Finding Out About Capillaries From Photon Fluorescence

The papillary dermis is the uppermost layer of the dermis that lies just below the epidermis of the skin. Of course the outer layers of the skin require constant supplies of blood and other chemicals in order to function properly. The papillary dermis is essential for this role as it is is filled with feeding capillaries and also gives skin its physical properties such as both being stretchy and resilient of damage. The name papillary dermis comes from the Latin for “protrusion” of “nipple” papilla as the papillary dermis has many small finger like protrusions towards and into the epidermal layer. Its these papillae that increase the surface area in contact between the dermis and epidermis and so also assist the transport of soluble molecules in between skin layers.

The understanding of the capillary networks between the skin layers is so important the techniques used to examine it are given their own name, capillaroscopy. Simple optical capillaroscopy can provide evidence for defects in patients microvascular systems and it is believed that the densities of capillary networks could demonstrate early evidence of arterial hypertension. However, just looking at the capillaries under a microscope does not reveal what chemicals are being transported and how the blood is interacting with the surroundings. For this, a method called multiphoton tomography is used which is where the optical harmonics of the capillaries can be probed so that the cellular structure of the tissue can be understood.

This paper has taken to using two photon excitation microscopy which is where a dye is made to fluoresce by incoming infrared radiation. Being “two photon” means that the dye requires two two photons to excite the same atom in two photon absorption resulting in the light given out being of higher frequency than the infrared put in. The results showed that the harmonic generated by these photons could be used visualise the structure of the capillaries in a living being. More was also learnt about the collagen makeup of the dermis and hopefully the techniques in this paper will prove even more useful in the future.

Paper links: Two-photon autofluorescence lifetime imaging of human skin papillary dermis in vivo: assessment of blood capillaries and structural proteins localization

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