Exploring chitin morphologies in cuticle fragments of Xiphopenaeus kroyeri by atomic force microscopy

Shells of Xiphopenaeus kroyerishrimp were submitted to mild acid and alkaline treatments to produce α chitin films, which were characterised by infrared spectroscopy. Dynamic AC operational mode atomic force microscopy (AFM) was used to image the external surface and regions of an inner surface of the cuticle. All samples were scanned in air. No modification of the surface structure was observed even while scanning for a long time. Chitin was visualised as microfibrils of varying thicknesses and shapes. Bundles of cracked microfibrils, as well as nearly straight microfibrils occur in the exocuticle. Scanning of an inner region clearly disclosed a bundle of microfibrils in helicoidal pattern. Non-straight microfibrils were visualised in the rostrum, as well as bundles of straight microfibrils. Estimation of the crystals thickness showed that those pertaining to bundles generally have the largest diameters.