Poly(dimethylsiloxane) (PDMS) is a popular material for microfluidic devices due to its relatively low cost, ease of
fabrication, oxygen permeability and optical transmission characteristics. However, its highly hydrophobic surface is still
the main factor limiting its wide application, in particular as a material for biointerfaces. A simple and rapid method to
form a relatively stable hydrophilised PDMS surface is reported in this paper. The PDMS surface was treated with pure
undecylenic acid (UDA) for 10 min, 1 h and 1 day at 80 °C in a sealed container. The effects of the surface modification
were investigated using water contact angle (WCA) measurements, Fourier transform infrared spectroscopy in attenuated
total reflection mode (FTIR-ATR), and streaming zeta-potential analysis. The water contact angle of 1 day UDAmodified
PDMS was found to decrease from that of native PDMS (110 °) to 75 °, demonstrating an increase in
wettability of the surface. A distinctive peak at 1715 cm-1 in the FTIR-ATR spectra after UDA treatment was
representative of carboxylation of the PDMS surface. The measured zeta-potential (ζ) at pH 4 changed from -27 mV for
pure PDMS to -19 mV after UDA treatment. In order to confirm carboxylation of the surface visually, Lucifer Yellow
CH fluorescence dye was reacted via a condensation reaction to the 1 day UDA modified PDMS surface. Fluorescent
microscopy showed Lucifer Yellow CH fluorescence on the carboxylated surface, but not on the pure PDMS surface.
Stability experiments were also performed showing that 1 day modified UDA samples were stable in both MilliQ water
at 50 °C for 17 h, and in a desiccator at room temperature for 19.5 h.
Glaucoma is a common cause of blindness. Wireless, continuous monitoring of intraocular pressure (IOP) is an
important, unsolved goal in managing glaucoma. An IOP monitoring system incorporated into a glaucoma drainage
implant (GDI) overcomes the design complexity associated with incorporating a similar system in a more confined space
within the eye. The device consists of a micro-electro-mechanical systems (MEMS) based capacitive pressure sensor
integrated with an inductor printed directly onto a polyimide printed circuit board (PCB). The device is designed to be
incorporated onto the external plate of a therapeutic GDI. The resonance frequency changes as a function of IOP, and is
tracked remotely using a spectrum analyzer. A theoretical model for the reader antenna was developed to enable
maximal inductive coupling with the IOP sensor implant. Pressure chamber tests indicate that the sensor implant has
adequate sensitivity in the IOP range with excellent reproducibility over time. Additionally, we show that sensor
sensitivity does not change significantly after encapsulation with polydimethylsiloxane (PDMS) to protect the device
from fluid environment. In vitro experiments showed that the signal measured wirelessly through sheep corneal and
scleral tissue was adequate indicating potential for using the system in human subjects.
Here we describe a new class of near superhydrophobic surfaces formed using fluorinated polyhedral oligosilsesquioxane (FluoroPOSS) urethane hybrids and porous silicon gradients (pSi). We demonstrate that the surface segregation behavior of the hydrophobic fluoro component can be controlled by the type and nature of chain extender of the urethane and resultant hydrophobic association via intra or intermolecular aggregation. The surface film formed exhibits near superhydrophobicity. This work has significant potential for applications in antifouling and self-cleaning coatings, biomedical devices, microfluidic systems and tribological surfaces.
The control over surface wettability is of concern for a number of important applications including chromatography,
microfluidics, biomaterials, low-fouling coatings and sensing devices. Here, we report the ability to tailor wettability
across a surface using lateral porous silicon (pSi) gradients. Lateral gradients made by anodisation of silicon using an
asymmetric electrode configuration showed a lateral distribution of pore sizes, which decreased with increasing distance
from the electrode. Pore sizes were characterised using scanning electron microscopy (SEM) and atomic force
microscopy (AFM). Pore diameters ranged from micrometres down to less than 10 nanometres. Chemical surface
modification of the pSi gradients was employed in order to produce gradients with different wetting or non-wetting
properties. Surface modifications were achieved via silanisation of oxidised pSi surfaces introducing functionalities
including polyethylene glycol, terminal amine and fluorinated hydrocarbon chains. Surface modifications were
characterised using infrared spectroscopy. Sessile drop water contact angle measurements were used to probe the
wettability in regions of different pore size across the gradient. For the fluorinated gradients, a comparison of
equilibrium and dynamic contact angle measurement was undertaken. The fluorinated surface chemistry produced
gradients with wettabilities ranging from hydrophobic to near super-hydrophobic whereas pSi gradients functionalised
with polyethylene glycol showed graded hydrophilicity. In all cases investigated here, changes in pore size across the
gradient had a significant effect on wettability.
Inorganic/organic hybrid or composite materials have in the past shown novel and interesting properties, which are not observed for the individual components. In this context, the preparation of inorganic/polymeric composites from biodegradable and biocompatible constituents is a new concept, which may be of interest particularly for tissue engineering and drug delivery applications. We describe here the synthesis of nanostructured porous silicon (pSi) and poly(L-lactide) (PLLA) composites. The composites were produced using tin(II) 2-ethylhexanoate catalysed surface initiated ring opening polymerisation of L-lactide onto silanised porous silicon films and microparticles. The subsequent chemical, physiochemical and morphological characterisation was performed using Diffuse Reflectance Infrared Spectroscopy (DRIFTS), X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Differential Scanning Calorimetery (DSC), Thermogravimetric Analysis (TGA) and Contact Angle measurements. DRIFT spectra of the composites showed the presence of bands corresponding to ester carbonyl stretching vibrations as well as hydrocarbon stretching vibrations. XPS analysis confirmed that a layer of PLLA had been grafted onto pSi judging by the low Si content (ca. 3%) and O/C ratio close to that found for PLLA homopolymers. Comparison of the sessile drop contact angle produced by silanised pSi and PLLA grafted onto pSi showed an increase of ca. 40°. This is comparable to the increase in contact angle seen between blank silicon and spin-coated PLLA of ca. 44°. The AFM surface roughness after surface initiated polymerisation increased significantly and AFM images showed the formation of PLLA nanobrushes.
Current methods to produce short DNA strands (oligonucleotides) involve the stepwise coupling of phosphoramidites onto a solid support, typically controlled pore glass. The full-length oligonucleotide is then cleaved from the solid support using a suitable aqueous or organic base and the oligonucleotide is subsequently separated from the spent support. This final step, albeit seemingly easy, invariably leads to increased production costs due to increased synthesis time and reduced yields. This paper describes the preparation of a dissolvable support for DNA synthesis based on porous silicon (pSi). Initially it was thought that the pSi support would undergo dissolution by hydrolysis upon cleavage of the freshly synthesised oligonucleotide strands with ammonium hydroxide. The ability to dissolve the solid support after completion of the synthesis cycle would eliminate the separation step required in current DNA synthesis protocols, leading to simpler and faster synthesis as well as increased yields, however it was found that the functionalisation of the pSi imparted a stability that impeded the dissolution. This strategy may also find applications for drug delivery where the controlled release of carrier-immobilised short antisense DNA is desired. The approach taken involves the fabrication of porous silicon (pSi) microparticles and films. Subsequently, the pSi is oxidised and functionalised with a dimethoxytrityl protected propanediol to facilitate the stepwise solid phase synthesis of DNA oligonucleotides. The functionalisation of the pSi is monitored by diffuse reflectance infrared spectroscopy and the successful trityl labelling of the pSi is detected by UV-Vis spectroscopy after release of the dimethoxytrityl cation in the presence of trichloroacetic acid (TCA). Oligonucleotide yields can be quantified by UV-Vis spectroscopy.
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