Protein and Cell Interactions with Nanostructured Surfaces

Doctoral thesis, 2017

A great challenge of today’s implant development is to construct a surface that promotes tissue integration and avoids bacterial colonization. To avoid implant related infections, many argue that a surface promoting strong cell adhesion and tissue integration in favour for bacterial adhesion would solve the problem, the so-called race for the surface concept. However, important factors for tissue integration, such as roughness and surface chemistry, also affect the adhesion of bacteria and many surface features promoting tissue integration have been found to promote biofilm formation. Nanotechnology and the development of nanomaterials have resulted in the opportunity to design tailor made nanostructured implants with novel topographical and chemical surface properties. Such surface features have demonstrated its effect on protein adsorption, cellular interactions, tissue integration and bacterial accumulation. The development of using nanomaterials in medical device applications has only just begun and there is a large need for fundamental studies on the biological response to nanostructured biomaterials. The main objective of this thesis was to use nanoparticles to modify implant surfaces and study its effect on biomolecules, human cells, bacteria and immune reactions. More specifically, we wanted to investigate if surface modifications created by introducing nanotopography, favourable chemical species and crystal structure using different nanoparticles would alter the surface properties and subsequent impact on protein adsorption, human cell attachment and bacteria. In order to achieve these objectives, nanostructured surfaces were constructed using hydroxyapatite, titanium dioxide and silica nanoparticles with the use of three different approaches for immobilizing the nanoparticles onto the underlying substrate. Hydroxyapatite (HA) nanoparticles were applied to titanium substrates by spin coating, titanium dioxide nanoparticles were attached to titanium substrates using an alkoxide thin film as adhesive and silica nanoparticles were immobilized on silica substrates using self-assembly strategies and electrostatic interactions. The surfaces were characterized using various analytical techniques, such as SEM, AFM and XPS etc.  It was found that HA nanoparticles applied on titanium substrates did not affect the attachment and spreading of fibroblasts compared to uncoated titanium. Additionally, HA nanoparticles of different shapes and chemistry, coated onto titanium discs, did not increase Staphylococcus epidermidis biofilm formation compared to uncoated titanium. The developed TiO2 nanoparticle coating was photocatalytically active and found to elicit bactericidal properties upon UV irradiation. Studying the effect of silica nanoparticle curvature on immune complement activating proteins, it was found that smaller nanoparticles/high curvature significantly reduced the binding of complement protein C1q. Additionally, NMR was used to study the adsorption of human serum metabolites onto silica nanoparticles of various sizes and surprisingly, a curvature-dependent effect on the adsorption of several small metabolic molecules was found.