Needle assembly for liquid applicator

A needle assembly for a liquid applicator, comprising:

• a housing comprising a longitudinal channel, the channel comprising an upper open end and a lower open end;
• a needle bundle movably mounted in the channel, the needle bundle configured and mounted to be driven by a driving shaft to reciprocatively move along a longitudinal direction between a retracted position and an extended position;
• an elastic tubular member comprising a first end attached to the housing and a second end attached the needle bundle to bias the needle bundle to move longitudinally towards the retracted position, the tubular member comprising a first portion and a second portion thinner than the first portion, wherein a slanted boundary between the first portion and the second portion extends between the first end and the second end in both the longitudinal direction and a lateral perimetral direction of the tubular member to provide a lateral biasing force that biases the needle bundle laterally toward a lateral side of the channel.