0.5\) mm; narrow section length (L) of \(9.53\times 0.5\) mm; width overall (WO) of \(9.53\times 3.18\) mm; length overall (LO) of \(63.5\times 0.4\) mm; gauge length (G) of \(7.62\times 0.25\) mm; distance between grips (D) of \(25.4\times 5\) mm; and fillet radius (R) of \(12.7\times 1\) mm. The tests were conducted with the displacement control at crosshead speed of \(10\) mm/min. The load capacity of the testing machine was \(100\) kN. Strains were measured by the strain gauge of the testing machine and then corrected by the real length of each failed specimen (equal to its elongation at break). Charpy impact strength tests were carried out using a \"KM-5\" pendulum hammer (ZIP LLC, Ivanovo, Russia) in accordance with ASTM D 6110 (ISO 179). The size of the specimens was \(50\times 6\times 4\) mm\({}^{3}\). They possessed a V-shaped notch with a depth of \(2\) mm and a radius of curvature of \(0.25\) mm. At least four specimens of each type were tested. The arithmetic average of the all obtained results was taken as the impact toughness value. IR spectra were registered with the use of a \"NICOLET 5700\" spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). Wear resistance was evaluated using a \"2070 SMT-1\" friction testing machine (Tochpribor Production Association, Ivanovo, Russia) according to the \"block-on-ring\" scheme. Load (\(P\)) was 60 and 140 N; contact pressure was 9.7 and 32.4 MPa; and sliding speed (\(V\)) was 0.3 and 0.5 m-s\({}^{-1}\). Two combinations of the \(P\)-\(V\) conditions were applied. The \"moderate\" mode was at \(P=60\) N and \(V=0.3\) m-s\({}^{-1}\), as well as the \"severe\" one was at \(P=140\) N and \(V=0.5\) m-s\({}^{-1}\). A counterpart was made of the outer ring of the GCr15 bearing steel (HRC 60). It had a disk shape with a diameter of \(35\) mm and a width of \(11\) mm. The counterpart surface roughness was \(0.20\)-\(0.25\) mm.