Effect of molecular weight, crystallinity, and hydrophobicity on the acoustic activation of polymer-shelled ultrasound contrast agents.
Polymer-shelled microbubbles are applied as ultrasound contrast agents. To investigate the effect of the polymer on microbubble preparation and acoustic properties, polylactides with systematic variations in molecular weight, crystallinity, and end-group hydrophobicity were used. Polymer-shelled cyclodecane filled capsules were prepared by emulsification, and the cyclodecane was removed by lyophilization to obtain hollow capsules. Complete removal of cyclodecane from the microcapsules was only achieved for short chain (about M(w) 6000) crystalline polymers. The pressure threshold for acoustic destruction of the microbubbles was found to increase with molecular weight. Noncrystalline polymers showed a higher threshold for destruction than crystalline polymers. Hydrophobically modified short chain crystalline polymers showed the steepest increase in acoustic destruction after the threshold as a function of the applied pressure, which is a favorable characteristic for ultrasound mediated drug delivery. Microcapsules made with such polymers had an inhomogeneous surface including pores through which cyclodecane was lyophilized efficiently.
Chlon
Ceciel
C
Philips Research Europe, HTC11, 5656 AE, Eindhoven, The Netherlands.
Guédon
Constant
C
Verhaagen
Bram
B
Shi
William T
WT
Hall
Christopher S
CS
Lub
Johan
J
Böhmer
Marcel R
MR
D000162:Acoustics; D002214:Capsules / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry*; D003460:Crystallization; D043822:Cyclodecanes / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D019344:Lactic Acid / Q000138:chemical synthesis / Q000737:chemistry*; D045423:Microbubbles; D008854:Microscopy, Electron; D008970:Molecular Weight; D010316:Particle Size; D011091:Polyesters / Q000737:chemistry; D011100:Polyglycolic Acid / Q000138:chemical synthesis / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D016062:Porosity; D011312:Pressure; D013499:Surface Properties; D013696:Temperature
D002214:Capsules; D003287:Contrast Media; D043822:Cyclodecanes; D011091:Polyesters; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide)