Keynote Lecture III

KN-03

Tailormade Biointerfaces Through Surface-attached Polymer Networks

*J. Rühe¹

¹Universität Freiburg, Freiburg, Deutschland

Introduction:

The interactions of materials with a biological system are controlled by the topography and chemical composition of the surfaces of the biomaterial. Examples are the adhesion of cells to surfaces, the wetting of surfaces by contacting liquids and the adsorption of (bio)molecules from the surrounding medium. In many cases, materials which are perfect for device generation e.g. concerning their mechanical and optical properties, are not at all perfect concerning the interactions with the biosystem, i.e. they show insufficient biocompatility. Thin polymer coatings attached to the surfaces can overcome this problem and can help to tailor the surface properties of a material precisely to the specific needs laid out by the application. In the presentation a new strategy will be presented which allows to generate novel, micropatterned polymer coatings based on surface-attached polymer networks with tailor-made properties on a variety of different substrates, ranging from typical oxides to polymers and biological materials. We describe a strategy in which a thin polymer layer from a polymer precursor carrying appropriate photo- or thermally active groups is simply deposited onto the substrate by spraying, dip coating, painting or any other means of deposition and within a few seconds to minutes through UV-irradiation or short thermal curing of the dry polymer film surface attached polymer networks are formed which are directly ready to use.

Materials and Methods:

Firstly copolymers of the desired matrix polymer, which contain for example benzophenone or sulfonyl azide or diazocarboxyl groups as active components are generated. After deposition of a solid film of the polymers, short UV irradiation or short thermal treatment lead to crosslinking of the deposited polymer through C,H insertion reactions. In some cases even irradiation times of 1 min are sufficient. During crosslinking simultaneously surface-attachment of the polymer film occurs, so that the film is now covalently attached to the substrate. When water-soluble polymers are employed thin, surface-attached hydrogels are obtained. The process is universal for practically all polymers once the photoactive groups have been incorporated and leads to well defined polymer layers, which can carry a broad spectrum of functional groups. For example it is very simple to attach DNA, antibodies or polysaccharides this way to small hydrogel pads on chip surfaces. In addition to employ photolithography for structuring these surfaces the approach can also be easily used to print biointerfaces e.g. DNA chips onto almost any surface. The synthetic procedures for the generation of the polymers along with the deposition of these materials on various surfaces and the photochemical or thermal crosslinking and surface-attachment are described in the literature. The films are characterized by surface analytical tools and their performance against biological systems (cell adhesion, PCR reactions on the surfaces, ELISA-chips) is studied.

Results and Discussion:

Polymers bearing photochemically or thermally reactive groups which connect to neighboring C,H-groups upon activation (C,H insertion crosslinking, CHIC) can be used to tailor the interfaces between a large spectrum of materials - ranging from polymers to glass or metal surfaces - with biological systems. Because polymers are used to generate these layers a variety of standard coating methods and in many cases standard microlithographic techniques can be applied to generate two and three dimensional surface architectures in a very simple and versatile way. The coating process requires no complex equipment and is easy and fast to perform.

These coatings and architectures can be used for a variety of applications in the general field of biomaterials. One example is the generation of surface-attached hydrogels, which are essentially bioinert and they keep this property over extended periods of time (many months). We will show examples of how such coatings can be used for generation excellent hemocompatible materials and for the reduction of scar formation after a glaucoma treatment.

If further functional groups are incorporated such layers can also take on an active role in the interaction with a biomedical environment. We will show how such layers can be used to increase the sensitivity of biochips for DNA, protein or cell analysis (HPV and mastitis chips). In many cases the combination of a bioinert background and very specific probes are key to allow for a precise and reliable analysis especially in real serum samples.