Performance Comparison of Mechanical and Ferrofluidic Micropumps: Structural and Operational Perspectives

Abstract

Since the successful implementation of microfluidic technology in biomedical applications, research on micropumps—the central component of these systems—has gained significant momentum. Benefiting from advancements in pump materials and corresponding fabrication methods, micropumps have evolved from structurally complex mechanical designs to simpler non-mechanical configurations. This paper reviews well-developed mechanical micropumps, discussing their diaphragms, pump chambers, materials, and other aspects to outline their developmental trajectory and current applications, while also highlighting their limitations. After identifying the shortcomings of traditional micropumps, we introduce the concept of ferrofluid-based micropumps, emphasizing their structural simplicity, self-sealing capability, and recoverability. Previous research on ferrofluidic micropumps is summarized, demonstrating their superior performance in certain aspects. Finally, we provide an outlook on their potential applications in biomedicine and specialized fields.

1. Introduction

In biological [1,2,3,4], medical [5,6,7,8], and even space exploration [9,10] applications, precise control of minute fluid volumes—termed microfluidics [11,12,13,14]—has gained increasing attention. This technology encompasses fluid transport [15], separation [16,17], and mixing [18], exemplified by the following: (1) delivering biological samples to miniaturized analysis systems [19,20], (2) isolating magnetic beads from cells [21,22,23], and (3) conducting novel mixing reactions in microreactors [24,25]. While passive mechanisms like surface tension [26], gravity [27,28], or the Marangoni effect [29,30] can manipulate microfluids, they inherently lack control over flow volume, direction, and process termination—an unacceptable limitation for microfluidic systems requiring microliter-scale precision (e.g., insulin delivery [31,32]). This critical need for active actuation has driven the development of diverse micropumps [33,34,35,36] based on various working principles, each with distinct advantages and limitations. In recent years, microfluidics has been researched and applied in the biomedical and digital fields, as shown in Figure 1.

This review examines mechanical micropumps in microfluidics, analyzes their applications and shortcomings, and introduces an innovative alternative: ferrofluidic micropumps with superior performance characteristics.

In the 1980s, micropumps first found medical application when Sefton et al. [41] pioneered their use in controlled insulin delivery systems, maintaining diabetic patients’ blood glucose levels throughout the day while reducing needle frequency. For implantable micropumps, high volumetric flow rates are unnecessary (e.g., insulin requirements typically remain below 1 mL/day [42,43]), but precise dosing is critical. These systems must also generate sufficient back pressure to overcome substantial physiological pressures (approximately 25 kPa [44]). Furthermore, reliability, cost-effectiveness, and biocompatibility constitute essential evaluation metrics for implantable micropump designs [45,46,47]. Figure 2 shows some implantable microfluidic devices.

In recent years, miniaturized chemical and biological analysis systems [53,54,55] have garnered significant attention. Compared with conventional analytical platforms, these microsystems offer distinct advantages including reduced sample/reagent consumption [56], accelerated analysis rates, and minimized human-induced errors [57,58].

Micropumps represent ideal fluid-handling components for such systems, where their precise pumping capability ensures accurate reagent proportioning. However, widespread adoption remains hindered by fabrication complexity and high costs, leading researchers to prefer low-cost alternatives such as manual pipetting [59], external pneumatic actuation [60], or induced electroosmotic flow [61,62]. Current research has proposed several disposable micropump designs: Qi et al. [63] developed a reusable-magnet disposable electromagnetic micropump by decoupling expensive magnets from low-cost pump bodies; Meng et al. [64] created an economical PDMS-based micropump that uses medical-grade tape and filter paper to detect sickle cell detection, as shown in Figure 3 below; Ohashi et al. [65] engineered a sweat-collection chip incorporating disposable micropump components. Abate et al. [66] proposed a method to produce monodisperse emulsions using only microfluidic devices and manual syringes, eliminating the need for bulky pumps, control computers, and other additional equipment.

To address diverse application scenarios, over 200 novel micropump designs have been reported since their initial development. For systematic research, scholars typically classify micropumps into two categories based on the presence of moving parts [67]: (1) Mechanical micropumps containing oscillating diaphragms or pistons [68] as moving components, and (2) non-mechanical micropumps that convert various forms of non-mechanical energy into kinetic energy [69] without relying on moving parts. Mechanical micropumps, also termed displacement pumps, operate by displacing fluid through movable boundaries typically provided by pistons or elastic membranes [70], such as piezoelectric micropumps [71] and electrostatic micropumps [72]. In contrast, non-mechanical micropumps utilize field effects (e.g., electromagnetic [73] or thermal fields [74]) to induce ionization or phase changes in working fluids, thereby generating pressure and flow. Notably, we highlight an innovative design—the ferrofluidic micropump [75]—which leverages its unique liquid material (ferrofluid [76]) to achieve pumping through coordinated interaction with external magnetic fields.

To demonstrate the superior operational principles and application potential of ferrofluidic micropumps, we conduct a systematic comparison with mature mechanical micropump technologies. Our evaluation begins by classifying mechanical micropumps according to their actuator types, followed by detailed examinations of their core components, including pump bodies, diaphragms, and valves. Through this analysis, we identify inherent limitations of mechanical designs that highlight the advantages of ferrofluid-based alternatives. For standardized performance comparison, we employ two key metrics: maximum flow rate Q_max and maximum pressure difference ΔP_max, supplemented with dimensional parameters of pump chambers and diaphragms to assess spatial efficiency. Operational characteristics such as driving voltage U and working frequency f are analyzed for their impact on power consumption and operational safety. Notably, evaluation parameters for ferrofluidic micropumps shift focus from electrical inputs to magnetic field strength due to their fundamentally different actuation mechanism. The study presents three comprehensive comparison tables: one summarizing performance data of mechanical micropumps reported in the past decade, and another detailing geometric parameters (length, divergence angle, etc.) and materials of nozzle/diffuser elements used for flow rectification. Finally, we will select some mechanical micropumps and ferrofluidic micropumps and compare their flow rate and back pressure data to evaluate the performance of the two types of micropumps under conditions of comparable power consumption and safety levels. Special attention is given to the analysis of unidirectional valves and currently prevalent diffuser structures.

2. Mechanical Micropumps and Their Compositions

The current literature indicates that mechanical micropumps constitute the predominant category [77,78]. These pumps rely on internal movable boundaries or surfaces, typically implemented through either pistons or diaphragms [79]. While piston-based designs face challenges in miniaturized sealing technology, limiting their practical application, most contemporary mechanical micropumps employ deformable diaphragms as the dynamic boundary. The diaphragm’s oscillation modulates the pump chamber volume, enabling liquid transport through controlled pressure variations. A standard mechanical micropump comprises three key components: (1) a pump chamber (housing the diaphragm/piston), (2) an actuator, and (3) paired check valves (inlet and outlet), with the operational sequence illustrated in Figure 4. The actuator generates a driving force transmitted to the diaphragm, inducing pneumatic pressure changes that draw fluid into the chamber. This working principle exemplifies the fundamental mechanism of mechanical micropumps—coordinated interaction between the actuator and movable boundary to cyclically alter chamber volume (pressure), thereby producing controlled fluid discharge at specified flow rates.

It is important to note that micropump diaphragms are not always single-layer. For example, the multi-layer micropump developed by Nguyen et al. [80] contains three separate diaphragms, each driven by individual piezoelectric actuators, making it particularly suitable for peristaltic pumping. The structure is composed of four bonded material layers: the upper PDMS plate contains one rectangular channel and two inlet/outlet seals, while the lower PDMS plate integrates three rectangular micro-lightweight piezoelectric composite actuators, with an outer PMMA cover. During pumping, the actuators sequentially act on the three independent diaphragms, causing the fluid to move through the gaps to the outlet. When the first diaphragm is acted upon by the actuator’s force, fluid begins to enter; the system then applies force to the second diaphragm while removing the force from the first diaphragm, allowing the first diaphragm to return to its original position, creating a sealing effect that prevents backflow. Subsequently, the third diaphragm is forced to open the channel while the second diaphragm returns to its original state, pushing the fluid in the pump chamber out to the outlet. Finally, all diaphragms reset, completing the pumping process.

2.1. Actuator

Given the structural variations arising from different actuation principles, we categorize mechanical micropumps based on their actuator types. The predominant actuation methods include the following: piezoelectric [81,82,83], electrostatic [84], electromagnetic [85], pneumatic [86,87,88]. Current research indicates that piezoelectric actuators dominate the micropump field, representing the most extensively studied configuration.

The actuator applies force to the diaphragm, causing its deformation or displacement. Piezoelectric actuators operate based on the piezoelectric effect, where an applied voltage induces deformation in piezoelectric crystals (such as quartz and barium titanate-based ceramics), thereby deforming the attached diaphragm and altering the pump chamber volume. Electrostatic actuators essentially function as capacitors composed of two parallel electrodes, which exert force on the pump diaphragm positioned between the plates according to Coulomb’s law, resulting in its deformation. Electromagnetic actuators utilize magnetic effects, where external magnets apply force to either a pump diaphragm embedded with magnetic materials or a permanent magnet piston, inducing vibration. Pneumatic micropumps do not require specialized actuators.

Piezoelectric actuation, as the earliest driving principle applied in the field of micropumps, is characterized by a large driving force, long diaphragm stroke, and fast mechanical response. Currently, commercial piezoelectric materials mainly include lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF), and aluminum nitride (AlN). Among these, PZT materials are most commonly used due to their high electromechanical coupling coefficients, as evidenced by their adoption in studies by Munas et al. [89], Kan et al. [90], and Johnston et al. [91] using PZT-based piezoelectric actuators. Electrostatic actuators consist of conductive and insulating layers. The conductive layer typically employs metal thin films (aluminum, gold, copper) or doped semiconductors (polycrystalline silicon, graphene), while the insulating layer prevents short-circuiting between electrodes.

The fundamental structure of electromagnetic actuators resembles that of electromagnets, consisting of coils and magnetic core materials (e.g., Fe-Si alloys, Mn-Zn ferrites). The force exerted on the internal diaphragm can be expressed as

$$F={\displaystyle \frac{B^{2}S}{2{\mu }_0}}$$

(1)

where F represents the actuator force on the diaphragm (unit: newton, N); B denotes the magnetic flux density generated by the actuator (unit: tesla, T); S is the effective actuator area (unit: square meter, m²); μ₀ is the vacuum permeability (μ₀ = 4π×10⁻⁷ T·m/A). The magnetic flux density B can be approximated by

$$B={\mu }_{0}nI$$

(2)

where n is the number of coil turns per unit length; I is the current through the coil (unit: ampere, A).

$$B\propto \mathrm{c}{\displaystyle \frac{NI}{L}}$$

(3)

where I represents current (unit: A), and L denotes the characteristic length of the actuator coil. This indicates that the magnetic field strength is directly proportional to the number of coil turns and current, while inversely proportional to the actuator’s dimensions. Theoretically, achieving sufficient actuation force requires increasing coil turns and current while minimizing inter-coil gaps. However, excessive coil turns may lead to device bulkiness, and high current can cause Joule heating that risks actuator burnout. Current electrostatic actuators typically employ 50–200 coil turns. For particularly miniaturized MEMS micropumps, fewer turns are required—for instance, Amrani et al. [92] utilized a 12-turn coil to reduce device size.

The actuation mechanisms for mechanical micropumps are not limited to the four types mentioned above but also include other principles such as phase change actuation and shape memory alloy (SMA) actuation. Figure 5 summarizes the currently dominant actuator technologies in the field.

The author created a table (

Table 1. Advantages, disadvantages, and applications of various types of mechanical micropumps.

Type	Advantages	Disadvantages	Applications
Piezoelectric	High output pressure Fast response Low power consumption No thermal effect	High driving voltage Fragile Sensitive to air bubbles Complex manufacturing	Biomedical Engineering Electronics Cooling
Electromagnetic	High output pressure Wide flow range No thermal effect Diverse fluid compatibility	Interference of magnetic field High power consumption Large size Complex structure	Point-of-Care Testing Drug Infusion Pump
Thermopneumatic	Simple structure Fast response Capability to manipulate extremely small droplets	Significant heating effect Compatible with only certain fluids Low pressure	Inkjet Print Head Microthruster for Satellites Spacecraft
Phase change	Enormous driving force High output pressure Simple structure Disposable use and packaging	Low energy efficiency Thermal effects Unsteady flow rate High dependency on fluid properties	MEMS Cooling Micromixer
Shape memory alloy	High output pressure Compact design Long stroke Low noise	Low work efficiency Thermal effect issues Limited fatigue life	Industrial Automation Automotive Industry
Electroactive polymer	Low driving voltage Potential biocompatibility Relatively simple structure	Low output force Low pressure Slow response speed	Biomedical Engineering Microdosing Applications

) summarizing the advantages, disadvantages, and typical applications of several types of mechanical micropumps shown in Figure 5.

2.2. Diaphragm

The diaphragm serves the critical function of altering the pump chamber volume. As previously mentioned, flexible membranes are typically employed to provide movable boundaries. These diaphragms are generally positioned either at the periphery [93] or center [94] of the pump chamber and connected to fixed boundaries. The diaphragm thickness directly impacts both the micropump’s driving force [95] and durability [96]. Standard diaphragm thicknesses range from 5 μm to 500 μm. For instance, Lin et al. [97] developed a valveless pneumatic micropump with a 300 μm thick diaphragm.

The diaphragm of the piezoelectric micropump is bonded to the actuator and placed on a metal substrate. The arrangement of diaphragms in electrostatic micropumps is divided into two types: the monolithic long diaphragm (5 mm scale, 60 μm thickness) fabricated by Machauf et al. [98] in 2005, and the series of diaphragms (eight pieces, each 2.5 μm wide with 1.0 μm spacing) made by Lee et al. [99] in 2012. A single diaphragm can cause alternating changes in the pump chamber volume through its own vibration, whereas multiple diaphragms are arranged parallel to each other with equal spacing and rely on the sequential action of an external actuator to move the diaphragms in turn, thereby opening the flow channel. After the fluid passes through, the diaphragms immediately return to their original state to seal the flow channel and prevent backflow. Additionally, it should be noted that the diaphragm in an electrostatic micropump is located in the middle of the pump chamber, so the number and thickness of the diaphragms affect the smoothness of fluid flow and the effective volume of the pump chamber, respectively. For electromagnetic micropumps, the diaphragm must be able to respond to external magnetic forces. Therefore, magnetic materials (Fe₃O₄) need to be uniformly mixed into the conventional diaphragm material or a soft magnetic metal layer must be coated. In 2019, Tahmasebipour et al. [100] used Fe₃O₄-doped PDMS material to fabricate a diaphragm, which reduced the diaphragm recovery time while maintaining biocompatibility.

In theory, the diaphragms of micropumps can vibrate bidirectionally, which has spurred a new research direction: bidirectional pumping. Bidirectional pumping helps reduce the vacuum time during micropump operation and improves pumping efficiency. Lin et al. [101] proposed a three-electrode electrostatic soft pump capable of bidirectional pumping for robotic applications. Nicola et al. [102] developed a dual-enzyme micropump by embedding β-glucosidase and urease into a patch, demonstrating inward flow (0.95 ± 0.37 μm·s⁻¹, 20 mM) in a cellobiose environment and outward flow (1.46 ± 0.47 μm·s⁻¹, 20 mM) in the presence of urea.

For pneumatic micropumps, a diaphragm is not mandatory. Pneumatic micropumps can rely on gas pressure acting on the diaphragm [103,104] to induce compression or expansion. Alternatively, they may utilize direct gas-driven liquid flow without requiring a physical diaphragm to separate the gas and liquid phases. For instance, Ni et al. [105] designed a diaphragm-less pneumatic micropump incorporating a pair of thin check-valve baffles as a substitute for the pump diaphragm. The diaphragm-based approach is widely used in biomedical applications, primarily because it prevents gas–liquid contact within the pump, thereby avoiding drug contamination [106]. The diaphragm-less design, on the other hand, eliminates the need for complex diaphragm fabrication, significantly reducing manufacturing difficulty.

However, it is interesting to note that the field of droplet microfluidics, which is closely related to pneumatic micropumps, heavily relies on the use of membrane structures. Micrometer-sized droplets serve as ideal reactors for researchers [107], and these highly valuable droplets require the driving force provided by pneumatic micropumps and microfluidic chips with varying channel dimensions equipped with membrane valves [108]. These membrane structures can be categorized into single-layer valves and multi-layer valves, capable of performing functions such as droplet generation, sorting, guidance, and trapping. Abate et al. [109] developed a single-layer membrane valve capable of continuously regulating flow rates. This valve combines the simplicity and ease of fabrication of stamped microfluidic devices with the precise control characteristics of membrane valves. In 2010, Abate et al. [110] further utilized high-speed single-layer membrane valves to control flow rates and perform sorting functions, even extending their applicability to live cells. Agnihotri et al. [111] employed a large number of single-layer microvalves to create a highly biocompatible droplet splitting and merging system. This system was designed to synthesize droplets of varying concentrations and types, enabling them to carry biological samples. Figure 6 illustrates the operational workflows of several chips based on pneumatic micropumps, which are renowned for their uniquely complex chip architectures and extensive utilization of valves.

2.3. Valves

Valves are responsible for the rectification of microfluid flow [112]. To suppress backflow, researchers have introduced various types of valves. In the early stages of micropump development, Spencer employed active flap valves made of piezoelectric bimorphs with dimensions of 0.4 mm × 4 mm × 20 mm. However, the opening and closing of active valves require external energy input, which is detrimental to system integration and hinders the automation of micropumps and their systems. Currently, most micropumps utilize passive valves, such as the ball valve used by Liu et al. [113], the flap valve employed by Cesmeci et al. [114], and the umbrella valve adopted by Jie et al. [115]. These valves demonstrate effective rectification in micropumps and do not require additional energy for actuation. Microvalves are typically comparable in size to the micropump body and are often fabricated as an integrated unit. Meanwhile, in droplet-based systems, valves find more extensive applications, particularly membrane valves. For instance, the multi-layer valve system developed by Grover et al. [116] delivers a flow rate of up to 380 nL/s at a driving pressure of 30 kPa and reliably seals against fluid pressures of up to 75 kPa, providing a simple and robust integrated solution for fluid manipulation in complex glass-based microfluidic and electrophoretic analysis devices. Raveshi et al. [117] utilized a microfluidic system based on single-layer valves to achieve selective droplet splitting, enabling parent droplets to move freely on the chip while ensuring accurate positioning and expulsion of smaller daughter droplets.

Ongoing development and research on valves, particularly for pneumatically driven microfluidic components, continues to advance. In 2011, Roy et al. [118] reported a rapid fabrication technique and demonstrated its application in creating and assembling pneumatic valves in multi-layer microfluidic devices entirely made of thermoplastics. Unlike conventional normally open valves (NO valves), Mohan et al. [119] proposed a pneumatically actuated normally closed valve (NC valve), which enhances the portability of microvalve systems.

However, compared to other components of the pump, microvalves demand higher fabrication precision and more complex manufacturing processes due to their open–close functionality, posing certain challenges in production and application. Similarly to diaphragms, many microvalves exhibit extremely thin structures and are prone to irreversible plastic deformation or even failure due to long-term cyclic vibration and repeated actuation, ultimately leading to pump malfunction.

To address these issues, researchers have adopted tapered diffusers to replace microvalves in developing valveless micropump designs. These diffusers operate on Bernoulli’s principle, utilizing asymmetric inlet/outlet widths to regulate internal fluid pressure, thereby preferentially directing microfluidic flow from narrow to wide sections while increasing flow velocity. The diffusers reduce device complexity and manufacturing difficulty by eliminating movable microvalve components, allowing integration of rectifying elements with the micropump body, which simplifies fabrication and minimizes leakage risks. Without moving parts, the micropump’s lifespan is no longer limited by microvalve durability, significantly extending the system’s operational lifetime. It should be noted that diffuser dimensions critically influence internal flow velocity, requiring computational fluid dynamics analysis to determine optimal diffuser geometry for achieving stable flow conditions in the micropump system. Key design parameters include tube length, expansion angle, and wide/narrow section dimensions, with specific geometric parameters from various researchers’ micropump diffusers presented in

Table 2. Geometric and performance characteristics of nozzle/diffuser (valveless): (length: diffuser tube length; Width 1: narrow-end width; Width 2: wide-end width; No—not mentioned).

Ref.	Year	Type	Length (μm)	Width 1 (μm)	Width 2 (μm)	Height (μm)	Angle (°)	Material
[120]	2015	PE	3000	No	75	No	8	Si
[121]	2023	PE	700	300	100	500	No	PDMS
[122]	2020	PE	1093	67	40	No	7	Si
[116]	2019	PE(PZT-5A)	1300	130	70	100	10	No
[123]	2018	EM(Cu)	1100	125	50	500	10	PDMS
[124]	2020	ES(Cu)	2300	500	100	No	16	PDMS
[125]	2018	EM	1000	No	No	No	15.64	PDMS
[126]	2020	PE(PZT)	No	2000	200	100	No	PMMA
[127]	2014	FMP	7484	2796	1054	1000	13.2	PMMA
[128]	2015	FMP	4963	1000	200	450	9.5	PMMA
[129]	2012	FMP	7484	2796	1054	1000	13.2	PMMA
[88]	2022	PM	No	No	No	No	9.5	PMMA
[130]	2024	EM	1553	1080	600	No	17.6	PDMS
[131]	2018	PM	1000	182.8	30	200	14	No
[132]	2023	No	1452	2774	1000	1500	62.8	PMMA

.

2.4. Pump Chamber and Pump Body Materials

The shape of pump chambers varies, with circular [133] and square [134] designs being the most common. Electrostatic micropumps typically adopt a square chamber due to the arrangement of internal electrode plates. In the 1980s, high-strength materials such as stainless steel [71] and low-carbon steel [134] were initially used for pump bodies. However, due to their poor corrosion resistance and limited machining precision (micron-level), metal-based pump structures gradually fell out of favor. To achieve a smaller size and higher integration [135], researchers turned to silicon and glass [136,137,138], which offered superior machining accuracy. With advancements in fabrication technology, transparent polymer materials—such as polymethyl methacrylate (PMMA) [139,140] and polydimethylsiloxane (PDMS) [141,142]—have gained prominence. These materials are favored not only for their excellent biocompatibility [143] but also for their low manufacturing cost [144]. Notably, their transparency enables real-time observation of fluid dynamics inside the pump, providing deeper insights into pumping mechanisms. This also facilitates optical research methods, such as particle tracking velocimetry (PTV), further advancing micropump studies. However, a critical limitation of these polymers is their proneness to deformation at elevated temperatures (around 80 °C). Thus, environmental temperature control is essential during operation. Additionally, if electromagnetic coils are integrated, excessive Joule heating must be avoided to prevent plastic deformation, which could lead to structural failure.

2.5. Fabrication Techniques

The development of micropumps has been closely tied to advancements in pump body machining technologies. In the early stages, due to the maturity of mechanical machining, metal-based micropumps progressed more rapidly. For instance, W. J. Spencer [145] utilized stainless steel as the pump body material.

With the refinement of higher-precision photolithography and lower-cost injection molding processes, non-metallic micropumps emerged and eventually became mainstream. Today, the field of micropump manufacturing has incorporated technologies such as CNC machining [146], CO₂ laser micromachining, and 3D printing [147,148,149]. A schematic diagram of these Machining Methods is shown in Figure 7. These methods enable the fabrication of complex structures that are difficult to achieve using conventional techniques like photolithography, etching, or injection molding. This diversification in manufacturing processes has expanded design possibilities, allowing for more intricate and optimized micropump architectures.

In the current micropump manufacturing industry, few researchers have explored monolithic fabrication processes. Instead, most adopt a multi-layer fabrication [136] and assembly approach. For example, Li et al. [150] successfully integrated a three-layer complex structure into a single micropump chip by rapidly injecting liquid metal into blind-end microchannels. Ni et al. [151] developed a five-layer micropump structure consisting of a PDMS substrate, a thin PDMS functional layer, a 150 μm thick PDMS flexible membrane, a glass plate with through-holes, and a PDMS top layer for pneumatic actuation.

The multi-layer approach enhances manufacturing flexibility, enabling precise fabrication and assembly of differently shaped layers [152], while also improving overall machining accuracy [153]. However, post-assembly bonding and sealing remain major challenges. Figure 8 illustrates a micropump chip fabricated using this multi-layer assembly technique.

2.6. External Equipment of Micropump

External devices provide the driving force for micropumps. For piezoelectric and electrostatic micropumps, the primary external equipment is a power supply. For driving PZT, the most widely used actuator material, a driving voltage of 50–200 V [155,156] is required. Electrostatic micropumps usually demand even higher driving voltages, ranging from 200 to 1000 V [157]. To ensure safe operation, series resistors (to limit current) and TVS diodes (for electrostatic discharge protection) must be incorporated into the circuit. The high operating voltages lead to complex and costly driving electronics [158], making voltage reduction a key research goal for both piezoelectric and electrostatic micropumps [159].

Electromagnetic micropumps require a controllable power supply to drive an electromagnet, which actuates an internal magnetic diaphragm.

For pneumatic micropumps, a high-pressure gas source is needed to deliver chemically stable gas. Industrial systems typically use oil-free air compressors, while laboratory setups rely on miniaturized high-pressure gas cylinders. To ensure safe operation within the micropump’s pressure limits, a pressure-reducing valve must be integrated. Additionally, biomedical applications often require an extra filtration system, leading to increased complexity and hindering miniaturization efforts.

To address these challenges, researchers have explored alternative gas generation methods. For example, Ochoa et al. [160] demonstrated a compact pneumatic micropump system by filling the pump chamber with a yeast solution and drugs, which produced low-pressure actuation gas through fermentation, effectively reducing the system’s overall size.

2.7. Applications of Mechanical Micropumps

The earliest mechanical micropumps were applied in the medical field, including drug delivery systems [161,162,163,164], in vitro diagnostics [165], and mechanistic studies of artificial organs [166] (such as the liver). Examples include a miniature pulmonary artery cell culture chip using mechanical micropumps as the power source [167] and the highly reliable integrated microfluidic plate for cell culture-based multi-organ microphysiological systems developed by Al-Hilal et al. [168]. Indeed, micropumps are not far removed from our daily lives. The printers we commonly use today leverage the advantages of piezoelectric micropumps to precisely control ink dosage, delivering superior performance compared to earlier printers that relied on micro-heaters to generate bubbles (incidentally, this “bubble jet” technology can also be classified as a type of thermal bubble micropump, which similarly falls under the category of micropumps).

As shown in Figure 9, the author presents schematic diagrams and physical images of (a,b) pulmonary artery cells and (c) a multi-organ cell culture chip.

In the chemical field, micropumps are used for quantitative delivery and addition of reagents, such as experimental testing of new reactions [170] and etching solution dispensing in the semiconductor industry [171]. In environmental and energy applications, there are micropump-based portable water quality detectors [172,173] and fuel cells [174]; in scientific research, applications include droplet generation [175] and organ-on-a-chip culture [176,177]. In aerospace, microfluidic technology can integrate the functions of a traditional laboratory into a micron-scale chip. Utilizing suitable mechanical micropumps enables unmanned space experiments, overcoming limitations such as restricted space environments, high experimental costs, and reliance on manual operations. Additionally, it allows for long-term experiment operation and remote data recording [178].

In the future, microfluidic devices primarily based on mechanical micropumps may trend toward miniaturization and integration. However, it is regrettable that although most existing cases are exemplary in laboratory-scale miniaturization techniques, they remain essentially independent functional modules—analogous to individual components in an integrated circuit—rather than truly integrated systems. Thorsen et al. [179] pioneered the convergence of microfluidics and electronic circuits by using a chip as a comparator and enzymes as mediators. Through bacterial colonies producing fluorescent outputs analogous to signal outputs in electronic circuits, they successfully achieved genuine integration of a microfluidic system. Using this as a foundational clue, continued research into the integration pathway of micropumps will undoubtedly unlock new applications for such technology.

2.8. Failure of Mechanical Micropumps

The failure of mechanical micropumps can be divided into three types: material fatigue, drive system failure, and fluid compatibility. The diaphragm of mechanical micropumps may undergo highly irreversible deformation or fracture due to long-term repeated vibration or overloaded operation, and even increasing diaphragm thickness and limiting voltage [92] cannot completely prevent diaphragm failure. Drive system failure manifests as actuator failure, such as piezoelectric ceramic cracking or electromagnetic coil burnout, which can be avoided by limiting voltage [180] and enhancing heat transfer [181]. Additionally, pumping unsuitable fluids such as corrosive substances [182], high-viscosity solutions [158], and gas-containing liquids [183] may damage the micropump and cause failure.

All three types of damage can lead to micropump failure. Material fatigue is inherent to the working principle of mechanical micropumps and can only be mitigated, not completely avoided. This demonstrates that mechanical micropumps have unavoidable and irreparable design limitations, resulting in certain application shortcomings, including short lifespan, high susceptibility to damage, and non-repairability.

2.9. Challenges of Mechanical Micropumps

Compared to the ferrofluidic micropump to be introduced next, mechanical micropumps have certain disadvantages, which are mainly concentrated in three aspects: high manufacturing difficulty, reliance on high driving voltage or current, and short lifespan. The author will provide a brief analysis below.

First, the manufacturing difficulty of mechanical micropumps is reflected in two parts: the processing of tiny movable components and the assembly of various parts. (1) The fabrication of miniature components, such as thin films or microelectrodes, requires these extremely small components to be manufactured with uniform thickness, which poses a challenge to manufacturing technology. (2) The assembly of movable components is another point that differs from ferrofluidic micropumps. Most mechanical micropumps can only function properly after all components are precisely installed; otherwise, the pump will fail. The challenges associated with assembly at this micron scale are immense.

Second, the reliance of mechanical micropumps on high driving voltage or high current stems from their own driving principles: Mechanical micropumps that rely on high driving voltage are mainly piezoelectric and electrostatic micropumps. The former is because the deformation of the piezoelectric film is proportional to the electric field strength, and only a sufficient voltage-provided electric field can drive the extremely thin film; the latter requires sufficient electrostatic force to operate, but due to the micron-sized air gap between the electrodes, a high voltage is needed. Micropumps known for high current mainly involve thermal bubble micropumps and electromagnetic micropumps. The former requires significant Joule heat to heat the medium fluid, while the latter relies on high current to generate a large Ampere force (Ampere force is proportional to current intensity). High driving voltage or high current makes it difficult to ensure safety during their use. In contrast, the ferrofluidic micropump only requires a power supply with a voltage ranging from a few volts to over ten volts, and its maximum current generally does not exceed 0.5 A. Moreover, this power supply does not directly act on the micropump chip but drives the permanent magnet to indirectly act on the ferrofluid inside the chip.

Finally, due to long-term exposure to high voltage or current, as well as wear and tear or fatigue caused by repeated vibration of internal movable components, mechanical micropumps are more prone to failure compared to ferrofluidic micropumps. If any single component fails, the entire mechanical micropump’s lifespan ends, and it is difficult to repair.

In summary, the development of mechanical micropumps can focus on reducing manufacturing and assembly difficulties and achieving low-voltage, low-current driving. Additionally, using materials that are less prone to fatigue and fracture to make mechanical micropump components may also become a solution to the micropump’s pain points.

For a clearer understanding, we have compiled relevant mechanical micropump images in Figure 10, and some representative working data is shown in

Table 3. Geometric and performance parameters of some mechanical micropumps. (PEA: piezoelectric actuator; ESA: electrostatic actuator; PMA: pneumatic actuator; EMA: electromagnetic actuator. Note: The following symbols in the table represent: \—not applicable; No—not mentioned. Additionally, to ensure the clarity and esthetics of the table, the units of physical quantities are specified as follows and will not be repeated within the table: driving voltage: U–V, back pressure: P–kPa, flow rate: Q–mL/min, frequency: f–Hz, and length dimensions: thickness–μm; size–mm).

Ref.	Year	Type	Diaphragm	Thickness	Material	Size	Valve	U	P	Q	f
[120]	2019	PE(PZT)	PDMS	250	No	Φ12	Diffuser	50	0.2	20	100
[121]	2016	PE(PZT)	Si	<20	Si	10 × 10	\	80	3.1	0.36	2.52 k
[101]	2015	PM	PDMS	200	\	4 × 4	Yes	No	30	496	3
[188]	2025	PE(PZT)	No	No	No	Φ38	\	100	0.78	200.7	43
[115]	2024	PE(PZT)	Copper	200	No	No	Umbrella	110	42.3	767	400
[189]	2019	PE	PMMA	No	No	Φ40, t0.8	Umbrella	60	0.82	No	300
[131]	2018	EM(Cu)	PDMS	100	PDMS	Φ10	Diffuser	No	0.35	0.52	45
[132]	2020	ES(Cu)	Iron-based MG	No	PDMS	Φ8	Diffuser	20	No	0.17	1
[113]	2018	EM(Cu)	NdFeB	5000	Teflon	Φ2, H35	Ball	No	0.54	0.21	5
[81]	2021	PE	No	200	stainless steel	Φ18	Spring	300	No	No	60
[63]	2022	EM(NdFeB)	PDMS	275	PMMA	Φ6	No	4.8	0.5	0.86	50
[128]	2023	PE	PDMS	No	PMMA	78 × 12	Yes	150	1.7	700	716
[190]	2018	EM	PDMS	No	PDMS	No	Diffuser	1.4	1.2	76 μL	9
[157]	2025	PE(PZT)	No	No	resin	22 × 22 × 5	\	42	No	618	22.5 k
[191]	2024	PE(PZT)	PET	50–200	PMMA	Φ25, H3	Umbrella	300	18.7	41.4	No
[192]	2024	PE(PZT)	No	No	PET	10 × 10 × 1	Cantilever	200	100	99.6	790
[193]	2021	PE(PZT)	PDMS	200	PMMA	60 × 60 × 12	Ball	448	15.3	131.6	750
[194]	2019	PE(PZT)	PI	40	PMMA	100 × 20 × 15	Cantilever	300	15	0.1	60
[129]	2024	PE(PZT)	PDMS	600	PDMS	Φ10, H0.5	Diffuser	9	No	5.69	25
[195]	2024	PE(PZT)	No	\	resin	35 × 35 × 0.8	\	100	19.74	20.12	120
[196]	2020	PE(PZT)	Si	100	PMMA	Φ25, 4	Diffuser	45	No	9.1	No
[130]	2020	PE(PZT)	PMMA	200	PDMS	Φ10	Diffuser	100	0.35	150	600

.

3. Composition and Development Status of Ferrofluidic Micropumps

In the classification of micropumps, ferrofluid belongs to non-mechanical micropumps as it contains no movable mechanical components. However, it can also be considered a piston pump since the internal ferrofluid functions as a “piston”. Compared to various mechanical micropumps mentioned above, ferrofluidic micropumps demonstrate distinct advantages due to their unique composition—ferrofluid—including non-contact operation, repairability, self-sealing capability, long lifespan, and simple structure.

3.1. Ferrofluid

Ferrofluid is a special type of liquid, consisting of a stable colloidal suspension where magnetic particles are uniformly dispersed in a liquid carrier medium, appearing as a black colloidal substance. It was invented by Stephen in 1963 [197]. Normally, ferrofluid does not exhibit magnetism, but under a magnetic field, it demonstrates ferromagnetic properties [198] and aggregates toward areas of stronger magnetic field intensity. When subjected to a sufficiently strong permanent magnet, the ferrofluid coalesces into a compact liquid mass, forming a piston-like structure within microchannels. By moving the external magnetic source, this piston can be precisely controlled. A typical ferrofluidic micropump system [199] comprises the pump body, ferrofluid, external magnetic source, motor, and power supply. Unlike mechanical micropumps that require high voltage and energy consumption, the power supply in ferrofluidic micropumps only provides energy for the motor, with these motors typically operating at rated voltages below 20 V [200], endowing ferrofluidic micropumps with superior safety and energy efficiency characteristics. Figure 11 shows a physical image of the magnetic fluid.

3.2. Actuating Magnets

Early ferrofluidic micropumps employed electromagnets [201] with adjustable magnetic fields and no moving mechanical parts as external driving magnetic sources. For example, Gusenbauer et al.’s micropump [79] utilized ten electromagnets with 200-turn coils driven by a 1–6 A current. Compared to permanent magnets as alternative magnetic sources, electromagnets offer superior controllability by enabling magnetic field activation and intensity adjustment through current variation. However, electromagnets fail to provide the required magnetic field strength [202] (typically around 0.3 T for micropump operation) as theoretically expected, while also presenting Joule heating challenges [203]. Researchers have progressively adopted permanent magnets (NdFeB, SmCo, etc.) with diameters in the range of 6–10 mm [204], which can generate magnetic fields up to 1 T while maintaining compact dimensions comparable to buttons and exhibiting no heat generation. Magnetic field intensity adjustment can be achieved by modifying the size and quantity of permanent magnets. Furthermore, to fully utilize strong magnetic fields, the distance between external magnetic sources and the micropump body should be minimized (maintained below 1 mm) [205].

3.3. Valves and Sealing Means

Unlike other micropumps, ferrofluidic micropumps achieve self-sealing [206]. In addition to the actuating magnetic source, conventional ferrofluidic micropumps incorporate a stationary sealing magnetic source positioned between the inlet and outlet. This attracts part of the ferrofluid within the microchannel to form a seal [207]. The pumped liquid must be immiscible with the ferrofluid (achieved by ensuring incompatibility between the ferrofluid carrier liquid and the pumped liquid), while also exhibiting poorer wettability to the pump body than the ferrofluid. These conditions prevent backflow of the pumped liquid to the inlet. Consequently, ferrofluidic micropumps require no valves to suppress backflow. However, some researchers have incorporated check structures to accommodate specific designs. For instance, in 2018, Liu et al. [208] employed a C-shaped baffle with a 7.1 mm inner diameter and a 7.5 mm outer diameter in a ferrofluidic micropump; Zhu et al. [209] created a fish-mouth baffle to coordinate with kerosene-based ferrofluid in the micropump; and Tang et al. [210] fabricated a butterfly valve for the micropump using polyimide (PI) slices, movable magnets, and elastic silicone diaphragms.

3.4. Pump Body and Manufacturing

3.4.1. Classification of Pump Body Shapes

Current ferrofluidic micropump designs can be categorized into three types: annular, circular, and linear configurations. The annular pump design originated from Hatch et al.’s [205] pioneering work on ferrofluidic micropumps incorporating stationary magnetic sources for self-sealing functionality, representing the initial proposed micropump architecture (shown in Figure 12). Distinct from conventional micropumps, this design eliminates reliance on adhesives or sealants by utilizing the inherent properties of ferrofluid to achieve sealing.

3.4.2. Fabrication of Ferrofluidic Micropumps

To facilitate the observation of ferrofluid motion in micropumps, current mainstream pump body materials are predominantly transparent, including PMMA, PDMS, and glass. Important considerations include the following: PMMA’s poor heat resistance requires avoidance in environments at 80 °C or higher; while glass exhibits fragility and poor machinability with high processing costs, its chemical inertness makes it perfectly suitable for chemical microreactors [211,212,213].

Currently available fabrication methods primarily include the following options: ① Soft lithography, once introduced by Unger et al. [214] in the year 2000 in the journal Science, enables the creation of complex microchannels and is suitable for soft materials like PDMS, as demonstrated by Liu et al.’s [208] PDMS micropump with C-shaped baffles. ② MEMS processing employs lithography or etching to produce precise microchannels in rigid materials such as glass and silicon, exemplified by silicon-based pump bodies fabricated by Hatch et al. [205] in 2001 and Hartshorne et al. [215] in 2004. ③ Three-dimensional printing is exclusively applicable to resins and can construct complex micropump structures (e.g., miniature diffusers), though material limitations result in surface roughness—Gusenbauer et al. [79] utilized this approach in 2018, employing Stratasys J750 polymer to manufacture electromagnetically driven micropumps.

3.5. Pump Chamber and Piston of Ferrofluidic Micropumps

During the pumping process, the ferrofluidic micropump chamber is divided into inlet and outlet chambers by boundaries formed by the piston and stationary ferrofluid [76]. When the moving magnetic source aligns with the sealing magnetic source, the piston merges with the stationary ferrofluid into a single mass, eliminating the separation between the inlet and outlet chambers. As the moving magnetic source departs, the piston reforms and draws in the pumped liquid from the inlet, creating the inlet chamber between the inlet and the piston. When the pumped liquid reaches the outlet area, it stops and waits for the piston to remerge with the stationary sealing ferrofluid. Upon reforming, the area between the piston and the outlet becomes the outlet chamber, where the pumped liquid is finally expelled to complete the pumping cycle. During continuous operation, both inlet and outlet chambers coexist simultaneously, separated by the piston, with their volumes constantly changing.

3.6. Failure and Restart of Ferrofluidic Micropumps

Ferrofluidic micropumps contain no movable mechanical components, and their pumping failures can be categorized into three types: ① Piston disintegration: Due to excessive bubble presence [216] (caused by high-speed rotation or bubbles in the pumped liquid) or ferrofluid loss, the ferrofluid can no longer form a stable, compact piston that fills the channel cross-section, rendering the micropump non-functional. ② External actuation magnetic source failure, primarily occurring in electromagnets, manifested as excessive Joule heat generation and coil burnout. ③ Miscibility between the pumped liquid and ferrofluid or backflow through the boundary layer, resulting from incompatibility between the pumped liquid and selected ferrofluid type, requiring the selection of ferrofluid materials that are immiscible with the pumped liquid and exhibit higher affinity to the channel wall material.

For ferrofluidic micropumps, types ② and ③ can be avoided through proper selection of magnetic sources and ferrofluid types, while the first point indicates that a theoretically infinite lifespan is achievable by operating within appropriate speed ranges and timely ferrofluid replenishment. Below are the pumping performance data for selected ferrofluidic micropumps.

Table 4. Geometric parameters and performance characteristics of representative ferrofluidic micropumps (No—data not reported in the reference; \—parameter not applicable; +—variant based on prototype design; Φ—diameter; H—pump chamber/magnet height; d—hydraulic diameter of flow channel. The units for some parameters are listed as follows: Pressure—kPa, velocity—μL/min, size—mm, field—mT).

Ref.	Year	Construction	Pressure	Velocity	Material	Layer	Size	Fabrication	Magnet	Field
[75]	2024	Circle	1.35	1756.3	PMMA	2	Φ10, H0.5	No	PM, 1, Φ5	495
[217]	2020	Hemicycle	No	9.02	PMMA	2	Φ50, 0.4 × 0.4	CNC	PM, 2, Φ15, t5	160
[79]	2018	Annular	No	3.5 × 105	Stratasys J750	2	Φ80, H30, d7	3D Printing	EM, 10, 200 N, 1–6 A	No
[201]	2006	Annular	No	3.8	Si	4	No	Etching coating	PM, 2	95
[218]	2013	Annular	No	No	PDMS	3	Φ15, H0.5	Injection molding	PM, 1	No
[219]	2014	Annular+	No	128	PMMA	2	Φ21, d1	CO2 laser	PM, 2	No
[77]	2004	Circle	2	No	Si	2	15 × 28 × 0.8	MEMES	PM, 1, Φ3, t2	340
[220]	2015	Liner+	0.99	934	PMMA	6	Φ6, H1	CO2 laser	PM, 1	510
[221]	2015	Circle	0.65	1310	PMMA	4	Φ3.5, H2	CO2 laser	PM, 1, 4 × 6 × 2	1200
[208]	2018	Annular	1.13	49.32	PDMS	2	Φ25, H3.5	Soft lithography	PM	450
[222]	2012	Annular	0.66	93	PMMA	2	Φ21, d4	CO2 laser	PM	No
[215]	2004	Liner	12	No	Glass	2	3 × 4	Photo etching	PM, 2	No
[205]	2001	Annular	1.32	45.8	Si	4	No	Photo etching	PM, 1, Φ6, t3	350
[223]	2006	Liner	0.2	1200	Glass	\	Φ44	No	EM, 7	No
[224]	2005	Liner	2.5	30	PMMA	7	0.1 × 22 × 6	Powder blasting	PM, 1	80

shows geometric parameters and performance characteristics of representative ferrofluidic micropumps.

3.7. Application Fields

Due to their self-sealing and non-contact characteristics, ferrofluidic micropumps and their fundamental principles demonstrate significant application potential and value across multiple domains including biomedical applications [225,226,227], point-of-care diagnostics [228,229,230], bioanalysis [231,232,233], microelectronic cooling [234,235], as well as microgravity and extreme-environment applications [122,123]. For instance, Chang et al. [218] enhanced a ferrofluidic micropump structure by incorporating four 14 mm × 7 mm annular microchannels as reaction zones, developing a medium-flow-rate microchip for immunoassays. Ahn et al. [77] fabricated a semicircular ferrofluidic micropump device using silicon for contact-free biological sample handling. Peng et al. [124] successfully addressed 10 nl level microfluid manipulation in sealed glass wafers using ferrofluidic micropump principles, with important implications for electronics, biomedicine, and chemical synthesis. Park et al. [125] integrated magnetic beads with micropumps to create a miniature permanent magnet-driven bead extraction system, enabling precise bead retention and release operations for DNA extraction processes. Hamilton et al. [126] developed magnetically actuated pumps and valves for controlling low-magnetic swimmers, with this remote manipulation technology inspiring micropump researchers to implement targeted fluid and sample control in microdomains through ferrofluid-based remote actuation in microchips, potentially enabling precise cellular and fluid manipulation at the microscale. Based on microfluidic simulation analysis, Zhou et al. [236] proposed a semi-Y-shaped labyrinth seal to reduce leakage.

Although ferrofluidic micropumps do offer several unique advantages, they also suffer from certain inherent limitations—much like the fundamental drawbacks of most mechanical micropumps—which have hindered their widespread adoption. The key issues are outlined below: 1. Biocompatibility constraints: ferrofluid materials are generally incompatible with most biological substances and can contaminate pumped bio-samples. This significantly restricts their application in biomedical and diagnostic fields. 2. Long-term loss of ferrofluid: During extended operation, the ferrofluid may gradually be carried away by the working fluid, leading to volumetric loss and eventual failure of the pump. 3. Evaporation of carrier liquid: If a ferrofluidic micropump system remains idle for prolonged periods, the base carrier liquid in the ferrofluid may evaporate, resulting in loss of function.

Despite these challenges, researchers have begun exploring strategies to facilitate the practical implementation and real-world translation of ferrofluidic micropump technologies. In 2025, Li and his team completed a series of studies, including investigations into the driving mechanisms of ferrofluidic micropumps under annular microscale constraints [199], analyses of dynamic morphological transformations in rotating and stationary ferrofluids under varying magnetic field polarities and mass fractions [216], and research on bubble formation mechanisms within ferrofluidic micropumps [237]. These studies collectively advanced the practical application of ferrofluidic micropump technology.

3.8. Performance Comparison

Obviously, for micropumps, flow rate and back pressure are two extremely important parameters. To provide a more intuitive comparison of the performance between mechanical micropumps and ferrofluidic micropumps, the author presents a table comparing their flow rates and back pressures, along with evaluations based on their parameter ranges. Due to space constraints, the following discussion only addresses the micropumps included in the table and cannot fully cover all types or their precise upper and lower limits.

As shown in

Table 5. Comparison of pumping performance between mechanical micropumps and ferrofluidic micropumps.

Ref.	First Author	Year	Type	P (kpa)	Q (mL/min)
[75]	Wang, Y.	2024	Ferrofluidic Micropump	1.35	1756.3
[220]	Ashouri, M.	2015	Ferrofluidic Micropump	0.994	934
[221]	Ashouri, M.	2015	Ferrofluidic Micropump	0.647	1310
[202]	Liu, B.D.	2018	Ferrofluidic Micropump	1.13	49.32
[199]	Hatch, A.	2001	Ferrofluidic Micropump	1.32	45.8
[120]	Gidde, R.R.	2019	Piezoelectric Micropump (PZT-5A)	0.2	20
[134]	Aggarwal, S.	2016	Piezoelectric Micropump (PZT)	3.1	0.36
[188]	Huang, J.	2025	Piezoelectric Micropump (PZT-5A)	0.784	200.7
[63]	Qi, C.	2022	Electrostatic Micropump (NdFeB)	0.5	0.86
[208]	Liu, B.D.	2018	Electrostatic Micropump (Cu)	0.539	0.21
[190]	Rusli, M.Q.A.	2018	Electrostatic Micropump	1.2	0.076
[238]	Lin, Y.	2015	Pneumatic Micropump	30	496
[97]	Lin, J.L.	2022	Pneumatic Micropump	68.95	12.48
[138]	Ni, J.	2012	Pneumatic Micropump	25	0.034
[98]	Machauf, A.	2005	Electrostatic Micropump (Cu)	\	0.001
[239]	Han, J.	2012	Electrostatic Micropump (Cu)	\	0.11
[99]	Lee, K.S.	2013	Electrostatic Micropump (Cu)	\	40/250/150
[160]	Ochoa, M.	2012	Thermopneumatic Micropump	5.86	0.23

, the flow rate of current ferrofluidic micropumps (i.e., FM) can range from tens of ml/min to thousands of ml/min, while the back pressure generally fluctuates around 1 kPa, with a maximum of 1.35 kPa. In contrast, piezoelectric (PE) micropumps have a lower flow rate compared to ferrofluidic micropumps but can overcome a higher maximum back pressure. Moreover, there appears to be an inverse relationship between their flow rate and back pressure, requiring users to make a trade-off between the two values. Electromagnetic (EM) micropumps have a slightly narrower range of back pressure compared to piezoelectric micropumps but overlap significantly with the back pressure range of ferrofluidic micropumps. However, their flow rate only fluctuates within a few hundred nanoliters, failing to reach even 1 milliliter. Pneumatic (PM) micropumps exhibit an exceptionally high back pressure, reaching an astonishing 68.95 kPa, which is a remarkable figure, though their flow rate is relatively small. Data on electrostatic (ES) micropumps regarding back pressure is temporarily unavailable in the table, but their extremely low flow rate is already noteworthy. Limited data is available for thermal bubble (TPM) micropumps, but it can be observed that their back pressure is higher than that of conventional ferrofluidic micropumps, while their flow rate is relatively low. From this, it can be concluded that another advantage of ferrofluidic micropumps lies in their high flow rate, enabling them to handle most microfluidic pumping tasks.

4. Conclusions

In the above content, we have broadly summarized the application areas of mechanical micropumps and classified them according to their driving principles. Subsequently, we focused on describing the structures and working principles of four specific types of micropumps: piezoelectric micropumps, known for their fast response speed and high control precision; electrostatic micropumps, which are easily miniaturized and integrated; electromagnetic micropumps, recognized for their high output force and strong driving capability; pneumatic micropumps, valued for their simple structure and bio-sample compatibility. To enrich the discussion, we referenced the work of pioneers and colleagues in academia who have studied mechanical micropumps. We also introduced the novel ferrofluidic micropump, elaborating on its advantages, including a simple structure, no moving parts, long lifespan, non-contact manipulation, and low driving voltage. Performance parameters from numerous peer research findings were provided, revealing that ferrofluidic micropumps exhibit outstanding pumping performance in the field of micropumps. However, challenges hindering the practical application of ferrofluidic micropumps were also addressed, such as incompatibility with certain samples and the tendency of magnetic fluids to evaporate. These issues are expected to be resolved in future research.

Overall, micropumps play significant roles in biomedical, scientific research, and industrial applications. With their precise fluid volume control capabilities, they hold great importance in accurate drug delivery, implantable micropumps, and microfluidic chips as core research components. Different micropump principles suit various working scenarios, demonstrating advantages of miniaturization, high integrability, and automation. As primary micropump components, mechanical micropumps have matured considerably, giving rise to various actuation principles including piezoelectric, electrostatic, electromagnetic, and pneumatic types. These have found substantial applications supporting cell culture, bioanalysis, aerospace, and other fields. However, due to inherent actuation principles, mechanical micropumps face challenges like high fabrication difficulty, large driving voltages, and short lifespans that prove extremely difficult to resolve. Ferrofluidic micropumps, as a novel non-mechanical alternative, leverage their non-contact operation, self-sealing capability, long lifespan, and restartability to enable targeted biological sample manipulation, remote detection, and leak-free microelectronic cooling in vivo or in extreme environments. Compared to traditional mechanical micropumps, they demonstrate clearer advantages by maintaining pumping efficiency while reducing failure risks, offering higher environmental safety, and representing a micropump technology worthy of focused development.