A pumping mechanism, comprising: a cam comprising a central axis; a chassis comprising a recess within which the cam fits in a lengthwise extension along the central axis, wherein the recess comprises a sidewall that defines an interior of the recess; and a plurality of fingers (72, 74, 76, 78) coupled to the cam and configured to move in a direction transverse to the central axis, wherein each of the plurality of fingers (72, 74, 76, 78) comprises a body (72a, 74a, 76a, 78a) and a protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) comprising a distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) and a proximal end (424, 424a, 424b, 424c, 424d, 424e, 424f, 424g, 424h), wherein the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) extends from the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) outward from a side region (72c,d, 74c,d, 76c,d, 78c,d) of the body (72a, 74a, 76a, 78a) in a direction transverse to the direction of movement of the plurality of fingers (72, 74, 76, 78) such that the proximal end (424, 424a, 424b, 424c, 424d, 424e, 424f, 424g, 424h) is in surface contact with the sidewall of the recess, characterized in that the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) of the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) is fitted within a cavity (520, 520a, 520b, 520c, 520d, 520e, 520f, 520g, 520h) formed in the side region (72c,d, 74c,d, 76c,d, 78c,d) of the body (72a, 74a, 76a, 78a), wherein a spring (522, 522a, 522b, 522c, 522d, 522e, 522f, 522g, 522h) is fitted within the cavity (520, 520a, 520b, 520c, 520d, 520e, 520f, 520g, 520h), wherein the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) of the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) contacts the spring (522, 522a, 522b, 522c, 522d, 522e, 522f, 522g, 522h). a cam comprising a central axis; a chassis comprising a recess within which the cam fits in a lengthwise extension along the central axis, wherein the recess comprises a sidewall that defines an interior of the recess; and a plurality of fingers (72, 74, 76, 78) coupled to the cam and configured to move in a direction transverse to the central axis, wherein each of the plurality of fingers (72, 74, 76, 78) comprises a body (72a, 74a, 76a, 78a) and a protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) comprising a distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) and a proximal end (424, 424a, 424b, 424c, 424d, 424e, 424f, 424g, 424h), wherein the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) extends from the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) outward from a side region (72c,d, 74c,d, 76c,d, 78c,d) of the body (72a, 74a, 76a, 78a) in a direction transverse to the direction of movement of the plurality of fingers (72, 74, 76, 78) such that the proximal end (424, 424a, 424b, 424c, 424d, 424e, 424f, 424g, 424h) is in surface contact with the sidewall of the recess, characterized in that the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) of the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) is fitted within a cavity (520, 520a, 520b, 520c, 520d, 520e, 520f, 520g, 520h) formed in the side region (72c,d, 74c,d, 76c,d, 78c,d) of the body (72a, 74a, 76a, 78a), wherein a spring (522, 522a, 522b, 522c, 522d, 522e, 522f, 522g, 522h) is fitted within the cavity (520, 520a, 520b, 520c, 520d, 520e, 520f, 520g, 520h), wherein the distal end (422, 422a, 422b, 422c, 422d, 422e, 422f, 422g, 422h) of the protrusion (420, 420a, 420b, 420c, 420d, 420e, 420f, 420g, 420h) contacts the spring (522, 522a, 522b, 522c, 522d, 522e, 522f, 522g, 522h).