With advances in point-of-care testing (POCT) in medicine, new research avenues are open for microfluidic technology. Microfluidic devices meet many strict requirements in POCT, such as portability and low test costs [1]. There have been considerable research advances in the field of microfluidic systems; however, controlling the flow continues to remain a challenge, especially in the field of POCT. In contemporary microfluidic systems, flow control is achieved using a traditional peristaltic pump, a syringe pump, or a pressurized flow controller; however, these usually need an additional external drive [2], making these methods not suitable for POCT. Self-driven microfluidic technology, on the other hand, is a new fluid control method that does not require external electronic components or moving parts, and it is robust, flexible, and portable. Examples of microfluidic systems are a finger driven pump [3], vacuum pump [4], capillary driven pump [5], paper driven pump [6] (including paper transverse flow and paper microfluidic components), and gravity driven pump [7] [8]. In some of these microfluidic technologies, it is challenging to accurately control the flow; also, they may not have large pumping capacities. Because of this, they are not suitable for application in fields that need a preset flow. In the past decade, degassing-driven modular plug-and-play PDMS micropumps and microfluidic chips have become an important part of self-driven microfluidic devices. Studies have demonstrated that silicone rubber has several advantages in “degassing driving fluid” technology. Silicone rubber is highly porous and has high permeability; it comprises a flexible silicone oxygen chain, provides free volume in its structure, and allows gas diffusion [9], because of which, it is widely used for manufacturing microfluidic devices.
The mechanism of the PDMS degassing drive flow depends on channel and equipment geometry, and it is sensitive to several parameters, as described by Zhao et al. [10] and Liang et al. [11]. Some studies have presented applications that have demonstrated the ability to control certain mechanisms based on this flow, such as point-of-care (POC) diagnostics [12, 13], digital PCR [14], and DNA analysis [15, 16]. In 2012, Maeda et al. proposed a simple flow control method for a polydimethylsiloxane (PDMS)-based microfluidic device [15]. In 2012, Zhao et al. reported a modular PDMS plug-and-play micropump [11]. The pressure produced by these micropumps can be adjusted by controlling parameters such as the surface area and volume of the PDMS coating; however, these devices focus on moving low-volume samples. Moreover, the pumping flow per unit time of the micropump is only in the nanoliter range in a 0.5-mm Teflon tube [11, 17, 18].
In 2016, Tanaka et al. [19] demonstrated an agarose micropattern method using degassed PDMS substrates and applied it in cell culture experiments. In 2015, Li et al. [20] established a degassed PDMS-based microfluidic droplet generator; it could generate monodispersed droplets. However, these pumping methods have short working durations and low efficiencies.
Microsystems are typically designed to analyze small sample sizes; however, some biomedical and environmental applications—that require detection of low concentrations of analytes—require processing of large volumes of fluids. For example, at least 1 mL of blood must be analyzed to detect one circulating tumor cell (CTC) in the early stage of the disease [21]. The same is true for the detection of nucleic acids, proteins, bacteria, or viruses in blood [22]. In such cases, a preconcentration step is usually required [23]. Contemporary self-driven microsystems can typically process a maximum of few microliters at a time, limiting their applications. In 2020, Jaione et al. proposed a modular polymer micropump that enables high-volume sample drive by using a combination of multiple modules [24]. However, when high pumping capacity is required in a short pumping time, several modules need to be overlapped, which makes the pump body too large.
To solve the abovementioned problems, we developed a self-driven micropump with a large driving capacity and stable pumping performance, as shown in Fig. 1. Compared with contemporary methods, the injection molding process using PDMS is highly versatile, simple, and enables rapid prototyping. Studies have shown that the pressure generated by PDMS is proportional to the effective surface area of the micropump [10]. Therefore, the micropump should have a higher effective area, that is, its porosity in a certain volume should be higher, to enable greater driving ability. Accordingly, in this study, we used a “sugar particle mixing method,” that is, a mixture of a PDMS crosslinking agent and brown sugar particles is cured. Then, the brown sugar is melted in a bath to achieve elasticity, porosity, and a large surface area of PDMS, achieving a high driving force in the microfluidic device. Moreover, by controlling the thickness of the silicone package layer, the pumping capacity of the pump body can be controlled, providing flexibility for use in self-driven micropumps with different specifications and pumping needs.
This study describes the performance of self-driven micropumps and demonstrates their versatility with microfluidic devices designed for some common microfluidic operations using microfluidic networks such as mixing and bisection. Finally, we evaluate the performance of these devices and perform an independent colorimetric test for starch detection.