Stability of naked DNA and PEI:DNA complexes after sonication assessed by agarose gel electrophoresis. (A) Stablity of naked DNA after sonication: (a) molecular weight markers; (b) untreated DNA; (c) 0.5 MPa, 240 ms; (d) 0.75 MPa, 240 ms; (e) 1.0 MPa, 240 ms; (f) 1.5 MPa, 240 ms; (g) 2.0 MPa, 240 ms; (h) 1.5 MPa, 300 ms; (i) 1.5 MPa, 360 ms; (j) 0.5 MPa, 420 ms; (k) 0.5 MPa, 480 ms; (l) sham ultrasound. (B) Stability of PEI:DNA complexes after sonication: (a) molecular weight marker; (b) naked DNA, sham ultrasound; (c) PEI:DNA complex, sham ultrasound; (d) 0.5 MPa, 240 ms; (e) 0.75 MPa, 240 ms; (f) 1.0 MPa, 240 ms; (g) 1.5 MPa, 240 ms; (h) 2.0 MPa, 240 ms; (i) 1.5 MPa, 180 ms; (j) 1.5 MPa, 300 ms; (k) 1.5 MPa, 360 ms; (l) 1.5 MPa, 420 ms. OC = Open circular DNA, SC = supercoiled DNA.