Advanced surface treatment of elastomeric polydimethylsiloxane for cell stretching applications

Abstract

Polydimethylsiloxane (PDMS) elastomer is widely used in dynamic biological microfluidic applications. Hydrophobic pristine PDMS does not support cell attachment and culture, especially in dynamic conditions. Regardless, PDMS has too many useful properties as a base material for dynamic cell culture systems to be easily replaced. The good elastic properties, mouldability, transparency, chemical inertness, and biocompatibility of PDMS are enough to justify its use in large scale in the biomedical field. Therefore, PDMS surface treatment is nowadays considered as an essential step in using the material, especially for longer culture periods and dynamic culture conditions. To understand cell behaviour and stem cell differentiation better during cyclic stretching, it is important to study different durable surface treatment methods. The primary goal of this thesis work was to covalently bind collagen type I to cell culture substrates fabricated from Sylgard® 184 PDMS composite for long term cell stretching experiments with methods found in the literature. The secondary goal was to propose a novel surface treatment method to improve upon the existing methods. Seven different surface treatment methods, four of which were novel ascorbic acid (AA) based methods, were studied in this thesis using immunofluorescent imaging and cell culture experiments. The experiments were divided in five phases in chronological order to reflect the evolution of the surface treatment methods and the experiments. In phase one (P1), physisorption and Covalent Method 1 were imaged using fluorescent microscope. In phase two (P2), a novel Covalent Method 2 in two variations was proposed and subsequently imaged using fluorescent microscope. In phase three (P3), physisorption, Covalent Method 1, and Covalent Method 2 in three variations were tested in static human adipose stem cell (hAdSC) culture for 14 days. In phase four (P4), Covalent Method 1 and Covalent Method 2 in two variations were tested in static and dynamic hAdSC culture for 13 days. Phase five (P5) introduced Covalent Method 3 that was imaged with fluorescent microscope and tested in static hAdSC culture for four days. Collagen type I was successfully labelled and imaged from all of the coatings. Cells were also successfully cultured in static and dynamic environments. The results showed that the novel AA crosslinked Covalent Method 2 was superior to the physisorption method and Covalent Method 1 in immobilizing collagen as well as in cell culture tests. The cell culture tests were conducted and PDMS surface treatment methods were developed for Human Spare Parts project funded by Tekes, the Finnish Funding Agency for Innovation and WoodBone project funded by the Academy of Finland.