A tip assembly for introducing a composition in a fluid into cells comprising: an attachment portion open to the atmosphere that proximally connects to a flow device that generates at least one of a positive pressure or a negative pressure for directing the fluid; a channel portion contiguous to and distal to the attachment portion and the flow device; a constriction portion contiguous with the channel portion, wherein a constriction portion inner diameter and a constriction portion cross sectional area are smaller than a channel portion inner diameter and a channel portion cross sectional area, wherein a distal end of the constriction portion comprises an opening for ejecting or drawing the fluid, wherein increased fluid velocity and a decreased pressure in the fluid in the constriction portion compared to velocity and pressure in the channel portion affects membrane permeability of the cells, whereby the decreasing pressure in the tip assembly introduces the composition into the cells through the membrane, and wherein the channel portion curvature and constriction inner curvature characterize a fluid path for the fluid flowing through the tip assembly, wherein the channel portion curvature and constriction inner curvature necessary for introducing the composition into the cells comprises a formula represented in two dimensions is f x = p 1 x 7 + p 2 x 6 + p 3 x 5 + p 4 x 4 + p 5 x 3 + p 6 x 2 + p 7 x + p 8 wherein x is a radial distance from a center axis on the fluid path to an inner surface of the tip and coefficients with 95% confidence bounds in parentheses comprise: p1 is -2.611e -16 (-6.043e -16, 8.206e -17), p2 is 3.954 e-13 (-3.195 e-13, 1.11 e-12), p3 is -1.845 e-10 (-7.821 e-10, 4.131 e-10), p4 is 1.662 e-08 (-2.394 e-07, 2.726 e-07), p5 is 7.537 e-06 (-5.186 e-05, 6.694 e-05), p6 is -0.002137 (-0.009375, 0.005101), p7 is -0.003185 (-0.4114, 0.4051), and p8 = 268.6 (261, 276.3), or f x = p 1 x 8 + p 2 x 7 + p 3 x 6 + p 4 x 5 + p 5 x 4 + p 6 x 3 + p 7 x 2 + p 8 x + p 9 wherein x is a radial distance from a center axis on the fluid path to an inner surface of the tip and coefficients with 95% confidence bounds in parentheses comprise: p1 is 2.285 (1.388, 3.182), p2 is 3.465 (1.782, 5.149), p3 is -15.68 (-20.04, -11.32); p4 is -20.38 (-27.24, -13.52); p5 is 44.27 (36.5, 52.04); p6 is 53.96 (45.69, 62.23); p7 is -58.72 (-64.02, -53.42), p8 is - 123.5 (-126.4, -120.6), and p9 is 186.5 (185.6, 187.4). an attachment portion open to the atmosphere that proximally connects to a flow device that generates at least one of a positive pressure or a negative pressure for directing the fluid; a channel portion contiguous to and distal to the attachment portion and the flow device; a constriction portion contiguous with the channel portion, wherein a constriction portion inner diameter and a constriction portion cross sectional area are smaller than a channel portion inner diameter and a channel portion cross sectional area, wherein a distal end of the constriction portion comprises an opening for ejecting or drawing the fluid, wherein increased fluid velocity and a decreased pressure in the fluid in the constriction portion compared to velocity and pressure in the channel portion affects membrane permeability of the cells, whereby the decreasing pressure in the tip assembly introduces the composition into the cells through the membrane, and wherein the channel portion curvature and constriction inner curvature characterize a fluid path for the fluid flowing through the tip assembly, wherein the channel portion curvature and constriction inner curvature necessary for introducing the composition into the cells comprises a formula represented in two dimensions is f x = p 1 x 7 + p 2 x 6 + p 3 x 5 + p 4 x 4 + p 5 x 3 + p 6 x 2 + p 7 x + p 8 wherein x is a radial distance from a center axis on the fluid path to an inner surface of the tip and coefficients with 95% confidence bounds in parentheses comprise: p1 is -2.611e -16 (-6.043e -16, 8.206e -17), p2 is 3.954 e-13 (-3.195 e-13, 1.11 e-12), p3 is -1.845 e-10 (-7.821 e-10, 4.131 e-10), p4 is 1.662 e-08 (-2.394 e-07, 2.726 e-07), p5 is 7.537 e-06 (-5.186 e-05, 6.694 e-05), p6 is -0.002137 (-0.009375, 0.005101), p7 is -0.003185 (-0.4114, 0.4051), and p8 = 268.6 (261, 276.3), or f x = p 1 x 8 + p 2 x 7 + p 3 x 6 + p 4 x 5 + p 5 x 4 + p 6 x 3 + p 7 x 2 + p 8 x + p 9 wherein x is a radial distance from a center axis on the fluid path to an inner surface of the tip and coefficients with 95% confidence bounds in parentheses comprise: p1 is 2.285 (1.388, 3.182), p2 is 3.465 (1.782, 5.149), p3 is -15.68 (-20.04, -11.32); p4 is -20.38 (-27.24, -13.52); p5 is 44.27 (36.5, 52.04); p6 is 53.96 (45.69, 62.23); p7 is -58.72 (-64.02, -53.42), p8 is - 123.5 (-126.4, -120.6), and p9 is 186.5 (185.6, 187.4).