ABSTRACT
Microencapsulation of insulin-secreting cells is a potential therapy for Type I diabetes. Critical requirements for therapeutic use are the high number of beta-cells to be implanted and a fast insulin diffusion through the encapsulating membrane. The use of thin, conformal coating for beta-cell encapsulation may be a way to reach these goals by decreasing the capsule void volume. This study focuses on the production of very thin membranes by interfacial photopolymerization of beta-cell clusters. Two types of photosensitizing dyes were used: Eosin Y, which stains the cell surface as well as the cytoplasm, and a lipophilic-derivatized eosin that specifically stains the cell membrane. The fraction of encapsulated clusters and membrane thickness were studied as a function of irradiation parameters. In the case of Eosin Y, the fraction of encapsulated clusters is found to depend mainly on an optimal light dose for and above which complete encapsulation is obtained. We found that the membrane thickness decreased with decreasing irradiation time, but does not depend on irradiation intensity. Using Eosin Y, 16 microm thick coatings were obtained, together with a high fraction of encapsulated clusters. The coating thickness was further reduced to 10 microm by using the lipophilic-derivatized eosin photoinitiator. Cell viability and functionality were studied following the encapsulation process using vital staining and measurement of insulin secretion. Cell viability and functionality were preserved following the encapsulation process with Eosin Y and for sufficiently low lipophilic dye concentration. Although it still requires further improvement, the method proposed here provides a promising route to obtain thinner coatings, down to a few microns.
Subject(s)
Cell Culture Techniques/methods , Eosine Yellowish-(YS)/metabolism , Fluorescent Dyes/metabolism , Islets of Langerhans/growth & development , Analysis of Variance , Animals , Cell Aggregation/physiology , Cell Survival , Insulin/metabolism , Insulin Secretion , Islets of Langerhans/cytology , Islets of Langerhans/metabolism , Mice , PhotochemistryABSTRACT
In view of future generations of biosensors and advanced biomaterials, photochemistry in the near field using scanning near-field optical microscopy is investigated. The potential of direct near-field-induced photoactivation is demonstrated on standard photoresist. Photoimmobilization of maleimidoaryldiazirine on silicon substrates and bovine serum albumin on glass substrates is achieved, opening the way to a controlled biopatterning of surfaces with submicrometer feature size. The obtained patterns are characterized using atomic force microscopy, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and near-field fluorescence microscopy.
Subject(s)
Biosensing Techniques/methods , Adsorption , Animals , Cattle , Microscopy, Atomic Force , Microscopy, Confocal , Microscopy, Fluorescence , Photochemistry , Serum Albumin, Bovine/chemistry , Serum Albumin, Bovine/metabolism , Spectrometry, Mass, Secondary Ion , Surface Properties , TransducersABSTRACT
Shear force mapping on thiolipid Langmuir-Blodgett monolayers probed with Al-coated tips leads to a contrast highly dependent on the monolayer molecular organization, which does not correspond to the topographical relief of the sample. The use of functionalized surface probes offers the possibility to better control the probe-to-sample interaction. In addition, hydrophilic surface probes are totally insensitive to alkyl chain arrangements in the monolayer. Hydrophobic probes, instead, can be chosen to map shear force on soft samples in liquid environment, since their mechanical properties are not influenced by the surrounding liquid.
Subject(s)
Phospholipids/chemistry , Sulfhydryl Compounds/chemistry , Microscopy, Fluorescence/methods , Stress, MechanicalABSTRACT
An improved method for producing fiber tips for scanning near-field optical microscopy is presented. The improvement consists of chemically etching quartz optical fibers through their acrylate jacket. This new method is compared with the previous one in which bare fibers were etched. With the new process the meniscus formed by the acid along the fiber does not move during etching, leading to a much smoother surface of the tip cone. Subsequent metallization is thus improved, resulting in better coverage of the tip with an aluminum opaque layer. Our results show that leakage can be avoided along the cone, and light transmission through the tip is spatially limited to an optical aperture of a 100-nm dimension.
ABSTRACT
A holographic technique, which consists of writing a phase grating onto a photopolymer layer and recording the time evolution of its diffraction efficiency, is presented for a scattering hydrogel. The influence of photopolymer thickness and writing laser intensity is investigated. Writing parameters that yield maximum diffraction efficiency are determined. A thickness greater than 1/3 of the scattering length results in the diffusion of light in the sample, leading to a decreased diffraction efficiency of the grating. This behavior can be explained by a combination of chemical diffusion and optical scattering. Finally, a calibration of diffraction efficiency with respect to a gel and sol fraction is presented.
ABSTRACT
Optical low-coherence ref lectometry is applied for the first time to our knowledge to investigate diffusive biological tissues with a single-mode fiber probe. Samples of fresh arteries are studied, using the backscattered light from the tissue. The probed volume in the vicinity of the fiber tip is estimated to be below 6.7 x 10(-10) cm(3). This noninvasive method allows one to determine optical parameters, such as the index of refraction and the transmission properties, and the tissue thickness.
