Effects of Hydrophilicity, Adhesion Work, and Fluid Flow on Biofilm Formation of PDMS in Microfluidic Systems

Abstract

Polydimethylsiloxane (PDMS) has been the most widely used material in microfluidic systems, especially for cell biology applications. However, the antibacterial performance of PDMS in flow conditions has never been reported in the literature. In this paper, we analyzed the effects of contact angle (CA), adhesion force (work), and surface free energy on the antibacterial activities of PDMS by varying the ratio of curing agents (crosslinking degree) and surface modification with oxygen plasma. The results show that the Young’s modulus has no particular effects on bacterial adhesion compared to the CAs of samples. For the first time, we analyzed the adhesion work (AW) effect on biofilm formation, and we found that biofilms tend to form on the surface with less AW. Furthermore, we analyzed the dual effect of hydrophilicity and shear force induced by fluid flow on the bacterial adhesion in PDMS microfluidic systems. We found that at low flow rates in microfluidic conditions, the adhesion of the bacteria on the PDMS surface is inhibited when the fluid flow exceeds a certain value. It required higher shear force to inhibit bacterial adhesion on the hydrophilic surface than on the hydrophobic surface. Therefore, hydrophilicity might be the dominant factor affecting bacterial adhesion.

Implication of Surface Properties, Bacterial Motility, and Hydrodynamic Conditions on Bacterial Surface Sensing and Their Initial Adhesion

“…For instance, Rodesney et al (2017) found that applied shear stress to biofilm resulted in increased levels of c-di-GMP signal in P. aeruginosa, which then promote biofilm development. It has been proposed that fluid shear creates a positive feedback loop, initiating biofilm formation by stimulating EPS production and providing nutrients for growth (Zhu et al, 2020).…”

Merits and advances of microfluidics in the pharmaceutical field: design technologies and future prospects

“…Therefore, the unmodified PDMS is restricted to producing water in oil emulsion (w/o) (Mata et al., 2005 ). In order to increase the hydrophilic properties of PDMS, surface modifications can be done using ultraviolet irradiation, oxygen plasma (Long et al., 2017 ; Ruben et al., 2017 ; Zhu et al., 2020 ), corona discharge (Bashir et al., 2018 ), layer by layer deposition (Choi et al., 2018 ; Zhang et al., 2019 ), sol-gel methods (Abate et al., 2008 ), and surface treatment with surfactant (Fu et al., 2017 ; Khemthongcharoen et al., 2021 ). Using oxygen plasma, PDMS-based microfluidic surface modification carried out by Long et al.…”

A high-throughput integrated biofilm-on-a-chip platform for the investigation of combinatory physicochemical responses to chemical and fluid shear stress

“…Biofilms are surface-adhered aggregations of bacteria encased in a self-developed extracellular polymeric substance (EPS). EPS functions as a protective shield against environmental stresses, such as temperature variations, fluid shear stress (FSS), changes in ions, pH [1], and it also promotes antibacterial resistance [2]. For this reason, it is difficult to remove these 3D tissue-like structures from their substrates mechanically, and from the chemical point of view, the required dosage of an antibiotic drug to kill bacteria in a biofilm is usually higher than the concentration needed to kill them in the planktonic phase [3,4].…”

“…Physically, fluid shear stress is a key player in biofilm formation and behavior in the real world although it is still poorly understood to date [2,15]. Not only does the hydrodynamics of the bulk flow affect the biofilm's life-cycle, it can also have an impact on biofilm-chemical interaction [16].…”

“…A comprehensive understanding of the combined effect of physicochemical parameters, such as fluid shear stress and antibiotics, on biofilms is a crucial step in the neverending battle against bacteria [17]. Biofilms are exposed to various magnitudes of FSS in vivo, in piping systems, and also with respect to medical tools [1,2,18]. The FSS value may vary from 0-20 dyne/cm 2 covering a wide range of biological, biomedical, and industrial applications [4,12,[19][20][21][22][23][24].…”