ICMCTF2008 Session TS3-1: Bioactive Coatings and Surface Biofunctionalization

Monday, April 28, 2008 10:00 AM in Room Sunrise

Monday Morning

Start	Invited?	Item
10:00 AM	Invited	TS3-1-1 Surface Functionalization of Surgical Implants for Cell Guidance and Control I. Gotman (Technion - Israel Institute of Technology, Israel) Initial cellular reactions occurring at the implant site determine, to a great extent, the development of the implant-bone tissue interface and, eventually, implant fixation and osseointegration. A variety of morphological, chemical and coating approaches to surface modification of existing biomaterials have been developed in order to achieve the desired biological response. These methods rely either on providing an acceptable environment for bone apposition or on precipitation of biologically equivalent calcium phosphate, however they do not have the ability of guiding new bone formation by direct bone cell control. This may be achieved through implant biofunctionalization - incorporation of molecular signaling functionalities having a proven influence of bone cell behavior. One approach to induce bone regeneration that will be discussed in this talk is the use of growth factors, mostly bone morphogenetic proteins, BMP. BMPs attract progenitor cells (notably mesenchymal stem cells - MSC) to the implantation site and differentiate them into the osteogenic lineage. BMPs, however, have very short biological half-lives and their biological effect is largely unpredictable unless they are administrated via a controlled delivery system. It will be shown that biofunctionalization of porous scaffolds by encaging BMPs in bioresorbable surface layers, either biomimetic calcium phosphates or sol-gel glasses, has a potential to provide slow BMP release required for successful bone regeneration. Another biofuntionalization approach that will be dwelt upon in this talk is surface grafting with peptides simulating the cell-binding ability of extra-cellular matrix (ECM).
10:40 AM		TS3-1-4 Smart Modification of Magnetron Sputtered TiN Surfaces for Stimulated Differentiation M. Manso Silván (Universidad Autónoma de Madrid, Spain); C. Rodríguez Navas (Departamento de Biología Molecular, CBMSO-UAM, Spain); J. Martínez Duart (Departamento de Física Aplicada UAM, Spain); J.P. García Ruiz (Departamento de Biología Molecular, CBMSO-UAM, Spain) The biomedical applications of TiN and modified TiN coatings are in expansion due to the advanced physicochemical properties in conjunction with biocompatibility. The electrical properties of these films are revisited in this work aiming at a controlled surface modification. A plasma oxidation process is used to tune the originally high electrical conductance of TiN to that of a wide band gap semiconductor. A capacitively coupled plasma reactor with Ar/O₂ mixtures was used to oxidize the surfaces of thin (50 nm) magnetron sputtered TiN films deposited onto Si substrates. Both optical (UV-vis reflectance spectroscopy) and electrical (sheet resistance measurements) properties were traced to follow a graded modification. Pluripotent human mesenchymal stem cells (hMSCs) were exposed to the resulting TiN surfaces in both proliferation and osteoblastic differentiation biomolecular environments. HMSCs response was evaluated by fluorescence microscopy (double staining with 594 and 488 nm emissions). Cells adhered to TiN, modified TiN substrates and gelatine covered glass controls show that, completely oxidized surfaces are better adapted for proliferation purposes while unmodified surfaces are ideal for differentiation as denoted by the development of characteristic cytosolic prolongations. These results support the interest on competitive surface conditions created by TiN/TiO_x based dielectric contrasts by mask micropatterning for the development of hMSCs.
11:00 AM	Invited	TS3-1-5 Surface Immobilization and Characterization of Biomolecules D.G. Castner (University of Washington) Immobilized proteins mediate the interactions between a material and its biological environment. We have used XPS, ToF-SIMS and SPR to investigate protein immobilization onto surfaces containing nitrilotriacetic acid (NTA) or N-hydroxysuccinimide (NHS) headgroups. NHS surfaces were prepared by self-assembly of NHS ester oligo(ethylene glycol) thiols (NHS-OEG) onto gold. Aging of these films in ambient air resulted in hydrolysis of some NHS groups, oxidation of some thiols, and deposition of adventitious hydrocarbon contaminants. Overnight immersion under water produced complete hydrolysis and removal of the NHS chemistry. Regeneration of the hydrolyzed surfaces produced surfaces with bound NHS concentrations approximately 50% of those on freshly prepared monolayers. Protein immobilization onto NHS surfaces occurs primarily through the amine groups on the side chains of lysine residues present on the protein surface, resulting in the proteins being immobilized in a random orientation. Mixed monolayers containing NTA headgroups and OEG chains were self-assembled onto a gold surface. The surface concentration of NTA headgroups was 0.9-1.3 molecule/nm² in the mixed NTA/OEG monolayers, compared to 1.9 molecule/nm² in pure NTA monolayers. The NTA headgroups were slightly reoriented toward an upright position after OEG incorporation. Histagged, proteins were specifically and reversibly immobilized onto Ni(II)-treated mixed NTA monolayers in well-defined orientations. ToF-SIMS was used to compare the controlled orientation of histagged proteins on NTA surfaces with the random orientation of proteins on NHS surfaces. These model systems were then extended to examine the patterning of proteins and DNA oligomers on microarray slides with surface-active NHS groups.