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 and grooves situated on the stator refining surface, the bars each comprising a leading sidewall and a trailing sidewall that is opposite of the leading sidewall ; and an irregular surface on the leading sidewall of at least one of the bars , wherein the irregular surface includes multiple protrusions extending outwardly from the leading sidewall of the at least one of the bars towards a trailing sidewall on an adjacent bar ; wherein the trailing sidewall on the adjacent bar 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 . a stator refining surface affixed to a substrate ; multiple bars and grooves situated on the stator refining surface, the bars each comprising a leading sidewall and a trailing sidewall that is opposite of the leading sidewall ; and an irregular surface on the leading sidewall of at least one of the bars , wherein the irregular surface includes multiple protrusions extending outwardly from the leading sidewall of the at least one of the bars towards a trailing sidewall on an adjacent bar ; wherein the trailing sidewall on the adjacent bar 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 . 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 . <EOS>