1. Introduction
一、简介

Neuromodulation is the physiological process of regulating neural activity through the targeted delivery of stimuli, such as electrical stimulation or chemical agents, to specific neural structures within the body. Various neurochemicals, including neurotransmitters (e.g., acetylcholine, dopamine, glutamate, and GABA) and neuromodulators (e.g., ions, amino acids, and peptides) modulate neural physiological and pathological processes in the central nervous systems. Chemical neuromodulation relies on the delivery of neurochemicals to the targeted brain regions, which bind to specific receptors or channels on the cell membrane to activate or inhibit neural activities.^1,2 Chemical neuromodulation provides a powerful tool to investigate signal transmission and processes in the central nervous system.³ It is also useful for the treatment of movement disorders, pain, and depression in the clinic.^4–6 Beyond endogenous membrane receptors, chemogenetic strategies, such as the employment of the designer receptors exclusively activated by designer drugs (DREADDs), have been developed to improve the spatial and temporal modulation of G protein signaling in vivo.⁷ Due to the promising translational applications, chemical neuromodulation through various neuromodulators gains increasing interest.^8,9 In the development of neuromodulation modalities aimed at increased specificity and reduced invasiveness, it is necessary to precisely control the distribution of neurochemicals within the brain, ensuring high spatiotemporal resolution for precise chemical neuromodulation.¹⁰
神经调节是通过向体内特定神经结构有针对性地传递刺激（例如电刺激或化学制剂）来调节神经活动的生理过程。各种神经化学物质，包括神经递质(例如乙酰胆碱、多巴胺、谷氨酸和GABA)和神经调节剂(例如离子、氨基酸和肽)调节中枢神经系统中的神经生理和病理过程。化学神经调节依赖于将神经化学物质输送到目标大脑区域，这些区域与细胞膜上的特定受体或通道结合以激活或抑制神经活动。 ^1,2化学神经调节提供了研究中枢神经系统信号传输和过程的强大工具。 ³它对于临床上运动障碍、疼痛和抑郁症的治疗也很有用。 ^4-6除了内源性膜受体之外，化学遗传学策略（例如使用专门由设计药物激活的设计受体 (DREADD)）已被开发用于改善体内G 蛋白信号传导的空间和时间调节。 ⁷由于有前景的转化应用，通过各种神经调节剂进行的化学神经调节越来越受到人们的关注。 ^8,9在开发旨在提高特异性和减少侵袭性的神经调节方式时，有必要精确控制神经化学物质在大脑内的分布，确保精确化学神经调节的高时空分辨率。¹⁰

Recently, the development of stimuli-responsive controlled release systems offers new opportunities for precise chemical neuromodulation.¹¹ Neuromodulators can be loaded into the delivery systems, such as liposomes or polymeric nanoparticles, and released at the targeted area under optical, acoustic, or magnetic stimulation (Fig. 1). The stimuli-responsive delivery systems take advantage of the traditional methods of drug administration, such as increasing the stability of neuromodulators especially neuropeptides in vivo, and enhancing the accumulation in the brain.^12,13 More importantly, the controlled release of neuromodulators in the local brain can facilitate the study of fast signal transmission in the brain. For example, Xiong et al. measured the spatiotemporal scale of neuropeptide volume transmission in the mouse cortex by the rapid neuropeptide release from gold-coated liposomes under the irradiation of near-infrared (NIR) laser pulses and optical sensing.¹⁴ On the other hand, stimuli-responsive delivery systems can enhance the efficacy of neuromodulation and reduce the side effects of neuromodulators. For example, Lea-Banks et al. demonstrated that localized anesthesia could be achieved by focus ultrasound-induced release from pentobarbital-loaded nanodroplets with lipid shell and decafluorobutane core in a specific brain region without disrupting the blood–brain barrier (BBB) and off-target effects.¹⁵
最近，刺激响应控制释放系统的发展为精确的化学神经调节提供了新的机会。 ¹¹神经调节剂可以加载到脂质体或聚合物纳米颗粒等递送系统中，并在光学、声学或磁刺激下在目标区域释放（图 1 ）。刺激响应递送系统利用了传统的给药方法，例如增加神经调节剂尤其是神经肽在体内的稳定性，并增强在大脑中的积累。 ^12,13更重要的是，局部大脑中神经调节剂的受控释放可以促进大脑中快速信号传输的研究。例如，熊等人。通过在近红外（NIR）激光脉冲和光学传感的照射下从金包被的脂质体中快速释放神经肽，测量了小鼠皮质中神经肽体积传输的时空尺度。 ¹⁴另一方面，刺激响应传递系统可以增强神经调节的功效并减少神经调节剂的副作用。例如，Lea-Banks等人。证明可以通过聚焦超声诱导在特定脑区域释放具有脂质壳和十氟丁烷核心的戊巴比妥纳米滴来实现局部麻醉，而不会破坏血脑屏障（BBB）和脱靶效应。 ¹⁵

Stimuli-responsive materials have garnered significant attention due to their potential applications in targeted drug delivery, tissue engineering, biosensing, and theranostics. As mentioned above, the emerging stimuli-responsive controlled release systems also offer powerful tools for precise neuromodulation. Herein, we summarize the recent advances in fabricating stimuli-responsive materials for neuromodulation for the first time and provide insights into developing the next generation of stimuli-responsive materials for safe, effective, and precise neuromodulation. We focus on two key aspects: the biological barrier for neuromodulator delivery and the innovations in the delivery systems for neuromodulation. We first discuss how the BBB extracellular space and matrix work as the biological barrier for targeted neuromodulator delivery. Next, we summarize the recent development of stimuli-responsive controlled systems for neuromodulation from the perspective of different external triggers, including light, ultrasound, and magnetic fields. We emphasize the design of controlled release systems and the release mechanism. Finally, we provide an outlook on future endeavors toward more safe and precise chemical neuromodulation techniques.
刺激响应材料由于其在靶向药物递送、组织工程、生物传感和治疗诊断学中的潜在应用而引起了极大的关注。如上所述，新兴的刺激响应控制释放系统也为精确的神经调节提供了强大的工具。在此，我们首次总结了制造用于神经调节的刺激响应材料的最新进展，并为开发下一代安全、有效和精确的神经调节刺激响应材料提供了见解。我们重点关注两个关键方面：神经调节剂递送的生物屏障和神经调节递送系统的创新。我们首先讨论 BBB 细胞外空间和基质如何作为靶向神经调节剂递送的生物屏障。接下来，我们从不同的外部触发因素（包括光、超声和磁场）的角度总结了神经调节刺激响应控制系统的最新发展。我们强调控释系统和释放机制的设计。最后，我们对未来更加安全和精确的化学神经调节技术的努力进行了展望。

2. Biological barrier for delivery of neuromodulators to the brain
2.将神经调节剂输送到大脑的生物屏障

To achieve the desired outcomes of neuromodulators in the brain, controlled release systems must be accurately delivered to specific brain regions. Currently, delivery methods include intravenous injection and intracerebral injection into targeted areas. The systemic route offers convenience and non-invasiveness compared with the intraparenchymal injection, but its effectiveness is considerably reduced by the BBB.^16–18 The BBB, a selectively permeable barrier comprised of brain microvascular endothelial cells linked by tight junctions and surrounded by pericytes and astrocytic endfeet, maintains brain homeostasis by regulating molecular transport and protecting the brain from blood-borne toxins and pathogens. However, it also blocks over 98% of small-molecule drugs and all macromolecular therapeutics from entering the brain.^19–21 To bypass the BBB, delivery systems can be modified with a targeting ligand (e.g., a monoclonal antibody or peptide) that binds to specific receptors, facilitating transcellular transport.^22–25 This method of active targeting is advancing rapidly for treating brain diseases, including tumors, Alzheimer's disease, and Parkinson's disease, and could potentially be utilized for neuromodulator delivery.²⁰ Furthermore, using focused ultrasound in conjunction with microbubbles to temporarily enhance BBB permeability represents a novel physical approach, improving the delivery efficiency of therapeutics.^26,27 In a similar vein, nanodroplets containing decafluorobutane and an anesthetic drug, activated by focused ultrasound, have successfully breached the BBB to administer the drug directly to targeted regions, achieving localized anesthesia in the motor cortex of rat.^15,28 Recently, Qin et al. introduced an innovative technique for optically modulating the BBB through laser stimulation of gold nanoparticles targeted at tight junctions, enhancing the permeability of both the BBB and the blood-spinal cord barrier.^21,29 Employing this technique enabled the administration of bombesin to the spinal cord, effectively inducing itch responses in mice.
为了在大脑中实现神经调节剂的预期结果，必须将受控释放系统准确地输送到特定的大脑区域。目前，递送方法包括静脉注射和脑内注射到目标区域。与实质内注射相比，全身途径提供了便利性和非侵入性，但其有效性因血脑屏障而大大降低。 ^16–18血脑屏障是一种选择性渗透屏障，由紧密连接的脑微血管内皮细胞组成，并被周细胞和星形胶质细胞末足包围，通过调节分子运输和保护大脑免受血源性毒素和病原体的侵害来维持大脑稳态。然而，它还能阻止 98% 以上的小分子药物和所有大分子治疗药物进入大脑。 ^19–21为了绕过血脑屏障，可以使用与特定受体结合的靶向配体（例如单克隆抗体或肽）来修改递送系统，从而促进跨细胞转运。 ^22-25这种主动靶向方法在治疗脑部疾病（包括肿瘤、阿尔茨海默病和帕金森病）方面正在迅速发展，并且有可能用于神经调节剂的输送。 ²⁰此外，使用聚焦超声与微泡结合来暂时增强血脑屏障渗透性代表了一种新颖的物理方法，可以提高治疗的传递效率。^26,27同样，含有十氟丁烷和麻醉药物的纳米液滴在聚焦超声波激活下，已成功突破血脑屏障，将药物直接注射到目标区域，实现大鼠运动皮层的局部麻醉。 ^15,28最近，Qin等人。推出了一种创新技术，通过激光刺激紧密连接处的金纳米粒子来光学调节血脑屏障，从而增强血脑屏障和血脊髓屏障的通透性。 ^21,29采用这种技术可以将铃蟾肽注射到脊髓，有效诱导小鼠的瘙痒反应。

Irrespective of the method used for administering delivery systems to the brain, all such systems and the neuromodulators they release must traverse a considerable distance within the narrow extracellular space (ECS) to reach their target neurons and elicit effects. The ECS's heterogeneity in width, with an average estimated at 40–60 nm based on quantum dots diffusion analysis,³⁰ poses a significant challenge to nanoparticle diffusion. In addition to ECS geometry, the extracellular matrix—comprising proteoglycans, hyaluronan, and various small linking proteins—serves as an additional barrier to drug distribution within the brain (Fig. 2). For instance, the presence of increasing malignancy in astrocytic tumors has been shown to slow ECS diffusion due to glycoprotein production.³¹ Moreover, treatment with hyaluronidase has been shown to accelerate neuropeptide transmission in the mouse cortex.³² Nance et al. demonstrated that enhancing the surface density of poly(ethylene glycol) (PEG) on 40 nm and 100 nm polymeric nanoparticles can facilitate diffusion in human and rat brain ECS.³³ It is noteworthy that neuromodulators typically require binding to specific receptors on the cell membrane, resulting in minimal brain cell uptake. Song et al. reported that PEGylation of poly(lactic acid) surfaces reduces internalization by neurons, astrocytes, and microglia, whereas aldehyde modification has the opposite effect.³⁴ Furthermore, the surface charge of nanoparticles critically influences their brain ECS distribution. Dante et al. showed that negatively charged inorganic nanoparticles tend to interact with neuronal membranes and accumulate at the synaptic cleft, in contrast to positively and neutrally charged nanoparticles, which showed no neuronal association.³⁵ The success of neuromodulation significantly depends on the fate of delivery systems within the brain ECS, warranting further research.
无论使用何种方法向大脑施用递送系统，所有此类系统及其释放的神经调节剂都必须在狭窄的细胞外空间 (ECS) 内穿越相当长的距离才能到达其目标神经元并引发效应。 ECS 的宽度不均匀性，根据量子点扩散分析，平均估计为 40-60 nm， ³⁰对纳米粒子扩散提出了重大挑战。除了 ECS 几何结构外，细胞外基质（包含蛋白聚糖、透明质酸和各种小连接蛋白）也是药物在大脑内分布的额外屏障（图 2 ）。例如，星形细胞肿瘤中恶性肿瘤的增加已被证明会因糖蛋白的产生而减慢 ECS 扩散。 ³¹此外，透明质酸酶治疗已被证明可以加速小鼠皮质中的神经肽传输。 ³²南斯等人。证明增强 40 nm 和 100 nm 聚合物纳米颗粒上聚乙二醇 (PEG) 的表面密度可以促进人和大鼠脑 ECS 中的扩散。 ³³值得注意的是，神经调节剂通常需要与细胞膜上的特定受体结合，从而导致脑细胞的摄取最小化。宋等人。据报道，聚乳酸表面的聚乙二醇化减少了神经元、星形胶质细胞和小胶质细胞的内化，而醛修饰则具有相反的效果。 ³⁴此外，纳米粒子的表面电荷严重影响其大脑 ECS 分布。但丁等人。研究表明，带负电的无机纳米颗粒倾向于与神经元膜相互作用并在突触间隙积聚，而带正电和中性电荷的纳米颗粒则没有神经元关联。 ³⁵神经调节的成功很大程度上取决于大脑 ECS 内传递系统的命运，需要进一步研究。

3. Stimuli-responsive controlled release systems for neuromodulation
3.用于神经调节的刺激响应控制释放系统

Stimuli-responsive controlled-release systems can deliver neurochemicals to targeted neurons when triggered by physical or chemical stimuli. Such systems are typically composed of nano-carriers with stimuli-responsive units and neurochemicals aimed at particular receptors or channels (Table 1). Most neurochemicals are hydrophilic, which can be conjugated to the nano-carrierrs with a stimuli-responsive linker or physically encapsulated in the hydrophilic space of nano-carriers. The stimuli-responsive unit is primarily designed to respond to endogenous (e.g., pH, redox) or exogenous (e.g., light, sound, magnetic fields) stimuli.
当受到物理或化学刺激触发时，刺激响应控释系统可以将神经化学物质输送到目标神经元。此类系统通常由具有刺激响应单元的纳米载体和针对特定受体或通道的神经化学物质组成（表1 ）。大多数神经化学物质是亲水性的，可以通过刺激响应连接体与纳米载体缀合或物理封装在纳米载体的亲水空间中。刺激响应单元主要被设计为响应内源性（例如，pH、氧化还原）或外源性（例如，光、声音、磁场）刺激。

Stimulus-responsive module 刺激响应模块	Release mechanism 释放机构	Delivery systems 输送系统	Cargo 货物	In vitro effect 体外效果	In vivo effect 体内作用	Advantages 优点	Ref. 参考号
Light-responsive 光响应	Photolysis 光解作用	Caged compound 笼式复合物	Opioid neuropeptides 阿片类神经肽	Activating mu opioid receptor-coupled K+ channels 激活 mu 阿片受体偶联 K +通道	—	Rapid release 快速发布	36
	Photolysis 光解作用	Caged compound 笼式复合物	Neuropeptides: gastrin-releasing peptide, oxytocin, substance P, cholecystokinin 神经肽：胃泌素释放肽、催产素、P物质、缩胆囊素	—	Neuropeptide signaling in intact tissue preparations 完整组织制剂中的神经肽信号转导	Precise spatial and temporal control of neuropeptide signaling 神经肽信号传导的精确空间和时间控制	37
	Photolysis 光解作用	Caged compound 笼式复合物	Mu opioid receptor-selective peptide agonist Mu阿片受体选择性肽激动剂	—	Rapid, opioid-dependent increase in mouse ventral tegmental area 阿片类药物依赖性小鼠腹侧被盖区快速增加	Rapid behavioral changes observable, high spatiotemporal precision 可观察到快速的行为变化，时空精度高	38
	Photolysis 光解作用	Caged compound 笼式复合物	Opioid receptor agonists 阿片受体激动剂	—	Activation of various brain regions induced local alterations in receptor occupancy, metabolic activity, and affected pain- and reward-related behaviors 不同大脑区域的激活引起受体占据、代谢活动的局部改变，并影响与疼痛和奖励相关的行为	High spatiotemporal precision in drug delivery and receptor activation 药物输送和受体激活的高时空精度	39
	Photolysis 光解作用	DNA nanostructure loads cargo with photolabile linker DNA 纳米结构装载带有光不稳定接头的货物	Glutamic acid 谷氨酸	Activating Ca2+ signaling pathways in primary hippocampal neurons 激活初级海马神经元中的 Ca 2+信号通路	—	Controlled release of a wide range of bioactive molecules 多种生物活性分子的受控释放	40
	Photolysis 光解作用	DNA nanostructure loaded with photoresponsive polymers 负载光响应聚合物的DNA纳米结构	DHEA	Revealing the kinetics of neuronal activation 揭示神经元激活的动力学	Spatial control at the level of single endosomes within a single cell 单细胞内单个核内体水平的空间控制	Triggered release with spatial and temporal precision at designated cells 在指定细胞处以空间和时间精度触发释放	41
	Photolysis 光解作用	Upconversion nanoparticle coated by zeolitic imidazolate framework–8 沸石咪唑酯骨架包覆的上转换纳米颗粒–8	Nitrosothiol 亚硝基硫醇	Activating the differentiation pathway for a markedly pronounced outgrowth of neuronal processes 激活分化途径，使神经元过程明显生长	Fostering the regrowth of damaged motor neuron axons in zebrafish and enhanced motor function recovery in rats following traumatic spinal cord injury 促进斑马鱼受损运动神经元轴突的再生并增强大鼠脊髓损伤后运动功能的恢复	The pleiotropic effects of NO NO的多效性作用	42
	Photoisomerization 光致异构化	Photoswitchable nanovesicle 光开关纳米囊泡	SKF81297	Activating cultures of primary striatal neurons 原代纹状体神经元的激活培养物	—	Highly controllable molecular release 高度可控的分子释放	43
	Photothermal 光热	Liposomes containing a photosensitizer and gold nanorods 含有光敏剂和金纳米棒的脂质体	Tetrodotoxin or other nerve-blocking agents 河豚毒素或其他神经阻滞剂	—	Local anesthetic 局部麻醉	—	44–46
	Photothermal 光热	Polymeric nanoparticle with photosensive PDPP 具有光敏性PDPP的聚合物纳米颗粒	Fasudil 法舒地尔	—	Significantly reducing the firing frequency of ventral tegmental area dopamine neurons involved in depression-like behaviors 显着降低参与抑郁样行为的腹侧被盖区多巴胺神经元的放电频率	—	47
	Photothermal 光热	pNIPAM composite hydrogel embedded with PPy nanoparticles 嵌入PPy纳米颗粒的pNIPAM复合水凝胶	Netrin or semaphorin 3A; glutamate Netrin或信号蛋白3A；谷氨酸盐	Triggering local signal transduction in a neural network or neuronal cell subdomain with micro-scale precision 以微尺度精度触发神经网络或神经元细胞子域中的局部信号转导	Remote control of brain activity 远程控制大脑活动	Versatility and ease-of-use 多功能性和易用性	48
	Photomechanical 照相冲印	Liposomes tethered hollow gold nanoshells 束缚空心金纳米壳的脂质体	Glutamate, potassium chloride, muscimol, and specific dopamine agonists 谷氨酸、氯化钾、蝇蕈醇和特定多巴胺激动剂	—	Repeated and stable neural manipulation modulated by laser intensity 由激光强度调制的重复且稳定的神经操作	Controlled release of a wide range of chemicals 多种化学品的受控释放	49
	Photomechanical 照相冲印	Liposomes with gold nanoparticles coating 具有金纳米颗粒涂层的脂质体	IP3	Triggering calcium signaling in cancer cells and primary DRG neurons through the release of IP3 通过释放 IP3 触发癌细胞和原代 DRG 神经元中的钙信号传导	—	Rapid release 快速发布	50
	Photomechanical 照相冲印	Rad-PC-Rad nanovesicles coated with gold Rad-PC-Rad 纳米囊泡涂有金	IP3	Rapid unpacking of IP3 triggers intracellular Ca2+ dependent signaling pathways in living cells IP3 的快速解包触发活细胞中的细胞内 Ca 2+依赖性信号通路	Enabling biomolecules to be released up to 4 millimeters in the rodent brain 使生物分子能够在啮齿动物大脑中释放达 4 毫米	High photosensitivity 高感光度	51
	Photodynamic 光动力	Liposomes with NIR-absorbing photosensitizer 具有近红外吸收光敏剂的脂质体	Tetrodotoxin 河豚毒素	—	Sciatic nerve blockade 坐骨神经阻滞	—	52 and 53 52 和 53
Ultrasound-responsive 超声波响应	Sono-mechanical 超声波机械	Liposomes tethered to microbubbles 束缚在微泡上的脂质体	Muscimol 蝇蕈醇	—	Focal modulation of the propagation of neuronal activity in the rodent vibrissae sensory-motor pathway 啮齿动物触须感觉运动通路中神经元活动传播的局部调节	High target specificity 目标特异性高	54
	Sono-mechanical 超声波机械	Nanoemulsions with a block copolymer matrix and a liquid perfluorocarbon (PFP) core 具有嵌段共聚物基质和液体全氟化碳 (PFP​​) 核的纳米乳液	Propofol 异丙酚	—	Silencing of seizure activity in vivo 体内癫痫发作活动的沉默	Noninvasive targeted transcranial neuromodulation 无创靶向经颅神经调节	55
	Sono-mechanical 超声波机械	Nanoemulsions with a PEG-PLGA block copolymer matrix and a liquid PFP core 具有 PE​​G-PLGA 嵌段共聚物基质和液体 PFP 核的纳米乳液	Propofol 异丙酚	—	Noninvasive mapping of the changes in functional network connectivity associated with pharmacologic action at a particular brain target 无创绘制与特定大脑目标的药理作用相关的功能网络连接变化	—	56
	Sono-mechanical 超声波机械	Nanodroplets with liquid decafluorobutane core 具有液体十氟丁烷核心的纳米液滴	Pentobarbital and a GABAA receptor agonist 戊巴比妥和 GABAA 受体激动剂	—	Inducing local anesthesia in the motor cortex of rats 诱导大鼠运动皮层局部麻醉	—	15 and 28
	Sonodynamic 声动力	Liposome with unsaturated lipids and protoporphyrin IX 含有不饱和脂质和原卟啉 IX 的脂质体	Tetrodotoxin 河豚毒素	—	Sciatic nerve blockade 坐骨神经阻滞	On-demand local anesthesia 按需局部麻醉	57 and 58 57 和 58
Magnetic field-responsive 磁场响应	Magnetic-thermal 磁热	lron oxide MNPs and thermally labile linkers 氧化铁 MNP 和热不稳定连接体	Allyl isothiocyanate 异硫氰酸烯丙酯	Triggering Ca2+ influx and action potential firing 触发 Ca 2+流入和动作电位放电	—	Low required concentration 所需浓度低	59
	Magnetic-thermal 磁热	Polymeric nanoparticles based on MNPs and poly(sebacic acid) composites 基于MNP和聚癸二酸复合材料的聚合物纳米颗粒	Protons 质子	Remote triggering acid-sensing ion channels to evoke intracellular calcium influx in neurons 远程触发酸敏离子通道引起神经元细胞内钙流入	—	Wireless modulation of local pH 无线调节局部 pH 值	60
	Magnetic-thermal 磁热	Thermally responsive liposomes loaded with MNPs 负载 MNP 的热响应脂质体	CNO, SKF-38393 SCH-23390 CNO，SKF-38393 SCH-23390	—	Providing precise molecular control over neural circuits and enabling rapid activation of both genetically engineered and naturally expressed receptors 对神经回路提供精确的分子控制，并能够快速激活基因工程和自然表达的受体	Interrogating pharmacologically targeted neural populations in subjects that are freely moving 询问自由活动受试者的药理学目标神经群	61
	Magnetic-thermal 磁热	Polymeric nanoparticles with MNPs and poly(oligo (ethylene glycol) methyl ether methacrylate) brushes 具有 MNP 和聚（低聚（乙二醇）甲醚甲基丙烯酸酯）刷的聚合物纳米颗粒	Dopamine 多巴胺	Enhancing the activity of ∼50% of striatal neurons subjected to the treatment 增强约 50% 接受治疗的纹状体神经元的活性	—	On-demand release of multiple microdoses 按需释放多个微剂量	62
	Magneto-mechanical 磁力机械	MNPs in Ca2+ cross-linked hydrogels Ca 2+交联水凝胶中的 MNP	Levodopa 左旋多巴	Stimulating the proliferation of dopaminergic neurons and the expression of dopaminergic phenotype 刺激多巴胺能神经元的增殖和多巴胺能表型的表达	—	—	63

Only a few studies have reported the endogenous stimulus-responsive systems for neuromodulation. Lei et al. activated or blocked the neuromicroenvironment in pancreatic cancer by loading Ferritin nanoparticles with the muscarinic agonist carbachol and the muscarinic antagonist atropine, respectively. The Ferritin nanoparticles can release drugs in the weakly acidic environment (pH 6.5) of pancreatic tumors, and the drugs are further released in the lysosomes (pH 5.0) of tumor cells to modulate the early invasive growth and metastatic spread of pancreatic cancer progression.⁶⁴ Zuo et al. crafted an amphiphilic block copolymer incorporating boron-based reactive oxygen species (ROS) scavengers to deliver the KCC2 agonist CLP-257 to the targeted areas affected by spinal cord injury.⁶⁵ This nano-carrier exhibits high sensitivity to ROS stimulation, mitigates the accumulation of ROS in the lesion area, and activates the dormant neural circuits by stimulating the KCC2 gene and reducing the excitability of inhibitory interneurons. In addition, gasotransmitters such as nitric oxide (NO), hydrogen sulfide, and carbon monoxide can be released from the corresponding donors in the presence of enzymes or intercellular reducing agents such as glutathione and play crucial roles in synaptic plasticity and neural communication.^66–68 Modifying the gasotransmitter donor with peptides or targeted substances to form nanoparticles can improve the stability and efficacy of gasotransmitters. For example, Pal et al. developed a new method for delivering NO by combining a self-assembling peptide with a nitrated aspirin to form soft nanospheres that can control and sustain the release of NO in the presence of intercellular glutathione. The platform displayed a significantly greater amount of NO release in cellular environments, leading to neurite outgrowth.⁶⁹
只有少数研究报道了用于神经调节的内源性刺激响应系统。雷等人。通过分别用毒蕈碱激动剂卡巴胆碱和毒蕈碱拮抗剂阿托品负载铁蛋白纳米颗粒，激活或阻断胰腺癌中的神经微环境。铁蛋白纳米粒子可以在胰腺肿瘤的弱酸性环境（pH 6.5）中释放药物，并在肿瘤细胞的溶酶体（pH 5.0）中进一步释放药物，以调节胰腺癌进展的早期侵袭性生长和转移扩散。 ⁶⁴左等人。制作了一种含有硼基活性氧 (ROS) 清除剂的两亲性嵌段共聚物，可将 KCC2 激动剂 CLP-257 输送到受脊髓损伤影响的目标区域。 ⁶⁵这种纳米载体对 ROS 刺激表现出高度敏感性，减轻病变区域 ROS 的积累，并通过刺激 KCC2 基因和降低抑制性中间神经元的兴奋性来激活休眠的神经回路。此外，在酶或谷胱甘肽等细胞间还原剂存在的情况下，一氧化氮（NO）、硫化氢和一氧化碳等气体递质可以从相应的供体中释放出来，并在突触可塑性和神经通讯中发挥至关重要的作用。 ^66–68用肽或靶向物质修饰气体递质供体形成纳米颗粒可以提高气体递质的稳定性和功效。例如，帕尔等人。开发了一种递送 NO 的新方法，通过将自组装肽与硝化阿司匹林结合形成柔软的纳米球，可以在细胞间谷胱甘肽存在的情况下控制和维持 NO 的释放。该平台在细胞环境中显示出显着大量的 NO 释放，导致神经突生长。⁶⁹

In terms of external stimuli, optical stimulation stands out for its high spatial and temporal resolution but with limited penetration depth (∼1–1.5 mm).⁷⁰ Acoustic stimulation, especially through non-invasive methods like focus ultrasound (FUS), possesses the capacity to penetrate deep tissues (>50 mm) with a spatial resolution inversely related to the penetration depth (in general >1 mm³ and temporal precision >10 ms).^71,72 Furthermore, magnetic fields are recognized for their non-invasiveness and ability to access deep brain regions with little attenuation, presenting clinical pathways for treating neurological and psychiatric disorders.⁷³ The strategies to fabricate the controlled-release systems in response to these external stimuli are pretty similar to those used in drug delivery. For example, o-nitrobenzyl derivatives are commonly used for photolysis under a light stimulus to release the active neurochemical and gold nanoparticles are often used for photothermal triggered release. Meanwhile, micro/nano-bubbles are the most investigated delivery systems upon ultrasound stimulus and iron oxide nanoparticles are widely used for magnetic-thermal triggered release.
就外部刺激而言，光刺激因其高空间和时间分辨率而脱颖而出，但穿透深度有限（∼1-1.5 mm）。 ⁷⁰声刺激，特别是通过聚焦超声 (FUS) 等非侵入性方法，具有穿透深层组织 (>50 mm) 的能力，其空间分辨率与穿透深度成反比（一般 >1 mm ³ ，时间精度 > 10 毫秒）。 ^71,72此外，磁场因其非侵入性和能够以很小的衰减进入大脑深部区域而被认可，为治疗神经和精神疾病提供了临床途径。 ⁷³制造响应这些外部刺激的控释系统的策略与药物输送中使用的策略非常相似。例如，邻硝基苄基衍生物通常用于在光刺激下进行光解以释放活性神经化学物质，而金纳米颗粒通常用于光热触发释放。同时，微/纳米气泡是超声刺激下研究最多的递送系统，氧化铁纳米颗粒广泛用于磁热触发释放。

Despite the above similarity, delivering neurochemicals to the brain is challenging because of the complicated brain microenvironment and low active concentration of neurochemicals. Many advances have been made to develop various stimuli-responsive systems for neuromodulation, which are summarized below. Here, we delve into the unique attributes of each system and discuss the potential challenges and considerations pivotal to their application in neuromodulation.
尽管存在上述相似之处，但由于复杂的大脑微环境和神经化学物质的活性浓度较低，将神经化学物质输送到大脑仍然具有挑战性。在开发用于神经调节的各种刺激响应系统方面已经取得了许多进展，总结如下。在这里，我们深入研究每个系统的独特属性，并讨论其在神经调节中应用的潜在挑战和关键考虑因素。

3.1. Light-responsive
3.1.光响应

Expanding the spectral absorption range of materials into the NIR region has notably advanced the development of stimulus-responsive materials. The NIR spectrum (700–1700 nm), especially the second NIR window (NIR-II, 1000–1700 nm), offers distinct advantages over the visible spectrum (400–700 nm), including deeper tissue penetration and reduced phototoxicity.^74,75 Consequently, this opens promising avenuesfor conducting neuroimaging and neuromodulation studies in deep brain regions.^76,77 Neuromodulation via light-induced release of neuroactive substances involves five main mechanisms: photolysis, photoisomerization, photothermal, photomechanical, and photodynamic mechanisms.
将材料的光谱吸收范围扩展到近红外区域显着促进了刺激响应材料的开发。 NIR 光谱 (700–1700 nm)，尤其是第二个 NIR 窗口（NIR-II，1000–1700 nm），与可见光谱 (400–700 nm) 相比具有明显的优势，包括更深的组织渗透和降低的光毒性。 ^74,75因此，这为在大脑深部区域进行神经影像和神经调节研究开辟了有希望的途径。 ^76,77通过光诱导释放神经活性物质进行神经调节涉及五种主要机制：光解、光异构化、光热、光机械和光动力机制。

3.1.1. Photolysis mechanism
3.1.1.光解机理

Photolysis is a chemical process in which the molecules are broken down into smaller parts after photon absorption. By employing light to catalyze changes within molecules, the modulation of neuronal activity achieves exceptional spatial and temporal accuracy. Caged compounds are probes sensitive to light that package biomolecules in an inactive state with photoremovable protecting groups, which have been applied in various biomolecules such as neurotransmitters, neuropeptides, receptor agonists or antagonists, and metal ions.^78,79 Once initiated by light at specific wavelengths, the caged compounds can recover the activity with kinetic rates at the microsecond level.^80,81
光解是一种化学过程，其中分子在吸收光子后分解成更小的部分。通过利用光催化分子内的变化，神经元活动的调节实现了卓越的空间和时间精度。笼状化合物是对光敏感的探针，将生物分子以光可去除的保护基包装在非活性状态，已应用于各种生物分子，如神经递质、神经肽、受体激动剂或拮抗剂以及金属离子。 ^78,79一旦被特定波长的光引发，笼中的化合物就可以以微秒级的动力学速率恢复活性。 ^80,81

Banghart et al. used a dimethoxynitrophenethyl (DMNPE) caging group, which contains a neutral methyl group, affording light-sensitive forms of the mu-opioid receptor agonist oxymorphone and the antagonist naloxone: photoactivatable oxymorphone (PhOX) and photoactivatable naloxone (PhNX) (Fig. 3(a) and (b)).³⁹ These molecules can be photoactivated in the brain with sub-second flashes of light through implanted optical fibers to drive rapid changes in neural circuit function (Fig. 3(c)). In vivo experiments showed that photoactivation of PhOX and PhNX in the brain leads to alterations in various pain- and reward-related behaviors (Fig. 3(d)–(f)). This approach facilitates detailed studies of opioid-sensitive circuits in animals and minimizes side effects due to drug action at other sites. More recently, the same group introduced a cutting-edge biomimetic caging strategy by extending the C-terminus of neuropeptides with photocleavable amino acids to emulate pro-neuropeptides.³⁷ Furthermore, the group synthesized CNV-Y-DAMGO, a novel caged version of the μ-opioid receptor-selective peptide agonist DAMGO.³⁸ The carboxy-nitroveratryl (CNV) group is appended to the N-terminal tyrosine phenol of DAMGO, which reduces the affinity of DAMGO for mu-opioid receptors. Photoactivation at the ventral tegmental area led to a fast increase of locomotor activity of mice after the flash in 1 second, reaching a transient steady state within 2 seconds. However, most of the protecting groups are sensitive to UV and violet wavelengths and have to be compatible with fiber photometry for in vivo applications. Meanwhile, the caged compounds, especially caged peptides, are not stable in vivo due to the degradation induced by the peptidase.^82,83 Jiang et al. employed NIR light to initiate the release of NO from the upconversion nano-carrier, through specifical cleavage of the S–NO bond in the photochemical donor by light-converted UV energy. In vivo studies demonstrated that this system fostered the regrowth of damaged motor neuron axons in zebrafish and enhanced motor function recovery in rats following traumatic spinal cord injury.⁴²
班哈特等人。使用二甲氧基硝基苯乙基（DMNPE）封闭基团，其中含有中性甲基，提供μ阿片受体激动剂羟吗啡酮和拮抗剂纳洛酮的光敏形式：光活化羟吗啡酮（PhOX）和光活化纳洛酮（PhNX）（图3（ a) 和 (b) )。 ³⁹这些分子可以通过植入的光纤通过亚秒级闪光在大脑中被光激活，从而驱动神经回路功能的快速变化（图 3(c) ）。体内实验表明，大脑中PhOX和PhNX的光激活会导致各种疼痛和奖励相关行为的改变（图3（d）-（f） ）。这种方法有助于对动物阿片类药物敏感回路进行详细研究，并最大限度地减少药物在其他部位作用引起的副作用。最近，该小组引入了一种尖端的仿生笼策略，通过用可光裂解的氨基酸延伸神经肽的 C 末端来模拟前神经肽。 ³⁷此外，该小组还合成了 CNV-Y-DAMGO，这是 μ-阿片受体选择性肽激动剂 DAMGO 的新型笼式版本。 ³⁸羧基硝基藜芦基 (CNV) 基团附加到 DAMGO 的 N 末端酪氨酸苯酚上，这会降低 DAMGO 对 mu-阿片受体的亲和力。腹侧被盖区的光激活导致小鼠的运动活动在1秒内闪光后快速增加，并在2秒内达到短暂的稳态。然而，大多数保护基团对紫外线和紫色波长敏感，并且必须与体内应用的光纤光度测定兼容。 同时，由于肽酶诱导的降解，笼状化合物，尤其是笼状肽在体内不稳定。 ^82,83江等人。利用近红外光，通过光转换的紫外线能量对光化学供体中的 S-NO 键进行特异性裂解，从而引发上转换纳米载体释放 NO。体内研究表明，该系统促进斑马鱼受损运动神经元轴突的再生，并增强大鼠脊髓损伤后运动功能的恢复。⁴²

The development of DNA technology has led to the emergence of various DNA-based materials with unique shapes and sizes through the classical Watson–Crick base pairing-enabled self-assembly. These structures can selectively release drugs in response to external stimuli by integrating different molecular switches.^84,85 Kohman et al. utilized an innovative photosensitive cross-linker-labeled DNA origami to encapsulate molecules for 240–400 nm light-induced release (Fig. 4(a)).⁴⁰ This photolabile cross-linker features an o-nitrobenzyl (o-NB) motif for photocleavage, an azido group for coupling with alkyne-functionalized oligonucleotides, and an activated carbonate group for conjugation to cargo molecules possessing a free amino group. The cargoes encapsulated within the DNA nanocages range from small molecules to full-sized proteins. This approach demonstrated that glutamate-loaded DNA nanocage could trigger Ca²⁺ signaling in primary hippocampal neurons in vitro (Fig. 4(b) and (c)). Similarly, Veetil et al. used cell-targeted icosahedral DNA nanocapsules combined with light-responsive polymers to achieve light-induced targeted delivery of small molecules to specific cells of C. elegans.⁴¹ The DNA nanocapsules are constructed by icosahedral DNA assembly methods, with a large internal space capable of loading stimuli-responsive polymers. Dehydroepiandrosterone, a neurosteroid known for enhancing neurogenesis and neuronal survival, and precisely controls when neurons are activated, is attached to 10 kDa dextran through a photocleavable 2,4-dimethoxy nitrobenzyl linker, and designed to be released upon photoirradiation at 400 nm. Modifications to the external surface of these nanocapsules enable targeting of specific cell types in Caenorhabditis elegans. Light-mediated release of DHEA immediately raised intracellular Ca²⁺ in neurons and revealed the kinetics of this precise neuronal activation. However, multifunctional polymer–DNA nanomaterials encounter several challenges, such as rapid metabolism, targeting inaccuracies, and instability, which currently restrict their clinical utility.⁸⁴
DNA技术的发展通过经典的沃森-克里克碱基配对自组装技术，出现了各种具有独特形状和尺寸的基于DNA的材料。这些结构可以通过整合不同的分子开关来选择性地释放药物以响应外部刺激。 ^84,85科曼等人。利用创新的光敏交联剂标记的 DNA 折纸来封装分子，以进行 240-400 nm 光诱导释放（图 4(a) ）。 ⁴⁰这种光不稳定的交联剂具有用于光裂解的邻硝基苯甲基( o -NB) 基序、用于与炔官能化寡核苷酸偶联的叠氮基以及用于与具有游离氨基的货物分子缀合的活化碳酸酯基团。 DNA 纳米笼内封装的货物范围从小分子到全尺寸蛋白质。该方法证明负载谷氨酸的DNA纳米笼可以在体外触发原代海马神经元中的Ca ²⁺信号传导（图4（b）和（c） ）。同样，Veetil等人。利用细胞靶向的二十面体 DNA 纳米胶囊与光响应聚合物相结合，实现光诱导将小分子靶向递送至秀丽隐杆线虫的特定细胞。 ⁴¹ DNA 纳米胶囊采用二十面体 DNA 组装方法构建，具有较大的内部空间，能够装载刺激响应聚合物。 脱氢表雄酮是一种神经类固醇，以增强神经发生和神经元存活而闻名，并精确控制神经元何时被激活，通过可光裂解的 2,4-二甲氧基硝基苄基连接体连接到 10 kDa 葡聚糖，并设计为在 400 nm 光照射时释放。这些纳米胶囊外表面的修饰能够靶向秀丽隐杆线虫中的特定细胞类型。光介导的 DHEA 释放立即增加了神经元中的细胞内 Ca ²⁺并揭示了这种精确的神经元激活的动力学。然而，多功能聚合物-DNA纳米材料面临着快速代谢、靶向不准确和不稳定等挑战，目前限制了其临床应用。⁸⁴

3.1.2. Photoisomerization mechanism
3.1.2.光异构化机理

Photoisomerization hinges on the capacity of specific molecules to modify their conformation in response to light exposure. A prime instance of this phenomenon is the controlled isomerization of azobenzene under UV/visible light. Azobenzene is characterized by its thermodynamically stable trans form and a metastable cis form. Exposure to UV light induces a transition from the trans form to the cis form (trans → cis). Conversely, the cis structure can revert to the trans configuration (cis → trans) when exposed to a particular wavelength of visible light or in darkness, thus realizing a fully reversible isomerization.^86–88 Due to its photochromic attributes, azobenzene is a pivotal element in various molecular devices and functional materials. In recent years, two photon excitation of azobenzene photoswitches has been used in the field of neuromodulation, which can achieve precise manipulation of glutamate receptors (GluRs) on neuronal cell membranes.⁸⁹ Recent advancements have extended the application of photoswitches to lipids, named “Photolipids”, which contain an azobenzene group in their lipid tails. Photolipids are innovative tools for modulating lipid bilayer properties with light, including the photoswitchable phosphatidylcholine derivative, azo-PC. Upon illumination, azo-PC changes structural conformation, thus modifying its lateral interaction within the lipid bilayer.^90–94 This functionality enables nanocarriers to dynamically control the release of cargo on demand through alterations in membrane permeability, presenting a novel approach for in situ manipulation of phospholipid bilayer membranes.^95,96
光异构化取决于特定分子响应光照射而改变其构象的能力。这种现象的一个主要例子是偶氮苯在紫外/可见光下的受控异构化。偶氮苯的特征在于其热力学稳定的反式形式和亚稳定的顺式形式。暴露于紫外线会诱导从反式形式转变为顺式形式（反式→顺式）。相反，当暴露于特定波长的可见光或黑暗中时，顺式结构可以恢复为反式构型（顺式→反式），从而实现完全可逆的异构化。 ^86–88由于其光致变色特性，偶氮苯是各种分子器件和功能材料中的关键元素。近年来，偶氮苯光开关的二光子激发被应用于神经调节领域，可以实现对神经元细胞膜上谷氨酸受体（GluRs）的精确操控。 ⁸⁹最近的进展已将光开关的应用扩展到脂质，称为“光脂质”，其脂质尾部含有偶氮苯基团。光脂质是用光调节脂质双层特性的创新工具，包括光可切换磷脂酰胆碱衍生物、偶氮-PC。光照后，azo-PC 会改变结构构象，从而改变其在脂质双层内的横向相互作用。^90–94这一功能使纳米载体能够通过改变膜渗透性来动态控制按需释放的货物，为磷脂双层膜的原位操纵提供了一种新方法。^95,96

In a recent study, Xiong et al. introduced a new type of photoswitching nanovesicles called “azosome,” made by adding azo-PC to precisely control neuronal activity.⁴³ Azo-PC can change shape reversibly when exposed to 365 nm and 455 nm light, significantly altering the lipid bilayer's thickness (Fig. 5(a) and (b)). This change is due to the random arrangement of cis-azobenzene groups in the bilayer and the reduced thickness, which increases the permeability of the cis-azo-PC bilayer. By using 365 nm and 455 nm light, substances can be quickly released from the azosome in less than three seconds. This study demonstrated that SKF-81297, a drug that activates dopamine D1-receptors, could be released from the azosome, activating primary striatal neuron cultures (Fig. 5(c)). The release from photoswitchable nanovesicles does not cause any side effects such as heat or ROS, providing a safe and precise tool for neuromodulation.
在最近的一项研究中，Xiong等人。推出了一种名为“azosome”的新型光开关纳米囊泡，通过添加偶氮 PC 制成，以精确控制神经元活动。 ⁴³ Azo-PC 在暴露于 365 nm 和 455 nm 光时可以可逆地改变形状，显着改变脂质双层的厚度（图 5(a) 和 (b) ）。这种变化是由于双层中顺式偶氮苯基团的随机排列和厚度的减小，从而增加了顺式偶氮-PC双层的渗透性。通过使用 365 nm 和 455 nm 光，物质可以在不到三秒的时间内从偶氮体中快速释放。这项研究表明，SKF-81297（一种激活多巴胺 D1 受体的药物）可以从偶氮体中释放，激活初级纹状体神经元培养物（图 5（c） ）。光开关纳米囊泡的释放不会引起任何副作用，例如热或ROS，为神经调节提供了安全而精确的工具。

3.1.3. Photothermal mechanism
3.1.3.光热机理

For photothermal triggered release, the materials absorb incident light and change light energy into heat, rapidly elevating the temperature. The localized heat can induce a phase transition in the temperature-sensitive delivery systems, such as the destabilization of liposome membranes or the liquefaction of hydrogel matrices, leading to the controlled release of the encapsulated neuromodulators.^97,98 Li et al. synthesized a drug delivery system composed of conjugated polymer as a photosensitive group and fasudil as the drug cargo to achieve photothermal modulation of depression-related ion channels by releasing drugs with NIR light.⁴⁷ The photothermal conversion efficiency of NPs-F was 57.48% under 808 nm laser irradiation, ensuring the nanoparticles reached 40–42 °C for the drug release in 50 s. Conjugated polymer nanoparticles successfully crosses the BBB by increasing the permeability of the BBB through local heat generation, and significantly reduces firing frequency of ventral tegmental area dopamine neurons which are involved in depression-like behaviors. In parallel, the Kohane lab has made significant contributions to the field of local analgesia.^44–46 By attaching gold nanorods to thermosensitive liposomes, tetrodotoxin (TTX) or other nerve-blocking agents can be released under the NIR light (Fig. 6(a)). Gold nanorods were synthesized with pronounced absorbance at 730 nm, coinciding with the peak absorbance wavelength of the photosensitizer in liposomes. These liposomes offer remotely regulated, sustained local anesthesia and enable a specified release event or degree of nerve blockade at reduced irradiance, enhancing safety, or achieving deeper tissue penetration at the same irradiance level (Fig. 6(b) and (c)). Furthermore, the development of low-temperature-sensitive liposomes with gold nanorods enables more efficient light absorption, minimizes thermal toxicity risks, and reduces the irradiation time needed for drug release.⁴⁶ 1-Palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine is the key component of the low-temperature-sensitive liposomes, which could form nanopores in the liposomes at mild hyperthermia and accelerate the escape of the payload.
对于光热触发释放，材料吸收入射光并将光能转化为热量，从而迅速升高温度。局部热量可以诱导温度敏感的递送系统中的相变，例如脂质体膜的不稳定或水凝胶基质的液化，从而导致封装的神经调节剂的受控释放。 ^97,98李等人。合成了一种由共轭聚合物作为光敏基团和法舒地尔作为药物载体组成的药物递送系统，通过近红外光释放药物来实现抑郁相关离子通道的光热调节。 ⁴⁷ NPs-F 在 808 nm 激光照射下的光热转换效率为 57.48%，确保纳米颗粒在 50 s 内达到 40-42 °C 的药物释放。共轭聚合物纳米粒子通过局部发热增加血脑屏障的渗透性，成功穿过血脑屏障，并显着降低参与抑郁样行为的腹侧被盖区多巴胺神经元的放电频率。与此同时，小羽实验室为局部镇痛领域做出了重大贡献。 ^44-46通过将金纳米棒附着到热敏脂质体上，河豚毒素（TTX）或其他神经阻滞剂可以在近红外光下释放（图6（a） ）。合成的金纳米棒在 730 nm 处具有明显的吸光度，与脂质体中光敏剂的峰值吸光度波长一致。 这些脂质体提供远程调节、持续的局部麻醉，并在降低的辐照度下实现指定的释放事件或神经阻滞程度，增强安全性，或在相同的辐照度水平下实现更深的组织穿透（图6（b）和（c） ）。此外，开发具有金纳米棒的低温敏感脂质体可以更有效地吸收光，最大限度地降低热毒性风险，并减少药物释放所需的照射时间。 ⁴⁶ 1-棕榈酰-2-羟基-sn-甘油-3-磷酸胆碱是低温敏感脂质体的关键成分，在温和的高温下可以在脂质体中形成纳米孔，加速有效负载的逃逸。

Composite hydrogels, which swell when heated to release drugs, have also proven useful in neural regulation.⁹⁹ Li et al. crafted microscale thermosensitive composite hydrogels from poly(N-isopropylacrylamide) (pNIPAM) infused with polypyrrole (PPy) nanoparticles. The pNIPAM hydrogel offers a thermally responsive capability, while the PPy nanoparticles serve as photothermal transducers. The system can deliver various neuro-modulating molecules, including small chemicals and large proteins, without relying on complex chemical bonding processes to link the molecules together.⁴⁸ NIR-triggered delivery of glutamate into the rat auditory cortex resulted in synchronized spiking activity, showcasing the potential for non-invasive neural modulation in living organisms. Similarly, other researchers have demonstrated thermoresponsive hydrogels of different designs can utilize the thermal effects generated by photoinduction for the targeted release of local anesthetics, thereby extending the drug's period of effectiveness.^100,101 These investigations highlight the capability of photothermal methods to precisely modulate neural activity. Nonetheless, extensive research is necessary to thoroughly assess the long-term impacts and the safety of photothermal effects in living organisms.
复合水凝胶在加热时会膨胀以释放药物，也被证明可用于神经调节。 ⁹⁹李等人。由注入聚吡咯（PPy）纳米粒子的聚（ N-异丙基丙烯酰胺）（pNIPAM）制成的微型热敏复合水凝胶。 pNIPAM 水凝胶具有热响应能力，而 PPy 纳米颗粒则充当光热传感器。该系统可以输送各种神经调节分子，包括小化学物质和大蛋白质，而不依赖复杂的化学键合过程将分子连接在一起。 ⁴⁸近红外触发的谷氨酸递送至大鼠听觉皮层导致同步尖峰活动，展示了生物体中非侵入性神经调节的潜力。同样，其他研究人员也证明了不同设计的热响应水凝胶可以利用光诱导产生的热效应来定向释放局部麻醉剂，从而延长药物的有效期。 ^100,101这些研究凸显了光热方法精确调节神经活动的能力。尽管如此，还需要进行广泛的研究来彻底评估光热效应对生物体的长期影响和安全性。

3.1.4. Photomechanical mechanism
3.1.4.光机械机构

Nanomechanical transduction in plasma nanovesicles irradiated by a single, short laser pulse has shown great promise in neuromodulation. When subjected to ultrashort laser pulse irradiation (ps, fs), nanovesicles integrated with or coated by plasmonic gold structures rapidly heat to elevated temperatures. This heating stimulates the formation of transient nanoscale vaporizing bubbles that undergo growth and rupture within nanoseconds, producing nanoscale mechanical effects that allow cargo to leak out of nanovesicles.^102–104 For example, Nakano et al. linked hollow gold nanoshells (HGNs) to liposomes by thiol–gold interaction to develop a nano-carrier for the controlled release of neuromodulators (glutamate, potassium chloride, muscimol and specific dopamine agonists) upon exposure to an 890 nm femtosecond laser.⁴⁹ This system enables repeated, multiple releases and significantly impacts long-term synaptic plasticity (Fig. 7(a)). In a parallel study, Li et al. utilized NIR laser pulses to liberate cytoplasmic inositol triphosphate (IP3) from liposomes coated with gold nanoparticles ranging from 2.1 to 5.3 nanometers.⁵⁰ The phenomenon of strong plasmonic coupling among assemblies of gold nanoparticles induces a red shift in the localized surface plasmon resonance spectra. This shift not only augments the surface-enhanced Raman scattering properties but also significantly improves photothermal conversion efficiency.^105–107 This technique facilitates cellular signaling activation in a non-thermal, ultrarapid, and exceptionally precise manner, underscoring the efficacy of photomechanical approaches in accurately governing intracellular processes without heat generation (Fig. 7(b)).
单一短激光脉冲照射的等离子体纳米囊泡中的纳米机械转导在神经调节方面显示出了巨大的前景。当受到超短激光脉冲照射（ps、fs）时，与等离子体金结构集成或涂覆的纳米囊泡迅速加热至高温。这种加热刺激瞬态纳米级汽化气泡的形成，这些汽化气泡在纳秒内生长和破裂，产生纳米级机械效应，使货物从纳米囊泡中泄漏出来。 ^102–104例如，Nakano等人。通过硫醇-金相互作用将空心金纳米壳 (HGN) 连接到脂质体，开发出一种纳米载体，用于在暴露于 890 nm 飞秒激光时控制神经调节剂（谷氨酸、氯化钾、蝇蕈醇和特定多巴胺激动剂）的释放。 ⁴⁹该系统可实现重复、多次释放，并显着影响长期突触可塑性（图 7(a) ）。在一项平行研究中，Li等人。利用近红外激光脉冲从涂有 2.1 至 5.3 纳米金纳米颗粒的脂质体中释放细胞质肌醇三磷酸 (IP3)。 ⁵⁰金纳米粒子组件之间的强等离子体耦合现象会引起局域表面等离子体共振光谱的红移。这种转变不仅增强了表面增强拉曼散射特性，而且还显着提高了光热转换效率。^105–107该技术以非热、超快速和异常精确的方式促进细胞信号激活，强调了光机械方法在准确控制细胞内过程而不产生热量方面的功效（图 7(b) ）。

Furthermore, Xiong et al. constructed gold-coated mechanically responsive nanovesicles with the artificial phospholipid Rad-PC-Rad and gold-coating (Fig. 7(c)).⁵¹ They synthesized 1,3-diamidophospholipid Rad-PC-Rad by replacing the carboxylic acid ester part of the natural phospholipid with an amide bond. They also altered its structure at the glycerol backbone from the natural sn-1,2 to a sn-1,3 arrangement. With the particular structure, Rad-PC-Rad could form intermolecular H-bonding networks and d-shaped liposomes with defect edges, which are sensitive to shear stress.^108,109 The gold coating on the surface of these nanovesicles can be activated by NIR picosecond laser pulses, thus creating nanomechanical stress and leading to almost complete vesicle cargo release in sub-seconds. This novel ultra-photosensitive nanovesicle system combined the mechano-responsive nanovesicles and light-induced nanomechanical force and achieved efficient release down to 4 mm deep in the mouse brain. Furthermore, there was no global heating from the gold-coated mechanically responsive nanovesicles under the NIR laser pulse irradiation, minimizing the side effects. This system provides a new avenue for remote neuromodulation in deep brain regions.
此外，熊等人。用人工磷脂Rad-PC-Rad和金涂层构建了金涂层机械响应纳米囊泡（图7（c） ）。 ⁵¹他们通过用酰胺键取代天然磷脂的羧酸酯部分，合成了 1,3-二酰胺磷脂 Rad-PC-Rad。他们还将甘油主链的结构从天然的sn -1,2 排列改变为sn -1,3 排列。由于Rad-PC-Rad的特殊结构，可以形成分子间氢键网络和具有缺陷边缘的D形脂质体，对剪切应力敏感。 ^108,109这些纳米囊泡表面的金涂层可以被近红外皮秒激光脉冲激活，从而产生纳米机械应力，并导致在亚秒内几乎完全释放囊泡货物。这种新颖的超光敏纳米囊泡系统将机械响应纳米囊泡和光诱导纳米机械力相结合，并在小鼠大脑深处实现了4毫米的有效释放。此外，在近红外激光脉冲照射下，镀金的机械响应纳米囊泡不会产生全局加热，从而最大限度地减少了副作用。该系统为大脑深部区域的远程神经调节提供了一条新途径。

3.1.5. Photodynamic mechanism
3.1.5。光动力机制

In addition to the above methods, Kohane lab has engineered a photosensitive liposome with photosensitizer PdPC(OBu)8(18) for the photodynamically triggered release and on-demand nerve blockade.^52,53 When exposed to NIR light, the photosensitizer PdPC(OBu)8(18) generates ROS, leading to the peroxidation of unsaturated lipids within liposome membranes.⁸⁷ This chemical reaction initiates the formation of a new α-bond and a 1,5-hydrogen shift, transforming the lipid composition to a hydrophilic state. This alteration destabilizes the hydrophobic interactions essential for liposome integrity, thus facilitating the release of tetrodotoxin. Employing this innovative approach allows for multiple, adjustable instances of local anesthesia, demonstrating a significant advancement in controlled drug delivery mechanisms.¹¹⁰
除了上述方法外，Kohane 实验室还设计了一种含有光敏剂 PdPC(OBu)8(18) 的光敏脂质体，用于光动力触发释放和按需神经阻断。 ^52,53当暴露于近红外光时，光敏剂 PdPC(OBu)8(18) 会产生 ROS，导致脂质体膜内不饱和脂质发生过氧化。 ⁸⁷这种化学反应引发新 α-键的形成和 1,5-氢位移，将脂质成分转变为亲水状态。这种改变破坏了脂质体完整性所必需的疏水相互作用的稳定性，从而促进河豚毒素的释放。采用这种创新方法可以实现多次、可调节的局部麻醉，这证明了受控药物输送机制的重大进步。 ¹¹⁰

3.2. Ultrasound-responsive
3.2.超声波响应

Contrary to invasive techniques such as deep brain stimulation and spinal cord stimulation, which require surgical implantation and pose complications, ultrasound represents a safer, non-invasive alternative for brain stimulation. Furthermore, FUS offers greater spatial precision (targeting region dimensions up to 1–2 mm³) and the ability to effectively target deeper brain structures (several centimeters of penetration can be achieved clinically) than non-invasive methods such as transcranial electrostimulation and transcranial magnetic stimulation.⁷² Consequently, ultrasound neuromodulation has emerged as a potent instrument for investigating neural circuits and managing neurological disorders, attracting significant scientific interest. Sonogenetics, a novel neuromodulation approach derived from optogenetics and chemical genetics, employs acoustic stimulation to activate genetically modified expression of mechanosensory or temperature-sensitive ion channels, aiming to precisely modulate targeted neuronal populations.¹¹¹ In this study, we focus on the ultrasound-triggered release of neuromodulators rather than other ultrasound neuromodulation techniques.
与深部脑刺激和脊髓刺激等需要手术植入并造成并发症的侵入性技术相反，超声波代表了一种更安全、非侵入性的脑刺激替代方案。此外，与经颅电刺激和经颅磁等非侵入性方法相比，FUS 具有更高的空间精度（目标区域尺寸高达 1-2 mm ³ ），并且能够有效地瞄准更深层的大脑结构（临床上可以实现几厘米的穿透力）。刺激。 ⁷²因此，超声神经调节已成为研究神经回路和治疗神经系统疾病的有效工具，引起了科学界的极大兴趣。声遗传学是一种源自光遗传学和化学遗传学的新型神经调节方法，利用声刺激来激活机械感觉或温度敏感离子通道的基因修饰表达，旨在精确调节目标神经元群。 ¹¹¹在这项研究中，我们重点关注超声触发的神经调节剂释放，而不是其他超声神经调节技术。

3.2.1. Sono-mechanical mechanism
3.2.1.声波机械机构

Ultrasonic waves can generate high-intensity localized pressure waves, including cavitation and radiation, that can lead to temperature increases, mechanical stress, and cell death. Sonoporation employs acoustic cavitation in the ultrasonic range to enhance the permeability of the cell plasma membrane, which is widely used in molecular biology and non-viral gene therapy to facilitate the uptake of large molecules into cells.¹¹² In recent years, interest in sonomechanical-mediated neuromodulation has gradually increased.¹¹³ Recent developments in nanoparticle technology and FUS devices have created promising opportunities for targeted drug delivery across the BBB. Airan et al. demonstrated that applying transcranial FUS to polyethylene glycol-polycaprolactone block copolymeric nanoemulsions with a liquid perfluorocarbon core could induce a phase transition of perfluorocarbon from liquid to gas (Fig. 8(a)).^55,114 Propofol is a small molecule, fat-soluble drug that readily crosses the BBB and enters the brain through the bloodstream without compromising the integrity of the barrier. It is sonicated at a frequency of 1 MHz, allowing precise targeting within the brain (Fig. 8(b) and (c)). This approach significantly mitigated seizures in an acute rat epilepsy model, demonstrating the potent neuromodulatory effects of propofol when released in targeted brain regions. Moreover, the chemical properties of phase-change nanoparticles allow stable encapsulation of virtually any hydrophobic small molecule drug. Given that hydrophobic small molecules can generally cross the BBB, phase-change nanoparticles could in principle, encapsulate almost any drug of neuropsychiatric interest. The same group further employed a similar design to demonstrate how ultrasonic drug uncaging induces changes in the network-level functional connectivity, showing that it causes secondary changes in brain regions connected to the sonicated target.⁵⁵ Similarly, Lea-Banks et al. utilized ultrasound-responsive nanodroplets to trigger the release of pentobarbital under FUS for the local anesthesia in the motor cortex of rats without compromising the BBB's integrity.²⁸ The same team also reported the spatial precision of this nanodroplet-mediated drug delivery within the brain through direct mapping of BBB-penetrating dye release in both a simulated tissue model and the rat brain.¹⁵ Noteworthy, ultrasound-responsive nanodroplets offer significant advantages as drug carriers with limited systemic spread, longer circulation times than traditional microbubbles, and a specific vaporization threshold for controlled drug release.¹¹⁵
超声波可以产生高强度的局部压力波，包括空化和辐射，从而导致温度升高、机械应力和细胞死亡。声孔作用利用超声波范围内的声空化来增强细胞质膜的通透性，广泛应用于分子生物学和非病毒基因治疗，以促进大分子摄取到细胞中。 ¹¹²近年来，人们对声机械介导的神经调节的兴趣逐渐增加。 ¹¹³纳米颗粒技术和 FUS 设备的最新发展为跨 BBB 的靶向药物输送创造了充满希望的机会。艾兰等人。证明将经颅FUS应用于具有液体全氟化碳核的聚乙二醇-聚己内酯嵌段共聚物纳米乳液可以诱导全氟化碳从液体到气体的相变（图8（a） ）。 ^55,114异丙酚是一种小分子脂溶性药物，可轻松穿过血脑屏障并通过血流进入大脑，而不会损害屏障的完整性。它以 1 MHz 的频率进行声波处理，从而可以在大脑内精确定位（图 8(b) 和 (c) ）。这种方法显着减轻了急性大鼠癫痫模型中的癫痫发作，证明了异丙酚在目标大脑区域释放时具有强大的神经调节作用。此外，相变纳米粒子的化学性质允许稳定封装几乎任何疏水性小分子药物。 鉴于疏水性小分子通常可以穿过血脑屏障，相变纳米颗粒原则上可以封装几乎所有神经精神药物。该小组还采用了类似的设计来证明超声药物解禁如何引起网络级功能连接的变化，表明它会导致与超声处理目标相连的大脑区域发生二次变化。 ⁵⁵同样，Lea-Banks等人。利用超声响应纳米液滴在 FUS 下触发戊巴比妥的释放，对大鼠运动皮层进行局部麻醉，而不会损害 BBB 的完整性。 ²⁸该团队还通过在模拟组织模型和大鼠大脑中直接绘制 BBB 穿透染料释放图，报告了这种纳米液滴介导的药物在大脑内输送的空间精度。 ¹⁵值得注意的是，超声响应纳米液滴作为药物载体具有显着的优势，其全身扩散有限、循环时间比传统微泡更长，并且具有用于受控药物释放的特定蒸发阈值。¹¹⁵

Owing to the off-target effects within existing systemic treatments, central nervous system disorders pose significant treatment challenges. Ozdas et al. implemented a groundbreaking method by systemically injecting engineered ultrasound-controllable drug carriers and then applying an innovative two component Aggregation and Uncaging Focused Ultrasound Sequence (AU-FUS) to targeted areas within the brain (Fig. 9(a)).⁵⁴ Ultrasound-controlled drug carriers were developed by attaching drug-filled liposomes to ultrasound-sensitive microbubbles. These microbubbles have a core made of perfluorocarbon gas, and the liposomes can enclose a broad spectrum of small-molecule drugs. The attachment process utilizes thiol-maleimide chemistry, creating a carrier responsive to ultrasound for precise drug delivery. The initial sequence congregates drug carriers with millimeter accuracy in large numbers. The subsequent sequence releases the carrier's contents locally, ensuring high specificity towards the target without breaching the BBB. After the release, the drug can pass through the intact BBB locally (Fig. 9(b) and (c)). This approach allows for the circuit-specific modulation of sensory signaling in the motor cortex of rats by concentrating and liberating a GABAA receptor agonist from the ultrasound-controlled carriers. Notably, this method uses substantially less drug—1300 times less than traditional systemic injection techniques—and requires significantly lower ultrasound pressure, 20 times beneath the FDA's diagnostic imaging safety limit. It enables molecularly specific, localized modulation with minimal side effects, paving new paths for treating brain diseases.
由于现有全身治疗中的脱靶效应，中枢神经系统疾病带来了重大的治疗挑战。奥兹达斯等人。实施了一种突破性的方法，系统地注射工程超声可控药物载体，然后将创新的两部分聚集和解笼聚焦超声序列（AU-FUS）应用于大脑内的目标区域（图9（a） ）。 ⁵⁴超声控制的药物载体是通过将药物填充的脂质体附着到超声敏感的微泡上而开发的。这些微泡的核心由全氟化碳气体组成，脂质体可以包裹多种小分子药物。附着过程利用硫醇-马来酰亚胺化学，创建对超声波敏感的载体，以实现精确的药物输送。初始序列以毫米级精度聚集大量药物载体。随后的序列在本地释放载体的内容物，确保在不破坏血脑屏障的情况下对目标的高度特异性。释放后，药物可局部穿过完整的BBB（图9（b）和（c） ）。这种方法通过从超声控制的载体中浓缩和释放 GABAA 受体激动剂，可以对大鼠运动皮层中的感觉信号进行电路特异性调节。值得注意的是，这种方法使用的药物大大减少——比传统全身注射技术少 1300 倍——并且需要显着降低的超声压力，比 FDA 诊断成像安全限值低 20 倍。它能够以最小的副作用进行分子特异性、局部调节，为治疗脑部疾病铺平了新的途径。

3.2.2. Sonodynamic mechanism
3.2.2.声动力机制

The sonodynamic mechanism mainly relies on sonosensitizers to produce ROS under US stimulation and is often used in the sonodynamic therapy of tumors.¹¹⁶ Rwei et al. introduce this technique for ultrasound-triggered local anesthesia.⁵⁸ US acted on the sonosensitizer protoporphyrin IX in liposomes to generate ROS, peroxidating unsaturated lipids in the bilayers and leading to the cargo release. In vivo experiments showed that the US-triggered release of tetrodotoxin from the liposomes could achieve repeatable nerve blocks in rats, and the duration of the effectiveness of the nerve block depended on the extent and intensity of the ultrasound waves used. No effective nerve block occurred below ultrasonic intensities of approximately 1 W cm⁻², above which the duration of the nerve block increased with ultrasound intensity. And insonation pulses of 2, 5 and 10 min induced nerve blocks with mean durations of 0.2 h, 0.5 h and 2.3 h, respectively. Thereby, adjustments of US parameters enable precise control over the release amount and duration of tetrodotoxin, facilitating accurate management of local anesthetic effects. Such control meets diverse pain management needs with high reproducibility and safety, offering safer and more personalized treatment options for patients.
声动力机制主要依靠声敏剂在超声刺激下产生ROS，常用于肿瘤的声动力治疗。 ¹¹⁶ Rwei等人。介绍这种超声触发局部麻醉技术。 ⁵⁸ US 作用于脂质体中的声敏剂原卟啉 IX，产生 ROS，过氧化双层中的不饱和脂质并导致货物释放。体内实验表明，超声触发脂质体释放河豚毒素可以在大鼠中实现可重复的神经阻滞，并且神经阻滞有效的持续时间取决于所使用的超声波的范围和强度。在大约1 W cm ^-2的超声强度以下，没有发生有效的神经阻滞，高于该强度，神经阻滞的持续时间随着超声强度的增加而增加。 2、5 和 10 分钟的声波脉冲诱导神经阻滞的平均持续时间分别为 0.2 小时、0.5 小时和 2.3 小时。因此，调整超声参数可以精确控制河鲀毒素的释放量和持续时间，有利于精确管理局部麻醉效果。这种控制具有高重复性和安全性，满足多样化的疼痛管理需求，为患者提供更安全、更个性化的治疗选择。

Despite the promising prospects of US-triggered release for neuromodulation, several challenges, particularly concerning safety and drug delivery efficacy, remain to be addressed. The employment of perfluorocarbon-based systems, although therapeutically potential, involves a cavitation mechanism that incites safety concerns due to the risks associated with inertial cavitation and consequent microscale blood vessel deformations.¹¹⁷ Furthermore, the solubility of most drugs in perfluorocarbons is limited, curtailing the drug loading capacity within the particle shells. The ongoing refinement and exploration of these techniques not only promises to enrich our comprehension of neural circuits and signals but also to transform the treatment paradigm for neurological disorders.
尽管美国触发的神经调节释放前景广阔，但仍存在一些挑战，特别是在安全性和药物输送功效方面，仍有待解决。基于全氟化碳的系统的使用虽然具有治疗潜力，但涉及空化机制，由于与惯性空化和随之而来的微尺度血管变形相关的风险，该机制引起了安全问题。 ¹¹⁷此外，大多数药物在全氟化碳中的溶解度有限，从而限制了颗粒壳内的药物负载能力。这些技术的不断完善和探索不仅有望丰富我们对神经回路和信号的理解，而且还将改变神经系统疾病的治疗范式。

3.3. Magnetic field-responsive
3.3.磁场响应

Magnetic fields, which do not necessitate direct contact with the patient's body and provide real-time magnetic response, are considered one of the most effective external physical stimuli for the precise activation of drug release. Techniques for magnetic field-based neuromodulation through controlled release rely on magnetic nanoparticles (MNPs) that can convert magnetic fields into signals recognized by biological receptors.^118,119 These techniques are categorized into two principal types: magnetic-thermal mechanisms, which transform magnetic fields into heat, and magneto-mechanical mechanisms, which convert magnetic fields into force or torque. These mechanisms are discussed below.^73,120
磁场不需要与患者身体直接接触并提供实时磁响应，被认为是精确激活药物释放的最有效的外部物理刺激之一。通过受控释放进行基于磁场的神经调节技术依赖于磁性纳米粒子（MNP），它可以将磁场转化为生物受体识别的信号。 ^118,119这些技术分为两种主要类型：磁热机制（将磁场转化为热量）和磁机械机制（将磁场转化为力或扭矩）。下面讨论这些机制。 ^73,120

3.3.1 Magnetic-thermal mechanism
3.3.1磁热机制

Magnetic-thermal release of neuromodulators predominantly employs MNPs and alternating magnetic fields (AMFs). The magnetism of MNPs is closely related to their size, morphology, and structure. For example, particles below the 50 nm threshold can achieve higher heating efficiency, related to the relaxation time of MNPs in AMF.¹²¹ When exposed to AMF with sufficient frequency and intensity, MNPs can transform AMF energy into heat via hysteresis loss, thereby eliciting biostimulation.¹²² Distinct from the photothermal mechanism, a small range of thermal induction via MNPs in AMFs triggers the local release of neuromodulatory compounds, thus circumventing the possibility of thermotoxicity in the whole brain region.
神经调节剂的磁热释放主要采用 MNP 和交变磁场 (AMF)。 MNPs的磁性与其尺寸、形态和结构密切相关。例如，低于 50 nm 阈值的颗粒可以获得更高的加热效率，这与 AMF 中 MNP 的弛豫时间有关。 ¹²¹当以足够的频率和强度暴露于 AMF 时，MNP 可以通过磁滞损耗将 AMF 能量转化为热量，从而引发生物刺激。 ¹²²与光热机制不同，AMF 中 MNP产生的小范围热感应会触发神经调节化合物的局部释放，从而避免整个大脑区域发生热毒性的可能性。

Introducing a change in the chemical structure of the delivery systems by the heat generated by MNPs is a strategy for magnetothermal triggered release. In a pivotal study, Romero et al. utilized 4,4′-azobis(4-cyanovaleric acid) (ACVA), a thermal labile linker, covalently bonded to iron oxide MNPs. The isothiocyanate (AITC), a TRPV1 calcium channel agonist, was then conjugated to ACVA.⁵⁹ ACVA was cleaved under the magnetothermal to release AITC, allowing calcium to flow in by activating TRPV1 channels and activating specific neurons. This approach achieved pharmacological excitation of ion channel function with a latency of around 12 s and low particle concentration (three orders of magnitude less) than the studies using bulk heating of magnetothermal effect. Park et al. devised a method for local pH adjustment by combining MNPs with polyanhydrides (or polyesters), whereby MNP-induced heating accelerates hydrolytic degradation of polymers.⁶⁰ This degradation releases carboxyl groups, leading to a localized pH reduction around the acid-sensing ion channel (ASIC) (Fig. 10(a)). The deployment of such chemomagnetic nanosensors to transform AMF signals into protons facilitates ASIC-mediated signaling in neurons (Fig. 10(b)) and modulates the activity of ASIC-abundant neurons in the brain (Fig. 10(c)), offering novel insights into proton-mediated ion channel activation within the nervous system.
通过 MNP 产生的热量改变递送系统的化学结构是磁热触发释放的策略。在一项关键研究中，Romero等人。使用 4,4'-偶氮双（4-氰基戊酸）（ACVA），一种热不稳定连接体，与氧化铁 MNP 共价键合。然后将异硫氰酸酯 (AITC)（一种 TRPV1 钙通道激动剂）与 ACVA 缀合。 ⁵⁹ ACVA 在磁热作用下裂解，释放 AITC，通过激活 TRPV1 通道并激活特定神经元，使钙离子流入。与使用磁热效应整体加热的研究相比，该方法实现了离子通道功能的药理激发，延迟时间约为 12 秒，颗粒浓度较低（低三个数量级）。帕克等人。设计了一种通过将 MNP 与聚酸酐（或聚酯）结合来调节局部 pH 值的方法，从而 MNP 诱导的加热加速聚合物的水解降解。 ⁶⁰这种降解会释放羧基，导致酸敏感离子通道 (ASIC) 周围的局部 pH 值降低（图 10(a) ）。这种化学磁纳米传感器将AMF信号转化为质子，促进了神经元中ASIC介导的信号传导（图10（b） ），并调节大脑中ASIC丰富的神经元的活动（图10（c） ），提供了新颖的方法。深入了解神经系统内质子介导的离子通道激活。

Modulating the permeability of the liposome membrane through the heat generated by MNPs under AMFs is an alternative strategy for magnetothermal-triggered release. By elevating the external temperature beyond the phase transition temperature of the liposomes, their membrane shifts from a stable gel to a fluid state. This transition facilitates transient cavitation, characterized by microbubble formation and collapse, thereby enhancing membrane permeability.¹²³ For example, Rao et al. engineered temperature-sensitive nanoliposomes loaded with chemical payloads (drugs or receptor agonists and antagonists) and 25 nm iron oxide MNPs in the liposomes with a phase-transition temperature of 43 °C.⁶¹In vitro release tests showed that the payload released due to local MNPs heating inside magnetic liposomes increased with the duration of AMF stimulation, while only a negligible increase in the temperature of the bulk solution was observed. This method allows for the precise and temporal modulation of specific neural activities by remotely controlling drug release at particular brain regions. Furthermore, the targeted delivery of chemomagnetic particles to the ventral tegmental area facilitates the remote modulation of motivated behavior in mice. Similarly, coating with thermosensitive polymers achieves comparable outcomes. Guntnur et al. developed a method where MNPs were coated with thermoresponsive poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) brushes (Fig. 11(a)).⁶² These brushes collapsed upon heating, enabling the controlled release of dopamine through remote activation by AMF. This dopamine release amplified the response of dopamine ion channels on cell surfaces, boosting the activity of treated striatal neurons by approximately 50% (Fig. 11(b)). The applied 20 s of AMF was sufficient for MNPs to raise the local temperature and trigger the thermodynamic phase transition of POEGMA brush coating. During the 40 s of recovery, MNPs cooled down, allowing the reswelling of POEGMA brushes. The reversible thermodynamic phase transition of POEGMA brushes allowed for the on-demand release of dopamine in multiple microdoses to excite striatal neural activity (Fig. 11(c)). It is important to notice that this approach relies on local nanoscale heating effects. This method not only overcomes the possibility of therapeutic cargo degradation due to heat confinement inside the nano-carrier, but also offers reversible and safe temporal control over neuron-specific ligand–receptor interactions.
通过 MNP 在 AMF 下产生的热量来调节脂质体膜的渗透性是磁热触发释放的另一种策略。通过将外部温度升高到脂质体的相变温度以上，它们的膜从稳定的凝胶转变为流体状态。这种转变促进了瞬时空化，其特征是微泡的形成和破裂，从而增强了膜的渗透性。 ¹²³例如，Rao等人。工程化的温度敏感纳米脂质体负载化学有效负载（药物或受体激动剂和拮抗剂）和脂质体中的25 nm氧化铁MNP，相变温度为43°C。 ⁶¹体外释放测试表明，由于磁性脂质体内局部 MNP 加热而释放的有效负载随着 AMF 刺激持续时间的延长而增加，而仅观察到本体溶液温度的增加可以忽略不计。这种方法可以通过远程控制特定大脑区域的药物释放来精确和暂时地调节特定的神经活动。此外，将化学磁性颗粒定向递送至腹侧被盖区有助于远程调节小鼠的动机行为。同样，用热敏聚合物涂层也能达到类似的效果。冈特努尔等人。开发了一种用热响应性聚（低聚（乙二醇）甲醚甲基丙烯酸酯）（POEGMA）刷涂覆 MNP 的方法（图 11（a） ）。 ⁶²这些刷子在加热时会塌陷，从而能够通过 AMF 远程激活来控制多巴胺的释放。 这种多巴胺的释放放大了细胞表面多巴胺离子通道的反应，将治疗后的纹状体神经元的活性提高了约50%（图11（b） ）。应用 20 秒的 AMF 足以使 MNP 升高局部温度并触发 POEGMA 刷涂的热力学相变。在 40 秒的恢复过程中，MNP 冷却，使 POEGMA 刷重新膨胀。 POEGMA刷的可逆热力学相变允许按需释放多微剂量的多巴胺以激发纹状体神经活动（图11（c） ）。值得注意的是，这种方法依赖于局部纳米级加热效应。这种方法不仅克服了由于纳米载体内的热限制而导致治疗性货物降解的可能性，而且还提供了对神经元特异性配体-受体相互作用的可逆且安全的时间控制。

3.3.2 Magneto-mechanical mechanism
3.3.2磁力机械机构

It is important to highlight that recent investigations have delved into the magneto-mechanical steering action of MNPs when subjected to a magnetic field. This mechanism facilitates remote manipulation of mechanical forces at the cellular or molecular scale at low-frequency AMFs without heat generation.^124,125 In the study conducted by Kondaveeti et al., magnetic-responsive hydrogels were formed by crosslinking alginate and xanthan gum with Ca²⁺ and in situ synthesis of MNPs.⁶³ The resultant repulsion or attraction between MNPs caused local compression and stretching of hydrogels under the external magnetic field and led to the levodopa release with a release rate of 64 ± 6% of the initial load after 30 hours. The cell adhesion and proliferation of human neuroblastoma SH-SY5Y cells on the levodopa-loaded magnetic hydrogels were observed when exposed to the static external magnetic field. This study reveals a strategy for customizing and developing new biocompatible, magnetic-responsive materials for controlled levodopa release and the treatment of Parkinson's disease.
需要强调的是，最近的研究深入研究了 MNP 在磁场作用下的磁机械转向作用。这种机制有利于在低频 AMF 下在细胞或分子尺度上远程操纵机械力，而不产生热量。 ^124,125在 Kondaveeti等人进行的研究中。 ，通过用Ca ²⁺交联海藻酸盐和黄原胶以及原位合成MNP 形成磁响应水凝胶。 ⁶³ MNP 之间产生的排斥或吸引力导致水凝胶在外部磁场下局部压缩和拉伸，导致左旋多巴释放，30 小时后释放率为初始负载的 64 ± 6%。当暴露于静态外磁场时，观察人神经母细胞瘤SH-SY5Y细胞在负载左旋多巴的磁性水凝胶上的细胞粘附和增殖。这项研究揭示了定制和开发新型生物相容性磁响应材料的策略，用于控制左旋多巴释放和治疗帕金森病。

However, the caveat is that the translation of MNPs into clinical settings is hindered by challenges related to cytotoxicity, genotoxicity, in vivo metabolic pathways, and other safety concerns of MNPs, all of which require exhaustive evaluation. Consequently, the advancement of MNP-based drug delivery systems necessitates collaborative efforts across disciplines and detailed research to verify their safety and efficacy, as well as optimize their therapeutic potential.⁷³ Furthermore, achieving magnetochemical neuromodulation in cells and various neuron populations in larger animals, such as primates, remains an imperative goal.
然而，需要注意的是，MNP 向临床环境的转化受到与细胞毒性、基因毒性、体内代谢途径以及 MNP 其他安全问题相关的挑战的阻碍，所有这些都需要详尽的评估。因此，基于 MNP 的药物输送系统的进步需要跨学科的合作和详细的研究，以验证其安全性和有效性，并优化其治疗潜力。 ⁷³此外，在灵长类等大型动物的细胞和各种神经元群体中实现磁化学神经调节仍然是一个迫切的目标。

4. Conclusions and perspective
4结论与展望

In the evolving landscape of neurotherapeutics, stimuli-responsive controlled release systems stand at the forefront of innovation, offering promising avenues for precise, targeted, and minimally invasive neuromodulation. Recent advances in this field, propelled by nanotechnology, have brought us closer to addressing some persistent challenges in neuromodulation. Specifically, it has examined delivery systems that utilize various energy exchange modes to address the limitations associated with direct physical or chemical stimulation, such as lack of specificity and invasiveness. However, there remains ample scope for improvement, especially from a material design standpoint.
在不断发展的神经治疗领域，刺激响应控制释放系统处于创新的前沿，为精确、有针对性和微创的神经调节提供了有前景的途径。在纳米技术的推动下，这一领域的最新进展使我们更接近于解决神经调节中一些持续存在的挑战。具体来说，它已经检查了利用各种能量交换模式来解决与直接物理或化学刺激相关的限制的输送系统，例如缺乏特异性和侵入性。然而，仍然有很大的改进空间，特别是从材料设计的角度来看。

First, enhancing the ability of these systems to penetrate the BBB with minimal invasiveness is crucial. The prevalent reliance on local injections presents a significant drawback, necessitating invasive procedures that heighten the risk of complications and restrict the broad applicability of these therapies. We should focus on exploring strategies for delivering these systems across the BBB into the central nervous system via transcellular or paracellular pathways, such as targeting receptors that promote endothelial transcytosis or transient opening BBB.¹²⁶ Designing materials and delivery systems capable of non-invasively overcome the BBB will not only expand the therapeutic window but also enhance patient compliance and curative effect. Second, it is vital to develop safer methods for neuromodulator release. While current techniques are effective, they can lead to undesirable side effects, such as heat generation or ROS production, negatively impacting neural activity and overall brain health. Innovating release mechanisms that avoid these complications, potentially through the employment of biocompatible materials and energy-efficient stimuli (e.g., the release triggered by nano-mechanical force), is essential for reducing side effects and enhancing therapeutic efficacy. Thirdly, prioritizing the exploration of interactions between nanomaterials and the brain is indispensable. Despite significant progress in designing and applying nanomaterials for neuromodulation, investigations into their long-term effects on neural tissues and the brain's milieu are limited. Bridging this knowledge gap is imperative to confirm the safety, efficacy, and biocompatibility of these systems over prolonged durations. It necessitates to conduct thorough biocompatibility evaluations and detailed mechanistic analyses.
首先，增强这些系统以最小侵入性穿透血脑屏障的能力至关重要。对局部注射的普遍依赖存在一个显着的缺点，需要侵入性手术，这增加了并发症的风险并限制了这些疗法的广泛适用性。我们应该重点探索通过跨细胞或细胞旁途径将这些系统穿过血脑屏障进入中枢神经系统的策略，例如靶向促进内皮转胞吞作用或短暂打开血脑屏障的受体。 ¹²⁶设计能够非侵入性克服 BBB 的材料和输送系统不仅可以扩大治疗窗口，还可以提高患者的依从性和疗效。其次，开发更安全的神经调节剂释放方法至关重要。虽然当前的技术是有效的，但它们可能会导致不良的副作用，例如热量产生或活性氧产生，对神经活动和整体大脑健康产生负面影响。创新释放机制，避免这些并发症，可能通过使用生物相容性材料和节能刺激（例如，由纳米机械力触发的释放），对于减少副作用和提高治疗效果至关重要。第三，优先探索纳米材料与大脑之间的相互作用是必不可少的。尽管在设计和应用用于神经调节的纳米材料方面取得了重大进展，但对其对神经组织和大脑环境的长期影响的研究仍然有限。弥合这一知识差距对于确认这些系统长期的安全性、有效性和生物相容性至关重要。 有必要进行彻底的生物相容性评估和详细的机制分析。

In conclusion, the latest developments in stimuli-responsive controlled release systems signal a new era in neuromodulation. Enhancing BBB penetration designs, formulating safer release techniques, and deepening our grasp of the nanomaterial–brain interface are essential research and development directions. Moreover, establishing clear, uniform criteria for toxicity and genotoxicity evaluation is crucial for the clinical development and application of these stimulus-responsive drug delivery nanoplatforms. With ongoing technological innovation and interdisciplinary collaboration, the future is poised for realizing safer, more effective, and personalized neuroregulatory applications.
总之，刺激响应控制释放系统的最新发展标志着神经调节的新时代的到来。增强BBB渗透设计、制定更安全的释放技术以及加深对纳米材料-大脑界面的掌握是重要的研发方向。此外，建立明确、统一的毒性和遗传毒性评估标准对于这些刺激响应性药物输送纳米平台的临床开发和应用至关重要。通过持续的技术创新和跨学科合作，未来有望实现更安全、更有效和个性化的神经调节应用。

Author contributions  作者贡献

All authors conceptualized the article, wrote the original draft, and reviewed/edited the article. H. X. served as a project administrator and provided funding acquisition.
所有作者都构思了这篇文章，撰写了初稿，并审阅/编辑了这篇文章。 HX 担任项目管理员并提供资金收购。

Conflicts of interest  利益冲突

There are no conflicts to declare.
没有需要声明的冲突。

Acknowledgements 致谢

This work was partially supported by the Science and Technology Program of Guangzhou (2024A04J4921 to H. X.), Guangdong Basic and Applied Basic Research Foundation (2023A1515110019 to H. X.), and Guangdong-Hong Kong Joint Laboratory for Psychiatric Disorders (2023B1212120004).
这项工作得到了广州市科技计划项目（2024A04J4921至HX）、广东省基础与应用基础研究基金（2023A1515110019至HX）和粤港精神疾病联合实验室（2023B1212120004）的部分支持。

Notes and references 注释和参考文献