Application of membrane technology in microfluidic devices

This dissertation describes the application of membrane technology in microfluidic devices. The presented research is of a conceptual and explorative nature. Chapter 2 contains an overview of the state-of-the-art in the integration and application of membranes in microfluidic devices, with a special focus on devices made of PDMS. Chapter 3 describes a new micro replication method for the preparation of polymeric microfluidic chips with tunable porosity: phase separation micromolding (PSμM). It is demonstrated that the channel walls of these devices have membrane characteristics. Chapter 4 focuses on fundamental aspects of membrane-based micro gas-liquid contactors, made by micro milling of plastic substrates and clamping of membranes. Subsequent numerical modeling shows that the behavior of micro gas liquid systems can be predicted with acceptable results using a 2D model with very basic assumptions. The second part of the chapter concerns the use of gases for control of micro environments. A proof-of-principle is demonstrated for pH control in micro fermentation experiments. In Chapter 5, the approach of gas-liquid contacting is further exploited for the local creation of stationary and transient pH concentration gradients. Chapter 6 is dedicated to the preparation of thin porous polymeric coatings in small channels, based on phase separation of a polymer solution. It is demonstrated that the morphology of the coating can be tuned and that particles can be incorporated, leading to functionalized coatings. A proof of principle is demonstrated for a Pt functionalized coating by showing catalytic partial oxidation of glucose. In Chapter 7, a selection of tips, tricks and new concepts is presented for the use of membranes in microfluidic devices. Simple and cheap approaches include the use of hollow fibers and embossing of micro structures in porous membranes. In Chapter 8, an evaluation of the total project is given, in which the basic accomplishments are summarized, recommendations are given and common pitfalls are identified. The thesis ends with a broad outlook.