PDMS-Zwitterionic Hybrid for Facile, Antifouling Microfluidic Device Fabrication

Tuning the Surface Properties and Biofouling Resistance of Fluorinated Siloxane Copolymers

This study explores the suitability of fluorinated polysiloxanes in medical applications through biofouling studies with Escherichia coli MG1655 (E. coli) and Pseudomonas aeruginosa PAO1 (P. aeruginosa). Commercially available fluorinated poly(dimethylsiloxane) poly(trifluoropropyl methylsiloxane) (PTFPMS) exhibits a significantly higher resistance to biofouling compared to traditional poly(dimethylsiloxanes) (PDMS), such as Sylgard 184. The enhanced resistance is likely due to the reduction in surface energy and friction coefficients due to the incorporation of fluorine groups. Varying the fluorination content from 0 to 35 mol % trifluoropropylmethylsiloxane (TFPMS) in cross-linked PDMS exhibits consistent patterns in tribological and surface data: increased fluorination decreases friction and surface energy while increasing roughness. Profilometry reveals the formation of circular domains as fluorine groups are introduced, which increase in size with higher fluorine content. Corresponding roughness measurements show a significant rise in three dimensional (3D) root-mean-square roughness (Sq) from 0.07 ± 0.06 μm for PDMS to 1.89 ± 0.02 μm for 22.7 mol % TFPMS. Tribological data mirror the roughness trend: the friction coefficients decrease as roughness increases. Contact angle measurements for water increase from 100° to a plateau of 110°, while those for diiodomethane increase from 65° to a plateau of 90°. Contact angle hysteresis indicates that the minimum fluorination needed to impact hydrophobicity is 22.7 mol %. Lap shear tests confirm bulk adhesion of 35 mol % TFPMS to glass (0.45 ± 0.23 MPa) and to PDMS (0.10 ± 0.04 MPa). 35 mol % TFPMS exhibits 2.7 (rough) to 10 (smooth) times lower cell adhesion for E. coli and 1.7 (smooth) to 43 (rough) times lower cell adhesion for P. aeruginosa compared to PDMS. These findings highlight how a mechanistic understanding of how polymer structure and chemistry influence fouling resistance, with implications extending beyond the medical field to many industries requiring antifouling surfaces.

Antifouling Zwitterionic Polymer Coatings for Blood-Bearing Medical Devices

Blood-bearing medical devices are essential for the delivery of critical care medicine and are often required to function for weeks to months. However, thrombus formation on their surfaces can lead to reduced device function and failure and expose patients to systemic thrombosis risks. While clinical anticoagulants reduce device related thrombosis, they also increase patient bleeding risk. The root cause of device thrombosis and inflammation is protein adsorption on the biomaterial surfaces of these devices. Protein adsorption activates the coagulation cascade and complement, and this, in turn, activates platelets and white blood cells. Surface modifications with zwitterionic polymers are particularly effective at reducing protein adsorption as well as conformational changes in proteins due to their hydrophilicity. Multiple coating strategies have been developed using carboxybetaine (CB), sulfobetaine (SB), and 2-methacryloyloxyethyl phosphorylcholine (MPC) zwitterionic polymers applied to the metals and hydrophobic polymers that make up the bulk of blood-bearing medical devices. These coatings have been highly successful at creating large reductions in protein adsorption and platelet adhesion during studies on the order of hours on flat surfaces and at reducing thrombus formation for up to a few days in full medical devices. Future work needs to focus on their ability to limit inflammation, particularly during hemodialysis, and in providing anticoagulation on the order of weeks, particularly in artificial lungs.

Rapid Construction of Liquid-like Surfaces via Single-Cycle Polymer Brush Grafting for Enhanced Antifouling in Microfluidic Systems

Liquid-like surfaces have demonstrated immense potential in their ability to resist cell adhesion, a critical requirement for numerous applications across various domains. However, the conventional methodologies for preparing liquid-like surfaces often entail a complex multi-step polymer brush modification process, which is not only time-consuming but also presents significant challenges. In this work, we developed a single-cycle polymer brush modification strategy to build liquid-like surfaces by leveraging high-molecular-weight bis(3-aminopropyl)-terminated polydimethylsiloxane, which significantly simplifies the preparation process. The resultant liquid-like surface is endowed with exceptional slipperiness, effectively inhibiting bacterial colonization and diminishing the adherence of platelets. Moreover, it offers promising implications for reducing the dependency on anticoagulants in microfluidic systems constructed from PDMS, all while sustaining its antithrombotic attributes.

Surface-segregating zwitterionic copolymers to control poly(dimethylsiloxane) surface chemistry

The use of microfluidic devices in biomedicine is growing rapidly in applications such as organs-on-chip and separations. Polydimethylsiloxane (PDMS) is the most popular material for microfluidics due to its ability to replicate features down to the nanoscale, flexibility, gas permeability, and low cost. However, the inherent hydrophobicity of PDMS leads to the adsorption of macromolecules and small molecules on device surfaces. This curtails its use in "organs-on-chip" and other applications. Current technologies to improve PDMS surface hydrophilicity and fouling resistance involve added processing steps or do not create surfaces that remain hydrophilic for long periods. This work describes a novel, simple, fast, and scalable method for improving surface hydrophilicity and preventing the nonspecific adsorption of proteins and small molecules on PDMS through the use of a surface-segregating zwitterionic copolymer as an additive that is blended in during manufacture. These highly branched copolymers spontaneously segregate to surfaces and rearrange in contact with aqueous solutions to resist nonspecific adsorption. We report that mixing a minute amount (0.025 wt%) of the zwitterionic copolymer in PDMS considerably reduces hydrophobicity and nonspecific adsorption of proteins (albumin and lysozyme) and small molecules (vitamin B12 and reactive red). PDMS blended with these zwitterionic copolymers retains its mechanical and physical properties for at least six months. Moreover, this approach is fully compatible with existing PDMS device manufacture protocols without additional processing steps and thus provides a low-cost and user-friendly approach to fabricating reliable biomicrofluidics.

Challenge of material haemocompatibility for microfluidic blood-contacting applications

Biological applications of microfluidics technology is beginning to expand beyond the original focus of diagnostics, analytics and organ-on-chip devices. There is a growing interest in the development of microfluidic devices for therapeutic treatments, such as extra-corporeal haemodialysis and oxygenation. However, the great potential in this area comes with great challenges. Haemocompatibility of materials has long been a concern for blood-contacting medical devices, and microfluidic devices are no exception. The small channel size, high surface area to volume ratio and dynamic conditions integral to microchannels contribute to the blood-material interactions. This review will begin by describing features of microfluidic technology with a focus on blood-contacting applications. Material haemocompatibility will be discussed in the context of interactions with blood components, from the initial absorption of plasma proteins to the activation of cells and factors, and the contribution of these interactions to the coagulation cascade and thrombogenesis. Reference will be made to the testing requirements for medical devices in contact with blood, set out by International Standards in ISO 10993-4. Finally, we will review the techniques for improving microfluidic channel haemocompatibility through material surface modifications-including bioactive and biopassive coatings-and future directions.

Bioengineering Strategies to Create 3D Cardiac Constructs from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) can be used to generate various cell types in the human body. Hence, hiPSC-derived cardiomyocytes (hiPSC-CMs) represent a significant cell source for disease modeling, drug testing, and regenerative medicine. The immaturity of hiPSC-CMs in two-dimensional (2D) culture limit their applications. Cardiac tissue engineering provides a new promise for both basic and clinical research. Advanced bioengineered cardiac in vitro models can create contractile structures that serve as exquisite in vitro heart microtissues for drug testing and disease modeling, thereby promoting the identification of better treatments for cardiovascular disorders. In this review, we will introduce recent advances of bioengineering technologies to produce in vitro cardiac tissues derived from hiPSCs.