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The fabrication of functional 3D tissues is a major goal in tissue engineering. While electrospinning is a promising technique to manufacture a structure mimicking the extracellular ...matrix, cell infiltration into electrospun scaffolds remains challenging. The robust and in situ delivery of cells into such biomimetic scaffolds would potentially enable the design of tissue engineered constructs with spatial control over cellular distribution but often solvents employed in the spinning process are problematic due to their high cytotoxicity. Herein, microfluidic cell encapsulation is used to establish a temporary protection vehicle for the in situ delivery of cells for the development of a fibrous, cell-laden hybrid biograft. Therefore a layer-by-layer process is used by alternating fiber electrospinning and cell spraying procedures.
Both encapsulation and subsequent electrospraying of capsules has no negative effect on the viability and myogenic differentiation of murine myoblast cells. Propidium iodide positive stained cells were analyzed to quantify the amount of dead cells and the presence of myosin heavy chain positive cells after the processes was shown. Furthermore, encapsulation successfully protects cells from cytotoxic solvents (such as dimethylformamide) during in situ delivery of the cells into electrospun poly(vinylidene fluoride-co-hexafluoropropylene) scaffolds. The resulting cell-populated biografts demonstrate the clear potential of this approach in the creation of viable tissue engineering constructs.
Infiltration of cells and their controlled spatial distribution within fibrous electrospun membranes is a challenging task but allows for the development of functional highly organized 3D hybrid tissues. Combining polymer electrospinning and cell electrospraying in a layer-by-layer approach is expected to overcome current limitations of reduced cell infiltration after traditional static seeding. However, organic solvents, used during the electrospinning process, impede often major issues due to their high cytotoxicity. Utilizing microfluidic encapsulation as a mean to embed cells within a protective polymer casing enables the controlled deposition of viable cells without interfering with the cellular phenotype. The presented techniques allow for novel cell manipulation approaches being significant for enhanced 3D tissue engineering based on its versatility in terms of material and cell selection.
We report the fabrication of non-emissive short- and long-pass filters on plastic for high sensitivity fluorescence detection. The filters were prepared by overnight immersion of titania-coated ...polyethylene terephthalate (PET) in an appropriate dye solution - xylene cyanol for short-pass filtering and fluorescein disodium salt for long-pass filtering - followed by repeated washing to remove excess dye. The interface between the titania and the dye molecule induces efficient quenching of photo-generated excitons in the dye molecule, reducing auto-fluorescence to negligible values and so overcoming the principal weakness of conventional colour filters. Using the filters in conjunction with a 505 nm cyan light-emitting diode and a Si photodiode, dose-response measurements were made for T8661 Transfluosphere beads in the concentration range 1 × 10(9) to 1 × 10(5) beads μL(-1), yielding a limit of detection of 3 × 10(4) beads μL(-1). The LED/short-pass filter/T8661/long-pass filter/Si-photodiode combination reported here offers an attractive solution for sensitive, low cost fluorescence detection that is readily applicable to a wide range of bead-based immunodiagnostic assays.
We demonstrate that single cells can be controllably compartmentalized within aqueous microdroplets; using such an approach we perform high-throughput screening by detecting the expression of a ...fluorescent protein in individual cells with simultaneous measurement of droplet size and cell occupancy.
We report the use of thin-film organic photodiodes as integrated optical detectors for microscale chemiluminescence. The copper phthalocyanine–fullerene (CuPc–C
60) small molecule photodiodes have an ...external quantum efficiency of ∼30% at 600–700
nm, an active area of 2
mm
×
8
mm and a total thickness of ∼2
mm. Simple detector fabrication, based on layer-by-layer vacuum deposition, allows facile integration with planar chip-based systems. To demonstrate the efficacy of the approach, CuPc–C
60 photodiodes were used to monitor a peroxyoxalate based chemiluminescence reaction (PO-CL) within a poly(dimethylsiloxane) (PDMS) microfluidic device. Optimum results were obtained for applied reagent flow rates of 25
μL/min, yielding a CL signal of 8.8
nA within 11
min. Reproducibility was excellent with typical relative standard deviations (R.S.D.) below 1.5%. Preliminary quantitation of hydrogen peroxide yielded a detection limit of ∼1
mM and linearity over at least three decades. With improved sensitivity and when combined with enzymatic assays the described integrated devices could find many applications in
point-of-care diagnostics.
We use electromodulation spectroscopy and modeling studies to probe the electric‐field distribution in polyfluorene‐based polymer light‐emitting diodes containing poly(3,4‐ethylenedioxythiophene) ...poly(styrene sulfonate). The bulk internal field is shown to be zero under ordinary operating conditions, with trapped electrons close to the anode fully screening the bulk semiconductor from the external field. The effect has far‐reaching implications for the understanding and optimization of organic devices.
Electromodulation spectroscopy and modeling studies are used to probe the electric field distribution in polymer light‐emitting diodes. The bulk internal field is shown to be zero under ordinary operating conditions, with trapped electrons close to the anode fully screening the bulk semiconductor from the external field. The effect has far‐reaching implications for the understanding and optimization of organic devices.
We report the fabrication of high quality monolithically integrated optical long-pass filters, for use in disposable diagnostic microchips. The filters were prepared by incorporating dye molecules ...directly into the microfluidic chip substrate, thereby providing a fully integrated solution that removes the usual need for discrete optical filters. In brief, lysochrome dyes were added to a poly(dimethylsiloxane) (PDMS) monomer prior to moulding of the microchip from a structured SU-8 master. Optimum results were obtained using 1 mm layers of PDMS doped with 1200 microg mL(-1) Sudan II, which resulted in less than 0.01% transmittance below 500 nm (OD 4), >80% above 570 nm, and negligible autofluorescence. These spectral characteristics compare favourably with commercially available Schott-glass long-pass filters, indicating that high quality optical filters can be straightforwardly integrated into the form of PDMS microfluidic chips. The filters were found to be robust in use, showing only slight degradation after extended illumination and negligible dye leaching after prolonged exposure to aqueous solutions. The provision of low cost high quality integrated filters represents a key step towards the development of high-sensitivity disposable microfluidic devices for point-of-care diagnostics.
We describe the design, fabrication and use of a single-layered poly(dimethylsiloxane) microfluidic structure for the entrapment and release of microdroplets in an array format controlled entirely by ...liquid flow. Aqueous picoliter droplets are trapped en masse and optically monitored for extended periods of time. Such an array-based approach is used to characterize droplet shrinkage, aggregation of encapsulated E. coli cells and enzymatic reactions. We also demonstrate that trapped droplets may be recovered from the microfluidic array for further processing.
We describe a high resolution laser polarimeter built from commodity optical components. The optical rotation angle is determined by measuring the phase difference between two harmonically modulated ...polarised laser beams - an 'object beam' that passes through the sample under test and a 'reference beam' that bypasses the sample. The complete polarimeter may be assembled from low cost off-the-shelf parts for less than £300 (UK Sterling). Data acquisition and analysis are carried out on a microcontroller running an efficient algorithm based on the sliding Discrete Fourier Transform. Despite its low cost, the polarimeter is a fully automatic, research-grade instrument with an accuracy of ±0.0013° and a precision of ±0.0028° - comparable to far costlier commercial instruments. The polarimeter's ease of use, compact size, fast measurement times and high angular resolution make it a capable and versatile tool for analytical science, while its low cost means it is ideally suited for use in resource-constrained environments and process monitoring. The polarimeter is released here as open hardware, with technical diagrams, a full parts list, and source code for its firmware included as Supplementary Information.
Microdroplets: a sea of applications? Huebner, Ansgar; Sharma, Sanjiv; Srisa-Art, Monpichar ...
Lab on a chip,
2008, Letnik:
8, Številka:
8
Journal Article
Recenzirano
The exploitation of microdroplets produced within microfluidic environments has recently emerged as a new and exciting technological platform for applications within the chemical and biological ...sciences. Interest in microfluidic systems has been stimulated by a range of fundamental features that accompany system miniaturization. Such features include the ability to process and handle small volumes of fluid, improved analytical performance when compared to macroscale analogues, reduced instrumental footprints, low unit cost, facile integration of functional components and the exploitation of atypical fluid dynamics to control molecules in both time and space. Moreover, microfluidic systems that generate and utilize a stream of sub-nanolitre droplets dispersed within an immiscible continuous phase have the added advantage of allowing ultra-high throughput experimentation and being able to mimic conditions similar to that of a single cell (in terms of volume, pH, and salt concentration) thereby compartmentalizing biological and chemical reactions. This review provides an overview of methods for generating, controlling and manipulating droplets. Furthermore, we discuss key fields of use in which such systems may make a significant impact, with particular emphasis on novel applications in the biological and physical sciences.
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