8 research outputs found
Patterning and Biofunctionalization of Antifouling Hyperbranched Polyglycerol Coatings
We demonstrate the patterned biofunctionalization
of antifouling
hyperbranched polyglycerol (HPG) coatings on silicon and glass substrates.
The ultralow fouling HPG coatings afforded straightforward chemical
handles for rapid bioconjugation of amine containing biomolecular
species. This was achieved by sodium periodate oxidation of terminal
HPG diols to yield reactive aldehyde groups. Patterned microprinting
of sodium periodate and cell adhesion mediating cyclic peptides containing
the RGD sequence resulted in an array of covalently immobilized bioactive
signals. When incubated with mouse fibroblasts, the HPG background
resisted cell attachment whereas high density cell attachment was
observed on the peptide spots, resulting in high-contrast cell microarrays.
We also demonstrated single-step, in situ functionalization of the
HPG coatings by printing periodate and peptide concurrently. Our results
demonstrate the effectiveness of antifouling and functionalized HPG
graft polymer coatings and establish their use in microarray applications
for the first time
Gold-Decorated Porous Silicon Nanopillars for Targeted Hyperthermal Treatment of Bacterial Infections
In
order to address the issue of pathogenic bacterial colonization of
diabetic wounds, a more direct and robust approach is required, which
relies on a physical form of bacterial destruction in addition to
the conventional biochemical approach (i.e., antibiotics). Targeted
bacterial destruction through the use of photothermally active nanomaterials
has recently come into the spotlight as a viable approach to solving
the rising problem of antibiotic resistant microorganisms. Materials
with high absorption coefficients in the near-infrared (NIR) region
of the electromagnetic spectrum show promise as alternative antibacterial
therapeutic agents, since they preclude the development of bacterial
resistance and can be activated on demand. Here were report on a novel
approach for the fabrication of gold nanoparticle decorated porous
silicon nanopillars with tunable geometry that demonstrate excellent
photothermal conversion properties when irradiated with a 808 nm laser.
These photothermal antibacterial properties are demonstrated <i>in vitro</i> against the Gram-positive bacteria <i>Staphylococcus
aureus</i> (<i>S. aureus</i>) and Gram-negative <i>Escherichia coli</i> (<i>E. coli</i>). Results show
a reduction in bacterial viability of up to 99% after 10 min of laser
irradiation. We also show an increase in antibacterial performance
after modifying the nanopillars with <i>S. aureus</i> targeting
antibodies causing up to a 10-fold increase in bactericidal efficiency
compared to <i>E. coli</i>. In contrast, the nanomaterial
resulted in minimal disruption of metabolic processes in human foreskin
fibroblasts (HFF) after an equivalent period of irradiation
Surface-Initiated Hyperbranched Polyglycerol as an Ultralow-Fouling Coating on Glass, Silicon, and Porous Silicon Substrates
Anionic ring-opening polymerization
of glycidol was initiated from
activated glass, silicon, and porous silicon substrates to yield thin,
ultralow-fouling hyperbranched polyglycerol (HPG) graft polymer coatings.
Substrates were activated by deprotonation of surface-bound silanol
functionalities. HPG polymerization was initiated upon the addition
of freshly distilled glycidol to yield films in the nanometer thickness
range. X-ray photoelectron spectroscopy, contact angle measurements,
and ellipsometry were used to characterize the resulting coatings.
The antifouling properties of HPG-coated surfaces were evaluated in
terms of protein adsorption and the attachment of mammalian cells.
The adsorption of bovine serum albumin and collagen type I was found
to be reduced by as much as 97 and 91%, respectively, in comparison
to untreated surfaces. Human glioblastoma and mouse fibroblast attachment
was reduced by 99 and 98%, respectively. HPG-grafted substrates outperformed
polyethylene glycol (PEG) grafted substrates of comparable thickness
under the same incubation conditions. Our results demonstrate the
effectiveness of antifouling HPG graft polymer coatings on a selected
range of substrate materials and open the door for their use in biomedical
applications
Porous Silicon-Based Cell Microarrays: Optimizing Human Endothelial Cell-Material Surface Interactions and Bioactive Release
Porous
silicon (pSi) substrates are a promising platform for cell
expansion, since pore size and chemistry can be tuned to control cell
behavior. In addition, a variety of bioactives can be loaded into
the pores and subsequently released to act on cells adherent to the
substrate. Here, we construct a cell microarray on a plasma polymer
coated pSi substrate that enables the simultaneous culture of human
endothelial cells on printed immobilized protein factors, while a
second soluble growth factor is released from the same substrate.
This allows three elements of candidate pSi scaffold materialstopography,
surface functionalization, and controlled factor releaseto
be assessed simultaneously in high throughput. We show that protein
conjugation within printed microarray spots is more uniform on the
pSi substrate than on flat glass or silicon surfaces. Active growth
factors are released from the pSi surface over a period of several
days. Using an endothelial progenitor cell line, we investigate changes
in cell behavior in response to the microenvironment. This platform
facilitates the design of advanced functional biomaterials, including
scaffolds, and carriers for regenerative medicine and cell therapy
Dense Arrays of Uniform Submicron Pores in Silicon and Their Applications
We report a versatile particle-based
route to dense arrays of parallel
submicron pores with high aspect ratio in silicon and explore the
application of these arrays in sensors, optics, and polymer micropatterning.
Polystyrene (PS) spheres are convectively assembled on gold-coated
silicon wafers and sputter-etched, resulting in well-defined gold
disc arrays with excellent long-range order. The gold discs act as
catalysts in metal-assisted chemical etching, yielding uniform pores
with straight walls, flat bottoms, and high aspect ratio. The resulting
pore arrays can be used as robust antireflective surfaces, in biosensing
applications, and as templates for polymer replica molding
Versatile Particle-Based Route to Engineer Vertically Aligned Silicon Nanowire Arrays and Nanoscale Pores
Control
over particle self-assembly is a prerequisite for the colloidal templating
of lithographical etching masks to define nanostructures. This work
integrates and combines for the first time bottom-up and top-down
approaches, namely, particle self-assembly at liquid–liquid
interfaces and metal-assisted chemical etching, to generate vertically
aligned silicon nanowire (VA-SiNW) arrays and, alternatively, arrays
of nanoscale pores in a silicon wafer. Of particular importance, and
in contrast to current techniques, including conventional colloidal
lithography, this approach provides excellent control over the nanowire
or pore etching site locations and decouples nanowire or pore diameter
and spacing. The spacing between pores or nanowires is tuned by adjusting
the specific area of the particles at the liquid–liquid interface
before deposition. Hence, the process enables fast and low-cost fabrication
of ordered nanostructures in silicon and can be easily scaled up.
We demonstrate that the fabricated VA-SiNW arrays can be used as in
vitro transfection platforms for transfecting human primary cells
“Thunderstruck”: Plasma-Polymer-Coated Porous Silicon Microparticles As a Controlled Drug Delivery System
Controlling
the release kinetics from a drug carrier is crucial to maintain a
drug’s therapeutic window. We report the use of biodegradable
porous silicon microparticles (pSi MPs) loaded with the anticancer
drug camphothecin, followed by a plasma polymer overcoating using
a loudspeaker plasma reactor. Homogenous “Teflon-like”
coatings were achieved by tumbling the particles by playing AC/DC’s
song “Thunderstruck”. The overcoating resulted in a
markedly slower release of the cytotoxic drug, and this effect correlated
positively with the plasma polymer coating times, ranging from 2-fold
up to more than 100-fold. Ultimately, upon characterizing and verifying
pSi MP production, loading, and coating with analytical methods such
as time-of-flight secondary ion mass spectrometry, scanning electron
microscopy, thermal gravimetry, water contact angle measurements,
and fluorescence microscopy, human neuroblastoma cells were challenged
with pSi MPs in an in vitro assay, revealing a significant time delay
in cell death onset
Delivery of Flightless I siRNA from Porous Silicon Nanoparticles Improves Wound Healing in Mice
Flightless
I (Flii), a cytoskeletal actin remodelling protein,
is elevated in wounds and is a negative regulator of wound healing.
Gene silencing using small interfering RNA (siRNA) is an attractive
approach to antagonize Flii, and therefore holds significant promise
as a therapeutic intervention. The development of siRNA therapeutics
has been limited by an inability of the siRNA to cross the cell surface
plasma membrane of target cells and also by their degradation due
to endogenous nuclease action. To overcome these limitations, suitable
delivery vehicles are required. Porous silicon (pSi) is a biodegradable
and
high surface area material commonly used for drug delivery applications.
Here we investigated the use of pSi nanoparticles (pSiNPs) for the
controlled release of Flii siRNA to wounds. Thermally hydrocarbonized
pSiNPs (THCpSiNPs) were loaded with Flii siRNA and then coated with
a biocompatible chitosan layer. Loading regimens in the order of 50
μg of Flii siRNA per mg of pSi were achieved. The release rate
of Flii siRNA was sustained over 35 h. With addition to keratinocytes <i>in vitro</i>, reduced Flii gene expression in conjunction with
lowered Flii protein was observed, in concert with increased cell
migration and proliferation. A significant improvement in the healing
of acute excisional wounds compared to controls was observed from
day 5 onward when Flii siRNA-THCpSiNPs were intradermally injected.
THCpSiNPs therefore are an effective vehicle for delivering siRNA,
and nanoparticle-based siRNA delivery represents a promising therapeutic
approach to improve wound healing