Functionalized Biomaterial Surfaces by Micro- and Nanofabrication

Doctoral thesis, 2002

In the field of biomaterials, well-defined nano- and micropatterns or features at material surfaces can serve both as models for investigating material-biosystem interactions and as functional features for inducing, hindering or measuring specific bioreactions or biologic responses. Important bioreactions include protein adsorption and conformation, cell attachment and function, and adhesion and function of organized tissues or whole organisms. In this thesis, several studies are presented where the following functionalized materials have been micro- or nanopatterned and evaluated in biological systems: (1) Silicon substrates with patterned silver nanoparticles for probing biomolecule detection via SERS; (2) titania ceramic substrates with micro-cavities for culturing liver cells in vitro with preserved phenotype; (3) elastic silicone coatings with micro-pyramids and riblets to prevent marine biofouling by barnacle attachment; (4) silicon and epoxy model porous substrates containing interconnecting microchannels to investigate cell attachment and spreading as a function of substrate porosity; (5) silicon substrates with standing cantilevers for investigation of mechanical cell-substrate interactions. In all these studies, the main task was to achieve a well-controlled and systematic variation of the most relevant surface microscopic characteristics (chemical, topographical or mechanical), in order to tune or optimize the surfaces for their best functional performance, or to gain phenomenological understanding of how microscopic surface properties influence physical or biological interactions at surfaces. Electron beam lithography, photolithography and micro-replication techniques (such as injection molding, embossing and casting) were used to pattern biological test substrates on nanometer and micrometer length scales. Geometrical parameters and surface morphology of microfabricated surfaces were evaluated by scanning electron microscopy and stylus profilometry. Several surface sensitive techniques (x-ray photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectroscopy, contact angle measurements) were used to characterize chemical composition and wettability of the surfaces. Micromechanical characteristics of fabricated flexible structures were probed using atomic force microscopy in "force calibration" mode. It is demonstrated that the lithographic and replication methods used are excellent tools for preparing well-controlled micro- and nanopatterned surfaces in several materials. By systematically varying parameters of such patterns, mechanisms involved in such diverse areas as surface enhanced Raman scattering and marine biofouling have been proposed or verified. In addition, these patterning methods offer the possibility to design cell culture substrates that enhance the preservation of cell phenotype, or, alternatively, intentionally modify their behavior. The latter led to the discovery and development of a new way to measure and map the lateral forces exerted by cells on material surfaces in vitro.