Ultrasound-sensitive polymers

Microbubbles having a shell of poly(acrylic acid) and phospholipids have been reported as another ultrasound-sensitive system (Du et al., 2011). Poly(acrylic acid) had no interaction with liposomes at neutral pH, but bound to the surface of liposomes at acidic pH below its of 4.5. From these results, design of suitable polymers and control of interaction between the particles and cellular surface are expected to advance the ultrasound-sensitive drug delivery systems. 

Since there is a time-temperature superposition for polymers, the frequency and temperature dependences of the acoustic properties are inversely related, so that decrease in temperature correspond to the effect of increases in frequency. This behavior is illustrated by comparing Fig. 60.5(a) and (b) which display the temperature and frequency sensitivity for two polymers [1]. Since measurements over a wide temperature range are more readily made than those over a corresponding frequency range, the combination of the data from measurements over a wide temperature range and a modest frequency range usually serve to define the entire spectrum. The frequency sensitivity of ultrasound... 

B.B. Thomas and W.J. Alexander analysing the relation intensity-cavitation-temperature founded that the degradation is most sensible is more sensitive to the power changes, espeeially at boundary eonditions. The increase of ultrasound power expands the range of temperature within whieh the polymers degradation oeeur [1154]. 

Polymers responsive to the body s external stimuli contain polymers sensitive to temperature, near-infrared light, ultrasound, magnetic fields, light, and electrics fields. These kinds of energy, which are supplied from outside of the body, are used for drug delivery systems. 

Kwok et al. have reported on the development of ULS-sensitive barrier membranes able to give a pulsatile drug release. A co-polymer of 2-hydroxyl methacrylate (HEMA) and PEG dimethacrylate was loaded with particulate insulin and PEG, after which the surface of the polymer was coated with methylene chains. Upon exposure to ultrasound the methylene chains became disordered, permitting the insulin to diffuse out of the matrix [100,101]. 

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