A mechanical refiner for refining lignocellulosic material having opposing plates comprising a rotor refiner plate and a stator refiner plate, the stator refiner plate comprising: a stator refining surface affixed to a substrate; multiple bars (20, 120) and grooves situated on the stator refining surface, the bars (20, 120) each comprising a leading sidewall (28, 128) and a trailing sidewall (30, 130) that is opposite of the leading sidewall (28, 128); and an irregular surface on the leading sidewall (28, 128) of at least one of the bars (20, 120), wherein the irregular surface includes multiple protrusions extending outwardly from the leading sidewall (28, 128) of the at least one of the bars (20, 120) towards a trailing sidewall (30, 130) on an adjacent bar (20, 120); wherein the trailing sidewall (30, 130) on the adjacent bar (20, 120) has a smooth surface and lacks the irregular surface, wherein each bar is arranged at a feeding angle with respect to a radial line crossing the refiner plate, wherein at a radially inward inlet of the refining surface, the bars are arranged at a feeding angle of at least 10 degrees, and wherein the feeding angles increase continuously and gradually along a radially outward direction of the bars, wherein at least one protrusion of the irregular surface comprises: a first sidewall, a second sidewall, and a curved sidewall between the first sidewall and second sidewall; and a sloped ramp extending up from a bottom of a groove to the bottom edge of the second sidewall; wherein a top edge of the second sidewall, an interior corner formed by the curved sidewall, and the first sidewall are at a ridge at the top of the bar (20, 120). a stator refining surface affixed to a substrate; multiple bars (20, 120) and grooves situated on the stator refining surface, the bars (20, 120) each comprising a leading sidewall (28, 128) and a trailing sidewall (30, 130) that is opposite of the leading sidewall (28, 128); and an irregular surface on the leading sidewall (28, 128) of at least one of the bars (20, 120), wherein the irregular surface includes multiple protrusions extending outwardly from the leading sidewall (28, 128) of the at least one of the bars (20, 120) towards a trailing sidewall (30, 130) on an adjacent bar (20, 120); wherein the trailing sidewall (30, 130) on the adjacent bar (20, 120) has a smooth surface and lacks the irregular surface, wherein each bar is arranged at a feeding angle with respect to a radial line crossing the refiner plate, wherein at a radially inward inlet of the refining surface, the bars are arranged at a feeding angle of at least 10 degrees, and wherein the feeding angles increase continuously and gradually along a radially outward direction of the bars, wherein at least one protrusion of the irregular surface comprises: a first sidewall, a second sidewall, and a curved sidewall between the first sidewall and second sidewall; and a sloped ramp extending up from a bottom of a groove to the bottom edge of the second sidewall; wherein a top edge of the second sidewall, an interior corner formed by the curved sidewall, and the first sidewall are at a ridge at the top of the bar (20, 120). a first sidewall, a second sidewall, and a curved sidewall between the first sidewall and second sidewall; and a sloped ramp extending up from a bottom of a groove to the bottom edge of the second sidewall; wherein a top edge of the second sidewall, an interior corner formed by the curved sidewall, and the first sidewall are at a ridge at the top of the bar (20, 120).