Protein release profiles and morphology of biodegradable microcapsules containing an oily core.

A process for the coating of polymer microspheres with the same or different polymers and the characterization of these particles is described. Coated microspheres were manufactured from degradable and non-degradable polymers. Several physicochemical methods were used to establish that the particles were fully coated. Polarized light microscopy revealed strong birefringence of coated microspheres resulting in the appearance of Maltese Crosses on coated microspheres. After staining the core and the coating of particles using different fluorescent dyes, the uneven distribution of the dyes in the core and on the surface allows one to verify the coating success. After cutting microspheres using a cryomicrotome we were able to assess the microstructure of the coated microspheres. Electron Spectroscopy for Chemical Analysis (ESCA) was used to determine the surface composition of coated microspheres. Determining the carbon and oxygen content of samples we were able to verify the completeness of the coating procedure. To examine the benefit of coating microspheres, the effect of coating on the release of tetanus toxoid from polylactide microspheres was studied as a possible pharmaceutical application.

Development and characterization of microencapsulated microspheres.

Impulse mirage effect/photothermal deflection spectrometry may be used to detect depth-dependent optical absorption in materials, through the time dependence of the probe beam deflection signal occurring in response to sample irradiation with a short excitation pulse. In this work a theoretical expression was derived for the normal and transverse photothermal deflection signals which occur in a sample with homogeneous thermal properties but where optical absorptivity varies with depth from the surface. An analytical solution of moderate simplicity is obtained for several cases of experimental interest, with three-dimensional heat conduction effects included. The depth profile resolution obtained with the mirage effect method is critically dependent on the distance between the sample layer probed and the offset position of the probe beam in the fluid layer above the sample. Saturation conditions and conditions for obtaining optimal depth resolution of continuous and discrete optical profiles are examined in detail.

Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part I: Theory

Impulse mirage effect spectroscopy is developed in this work as a nondestructive method for depth profiling the optical properties of samples which are nearly thermally homogeneous with depth. Both a theory and an experimental methodology are presented. An inverse scattering theory of the experimental photothermal deflection signal is derived, based on a previous theory of the impulse mirage effect, which takes into account the effect of Fresnel diffraction on the probe beam. To reconstruct the depth profile of heat source density generated by light absorption in an unknown sample, we have applied our inverse theory to the experimental impulse response, using a regularized minimum square error reconstruction algorithm based on our previously published expectation minimum principle. Because this reconstruction problem is ill posed, it was necessary to identify and compensate for all experimental bias errors significantly affecting the fidelity of the depth profiles. A procedure for obtaining the overall best-fit model of the depth profile given the minimum prior experimental information is presented. These procedures have produced an agreement between the experimental and theoretically predicted mirage effect response to within typical root-mean-square error levels of 0.5% or less.

Depth Profiling of Optical Absorption in Thin Films via the Mirage Effect and a New Inverse Scattering Theory. Part I: Principles and Methodology

Laser mirage effect (photothermal deflection) spectroscopy was used in this work to determine depth profiles of the optical absorptivity of thin polymer films whose thermal properties were approximately invariant with depth. A variety of well-characterized laminates and continuous samples were examined. The key experimental variables affecting optical depth profile resolution were the offset of the probe beam above the surface, the thermal properties of the fluid medium in which optical deflection occurs, and the relative depths of the subsurface features to be resolved. The accuracy of the experimental signal was found to depend on several key factors which included the electrical bandwidth of the electronic detection system and the linearity of the photothermal deflection signal. Experimental procedures for ensuring quantitative signal recovery are described, and a theoretical interpretation of the depth dependence of the mirage signal was made by means of a model presented in a companion paper.

Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part II: Measurements Using Wide-Band Modulated Excitation

A confocal laser scanning microscope has been applied to the detailed study of non-invasive mapping on targeted systems. This paper aims to show, by particular reference to specific problems, the wide ranging potential of the technique for the analytical community. The specific problems successfully tackled by the technique include characterization of two types of inert support bodies and the precursor/enzyme distributions therein, the effect of processing on dye penetration in fibres, mapping the interdependence and growth patterns in bacterial colonies and non-invasive examination of epidermal tissue layers.

Tutorial review?Applications of confocal laser scanning microscopy in in-situ mapping

Many consumer products are complex physico-chemical systems, and there is a need to characterize them in the three spatial dimensions and in time. Spectroscopic imaging provides the opportunity to do this non-destructively and in-situ. New developments in detector technology, microscope optics and spectroscopics probes are beginning to generate new types of imaging experiments. Several application examples are given covering both macro- and micro-imaging.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

John J. Birmingham

Papers

Tutorial review?Applications of confocal laser scanning microscopy in in-situ mapping

Industrial applications of spectroscopic imaging