Abstract
Surface modification enables the creation of bioactive implants using traditional material substrates without altering the mechanical properties of the bulk material. For applications such as bone plates and stents, it is desirable to modify the surface of metal alloy substrates to facilitate cellular attachment, proliferation, and possibly differentiation. In this work we present a general strategy for altering the surface chemistry of nickel-titanium (NiTi) shape memory alloy in order to covalently attach self-assembled peptide amphiphile (PA) nanofibers with bioactive functions. Bioactivity in the systems studied here includes biological adhesion and proliferation of osteoblast and endothelial cell types. The optimized surface treatment creates a uniform TiO2 layer with low levels of Ni on the NiTi surface, which is subsequently covered with an aminopropylsilane coating using a novel, lower temperature vapor deposition method. This method produces an aminated surface suitable for covalent attachment of PA molecules containing terminal carboxylic acid groups. The functionalized NiTi surfaces have been characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and atomic force microscopy (AFM). These techniques offer evidence that the treated metal surfaces consist primarily of TiO2 with very little Ni, and also confirm the presence of the aminopropylsilane overlayer. Self-assembled PA nanofibers presenting the biological peptide adhesion sequence Arg-Gly-Asp-Ser are capable of covalently anchoring to the treated substrate, as demonstrated by spectrofluorimetry and AFM techniques. Cell culture and scanning electron microscopy (SEM) demonstrate cellular adhesion, spreading, and proliferation on these functionalized metal surfaces. Furthermore, these experiments demonstrate that covalent attachment is crucial for creating robust PA nanofiber coatings, leading to confluent cell monolayers.
Original language | English (US) |
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Pages (from-to) | 1085-1098 |
Number of pages | 14 |
Journal | Biomaterials |
Volume | 29 |
Issue number | 8 |
DOIs | |
State | Published - Mar 2008 |
Funding
The authors gratefully acknowledge funding support from the National Science Foundation through Grant DMR-0505772 and the National Institutes of Health through Grants 1 R01 DE015920-01A1, 5 R01 DE015920, and 5 R01 EB003806. XPS and ToF-SIMS were performed in the Keck Interdisciplinary Surface Science (Keck II) Center at Northwestern University. AFM was performed in the Nanoscale Integrated Fabrication, Testing and Instrumentation (NIFTI) Center at Northwestern University. Electron microscopy was performed in the Electron Probe Instrumentation Center (EPIC) at Northwestern University. Peptide synthesis and purification, fluorimetry, and cell work were performed in the Institute for BioNanotechnology in Medicine (IBNAM) at Northwestern University. We thank Dr. James Hulvat for his technical help with experiments at IBNAM, Dr. Nick Wu for his technical help with experiments at Keck II, Dr. Gajendra Shekhawat for his technical help with experiments at NIFTI, and Mr. Ben Myers for his technical help with experiments at EPIC. We thank also Nitinol Devices & Components, Inc. (Fremont, CA) for donation of the NiTi strips used in this study.
Keywords
- APTES
- Biofunctionalization
- Covalent attachment
- Nickel-titanium
- Peptide amphiphile nanofibers
- Self-assembly
ASJC Scopus subject areas
- Mechanics of Materials
- Ceramics and Composites
- Bioengineering
- Biophysics
- Biomaterials