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Bio-optics with a
Light Scattering Microscope

Unlike layers of cultured cells, biological tissues do not consist of only one cell type, but of a mixture of different cell types, extracellular matrix and large structures embedded in the cell layers.

The specialized cells that give the tissue its function have to be maintained by various other cell types which are present in a wide variety of different tissues:
Macrophages remove dying cells and unwanted excellular matrix. Lymphocites and other white blood cells destroy infectious organisms.
Extracellular matrix (mainly consisting of  proteins assembled to various structures) is needed to provide mechanical stability in all kinds of tissues.
Supercellular structures like blood vessels are embedded in tissue and function as support systems for the tissue, wheras other structures 'only' use the tissue as 'embedding medium' (e.g. hair and sweat glands) .

Therefore, biological tissues can be described as highly heterogenous systems.


Up to now, optical properties of biological tissues have mostly been measured by light scattering techniques that average over all the different structures present in the tissue. No information about the local structures being averaged could be obtained by these experiments.

With our new SCATTERING MICROSCOPE, we present a way to measure the static or dynamic scattering of  tissue samples and are able to gain the visual information about the structures we scatter from by simultanous microscopy.

Therefore, local heterogeneities of biological tissues can be probed and by a statistical analysis of many measurements, we are also able to calculate averages to compare our technique with others.
 


As an example, we have measured cryomicrotome- slices of pigskin.

On the LEFT side, the real space images are shown, on the RIGHT the scattering patterns.
The real space images have a width of 60 micrometer.


1
This relatively homogeous skin tissue area results in a relatively isotropic scattering pattern, though small anisotropic features can be seen
 


2
A hair is embedded in skin tissue. As the laser beam is scattered from the hair (on the right side of  the images) and the surrounding tissue (on the left), the scattering pattern shows strong left- right  anisotropy.
 
 

 Using the Scattering Scope for biological samples, we are......


... and have to thank
 

  •     Megan Valentine, send email to mvalenti@deas.harvard.edu


    •      for setting it up.

    Alois Popp
    Department of Physics
    Harvard University
    40 Oxford Street, ESL
    Cambridge, MA 02138
    617-496-8049