Phospholipid-coated microbubbles are being developed for several biomedical applications, but little is known about the effect of temperature on the viscoelastic properties of the shell. Here, we report on the use of a photoacoustic technique to study the shell properties of individual microbubbles as a function of temperature. The microbubbles were driven into small-amplitude oscillations by ultrasound waves generated from the absorption of an intensity-modulated infrared laser, and these oscillations were detected by forward-light scattering of a second blue laser. The drive laser modulation frequency was swept to determine the resonant response of 2-4 μm radius microbubbles. Lipid shell elasticity and viscosity were determined by modeling the microbubble response as a linear harmonic oscillator. The results from slow heating showed a linear decrease in elasticity and viscosity between 21 and 53 °C and a corresponding increase in the maximum oscillation amplitude. Rapid heating to 38 °C, on the other hand, showed a transient response in the viscoelastic properties, suggesting shell rupture and reformation during microbubble growth and subsequent dissolution. These effects are important for biomedical applications, which require warming of the microbubbles to body temperature.

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测量温度对微泡粘弹性特性影响的光声技术

磷脂包被的微泡正在开发用于多种生物医学应用，但人们对温度对外壳粘弹性的影响知之甚少。在这里，我们报告使用光声技术来研究作为温度函数的单个微泡的壳特性。微泡被强度调制红外激光吸收产生的超声波驱动成小幅度振荡，这些振荡通过第二个蓝色激光的前向光散射检测到。扫描驱动激光调制频率以确定 2-4 μm 半径微泡的共振响应。通过将微泡响应建模为线性谐振子来确定脂壳弹性和粘度。缓慢加热的结果表明弹性和粘度在 21 到 53 °C 之间线性下降，最大振幅相应增加。另一方面，快速加热至 38°C，显示粘弹性的瞬态响应，表明在微气泡生长和随后的溶解过程中壳破裂和重新形成。这些效应对于需要将微泡加热至体温的生物医学应用非常重要。