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ABSTRACT: This paper reports on the extremely superhydrophobic behavior of supercritical CO2 processed silicon nanowires SiNWs) with a contact angle in excess of ∼177°. Vertically aligned silicon nanowires with 10
nm to 40 nm diameter and 1 mm to 3 mm in length were obtained by electroless etching (EE) technique. The asfabricated SiNWs
were superhydrophilic with no water droplet formation (zero contact angle), and were then completely transformed to an extreme
superhydrophobic state when their nanoscale surface roughness is combined with trichlorosilane hydrophobic coating. The processed
SiNW array was so hydrophobic that water droplets always bounced off the surface and did not allow contact angle measurements
to be obtained unless the substrate was intentionally given a concave-curvature by vacuum suction. Utilization of a hydrophobically
surface-treated micro-pipette syringe enabled the release of a water droplet onto this extremely superhydrophobic surface
for contact angle measurement. To prevent severe nanowire agglomeration during the drying process of wet etched SiNWs, supercritical
CO2 drying was utilized, which process significantly improved the nano configuration and enhanced hydrophobicity.
Keywordssuperhydrophobic surface–electroless etching–silicon nanowires–contact angle
Electronic Materials Letters 04/2012; 6(2):59-64. · 1.82 Impact Factor
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09/2011; , ISBN: 978-953-307-609-6
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ABSTRACT: Surface engineering approaches that alter the topological chemistry of a substrate could be used as an effective tool for directing cell interactions and their subsequent function. It is well known that the physical environment of nanotopography has positive effects on cell behavior, yet direct comparisons of nanotopographic surface chemistry have not been fully explored. Here we compare TiO(2) nanotubes with carbon-coated TiO(2) nanotubes, probing osteogenic cell behavior, including osteoblast (bone cells) and mesenchymal stem cell (MSC) (osteo-progenitor cells) interactions with the different surface chemistries (TiO(2) vs. carbon). The roles played by the material surface chemistry of the nanotubes did not have an effect on the adhesion, growth or morphology, but had a major influence on the alkaline phosphatase (ALP) activity of osteoblast cells, with the original TiO(2) chemistry having higher ALP levels. In addition, the different chemistries caused different levels of osteogenic differentiation in MSCs; however, it was the carbon-coated TiO(2) nanotubes that had the greater advantage, with higher levels of osteo-differentiation. It was observed in this study that: (a) chemistry plays a role in cell functionality, such as ALP activity and osteogenic protein gene expression (PCR); (b) different cell types may have different chemical preferences for optimal function. The ability to optimize cell behavior using surface chemistry factors has a profound effect on both orthopedic and tissue engineering in general. This study aims to highlight the importance of the chemistry of the carrier material in osteogenic tissue engineering schemes.
Acta biomaterialia 03/2011; 7(6):2697-703. · 3.98 Impact Factor
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ABSTRACT: Surface engineering approaches that alter the physical topography of a substrate could be used as an effective tool and as an alternative to biochemical means of directing stem cell interactions and their subsequent differentiation. In this paper we compare hydrophobic micro- vs. nanopillar type fabrication techniques for probing mesenchymal stem cell (MSC) interaction with the surface physical environment. The roles played by the topography of the nanopillar in particular influenced MSC growth and allowed for regulatory control of the stem cell fate. The nanopillar induced large 3-D cell aggregates to form on the surface which had up-regulated osteogenic specific matrix components. The ability to control MSC differentiation, using only the topographical factors, has a profound effect on both MSC biology and tissue engineering. This study aims to highlight the importance of the physical material carrier in stem cell based tissue engineering schemes.
Acta biomaterialia 02/2011; 7(2):683-90. · 3.98 Impact Factor
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ABSTRACT: Loading or filling nanostructures with antibiotics can be one of the relevant approaches for obtaining a controlled drug release rate. Vertically aligned silicon nanowire (SiNW) arrays with 10-40 nm diameter wires having 1-3 microm in length obtained by the electroless etching (EE) technique are used in this study as novel nanostructures for mediating drug delivery. Here we report controlled antibiotic activity and sustained bioavailability from SiNW arrays and also show microstructural manipulations for a tunable release rate. As well, we have demonstrated biodegradability of SiNWs in phosphate buffer saline (PBS) solution. Strikingly suppressed cell and protein adhesion was observed on our SiNW surface, which indicates a reduced probability for biofouling and drug release impediments. Such antibiotic release from the nanowire-structured surface can provide more reliable antibiotic protection at a targeted implantation or biosensor site.
Nano Letters 08/2009; 9(10):3570-4. · 13.20 Impact Factor
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ABSTRACT: The titanium dioxide (TiO(2)) nanotube surface enables significantly accelerated osteoblast adhesion and exhibits strong bonding with bone. We prepared various sizes (30-100 nm diameter) of titanium dioxide (TiO(2)) nanotubes on titanium substrates by anodization and investigated the osteoblast cellular behavior in response to these different nanotube sizes. The unique and striking result of this study is that a change in osteoblast behavior is obtained in a relatively narrow range of nanotube dimensions, with small diameter ( approximately 30 nm) nanotubes promoting the highest degree of osteoblast adhesion, while larger diameter (70-100 nm) nanotubes elicit a lower population of cells with extremely elongated cellular morphology and much higher alkaline phosphatase levels. Increased elongation of nuclei was also observed with larger diameter nanotubes. By controlling the nanotopography, large diameter nanotubes, in the approximately 100 nm regime, induced extremely elongated cellular shapes, with an aspect ratio of 11:1, which resulted in substantially enhanced up-regulation of alkaline phosphatase activity, suggesting greater bone-forming ability than nanotubes with smaller diameters. Such nanotube structures, already being a strongly osseointegrating implant material, offer encouraging implications for the development and optimization of novel orthopedics-related treatments with precise control toward desired cell and bone growth behavior.
Acta biomaterialia 06/2009; 5(8):3215-23. · 3.98 Impact Factor
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ABSTRACT: Implant topography is critical to the clinical success of bone-anchored implants, yet little is known how nano-modified implant topography affects osseointegration. We investigate the in vivo bone bonding of two titanium implant surfaces: titanium dioxide (TiO(2)) nanotubes and TiO(2) gritblasted surfaces. In previous in vitro studies, the topography of the TiO(2) nanotubes improved osteoblast proliferation and adhesion compared with gritblasted titanium surfaces. After four weeks of implantation in rabbit tibias, pull-out testing indicated that TiO(2) nanotubes significantly improved bone bonding strength by as much as nine-fold compared with TiO(2) gritblasted surfaces. Histological analysis confirmed greater bone-implant contact area, new bone formation, and calcium and phosphorus levels on the nanotube surfaces. It is anticipated that further studies will contribute to a better understanding of the effect of implant nanotopography on in vivo bone formation and bonding strength.
Journal of Biomedical Materials Research Part A 05/2009; 92(3):1218-24. · 2.63 Impact Factor
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ABSTRACT: Two important goals in stem cell research are to control the cell proliferation without differentiation and to direct the differentiation into a specific cell lineage when desired. Here, we demonstrate such paths by controlling only the nanotopography of culture substrates. Altering the dimensions of nanotubular-shaped titanium oxide surface structures independently allowed either augmented human mesenchymal stem cell (hMSC) adhesion or a specific differentiation of hMSCs into osteoblasts by using only the geometric cues, absent of osteogenic inducing media. hMSC behavior in response to defined nanotube sizes revealed a very dramatic change in hMSC behavior in a relatively narrow range of nanotube dimensions. Small (approximately 30-nm diameter) nanotubes promoted adhesion without noticeable differentiation, whereas larger (approximately 70- to 100-nm diameter) nanotubes elicited a dramatic stem cell elongation (approximately 10-fold increased), which induced cytoskeletal stress and selective differentiation into osteoblast-like cells, offering a promising nanotechnology-based route for unique orthopedics-related hMSC treatments.
Proceedings of the National Academy of Sciences 02/2009; 106(7):2130-5. · 9.68 Impact Factor
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ABSTRACT: The in vitro endothelial response of primary bovine aortic endothelial cells (BAECs) was investigated on a flat Ti surface vs a nanostructured TiO2 nanotube surface. The nanotopography provided nanoscale cues that facilitated cellular probing, cell sensing, and especially cell migration, where more organized actin cytoskeletal filaments formed lamellipodia and locomotive morphologies. Motile cell protrusions were able to probe down into the nanotube pores for contact stimulation, and focal adhesions were formed and disassembled readily for enhanced advancement of cellular fronts, which was not observed on a flat substrate of titanium. NOx and endothelin-1 functional assays confirmed that the nanotubes also up-regulated an antithrombic cellular state for maintaining vascular tone. The enhanced endothelial response to TiO2 nanotubes is significant for a potential modification of vascular stent surfaces in order to increase the rate and reliability of endothelialization and endothelial cell migration onto the stent for repairing arterial injury after activation.
Nano Letters 04/2008; 8(3):786-93. · 13.20 Impact Factor
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ABSTRACT: Vertically aligned yet laterally spaced nanoscale TiO2 nanotubes have been grown on Ti by anodization, and the growth of MC3T3-E1 osteoblast cells on such nanotubes has been investigated. The adhesion/propagation of the osteoblast is substantially improved by the topography of the TiO2 nanotubes with the filopodia of growing cells actually going into the nanotube pores, producing an interlocked cell structure. The presence of the nanotube structure induced a significant acceleration in the growth rate of osteoblast cells by as much as approximately 300-400%.
Journal of Biomedical Materials Research Part A 08/2006; 78(1):97-103. · 2.63 Impact Factor
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ABSTRACT: The titanium dioxide (TiO2) nanotube surface enables significantly accelerated osteoblast adhesion and exhibits strong bonding with bone. We prepared various sizes (30–100 nm diameter) of titanium dioxide (TiO2) nanotubes on titanium substrates by anodization and investigated the osteoblast cellular behavior in response to these different nanotube sizes. The unique and striking result of this study is that a change in osteoblast behavior is obtained in a relatively narrow range of nanotube dimensions, with small diameter (∼30 nm) nanotubes promoting the highest degree of osteoblast adhesion, while larger diameter (70–100 nm) nanotubes elicit a lower population of cells with extremely elongated cellular morphology and much higher alkaline phosphatase levels. Increased elongation of nuclei was also observed with larger diameter nanotubes. By controlling the nanotopography, large diameter nanotubes, in the ∼100 nm regime, induced extremely elongated cellular shapes, with an aspect ratio of 11:1, which resulted in substantially enhanced up-regulation of alkaline phosphatase activity, suggesting greater bone-forming ability than nanotubes with smaller diameters. Such nanotube structures, already being a strongly osseointegrating implant material, offer encouraging implications for the development and optimization of novel orthopedics-related treatments with precise control toward desired cell and bone growth behavior.
Acta Biomaterialia.
