Novel biomedical applications of supported lipid bilayers

Abstract

Studying and steering cell behaviour on artificial surfaces is challenged by the correct presentation of ligands and interaction with cells. Cell membrane mimics such as supported lipid bilayers (SLBs) offer unique possibilities in this field. For example, ligands that are displayed on SLBs can move in 2D while prohibiting non-specific interaction with proteins and cells. The aim of the work described in the thesis is to explore novel biomedical applications of SLBs with implications for (1) membrane separation, (2) surface gradient formation and (3) artificial cell interfaces for in vivo use. (1) Membrane separation by means of electrophoresis suffer from large applied potentials that prevent down-scaling to low-power nano-analytical devices and can cause damage to the SLB. In this part of the work a chip-based system was fabricated in a process that consumes only 100s of millivolts. This achievement was made possible through the addition of a sacrificial electrochemical reaction during SLB electrophoresis. (2) Concentration gradients of charged analytes within the SLB-based gradients do not display temporal stability and can therefore not be easily used as e.g. a continuous gradient for the study of binding events. In this part of the work the SLB electrophoresis system was used to generate surface gradients of charged functional groups in gel-state SLBs. These gradients proved stable in time conveniently at room temperature and could be modified with various bioactive compounds such as mannose to study the binding of E. coli under relevant physiological shear stresses. (3) Even though SLBs have been used extensively in vitro, their application in vivo has been limited due to the air instability of these layers. In this part of the work the interligand spacing and lateral mobility of cell adhesive ligands was varied in SLBs and studied in cell culture. Chondrocyte and preosteoblastic cell behaviour could be tuned in terms of cell adhesion, cell spreading, cytoskeletal organization and the extent of matrix deposition. Ultimately, the preparation of a cholesterol-modified biopolymer allowed us to prepare air-stable biomaterial SLB, which were equally non-fouling and, when bioactive ligands were included, able to steer mesenchymal stem cell fate.