Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States.
Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215, United States.
Acc Chem Res. 2024 Jun 4;57(11):1595-1607. doi: 10.1021/acs.accounts.4c00119. Epub 2024 May 17.
High-precision neuromodulation plays a pivotal role in elucidating fundamental principles of neuroscience and treating specific neurological disorders. Optical neuromodulation, enabled by spatial resolution defined by the diffraction limit at the submicrometer scale, is a general strategy to achieve such precision. Optogenetics offers single-neuron spatial resolution with cellular specificity, whereas the requirement of genetic transfection hinders its clinical application. Direct photothermal modulation, an alternative nongenetic optical approach, often associates a large temperature increase with the risk of thermal damage to surrounding tissues.Photoacoustic (also called optoacoustic) neural stimulation is an emerging technology for neural stimulation with the following key features demonstrated. First, the photoacoustic approach demonstrated high efficacy without the need for genetic modification. The generated pulsed ultrasound upon ns laser pulses with energy ranging from a few μJ to tens of μJ is sufficient to activate wild-type neurons. Second, the photoacoustic approach provides sub-100-μm spatial precision. It overcomes the fundamental wave diffraction limit of ultrasound by harnessing the localized ultrasound field generated through light absorption. A spatial precision of 400 μm has been achieved in rodent brains using a fiber-based photoacoustic emitter. Single-cell stimulation in neuronal cultures in vitro and in brain slices ex vivo is achieved using tapered fiber-based photoacoustic emitters. This precision is 10 to 100 times better than that for piezo-based low-frequency ultrasound and is essential to pinpoint a specific region or cell population in a living brain. Third, compared to direct photothermal stimulation via temperature increase, photoacoustic stimulation requires 40 times less laser energy dose to evoke neuron activities and is associated with a minimal temperature increase of less than 1 °C, preventing potential thermal damage to neurons. Fourth, photoacoustics is a versatile approach and can be designed in various platforms aiming at specific applications. Our team has shown the design of fiber-based photoacoustic emitters, photoacoustic nanotransducers, soft biocompatible photoacoustic films, and soft photoacoustic lenses. Since they interact with neurons through ultrasound without the need for direct contact, photoacoustic enables noninvasive transcranial and dura-penetrating brain stimulation without compromising high precision.In this Account, we will first review the basic principles of photoacoustic and discuss the key design elements of PA transducers for neural modulation guided by the principle. We will also highlight how these design goals were achieved from a materials chemistry perspective. The design of different PA interfaces, their unique capability, and their applications in neural systems will be reviewed. In the end, we will discuss the remaining challenges and future perspectives for this technology.
高精度神经调控在阐明神经科学基本原理和治疗特定神经疾病方面发挥着关键作用。基于亚微米尺度衍射极限定义的空间分辨率的光神经调控是实现这种精度的一般策略。光遗传学提供了具有细胞特异性的单神经元空间分辨率,但其对基因转染的要求阻碍了其临床应用。直接光热调制是一种替代的非遗传光学方法,通常伴随着较大的温度升高,并存在热损伤周围组织的风险。光声(也称为光声)神经刺激是一种新兴的神经刺激技术,具有以下关键特征。首先,光声方法在不需要基因修饰的情况下表现出高效性。在纳秒激光脉冲下产生的短暂超声,能量范围从几微焦耳到几十微焦耳,足以激活野生型神经元。其次,光声方法提供了亚 100μm 的空间精度。它通过利用光吸收产生的局部超声场来克服超声的基本波衍射极限。在啮齿动物大脑中使用光纤式光声发射器实现了 400μm 的空间精度。在体外神经元培养物和脑片中进行单细胞刺激使用基于锥形光纤的光声发射器来实现。这种精度比基于压电的低频超声提高了 10 到 100 倍,对于精确定位活体大脑中的特定区域或细胞群体至关重要。第三,与通过温度升高的直接光热刺激相比,光声刺激需要少 40 倍的激光能量剂量来引发神经元活动,并且与低于 1°C 的最小温度升高相关,从而防止潜在的热损伤神经元。第四,光声是一种多功能的方法,可以针对特定应用设计各种平台。我们的团队展示了光纤式光声发射器、光声纳米换能器、软生物相容光声膜和软光声透镜的设计。由于它们通过超声与神经元相互作用,而无需直接接触,光声可以实现非侵入性的颅穿透和硬脑膜穿透脑刺激,而不会降低高精度。在本报告中,我们将首先回顾光声的基本原理,并根据该原理讨论神经调制用 PA 换能器的关键设计要素。我们还将从材料化学的角度强调如何实现这些设计目标。将回顾不同的 PA 接口的设计、它们的独特功能及其在神经系统中的应用。最后,我们将讨论该技术的剩余挑战和未来展望。
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